•NRLF
B E SOD
PL3NTS
FROM THE LIBRARY OF
WILLIAM A. SETCHELL,i864-i943
PROFESSOR OF BOTANY
BIOLOGY LIBRARY
WILLIAM A. SETCHELL
WATER PLANTS
CAMBRIDGE UNIVERSITY PRESS
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Nymphaea lutea, L. The Yellow Waterlily, showing rhizome and submerged leaves
from a woodcut in Otto von Brunfels' Herbarum vivae eicones, 1530 (reduced).
WILLIAM A. SETCHELJL
WATER PLANTS
A STUDY OF AQUATIC ANGIOSPERMS
BY
AGNES ARBER, D.Sc., F.L.S.
FELLOW OF NEWNHAM COLLEGE, CAMBRIDGE,
AND KEDDEY FLETCHER-WAR R STUDENT OF THE
UNIVERSITY OF LONDON
WITH A FRONTISPIECE AND
ONE HUNDRED AND SEVENTY-ONE TEXT-FIGURES
* ' '
V * * » •» ^ •» ,\
CAMBRIDGE
AT THE UNIVERSITY PRESS
1920
A7
LN
TO THE MEMORY OF
E. A. N. A.
BIOLOGY LIBRARY
PREFACE
IT was affirmed a few years ago, by one of the most eminent
of living biologists, that it "is no time to discuss the origin
of the Mollusca or of Dicotyledons, while we are not even sure
how it came to pass that Primula obconica has in twenty-five
years produced its abundant new forms almost under our eyes.'*
To this statement I venture to demur. I yield to none in my
admiration for the results achieved by the analytical methods
introduced by Mendel, and I do not doubt the possibility that
the direct experimental study of variations and their inheritance
may eventually play a large part in bringing the tangled
problems of evolution into the full daylight for which we all
hope. But this is no reason for condemning those countless
uncharted routes which may lead, even if circuitously, to the
same goal. Any step towards the solution of the essentially
historical problems of Botany — for example those concerned
with the origin and development of such morphological groups
as the Dicotyledons, or of such biological groups as the Aquatic
Angiosperms — must necessarily contribute some mite to our
conceptions of the course of evolution. These less direct
methods of approaching the central problem of biology may
perhaps, at the best, bring only a faint illumination to bear
upon it, but in the deep obscurity involving all evolutionary
thought at the present time, we cannot afford to despise the
feeblest rush-light; even the glimmering of a glow-worm may
at least enable us to read the compass, and learn in which
direction to expect the dawn.
I approached the study of Water Plants with the hope that
the consideration of this limited group might impart some
degree of precision to my own misty ideas of evolutionary
processes. Botanists seem to be universally agreed that the
VI
PREFACE
Aquatic Angiosperms are derived from terrestrial ancestors,
and have adopted the water habit at various times subsequent
to their first appearance as Flowering Plants. The hydrophytes
thus present the great advantage to the student, that they
form a group for whose history there is a generally accepted
foundation. Throughout the present study I have constantly
borne phylogenetic questions in mind, and the first three Parts
of this book may be regarded as a clearing of the ground for
the more theoretic considerations concerning the evolutionary
history of water plants to which the Fourth Part is mainly
devoted. In that section of the book, and sporadically in the
earlier chapters, I have set down such speculations as have
been borne in upon me in the course of a study of water plants
with which I have been occupied more or less continuously for
the last ten years.
The literature relating to Aquatic Angiosperms has now
grown to such formidable proportions that I have felt the
necessity of trying to provide some clue to the labyrinth. With
this end in view I have given a bibliography of the principal
sources, which includes a brief indication of the nature and
scope of each work, with page numbers showing where it is
cited in the text. For the convenience of those seeking informa-
tion about any particular plant, I have indexed the families and
genera named in the titles enumerated, and in the notes regard-
ing the contents of each memoir. I found it impracticable to
compile a subject index to the bibliography, but the references
under the individual chapters to some extent serve this purpose.
It is a pleasure to express my grateful appreciation of the
kindness of those botanists who have helped me in various
ways during the preparation of this book. I am particularly
indebted to Professor A. C. Seward, F.R.S. for valuable sug-
gestions and advice; to Dr H. B. Guppy, F.R.S. for reading
the pages in Part IV which treat of Distribution; to the
Hon. Mrs Huia Onslow (Miss M. Wheldale) for some helpful
criticism of the chapters dealing with physiological questions ;
to Mr F. W. Lawfield, M.A. for aid in fenland botany; and —
PREFACE vii
last but not least — to Miss Gulielma Lister, who, many years
ago, showed me the winter-buds of the Frogbit in a pool in
Epping Forest, and awoke in me the desire to know more of
the ways of water plants.
I have to thank the Councils of the Linnean Society, and
the Cambridge Philosophical Society, and the Editors of The
Annals of Botany^ The Journal of Botany^ and The American
Naturalist^ for permission to incorporate in this book parts of
the text and illustrations of certain of my papers which have
appeared in their publications.
Of the figures in the present book, about one-third are
original; these are indicated by the initials A. A. The
sources of the others are acknowledged in the legends, but
I must take this opportunity of expressing my obligation to
the numerous authors from whose memoirs they are derived.
I am indebted to the Clarendon Press for the use of the block
for Fig. 127. The photographic reproduction of a number of
the illustrations has been carried out by Mr W. Tarns, while
some have been re-drawn by Miss Evelyn McLean. I have to
thank my sister, Miss Janet Robertson, for the design repro-
duced on the cover, which is based upon a wood-cut of the
Yellow Waterlily in Lobel's "Kruydtboeck," of 1581. I am
much indebted to my father for reading and criticising my
manuscript and proofs.
To my husband, E. A. Newell Arber, I owed the original
impulse to attempt the present study, which arose out of his
suggestion that life in Cambridge offered unique oppor-
tunities for the observation of river and fenland plants. To
his memory I dedicate this book.
AGNES ARBER.
BALFOUR LABORATORY,
CAMBRIDGE.
March i, 1920.
CONTENTS
PART I
WATER PLANTS AS A BIOLOGICAL GROUP, WITH A CON-
SIDERATION OF CERTAIN TYPICAL LIFE-HISTORIES
CHAP. PAGE
I. WATER PLANTS AS A BIOLOGICAL GROUP ... 3
(i) Introduction ...... 3
(ii) Biological Classification of Hydrophytes . . 5
II. THE LIFE-HISTORY OF THE ALISMACEAE ... 9
III. THE LIFE-HISTORY OF THE NYMPHAEACEAE AND OF
LlMNANTHEMUM ...... 24
IV. THE LIFE-HISTORY OF HYDROCHARIS^ STRA TIOTES, AND
OTHER FRESH-WATER HYDROCHARITACEAE . . 42
V. THE LIFE-HISTORY OF THE POTAMOGETONACEAE OF
FRESH WATERS ...... 58
VI. THE LIFE-HISTORY OF THE LEMNACEAE AND OF PISTIA 73
VII. THE LIFE-HISTORY OF CERATOPHYLLUM ... 84
VIII. THE LIFE-HISTORY OF THE AQUATIC UTRICULARIAS AND
OF ALDROVANDIA . . . . . . 91
IX. THE LIFE-HISTORY OF THE TRISTICHACEAE AND
PODOSTEMACEAE . . . . . .112
X. THE LIFE-HISTORY OF THE MARINE ANGIOSPERMS . 123
PART II
THE VEGETATIVE AND REPRODUCTIVE ORGANS OF
WATER PLANTS, CONSIDERED GENERALLY
XL LEAF TYPES AND HETEROPHYLLY IN AQUATICS . . 139
(i) Types of Leaf in Water Plants . . 1 39
(ii) The Facts of Heterophylly under Natural
Conditions . . . . . .143
(iii) The Interpretation of Heterophylly . . 155
XII. THE ANATOMY OF SUBMERGED LEAVES . . .163
XIII. THE MORPHOLOGY AND VASCULAR ANATOMY OF
AQUATIC STEMS . . . . . .172
XIV. THE AERATING SYSTEM IN THE TISSUES OF HYDRO-
PHYTES . ..... 183
CONTENTS
204
210
227
239
CHAP. PAGE
XV. LAND FORMS OF WATER PLANTS, AND THE EFFECT
OF WATER UPON LAND PLANTS .
XVI. THE ROOTS OF WATER PLANTS
XVII. THE VEGETATIVE REPRODUCTION AND WINTERING
OF WATER PLANTS .....
XVIII. THE FLOWERS OF WATER PLANTS AND THEIR RELA-
TION TO THE ENVIRONMENT
XIX. THE FRUITS, SEEDS AND SEEDLINGS OF WATER
PLANTS ........
PART III
THE PHYSIOLOGICAL CONDITIONS OF PLANT LIFE
IN WATER
XX. GASEOUS EXCHANGE IN WATER PLANTS . . 253
XXI. ABSORPTION OF WATER AND TRANSPIRATION
CURRENT IN HYDROPHYTES .... 260
XXII. THE INFLUENCE OF CERTAIN PHYSICAL FACTORS IN
THE LIFE OF WATER PLANTS . . .273
XXIII. THE ECOLOGY OF WATER PLANTS . . . 285
PART IV
THE STUDY OF WATER PLANTS FROM THE PHYLOGENETIC
AND EVOLUTIONARY STANDPOINTS
XXIV. THE DISPERSAL AND GEOGRAPHICAL DISTRIBUTION
OF WATER PLANTS ..... 295
XXV. THE AFFINITIES OF WATER PLANTS AND THEIR
SYSTEMATIC DISTRIBUTION AMONG THE ANGIO-
SPERMS ....... 308
(i) The Affinities of Certain Aquatic Angio-
sperms . . . . . 308
(ii) Theoretical Considerations . . . 317
XXVI. THE THEORY OF THE AQUATIC ORIGIN OF MONO-
COTYLEDONS ...... 322
XXVII. WATER PLANTS AND THE THEORY OF NATURAL
SELECTION, WITH SPECIAL REFERENCE TO THE
PODOSTEMACEAE .....
XXVIII. WATER PLANTS AND THE 'LAW OF Loss' IN
EVOLUTION
327
336
BIBLIOGRAPHY
INDEX TO BIBLIOGRAPHY
INDEX
349
415
422
LIST OF ILLUSTRATIONS
FIG. PAGE
Nymphaea lutea, L. [Otto von Brunfels, Herbarum vivae
eicones, 1530] ........ Frontispiece
1. Sagittaria sagittifolia, L. Inflorescence. [A. A.] 10
2. Sagittaria sagittifolia, L. Infructescence. [A. A.] 10
3. " Gramen bulbosum aquaticum" [Gaspard Bauhin, 1620] . . II
4. Sagittaria sagittifolia, L. Tuber and submerged leaves. [A. A.] . 13
5. Sagittaria sagittifolia, L. Leaves. [A. A.] 14
6. Sagittaria sagittifolia, L. Plant with stolons and tubers. [A. A.] . 16
7. Sagittaria sagittifolia, L. Base of plant with old tuber and young
stolons. [A. A.] 18
8. Sagittaria sagittifolia, L. Diaphragm of petiole. [Blanc, M. le
(1912)] ..... 19
9. Ecbinodorusranunculoides^L.^Engtlm. Land and water forms. [A. A.] 21
10. Nymphaea lutea, L. Rhizome. [A. A.] 25
11. Castalia alba, Greene. Rhizome. [A. A.] 26
12. Nymphaea lutea, L. Rhizome with submerged leaves. [A. A.] . 27
13. Castalia alba, Greene. Seedlings. [Massart, J. (1910)] . . 28
14. Cabomba. Shoot with floating and dissected submerged leaves.
[Goebel, K. (1891-1893)] . . 29
15. Castalia alba, Greene. Peduncle and flower-bud. [A. A.] . . 31
16. Victoria regia, Lindl. Seedling. [A. A.] 33
17. Nymphaea lutea, L. Fruit. [A. A.] 34
1 8. Nymphaea lutea, L. Seedlings. [A. A.] ..... 35
19. Castalia Lotus, Tratt. Germination of tuber. [Barber, C. A. (1889)] 37
20. Brasenia. Mucilage hairs. [Goebel, K. (1891-1893)] ... 38
21. Map of existing and extinct distribution of Nelumbo. [Berry, E. W.
(I91?)] • 39
22. Limnanthemum nymphoides, Hoifmgg. and Link. [A. A.] . . 41
23. Limnanthemum nymphoides, Hoffmgg. and Link. Rhizome. [Wagner,
R. (1895)] . 41
24. Hydrocharis Morsus-ranae, L. Buds. [A. A.] .... 43
25. Hydrocharis Morsus-ranae, L. Leaf anatomy. [A. A.] ... 44
26. Hydrocharis Morsus-ranae, L. Stomate. [A. A.] .... 45
27. Hydrocharis Morsus-ranae, L. T. S. submerged leaf. [A. A.] . 45
28. Hydrocharis Morsus-ranae, L. Midrib and inverted bundle from
leaf. [A. A.] 46
29. Hydrocharis Morsus-ranae, L. Plant with turions. [A. A.] . . 47
xii LIST OF ILLUSTRATIONS
FIG. PAGE
30. Hydrocbaris Morsus-ranae, L. Turion plantlet. [A. A.] . . 49
31. Stratiotes aloides, L. Stem bisected. [Arber, A. (1914)] . . 49
32. Stratiotes aloides, L. Habit drawing. [Nolte, E. F. (1825)] . . 53
33. Stratiotes abides, L. Female flower. [A. A.] .... 54
34. Elodea canadensis, Michx. Wintering shoot. [Raunkiaer, C. (1896)] 55
35. Elodea ioensis, Wylie. Male flowers. [Wylie, R. B. (1912)] . . 56
36. Potamogeton perfoliatus, L. Winter shoots. [A. A.] 59
37. Potamogeton. Branch system. [Sauvageau, C. (1894)] ... 60
38. Potamogeton zosterifolius, Schum. Vascular strands and bast bundles
of leaf. [Raunkiaer, C. (1903)] 6l
39. Potamogeton pulcber, Tuckerm., P. natans, L. and P. crispus, L.; —
stem-stele. [Chrysler, M. A. (1907)] 62
40. Potamogeton crispus, L., P. lucens, L., P. pusillus, L., P. pectinatus,
L.;— stem-stele. [Schenck, H. (1886)] 64
41. Potamogeton natans, L., P. densus, L., P. pectinatus, L.; — root
anatomy. [Schenck, H. (1886)] 65
42. Potamogeton crispus, L. Germinating turion. [A. A.] ... 67
43. Potamogeton crispus, L. Germinated turion at advanced stage.
[Sauvageau, C. (1894)] 68
44. Potamogeton rufescens, Schrad. T. S. turion. [Gliick, H. (1906)] . 69
45. Zannicbellia polycarpa, Nolte. Flowers. [A. A.] .... 70
46. Potamogeton perfoliatus, L. Fruit wall. [A. A.] .... 72
47. Spirodela polyrrbiza, Schleid. Inflorescence. [Hegelmaier, F. (1871)] 74
48. Lemnagibba, L. [Hegelmaier, F. (1868)] 76
49. Lemna trtsulca, L. [Kirchner, O. von, Loew, E. and Schroter, C.
(1908, etc.)] . . . -79
50. Lemna trisulca, L. Flowering shoot. [Hegelmaier, F. (1868)] . 79
51. Lemna trisulca, L. T. S. bundle from stalk of frond. [Schenck, H.
(1886)] - 79
52. Lemna trisulca, L. Germination. [Hegelmaier, F. (1868)] . . 81
53. Pistia Stratiotes, L. Leaf apex. [Minden, M. von (1899)] . . 82
54. Ceratopbyllum demersum, L. Flowers. [A. A.] .... 85
55. Ceratophyllum demersum, L. Seedling. [Guppy, H. B. (I8941)] . 86
56. Ceratophyllum demersum, L. Stem-stele. [Schenck, H. (1886)] . 87
57. Ceratopbyllum demersum, L. Rhizoid. [Gliick, H. (1906)] . . 89
58. Ceratopbyllum demersum, L. Leaves of water shoot and rhizoid.
[Gliick, H. (1906)] . .89
59. Utricularia neglecta, Lehm. Leaf with bladders. [Gliick, H. (1906)] 92
60. Utricularia flexuosa, Vahl. Section through bladder. [Goebel, K.
(1891-1893)] 92
61. Utricularia Bremii, Heer. Glands from bladder. [Meierhofer, H.
93
LIST OF ILLUSTRATIONS xiii
FIG. PAGE
62. Utricularia Bremii, Heer. Part of leaf with bladder. [Meierhofer, H.
(!902)] - 95
63. Utricularia minor, L., with earth-shoot. [Gliick, H. (1906)] . . 96
64. Utricularia minor, L. Leaves of water- and earth-shoots. [Gliick, H.
(1906)] . ... 96
65. Utricularia vulgaris, L., with air-shoot. [Goebel, K. (1891-1893)] 98
66. Utricularia neglecta, Lehm. Rhizoids. [Gliick, H. (1906)] . . 99
67. Utricularia vulgaris, L. Germinating seed. [Kamienski, F. (1877)] 100
68. Utricularia exoleta, R.Br. Germinating seed. [Goebel, K. (1891)] 100
69. Utricularia minor, L. Foliage leaf and turion leaf. [Gliick, H.
(1906)] . . 102
70. Utricularia vulgaris, L. Leaf with adventitious shoots. [Goebel, K.
(1904)] . . 104
71. Utricularia vulgaris, L. Inflorescence axis with adventitious shoots.
[Luetzelburg, P. von (1910)] 105
72. Utricularia vulgaris, L. Apical development of shoot. [Pringsheim,
N. (1869)] 106
73. Utricularia vulgaris, L. Developing leaf. [Meierhofer, H. (1902)] 107
74. Utricularia minor, L. Anatomy of leaf. [Schenck, H. (1886)] . 108
75. Aldrovandia vesiculosa, L. Leaves. [Caspary, R. (1859)] • • IIX
76. Hydrobryum olivaceum, (Gardn.) Tul. [Warming, E. (i8832)] . 115
77. Dicraea elongata, (Gardn.) Tul. [Warming, E. (i 88 32)] . . 115
78. Dicraea stylosa, Wight. Seedling. [Willis, J. C. (1902)] . . 115
79. Dicraea stylosa, Wight. [Warming, E. (i8832)] .... 116
80. Dicraea stylosa, Wight. Anatomy of thallus. [Willis, J. C. (1902)] . 118
81. Oenone multibranchiata, Matt. [Matthiesen, F. (1908)] . . 119
82. Podostemon Barberi, Willis. Cleistogamic flower. [Willis, J.C. (1902)] 121
83. Cymodocea aequorea, Kon. [Bornet, E. (1864)] .... 124
84. Cymodocea aequorea, Kon. [Sauvageau, C. (I89I1)] . . .125
85. Zostera marina, L. Anatomy of leaf. [Sauvageau, C. (I89I1)] . 128
86. Zostera marina, L. Median bundle of leaf. [Sauvageau, C. (I89I1)] 128
87. Halopbila ovalis, (R. Br.) Hook. fil. [Balfour, I. B. (1879)] . .130
88. Halodule uninervis, Boiss. [Sauvageau, C. (I89I1)] . . .132
89. Posidonia Caulini, Kon. Anatomy of leaf . [Sauvageau, C. (1891 x)] 132
90. Sagittaria sagittifolia, L. Young plant with ribbon leaves. [A. A.] 141
91. Aponogetonfenestralis, (Poir.) Hook. f. Perforated leaf. [Sergueeff,
M. (1907)] . . 142
92. Ranunculus Purschii, Rich. Water leaf and land leaf. [Goebel, K.
(1891-1893)] . . 144
93. Ranunculus hederaceus, L. [A. A.] . . . . . .145
94. Callitricbe verna, L. Heterophylly. [A. A.] .... 147
95. Hippuris vulgaris, L. Water leaves and air leaves. [Gliick, H. (191 1)] 147
xiv LIST OF ILLUSTRATIONS
FIG. PAGE
96. Hippuris vulgaris, L. A case of air leaves followed by water leaves.
[A. A.] ... .148
97. Sium latifolium, L. Heterophylly. [A. A.] 149
98. Sium latifolium, L. Submerged leaf. [A. A.] . . . .150
99. Polygonum amphibium^L. Water and land forms. [Massart, J. (1910)] 152
100. Polygonum amphibium, L. Epidermis of water and land leaves.
[Massart, J. (1910)] 152
101. Alisma Plantago, L. Seedlings. [A. A.] 153
102. Alisma Plantago, L. Water form. [A. A.] 153
103. Potamogeton natans, L. Effect of transferring land plant to water.
[Goebel, K. (1891-1893)] . 154
104. Potamogeton fluitans, Roth. Effect of poor nutrition in water upon
a land plant. [Esenbeck, E. (1914)] 158
105. Potamogeton natans, L. Effect of growth as a cutting. [Esenbeck, E.
(1914)] . . 159
106. Elodea canadensis, Michx. Leaf anatomy. [Schenck, H. (1886)] . 165
107. Submerged stomates of Callapalustris, L. and Potamogeton natans, L.
[Porsch, O. (1905)] 167
108. Potamogeton densus, L. Leaf apex. [Sauvageau, C. (I89I1)] . . 167
109. Myriopbyllum spicatum, L. Leaf anatomy. [Schenck, H. (1886)] . 168
no. Myriopbyllum verticillatum, L. Trichomes. [Perrot, iL (1900)] . 170
in. Callitricbe verna, L. Leaf anatomy of land and water forms.
[Schenck, H. (1886)] . 170
112. Hippuris vulgaris, L. Rhizome. [Irmisch, T. (1854)] . . . 173
113. Ranunculus trichopbyllus, Chaix. Stem anatomy. [A. A.] . . 176
114. Callitriche stagnalis, Scop. Stem stele of land and water forms.
[Schenck, H. (1886)] ... . . . 176
115. Hippuris vulgaris, L. Relation of cauline and leaf trace xylem.
[A. A.] 178
116. Myriopbyllum spicatum, L. Stem anatomy. [Vochting, H. (1872)] 179
117. Myriophyllum spicatum, L. Details of stem anatomy. [Vochting, H.
(1872)] . "... 179
n8. Potamogeton natans , L. Diaphragm of stem. [Blanc, M. le (1912)] . 184
119. Hippuris vulgaris, L. Development of stem diaphragms. [A. A.] . 184
1 20. Hippuris vulgaris, L. Origin of cortical lacunae in stem. [Barratt, K.
(I9l6)] - 185
121. Stratiotes aloides, L. Origin of cortical lacunae in root. [Arber, A.
(1914)] . . 186
122. Jussiaea peruviana, L. Aerenchyma. [Schenck, H. (1889)] . . 190
123. Neptunia oleracea, Lour. Floating shoot. [Rosanoff, S. (1871)] . 191
124. Nesaea verticillata, H. B. & K. Floating tissue. [Schrenk, J. (1889)] 193
125. Potamogeton natans, L. Land form. [A. A.] .... 196
LIST OF ILLUSTRATIONS xv
FIG. PAGE
126. Ranunculus aquatilis, L. Water and land seedlings. [Askenasy, E.
(1870)] . .196
127. Hottonia palustris, L. Land and water forms. [Prankerd, T. L.
(1911)] . . . . 197
128. Littorella lacustris, L. Water and land forms. [Gluck, H. (1911)] . 198
129. Caltha palustris, L. Submerged and air leaves. [Gluck, H. (1911)] 199
130. Cirsium anglicum, D. C. Land and water forms. [Gluck, H. (1911)] 199
131. Water forms of Cuscuta alba, J. & C. Presl, Echinodorus ranuncu-
loides (L.), Engelm. and Trifolium resupinatum, L. [Gluck, H.
(1911)] . .... 199
132. Hydrocotyle vulgaris, L. Water shoot. [A. A.] .... 201
133. Cardamine pratensis, L. Anatomy of aerial and submerged plants.
[Schenck, H. (1884)] 202
134. Ranunculus Flammula, L. Floating leaved form and land form.
[Gluck, H. (1911)] . . 203
135. Ranunculus Flammula, L. Submerged form. [Gluck, H. (1911)] . 203
136. Hydrilla verticillata, Presl. Tendril roots. [Kirchner, O. von, Loew,
E. and Schroter, C. (1908, etc.)] 205
137. Zannichellia palustris, L. and Potamogeton densus, L. Tendril roots.
[Hochreutiner, G. (1896)] 206
138. Callitriche stagnalis, Scop. Root stele. [Schenck, H. (i 886)] . 209
139. Vallisneria spiralis, L. Root anatomy. [Schenck, H. (1886)] . 209
140. Naias major, All. and N. minor, All. Root anatomy. [Sauvageau, C.
(1889!)]. ..... ... 209
141. Cardamine pratensis, L. Leaves bearing adventitious plantlets.
[A. A.] . . . .2,7
142. Littorella lacustris, L. [A. A.] 218
143. Utricularia intermedia, Hayne. Turion leaf and foliage leaf.
[Goebel, K. (1891-1893)] 220
144. Myriophyllum verticillatum, L. Habit drawing with inflorescence
and turions. [A. A.] 221
145. Myriophyllum verticittatum, L. Germinating turion. [A. A.] . . 222
146. Myriophyllum verticillatum, L. Land form with turions. [Gluck, H.
(1906)] . . ... 223
147. Echinodorus ranuncukides, (L.) Engelm. var. repens f. terrestris.
[Gliick, H. (1905)] . 224
148. Caldesia parnassifolia, (Bassi) Parl. With turions. [Gliick, H. (1905)] 225
149. Caldesia parnassifolia, (Bassi) Parl. With turions. [Gliick, H. (1905)] 225
150. Utricularia inflata, Walt. Floating organs. [Goebel, K. (1891-
1893)] ... . . .229
151. Hippuris vulgaris, L. Habit drawing. [A. A.] . . . .231
152. Peplis Portula, L. Flowers. [A. A.] 232
153. Heter anther a dubia, (Jacq.) MacM. Cleistogamic flower. [Wylie,
234
xvi LIST OF ILLUSTRATIONS
FIG. PAGE
154. Callitriche verna, L. Flowering shoot. [A. A.] . . . 237
155. Pontederia rotundifolia, L. Flowering shoot. [Hauman-Merck, L.
(191 31)] . 240
156. Limnanthemum nymphoides, Hoffmgg. and Link. Fruit and seed.
[A. A.] . . 240
157. Limnanthemum nympbotdes, Hoffmgg. and Link. Fruit wall. [A. A.] 242
158. Elatine bexandra, D. C. Germination of seed. [Klebs, G. (1884)] 245
159. Zannicbellia polycarpa, Nolte. Fruit. [Raunkiaer, C. (1896)] . 246
160. TrapanatanSjL,. Seed and germination. [Goebel, K. (1891-1893)] 247
161. Zoster a marina, L. Fruit. [Raunkiaer, C. (1896)] .... 248
162. Transpiration experiment. [Sauvageau, C. (I89I1)] . . . 262
163. Callitriche autumnalis, L. Leaf apex. [Borodin, J. (1870)] . . 268
164. Hydrocleis nymphoides, Buchen. Apical cavity of leaf. [Sauvageau,
C. (1893)] ... 270
165. Section across White Moss Loch. [Matthews, J. R. (1914)] . . 288
1 66. Ruppia bracbypus, J. Gay. Fruit. [Raunkiaer, C. (1896)] . .319
167. Potamogeton lucens, L. Range of leaf form. [Raunkiaer, C. (1896)] 339
1 68. Potamogeton natans, L. Range of leaf form. [Raunkiaer, C. (1896)] 339
169. " Lamina " of Pontederia cordata, L. and Eicbbornia speciosa, Kunth.
[Arber,A. (1918)] . 341
170. Leaf anatomy of Pontederiaceae. [Arber, A. (1918)] . . . 342
171. Leaf anatomy of Sagittaria. [Arber, A. (1918)] .... 345
PART I
WATER PLANTS AS A BIOLOGICAL GROUP,
WITH A CONSIDERATION OF CERTAIN TYPICAL
LIFE-HISTORIES
A. W. P.
"If... an inquiry into the Nature of Vegetation may be of good
Import; It will be requisite to see, first of all, What may offer it
self to be enquired of; or to understand, what our Scope is: That so
doing, we may take our aim the better in making, and having
made, in applying our Observations thereunto."
Nehemiah Grew, The Anatomy of Plants, 1682.
[ 3 ]
CHAPTER I
WATER PLANTS AS A BIOLOGICAL GROUP
(i) INTRODUCTION
WE are living at the present day in what may be described
botanically as the Epoch of Angiosperms, or Flowering
Plants. The members of this group now represent the dominant
type of vegetation and are distributed over nearly all the land
surfaces of the globe. The vast majority are typically terrestrial,
carrying on their existence with their flowers and leafy shoots in
the air, but with their roots embedded in soil of varying degrees
of moisture, from which they derive their water supply. This
water supply is one of the prime necessities of their life, and in
their relation thereto, the plasticity of their organisation is
notably exhibited. At one end of the scale there are plants which
can withstand long periods of drought and are capable of flou-
rishing under desert conditions in which the water supply is
minimal. At the other extreme we meet with hydrophytes —
plants which have exchanged terrestrial for aquatic life. Those
which have embraced this change most thoroughly, live with
their leafy shoots completely submerged, and have, in some
cases, ceased to take root in the substratum, so that all their
vegetative life is passed floating freely in the water — which is to
them what atmosphere and soil are to terrestrial plants. The
ultimate term in the acceptance of aquatic conditions is reached
in certain hydrophytes with submerged flowers, in which even
the pollination is aquatic — water replacing air as the medium
through which the pollen grain is transferred to the stigma.
These fundamental changes in habit are necessarily associated
with marked divergences from the structure and life-history of
land plants. The result has been that the aquatic flowering
plants have come to form a distinct assemblage, varying widely
4 j INTRODUCTION [CH.
among themselves, but characterised, broadly speaking, by a
number of features associated with their peculiar mode of life.
It is the biological group thus formed which we propose to
study in the present book.
There is good reason to assume that the Angiosperms were
originally a terrestrial group and hence that the aquatic Flower-
ing Plants existing at the present day can trace back their pedi-
gree to terrestrial ancestors. If this be the case, we may interpret
the various gradations existing within the hydrophytic group
as illustrating a series of stages leading from ordinary terrestrial
life to the completest adoption of an aquatic career. At one end
of the series we have plants which are normally terrestrial, but
which are able to endure occasional submergence, while at the
other end we have those wholly aquatic species whose organisa-
tion is so closely related to water life that they have lost all
capacity for a terrestrial existence. Between these extremes
there is an assemblage of forms, bewildering in number and
variety. In order to clear one's ideas, it is necessary to make
some attempt to classify hydrophytes according to the degree to
which they have become committed to water life. It must be
realised, however, that, though such a scheme is convenient and
helpful in * pigeon-holeing ' the known facts about aquatics,
little stress ought to be laid upon it, except as illustrating the
striking variety of form and structure met with among these
plants. A classification of aquatics on biological lines is highly
artificial, and, since it sometimes places in juxtaposition plants
which are quite remote in natural affinity, it has only an indirect
bearing on questions of phylogeny.
The classification of aquatics which forms the second part of
the present chapter, is based upon a scheme put forward by
Schenck1 more than thirty years ago, which in its main outlines
has never been superseded. But the wider knowledge of the
group, which has been acquired since that date, has resulted, as
is so often the case, in the blurring of the sharp lines of demar-
cation between the individual bionomic classes recognised at an
1 Schenck, H. (1885).
i] BIOLOGICAL CLASSIFICATION 5
earlier stage. The present writer has freely modified Schenck's
scheme, and has carried the sub-division to a further point. The
various types met with amongst aquatics are arranged in a linear
series for the sake of simplicity ; but this plan is obviously open
to the same criticisms as all other linear systems, whether bio-
logical or phylogenetic. The following classification is outlined
with the utmost brevity, and aims merely at supplying a key to
the biological forms encountered. The life-histories of typical
plants illustrating the characters of the more important sub-
divisions will be considered in some detail in Chapters n— x;
but the order in which the life-histories are grouped in these
chapters has been determined mainly by reasons of natural
affinity, and thus bears no close relation to the following
scheme.
(2) BIOLOGICAL CLASSIFICATION OF HYDROPHYTES
I. Plants rooted in the soil.
A. Plants which are essentially terrestrial, but which are
capable of living as submerged water plants, though without
marked adaptation of the leaves to aquatic life.
E.g., Achillea ptarmica, L. (Sneezewort).
Cuscuta alba^ J. and C. Presl (Dodder).
Glechoma hederacea^ L. (Ground Ivy).
B. Plants which are sometimes terrestrial, but sometimes
produce submerged leaves differing markedly from the air
type. The air leaves are associated with the flowering stage.
E.g., Certain Umbelliferae, such as Slum latifolium^ L.
(Water Parsnip).
C. Plants which produce three types of leaf, (a) submerged,
(ft) floating and (c) aerial, according to the conditions — internal
or environmental.
(i) Plants in which the aerial type of leaf is generally
associated with the flowering stage.
E.g., Many Alismaceae, such as Sagittaria sagitti-
folia, L. (Arrowhead).
6 BIOLOGICAL CLASSIFICATION [CH.
(ii) Plants in which the floating type of leaf is generally
associated with the flowering stage.
E.g., Nymphaea lutea^ L. (Yellow Waterlily).
Castalia albay Greene (White Waterlily).
Various Batrachian Ranunculi (Water Butter-
cups).
Callitriche verna, L. (Water Starwort).
Potamogeton natans^ L. (Pondweed).
D. Plants which may, in certain cases, occur as land forms,
but are normally submerged and are characterised by a creep-
ing axis bearing long, branching, leafy shoots with no floating
leaves, or by a plexus of leafy, rooting shoots without a creeping
rhizome.
(i) Leafy aerial shoots produced at the flowering period.
E.g., Myriophyllum verticillatum, L. (Water Mil-
foil).
Hippuris vulgaris, L. (Mare's-tail).
(ii) Inflorescence raised out of the water, but no aerial
foliage leaves except in the land forms.
E.g., J^yriophyllum (except M. verticillatum) (Water
Milfoil).
Hottonia palustris, L. (Water Violet).
Many Potamogetons (Pondweeds).
(iii) Inflorescence submerged, but essential organs raised
to the surface.
E.g., Elodea canadensis^ Michx. (Water Thyme).
(iv) Inflorescence entirely submerged and pollination
hydrophilous.
E.g., Naias.
Zannichellia (Horned Pondweed).
Zostera (Grass- wrack).
Callitriche autumnalis^ L. (Water Starwort).
Halophila.
i] BIOLOGICAL CLASSIFICATION 7
E. Plants which in some cases may occur as land forms, but
which are very commonly submerged, and are characterised by
an abbreviated axis from which linear leaves arise.
(i) Inflorescence raised above the water or borne on a land
plant.
E.g., Lobelia Dortmanna, L. (Water Lobelia).
Littorella lacustris, L.
Sagittaria teres, Wats.
(ii) Inflorescence sometimes raised above water or some-
times submerged.
E.g., Subularia aquatica, L. (Awlwort).
F. Plants which are entirely submerged as regards the vege-
tative organs and which have a thallus (morphologically either
of root or shoot nature) attached to the substratum. The
flowers are aerial.
Tristichaceae and Podostemaceae.
II. Plants which are not rooted in the soil, but live unattached in
the water.
(A transition between I and II is found in Stratiotes abides,
L. (Water Soldier), which is rooted during part of the year but
floats freely during another part. There are also a number of
rooted plants, such as Hottonia -palustris and Elodea canadensis,
which are capable of living unattached for considerable periods.)
A. Plants with floating leaves or leaf-like shoots. Flowers
raised into the air.
(i) Roots not penetrating the soil.
E.g., Hydrocharis Morsus-ranae, L. (Frogbit).
Sfirodela polyrrhiza, Schleid., 1 (Duck-
Lemna minor, L. and L. gibba, L.J weeds).
(ii) Rootless.
Wolffia (Rootless Duckweed).
BIOLOGICAL CLASSIFICATION [CH. i
B. Plants entirely or partially submerged.
(i) Rooted, but roots not penetrating the soil. Floating
shoots, formed at flowering time, which raise the flowers
into the air.
Lemna trtsulca^ L. (Ivy-leaved Duckweed),
(ii) Rootless.
(a) Inflorescence raised out of the water.
Aldrovandia.
Utricularia (Bladderwort).
(£) Flowers submerged; hydrophilous pollination.
Cer atop hy Hum (Horn wort).
[ 9 ]
CHAPTER II
THE LIFE-HISTORY OF THE
ALISMACEAE
THE Alismaceae1 are perhaps the most typically amphi-
bious of all water plants and they vary in appearance
according to their environment in a thoroughly protean fashion.
The Arrowhead, Sagittaria sagittifolia, L., may be chosen for
description as a characteristic member of the family. Seen in
ditches and backwaters in the late summer, its fine sagittate
leaves and bold inflorescences2 (Fig. i, p. 10) make it one of the
most striking of our water plants. It is apparently insect polli-
nated, but the records on the subject seem to be confined to the
statement that, in the Low Countries, certain species of Fly have
been observed to visit the flowers3. The present writer has once
noticed a Water-snail crawling over a female flower and engaged
in eating the perianth; it is conceivable that these animals may
play an occasional part in pollination. The large fruits, whose
hassock-shaped receptacles are completely clothed with com-
pressed, winged achenes, give the plant a highly individual
character (Fig. 2, p. 10).
In complete contrast to the flowering form, is the guise
which the Arrowhead assumes in deep and rapidly-flowing
water. As long ago as 1596* a tuber, bearing strap-shaped
leaves, was described by Gaspard Bauhin under the name of
"Gramen bulbosum," while in 1 62O5 he published a figure of it,
1 For a systematic review of the Alismaceae see Buchenau, F. (I9O31),
and, for a general study of their life-history, Gliick, H. (1905); Gliick's
work has been largely drawn upon in the present chapter.
2 On the detailed structure of the reproductive organs see Schaffner,
J. H. (1897). 3 MacLeod, J. (1893).
4 Bauhin, G. (1596). 5 Ibid. (1620).
10
ALISMACEAE
[CH
FIG. i. Sagittaria sagittifolia,
L. Top of inflorescence, August
17. JQi?- 6* = whorl of male
flowers; $ = whorl of female
flowers with withered perianths,
(fnat. size.) [A. A.]
FIG. 2. Sagittaria sagittifolia, L. Top of
infructescence, September 8, 1917. (f nat.
size.) A, Longitudinal section of fruit. [A. A.]
n] "GRAMEN BULBOSUM AQUATICUM ' n
which is here reproduced (Fig. 3). A century later, Loeselius1
recognised these strap-shaped leaves as belonging to the Arrow-
head; under the name of "Sagittaria aquatica foliis variis,"
FIG. 3. Sagittaria sagittifolia, L. An illustration given by Gaspard Bauhin in the
Prodromes Theatri Botanici, 1620, under the name of " Gramen bulbosum aquati-
cum/' but which in reality represents a germinated tuber of the Arrowhead, bearing
ribbon-leaves.
he figured a plant bearing both ribbon-leaves and leaves of
sagittate shape. The ribbon-leaved, deep-water form has been
distinguished as f. vallisneriifolia. An opportunity of examining
1 Loeselius, J. (1703).
12 ALISMACEAE [CH.
the plant in its submerged state sometimes occurs when weeds
are being cleared out of a river. The semi-transparent leaves —
which have been regarded by some authors as purely petiolar1,
while others consider them to represent the entire leaf in a
rudimentary form2 — often grow to great lengths; the present
writer has measured one as long as 6 ft. 9 in.3 from the river
Cam. As many as twenty ribbon-leaves are said to be some-
times borne by a single plant in very deep water4. The
streaming ribbon-leaves of Sagittaria and other submerged
plants with the same type of foliage, have a singular beauty
when seen forming, as it were, a meadow beneath the surface of
the water, moving in the current in a way that recalls a field
of wheat swayed by the wind.
The ribbon-leaved form of Sagittaria sagittifolia is generally
sterile, but the appearance of flowers at this stage is not un-
known5. In moderately shallow water, transitions between the
aquatic and aerial types of leaf may be observed. The first-
formed leaves are band-shaped and submerged, while later ones
begin to spread at the apex so as to form a distinct lamina.
Some of these transitional leaf-blades, which are of lanceolate
to ovate form, float on the water. In another species, Sagittaria
natans*, these floating leaves represent the mature type of leaf
and are associated with the inflorescence, but, in the Arrowhead
itself, yet a third kind of leaf is produced. The abbreviated axis
gives off, in succession to the leaves with floating blades, others
whose petioles rise into the air and whose laminae become more
and more sagittate at the base, until the typical arrowhead form
is achieved. The band-shaped leaves, though characteristic of
the plant which is wholly or partially submerged, are not con-
fined to it. The first leaves produced by a germinating seed or
tuber are ribbon-like, whether the plantlet develops in air or
water. At the end of May, the present writer has found young
1 Candolle, A. P. de (1827). 2 Goebel, K. (1880).
3 A length of two metres (6 ft. 6 in.) has been recorded by Costantin,
J. (1886). 4 /to. (1886).
5 Kirschleger, F. (1856). 6 Wachter, W.
n] THE ARROWHEAD 13
plants growing from tubers, among the drift at the edge of a
river, with a varying number of ribbon-like leaves, succeeded
in some cases by one or two of slightly spathulate form (Fig. 4).
Fig. 5, p. 14 represents a young plant found in July which shows
a series of leaf stages between the early band-like form and the
FIG. 4. Sagittaria sagittifolia, L. Plant with soft submerged leaves growing from
a tuber, t; from river drift at the edge of the Cam near Waterbeach, May 31, 1911.
(fnat. size.) [A. A.]
mature * arrowhead ' type. The significance of this heterophylly
and its relation to the environment will be discussed in Chapter xi .
.Sagittaria^ like the other Alismaceae, is characterised by the
presence of mucilage-secreting trichomes, in the form of scales,
in the axils of the leaves. In a paper published a few years ago,
ALISMACEAE
[CH,
FIG. 5. Sagittaria sagitti folia, L. Young plant, July 16, 1910, showing
transitions from ribbon-shaped to arrowhead type of leaf. (Reduced.)
[A. A.]
n] THE ARROWHEAD 15
two American writers1, in describing the seedling of Sagittaria
variability allude to the occurrence of a cellular plate just within
the cotyledonary sheath. They refer to this as " a vestigial
structure " and interpret it as probably representing a second
cotyledon. It appears, however, to the present writer that it is
much more reasonable, judging from the figure and description
given, to suppose that this scale is merely one of the " squamulae
intravaginales," whose existence in the seedlings of Sagittaria
was placed on record by Fauth2. These structures, which are
so common among water plants, belong to the category of
hairs; they contain no vascular tissue and cannot be homolo-
gised with a foliar organ such as the cotyledon.
Plants of the Arrowhead, carefully dug up in the late summer,
are found to show preparations for the winter's rest and for next
season's growth3. From among the bases of the crowded leaves
arising on the short main axis, a number of white stolons protrude
(j, Fig. 6, p. 1 6), distinguished from the roots by their greater
thickness. They each bear one or more scale-leaves and terminate
in a bud (/). The present writer measured a stolon on July 1 6,
1910, which had reached a length of 25 cms.4. Later on, the
two internodes below the terminal bud swell up and form a
tuber which may be 5 cms. long. As many as ten stolons may
arise from the base of a single plant, so that, where Sagittaria
grows freely, a very large quantity of tubers are produced. One
author5 records that he collected two to three litres of tubers on
digging up soil whose superficial area was one square metre. By
a downward curve of the stolons, these reproductive bodies are
carried some depth into the mud, where they pass the winter.
The mature tubers are coloured blue by anthocyanin, which
1 Coulter, J. M. and Land, W. J. G. (1914).
2 Fauth, A. (1903).
3 Nolte, E. F. (1825), Walter, F. (1842) and M (inter, J. (1845).
4 The stolons seem to develop earlier in terrestrial plants than in
plants growing in water. The present writer has found that vigorous plants
growing in water may show only quite short stolons in the middle of
August. 5 Klinge, J. (i 88 1).
i6
ALISMACEAE
[CH,
FIG. 6. Sagittaria sagittifolia, L. Plant dug up July 16, 1910,
with five stolons (s) growing from its base among roots, and
terminating in young tubers (t). (J nat. size.) [A. A.]
n] THE ARROWHEAD 17
occurs in the epidermis. The blue tint seems very constant; it is
recorded by European writers and is shown in the coloured
illustrations to that splendid Japanese flora, "Honzo Zufu1."
The store of reserve material, laid up in the tuber for the
succeeding year's growth, makes the Arrowhead a potential
food plant. In Germany the tubers are sometimes employed to
feed pigs under the name of "Bruch-Eicheln2." They are used
in Japan3, while in China the plant is actually grown for the
sake of its tubers, which, in cultivation, reach the size of a
clenched fist4. The tubers of the related Sagittaria variabilis,
sometimes called "Swan's Potatoes5," are said to be eaten by
the American Indians under the name of" Wapatoo6."
By winter time, the decay of the stolons sets the tubers free
from the parent plant, which does not itself survive until the
next season. In the spring, the apical region of the tuber grows
out into an elongated axis bearing scale leaves, and carrying
the terminal bud up to the surface of the mud, where it pro-
duces a new plant. Food is absorbed from the parent tuber for
some time; it is possible to find a plant still attached to the tuber
from which it arose (Fig. 7, p. 1 8) and already itself producing
the stolons (j/2) which will develop into the tubers of the next
generation. At this stage the parent tuber (/) has given up its
stores of food material and is in a dry, spongy, exhausted state.
The conditions which influence tuber formation will be dis-
cussed in Chapter xvn, when the wintering of water plants
comes under consideration.
The Arrowhead is reproduced by seed as well as vegetatively.
The tubers suffice for colonisation of a limited area, but the
seeds serve to distribute the species over greater distances. The
mericarps, which each enclose a single seed, are flattened and
air-containing; they are suitable for dispersal either by wind or
water. Their specific gravity is still further lowered by the
presence of an oil in the secretory ducts of the pericarp. The
1 Anon. (1828). 2 Walter, F. (i 842).
3 Anon. (1895). 4 Qsbeck, P. (1771).
5 Paillieux, A. and Bois, D. (1888). 6 Buchenau, F. (1882).
A. W. P.
1 8 ALISMACEAE [CH.
surface of the mericarps is non-wettable and they often float
for long periods, sometimes until frost produces waterlogging
of the fruit wall. After the decay of the latter, the embryo is
still protected by the cuticularised testa1.
The petioles of Sagittaria sagittifolia contain lacunae crossed
at intervals by diaphragms (D in Fig. 8). A peculiarity, which
has been recorded in connexion with the life-history, is that not
st
FIG. 7. Sagittaria sagittifolia, L. Base of plant dug up July 16, 1910, showing
remains of old stolon (stj from plant of previous year bearing tuber (t) with scale
leaves (sc) ; the plant of the current year has also produced a stolon (stz) which will
give rise to a tuber later in the autumn. At this stage the old tuber is dry and
spongy in texture, having contributed all its reserves to the plant which has sprung
from it. (§ nat size.) [A. A.]
only roots but also stolons may sometimes break through the
diaphragms of the leaf-sheath of living leaves and penetrate as
far as 10 cms., running in the petiole parallel to its long axis2.
It would be interesting to know whether any significance is to
1 Fauth, A. (1903). 2 Klinge, J. (1881).
ii] THE WATER PLANTAIN 19
be attached to this observation, which, as its author points out,
suggests a case of auto-parasitism.
After the Arrowhead, probably the best known British
member of the Alismaceae
is the Water Plantain,
Alisma Plantago^ L.1 Ac-
cording to modern views2,
this Linnean species in-
cludes two plants which
are each worthy of spe-
cific rank — Alisma Plan-
tago^ (L.) Michalet, and
A. graminifolium, Ehrh.
The former is more suited
to land life, while the
latter is typically a water
plant. A. PlantagO) (L.)
Mich, generally lives in FIG. 8. Sagittaria sagUtifolia, L. Diaphragm (D)
, n 1 • of petiole in transverse section. T = wall of
shallow water, where air la^una. L = lacuna [BlanCj M le (igi2)^
leaves form the chief as-
similatory organs. These are preceded, however, by band-shaped
primary leaves (Fig. 101 #, p. 153) and then generally some
swimming leaves (Fig. 102, p. 1 53), so that the Water Plantain,
like the Arrowhead, produces three distinct types of leaf. In
dark situations the swimming leaves may be replaced by sub-
merged leaves differing from the ordinary submerged band-leaves
in possessing a distinct lamina. This species only flowers suc-
cessfully in relatively shallow water in which air leaves can be
produced; in moderately deep water, in which submerged and
swimming leaves occur, a reduced inflorescence is occasionally
formed, but, in very deep water, where all the leaves are band-
shaped and submerged, flowers are always absent. Alisma
graminifolium^ on the other hand, has its optimum growth in
1 On the details of fertilisation, etc., in this species see Schaffner, J. H.
(1896).
2Gluck, H. (1905).
2 — 2
20 ALISMACEAE [CH.
deeper water than A. Plantago and is capable of flowering at a
stage when it bears band-shaped leaves alone. It was figured in
this condition by Loeselius1, more than two hundred years ago,
under the name of "Plantago aquatica." It never, either in the
seedling or adult form, produces floating leaves. It grows and
flowers best in 50 to 70 cms. of water; at a greater depth
(2 to 4 metres) flowering is inhibited. In spite of the marked
tendency of this species towards a strictly aquatic life, a land
form can be obtained in cultivation ; this proves to be identical
with the plant, sometimes found wild, which has been called
Alisma arcuatum^ Mich.
Another closely related genus is represented by the pretty
little Echinodorus ranunculoides, whose different forms can be
observed, among many other water plants, at Wicken Fen near
Cambridge — an untouched fragment of fenland, which has re-
tained many of its primitive features. Fig. 9 C shows the young
aquatic form, with both narrow submerged leaves and leaves
with floating blades. An entirely submerged form has been
described, which may flower under water at a depth of three
feet2. Fig. 9 B shows the luxuriance which the mature plant
may attain, when it grows in water, but raises its leaves and
flowers into the air, while Fig. 9 A indicates the general dwarf-
ing of the land form. Fig. 147, p. 224, shows the transitions
which sometimes occur in this species between inflorescences
and entirely vegetative rosettes. The related genus Elisma,
with its single species, E. natans^ (L.) Buchenau, is chiefly in-
teresting on account of a similar intimate relationship between
the inflorescence and the vegetative shoot. The bracts of the
inflorescence are in whorls of three ; flowers typically arise in
the axils of two of the bracts, while a leafy shoot is developed in
the axil of the third. The inflorescences are thus partly repro-
ductive and partly vegetative; there are also certain purely
vegetative off-shoots, which may be interpreted, in a morpho-
logical sense, as inflorescences which have become wholly
sterile.
1 Loeselius, J. (1703). 2 West, G. (1910).
THE LESSER WATER PLANTAIN
21
FIG. 9. Echinodorus ranunculoides, (L.) Engelm. A, plant from a dried up fen,
August 5, 1911 ; B, plant growing in water in a ditch, with aerial leaves only, and
very long petioles and flower stalks, June 27, 1914; C, plant with submerged and
floating leaves only, from a shallow pool, June 27, 1914. (Reduced.) [A. A.]
22 ALISMACEAE [CH.
Another case, in which the replacement of the inflorescence
by vegetative structures has been carried much further, is that
viCaldesia-parnasslfolia^ (Bassi) Parl., a plant which is somewhat
widely distributed in Southern Europe, but does not reach
Britain. When it grows in water 30 to 60 cms. deep, the ' in-
florescences ' often bear, instead of flowers, vegetative buds
about 2 cms. long, which are able to reproduce the plant
(Figs. 148 and 149, p. 225). Sometimes these 'turions' as
they are called, and also flowers, may occur in the same whorl.
Gllick, to whose work on the Alismaceae we owe so much,
regards these buds as flower rudiments, which, in consequence
of submerged life, have developed in a degenerate vegetative
form. This species seems to be losing its power of sexual
reproduction, for, even when it bears flowers, they commonly
fail to set fertile seed. It affords a good instance of a tendency,
common among water plants, to substitute vegetative for
sexual reproduction; this characteristic will be discussed more
fully in Chapter xvn.
The range of leaf-form met with amongst the Alismaceae —
not only in passing from species to species, but also in the same
individual under different conditions — prompts one to ask
which of these divergent types are fundamental and which are
derived. Gllick's study of the family has led him to the conclu-
sion that the ribbon form of leaf is primitive, and, on this
assumption, he suggests the following scheme, as representing
successive phyletic stages which may have occurred in the
evolution of the leaves ; he admits, however, that the series may
conceivably be read in the reverse order. This seriation merely
illustrates possible progressive steps and, obviously, does not
represent the actual phylogeny of the genera, since examples of
Stage I, the most primitive leaf type, and Stage VI, the most
highly evolved, are to be found within the limits of the one
genus Sagittaria.
Stage I. Band leaves alone developed, e.g. Sagittaria feres, Watson.
Stage Ha. Band leaves extremely important and associated with the
n] LEAVES OF ALISMACEAE 23
flower, but leaves with lanceolate blades also occurring, e.g. Alisma grami-
nifolium, Ehrh.
Stage II b. Band leaves of considerable importance, but the flowering
stage generally associated with aerial leaves with lanceolate blades^ e.g.
Echinodorus ranunculoides^ (L.) Engelm.
Stage III. Band leaves still important and sometimes associated with
the flower, but floating leaves also produced, with a broadly elliptical
lamina, sharply marked off from the petiole, e.g. Elisma natans, (L.)
Buchenau.
Stage IV a. Band-shaped leaves produced, as well as floating leaves and
air leaves with a slightly cordate base, e.g. Damasonium stellatum, (Rich.)
Pers.
Stage IV b. Similar to Stage 1 Va, but the band leaves of less importance,
e.g. Alisma Plantago, (L.) Mich.
Stage V. Similar to Stage IV, but the base of the lamina definitely cor-
date, giving a Nymphaeaceae-like leaf. Band leaves extremely reduced,
e.g. Caldesia parnassifoliay (Bassi) Parl.
Stage VI. Air leaves of sagittate form. In the transition from the band
leaves to the mature leaves analogies can be found for all the preceding
types, e.g. Sagittaria sagittifolia, L.
CHAPTER III
THE LIFE-HISTORY OF THE NYMPHAEACEAE
AND OF LIMNANTHEMUM
^ I ^HE Nymphaeaceae, like the Alismaceae dealt with in
JL the last chapter, are a typically aquatic family, but, in
the Nymphaeaceae, the water habit has become even more
firmly established than in the Alismaceae, land forms being
relatively rare. The dominant type of leaf has a floating blade,
whereas, although this form of leaf occurs among the Alisma-
ceae, it occupies as a rule a minor place. The rhizome again,
which is seldom a conspicuous organ in the Alismaceae, as-
sumes considerable importance in the case of some Nymph-
aeaceae, although the family includes also a number of annuals.
Our British Waterlilies perenniate by means of rhizomes;
these are rich in starch and in the case of some foreign species
are used for food1. That of the Yellow Waterlily is epigeal2,
with the result that small specimens are occasionally torn from
their moorings and found among river drift. The hypogeal
rhizomes of the White Waterlily, on the other hand, can seldom
be obtained unless they are actually dragged up with a boat-
hook out of the mud. The rhizome of Nymphaea lutea, L.3 is a
very striking object (Fig. 10 A). It is slightly flattened and of
a greenish colour on the upper surface, but pallid and yellowish
below. It is decorated with the scars of the leaves (/.j.) of
previous years — punctuated by the vascular strands which
supplied them — and also with the scars of the peduncles (/>.J.),
which can be distinguished by their rounded form. With each
leaf-base, three roots are usually associated ; at r^ these roots can
1 Paillieux, A. and Bois, D. (1888).
2Royer,C. (1881-1883).
3 = Nuphar luteumy Sibth. et Sm.
CH. in] WATERLILY RHIZOMES 25
be seen as rudiments and at rz as scars, while numerous groups
of three mature roots are also shown (e.g. r2). Fig. 10 B repre-
sents such a group in further detail. The root system is very
elaborate, since the adventitious roots bear branches (Fig. io5)
which themselves branch again (Fig. 10 C). At the apex arises
the rosette of leaves and flower stalks belonging to the current
year, and lateral buds may also be produced (Fig. 10 A^ /.£.).
The rhizome may be as thick as a man's arm.
FIG. 10. Nymphaea lutea, L. June 30, 1913. A, Part of old rhizome, bases, only,
of leaves indicated and all root-branches omitted ; p.s. = scar of peduncle; l.s. = leaf-
scar; rlt group of three rudimentary roots arising from a leaf base; r2, correspond-
ing group of three roots fully developed; rs, scars of three dead roots; ap, apical
region of rhizome; l.b., lateral branch bearing leaves of submerged type only.
B and C, roots in greater detail, placed horizontally to save space. B, three young
roots from a single leaf-base to show laterals ; C, part of an old root to show branch-
ing of laterals. (J nat. size.) [A. A.I
Castalia alba 1, Greene, has a shorter rhizome with the leaves
crowded in the apical region (Fig. 1 1 A, p. 26). When the older
leaves and flower stalks have been removed to expose the apical
bud, the most remarkable feature revealed is the occurrence of
large membranous stipules, one of which accompanies each
young leaf adaxially; each appears to represent a fused pair
(j/. in Fig. 1 1 #, C, D). A larger number of roots is associated
with each leaf than in the case of the Yellow Waterlily. These
i = Nymphaea alba, L,
26 NYMPHAEACEAE [CH.
roots may be seen in Fig. n A, and their rudiments (r.) in Fig.
1 1 B and D. In Nymphaea lute a stipules are absent but the
FIG. ii. Caslalia alba, Greene. Apical part of rhizome pulled up from bottom of
water, June 30, 1913. In A, the leaves and flowers have mostly been cut away to
show the young flower buds, the young leaves and the stipules which protect them.
In B, C, D, three views are given of a young leaf and its stipule (or pair of stipules
united on the adaxial side) st. In B and D the rudiments of the roots, r., are seen
at the leaf-base. ($ nat. size.) [A. A.]
petioles are winged, and the stipules seem to be replaced by a
silky fringe of hairs1.
1 IrmischjT. (1853).
in] THE YELLOW WATERLILY 27
Sometimes, if a young rhizome ofNymphaea lute a be brought
up from the bottom of the water, it will be found to bear leaves
differing widely from the familiar floating type1. They are
wholly submerged, relatively short-stalked, translucent, sinu-
ous, and of a delicate, flaccid texture recalling the fronds of Ufoa
(Fig. 12). In a wood-cut in the famous Herbarum vtvae eicones
FIG. 12. Nymphaea lutea, L. Leafy rhizome found floating on Cam near Water-
beach, May 17, 1911. Leaves all of submerged type, flaccid, translucent and some-
what sinuous at the margin. Rhizome shows leaf-scars, and root-scars in rows of
two or three on leaf-bases on under side. (£ nat. size.) [A. A.]
of Otto von Brunfels (i 530) — reproduced in the Frontispiece of
the present book— some of the outer leaves with short petioles
undoubtedly belong to this type, though no description of the
submerged leaves of the Waterlilies occurs in botanical litera-
ture until a hundred years later2. They were re-discovered —
1Royer, C. (1881-1883), Arcangeli, G. (1890), Brand, F. (1894).
2 Bauhin, G. (1623). See also Desmoulins, C. (1849).
28
NYMPHAEACEAE
[CH.
like so many matters well known to the ancients — in the nine-
teenth century1.
These submerged leaves, which are stomateless, are charac-
teristically produced in the winter and spring2, and are usually
succeeded, in the course of the season, by floating leaves; in
FIG. 13. Castalia alba, Greene. Seedlings of various ages illustrating the effect of
sowing at different levels on or in the mud (M) at the bottom of the water (W) ;
accommodation takes place in length of first internode, acicular first leaf, and
petiole of second leaf with ovate lamina. [Massart, J. (1910).]
deeper, rapidly flowing water, however, foliage of the submerged
type may be exclusively produced for years, even when the
plant is so old as to have a massive rhizome3. If the water does
1 The submerged leaves of Nuphar minima^ Smith, were described by
Spenner, F. C. L. (1827).
2 Costantin, J. (1886). 3 Goebel, K. (1891-1893).
m] THE WATER-SHIELD 29
not freeze, the submerged leaves may vegetate throughout the
winter. In 1911, the present writer observed a number of
plants of the Yellow Waterlily flowering without having pro-
duced any but submerged leaves. Possibly this was associated
with the peculiarly brilliant sunshine of that summer, which may
have supplied the submerged leaves with unwontedly intense
light for assimilatory purposes.
Castalia alba produces submerged leaves less freely than
Nymphaea lutea and they are said to be incapable of surviving
the winter; the first leaves of the seedling are of this type
(Fig. 13).
FIG. 14. Cdbomba aquatica. Habit drawing to show entire floating leaves and
dissected submerged leaves. [Goebel, K. (1891-1893).]
The American Water-shield, Cabomba, which is placed in a
different tribe from Castalia and Nymphaea, and might, indeed,
almost be assigned to a different family, produces submerged
leaves of a very distinct type1 (Fig. 14). They are finely dissected
and comparable with the submerged leaves of various Batrachian
Ranunculi.
1 Goebel, K. (1891-1893) and Raciborski, M. (18942).
30 NYMPHAEACEAE [CH.
The floating leaves of the British Waterlilies are typical of
swimming leaves in general. The lamina is coriaceous and non-
wettable. No leaf which attains to any size can float success-
fully unless it be of a strong, leathery texture, since the motion
of the water exposes it to tearing, and in heavy rain it is
liable to be much more severely battered than an air leaf, which
can yield freely in a medium so elastic as the atmosphere1.
The normal stomates are borne upon the upper surface of the
floating leaves, where they are in contact with the air, but water
stomates have been observed on the lower surface in two Ameri-
can species of Nympkaea2. These water pores occur in direct
communication with the finest ramifications of the tracheal
system. The floating leaves are differentiated from the sub-
merged leaves at a very early stage, stomates being developed
while the leaf is still in the bud3. Floating leaves of an orbicular
or peltate form4, more or less recalling those of the Nymphaea-
ceae, occur both among Monocotyledons and Dicotyledons
and appear to be well adjusted to their particular type of habitat.
It is clear, in the first place, that a leaf with an entire outline
is less easily wetted and submerged than one which is sub-
divided. It is obvious, also, that the centre of gravity of a
floating leaf which approximates to the circular form, lies at its
central point, and that this is therefore the most mechanically
economical position for petiolar support5. In a peltate leaf,
such as that of Victoria regia^ this position is approximately
achieved, while, in the orbicular Waterlily leaf with a deep sinus
at the base, some approach is made to the same condition.
All the floating leaves belonging to any associated group of
plants, unlike a corresponding series of air leaves, have, without
exception, to expand their laminae in one horizontal plane.
The competition among the leaves for space is shown by the
way in which every available square inch of water surface is
1 Schenck,H. (1885). 2 Schrenk, J. (1888). 3 Costantin, J. (1886).
4 For a mathematical demonstration of the physical advantages accru-
ing to a floating leaf from a circular form, see Hiern, W. P. (1872).
*Jahn,E.(i897).
in] FLOATING LEAVES 31
covered in any spot where Waterlilies abound. In the case of
Nymphaea and Castalia^ a place in the sun is secured through
the pliability of the petioles, which vary in length according
to the depth of the water, but do not rigidly determine the
position of the lamina. The variation in length of the peduncles
goes hand in hand with that of the petioles. The present writer
has measured a peduncle of Castalia alba over six feet in length,
and such length is by no means uncommon; Fig. 15 shows the
proportion borne by peduncle to flower in this case, the peduncle
being represented coiled in
order to include its entire
length in the sketch. It is
rather curious that in the
gigantic Victoria regia this
great elongation of the peti-
oles and peduncles does not
occur; the plant flourishes
in the shallows and has been
recorded in the Amazon
region in water only two
feet deep1.
Another result of the
length and flexibility of the
leaf-stalk in the Waterlilies
is that the lamina can re-
spond freely to the move-
ment of the water and
is
hence less liable to be sub-
merged. This response is
also shown in many other
FIG. 15. Castalia alba, Greene. Peduncle
and flower-bud to show great proportionate
length of peduncle. The peduncle, which was
more than 6 feet long, is represented coiled
in order to include its whole length in the
«U^*.o ,Trk:~U ~~~ * t. A m order to include its wnoie lengtn in me
plants Which are rooted at diagram. (Reduced.) May 30, 1911. [A. A.]
the bottom of the water
and bear floating leaves. Potamogeton natans* is a good example.
Here the axis from which the leaves arise, instead of being a
solid rhizome lying in or on the mud, as in the Waterlilies,
1 Spruce, R. (1908). a Jahn, E. (1897).
32 NYMPHAEACEAE [CH.
takes the form of a slender stem occupying a slanting position
in the water. The petioles arise obliquely from the flexible axis,
to which they have a very pliable attachment. If the stem be
pushed to and fro in the water, the leaves follow all its move-
ments while yet retaining their position on the surface. In the
case of such a hydrophyte as Hydrocharis, on the other hand,
in which not only the leaves but the rosette as a whole floats
freely, the entire plant responds to every movement of the water.
In spite, however, of a form and structure suited, up to a certain
point, to their environment, floating leaves still remain liable to
serious risks of wetting and submergence; this is proved by the
fact that plants bearing such leaves are quite unable to colonise
windy and exposed surfaces where the water is liable to be
rough1.
In the summer, in addition to the floating leaves of Castalia
alba, others may be seen which rise well above the water surface
and are typical air leaves in appearance. The White Waterlily
is even able, on occasion, to develop a terrestrial form which can
vegetate for an entire summer without submergence2. The
leaves of this land form are described as generally being
short-stalked, with their lower surfaces almost on the ground.
Eighteen centimetres is the greatest diameter recorded: the
margins are inrolled towards the upper side.
We showed that in the Alismaceae it is possible to arrange
the species in a series beginning with those in which the leaves
are extremely simple and concluding with those in which they
are highly differentiated, such as Sagittaria sagittifolia. We also
pointed out that in the Arrowhead the successive juvenile leaves
epitomised the series — recalling the various mature forms of leaf
characteristic of the less highly differentiated species. In both
respects the Nymphaeoideae run strictly parallel with the Alis-
maceae. Victoria regia may be regarded as occupying the same
position among the Nymphaeoideae as Sagittaria sagittifolia
1 See pp. 288, 289.
2 Bachmann, H. (1896). A land form of Nuphar pumilum (Nymphaea
pumila^ Hoffm.) was obtained experimentally by Mer, £ (I8821).
Ill]
SEEDLINGS OF VICTORIA REGIA
33
among the Alismaceae. The leaf-succession in the Giant
Waterlily of the Amazons was long ago recorded1, but the full
appreciation of its significance we owe to Gwynne-Vaughan2,
who contributed greatly to
our knowledge of the Nym-
phaeaceae. He pointed out
that the successive leaves
of the Victoria regia seedling
show a progressive change
from the acicular primor-
dial leaf to the peltate form
of the mature leaf. The fol-
io wing account of the series
is derived from his work :
The first leaf is acicular
and without a blade (/a in
Fig. 1 6).
The second leaf is elon-
gate lanceolate, sometimes
with two hastate lobes, and
resembles the adult leaves
of Barclay a (/2 in Fig. 1 6).
The third leaf \s elongate-
hastate to deltoid-hastate,
recalling the sagittate
leaves of Castalia pygmaea,
Salisb., etc. At the base of
the lamina, just above the
insertion of the petiole, FIG. 1 6. Victoriaregia.Undl. Seedling, showing
there is a little pocket or a£c;jlar first; leaf '/• and ha*tate sec°nd and
r. ^ third leaves 12 and ls. (According to Gwynne-
pOUch On the adaxial Side, Vaughan, D. T. (1897), the second leaf is more
whirh ar^Mrcf^ K/» fru-m^rl commonly lanceolate.) st., stipules of second
Which appears tO Deformed leaf which protect the third. (Nat. size.) [A. A.]
by the fusion of the auricles
at their bases.
The fourth leaf is the first swimming leaf, and is distinctly
1 Trecul, A. (1854). 2 Gwynne-Vaughan, D. T. (1897).
A.W. P.
34 NYMPHAEACEAE [CH.
peltate, by the further fusion of the two auricles. It recalls
the adult leaf of many Castalias, e.g. Castalia Lotus, Tratt.
It is the first leaf to bear spines.
The succeeding leaves become more and more orbicular in
outline, as the auricles become fused along a successively
greater part of their length. As in the case of Sagittaria sagitti-
folia, the leaf of the mature plant passes, in its youth, through
stages parallel to those permanently retained by the embryonic
leaves.
The flowers of the Nymphaeaceae do not show any obvious
relationship to their aquatic life, except perhaps in the case
of Euryale ferox1, which is described as exhibiting submerged
cleistogamy. The enormous flowers of Victoria regia^ the Giant
Waterlily, apparently attract night-flying insects, but no
critical observations seem to have been made in the native
haunts of the plant. In captivity, each flower partially opens
one evening, closes next morning and opens
completely on the next evening. It remains
open until the hotter hours of the suc-
ceeding day, when it finally closes2. When
the flowers open they exhale a strong scent,
and much heat is also evolved; the tempera-
ture of the flower may rise to 10° C. above
that of the surrounding air. The heat and
perfume are developed mainly in the
carmine-red, sigma-shaped outgrowths at FlG I?> ^ymphaealutea>
the apices of the carpels, apparently at the L- Fruit showing Per-
c i 11-11 • Q sistent calyx. August n,
expense of the starch which they contain3. I9IO (jnat.size.) [A.A.j
The flower sinks after pollination, and the
fruit ripens in the water about six weeks after flowering4.
The fruits and seedlings5 of our British Waterlilies are of
considerable interest, although the young plants do not display
1 Goebel, K. (1891-1893). 2 Seidel, C. F. (1869).
3 Knoch, E. (1899). * Seidel, C. F. (1869).
5 For very early and good figures of the primordial leaves of the White
and the Yellow Waterlily see Tittmann, J. A. (1821).
m] FRUITS OF YELLOW WATERLILY 35
such an extensive series of leaf-forms as the seedling of Victoria
regia. The green bottle-shaped fruits which succeed the yellow
flowers ofNymphaea lutea (Fig.
17) are usually found floating
just at the surface of the water.
Water-fowl are occasionally
seen pecking at them1. In order
to follow the dehiscence and
germination, the present writer
brought some fruits collected
on October i, 1914, into the
laboratory, and kept them in an
aquarium. In the course of the
first few days the pericarp began
to disintegrate. The green fruit-
wall burst irregularly at the
base and the torn ' segments
gradually curled right up round
the stigmatic disc, disclosing
the seed-containing loculi.
These, which were snow-white,
owing to the presence of air
in their walls, soon became
detached from the fruit, and for
a time floated on the water,
either singly or in groups ; but,
in a couple of days or so, they
ill J , ' * FIG. 1 8. Nymphaea lutea, L. .4, seedling
had become water-logged and April 23, 1915 (x 2). B, seedling May 28,
B
had Sunk to the bottom of the
laroirootnairs;c,c=cotyledons;^.=plu-
bellT-jar2. It has been shown3 mule; llt 12, 13, first, second and third
that these detached loculi are leavesofplumule^=seed;o=operculum.
clothed with thin-walled cells
which secrete much mucilage outwards. The cells have at first
1Guppy, H. B. (1893).
2 On dehiscence of Castalia alba see p. 302.
3Raciborski, M. (18942).
3—2
36 NYMPHAEACEAE [CH.
a rich starch content, which diminishes as the mucilage is
developed — suggesting that the mucilage is formed at the
expense of the starch.
By November 24, 1914, the loculi under observation had
mostly decayed completely, and the seeds were set free. They
remained dormant throughout the winter, but by April 23,
1915, a large number had germinated and there was a forest
of slender, grass-like, first leaves arising from the bottom of the
bell-jar. Seedlings at this stage are shown in Fig. 1 8 A^p* 35 ; the
seed-coat opens by means of an operculum (o) to emit the radicle.
During the summer these seedlings developed a number of
submerged leaves with lanceolate blades (Fig. 18 5), which
increased in number until, on September 18, some of the
plants had as many as seven such leaves. In spite of the unna-
tural conditions under which they were living, many of the little
plants survived the winter and, by the spring of 1 9 1 6, they had
developed distinct but miniature rhizomes marked with leaf-
scars. The leaves were still of the submerged type only. But the
most interesting event of this second spring was the germina-
tion of a very large number of seeds which had remained dor-
mant for eighteen months. This delay in the sprouting of the
seeds is not unusual in water plants (see p. 243). Unfortunately
the frost of the very severe winter 1916-1917 destroyed the
aquarium, and these observations came to an abrupt end.
Vegetative reproduction, though not so universal among
Waterlilies as in some other groups of aquatics, is by no
means rare. In certain cases tubers are formed as part of the
ordinary course of development of the species, while in Castalia
Lotus1- the flowers may, under the abnormal conditions due to
cultivation, be replaced by tubers which can reproduce the
plant (Fig. 19). Like the seedlings, these young plants deve-
loped from a germinating tuber have a simple type of first
leaf ft).
The anatomy of the Nymphaeaceae has been investigated by
1 Barber, C. A. (1889).
m] POLYSTELY 37
Gwynne-Vaughan1. The rhizomes contain an indescribable con-
fusion of bundles, which he suggests may have been derived
from a simpler structure previously existent in a stem with
longer internodes; the adoption of a rhizomic habit, associated
with telescoping of the internodes, might well lead to this
extreme complexity. The most interesting anatomical feature
of the family, however, is the occurrence of polystely. In the
rhizome of Victoria regia
" all the root-bearing
bundles belonging to
the same leaf-base are
grouped together so as to
form a structure having
the appearance of a defi-
nite and distinct stele,"
in which about twenty
bundles form a ring.
However the most typi-
. 1 . FIG. 19. Castalia Lotus, Tratt. (Nymphaea Lotus,
Cal polystely OCCUrS, not L.) var. monstrosa. Germination in spring of a
in the rhizomes them- tuber which has developed in place of a flower ; /t,
simple first leal (Reduced.) [Barber, C. A. (1889).]
selves, but in the elon-
gated tuber-bearing stolons, which certain species of Castalia
produce as lateral branches. In the stolons of Castalia flava,
for instance, the bundles are arranged in four or five widely
separated groups or steles, each enclosed in an endodermis
and surrounding a protoxylem canal. In Cabomba, on the other
hand, it is the rhizome in which polystely occurs, though in
the simplest possible form; two steles occur throughout, each
consisting of a single pair of bundles. The significance of
polystely in aquatic plants will be considered in Chapter xm.
The Nymphaeaceae have a remarkably well-developed aerating
system in their leaf- and flower-stalks. The long peduncles of
Waterlily flowers are said to have been sold in the bazaars at
Cairo as tobacco pipes: the base of the flower, which was
1 Gwynne-Vaughan, D. T. (1897); see also Trecul, A. (1845) and
(1854), Wigand, A. (1871), Blenk, P. (1884), Strasburger, E. (1884), etc.
38 NYMPHAEACEAE [CH.
destroyed, formed a hollow for the lighted tobacco, and the
smoke passed through the
air-spaces in the stalk1.
The mucilage which coats
the young organs in most
of the Nymphaeaceae will
be considered later2. It is
secreted by glandular hairs
(Fig. 20).
Oiir ~Rrif-ic;h Waterlilips FlG' 2O' Brasenia Schreberi, J. F. Gmel. Part
sn wate ines of transverse section of yojmg leaf to show
belong tO the Central tribe thesecretoryhairs,w. h. .surrounded by alayer
r « r .-, XT , . of clear mucilage, m. [Goebel, K. (1891-93).]
of the family — Nymphaeoi-
deae — of which Euryale and Victoria also form part. Two
other tribes are recognised — the Cabomboideae and the Nelum-
bonoideae — which differ markedly from the Nymphaeoideae.
The Cabomboideae are in many respects relatively simple ; they
have free carpels, and Cabomba also has a less complex type of
anatomy than the rest of the family. Brasenia Schreberi, which
belongs to this tribe, is notable for the enormous development
of surface mucilage (Fig. 20) 2.
The Nelumbonoideae include the Sacred Lotus, Nelumbo
Nelumbo and one other living species belonging to the same
genus. In Cretaceous and Tertiary times the genus had, how-
ever, a cosmopolitan range (Fig. 2 1)3. This tribe, and the Water-
lilies proper, differ so much that they have been described as
having nothing in common except the number of cotyledons,
the polypetalous flowers, the numerous stamens, and the medium
in which they live4. The acyclic arrangement of the petals and
stamens might also be mentioned as constituting a similarity
to some of the Nymphaeoideae. The exalbuminous seeds5 and
the carpels sunk in the curious obconical receptacle, are indeed
difficult to reconcile with the characters of the other Water-
lilies. Gwynne-Vaughan6 pointed out that Nelumbo shows an
1 Raffeneau-Delile, A. (1841). 2 See pp. 271, 272.
3 Berry, E. W. (1917). 4 Trecul, A. (1854).
6 Wettstein, R. von (1888). 6 Gwynne-Vaughan, D. T. (1897).
in] NELUMBO AND LIMNANTHEMUM 39
almost complete absence, both in leaf and stem, of these fea-
tures that may be regarded as primitive for the family. Nelumbo
may possibly be interpreted as the most highly differentiated
of the Waterlilies, and part of its peculiarities may perhaps
be due to the fact that it is rather a marsh plant than a true
aquatic. Possibly it is a genus descended from aquatic ancestors,
which has reverted in some degree towards a terrestrial life1.
Another genus which, though extremely distant from the
Waterlilies in its systematic position, yet in its life-history
resembles them in some degree, may be mentioned at this
FIG. 21. Sketch map showing the existing and geologic distribution of Nelumbo.
The obliquely lined areas represent the range of the two existing species, while
the Cretaceous and Tertiary records which occur outside these areas are marked
by solid black circles. [Berry, E. W. (1917).]
point. This is Limnanthemum (Villarsia\ a member of the
Gentianaceae, which is represented in Britain by the beautiful
Z. nymphoides with its fringed yellow flowers. Like Castalia and
Nymphaea it has a rhizome at the bottom of the water while its
leaves float at the surface (Fig. 22, p. 41). The length of the inter-
nodes of the rhizome varies with the time of year2 (Fig. 23,
p. 41). In the autumn, the leaves are closely packed and the
adventitious roots hold the axis with its abbreviated internodes
close to the ground. In the spring, elongated internodes are
1 Dollo, L. (1912). 2 Wagner, R. (1895).
40 LIMNANTHEMUM [CH.
produced and the axis ends in a cymose inflorescence with a ter-
minal flower. The shoot morphology is somewhat puzzling, and
remained obscure until it was elucidated by Goebel1 who
studied L. indicum and other species from this point of view. In
plants of Limnanthemum^ examined at the flowering season, it is
found that a long stalk given off from the rhizome appears to bear
both a lamina and flowers, or, in other words, that the flowers
seem to arise laterally from a leaf-stalk. In reality this long
stalk is however the axis of the inflorescence, and only the short
segment of leaf-stalk above the inflorescence is actually the
petiole. This petiole has a short, sheathing base, which in
youth surrounds the inflorescence. In development, the foliage
leaf pushes the growing point to one side and comes to occupy
the terminal position. Goebel considers that this peculiar mode
of growth confers a definite biological advantage. The breadth
of the leaf-surface resting on the water gives the inflorescence
the necessary support, while the elongated inflorescence axis
forms a substitute for both the elongated petiole and peduncle
of the Waterlilies. The flower is raised well above the surface
of the associated leaf and thus rendered conspicuous to insects.
The products of assimilation find their way by the shortest
route to the ripening fruit, whereas in Castalia and Nymphaea
they have to descend many feet to the bottom of the water and
then rise again a similar distance to the flower, because there
is no connexion between lamina and flower, except via the
rhizome. But, as Goebel suggests, such an arrangement as that
met with in Limnanthemum would have less value in the case of
the Waterlilies, because the Nymphaeaceae store so much food
in their rhizomes that the ripening fruit is not dependent
upon the products of contemporaneous assimilation. It would
be utterly unsafe, however, to suppose that the morphological
differences between the Waterlilies and Limnanthemum are to be
explained on such simple adaptational lines, though it is obvious,
from the success which both families achieve, that their re-
spective types of construction must be well suited to aquatic life.
1 Goebel, K. (1891) and (1891-1893).
Ill]
LIMNANTHEMUM
FIG. 22. Limnanthemum nymphoides, Hoffmgg. and Link,
showing rhizome and leaf -scars. River Ouse. May 30,
1911. (Reduced.) [A. A.]
FIG. 23. Limnanthemum nymphoides, Hoffmgg. and Link. Rhizome with long
and short internodes; T, terminal flower. (Reduced.) [Wagner, R. (1895).]
CHAPTER IV
THE LIFE-HISTORY OF HTDROCHARIS,
STR4TIOTES, AND OTHER FRESH-WATER
HYDROCHARITACEAE
A BIOLOGICAL classification of water plants, such as
£\. that outlined in Chapter i, has little in common with
any phyletic scheme. The incompatibility between biological
and phylogenetic systems is particularly well illustrated in the
Hydrocharitaceae, which include — besides some marine ge-
nera— both marsh or shallow-water plants with air leaves, sub-
merged plants and floating plants. As an example of the latter
we may choose the Frogbit, Hydrocharis Morsus-ranae, the only
British plant with typical floating leaves which swims freely in the
water. Other members of the genus however, e.g., H. asiatica1
and H. parnassifo/ia2, have air leaves. In the case of H. Morsus-
ranae it is possible to produce a land form artificially3, and this
form has also been recorded on one occasion in nature4.
In places where the Frogbit flourishes, the surfaces of the
ditches and dykes which it inhabits are often completely covered
by its leaves, which resemble a miniature edition of those of the
White Waterlily. These leaves are produced in rosettes from a
tiny, abbreviated stem, which gives rise during the summer to
numerous lateral stolons, each ending in a rosette similar to the
parent, and repeating the production of stolons da capo. At the
base of each rosette, a number of roots of a greenish colour are
produced. They hang down into the water, but do not enter
the substratum except occasionally in the shallows5. These
roots bear, along the greater part of their length, a very large
number of unusually long root-hairs, which are well known as
1 Solereder, H. (1913). 2 Solereder, H. (1914). 3 Mer, E. (I8821).
4 Gluck, H. (1906). 5 Goebel, K. (1891-1893).
CH. iv] THE FROGBIT 43
favourable material for observing the rotation of protoplasm.
The roots, with their thick mat of root-hairs, get much tangled
together, and the countless stolons growing in every direction
are similarly enlaced, with the result that Hydrocharis forms a
thick carpet which can scarcely be submerged even by rough
movements of the water. Detritus collects between the root-
FIG. 24. Hydrocharis Morsus-ranae, L. A, dissection of a summer bud, just open-
ing; (i)-(vi) show the result of removing successive members. B (i), a bud of which
one leaf has unfolded ; B (ii) shows the result of removing the outer scale leaves
and the stipules of the first foliage leaf; ax± and ax2, stolons terminating in first
and second bud; flf fz, fs, successive foliage leaves; stl, st2, stipules belonging to
/! and/2; s and s, outer scale leaves; rx and rz, roots belonging to first and second
bud. [A. A.]
hairs and may serve as a source of food. This colonial mode of
growth offers serious resistance to the intrusion of other water
plants.
The bud, in which each stolon terminates, is enclosed in two
delicate, membranous scales (s and s Fig. 24 A (i)). These are
44 HYDROCHARITACEAE [CH.
interpreted as paired axillary stipules, whose leaf-blade is
generally rudimentary1. They are succeeded by a foliage leaf,
with its blade tightly inrolled (/j), whose stipules (st-^ enclose
the next foliage leaf (/2). The young stolon of the next genera-
tion (*#2) is also present in the bud. Fig. 24 B (i) shows a bud
at a later stage in which the first foliage leaf is fully expanded
and the root has grown to a considerable length.
oc.
FIG. 25. Hydrocharis Morsus-ranae, L. A, T.S. leaf; B, tangential section through
leaf at level of arrow in A ; C, upper epidermis with open stomates ( x 78 circa) ;
st. = stomate; ac. = air cavity; d^ = diaphragm in section; dz = diaphragm in
surface view; /= fibres; vb. = vascular bundle; xy. = xylem; p h. = phloem;
ue. = upper epidermis; le. = lower epidermis; c = thin layer of cuticle on upper
surface ; p = palisade parenchyma. [A. A.]
The structure of the lamina of Hydrocharis may be described
in some detail as an example of the anatomy of a floating leaf
(Fig. 25). The upper surface is clothed with an epidermis
whose cells contain a few chlorophyll grains. The outer wall
is sculptured internally, and bears a delicate layer of cuticle
externally. The stomates, which are confined to the upper
1 Glttck, H. (1901).
iv] THE FROGBIT 45
surface of the leaf, have slightly prominent, external, cuticular
ridges (Fig. 26); it is probable that here, as in Trianea and
in certain other plants with floating leaves, the closure of the
stomates is brought about by the approximation of these ridges,
rather than by the bulging of the ventral walls1. Haberlandt
has suggested that this form of stomate is adapted to diminish
the risk of capillary occlusion of the aperture by water.
The palisade parenchyma, which lies beneath the upper
epidermis, is, in normal leaves of Hydrocharis^ extremely well
differentiated (Fig. 25). On one occasion, however, in the
latter part of May, the present writer found a number of
plants which were entirely submerged, the winter buds having
FIG. 26. Hydrocharis Morsus-ranae, L. FIG. 27. Hydrocharis Morsus-ranae, L.
T.S. upper epidermis passing through a T.S. leaf of young plant growing entirely
stomate. (x3i8.) [A. A.] submerged at the bottom of a ditch,
May 17, 1911. (x78 circa.} [A. A.]
apparently been caught in an algal tangle at the bottom of a
ditch, so that they were unable to reach the surface, but un-
folded beneath the water. The green colour of these leaves was
unusually pale, and a section of one of them revealed the fact
that the palisade region was poorly differentiated, the cells
being scarcely elongated (Fig. 27); it was, in fact, a typical
' shade leaf.' The spongy mesophyll was developed normally.
In Hydrocharis this tissue is not distributed in the irregular
fashion with which we are familiar in land plants, but it takes
the form of plates of cells disposed in a polygonal mesh-work
over the lower epidermis, which itself contains a small amount
of chlorophyll (Fig. 25 $). Attention has been drawn by
1 Haberlandt, G. (1914).
46 HYDROCHARITACEAE [CH.
Solereder1 to an anatomical peculiarity of the laminae, the
occurrence, namely, of small inversely orientated bundles in the
mesophyll (Fig. 28)2.
Hydrocharis is generally described as dioecious, but further
observations are needed on this point. A botanist who examined
the species in Sweden records that, if the male and female
* plants ' are removed from the water without breaking the
intermediate stolons, they are found in reality to be shoots
xy-
FIG. 28. Hydrocharis Morsus-ranae, L. Midrib (m.) and adjacent inverted bundle
(i.b.) from transverse section of leaf. xy. = xylem ; ph. = phloem ; l.b. = lateral branch
of midrib ; px. = protoxylem. ( x 198 circa.} [A. A.]
belonging to the same complicated vegetative system, and not
separate individuals3.
Though the flowers of the Frogbit are not uncommon, seed
is hardly ever set in this country. The ripened seed vessels are to
1 Solereder, H. (1913).
2 £f. StratioteS) p. 52. See also pp. 337-345.
3Lindberg,S. O. (1873).
iv] THE FROGBIT 47
be found, however, in Continental stations; dehiscence is said to
be brought about through the pressure of a slimy mucilaginous
mass produced from the testas1. As in so many water plants,
vegetative reproduction is the chief method of continuance
of the species; it occurs by means of winter buds or * turions,'
which in the late summer begin to replace the ordinary
buds (Fig. 29). The turions differ from the leaf-buds, which
FIG. 29. Hydrocharis Morsus-ranae, L. Part of plant, October i, 1910, showing
turions, marked solid black. (Reduced.) [A. A.]
precede them throughout the spring and early summer, in the
fact that the two first scale leaves do not unfold, but firmly
enwrap the succeeding leaves, while the roots, instead of being
developed at once, remain within the axis as rudiments. The
iQoebel, K. (1891-1893).
48 HYDROCHARITACEAE [CH.
cells of the short, thick stem are packed with large, compound
starch grains. The stolons bearing winter buds are readily
distinguishable, since they incline downwards in the water,
whereas those bearing the summer buds are horizontal or turn
slightly upwards. By the early autumn (e.g. October i), the
turions are ripe and a slight touch detaches them at the absciss
layer, which traverses the stolon close to the base of the bud.
They sink through the water, owing to the starch with which
they are laden, and, since the centre of gravity lies in the solid,
basal region, the morphological apex always remains uppermost.
If a handful of turions be dropped into a tumbler of water,
it is very pretty to see them all balanced erect, only the tiny
segment of the stolon, between the absciss layer and the base
of the turion, resting on the bottom and forming, as it were, an
almost microscopic pedestal. They recall the little tumbling
toys made for children, which are so weighted that no treat-
ment, however rough, can prevent their coming to equilibrium
in the vertical position.
The turions, which are protected externally by a layer of muci-
lage, pass the winter in the mud at the bottom of the water. It has
been demonstrated experimentally that they can remain dormant
for at least two years without losing their power of germination.
The dormancy has been shown to be due to lack of light1 and
can be induced if the buds are not buried but are merely dark-
ened. The increased sunshine of spring or early summer is the
signal for renewed development. The present writer has found
that these turions will readily survive the winter at the bottom
of an ordinary rain-water tub. It was noticed in one season
that, whereas no plantlets were visible in the tub on May 10, by
May 1 5 about seven had risen to the top and were unfolding.
This occurred after a long period of warm weather. The de-
velopment of the little plants coincided remarkably in point of
time ; on May 1 6 they were practically all at the same stage
(Fig. 30). In each case the three outer scales had turned back
1 Terras, J. A. (1900). See also p. 280.
iv] THE WATER SOLDIER 49
so that their tips were below the base of the bud and four or five
foliage leaves had unfolded. The two first of these leaves had
tiny laminae; no roots were yet developed.
The rare land form of Hydrocharis Morsus-ranae produces
turions earlier in the year than the water form; they are gene-
rally subterranean l.
Stratiotes aloides, another British member of the Hydro-
charitaceae, resembles Hydrocharis very closely in its flower,
but is quite unique in vegetative structure. One of its names,
" Water Aloe," vividly suggests the character of its appearance.
-St.
FIG. 30. Hydrocharis Morsus-ranae, L. FIG. 31. Stratiotes aloides, L. Semi-
Young plant developed from a turion, diagrammatic sketch of stem, as it
showing the stage reached on May 16, appears in August, bisected longitudi-
1911. (Nat. size.) [A. A.] nally (v.c.= vascular region of stem;
c=stem cortex; l.t.= leaf- trace; /=leaf ;
st. = young stolon ; s = squamula intrava-
ginalis ; i= adventitious root) . (Slightly
enlarged.) [Arber, A. (1914).]
From an abbreviated, almost tuberous stem (Fig. 31) arise
a very large number of long, linear leaves, serrated at the
edge so sharply as to demand a caution in handling which
justifies the plant's generic name and also its commonest
English title — " Water Soldier." The leaves may be nearly two
feet long. Though the plants of Stratiotes live submerged for
the greater part of the year, the present writer has noticed, in
cultivating them among other aquatics, that their aloe-like form
has the effect of keeping the water surface above them clear of
swimming plants.
1 Gluck, H. (1906).
A. W. P.
50 HYDROCHARITACEAE [CH.
From the lower part of the stem of the Water Soldier, nu-
merous green, unbranched roots hang down into the water.
These roots may attain great lengths. On August n, 1910,
the present writer measured three roots, each over 40 inches
long, growing from the base of one big plant, while on June
30, 1913, seven roots belonging to a single plant, were found
to attain an average of nearly 33 inches in length. The rate
of growth of these roots is singularly rapid ; an elongation of
over 2 inches in 24 hours was several times recorded in the case
of plants growing under somewhat uncongenial conditions in
a London garden1. There is no doubt that, at stages when the
Water Soldier is floating freely, these long roots balance it in
an erect position ; if they are destroyed it is found that the plant
can no longer maintain its equilibrium.
The classic account of the life-history of Stratiotes aloides is
that by Nolte2 which was published nearly a century ago. He
describes the young plants as rising to the surface in the spring,
sinking at fruiting time and rising again, after the seed has been
shed, before finally sinking for the winter. The process appears,
however, to be much less regular than would be gathered from
Nolte's description3 and no later observer seems to have wit-
nessed the rising of the Water Soldier twice during the year.
The plants certainly show a gradual rise in the spring and
summer, while they sink again in the autumn, but the move-
ments probably vary with the depth and composition of the
water, and they may be influenced by the achievement or failure
of fertilisation. The actual mechanism of the rising and sinking
process has now been ascertained4. Stratiotes is apt to frequent
water rich in lime5 and the sinking in autumn is brought about
by the deposition of calcium carbonate upon the surface of
the leaves, until a point is reached at which the specific gravity
of the plant becomes higher than that of the surrounding
1 Arber, A. (1914). 2 Nolte, E. F. (1825).
3 Geldart, A. M. (1906) and Kirchner, O. von, Loew, E. and Schroter,
C. (1908, etc.).
4 Montesantos, N. (1913). 5 Davie, R. C. (1913).
iv] THE WATER SOLDIER 51
water1. It has been shown experimentally2 that, if the chalky
deposit be carefully removed from the surface of a plant which is
stationed at the bottom of the water, it immediately rises to the
top. In nature, the rising of the plant in spring is brought about
by the relative lightness of the young leaves, due to the absence
of a surface layer of calcium carbonate. As these young leaves
become more and more numerous in proportion to the old
leaves with their heavy deposit, the specific gravity of the plant
becomes less and less, until at last it is lighter than water and
floats up to the surface.
The incrustation of the leaves of Stratiotes is by no means
unique; it has long been known that aquatic plants living in
1 hard ' water are liable to become covered with a chalky coat.
The generally recognised explanation is that, since calcium car-
bonate is scarcely soluble except in water containing carbonic
acid, the abstraction of carbon dioxide, by the green organs of
aquatics, leaves the chalk as a deposit on their surfaces. This
theory is due to Pringsheim3, who demonstrated the truth of
his view by a series of very delicate experiments, in which he
actually observed microscopically the deposition of crystals of
calcium carbonate upon the surface of moss leaves, algal fila-
ments, etc., immersed in water containing carbon dioxide and
calcium carbonate in solution.
Owing to the curious mode of life of Stratiotes^ its youngest
leaves are usually entirely submerged, but when mature, they
may be submerged for part of the year but raised above the
surface for another part. It was formerly supposed that the
distribution of the stomates on the leaves could be directly
traced to the action of the environment. For instance, it has
been stated4 that, in a single leaf which was partly submerged
1 In justice to Nolte, it ought to be mentioned that he anticipated the
discovery that the rising and sinking of the plant was due to differences
in specific gravity between the old and young leaves, but he made the
mistake of supposing that the greater weight of the old leaves was due to
waterlogging. 2 Montesantos, N. (1913).
3 Pringsheim, N. (1888). * Costantin, J. (i8853) and (1886).
4—2
52 HYDROCHARITACEAE [CH.
and partly aerial, the exposed region bore stomates, while the
submerged part had none. Recent work has shown that this
is altogether too simple an account of the position. It has been
demonstrated1, for instance, that leaves which are entirely, or
almost entirely submerged, may nevertheless have stomates
throughout their entire length. On the other hand, in the case
of a plant which was growing at the bottom of the water, and
of which the outer leaves were partly aerial, it was found that
these outer leaves bore no stomates whatever, but a transition
to stomate-bearing leaves was observed among the younger
leaves; the youngest, which were also the deepest in the water,
bore the most numerous stomates. The interpretation sug-
gested by the writer to whom we owe these observations, is
that the leaf with stomates is the higher form, which can only
be developed in favourable surroundings, while the stomate-free
leaves are primary leaves, occurring typically under conditions
of poor nutrition. We shall return to this subject later on, in
considering heterophylly in general2.
Besides the epidermis, the other tissues of the leaf show
certain interesting features. The vascular skeleton consists of
five, or more, strong longitudinal veins united by transverse
connexions. Spirally thickened tracheids occur in the bundles
even in the submerged leaves. In the transverse section of the
rather thick lamina, besides the main row of normally orientated
bundles, there are two rows of small bundles, one row lying
near the under side and normally orientated, and the other
towards the upper surface and inversely orientated3. The occur-
rence of these inverted bundles in the leaves of the Hydrochari-
taceae is significant in connexion with the 'phyllode theory'
of the Monocotyledonous leaf4.
In the axil of each leaf of the Water Soldier are found the
mucilage-secreting scales (sguamulae intrav agin ales) character-
istic of the Helobieae5.
1 Montesantos, N. (1913). 2 See pp. 156-160.
3 Solereder, H. (1913). 4 Arber, A. (1918); see also p. 46.
5 Nolte, E. F. (1825) and Irmisch, T. (18582).
iv] THE WATER SOLDIER 53
If vigorous plants of Stratiotes be examined in the late sum-
mer, they will be found to have produced numerous lateral
stolons terminating in buds1 (Fig. 32). These buds do
not, like those of Hydrocharis, pass the winter in a closed con-
dition, but open at once, and may be described as winter-buds
FIG. 32. Stratiotes aloides, L. Plant after flowering in August, bearing five plant-
lets at the ends of stolons. (Reduced.) [Modified from Nolte, E. F. (1825).]
which germinate while attached to the parent plant. There is,
in fact, no interruption in the vegetative life, since the daughter
shoots, as soon as they become free from the parent axis in
autumn or winter, begin to form new winter-buds themselves.
In North Germany, the Water Soldier was described in 1860
1 Gluck, H. (1906).
54 HYDROCHARITACEAE [CH.
as so abundant as to be a troublesome weed, the plantlets sur-
viving the hardest winter1.
In the great majority of localities the continued existence of
Stratiotes depends absolutely upon bud-formation, since the
plant is dioecious, and only in a small part of its range is it
found with both male and female flowers. In England only the
female plant is usually met with (Fig. 33). There are some
records of the occurrence of hermaphrodite flowers2, but ripe
fa--'
A B C
FIG. 33. Stratiotes aloides, L. A, unopened female flower emerging from two
bracts (6). B, female flower with bracts and perianth removed to show ovary (o),
stigmas (st.) of which there are six, each bifurcated to base, and staminodes (sta.).
C, unfertilised fruit (o) emerging obliquely from the bracts. [A. A.]
seed does not seem to be formed in this country at the present
day, though fruits with seeds are known from Pliocene and
Pleistocene deposits3. The geographical distribution of the
sexes is rather curious. According to Nolte4, in the northerly
part of the range of the species only female plants occur, while
at the southern extremity the plants are either predominantly
or entirely male. In an intermediate area both sexes occur.
In addition to the Frogbit and the Water Soldier, Hydrilla
1 Klinsmann,F.(i86o). 2 Geldart, A.M. (1906). 3 Reid, €.(1893).
4 Nolte, E. F. (1825); see also Caspary, R. (1875).
iv] THE CANADIAN WATERWEED 55
verticillata, another member of the Hydrocharitaceae, has re-
cently been recorded from one station in Britain, though it is
typically a plant of warm climates1. But a fourth
genus, Elodea, represented by the Canadian
Waterweed, a submerged plant, which was
apparently introduced into this country about
i8432, has become very much more common
than any other member of the family. In nearly
all the localities in Britain, only the female plant
is found, though the male has been recorded
as occurring near Edinburgh3. The reproduc-
tion of Elodea canadensis, which is amazingly
rapid, is thus entirely vegetative; the snapping
of the slender, brittle stems sets free fragments
which live independently, while special winter- FIG. 34. Elodea
shoots may also be produced (Fig. 34). The %£££•*££
small leaves, which are arranged in whorls [Raunkiaer, c.
r i 11 1 • i i • • (1896).]
or three, are only two cells thick and it is to
their extreme delicacy that the plant probably owes its incapacity
to produce a land form 4.
The pollination mechanism of the genus Elodea is of some
significance, owing to the different phases met with in different
species. Most of the species have inconspicuous flowers. The
male flowers either become detached and rise separately to the
surface of the water, e.g. E. canadensis 5, or they are carried up
by the growth of their thread-like stalks, e.g. E. ioensis*
(Fig. 35, p. 56). The stigmas reach the surface owing to the
elongation of the floral tube which in E. canadensis may reach a
length of 30 cms.7. In an Argentine species, E. callitrichoides*, in
1 Bennett, A. (1914).
2 Marshall, W.(i852)and(i 857), Caspary,R. (18582) and SiddallJ. D.
(1885). See pp. 2 1 0-2 1 3 for a further account of the spread of this plant
in the British Isles. 3 Douglas, D. (1880).
4 Schenck, H. (1885). 5 Wylie, R. B. (1904).
6 Wylie, R. B. (1912), also E. canadensis according to Douglas, D.
(1880). 7 Wylie, R. B. (1904). 8 Hauman-Merck, L. (i9i32).
56 HYDROCHARITACEAE [CH.
which the pollination has been described in detail, the sub-
merged male buds are found to be each occupied by a bubble of
gas, probably carbon dioxide. Directly the flower reaches the
FIG. 35. Elodea ioensis, Wylie. i, open staminate flower attached to plant.
2, mature staminate flower enclosed within the spathe. 3, staminate flower
emerging from the spathe. 4, detached and empty staminate flower floating on
the water with elongated axis trailing. [Wylie, R. B. (1912).]
surface by the elongation of its filiform axis1, it opens suddenly
and at the same moment the pollen sacs dehisce explosively. It
thus comes about that abundant pollen floats on the surface of
1 This axis is mentioned by Caspary, R. (i8582) with the incorrect de-
scription " tubus calicis filiformis."
iv] POLLINATION AND LEAF FORM 57
the water, and surrounds the stigmas of the female flower. It
has been suggested that perhaps the pollen may be attracted
to the receptive surfaces by currents due to some secretion from
the stigmas. It has been shown in E. canadensis that the spines
on the outer coat of the pollen-grain hold back the surface-film
from contact with the body of the spore and thus imprison
enough air to keep it afloat1.
A somewhat different method, in which water also plays
a part, is found in Fallisneria^ while in Hydromy stria the
pollination is sometimes effected by wind and sometimes by
water3. In Elodea dens a 4, the large white flowers contain nectar,
and insect pollination occurs; this genus thus shows transitions
between the entomophilous members of the family, such as
Hydrockaris, and the hydrophilous and anemophilous genera.
Among vegetative characters, perhaps the most notable
feature of the Hydrocharitaceae is the great variation in the
form and mode of life of the leaf in the different genera. To
illustrate this we may briefly enumerate the leaf characters of
a few genera selected entirely from the fresh-water members
of the family.
Hydrocharis. In certain species, heart-shaped floating leaves alone.
Strattotes. Stiff, serrated, linear leaves, sometimes entirely submerged,
sometimes partially aerial.
Boottia. Lower leaves short-stalked and submerged; upper leaves long-
stalked and often aerial.
Ottelia. Leaves differentiated into submerged leaves, with a narrow
blade, and stalked leaves with broader blades, which may be submerged,
floating or aerial.
Vallisneria. Leaves entirely submerged, ribbon-like, growing in rosettes.
Hydrilla and Elodea. Leaves entirely submerged, short and linear,
growing on elongated axes.
Three genera of the Hydrocharitaceae, Enhalus^ Halophila
and Thalassia^ live in salt water; these we shall consider in
Chapter x.
1 Wylie, R. B. (1904). 2 See p. 235.
3 Hauman, L. (1915). 4 Hauman-Merck, L. (i9i32).
CHAPTER V
THE LIFE-HISTORY OF THE POTAMOGETONA-
CEAE OF FRESH WATERS1
POTAMOGETON, the central genus of the Potamoge-
tonaceae, includes the very numerous Pondweeds, so
common in temperate waters, and is the richest in species of all
our native aquatic genera. The Pondweeds are an exceedingly
difficult group from the point of view of the student of system-
atic botany, as the numerous species can, in many cases, only
be discriminated as the result of much experience. A character
which increases the difficulty of identifying them is the capa-
city for variation in form shown by one and the same individual.
The present writer took a typical shoot of Potamogeton perfoliatus
from the Cam in July, and kept it floating in a rain-water tub.
By October I most of the large perfoliate leaves had decayed
and those on the new shoots were so much narrower and less
perfoliate as to make it difficult to believe that they belonged
to the same species (Fig. 36). This power of variation in
leaf-form within one individual is a well-known feature of
P. perfoliatus. It has been recorded that an isolated plant in a
newly-dug clay-pit, observed during several years, changed so
much in the shape, colour and texture of the leaves as to give
rise to the idea that all the British forms of the species which
have been described, may possibly be mere states and not
variations2.
The most obvious difference between the Potamogetons and
the water plants hitherto considered, lies in the extreme com-
plexity of the shoot systems of the Pondweeds. The rhizomes
1 The marine Potamogetonaceae are considered in Chapter x.
2 Fryer, A., Bennett, A. and Evans, A. H. (1898-1915). This account
of the British Potamogetons is of the first importance.
CH. v] THE PONDWEEDS 59
form mats at the bottom of the water, retaining the soil in their
meshes and thus consolidating it, while, from these rhizomes, a
forest of leafy shoots rises into the water1. An examination
of the individual axes shows the branch system to be sympo-
dial 2. The shoots are of two kinds; the first is horizontal, more
or less buried in the soil, colourless and scale-bearing, while the
second is erect, floating to some degree, and producing perfect
leaves. Fig. 37, p. 60, illustrates the general scheme of branching.
The creeping stem is a sympodium formed by the union, end to
end, of the two first internodes of successive generations (I, II,
FIG. 36. Potamogeton perfoliatus, L. Detached floating shoot, October i, 1910,
showing how much the plant at this time of year may depart from the perfoliate
leaf type. Several ''winter shoots" have developed. (^ nat. size.) [A. A.]
Ill, etc.), the succeeding internodes constituting the erect stem.
In one season a great many of these rhizome units may be formed.
The first scale leaf of each erect shoot (#, a', a", a'") bears a
reserve bud on its axil, which may give rise to another segment
of rhizome, again repeating the entire process, so that the whole
ramification becomes extremely complicated. In Fig. 37, IF,
I IF, represents a reserve shoot, arising in the axil of c, the
third scale leaf of Shoot I. By the decay of the older parts of
the rhizomes fresh individuals become separated, and even the
1 Graebner, G. in Kirchner, O. von, Loew, E. and Schroter, C.
(1908, etc.). 2 Irmisch, T. (i8583) and Sauvageau, C. (1894).
6o
POTAMOGETONACEAE
[CH.
erect shoots, if detached from the parent, can form new plants.
The leafy shoots branch relatively sparsely in the large-leaved
forms, but more freely in those with small leaves.
FIG. 37. General branch system of a typical Potamogeton. I, II, III, . . .the different
shoot-generations; a, b, c: a', b', c',. . .the three first scale-leaves borne by each
shoot-generation; II', III' is a reserve shoot arising in the axil of leaf c belonging
to shoot I. [Adapted from Sauvageau, C. (1894).]
LEAVES OF THE PONDWEEDS
61
The various species of Potamogeton show transitions between
plants with floating leaves, capable of producing a land form,
and plants with submerged leaves, living entirely beneath the
water-surface, except that they raise their flowers slightly into
the air. Potamogeton natans may be taken as a type of the Pond-
weeds with floating leaves; these consist of a sheathing base
with stipules, a long petiole and an elliptical to lanceolate blade,
leathery in texture. The early leaves on each shoot, which do not
reach the water-surface, are phyllodic and represent only the
petioles of the perfect leaves. Intermediate leaf-forms also
occur, with small, spoon-like expansions of the apex1. The
relation between the narrow submerged
leaves and the broad floating leaves is
identical with that subsisting between
the two corresponding leaf-types in
Sagittaria. The land form of Potamogeton
natans is shown in Fig. 125, p. 196.
Another species of Potamogeton^
P. pulcher, Tuckerm., of N. America,
produces not only broad floating leaves
but broad submerged leaves, while
others, such as P. heterophyllus, Schreb.,
have ovate or oblong floating leaves,
but their submerged leaves are of a
narrower type.
The more completely aquatic species ...
form submerged leaves alone, with ** A ** •'
, r i it'- i i i T-. i FIG. 38. Potamogeton zosteri-
lammae of variable breadth. Examples foiius, Schum. Upper part
of this group are P. lucensy P.perfoliatus
and P. crispus. In these and related
species the blade is exceedingly thin,
often with only one plate of cells be-
tween the two epidermal layers, but it is supported by fibrous
strands running the length of the leaf (s in Fig. 38). The
lamina is often crisped or undulated at the margin in a
1 Schenck, H. (1885); see also Fig. 168, p. 339.
of leaf; mn, snlt sn.2, tn, vas-
cular bundles; s, bast bun-
dles; rs, bast bundle along
margin, (x 12 circa.) [Raun-
kiaer, C. (1903).]
62
POTAMOGETONACEAE
[CH.
graceful way. A similar undulation is characteristic of Apono-
geton ulvaceus. Baker1. A curious feature of the leaves of
various species, e.g. P. lucens and P. praelongus, is their shining
oily surface2, which is due to the presence, in the epidermal
cells, of large oil drops secreted by special colourless plastids.
The non-wettable, slippery surface thus produced may be, it is
suggested, a protection against water animals and micro-para-
sites. It has also been supposed that the oil may hinder diffu-
sion and hence prevent the soluble products of assimilation
from being washed out of the leaf. But it seems to the present
writer more probable that the oil is a mere by-product of the
plant's metabolism; there is no valid reason for making the
assumption that it performs any special function in the life-
history.
FIG. 39. Diagrammatic T.S. of stem stele of three species of Potamogeton to show
reduction and fusion of vascular strands. tlf 7\, *lf traces of next higher leaf;
*a. T2> *2> traces of second higher leaf; remaining strands cauline. A, P. pulcher,
Tuckerm. B, P. natans, L. C, P. crispus, L. [Chrysler, M. A. (1907).]
Such species as Potamogeton trichoides and P. pectinatus have
very narrow submerged leaves which are linear in form and
tender and translucent in texture.
The species belonging to Potamogeton and the allied genus
Zannichellia can be arranged, according to the anatomy of their
stems and roots, in a reduction series, beginning with the types
with floating leaves, whose axes show a complicated internal
structure, and ending with entirely submerged, narrow-leaved
species, in which the anatomy is reduced to a state of extreme
simplicity3. But it is uncertain whether this sequence completely
1 Krause, K. and Engler, A. (1906). 2 Lundstrom, A. N. (1888).
3 Schenck, H. (1886) and Raunkiaer, C. (1903).
vj STEM ANATOMY OF PONDWEEDS 63
represents the evolutionary history, since it is possible that
certain forms with floating leaves may have had a submerged
ancestry. The species whose central cylinder diverges least from
a normal terrestrial type, seems to be Potamogeton pulcher^
(Fig. 39 A). Here a section across an internode of the leafy
shoot reveals, within the central cylinder, three distinct bun-
dles (/! , jTj_ and /x) which are the traces of the leaf immediately
above, and three more (/2 , T2 and /2) which entered at a still
higher node. In addition there are several bundles which are
purely cauline. The type represented by our native P. natans
(Fig. 39 E] differs from that of P. pulcher in the fact that the
traces belonging to each leaf do not so fully retain their inde-
pendence in the central cylinder. P. perfoliatus belongs to the
type of P. natans. In P. crispus (Figs. 39 C and 40 A^ p. 64) the
stele is more condensed, the bundles being collected into three
groups. In very slender stems of this species, the two passages
in each group representing the xylem may fuse so that the
distinctness of the bundles is maintained by the phloems alone.
P. lucens2 (Fig. 40 R) has a median and two lateral bundle-
groups, but these are more reduced — the median group con-
sisting of one xylem passage and two phloem regions, and the
laterals, of one xylem passage, and one patch of phloem. In
this species the tendency to concentric arrangement begins to
make itself felt. In P. pusillus (Fig. 40 C) the lateral bundles
are entirely fused with the median, as far as the xylem is con-
cerned, but the phloems still remain distinct. In P. pectinatus
(Fig. 40 Z)) the ultimate term in the reduction series is reached :
a ring of phloem surrounds a single xylem passage. Zannichellia
closely resembles P. pectinatus \ ephemeral xylem vessels have
been detected in the apical region of the stem3. In the case of
the related genus Althenia^^ vessels are also retained in this
region and in the nodes.
1 Chrysler, M. A. (1907).
2 On this and other species, Sauvageau, C. (1894) should be consulted.
His account diverges in some points from that of Schenck.
3 Schleiden, M. J. (1837). * Prillieux, E. (1864).
POTAMOGETONACEAE
[CH.
end
C D
FIG. 40. Reduction series in central cylinder of stem in Potamogeton. A, P.
crispus, L. (cf. diagrammatic Fig. 39, C) (x 160) ;'B, P. lucens, L., in which fusion of
the strands has gone further, so that each of the three bundle groups has one
xylem only; mp = conjunctive tissue (xi3o); C, P. pusillus, L., in which the
xylems of all the individual bundles form a single central passage ( x 290) ; D, P.
pectinatus, L., completely concentric structure in which all trace of the component
bundles is lost; end = endodermis (x29o). [Schenck, H. (1886).]
v] ANATOMY OF THE PONDWEEDS 65
The tendency to condensation and simplification of the stem
stele, which is so well illustrated among the Potamogetons *, is,
as we shall see in Chapter xm, a characteristic of many aquatics.
The stem of the Pondweeds is, however, peculiar in that the
bundles are not confined to the central cylinder. In some spe-
cies there is a complicated system of cortical strands, occurring
at the intersection of the diaphragms separating the lacunae.
These cortical bundles communicate with one another and with
the axial strand by means of anastomoses at the nodes.
A B
FIG. 41. Structure of central cylinder of root in Potamogeton. A, P. natans, L.
gef, vessel; s, sieve tube with companion cell; p, pericycle; cj, conjunctive tissue
(x 470). B, P. densus, L. Similar to P. natans, but vessels and endodermis thin-
walled; sieve tubes shaded (x 470). C, P. pectinatus, L., xylem reduced to single
vessel (x 470). [Schenck, H. (1886).]
We have so far been considering the anatomy of the leafy
shoot alone. It should be noted that the structure of the hori-
zontal rhizome and of the inflorescence axis are often markedly
different. For instance, in the creeping stem of P. pulcher, the
central cylinder takes the form of " a truly dicotyledonous look-
ing ring of collateral bundles," while the flowering axis of
P. natans also has its vascular strands arranged in a regular
ring2.
1 Sanio, C. (1865) first recognised that the apparently simple axial
strand of certain Potamogetons was really the reduced representative of a
whole system of bundles.
2 Raunkiaer, C. (1903) and Chrysler, M. A. (1907).
A. W. P. z
66 POTAMOGETONACEAE [CH.
A similar reduction series to that met with in the central
cylinder of the stem can be traced in the root1. In Potamogeton
natans (Fig. 41 A^ p. 65) the root is pentarch and the walls of all
the elements, except the sieve tubes, are thickened. P. densus
(Fig. 41 B) has the same type of structure, but the cell- walls
remain thin. In P. fectinatus (Fig. 41 C) the five protoxylem
elements are absent, and the xylem is represented merely by
a single central vessel with delicate, spiral thickening2. The
structure of the root of Zannichellia is similar, but the axial
vessel is unthickened.
The Potamogetons tide over the winter in various ways. In
P. fectinatus^ the Fennel Pondweed, common in fresh and
brackish waters, the leafy shoots give rise to tubers in the
autumn. These tubers are usually formed by the swelling of
the two basal internodes of that part of the axis which would
otherwise become erect and leafy. Each tuber is enclosed in a
scale leaf and terminates in a bud ; it contains starch and, as it
is easily detached, it forms a means of vegetative multiplication.
Other species are reproduced by special buds, or turions3, in
which the leaves, rather than the axis, play the chief part. A
group of submerged Pondweeds with linear leaves, of which
P. pusillus and P. trichoides are examples, is characterised by
winter-buds enclosed in scales corresponding morphologically
to axillary stipules accompanied by rudimentary laminae. In
this group of species there is no rhizome, branching sympodially
in the mud, the only part corresponding to such a rhizome being
the elongated axis of the turion; the branched leafy shoots play
the chief role in the axial development. The whole vegetative
body in these species dies off in the autumn and the turions
alone remain. These buds are formed in great numbers, and
iSchenck, H. (1886).
2 Sauvageau,C. (18892) describes the roots ofP.pectinatus as having, in
general, a less degraded type of structure than that attributed to them by
Schenck, H. (1886).
3 Gliick, H. (1906) deals comprehensively with the turions of the
genus.
v] WINTER-BUDS OF THE PONDWEEDS 67
often many thousands lie on the soil at the bottom of the water.
They germinate without rising to the surface. The formation
of winter-buds in this group of Pondweeds, as indeed in
aquatics in general, is encouraged by unfavourable conditions1.
For instance, if the environment is otherwise satisfactory, but
the depth of the water is excessive, causing the plant to exhaust
itself in the production of long axes, turion formation may occur
unusually early in the year.
Potamogeton crzspus2 is related, in its wintering habits, to the
group just dealt with, but its turions are singular in certain
respects. The word * bud ' seems in this case to be a misnomer,
as the thick, toothed leaves of the turion do not enfold one
B
FIG. 42. Potamogeton crispus, L. Germinating turion. A, a turion from bottom of
water, March 16, 1912, with one lateral branch. B, the same turion, April n, 1912,
when it had developed a number of lateral branches and a root. (Nat, size.)
[A. A.]
another, but stand out at a wide angle from the axis. They are of
unusual consistency, being hard and horny. The turions may
be from 10 to 50 mm. long and bear three to seven leaves. As
their discoverer, Clos, pointed out more than sixty years ago,
their mode of germination is quite peculiar, since there is no
elongation of the axis, and further development is due entirely
to the production of axillary branches. The process of germi-
nation can be followed in Fig. 42 and Fig. 43, p. 68. Figs.
1 See pp. 222-224.
2 Clos, D. (1856), Treviranus, L. C. (1857), Hildebrand, F. (1861),
Coster, B. F. (1875) and Gluck, H. (1906).
5—2
68
POTAMOGETONACEAE
[CH,
FIG. 43. Potamogeton crispus, L. Advanced stage in the germination of
a turion (reduced). The first shoot, A, produced from the turion, T, has
given rise to three lateral sympodia, B, C, D. The first and second shoot-
generations of B have given rise to two reserve shoots, a and b. [Adapted
from Sauvageau, C. (1894).]
v] WINTER-BUDS OF THE PONDWEEDS 69
42 A and B were drawn from a bud which had passed the
winter at the bottom of a rain-water tub in the present writer's
garden. The turions of this species seem to be primarily repro-
ductive bodies, and to be only secondarily concerned with
tiding over the winter, for large numbers germinate without a
resting period. Not only the rhizomes, but certain of the leafy
shoots, are capable of lasting over the cold season, if they are
not actually frozen. The special winter branches differ some-
what from the summer shoots
in having leaves without a
crisped margin, and they have
hence been sometimes mis-
taken for a distinct species.
A second group of Pond-
weeds is characterised by
winter-buds whose enclosing
scales consist merely of axil-
lary stipules, the correspond-
ing blades having wholly
disappeared. Fig. 44 repre-
sents a transverse section
of a turion of Potamogeton
rufescens, which conforms to
this type. In this species the
winter-buds are formed
chiefly on the underground
rhizome, while in P.fluitans,
Roth — a species closely re- FIG. 44
lated to P. natans — they
occur in this situation only.
Potamogeton perfoliatus, L.
Potamogeton rufescens, Schrad.
T.S. through a turion. 'A and B, outer
scale leaves equivalent to stipules; I-IV,
foliage leaves, whose stipules are marked
1-4 and put in in solid black. Squamulae
intravaginales are omitted. (Enlarged.)
[After Gliick, H. (1906), Wasser- und
Sumpfgewachse, Bd. n, p. 160, Fig. 23.]
forms winter-buds which are
not deciduous but unfold in
situ (Fig. 36, p. 59).
In flower structure1, as well as in anatomy, a reduction series
iSchenck, H. (1885).
70 POTAMOGETONACEAE [CH.
can be traced in the Potamogetonaceae. This series ranges
from forms such as Potamogeton natans^ with an erect spike
of numerous flowers, through various intermediate types, to
the related genus Ruppia, in which the pollen_flqatsi_ajid the
2^f /stigmas are raised to the surface to receive it, and ultimately
to Zannichellia and various marine members of the family, in
which the pollination is entirely submerged. Even within the
genus Potamogeton itself, there are a number of gradations in
A B
FIG. 45. Zannichellia polycarpa, Nolte. A, shoot (nat. size) with flowers (/).
B, flowers (enlarged); st, stamen; g, gynaeceum; m.c., membranous cup. May 25,
1912. [A. A.]
the direction of submerged life. The flowers possess, typically,
four stamens, and four free carpels. They appear, at first glance,
to possess also four perianth members, but more careful exami-
nation reveals that these are, in reality, leaf-like outgrowths
from the staminal connective1. The spike of P. natans is sup-
ported above the water by the two floating leaves immediately
below it. These are always opposite (cf. Fig. 37, p. 60), although
otherwise the leaves are alternate. In some species, e.g. P. pec-
tinatus, the spikes, instead of being stiff and erect, are thin and
flexible, and float horizontally on the water. In these forms
1 Information as to the morphology and development of the flower and
fruit will be found in Hegelmaier, F. (1870), Schumann, K. (1892), etc.
v] THE HORNED PONDWEED 71
the flowers are distant, and when mature they are lifted, one by
one, a little above the water-surface. In other cases the inflo-
rescences are much reduced — only four flowers being developed
in Potamogeton pusillus — while in P. trichoides the individual
flowers are modified, the number of carpels being reduced to
one. In Zannichelliapolycarpa the flowers areunisexual (Fig. 45),
a male and female flower (or inflorescence) being found together
in one leaf-axil; the male flowers are generally reduced to a
single stamen (sf Fig. 45 B\ while several carpels with funnel-
shaped stigmas (g) are grouped together, and enclosed in a
membranous cup (m.c.*). This cup has been interpreted as a
spathe enclosing a group of female flowers, each reduced to one
carpel. The filament is at first very short, but elongates so as
to rise above the pistils at anthesis. The anther dehisces and the
pollen grains fall into the open mouths of the cornucopia-
shaped stigma, and slide down the stylar canal, whose diameter
is almost double that of the pollen grains. The descent of the
pollen grains through the water is due to the fact that when
they become ripe they are weighted with starch grains1.
Owing to the air spaces in the pericarp wall, the achenes of
some of the Potamogetons float for a time, before becoming
waterlogged and sinking. The air-containing tissue of the peri-
carp in P.perfoliatus, and the cuticularised epidermal layer (0.£.),
are shown in Fig. 46, p. 72.
The fruits of the Pondweeds, after becoming to all appear-
ance ripe, often rest for a considerable period before germina-
tion2, except in the case of P. densus, in which the achenes
sprout a few days after they fall. But this species is rather
remote from the rest of the genus in other respects, such as the
opposite arrangement of the leaves, and the absence of the
ligule. Sauvageau3 has shown by experiment that in P. crispus
it is the hard integument which delays germination; when the
embryo is laid bare by the removal of part of the seed coat,
sprouting rapidly occurs. The same author observed that when
1 Roze, E. (1887).
2 The delayed germination of aquatics in general is considered in
Chapter xix, p. 243. 3 Sauvageau, C. (1894).
72 POTAMOGETONACEAE [CH. v
fifty fruits of P. natans, which had been gathered in September,
1889, were kept in water at the temperature of the laboratory,
none germinated in 1 8 90 or 1891, six germinated in 1892, and
thirty in 1893, i.e. after lying dormant for three years and a
half.
FIG. 46. Potamogeton perfoliatus, L. Transverse section of fruit wall to show air
spaces in the outer region of the wall, and also the thick outer cell-wall of outer
epidermis (o.e.). The cross-hatching indicates the non-cuticularised part of the
wall: only the outermost surface layer, shown in black, is converted into cuticle
(c). Chlorophyll grains in epidermis. (x26o.) [A. A.]
The most striking feature of the Potamogetonaceae, as a
family, seems to be the remarkable reduction series shown by
the vegetative and reproductive organs — the degree of reduc-
tion serving in general as a gauge for the degree of completeness
with which the aquatic life has been adopted.
[73]
CHAPTER VI
THE LIFE-HISTORY OF THE LEMNACEAE1
AND OF PISTIA
EACH of the families with which we have been con-
cerned in the preceding chapters, has shown very great
variation in vegetative structure associated with the differing
degrees in which its members have adopted the aquatic habit.
In the Lemnaceae, which we propose now to discuss, we have,
on the other hand, a remarkably sophisticated and uniform
group of plants, all of which pass their life floating at or near
the surface of the water; the members of the family show,
throughout their structure, a high degree of similarity to one
another, and a marked difference from other aquatics. The
Duckweeds have a very wide range, and occur almost as
generally in the Tropics as in the northern countries where we
know them so well2.
In the Lemnaceae the modification of the vegetative body
has been carried so far that the usual distinction between stem
and leaf is no longer obviously maintained. The Duckweeds
are not unique in this disregard of morphological categories —
two other groups of water plants, the Utricularias and the
Podostemaceae, carry this infringement of botanical conven-
tions to an even more extreme point.
The little green fronds of the Duckweeds produce similar
fronds of the second order, and also inflorescences of an ex-
tremely reduced type (Fig. 47, p. 74 and Fig. 50, p. 79) from
pockets occurring on either side in the basal region. The nature
of the fronds has been very variously interpreted. Hegelmaier 3,
1 Hegelmaier, F. (1868) is still the classic monograph of this group.
See also Schleiden, M. J. (1839) and Hegelmaier, F. (1871) and (1885).
2Kurz, S. (1867).
3 Hegelmaier, F. (1868). For another view see Dutailly, G. (1878).
74 LEMNACEAE [CH.
in his monograph of the Lemnaceae, treats them as stem organs
which are modified to perform the work of leaves. Engler1, on
the other hand, follows van Horen2 in in-
terpreting the distal end of the frond as
foliar, while the proximal end is axial. Yet
a third view is that of Goebel 3 who expresses
the opinion that the leaf-like organs of the
Lemnaceae are actually leaves, pure and
simple. He explains the origin of the lateral
shoots of each generation from the base of
the preceding one, by assuming that the base FIG. 47. spirodeiapoiyr-
of each leaf has the power of functioning rhi*a> Schlf d- *nfl°r-
r o escence. stt and s/2,
as a growing point. Undoubtedly Engler's male flowers reduced
i • i • i i i to stamens; c., female
view — which is based upon a comprehen- flower reduced to a
sive study of the Araceae, and a critical gynaeceum;s£.,spathe;
/ r ~. i i -r /., lateral shoot. [Hegel-
exammation of Ptstta and the Lemnaceae — maier, F. (1871).]
may be accepted as the best founded. The
present writer has recently carried Engler's comparison further,
and has shown that the buds in the case of Pistia arise in
minute pockets closely recalling those of the Duckweeds4.
The three genera into which the family is divided — Spiro-
dela, Lemna and Wolffia — are all represented in Britain.
Spirodela polyrrhiza, Schleid.5, is the largest member of the
Lemnaceae; when it is growing vigorously its fronds attain to
about J- of an inch both in length and breadth. Several roots
with conspicuous root-caps hang from the underside of each
frond. They are somewhat heavier than water and their tips
are the heaviest part. It has been suggested that one of the
functions of these roots may be to ensure the equilibrium of the
plant 6. Spirodela forms special shoots which outlast the winter.
1 Engler, A. (1877). 2 Horen, F. van (1869).
3 Goebel, K. (1891-1893). 4 Arber, A. (i9i94).
5 For a description of the very rare flowers of this species see Hegel-
maier, F. (1871).
6 Gasparini, quoted by Hegelmaier, F. (1868); Ludwig, F. in Kirch-
ner, O. von, Loew, E. and Schroter, C. (1908, etc.).
vi] WINTER-BUDS OF GREATER DUCKWEED 75
Such turions are of great importance throughout the family,
since the flowers are rare and relatively little seed is set. The
winter-fronds of Spirodela are smaller than the summer ones
and almost kidney-shaped. The air spaces in the tissues are
reduced, and the cells are packed with starch, with the result
that the fronds are heavier than water. The roots remain un-
developed. These winter-buds become detached from the
parent frond in the autumn and sink to the bottom of the water.
In the spring, a lateral frond begins to grow out; in so doing it
absorbs the starch from the parent, and on this account, and also
by development of air spaces, the whole body becomes lighter
and rises to the surface1. The present writer has found that the
rising of the winter-buds can be induced, as early as January,
as a result of a few days in a warm room, even in a dim light.
The time of year at which the turions begin to be formed is
variable, and depends on external conditions. It has been shown
by van Horen2 that in shady places they develop very late or
even fail altogether, whereas they occur early in bright sun-
light, especially if the water is stagnant. Guppy 3, who has made
a special study of the habits of the Lemnaceae, mentions that
on one occasion he found a large number of plants of Spirodela
polyrrhiza in a ditch, producing winter-buds, at the beginning
of July, to an extent he had never seen before or since; the
conditions were precisely those indicated by the previous ob-
server as being favourable to the early occurrence of this phase
— namely almost stagnant water which was brilliantly insolated.
During the few weeks preceding the observation of the winter-
buds, Guppy records that the surface was frequently heated in
the day time to 80° Fahr. (nearly 27° C.). It is difficult to
understand why conditions so favourable for vegetative growth
should initiate turion formation, since in most water plants
their production is induced by a state of poor nutrition. Pos-
sibly the explanation may lie in the great size of the winter-bud
of the Lemnaceae in relation to the entire vegetative body of the
1 Hegelmaier, F. (1868). 2 Horen, F. van (1869).
^ Guppy, H. B. (1894*).
LEMNACEAE
[CH.
parent, when compared with the small proportion that the
turions of other aquatics bear to the plant producing them. To
synthesize enough starch to fill the cells of the winter-bud may
be a considerable tax on the parent frond, and may only be
possible under conditions peculiarly favourable for photo-
synthesis.
The commonest British Duckweed is Lemna minor, L.1,
which seems to be in some ways the
least specialised, among our native
species, for its particular mode of
life. No definite turions are formed,
and the plants are to be found
swimming at the surface of the
water at almost all seasons. When
frozen, the older fronds become
water-logged more readily than the
younger ones, and they sink to the
bottom, dragging down the young
laterals with them.
Another species, Lemna gibba,
L.2, is notable for having the under-
side of the frond modified as a
spongy aerenchyma — the gibbous
form so produced giving the species
its name (Fig. 48). The degree of
development of the air tissue varies
with the external conditions; the
fronds are most conspicuously
gibbous in running water where
the insolation is moderate3. At certain periods of the life-
FIG. 48. Lemna gibba, L., with
fruit,/. [Hegelmaier, F. (1868).]
1 On the flowering of Lemna minor see Brongniart, A. (1833) and
Kalberlah, A. (1895); on the gametophytes and fertilisation, Caldwell
O. W. (1899).
2 On the flowers and seed of Lemna gibba see Micheli, P. A. (1729)
and Brongniart, A. (1833)5 on the germination, Wilson, W. (1830).
3 Horen, F. van (1869).
vi] THE GIBBOUS DUCKWEED 77
history, flat fronds are however produced and we owe to Guppy1
the elucidation of the part played by the two types of shoot. He
observed one hot summer, when Lemna gibba flowered profusely
in July, that, during August, the gibbous plants gave rise to
numerous thin, flat fronds of a dark green hue. These were the
turions, and their appearance was accompanied by the death of
a large number of the gibbous mother-plants, a result which this
author attributes to exhaustion after flowering. Many of the
gibbous plants, however, survived and continued to bud off
winter-fronds except during the severest weather. Early in Feb-
ruary the budding recommenced, but the gibbous character was
not displayed until the weather became warmer. This author
thinks that for the development of the gibbosity the plants re-
quire an average daily maximum temperature at the surface of the
water, not much, if at all, under 70° Fahr. (21° C.). After cool
summers when Lemna gibba does not flower, no flat winter-buds
are formed, but the gibbous fronds survive until the next
spring. One of the reasons for the relative rarity of L. gibba,
as compared with L. minor, is probably that, as Guppy has
shown, it requires a higher temperature than that needed by
the Lesser Duckweed, both for initiation of budding in spring
and for flowering. Under suitable conditions, however, it shows
a wonderful vigour of vegetative growth. It has been recorded,
for instance, that an area of water of about half an acre, which
was edged on a certain date in June by a border of this plant
a few feet wide, nineteen days later was thickly covered with
the fronds over almost its entire surface2.
The surface-living Duckweeds can survive for a time if
stranded on the mud by the lowering of the water in which they
grow, and in cultivation it has been found possible to establish
land forms which can fulfil the whole cycle of normal vegetative
development3. For instance, Lemna minor has been grown for
as long as twenty months on wet mud, where it throve and
budded at all seasons of the year. Two plants set apart in
1 Guppy, H. B. (18942). 2 Hegelmaier, F. (1868).
3 Guppy, H. B. (18942).
78 LEMNACEAE [CH.
October had increased under these conditions to fifty in the
course of a year. Spirodela polyrrhiza can also be cultivated on
mud from the winter-buds through the summer phase to the
winter-buds again.
The genus Lemna contains another British species which is
more deeply committed to the water life than either L. minor or
L. gibba. This is L. trisuka^ L., the Ivy-leaved Duckweed, a
submerged plant, floating beneath the surface level1. The
fronds of L. /ra#/£# are longer than those of the other Duckweeds
and this elongation may be connected with the tempering of the
light due to its passage through a layer of water. Its shoots
form very decorative, symmetrical patterns, owing to the cir-
cumstance that branches of many different generations remain
attached to one another (Fig. 49). This fact is probably to be
associated with the relatively sheltered habitat of the Ivy-
leaved Duckweed, as compared with Lemna minor •, L. gibba>
etc.2. These floating species are exposed to all the surface move-
ments of the water — a fact which must encourage detachment.
That it is the difference between floating and submerged life
that determines the question of the fronds becoming isolated
or remaining attached, is confirmed by the fact that the partially
surface-floating, fertile fronds of L. trisulca (Fig. 50) tend
more to separation. In these fertile fronds the basal part, which
bears the inflorescence, floats on the surface, but the apical
region dips down into the water3. The sterile fronds and the
submerged part of the fertile fronds agree in having no sto-
mates, whereas the floating part of the fertile frond bears
stomates and approaches more closely in structure to the fronds
of Lemna minor than do the submerged sterile shoots. The very
simple vascular strands are dorsiventral with xylem above and
phloem below; one vessel and one sieve tube form a character-
istic combination4 (Fig. 51).
1 Clavaud, A. (1876) puts forward a theory concerning the cause of
submergence in this species which seems to be quite unfounded.
2 Schenck, H. (1885). 3 Hoffmann, J. F. (1840).
* Schenck, H. (1886).
VI]
THE IVY-LEAVED DUCKWEED
79
FIG. 49. Lemna trisulca, L. Habit drawing. (Slightly enlarged.)
[Kirchner, O. von, Loew, E. and Schroter, C. (1908, etc.).]
FIG. 50. Lemna trisulca, L. Flowering shoot. (Enlarged.)
[Hegelmaier, F. (1868).]
FIG. 51. Lemna trisulca,
L. T.S. bundle from stalk
of frond. One vessel (gef)
and one sieve tube (s)
with two companion cells.
(x475.) [Schenck, H.
(1886).]
8o LEMNACEAE [CH.
Wolffia^ the third and last genus of the Lemnaceae, enjoys
the distinction of including the most minute of all flowering
plants. The tiny, simple fronds are devoid of roots. The species
which occurs in England, Wolffia Michelii, Schleid., has fronds
which in no dimension exceed 1-5 mm., while W* brasiliensisy
Wedd., is described as being only one-half to two-thirds of this
size. Its discoverer, Weddell1, records that about twelve flower-
ing individuals of this tiny species could be accommodated upon
a single frond of Lemna minor. He noticed this little Wolffia
growing in the neighbourhood of that most gigantic of aquatics,
Victoria regia^ the Waterlily of the Amazons, and their propin-
quity drew from him the exclamation, "Singuliere bizarrerie
de la nature d'avoir seme ensemble ces deux vegetaux! " Our
native species winters at the bottom of the water, its minute
fronds being just sufficiently weighted with starch grains to
induce sinking.
The flowers of the Lemnaceae are reduced to the simplest
possible terms. Spirodela polyrrhiza2' (Fig. 47, p. 74), for
instance, has an inflorescence consisting merely of a spathe
(j/>.) enclosing two male flowers each represented by a stamen
only (j/j and j/2) and a female flower simply formed of a gynae-
ceum (£.) with one or two ovules. Lemna minor^, and probably
other members of the family, appear to be pollinated by insects.
The essential organs are raised above the water level, but they
are short and stiff, while the pollen is scanty, so anemophily
seems improbable. Small beetles and aquatic insects have been
observed crawling about among the flowering fronds, which are
markedly protandrous.
The seeds of the Lemnaceae, in the relatively rare cases in
which they are produced, may germinate as soon as they
are ripe in the summer — sometimes even while attached to the
parent plant — but in other cases they may rest through the
winter and defer germination until the spring4. Fig. 52
illustrates the seedling stage of Lemna trisulca.
1 Weddell, H. A. (1849). 2 Hegelmaier, F. (1871).
*Ludwig, F. (1881). ' 4 Hegelmaier, F. (1868).
VI]
DUCKWEED SEEDLINGS
81
The extreme reduction and specialisation, which charac-
terise the Lemnaceae, are united with great vigour and vitality.
We have already alluded (p. 77) to a special case of the rapid
power of vegetative reproduction shown by Lemna gibba, and
the same capacity characterises other members of the family.
Another remarkable trait of the Duckweeds is their power of
FIG. 52. Lemna trisulca, L. Germination. A , germinating seed with operculum (o)
just coming away. B, seedling seen from the side. C, seedling further developed,
seen from above, ch = chalaza, c = cotyledon, pi = plumule, / = lateral shoot
from plumule, 2 / = secondary lateral shoot, r = radicle. (Enlarged.) [Hegel-
maier, F. (1868).]
living and flourishing in water which is so full of organic im-
purities that no other Phanerogams can survive in it. If
introduced into water with a bad smell, they will purify it until
it is a fit habitation for small animals1.
1 Ludwig, F. in Kirchner, O. von, Loew, E. and Schroter, C. (1908,
etc.); see also p. 287.
A.W. P. 6
82 PISTIA [CH.
The Lemnaceae are generally regarded as related to the
Aroids, so it may be well to conclude this chapter by a
further reference to Pistia Stratiotes, L.1, the River Lettuce of
FIG. 53. Pistia Stratiotes, L. A, radial longitudinal section of leaf apex showing
groove into which the water pores open and the space beneath them into which
tracheids emerge. B, surface view of water pore. [Minden, M. von (1899).]
the Tropics — the member of the Araceae most nearly allied
to the Duckweeds. This plant has a floating rosette of leaves,
and multiplies by runners from which fresh rosettes arise. The
lower side of each sessile leaf bears a swelling, which may
reach the size of a pigeon's egg. This swelling consists of
spongy air-containing tissues, and serves as a float. The upper
i On Pistia see Koch, K. (1852), Hofmeister, W. (1858), Engler, A.
(1877) and Arber A.
vi] THE RIVER LETTUCE 83
and lower leaf-surfaces are covered with minute depressed
hairs, which prevent the leaves from being wetted1. Fig. 53
shows the apical opening, so often found in aquatics, through
which water is eliminated from the leaf2. Like the Lemnaceae,
Pistia represents a type which is singularly successful in the
matter of vegetative growth. Its reproduction is so rapid that
it sometimes chokes water-channels and proves a serious hin-
drance to navigation3.
1 Ito, T. (1899). 2 Minden, M. von (1899). See also p. 267.
3 This subject is dealt with more fully in Chapter xvn, p. 213.
6—2
84
CHAPTER VII
THE LIFE-HISTORY OF CERATOPHTLLUM
EACH of those aquatic families whose life-histories we
have hitherto considered, contains a considerable num-
ber of species, representing, in the case of the Lemnaceae, three
genera, while, in the case of the other groups discussed, the
number is much higher, as many as fourteen genera being in-
cluded, for instance, in the Hydrocharitaceae. The family
Ceratophyllaceae, the subject of the present chapter, offers a
marked contrast on this point, since it includes only a single
genus, containing three species, or, on other interpretations, one
alone1. Ceratophyllum, the Horn wort, is extremely isolated in
its structure and habits, so much so that there has been, at
various times, the widest diversity of opinion as to the posi-
tion which should be assigned to the family; the plant, from
its taxonomic wanderings, has been opprobriously styled " a
vegetable vagabond." The question of its affinities will be
discussed in Chapter xxv.
In the genus Ceratophyllum the aquatic habit seems to have
reached its ultimate expression. The plant not only lives entirely
submerged throughout its vegetative life, but even its stigmas
do not reach the surface, and the pollen is conveyed to them by
the water2. The Hornwort is monoecious, the male flowers con-
sisting of a group of stamens enclosed in a perianth of about
a dozen members (p in Fig. 54 5). These stamens, when the
flower is mature, become detached — the terminal expansion of
the connective acting as a float3 — and rise to the surface of the
water. They then dehisce and the pollen, having a specific
gravity very slightly higher than that of water, sinks gently,
iSchleiden, M. J. (1837).
2 Delpino, F. and Ascherson, P. (1871). 3 Ludwig, F. (i'88i).
CH. vn] THE HORNWORT 85
and thus comes into contact with the stigmas1. This water-
carriage of the pollen is the more striking, since the great
majority of aquatic plants show a strong tendency to retain the
aerial pollination mechanism of their terrestrial ancestors.
As regards vegetative structure, the most notable feature of
the Hornwort is the entire absence of roots. The radicle
'-St.
C B
FIG. 54. Ceratophyllum demersum, L. A, node bearing two male flowers (<£) (En-
larged) ; a branch (b) and all the leaves but two (I) have been cut across. B, a
single male flower on a larger scale; p, perianth of about 12 members; st, stamens.
On the left, a stamen is in the act of being squeezed out. C, $ flower; a, showing
perianth, style and stigmas; b, with perianth removed showing ovary. The stigma
varies from being single to being sometimes much more deeply bifid than in C.
[A. A.]
never develops beyond a rudimentary stage and no adventitious
roots are produced. Fig. 55, p. 86, shows a seedling2 with its re-
duced radicle (r). The seed germinates at the bottom of the water,
the plantlet rising to the surface when it is about three inches
long. The leaves of the first pair (/) are linear and decussate.
1 Willdenow, C. L. (1806), Dutailly, G. (1892), Roze, E. (1892),
Strasburger, E. (1902). 2 Guppy, H. B.
86
CERATOPHYLLUM
[CH.
r..--
FIG. 55. Ceratophyllum de-
mersum, L. Seedling one
week old. (Enlarged.) c= co-
tyledon; /= member of first
pair of leaves which decus-
sate with the cotyledons;
r= rudimentary radicle which
never elongates. [Guppy,
H. B. (I8Q41).]
The forked leaves characteristic of the mature plant (/ in
Fig. 54 A) p. 85) are not formed im-
mediately; they are preceded by a juve-
nile type which is simple and linear.
It is not until the fourth node above
the cotyledonary node that every mem-
ber of the whorl attains the characteristic
form. Each of the slender axes of the
mature plant, with its whorls of forked
leaves (B in Fig. 57, p. 89), often
occupies a more or less vertical position
in the water and quite deserves the
description given many years ago by
a German writer1: "A Christmas tree
for tiny water nixies." The Hornwort
sometimes flourishes at a considerable
depth; in Iowa it has been recorded to grow with marked success
beneath nearly thirty feet of water2.
The stem structure of Ceratophyllum may be taken to repre-
sent one of the ultimate terms in the reduction series met with
among Dicotyledonous water plants (Fig. 56). The fully-
developed internode has a central axial passage which has arisen
through the resorption of a small group of narrow-lumened
thin-walled procambial cells3. There is complete absence of
lignification.
The water content of the plant is very high, representing
88 per cent, of the total weight4, but as the young parts are
cuticularised to a degree unusual in submerged plants, the
texture of the shoots is less fragile than one might expect, and
collapse does not occur so rapidly in a dry atmosphere as in the
case of many hydrophytes. The curious mucilage-containing
hairs borne by the leaves, stamens, etc., have been much dis-
cussed5. They seem to differ from the common mucilage hairs
i Schleiden, M. J. (1837). 2 Wylie, R. B. (1912).
3 Sanio, C. (1865). 4 Schleiden, M. J. (1837).
5 Goppert, H. R. (1848), Borodin, J. (1870), Strasburger, E. (1902).
vii] THE HORNWORT 87
of water plants in not excreting any slime, and their special
function — if they possess one — remains a mystery.
It is characteristic of the Hornwort to occur sometimes in
such great abundance that it drives out nearly all other com-
petitors. It has been described, in the case of a certain Scottish
loch, as so luxuriant that a boat could only be rowed through
it with difficulty1. The present writer has seen it at Roslyn Pits,
near Ely, at the beginning of October, in such quantity that the
effect, on looking down into the water, was that of gazing into
a pure forest of C er atop hy Hum. The axis at this season of the year
FIG. 56. Ceratophyllum demersum, L. Vascular cylinder of stem in T.S. Small
xylem space in the centre; xylem parenchyma thickened; phloem zone well
developed with large sieve tubes, (x 130.) [Schenck, H. (1886).]
is extremely brittle, snapping asunder at the slightest touch
and thus giving rise to countless detached fragments capable
of reproducing the plant. The apical regions of the shoots are
more crowded with leaves and more deeply green than the rest
of the plant, but are scarcely specialised enough to be called
winter-buds2. During the cold season the stems remain at the
iWest, G. (1910).
2 The existence of these winter shoots was noted by Royer, C. (1881-
1883); that the plant may vegetate throughout the winter was recorded
by Irmisch, T. (1853).
88 CERATOPHYLLUM [CH.
bottom of the water, weighted down with a "living freight of
aquatic molluscs, insects and annelids1." The young shoots
formed in the spring, since they have not had time to become
so ballasted, rise erect in the water. The stems of the previous
year gradually decay away, and by the flowering time, in June
or July, they have practically disappeared. The fact that the
Hornwort, which has no surface layer of mucilage, becomes,
to so remarkable an extent, an asylum for aquatic animals, may
possibly be taken to afford some negative evidence for the
theory that the mucilaginous coat, which is almost universal
in hydrophytes, may have some value in preventing small
foreign organisms attaching themselves to the plant's surface.
In addition to the normal leafy shoots, a second type of
branch is produced, which appears in some degree to take the
place of the absent roots (Fig. 57)2. These shoots, which are
described as * rhizoid-branches,' are whitish in colour and bear
leaves with extremely fine and delicate segments. Fig. 58 shows
the contrast between a rhizoid-leaf (A) and a water-leaf (5).
The rhizoid-shoots penetrate into the mud, where they pre-
sumably serve as anchors and absorbing organs.
Although Cer atop hy Hum is not uncommon in northern lati-
tudes, there are certain indications that its birth-place may have
been in some more genial climate. Guppy3 has shown, for
instance, that a very high temperature is required for the matu-
ration of the fruit. He noticed that in the drought of the hot
summer of 1893, the ovaries ripened well in a shallow pond
where the temperature of the water always rose above 80° Fahr.
(27° C.) in the afternoons, and occasionally as high as 95°,
Fahr. (35° C.), while in the neighbouring waters, which were
not so much overheated, no fruits were produced. Curiously
enough, even in Fiji the fruit is only matured in the superheated
waters of shallow pools, tanks and ditches4. Conversely, the
vegetative organs cannot endure freezing, even for a period
so brief as to be quite harmless to many other aquatics;
1 Guppy, H. B. (1894!). 2 Glttck, H. (1906).
3 Guppy, H. B. (18941). 4 Guppy, H. B. (1906).
vn] RHIZOIDS OF THE HORNWORT 89
Guppy found that the shoots were mostly killed by five or six
days inclusion in ice.
B
FIG. 58. Ceratophyllumdemersum, L,
A, single leaf of a rhizoid. B, single
leaf of a water shoot (Enlarged.)
[After Gliick, H. (1906), Wasser-und
Sumpfgewachse, Bd. n, Figs. 27 A
and B, p. 195.]
FIG. 57. Ceratophyllumdemersum, L.
Part of an axis, A , which is lying on
the soil and bears a normal leaf-
whorl, B, and a rhizoid penetrating
the soil. The lowest leaf -whorl of
the rhizoid, U, has transition leaves.
(Slightly enlarged.) [After Gliick, H.
(1906), Wasser-und Sumpfgewachse,
Bd, n, PI. VI, Fig. 76.]
The various peculiarities of structure and habit to which
we have referred in the preceding pages, are not the only
90 CERATOPHYLLUM [CH. vn
singularities exhibited by Ceratophyllum. In 1877 a French
observer, Rodier1, recorded the existence of certain spontaneous
movements which characterise the shoots of this plant. He
noted that the shoot moved in one direction for six hours, and
then returned for another six — then moved for four hours in the
opposite direction, and in another four hours returned again to
its original position. Darwin 2 drew attention to certain obscu-
rities in Rodier's description, but no more recent work appears
to have been done on the subject; the movements of Cerato-
•phyllum might repay further investigation3.
1 Rodier, E. (iS;;1) and
2 Darwin, C. and F. (1880).
3 See also p. 281.
CHAPTER VIII
THE LIFE-HISTORY OF THE AQUATIC
UTRICULARIAS AND OF ALDROFANDIA
OF all our native aquatics, the Bladderworts (Utricularia)
diverge most in their vegetative characters from ordi-
nary terrestrial plants. When not in flower, they live wholly
submerged. Roots are entirely absent and the plant consists of
an elongated branching axis producing delicate, finely-divided
leaves on which small utricles are borne. This is not, however,
the only type of vegetative body represented in the genus.
Outside Europe there are a number of terrestrial species in
which entire leaves of a simple type are produced in addition
to bladder-bearing organs. The family to which the genus be-
longs— Lentibulariaceae — consists chiefly of aquatic and marsh
plants; it is probable that the water Utricularias, with which
alone we are concerned in this chapter, are the descendants
of marsh forms, which, in the course of evolution, have become
more and more completely involved in aquatic life1. It is im-
possible to draw a sharp line within the genus between the land
and water types; the terrestrial species sometimes produce
water forms, and the aquatic species can, to a limited extent,
take to life on land. Even among our native Bladderworts, we
find that, though Utricularia vulgaris cannot live except as a
submerged plant, U. minor and U. intermedia are able, on rare
occasions, to produce land forms2, which are so far adapted to
aerial life as to develop stomates — but in this condition they
do not flower. The land form of £7. minor is said to grow as a
close moss-like turf.
The little utricles borne by the leaves (Fig. 59, p. 92), which
give the Bladderworts their unique appearance, and to which
1Goebel,K. (1891-1893).
2 Gliick, H. (1906) and Luetzelburg, P. von (1910).
92 UTRICULARIA [CH.
they owe both their Latin and their English names, are hollow
structures with a small apical aperture, closed by a flap serving as
FIG. 59. Uhicularia neglecta, Lehm. A single trifid leaf with bladders. (Slightly
reduced.) [Adapted from Gliick, H. (1906), Wasser- und Sumpfgewachse, Bd. n,
PI. II, Fig. 15 6.]
FIG. 60. Utricularia flexuosa, Vahl. Longitudinal section through a bladder.
(Enlarged.) Kl. = valve. [Goebel, K. (1891-1893).]
a valve. Fig. 60 represents a section of the utricle of U.flexuosa^
a species which plays a part in India corresponding to that of
vm] THE BLADDERS OF THE BLADDERWORTS 93
U. vulgaris in Europe. Darwin1 describes the valve of Utricu-
laria neglecta as attached on all sides to the bladder, excepting
by its posterior margin, which is free and forms one edge of
the slit-like orifice. This margin is sharp, thin and smooth,
and rests on the edge of a rim or collar which projects into the
interior of the bladder. The collar obstructs any outward move-
ment, with the result that the valve can
only open inwards. The function of the
bladders was for a long time in dis-
pute. Certain ingenious but mistaken
theorisers regarded the little four-armed
hairs (Fig. 61), which occur within the
bladders, as root-hairs, and supposed
that the bladders existed in order to pro-
tect these delicate organs from the direct FlG- 6l-
c . Heer. Glands from the in-
action or light and the depredations or tenor of a bladder. [Meier-
Crustacea2! On a more plausible view, hofer' H- <I9°2^
it was maintained that the bladders were to be interpreted as
floats, which buoyed up the plant in the water. This idea has been
discounted, however, since many terrestrial Utricularias produce
large numbers of bladders; moreover it has been shown that
the Utricularias do not sink when all the bladders are removed3.
A third hypothesis now holds the field — namely, that the
bladders act as traps for small animals which serve as food for
the plant; this theory may now be considered to be fully proved.
Before the middle of the last century, Treviranus 4 had recorded
the rinding of a beetle and some small snails in the bladder
of a terrestrial Utricularia (U. Hookert) and had suggested the
comparison between these organs and the pitchers of Sarra-
cenia, Nepenthes, and other carnivorous plants. But it was not
until 1875 tnat the fact tnat our native Utricularias preyed
on small animals was definitely proved. In this year Cohn 5
1 Darwin, C. (1875). 2 Crouan (Freres) (1858).
3 Darwin, C. (1875), Busgen, M. (1888), Goebel, K. (18892) and
(1891-1893). * Treviranus, L. C. (1848!).
5 Cohn, F. (1875). See also Darwin, C. (1875).
94 UTRICULARIA [CH.
showed that in herbarium specimens of Utricularia vulgaris the
bladders often contained skeletal tissues of Crustacea and insect
larvae. He then tried the experiment of putting a living shoot
of this plant, which had empty utricles, into water rich in Cypris\
next morning nearly all the bladders contained Crustacea,
swimming about in a restless manner but unable to escape.
Rotifers, Infusoria, Rhizopods and other animals were also
present ; certain bladders containing as many as six living Crus-
tacea, as well as other animals, were described by the observer
as " a little menagerie of the microscopic water fauna." The
number of animals secured may sometimes be very great. It
has been recorded, for instance, that a plant of the Common
Bladderwort, introduced into water rich in Daphnidae, in one
case was found after 1 1 hours to have caught as many as twelve
of these little Crustacea in a single bladder1. Another plant,
which was about 1 5 cms. long, and bore fifteen fully developed
leaves, each with about six bladders, is reckoned to have en-
trapped at one time as many as 270 individuals of Chydorus
sphaericus1. It is a curious fact that different species of Utricu-
laria^ even when growing associated in the same water, may,
owing to some slight difference of habit, catch quite different
animals. In one case Goebel2 observed U. intermedia and U.
vulgaris growing together, but while U. intermedia had caught
chiefly Cypris, U. vulgaris had caught only Copepods. This is
to be explained by the fact that U. intermedia^ being anchored
at the bottom of the water, was only able to secure the Cypris,
which is a creeping form, while the Copepods, because they
were free-swimming, were entrapped by the bladders of the
unattached U. vulgaris. The animals are said to be attracted by
edible mucilage secreted by the hairs which grow on the blad-
ders of the Utricularias (Fig. 62), and especially on the valve
at the aperture2.
The observations which we have enumerated and many
others which might be cited, leave no room for doubt that the
iBusgen, M. (1888).
2 Goebel, K. (1891-1893).
vm] CARNIVOROUS HABIT 95
Utricularias do, as a matter of fact, catch animals in their
utricles, but the questions still remain whether the absorption
of organic material actually takes
place, and, if so, whether the
carnivorous habit is of definite
benefit to the plant. The inner
epidermis of the bladders is cuti-
cularised except as regards the
four-armed hairs (Fig. 61, p. 93)
which are thin-walled. These
hairs, in the case of a bladder
enclosing decaying animals, have
been seen to include oil-drops,
which may be presumed to be
derived from the animal tissues,
since the hairs in a bladder which
had received no food, showed no
such drops1. Experimental work
has also demonstrated that treat-
ment with ammonium nitrate,
etc., produces changes in the hairs which suggest that absorp-
tion has occurred2. These observations would not be sufficient
in themselves to prove that the entrapped animals serve as
a source of food for the plant, but a demonstration of this
point was supplied by certain comparative cultures of Utri-
cularias growing in water with or without animal life. From the
upshot of these experiments it appeared that the plants deprived
of animal food only showed about one-half of the growth
of those that were allowed to catch their prey in the normal
way3. A further problem which presents some difficulty is
that of the causes which bring about the death and absorption
of the entrapped animals. No highly poisonous substance
can be present in the bladders, since the imprisoned animals
FIG. 62. Utricularia Bremii, Heer.
Part of leaf with bladder. (Enlarged.)
[Meierhofer, H. (1902).]
1 Goebel, K. (1891-1893).
2 Darwin, C. (1875).
3Biisgen, M. (1888). See also Darwin, C. (1888), footnote to
96 UTRICULARIA [CH.
may remain alive in them for some days1. There is no doubt
that the bladders are capable of digesting small animals, algae,
etc., and, although no enzyme has yet been recognised, the
presence of benzoic acid has been demonstrated2. Owing to
the small size of the bladders, it must obviously be difficult
to obtain an adequate quantity of the secretions for investiga-
tion.
FIG. 63. Utricularia minor, L. Part of a
shallow- water plant, E= earth-shoot. Two
branches marked S at the base of the inflor-
escence axis have been cut off. i and 2 = bracts
on the inflorescence axis. (Reduced.) [Modified
from Gluck, H. (1906), Wasser- und Sumpf-
gewachse, Bd. n, PL II, Fig. 18.]
FIG. 64. Utriculariaminor,
L. a, green leaf of normal
submerged shoot ; b, colour-
less leaf of an earth-shoot.
In the latter the leaf seg-
ments are reduced to rudi-
ments indicated by S. (En-
larged.) [After Gluck, H.
( 1 906) , Wasser- und Sumpf-
gewachse, Bd. n, Figs. 2 a
and b, p. 42.]
Besides the normal leafy branches, which serve for assimila-
tion and also bear bladders, no less than three modified types
of vegetative shoot are borne by certain of the European
Utricularias — the * earth-shoot,' the breathing shoot or ' air-
shoot/ and the so-called 'rhizoid3.'
1 Cohn, F. (1875). 2 Luetzelburg, P. von (1910).
3 Goebel, K. (189 1-1893) and Gluck, H. (1906).
vm] < EARTH-SHOOTS ' AND < AIR-SHOOTS ' 97
In Utricularia minor ^ Bremii^ intermedia^ and ochroleuca^ cer-
tain shoots are formed which bear bladders on leaves of a
reduced type (E in Fig. 63, and b in Fig. 64). These branches,
which are known as * earth-shoots/ penetrate the mud at the
bottom of the water and apparently serve for purposes of an-
chorage, and for the absorption of raw food materials. They
have retained their power of entrapping small animals, but have
substituted the functions characteristic of roots for the assimi-
latory activities of the water-shoots. The bladders make
such efficient hold-fasts that, unless the soil be very soft,
it is difficult to pull the earth-shoots out of the substratum
without snapping the leaves and leaving the bladders behind.
Every transition can be observed between earth- and water-
shoots.
The British species of Utricularia which produce * earth-
shoots' never show the second form of modification, the * air-
shoot ' (L in Fig. 65, p. 98), which occurs only in U. vulgaris and
in the closely allied U. neglecta. These curious organs were ob-
served by Pringsheim2, who did not, however, understand their
nature, out called them 'Ranken' (tendrils). It is to Goebel3
that we owe a very plausible suggestion as to their biological
value, and to Gliick4 a definite view as to their morphological
status. They are, apparently, reduced inflorescences, and their
function is said to be to serve as breathing organs and to connect
the submerged vegetative body of the plant with the atmo-
spheric air. In the case of Utricularia vulgaris, the air-shoots are
fine, whitish, thread-like bodies, some centimetres long. They
bear very small undivided leaves, closely appressed to the shoot
and with stomates on their outer surfaces. The lower internodes
are much elongated. The tips reach the water surface and pro-
trude from it into the air, where the stomates can perform their
usual function. The 'air-shoots' are said to occur especially
1 Benjamin, L. (1848) described U. intermedia as 'rooted,' so it is
evident that he had observed the ' earth-shoots,' though mistaking their
morphological nature. 2 Pringsheim, N. (1869).
3 Goebel, K. (1891-1893). 4 Gluck, H. (1906).
A. W. P. 7
98 UTRICULARIA [CH.
when the plants are growing in a thick tangle — that is to say
under circumstances in which the oxygen starvation, to which
submerged plants are liable, must be particularly acute.
For the third type of modified shoot, the misleading term
'rhizoid' has been used; this name would have been more fitly
FIG. 65. Utricularia vulgaris, L. Part of shoot with bladder-bearing leaves, and
an air-shoot (L). (Enlarged.) [Goebel, K. (1891-1893).]
applied to the 'earth-shoots/ since in function they approxi-
mate to roots, and to the 'rhizoid shoots' of C er atop hy Hum1.
The 'rhizoids' are developed at the base of the inflorescence
in certain species of Utricularia (R in Fig. 66). They bear no
1 See pp. 88 and 89.
w
w
vm] < RHIZOIDS ' OF BLADDERWORTS 99
bladders, but their leaves are highly glandular and often bent
in a claw-like fashion1. They are firmer than the ordinary shoots
and do not collapse when lifted
from the water. Their function
is obscure, but it seems possible
that they play some part in
holding the inflorescence erect.
The Utricularias evidently have
a strong tendency towards the
production of specialised shoots
below the aerial part of the
flowering axis. Certain extra-
European members of the
genus (U. stellaris^ U. inflexa
and U. inflate. Fig. 150, p. 229)
have a wreath of air-containing
organs surrounding the base
of the inflorescence, and un-
doubtedly serving to keep it
erect in the water2. A vivid de-
scription is given by Spruce3,
in his account of his travels
on the Amazons, of a similar
arrangement in £7. quinqueradiata. This is a small species
with the usual submersed, finely divided leaves bearing
numerous bladders, but the flower-stalk, which is about two
inches high, has, midway, a large involucre of five horizontal
rays resembling the spokes of a wheel. This floats on the
surface and keeps the stalk always erect, and the solitary flower
well out of the water, " the whole recalling a floating night-
lamp, especially as the large yellow flower may be considered
to represent the flame."
Reproduction by seed appears to be less important among
iQoebel, K. (18892).
2 Benjamin, L. (1848), Treviranus, L. C. (1848!) and Wight, R.
(1849). 3 Spruce, R. (1908).
7—2
R R
FIG. 66. Utricularia neglecta, Lehm.
Base of inflorescence axis, /, with two
'rhizoids,' R. Three water-shoots, W,
cut away for simplicity. (Slightly re-
duced.) [After Gluck, H. (1906), Wasser-
und Sumpfgewachse, Bd. u, PI. IV,
Fig. 34 a.]
1OO
UTRICULARIA
[CH.
the Utricularias than the method of asexual propagation
shortly to be described. In the case of Utricularia minor , for
instance, ripe seeds are seldom obtained. When they occur,
they are found to be well suited to floating on water, as the
surface of the seed-coat is pitted and capable of retaining air
bubbles for a considerable time1. Eventually the testa becomes
thoroughly wetted and the seed sinks. The seedling is unique
in structure (Fig. 67). In U. vulgaris, which may serve as an
example, germination begins in spring at the bottom of the
FIG. 67. Utricularia vulgaris, L.
Geminating seed; s, seed coat; /,
primary leaves, (x about 19.)
[Adapted from Kamienski, F.
(1877)-]
FIG. 68. Utricularia exoleta, R.Br.
A and B, stages in germination;
c— ? cotyledons. In A the seed-coat
is removed. [Goebel, K. (1891).]
water. The following organs are produced2 — a number (6-12)
of simple primary leaves (/ in Fig. 67), a bladder, a conical
stem apex, from which the main axis develops laterally, and an
adventitious shoot (? an air-shoot). No root appears in the
seedling, and there is not even any rudiment of this organ in the
embryo3. In Utricularia exoleta*^ a small and simple aquatic
form found in Asia and tropical Australia, only two primary
leaves (? cotyledons) are formed, but this is perhaps to be inter-
preted as a case of reduction (Fig. 68).
1 Meister, F. (1900).
2 Warming, E. (1874) and Kamienski, F. (1877).
3 Merz, M. (1897). 4 Goebel, K. (1891).
vm] TURIONS OF BLADDERWORTS TO:
The Bladderworts are able to reproduce themselves success-
fully for long periods without having recourse to flowering and
fruiting. Utricularia intermedia^ for instance, was observed in
a certain district in Germany to propagate itself for years by
vegetative means, when the ditches in which it lived were cleared
too frequently to give it an opportunity of flowering1. The
organs of vegetative reproduction — the turions or winter-buds 2
— are spherical or egg-shaped bodies developed at the ends
of the shoots. The case of Utricularia vu/garis may be taken as
typical. In this species turion formation takes place, in normal
circumstances, between the beginning of August and the
middle of November. The apical region of the shoot produces
a number of reduced leaves separated by highly abbreviated
internodes. The concave leaves cover one another in imbricate
fashion and are closely packed into a firm ball, clothed with a
protective layer of mucilage. When the plant is grown in an
aquarium, water-snails are its chief enemies, but the winter-buds,
with their coat of hairs and slime, seem immune from the depre-
dations of these creatures3. The parent plant sinks to the bottom
in the autumn, owing to its tissues becoming water-logged, and
carries the turions with it. These, in spite of their firm texture,
are lighter than water, and, but for their attachment to the
decaying axis, would rise to the surface like pieces of cork. As
it is, they remain all through the winter stationary at the bottom,
but with their apices directed upwards. In the spring, the
turion is at last able to rise to the surface — the parent axis
having been reduced by months of rotting to little more than
a string-like vascular cylinder, which often adheres persistently
to the base of the winter-bud. The axis of the turion elongates
with remarkable rapidity, attaining three to six times its ori-
ginal length. The composition of the bud then becomes mani-
fest; a number of bud-scales occur at the base, followed by
several transition leaves and then normal foliage leaves which
iSchultz, F. (1873).
2 Benjamin, L. (1848), Gluck, H. (1906), etc.
3 Meister, F. (1900).
•IO2
UTRICULARIA
[CH.
receive additions by the apical growth of the germinating
turion. The bud-scales resemble reduced foliage leaves, but are
specially suited to be protective organs. They are firmer than
the other leaves and do not collapse on removal from the water.
They are also less subdivided, and bear a more conspicuous
development of hairs on their terminal segments — the hairs of
the successive leaves amounting, indeed, to a protective felt —
so that altogether they form an effective envelope for the bud.
In Utricularia minor, though the hairs
are absent, a similar result is obtained
by the leathery texture of the bud-scale
and by its form, which is less divided
than that of U. vulgaris. The contrast
between the foliage leaf and bud-scale
of U. minor is shown in Fig. 69 a and b.
In U. intermedia the turion generally
becomes free before the winter, and
swims among the shore plants instead
of spending the dead season at the
bottom of the water. The fact that the
turion is protected by an especially
thick coat of hairs, probably permits
it to lead this more exposed existence1.
Figs. 143 A and 143 B, p. 220, show
the bud-scale and normal leaf of this
species.
Though, under normal conditions, the turions are only formed
in the autumn, and carry the plant over the winter season, their
formation can be induced at any period of the year by condi-
tions of poor nutrition. In certain experiments made a few
years ago2, some turions of Utricularia minor, germinated under
starvation conditions on sand, after seventeen days had pro-
duced plants 14 cms. long. These were transferred to a culture
solution, and after five days, when they had had time to become
FIG. 69. Utricularia minor, L.
a, normal leaf of the shallow
water form, with a bladder;
6, leaf belonging to a turion.
(Enlarged.) [After Gliick, H.
(1906), Wasser-und Sumpfge-
wachse, Bd. n, Figs. 14 a and
b, p. 117.]
Schenck, H. (1885).
Luetzelburg, P. von (1910).
vin] MORPHOLOGY OF BLADDERWORTS 103
vigorous, they were returned to the sand. By the end of
twenty-seven days they had formed turions. These were cut off,
and the same alternation of sand culture and nutritive solutions
was repeated three times. Each time the effect of the starvation
culture was "to induce the formation of turions, so that the
plant went through the entire vegetative cycle, culminating in
' winter * buds, no less than four times between May and the
middle of December ! The last turions produced were only the
size of a pin's head.
In the preceding pages we have, for convenience, used the
terms 'shoot' and 'leaf ' for descriptive purposes, but it now
remains to consider how far current morphological conceptions
can be applied to so anomalous a genus as Utricularia. There
has probably been more controversy about the morphological
nature of the different organs of these plants, than about such
problems in the case of any other Angiosperm. It is not pro-
posed here to enter into the details of the discussion1 which
seems to have been singularly fruitless. In the upshot, the main
point, which emerges from a study of the literature, is that in
this genus the distinction habitually drawn by botanists be-
tween stem and leaf, breaks down completely. The bladder is
probably best interpreted as a modification of part of the
" leaf2," but even if this be conceded it does not carry us far,
since the nature of the " leaf" itself still stands in dispute. By
some authors, the entire vegetative body, apart from the in-
florescence axis, has been regarded as a root system, while
others view it either as wholly axial or as consisting of stem
and leaves. A view which has received considerable promi-
nence, is that the entire plant is a much divided leaf3, but if this
be so, it must, as Goebel has pointed out, be admitted that this
" leaf " possesses many characters which we are accustomed to
1 For an historical survey of the literature, see Goebel, K. (1891) and
Gluck, H. (1906).
2 Meierhofer, H. (1902). Another interpretation is illustrated in
Fig. 72 5, p. 1 06.
3 Kamieriski, F. (1877).
io4 UTRICULARIA [CH.
attribute to stems alone, viz. long continued apical growth1,
as well as power of bearing leaves and axillary branches and of
developing in more than one plane2. The fact that adventitious
shoots are produced on the leaves of other Lentibulariaceae is,
however, favourable to this view3. The unique pla'sticity of the
Utricularias is indicated by the many observations on regenera-
tion phenomena in the genus, which show that almost any part
FIG. 70. Utricularia vulgaris, L. Detached leaf with four adventitious shoots,
A, Alf Az, A3. (Enlarged.) [Goebel, K. (1904).]
of these plants can produce new shoots at will. For instance,
in U. neglecta^ detached leaves, or leaves connected with a dying
axis, can produce adventitious shoots which arise endogenously
at the points of forking of the leaves, or, more rarely, from the
stalks of the bladders4. Fig. 70 represents a case in which four
1 Hovelacque, M. (1888). 2 Goebel, K. (1891).
3 Goebel, K. (1904). 4 Gluck, H. (1906).
vm] REGENERATION IN BLADDERWORTS 105
shoots (yf, A^ , A<£ , A^j arose from a leaf of U. vulgaris. Again,
the inflorescences of various species, if cut off and immersed in
a culture solution, have been seen to give rise to lateral shoots
from the axils of their scale leaves. These branches may occur
in extraordinary abundance: in Utricularia vulgaris as many as
FIG. 71. Utricularia vulgaris, L. Inflorescence with numerous lateral shoots
arising in axils of scale leaves on inflorescence axis, after 47 days culture under
water on peat, and, later, with the addition of a culture solution. (Enlarged.)
[Luetzelburg, P. von (1910).]
nineteen lateral shoots have been observed to develop in con-
nexion with one scale1; Fig. 71 shows a large number of
branches growing from a submerged inflorescence of this
species. As illustrations of the numerous abnormalities on
1 Luetzelburg, P. von (1910).
io6
UTRICULARIA
[CH.
record, it may be noted that an inflorescence-bract sometimes
develops into a water-leaf or even an entire water-shoot, while
a bladder rudiment may develop into a water-shoot1. In the
development of the seedling, the primary leaves may be re-
placed by stolons 2.
The apical development of the Bladderworts gives little help
in interpreting their morphology. In Utricularia vulgaris (Fig.
72), for example, the apex of the shoot is coiled up in a singular
$,-.
FIG. 72. Utricularia vulgaris, L. A, spirally coiled end of a shoot, of which a is
the apex; Sj-s5, young shoots; V , youngest leaves; /, older leaves (between / and /'
some leaves have been removed) ; h, hairs (mucilage glands) ; i, young inflorescence
growing from the base of s6. B, developing bladder; a, curved apex of shoot;
slt first shoot, and /, single leaf or two leaves fused; a, s1 and / fuse to form
bladder; s2 is second shoot which may give rise to a branch or a secondary bladder.
[Adapted from Pringsheim, N. (1869).]
way which recalls a young fern frond. The " leaves " (/) arise
in two lateral rows, and there is a third row of rudiments fa-s^)
on the concave face, which give rise to air-shoots. The develop-
ing bladders on a leaf are indicated in Fig. 73, while Fig. 72 B
illustrates that view of the composite origin of the single
bladder which regards it as derived from both axial and foliar
elements3.
In general, the only safe conclusion to be drawn from a study
i Gliick, H. (1906). 2 Goebel, K. (1891).
3 Pringsheim, N. (1869).
-m.g.
VHI] ANATOMY OF BLADDERWORTS 107
of the available evidence regarding the nature of the organs in
the Bladderworts, seems to be that — in the present state of our
ignorance — the attempt to fit so elusive
a genus into the Procrustean bed of
rigid morphology, is doomed to failure.
It is probably best, as a purely provisional
hypothesis, to accept the view that the
vegetative body of the Utricularias par-
takes of both stem nature and leaf nature.
How such a condition can have arisen,
historically, from an ancestor possessing
well-defined stem and leaf organs, remains
one of the unsolved mysteries of phylo-
geny.
The anatomy1 of the water Utricu-
larias, though showing some curious
features, is less anomalous than their
morphology. In the stem of U. vulgaris,
the tracheids, of which one or more are present, are placed
sub-centrally, and surrounded by little groups of phloem.
Some degree of dorsiventrality is given to the structure by
the thin-walled character of the small lower sector of the
vascular cylinder in which the tracheids lie, while the con-
junctive tissue of the rest of the stele, towards the upper
side of the axis, is fibrous. The tracheal elements are of
the nature of "imperfect vessels," being formed from a file of
superposed cells, with imperforate, oblique, separation walls.
The incompleteness of the conducting elements is probably to
be associated with the relative unimportance of the transpira-
tion stream in a rootless submerged plant. The vascular cylinder
is surrounded by an endodermis, and the cortex is lacunar. The
structure of the inflorescence-axis differs very markedly from
that of the submerged stem ; the tracheids form a discontinuous
ring enclosing a large central pith containing phloem islands.
1 Tieghem, P. van (i 868) and (i 869!), Russow,E. (i 875), Schenck, H.
(1886) and Hovelacque, M. (1888).
b2
FIG. 73. Utricularia vul-
garis, L. Developing leaf
showing two young blad-
ders 6j and b.2; m.g., muci-
lage gland. (Enlarged.)
[Meierhofer, H. (1902).!
io8 UTRICULARIA [CH.
The submerged and aerial parts of the axis differ, in fact, so
conspicuously in their internal structure that van Tieghem1
suggested that, if they were submitted separately to an anato-
mist, he would probably attribute them to distinct and un-
related plants!
The leaf of Utricularia minor is typically that of a submerged
plant (Fig. 74) 2. The bundle is extremely small, consisting
generally of a single annular tracheid surrounded by thin-
walled, elongated elements. The air spaces in the mesophyll
reach to the epidermis, which contains the greater part of the
chlorophyll, and is the most conspicuous region of the leaf.
FIG. 74. Ulricularia minor, L. T.S. lower part of leaf, (xiys.)
[Schenck, H. (1886).]
It seems thoroughly in keeping with the uncannily abnormal
morphology and the exceptional carnivorous habits of the
Utricularias, that they should sometimes locate themselves in
odd situations. The oft-quoted case of those Bladderworts which
live in association with certain South American Bromeliads, is
an instance in point. The leaf rosettes of some Tillandsias form
vase-like cavities, which collect and retain water. Utricularia
nelumbifolia has been described by a traveller in Brazil3 as only
to be found growing in the water which collects in the bottom
of the leaves of a large Tillandsia occurring on an arid, rocky
part of the Organ Mountains, at about 5000 feet above the sea.
1 Tieghem, P. van (1868). 2 Schenck, H. (1886).
3 Gardner, G. (1846).
vin] EPIPHYTIC BLADDER WORTS 109
Such a habitat would be impossible for the Bladderwort without
the help of the Bromeliad's store of water, while the rich fauna
of this water gives it every chance of catching suitable prey1.
In the observer's own words, the Utricularia "propagates
itself by runners, which it throws out from the base of the
flower stem; this runner is always found directing itself towards
the nearest Tillandsia^ when it inserts its point into the water,
and gives origin to a new plant, which in its turn sends out
another shoot; in this manner I have seen not less than six
plants united."
In British Guiana a similar case has been described2. A huge
aloe-like Bromeliaceous plant, Brocchinia cordylinoides^ Baker,
grows in the Kaieteur savannah. It may be fourteen feet high,
and, in older specimens at least, the crown of leaves is supported
on a tall bare stem. Floating in the water retained in the axils
of the leaves, is found a beautiful Utricularia (U. Humboldtii,
Schombk.) "with flower stems 3 or 4 feet long, supporting its
many splendidly large violet flowers." This form of epiphytism
is not obligatory, since in Roraima, although both the Bromeliad
and the Utricularia occur, the Utricularia may live a terrestrial
life on marshy ground, instead of being associated with the
Bromeliad.
Many of the unusual characteristics of the Utricularias are
shared by another flowering plant, extremely remote from them
in its affinities — Aldrovandia vesiculosa, L., a member of the
Droseraceae. This plant has long had a peculiar fascination for
botanists, and a detailed memoir upon it by an Italian writer
appeared before the middle of the eighteenth century3. Like
the Bladderworts, Aldrovandia is rootless and free-floating, and,
but for its flowers, lives entirely submerged. It has a slender
axis bearing whorls of leaves; the older internodes and leaf
whorls die away successively, as new parts are formed at the apex.
1Goebel,K. (1891-1893).
2 Im Thurn, E. F. and Oliver, D. (1887).
3 Monti, G. (1747). For an analysis of this paper see Auge de Lassu
(1861).
no ALDROVANDIA [CH.
Aldrovandia, like the Bladderworts, is able to form turions;
these are the size of a pea and consist of a highly abbreviated
axis, which may bear as many as thirty-two leaf whorls. The
turions normally sink to the bottom of the water in the autumn,
owing to the weight of starch which they contain1, and rise
again in the spring; but it seems that they sometimes fail to
reach the surface in the succeeding season, and that the develop-
ing plant may even in June be found at the bottom, held there
by the remains of the winter-bud2. When the turions are kept
in an aquarium indoors, it is said that they sometimes fail to
sink, but remain floating throughout the winter3. In warmer
climates these winter-buds are not formed; in Bengal, for in-
stance, the plant is described as vegetating continuously through-
out the year4. Reproduction by seed also takes place. The
flowers are raised above the water, but the young fruits bend
down, and the ripening of the seeds takes place beneath the
surface5. The structure of the embryo recalls the other Drosera-
ceae, the only difference being that the primary root remains
rudimentary.
The leaves of Aldrovandia are highly peculiar in structure,
and serve, like the bladders of Utricularia^ for catching small
animals6. The broad petiole terminates in a roughly circular
bilobed lamina, and also bears, in its apical region, a number
of stiff projections, which at first glance suggest leaflets7, but
are probably only petiolar emergences8 (Fig. 75). Long sensi-
tive hairs are produced from the upper surface of the lamina
in the neighbourhood of the midrib ; the touching of these by
any passing animal results in the closure of the lobes 9, thus im-
1 Caspary, R. (1859 anc^ J862). 2 Maisonneuve, D. de (1859).
3 Schoenefeld, W. de (1860). 4 Roxburgh, W. (1832). "
5 Caspary, R. (1859 and 1862).
6 The proof that Aldrovandia is carnivorous is due to Cohn, F. (i 875),
though Delpino, F. (1871) had previously shown that the suffocation of
small animals occurs in the leaves.
7 Cohn, F. (1850). 8 Caspary, R. (1859 and 1862).
9 Mori, A. (1876) noted that the central region of the leaf was irritable.
VI 1 1]
CARNIVOROUS HABIT
in
prisoning the prey. The sensitiveness of the leaves is greatest
at rather high temperatures1. The Linnean name, " vesiculosa"
is an unfortunate one, since it suggests that the leaves form
actual bladders, whereas the lobes merely fold together like
those of Dionaea. Besides the irritable hairs, glands2 are also
present, which apparently secrete a digestive fluid and absorb
organic matter3.
There is good reason to suppose that both Aldrovandia and
the water Utricularias are descended from terrestrial ancestors
FIG. 75. Aldrovandia vesiculosa, L. i, whorl of leaves (about £ nat. size) ; 2 and 3,
individual leaves (x a£ circa}. Leaf is shown in natural position in 2, and with the
lobes open in 3. [Adapted from Caspary, R. (1859).]
which were already carnivorous. Aldrovandia is the only
aquatic member of the Droseraceae, a family which contains
well-known insectivorous types such as the Sundew, while the
aquatic Utricularias are associated both with terrestrial car-
nivorous members of the same genus, and with the insect-
catching Pinguiculas, which are not hydrophytes. The habit of
consuming animal food has thus not arisen de novo in connexion
with an aquatic existence, though this mode of life undoubtedly
affords unique opportunities to a carnivorous plant4.
1 Stein, B. (1874). 2 Fenner, C. A. (1904).
3 Darwin, C. (1875).
4 On Aldrovandia^ in addition to the papers cited in this chapter, see
Caspary, R. (i8584) and Hausleutner (I85O1) and (1851).
CHAPTER IX
THE LIFE-HISTORY OF THE TRISTICHACEAE
AND PODOSTEMACEAE1
ALL the families of aquatics hitherto considered are
JL\. represented in our own country; some of them, e.g. the
Potamogetonaceae, show a marked preference for temperate
regions, while others, e.g. the Lemnaceae, seem equally at home
in both the hotter and colder parts of the world. The Tristi-
chaceae and Podostemaceae, however, whose life-history we
propose to touch upon in the present chapter, are, with rare
exceptions, confined to the tropics. That they are essentially
plants of hot regions, is indicated by the statement of Dr Willis 2
that the forms living in the low-country of Ceylon and S. India
inhabit water which maintains a very constant temperature of
80° F. (27° C.). The two families together form an anomalous
group, characterised, as regards their morphology, by remark-
able variety, but agreeing, as regards their ecology, in one
singular feature — a preference for inhabiting water which flows
rapidly or even torrentially over a rocky substratum. This
peculiarity, sometimes rendered more noticeable by reason of
the striking colour of the plants, has been observed from the
earliest time at which Podostemads became known to botanists.
The first recognition of a member of this group as the type of a
1 General accounts of these plants will be found in Gardner, G. (1847),
Tulasne, L. R. (1852) and Warming, E. (1881, 1882, 1888 and
1891). They have only recently been divided into these two families
(Willis, J. C. 191 51), and many authors still refer to them all as Podo-
stemaceae.
2 Willis, J. C. (1902). This interesting memoir has been largely drawn
upon in the present chapter; it contains a bibliography of previous work.
See also Willis, J. C. (I9I41), (igiS1) and (iQiS2) and Matthiesen, F.
(1908).
CH. ix] HABITAT OF THE PODOSTEMADS 113
distinct family, occurred when Aublet1, nearly a century and a
half ago, discovered Mourera in rapidly running water in French
Guiana. In the case of a certain Venezuelan river, Goebel2
describes the bed, in places where the water flows quickly,
as quite green with a Podostemad, Marathrum utile^ growing on
the stones, and he points out that it flourishes more freely the
stronger the current; when the stream is slow it is replaced by
Mosses and Algae. Another writer3 observed Mourera fluvia-
tilis in the cataracts of a tributary of the Amazon, growing in
such abundance that the rocks, amongst which the waters
rushed, were veiled by it, and the colour was so vivid that the
river seemed — to use his own expression — "to flow over a carpet
of roses." This red hue of the vegetative organs, due to antho-
cyanin in the surface cells4, has been noted in many cases.
Miss Lister5, for instance, in her account of the occurrence of
a species of Tristicha in rapidly flowing water below the first
cataract of the Nile — one of the rare records of the appearance
of a member of these families outside the tropics — mentions
that, when the plant was wet and fresh, the colour was crimson.
The majority of the peculiarities of the Podostemaceae and
Tristichaceae are closely related to the nature of their habitat.
Life in rushing water — on rocks which are often water-worn
to smoothness and into which no roots can penetrate — is
obviously impossible except to plants which have a special
capacity for clinging to the substratum. In the Tristichaceae4
(e.g. Tristicha ramosissima and Weddellina squamulosd) a creeping,
thread-like organ is formed, which, though morphologically a
root, is dorsiventral in structure, and gives rise to leafy shoots
endogenously in acropetal succession. But this thread-like root
is not apparently competent to anchor the leafy shoots with the
necessary firmness, and additional organs called ' haptera * are
formed. They are produced exogenously from the creeping root,
and by their positive geotropism and power of flattening them-
1 Aublet, F. (1775). 2 Goebel, K. (1891-1893).
3 Weddell, H. A. (1872). 4 Willis, J. C. (1902).
5 Lister, G. (1903).
A. w. P.
n4 PODOSTEMACEAE [CH.
selves against the substratum, form firm attachment organs.
They also secrete a kind of cement which renders their
adhesion to the rock very close and permanent. These haptera
are found in many Podostemaceae. In Mourera fluviatilis, for
instance, they are sometimes almost tendril-like1, while in
certain cases they serve as storage organs for reserve carbo-
hydrates2.
In many of the Podostemaceae the creeping root discards its
root characteristics even more completely than in the Tristi-
chaceae, and becomes converted into a thallus, which either
follows out every irregularity in the substratum, or, remaining
more or less free, develops into all sorts of curious shapes3.
It still produces secondary shoots bearing leaves, but as the
root thallus becomes more important, the secondary shoots
become less so, until, in such genera as Hydrobryum (Fig. 76),
Farmeria, Dicraea (Fig. 77 and Fig. 79, p. 1 16), and Griffithiella
they are much reduced, and assimilation is mainly performed
by the thallus. A seedling of Dicraea stylosa, with the young
thallus (/^.) developed as a lateral outgrowth from the hypocotyl
(hyp.\ and bearing secondary shoots (s.s.~) is shown in Fig. 78 ;
the mature plant is represented in Fig. 79, p. 1 16.
The thallus of the Podostemads is sometimes amazingly
polymorphic; its capacity for developing in exceptional forms
depends, apparently, on the fact that it is not restricted by a
rigid skeletal system, and that nearly all the cells possess the
capacity for renewed meristematic activity. Griffithiella Hooker-
iana, for instance, has a thallus which may develop into various
shapes recalling different Algae that grow in moving water;
one of its forms resembles the basal cup of Himanthalia lorea.
Farmeria metzgerioides, again, recalls Delesseria Leprieurii,
while Podostemon subulatus simulates such an Alga as Eostrychia
Moritziana, which also grows in rapids. Willis, who draws
attention to these cases of simulation, alludes to the great
difficulty of interpreting such resemblances between plants far
1 Went, F. A. F. C. (1910). 2 Matthiesen, F. (1908).
3 See Willis, J. C. (1902) for further details.
IX
HYDROBRYUM AND DICRAEA
FIG. 76. Hydrobryum olivaceum, (Gardn.)
Tul. Thallus bearing endogenous flower-
ing shoots. (Enlarged.) [Warming, E.
(1883*).]
cot.
hyp
FIG. 78. Dicraea stylosa, Wight, f.
fucoides, Willis. Seedling with hypocotyl
(hyp.), cotyledons (cot.), thallus (th.), and
secondary shoots (s.s.). [Adapted from
Willis, J. C. (1902).]
FIG. 77. Dicraea elongata, (Gardn.) Tul.
Plant with three vertical roots bearing
flowers. These float in the water: they
spring from a horizontal creeping root.
(Nat. size.) [Warming, E. (i8832).]
n6 PODOSTEMACEAE [CH.
distant in relationship from one another, and adds, "it is
impossible at present to do more than point out these very
suggestive analogies of form which accompany analogy of the
FIG. 79. Dicraea stylosa, Wight. Plant somewhat reduced, showing the shoots
(g, g) arising from the band-like root thallus. [Warming, E. (18832).]
conditions of life, and which seem to indicate that an experi-
mental and comparative morphological study of the forms of
the Algae and Podostemaceae should be attended with inter-
ix] THALLUS OF PODOSTEMADS 1 1 7
esting results1." Even the Tristichaceae, which do not possess
these polymorphic thalli, show "remarkable similarities in
morphological features, and in the arrangement and anatomy
of the leaves, to many mosses or liverworts, especially to those
of wet situations1.'* The specific and varietal names given to
various members of these families — such as bryoides^ fucoides^
selaginoides and lichenoides — speak eloquently of their striking
resemblance to the lower plants, which the botanists who named
them have felt impelled to emphasize1.
The genus Lawia differs from those hitherto mentioned in
having a thallus which is not of root nature, but which origi-
nates by the fusion of flattened, dorsiventral shoots, while
Castelnavia also has a shoot thallus. In Lawia foliosa2* the
small thallus adheres so closely to the stones that it cannot
be separated from them. There are no haptera, but the thallus
is attached by hairs. The small simple leaves are without sto-
mates or vascular bundles. They have a midrib of elongated
cells, but their structure is altogether more simple than that of
the leaves of many Liverworts. In Lawia xeylanica1 the hypo-
cotyl, produced on the germination of the seeds, bends down
to the rock and becomes attached to it by unicellular rhizoids
from the superficial cells. The hypocotyl then expands and forms
a relatively large surface of attachment.
The internal structure of the Podostemads is similar to that
of many other submerged plants in reduction of xylem, absence
of stomates, and the presence of chlorophyll in the epidermis.
On the other hand, a character in which these plants diverge
from other hydrophytes is the presence of large quantities of
silica in the cells3. It seems on the whole most probable that
this silica is merely a useless by-product of the plant's meta-
bolism4. It has been suggested that it serves as a protection
against the attacks of animals5, but there seems little evidence
1 Willis,J. €.(1902).
2 Goebel, K. (i8S(f) and (1891-1893). In Goebel's earlier account
this plant is called Terniola (longipes?). 3 Goebel, K. (1891-1893).
4 Matthiesen, F. (1908). 5 Wachter, W. (1897!).
n8
PODOSTEMACEAE
[CH.
for this view. That these plants, with their large stores of
reserve starch, are, as a matter of fact, liable to be preyed upon,
is indicated by Im Thurn's1 observation that, in British Guiana,
when the rivers are low, and the rocks which underlie the rapids
are partially uncovered, a certain fish (Pacu myletes] collects at
the falls to feed on the leaves of
the Podostemads, which clothe the
rocks, and at this time of year
come into flower. This fact is so
well known that, at this season,
large numbers of Indians camp on
the sides of the falls, in order to
seize the opportunity of shooting
the fish.
The most important anatomical
peculiarity of the Podostemads is
the extreme reduction of the inter-
cellular spaces2; in this respect
the members of these families
contrast most markedly with other
water plants (Fig. 80). This feature
is probably to be associated with
the thorough aeration of the tor-
rential water which they frequent3.
Certain species, however, possess
delicate outgrowths from the sur-
face of the leaves which have been
interpreted as "gill-tufts" (Fig.
81). Possibly these structures to
some extent compensate for the lack of an internal aerating
system.
The water in which the Podostemaceae live is liable to
variations in level, and their habit of blooming when the sinking
FIG. 80. Dicraea stylosa, Wight, f .
fucoides, Willis. T.S. thallus to show
absence of intercellularspaces. ep.=
epidermis; p.c. = parenchymatous
cortex;y. &.=vascular bundle, (x 150
circa.) [Willis, J. C. (1902).]
1 ImThurn, E. F. (1883).
3 See pp. 256, 257.
Warming, E. (1881).
ix] "GILL-TUFTS" OF OENONE 119
of the water exposes them to entire or partial desiccation, "has
been repeatedly noted by travellers. Barrington Brown]1,'' in
describing his explorations up the Cuyuni River in British
FIG. 81. Oenone multibranchiata, Matthiesen. Part of flowering plant showing the
numerous "gill-tufts" on the upper surfaces of the leaves. [Matthiesen, F. (1908).]
Guiana, mentions the occurrence of Podostemaceae on the
rocks under water where the current runs strongest, and adds,
1 Brown, C. Barrington (1876).
120 PODOSTEMACEAE [CH.
"These plants bear very pretty flowers at this season of the
year [September] as soon as they are left uncovered by the
subsiding of the waters after the rainy season, but still kept
moist by the wash of the water's edge. One small-leaved
species has a little white star-shaped flower, on a short delicate
stem, which has a slight perfume and proves an attraction to
numerous species of wild bees." Im Thurn1, again, in his
account of the same regions, mentions Mourera fluviatilis and
Lads alata as growing "on the half-submerged rocks in most
of the falls. As the water decreases in the dry season, the tall
spikes of bright pink flowers of the former plant rise from their
large leaves, the edges of which are cut and curled into the like-
ness of moss, which lie flat on the rocks; and at the same time
and place innumerable tiny pink stars rise an inch or two over
the equally moss-like leaves of the Lads."
The vegetative parts of the Podostemads die very quickly
when out of their element, and the flowering and seed-setting,
both of which take place with the utmost rapidity when the
plants are exposed to the air, represent, as it were, their swan-
song. In Lawia zeylanica, Willis2 has observed that the enor-
mous amount of starch stored up in the flowering shoots
accounts for the great rapidity with which anthesis and seeding
take place. In the case ofRhyncolads macrocarpa, Goebel3 points
out that each inflorescence-bud is enclosed in a cavity formed
by the connate union of two leaves. These cavities are full of
water, so that the life of the flower-stalks is passed in an environ-
ment resembling that of ordinary aquatics inhabiting still
water; it is thus not surprising that these stalks differ from the
other vegetative organs in developing an aerating system, such
as is characteristic of water plants in general.
Both entomophily and anemophily occur among the Podo-
stemads. According to Willis, we can trace a series from certain
American Tristichaceae with conspicuous, entomophilous
1 Im Thurn, E. F. (1883). 2 Willis, J. C. (1902).
3 Goebel, K. (1891-1893).
9— If-
ix] FLOWERS AND SEEDS 1 2 1
flowers, to members of the Podostemaceae in which anemo-
phily or autogamy is associated with gradually increasing dorsi-
ventrality. To this subject we shall return
in Chapter xxvu. Cleistogamous flowers are
also sometimes produced (Fig. 82).
The peduncles of the Podostemaceae
contain little water-conducting tissue, and,
possibly in correlation with this, the seed-
development proves to be of a decidedly
xerophilous type1 — an illustration of the
conservatism of the reproductive organs of
aquatics and their tendency to retain terres-
trial characters. By disappearance of nucellar
tissue, a cavity is formed beneath the embryo-
sac which, at the time of fertilisation, is filled
with fluid. This cavity is bounded by the
strongly cuticularised inner wall of the inner
integument and the suberised cells of the
chalaza. It is open only on the side towards
the developing embryo, and is described as
"an ideal water reservoir." Mucilage is often
present in the neighbouring cells of the
inner integument and this may perhaps form
an additional protection against loss of water.
The seeds of the Podostemads are often small and numerous.
Those of Rhyncolacis macrocarpa are about as large as the largest
known pollen-grains (e.g. those ofMiraM/is). The seeds of this
species often germinate when caught in some cranny of the
parent, so that the old plant may support a number of seedlings.
The embryo is strictly rootless, but haptera grow out from the
hypocotyl2.
The morphology of the Tristichaceae and Podostemaceae
positively bristles with problems for the botanist, but great
caution has to be exercised in dealing with them, since it must
1 Magnus, W. and Werner, E. (1913).
2Goebel,K. (1891-1893).
FIG. 82. Podostemon
Barberi, Willis. Clei-
stogamic flower in
spathe (spa.), the
front of which is re-
moved to show the
gynaeceum (g), the
single stamen (st.) and
one of the two thread-
like organs represent-
ing the perianth or
staminodes (per-) •
[Simplified from
Willis, J. C. (1902).]
122 PODOSTEMACEAE [CH. ix
not be overlooked that the data are still highly incomplete, for,
as a recent writer has pointed out, we probably know only a
small proportion of the existing species belonging to these
families1. It was recorded a decade ago, for instance, that the
examination of a few kilometres of a river in Venezuela —
hitherto unexplored in this respect — yielded no less than four
species of Podostemaceae new to science2. The extremely local
distribution of many forms, their anomalous morphology and
progressive dorsiventrality, and the great variety of types of
structure which they present, offer every incentive to specula-
tion. Dr Willis has put forward certain far-reaching theoretical
views, based on his study of the group, and to these and related
questions we shall return in Chapter xxvn, when we are
touching upon the problem of Natural Selection.
1 Went, F. A. F. C. (1910). 2 Matthiesen, F. (1908).
CHAPTER X
THE LIFE-HISTORY OF THE MARINE
ANGIOSPERMS
THE small group of Phanerogams inhabiting the sea
consists of about thirty species1 belonging to two fami-
lies of that Cohort of Monocotyledons known as Helobieae.
The Hydrocharitaceae are represented by Halophila, Enhalus
and Thalassia, and the Potamogetonaceae by Zostera, Phyllo-
spadix, Posidonia, Cymodocea and Halodule (Diplanthera). The
thorough way in which the marine Helobieae have identified
themselves with their environment, is shown by the fact that
Cymodocea antarctica was actually included by Agardh2 in his
Species Algarum under the name of " AmphiboUs zoster ae-
folia" \ injustice to this author it should, however, be mentioned
that he lays stress upon the uncertainty of its position "in
catena entium." Zoster a marina^ the Grass- wrack, often grows
among Seaweeds as if it were one of themselves ; in lagoons of
the Mediterranean coast it has been observed in association
with Enteromorphay Codium tomentosum^ Padinapavonia, Dictyota
dichotomy and other Algae3, while in Danish waters it grows
in the midst of varied assemblages of brown, red and green
Seaweeds4. Zostera is even able to descend to considerable
depths in the sea ; in the Baltic its occurrence at 1 1 metres from
the surface has been recorded3. A species of Phyllospadix (a
genus allied to Zostera) is noted for its power of withstanding
the violence of the waves; it grows on the Californian coast "in
the heaviest surf and on the most exposed ocean shores5.**
Ascherson, whose work has done much to elucidate this
difficult group, pointed out about fifty years ago6 that the
1 Sauvageau, C. (iSgi1). 2 Agardh, C. A. (1821).
3 Flahault, C. in Kirchner, O von, Loew, E. and Schroter, C.
(1908, etc.). 4 Ostenfeld, C. H. (1908).
5 Dudley, W. R. (1894). 6 Ascherson, P. (1867).
i24 MARINE ANGIOSPERMS [CH.
Phanerogams inhabiting the sea were, at that time, less well
known than most of the higher groups of Algae. These marine
Angiosperms often grow in
deep water, and botanists
have been obliged to depend
chiefly on the study of casual
fragments washed up by the
waves, and thus have been
apt to miss the organs of
fructification altogether.
The marine Helobieae all
show a strong affinity, both
as regards vegetative habit
and reproductive methods.
They all have alternating
leaves in two ranks arising
from creeping stems. Supple,
ribbon-like leaves, sessile,
sheathing and capable of
following all the undulations
of the water, are most charac-
teristic, occurring in Enhalus,
Posidonia, Phyllospadix, Zos-
teray etc. Several Halophilas,
on the other hand, have broad
petiolate leaves with Potamo-
getott-\ike nervation, while
Cymodocea isoetifolia is dis-
tinguished by awl-shaped
succulent leaves1.
Submerged pollination
and Conferva-like pollen are FlG- 83' Cymodocea aequorea, Kon. Plant
characteristic of all the
marine Angiosperms. The
thread-like pollen was figured as early as 1792 by the Italian
in the middle of the third year of vegeta-
tion ; /= fruit from which plant has grown.
(Nat. size.) [Bornet, E. (1864).]
1 Ascherson, P. (1867) and Sauvageau, C.
and
x] CYMODOCEA 125
botanist, Cavolini1, who described it in the case of Posidonia as
"lanae instar gossipinae." The cases which he records are those
of "Zostera oceanica"(= Posidonia Caulini^ Kon.), "Phucagros-
tis major " (= Cy mo docea aequorea^ Kon.), and " Phucagrostis
minor" (= Zostera nana. Roth).
As a typical life-history of one of the marine Potamogeton-
aceae, that of Cymodocea aequorea, Kon. may be briefly outlined.
This plant was made the subject of a classic memoir by Bornet2,
FIG. 84. Cymodocea aequorea, Kon. T.S. leaf near base of limb showing median
bundle; t, t, sieve tubes. (x22o.) [Sauvageau, C.
from which the following account is derived. Cymodocea aequo-
rea (Fig. 83) is an herbaceous plant with a creeping stem, which
forms submarine meadows after the manner of Zostera marina.
It occurs in a number of localities in the Mediterranean, growing
on muddy sand, in shallow creeks which are not greatly ex-
posed to the shock of the waves. It is a perennial plant, which
is in full vegetation from May to October; during the other
months it is difficult to detect, for only a few short narrow leaves
1 Cavolini, F. (1792!) and (i7922). 2 Bornet, E. (1864).
126 MARINE ANGIOSPERMS [CH.
remain, with their green colour masked by a layer of various
animal and vegetable growths. Probably the plant does not
attain its full development until the fifth or sixth year, and an
individual may live for another six years or more after reaching
maturity. The rhizomes are fixed in the soil by long, whitish,
fibrous roots, which put out a great quantity of tortuous laterals.
The roots form a network, which holds in its meshes the
gravel and mud, and thus contributes towards maintaining the
stability of the bed of the creek in which the plant grows. The
leaves, which are linear and membranous, attain the length of
20 to 30 cms. Fig. 84, p. 125, shows the appearance of a trans-
verse section of the leaf near the base of the limb. At the
junction of the sheath with the blade there is a ligule which
Bornet compares with that of the Grasses. At the extreme base
of each young leaf, ten * squamulae intravaginales ' occur, and
the same structures are associated with the stamens and carpels.
The male and female flowers of Cymodocea aequorea^ which
are borne on separate plants, and are buried 2 or 3 cms. deep
in the soil of the sea-shore, mature about the end of May or the
beginning of June. Only the stamens and styles emerge into
the water. The flowers are solitary, and are borne without any
perianth in the axils of ordinary foliage leaves. The male flower
consists of a pedicel bearing two stamens, completely fused as
to their filaments. The double nature of the stamen is revealed
in the single large anther of a vivid red hue, which has eight
pollen sacs, and is supplied by two vascular strands. The female
flowers are only manifested externally by white, filamentous
styles, which emerge in groups of four from the sheaths of
certain leaves. Two of these styles correspond to each of the two
carpels which constitute the gynaeceum. The ovary is unilocular
with one ovule. Until the disappearance of the pollen-mother-
cell, the pollen grains are roundish, but at this stage they elon-
gate, without increasing in diameter, until they attain the
dimensions of about 2 mm. by -j-^ mm., thus becoming thread-
like. The fruits, which are ripe by August, are flat and oval,
being roughly i cm. long by 0-5 cm. wide. The endocarp is
x] CYMODOCEA AND ZOSTERA 127
filled by the embryo with its enlarged hypocotyl, enclosed in
a brown membrane. As the fruits develop, mature, and
become detached, while still buried in the soil, there is no
chance of their becoming disseminated, unless tempests or other
accidental causes stir up the sea bottom ; this explains the rarity
of their occurrence among shore debris. Bornet several times
found branches bearing two or three generations of fruits.
An Australian species of the same genus, Cymodoceaantarctica,
Endl., exhibits an interesting variant on C. aequorea in the
matter of the fruit1. The plant is annual, or at most biennial,
and the germination is viviparous. When the seedling attains
a length of 3 to 4 inches, it breaks away from the parent, but
carries with it a cup-like body (? the remains of the ovary wall)
which has been described as bearing " two unsymmetrical pairs
of basket-like spines." The " cup," on account of its relative
density, "retains the floating waif in an upright position, and
soon proves its ultimate use by acting as a grappling apparatus,
catching in the tangles of small algae etc." The young ^pfents'
develop spirally twisted roots, which presumably also serve for
anchorage2.
In Zostera marina^ L., the Grass-wrack of our shores, the
fertile and sterile plants are readily distinguishable from one
another, since in the fertile plant the stem is slender, erect, and
much branched, while that of the sterile individual is thick,
creeping, more luxuriantly leafy, and anchored to the soil by
adventitious roots developed in bundles beneath each leaf base3.
Figs. 85 and 86, p. 128, illustrate the leaf anatomy. The inflo-
rescence, unlike that of Cymodocea, consists of a number of male
and female flowers, reduced to stamens and carpels and enclosed
in a spathe. A French observer4 has given a vivid description
of a successful attempt to observe the actual pollination. Having
found a good locality for the purpose, in the month of June,
1872, in his own words, "j'allai m'installer avec mon micro-
1 Tepper, J. G. O. (1882) and Osborn, T. G. B. (1914).
2 See p. 205. 3 Gronland, J. (1851). 4 Clavaud, A. (1878).
128
MARINE ANGIOSPERMS
[CH.
FIG. 85. Zostera marina, L. T.S. leaf at base of limb between the median nerve
and a lateral nerve, phloem indicated by shading. [Sauvageau, C. (iSgi1).!
FIG. 86. Zostera marina, L. T.S. median bundle of leaf; t, sieve tubes, (x 220.)
[Sauvageau, C.
x] ZOSTER A AND HALOPHILA 129
scope dans la maison d'un ami, a quelques centaines de metres de
la plante, et je resolus de n'en point partir que je n'eusse de-
couvert, si c'etait possible, le mode de reproduction de Zos-
tera....l\ m'importait de ne pas rester plus longtemps dans une
incertitude qui commen9ait a me peser." On a favourable day,
hot and absolutely still, he went out in a boat and examined
some flowering plants. The three conditions in which the in-
florescences were found proved that cross pollination is ensured
by protogyny. Some were still enclosed in the spathes, with
the anthers intact ; others showed stigmatic branches, ready for
pollination or recently pollinated, emerging from the spathe,
while the stamens were still enclosed and not completely ripe;
in others again the stigmatic lobes had all fallen, while the
anthers were exposed, and either all empty, or the lower ones
empty and the upper ones in the act of dehiscence. The anthers
were seen to open, and eject the thread-like pollen which formed
a floating cloud. In pollen-grains, which had just been expelled
from the anther, an outgrowth was observed at a little distance
from one end. When pollinated stigmas were examined, it was
noticed that these outgrowths, which were, in fact, young pollen-
tubes, were forcing their way into the stylar tissue, between the
cells whose walls were becoming mucilaginous and separating
from one another. The pollination of Zostera is scarcely possible
except in still water, as any movement would carry the pollen
completely away from the scene of operations.
The best-known genus among the marine Hydrocharitaceae
is Halophila, three species having been investigated in detail
by Bayley Balfour1 and Holm2. Bayley Balfour himself col-
lected his material of H. ovalis, (R. Br.) Hook. fil. (H. ovata,
Gaudich.) and of H. stifulacea^ (Forsk.) Asch. on the reefs
surrounding the island of Rodriguez — east of Mauritius.
H. ovalis (Fig. 87) grows on spots just uncovered at full ebb
tide, while H. stipulacea prefers localities where it is always
submerged and subjected to a constant current. The rhizomes
are creeping, and produce numerous long filiform rootlets
1 Balfour, I. B. (1879). 2 Holm, T. (1885).
130 MARINE ANGIOSPERMS [CH.
bearing a thick matting of root hairs ; this tangle of roots fixes
the plant in the sand. The flowers are typically hydrophilous.
The filiform styles, which may be 26 mm. long, are receptive
throughout their entire length, and, though the individual pollen-
grains are not thread-like, the same result is secured by their
being united into strings1. The seed-coats form an admirable
protection for the embryo. The outermost cell-layer is conspi-
cuously thickened on all the walls except that forming the sur-
face of the testa. The next three cell-layers are cuticularised.
FIG. 87. Halophila ovalis, (R.Br.) Hook. fil. Portion of mature plant showing two
female flowers in spathes with three thread-like stigmas (st.) . (Enlarged.) [Balfour,
I. B. (1879).]
Since the testa of Zostera is similar in structure, it seems not
unlikely that in both cases the histological features bear some
relation to the mode of life. Bayley Balfour concludes, from the
general result of his researches, that Halophila forms a link
between the Hydrocharitaceae and Potamogetonaceae.
The leaf anatomy of the marine Helobieae has been studied
in great detail, partly because these plants are nearly always
1 The thread-like character of the pollen of Halophila was observed by
Gaudichaud, C. (1826) who also noticed the same feature in Cymodocea
antarctica.
x] LEAF ANATOMY 1 3 1
collected in a sterile and often fragmentary condition, and it
has thus become a matter of importance to systematists to be
able to identify them even when no organs of fructification are
present. It might have been expected that the examination of
the leaves of these plants, which show great similarity in external
form and all live completely submerged in a fairly uniform
environment, would reveal a monotony of internal structure.
But this expectation is far from being realised. Duchartre1
showed in 1872 that the genera Cymodocea (Fig. 84, p. 125) and
Zostera (Figs. 85 and 86, p. 128) could be distinguished from
one another, even in the absence of the flowers and fruit, on
anatomical grounds alone. This conclusion was carried much
further by Sauvageau2, who proved, as a result of detailed and
critical studies of the anatomy of the marine Phanerogams, that
(except among the Halophilas) the anatomy of the leaf gives
sufficient data for their exact generic and even specific deter-
mination. The variation occurring in the leaf structure is illus-
trated in Figs. 84, p. 125,85 and 86, p. 128, 88 and 89, p. 132.
Sauvageau pointed out, for instance, that the development of
the lignified fibres differs markedly in the three genera, Enhalus,
Thalassia and Halophila, and that it is thus impossible to
regard this mechanical system merely as an adaptive response to
the milieu. The differences that are displayed by the different
species afford, indeed, another example of the fixity and lack
of utility so often observed in specific differences; for it is not
conceivable that each of the detailed distinctions between the
closely related types of anatomy met with in the leaves of these
marine Angiosperms, is to be interpreted as having some
definite 'survival value,' though it may be broadly true that
some structural variations are more suited to life in a boisterous
sea and others to existence in calmer waters.
But though we cannot explain the different types of skeletal
system of the leaves on adaptive grounds, there are other leaf-
characters which seem definitely related to submerged life. In
1 Duchartre, P. (1872).
2 Sauvageau, C. (iSgo1), (iSgo2), (iSQO3) and (iSgi1).
9—2
132
MARINE ANGIOSPERMS
[CH.
FIG. 88. Halodule uninervis, Boiss. T.S. leaf at base of limb; a, a, secretory cells.
(x22o.) [Sauvageau, C.
FIG. 89. Posidonia Caulini, Kon. T.S. limb of leaf. A, i cm. from apex;
B, at base of limb, (x 145.) [Sauvageau, C.
x] THE ORIGIN OF THE GROUP 133
the marine Potamogetonaceae, the epidermis is characteristi-
cally free from stomates and very rich in chlorophyll. Liquid
exchange between the plant and the surrounding medium is
facilitated by the occurrence of openings at the leaf apices, with
which the median nerve is in direct communication. These
openings come into existence quite early in the history of the
leaf, and are due to the disappearance of the epidermis. In the
genus Posidonia, again, the fibres of the sheath survive and
form a protective covering for the younger leaves. Another small
peculiarity, which may be adaptive or may more probably be
an indication of community of origin — since it is common to
certain genera in the two families under consideration, but is
not found elsewhere — is the occurrence of " Flossenzahne "
or " dents nageoires " on the leaf margins1. These teeth are
formed by a peculiar elongation and wall-thickening of the
marginal cells.
The fact that a considerable number of Phanerogams live
and flourish in the sea, and that yet, on examination, these
marine types all prove to be restricted to representatives of two
related families, stimulates conjecture as to the origin of this
biological group. Both the families to which the flowering
plants of the sea belong are typically aquatic, and are widely
represented in fresh waters ; no marine Angiosperm has a close
affinity with any terrestrial plant. These facts suggest that the
flowering plants now living in the sea are not the immediate
descendants of land plants, but have been derived from ances-
tors which had already accommodated themselves to life in
inland waters. It would seem that, in order to be capable of em-
barking upon life in the sea, a flowering plant requires four special
faculties. These are, firstly, toleration towards a saline medium;
secondly, the power of vegetating while wholly submerged;
thirdly, the knack of developing a sufficiency of anchoring roots
to withstand the wash of waves and tide; and, fourthly, the
capacity for hydrophilous pollination, since any aerial method
must be doomed to failure, except in halcyon weather in a non-
1 Ascherson, P. and Graebner, P. (1907).
i34 MARINE ANGIOSPERMS [CH.
tidal sea. Both the families to which the marine Angiosperms
belong, fulfil these four conditions in the persons of some, at
least, of their fresh-water representatives. The existence of such
species as Potamogeton pectinatus and Zannichelliapalustris^]\\c}\
inhabit both fresh and brackish waters, and also of Ruppia and
Althenia (Potamogetonaceae), which typically occur in a brack-
ish medium — as well as of Vallisneria spiralis1 (Hydrocharita-
ceae) and Callitriche autumnalis^ (Callitrichaceae), which are
able to tolerate some salt — indicates how the transition from
fresh to saline water may have been bridged. The vegetative
organs, again, are entirely submerged in such genera as Elodea
and Vallisneria among the Hydrocharitaceae, and Tjannichellia^
Naias and many Pondweeds among the Potamogetonaceae.
Both families also contain a number of species with well-
developed root systems. Finally, floating pollen is carried by
water to the stigmas in some species of Elodea and Ruppia,
while actual submerged pollination is found in Naias and
Zannichellia. These families are thus in every respect prepared,
as it were, for the evolution of marine members. The reason
why other families have not produced any forms adapted to life
in the sea, seems to be that, though certain of their species may
fulfil some of the conditions which we have enumerated, they
fail in others — the one which is most rarely exhibited being a
tendency to sub-aquatic pollination. Myriophyllum spicatum and
Ranunculus Baudofii*, for example, have been observed to live
under conditions of slight salinity, but they are handicapped
for entry on marine life by the fact that they cannot be cross-
pollinated, unless the flowers are raised into the air. Cerato-
phyllum and Pseudo-callitriche^ on the other hand, owing to
their hydrophilous pollination, suggest themselves as possible
candidates for marine life, but Ceratophyllum lacks roots en-
tirely, and Pseudo-callitriche has no rhizome — obstacles that
may well prove insuperable. Conceivably in future ages, if the
1 Chatin, A. (18552). 2 Lebel, E. (1863).
3 Ostenfeld, C. H. (1908).
x] THE FUTURE OF THE GROUP 135
evolution of fresh-water plants proceeds on its present lines, a
greater number may reach the specialised stage of hydrophilous
pollination, and some of these may colonise the sea, thus demo-
cratising the narrow and exclusive circle of the Marine Angio-
sperms1.
1 In addition to the papers cited in this chapter the following references
may be mentioned :
Ascherson, P. (1870) and (1875); Chrysler, M. A. (1907); Cunning-
ton, H. M. (1912); Delpino, F. (1870); Delpino, F. and Ascherson, P.
(1871); Engler, A. (1879); Hofmeister, W. (1852); Magnus, P. (18702)
and(i872); Martens, G. von (1824); Sauvageau, C. (i8893)and(i89i3);
Solereder, H. (1913); Walsingham, Lord,and Payne-Gallwey,R.(i886);
Warming, E. (1871).
PART II
THE VEGETATIVE AND REPRODUCTIVE
ORGANS OF WATER PLANTS,
CONSIDERED GENERALLY
" If then the Anatomy of Vegetables be so useful a Mean, we ought
not to streighten it ; but to force this, as well as the rest, to its utmost
Extent. And therefore, first of all, To go through all the Parts,
with equal care ; examining the Root, Trunk, Branch, Leaf, Flozver,
Fruit, and Seed. . . . Together with the Knife it will be necessary to
joyn the Microscope', and to examine all the Parts, and every Way,
in the use of That. As also, that both Immediate, and Micro-
scopical Inspections, be Compared: since it is certain, That some
things, may be demonstrated by Reason and the Eye conjunct,
without a Glass, which cannot be discovered by it."
Nehemiah Grew, The Anatomy of Plants, 1682.
[ 139 ]
CHAPTER XI
LEAF TYPES AND HETEROPHYLLY IN AQUATICS
(i) TYPES OF LEAF IN WATER PLANTS
THE types of leaf characteristic of aquatics — excluding
those that rise wholly into the air and are thus comparable
with the leaves of terrestrial plants — fall into two groups: firstly,
those which float on the water surface, and thus preserve con-
tact on the ventral side with the atmosphere and on the dorsal
side with the water, and secondly, those which have more com-
pletely adopted the water life, since they keep up no direct
contact with the atmosphere, but live entirely submerged. The
general question of the relation of floating leaves to their en-
vironment has been discussed, in connexion with the Water-
lilies, on pp. 30—32. There is considerable monotony in the out-
line and structure of a large proportion of such leaves, associated
no doubt with the very definite and uniform physical condi-
tions to which they are subject. Submerged leaves, on the other
hand, are characterised by much greater variety. With a number
of exceptions, they fall mainly into two groups — those that
present a very thin, entire lamina, generally ribbon-shaped but
sometimes broad, and those in which the leaf blade is finely
subdivided, either by fenestration or dissection. In both these
types of leaf, the ratio of surface to volume is higher than is the
case in a normal, terrestrial lamina, and many botanists regard
their peculiarities as definite adaptations for obtaining from the
water an adequate supply of gases in solution. It is generally
assumed that the dissected type of leaf is the more efficient
form for the purpose. A Russian writer1 has recently proved,
however, that this assumption is scarcely borne out by a critical
examination of the facts. By measurements and calculations
1 Uspenskij, E. E. (1913).
1 40 TYPES OF LEAF IN WATER PLANTS [CH.
he shows that a cylindrical leaf, in order to have as high a ratio of
surface to volume as, for example, the broad, flat leaf of Pota-
mogeton perfoliatus, must be only I2o/x in diameter, whereas the
diameter of the segments of Myriophyllum spicatum leaves varies
from 22OjLtto38o/z, and of Ceratophyllum demersum^ from 600 ju,
to 75o/z, while even the ultimate divisions of the leaves of Ra-
nunculus trichophyllus reach 1 90, a. He admits that, apart from the
actual ratio of surface to volume, the dissected leaf may possibly
have an advantage over the corresponding flat leaf, in tapping a
greater volume of the medium1 ; he thinks, however, that though
this factor would be of importance in absolutely still water, its
significance is much reduced if, as is nearly always the case,
movement has to be taken into account. It may be added that the
dissected leaf possibly interferes less with its neighbours' light
than the undivided type of submerged leaf. From this enquiry
and from a general study of submerged leaves, it may perhaps
be concluded that both the dissected and flat types of leaf are
organs of tolerably equal efficiency for subaqueous gaseous
exchange, though the dissected leaf has the advantage of
offering less resistance to currents. Which type of leaf a sub-
merged plant shall produce is probably ultimately decided by
the general leaf morphology of its terrestrial ancestors, rather
than by environmental causes, much as coast scenery is often
determined by the forms of the pre-existing land surfaces,
rather than by the direct action of the ocean itself.
Among the undissected types of submerged leaf, the ribbon
leaf is conspicuous (Fig. 90); it is probably better adapted to
resist tearing than, for instance, the large, Ufoa-like submerged
laminae of the Waterlilies. Ribbon leaves are found among
many of the marine Angiosperms, such as Zostera, which are
subjected to the wash of waves and tide. Leaves of this type
sometimes grow to a notable length ; those of Sagittaria sagitti-
folia, as we have shown in Chapter u, may be more than two
yards long, while those of Vallisneria spiralis are said to be often
a yard or more in length, though hardly a quarter of an inch wide.
iSchenck, H. (1885).
xi] SUBMERGED LEAVES 14 1
Other types of submerged, radical leaf are the small, almost
cylindrical leaves of Lobelia Dortmanna and Littorella lacustris
(Fig. 142, p. 218), and the linear serrate leaves of Stratiotes
aloides (Fig. 32, p. 53), which are too firm and stiff to be called
ribbon leaves. In Lobelia and Littorella^ the shortness of the
leaves obviates the necessity of pliability to the motion of the
water, while in Stratiotes the need for flexibility is diminished
by the partially free-swimming habit of the plant and its pen-
chant for quiet waters.
FIG. 90. Sagittaria sagittifolia, L. Young plant produced from a tuber (T) and
bearing ribbon leaves only; tuber, with axis and scale leaves, and roots, indicated
in solid black. Drift at bank of Cam, May 31, 1911. (Nat. size.) [A. A.]
When the leaves, instead of being radical, are borne on a
pliable, elongated stem, the function of flexibility seems to be
taken over by the axis and the leaves are generally small and
simple, as in the case ofElodea canadensis. In Hippuris vulgaris,
however, the wrhorled, submerged leaves may reach a consider-
able length.
The finely divided type of submerged leaf takes two different
forms, according to whether the species to which it belongs
is Dicotyledonous or Monocotyledonous. There are numerous
examples of dissected, submerged leaves among the Dicoty-
i42 TYPES OF LEAF IN WATER PLANTS [CH.
ledons, the most familiar case being that of various Batrachian
Ranunculi. Among Monocotyledons the submerged leaves are
nearly always entire ; the character-
istic venation of this group does not
lend itself readily to the formation
of a dissected leaf. As Henslow1
has pointed out, dissection among
Dicotyledons is represented, in the
very few equivalent cases among
Monocotyledons, by fenestration,
which produces a similar result. He
adds the ingenious, but probably
untenable, suggestion that the fene-
stration of the aerial leaves of Tor-
nelia, Monstera^ etc., is a character
handed down to them from aquatic
ancestors. Among the Aponogetons
we meet with a slight and irregular
perforation of the leaves in A.
BernerianuS) (Decne.) Hook, fil.2,
while in A. (Ouvirandra) fenestralis
the mature leaves are completely
reticulate (Fig. 91). According to
Mlle Sergueeff3, who has made a
detailed study of the subject, the
young leaves are imperforate, the
perforations arising at a later stage
by destruction of the tissues. When
the perforations are formed, a fauna
r >r
and flora of Flagellates, Rotifers,
Bacteria and Algae accumulate in
their neighbourhood, without ap-
parently being responsible for their actual initiation ; probably
1 Henslow, G. (1893),
2 Krause, K. and Engler, A. (1906).
3 Sergueeff, M. (1907).
FIG. 91. Perforated leaf of -4£ono-
geton fenestralis, Hook. i.-Ouvi-
xi] THE LACE-PLANT OF MADAGASCAR 143
they merely make use of the debris of those cells which are
sacrificed to form the perforations.
That the fenestration in Ouvirandra may be of some value in
connexion with aeration was suggested by Goebel's statement
that the tissue of the leaf is poor in intercellular spaces1. Mlle
Sergueeff, however, shows that Goebel is in error on this point,
since numerous lacunae occur in the mesophyll, and she con-
cludes that the main function of fenestration is not aeration,
but the reduction of resistance to current. In this connexion it
may be recalled that all the imperforate, submerged leaves
found among the Aponogetons are thin and ribbon-shaped,
thus yielding easily to the movement of the water (e.g. A. angus-
tifolius. Ait.)2. It may also be significant that A. (Ouvirandra)
fenestraliS) in its Madagascan home, though it sometimes grows
in stagnant water, is also capable of living in torrents. Hans-
girg3 had previously suggested that some forms of submerged
leaf might be compared with those of such * anemophytes '
among terrestrial plants as Palms, Bananas, etc., in which the
slitting, sub-division and perforation of the leaves are interpreted
by some authors as modifications designed to avoid tearing by
the wind. But the view that would regard all types of submerged
leaf as definite adaptations to water life, probably needs con-
siderable revision. We do not propose to criticise it at this point,
since it is included in the broader question of the relation of leaf
form to environment, which is better considered in connexion
with heterophylly4.
(2) THE FACTS OF HETEROPHYLLY UNDER NATURAL
CONDITIONS5
The occurrence of two or more different types of leaf upon
one individual, which is so frequently characteristic of water
plants, has long attracted the interest of botanists.
1 Goebel, K. (1891-1893). 2 Krause,K.andEngler, A.(i9o6)
3 Hansgirg, A. (1903). 4 See Section (3) of this Chapter.
5 Arber, A. (i9i93) has been largely incorporated in Sections (2) and
(3) of this Chapter.
i44 HETEROPHYLLY [CH.
Lyte's Herball(i 578) contains a vivid description of hetero-
phylly in the Water Buttercup — a free translation of that given
in Dodoens' Histoire des Plantes of 1 557. Since this description
is also noteworthy for its insistence on the influence of external
conditions upon the form of the leaves, it may be cited here.
" Amongst the fleeting [floating] herbes, there is also a cer-
tayne herbe whiche some call water Lyverworte, at the rootes
whereof hang very many hearie strings like rootes, the which
doth oftentimes change his uppermost leaves according to the
places where as it groweth. That whiche groweth within the
water, carrieth, upon slender stalkes, his leaves very small cut,
much like the leaves of the common Cammomill, but before
they be under the water, and growing above about the toppe of
the stalkes, it beareth small rounde leaves, somewhat dented, or
unevenly cut about. That kind which groweth out of the water
in the borders of diches, hath none other but the small jagged
leaves. That whiche groweth adjoyning to the water, and is
sometimes drenched or over-
whelmed with water, hath also
at the top of the stalkes, small
rounde leaves, but much more
dented than the round leaves of
that whiche groweth alwayes in
the water."
The water and land leaves of
Ranunculus Purschii are illus-
trated in Fig. 92 A and B. The
heterophylly of the Water
Buttercups has been subjected
to a great deal of critical investi-
gation. It has been shown that,
in the case of Ranunculus aqua-
tilis^ L.1, it is impossible to say
at an early stage whether a leaf
rudiment will produce the floating or submerged form. Up
1 Askenasy, E. (1870). See also Rossmann, J. (1854).
B
FIG. 92. Ranunculus Purschii, Rich.
A , water leaf (£ nat. size) and B, leaf
of the land form (reduced). [Goebel,
K. (1891-1893)-]
xi] THE WATER BUTTERCUPS 145
to a certain point they develop alike and are both deeply sub-
divided ; then the water leaf ceases to change in shape and the
segments merely increase in size, while the floating leaf gradu-
ally assumes its typical, relatively entire form. In general, the
type of leaf produced by the plant can be changed at will by
altering the conditions. If a plant that has begun to grow on dry
land, be submerged, the new leaves produced by further growth
are of the submerged type. The existing leaves, though they
cannot alter their form, may, in the basal region which is still
capable of growth, develop transitional features as regards the
epidermis.
Among species related to Ranunculus heterophyllus. Fries,
in which floating as well as
submerged leaves are usually
present, we find some, such as
R. fluitans^ Lamk., in which the
floating leaves are rare, while in
R. circinatuS) Sibth. they are un-
known. On the other hand, R.
hederaceus, L. (Fig. 93), which
generally grows in shallow ponds
and ditches, possesses lobed reni-
form leaves only, and none that
are finely divided and belong to
the submerged type.
Heterophylly is not confined
to the Batrachian Ranunculi,
but is widespread in the genus.
Ranunculus Flammula, the Lesser
Spearwort, though generally
terrestrial, may live as a water
plant1, in which case it can develop both submerged and floating
leaves. The submerged leaves are not, however, subdivided as
in the case of Ranunculus heterophyllus. Heterophylly has also
1 Bailey, C. (i 8 87), West, G. (1910), Gluck,H. (191 1); references will
be found in West, G. (1910) to the earlier writers who observed this form.
FIG. 93. Ranunculus hederaceus, L.
An example of a Batrachian Ranun-
culus with undivided leaves, (f nat.
size.) Shallow pool, Ware Undercliff,
March 27, 1912. The gynaeceum, G,
is bending down to ripen under water.
[A. A.]
A. W. P.
146 HETEROPHYLLY [CH.
been recorded in R. sceleratus1^ R. Lingua2 and other species.
In R. sceleratus the present writer has observed that, in aerial
and in floating leaves, stomates occur on both surfaces, but in
the case of the floating leaf, the stomates were found to be
less numerous on the lower surface than in a leaf growing
in air.
The heterophylly of the Nymphaeaceae has been discussed
in Chapter in3, so it is now only necessary to recall that
aerial leaves, floating leaves and submerged leaves may occur,
the latter belonging either to the t/A^-like type of Nymphaea
and Castalia, or the dissected type of Cabomba.
Leaving the Ranales, it may be worth while to pass rapidly
in review the more pronounced cases of heterophylly met with
in the remaining families of Angiosperms.
In Callitriche verna the submerged leaves are not very
different, superficially, from the floating leaves, but are
distinguished by their narrower and more elongated form
(Fig- 94)-
Hippuris vulgaris furnishes a particularly well-marked in-
stance of heterophylly. In May, when its flowering shoots rise
out of the water, there is the sharpest contrast between the
close whorls of rigid, short, aerial leaves (B-D in Fig. 95) and
the submerged whorls, with their long, flaccid leaves, visible
beneath the water surface (A in Fig. 95; see also Fig. 151,
p. 231). Goebel records that he once found Hippuris growing
entirely submerged at a depth of 3 metres, with leaves 7 cms. or
more long4. Towards July, when the plant is at its period of
maximum activity, the new shoots formed under water, even at
a depth of 50 cms., are reported to be of the aerial type and to
bear stomates5. This statement is of importance in connexion
with the problem of the significance of heterophylly, which will
1 Ascherson, P. (1873), and Karsten, G. (i
2 Roper, F. C. S. (1885).
3 See pp. 27-29, and Figs. 12 and 14.
4 Goebel, K. (1891-1893).
5 Costantin, J. (1886).
xi] SUBMERGED LEAVES 147
be discussed later in the present chapter. When winter comes
on, the thin, submerged, stomateless type of leaf is again
produced. Fig. 96, p. 148, represents a rather curious case,
in which a shoot had reverted to submerged leaves (a) after
bearing aerial leaves (c). It had apparently been beaten down
into the water by heavy rains, and this involuntary return to
submerged life had induced the production of the submerged
type of leaf in the apical region.
FIG. 94. Callitriche verna, L. Shoot from a
ditch near the Cam, May 17, 1911, to show
the difference between the submerged and
floating leaves. The leaves down to, and
including, the pair marked a, a were floating.
(Reduced.) [A. A.]
FIG 95. Hippuris vulgaris, L.
Leaf whorls, (f nat. size.)
A, water leaves; B-D, air
leaves of land form. B and C
have fruits in the leaf axils.
[After Gluck, H. (1911),
Wasser- und Sumpfgewachse,
Bd. in, Figs. 23 a-d, p. 250.]
Among the Umbelliferae, a differentiation between water
leaves and aerial leaves is not at all uncommon. There are
several instances even among our native plants. Slum latifolium
is a very striking case. At the end of May, at Roslyn Pits, Ely,
the present writer has seen a quantity of this plant, in a non-
flowering condition, bearing three types of leaf — all three some-
times occurring on a single individual (Fig. 97, p. 149). These
were — firstly, submerged leaves, either simply-pinnate but
deeply incised (Fig. 98, p. 150), or compound-pinnate with
148
HETEROPHYLLY
[CH,
FIG. 96. Hippuns vulgaris, L. A shoot which was found lying horizontally in the
water, August 17, 1917. It had produced air leaves (c), but presumably in very
heavy rains, which had terminated a fortnight earlier, it had been beaten down
and had produced (6) transition leaves and (a) water leaves. An axillary shoot (ax)
bore water leaves. (£ nat. size.) Fig. 96 should be compared with Fig. 151,
p. 231, which shows the normal relations of the two leaf types. [A. A.]
xi] THE WATER PARSNIP 149
linear segments (a in Fig. 97): secondly, compound-pinnate air
leaves, with each leaflet of the second degree toothed and lobed
FIG. 97. Sium latifolium, L. Plant from Roslyn Pits, May 30, 1911, showing three
types of leaf : a, submerged compound-pinnate leaf with linear segments ; b, erect
air-leaf, compound-pinnate; c and d, erect air leaves, simply-pinnate. (Reduced.)
[A. A.]
(b in Fig. 97); and thirdly, air leaves, once pinnate, with the
leaflets toothed but not lobed (c and din Fig. 97). Some small
plants were found bearing the submerged type of leaf alone.
150 HETEROPHYLLY [CH.
Where the three types were borne together, the simply-pinnate
leaves were the latest to be produced, and the submerged leaves
the earliest, while the compound-
pinnate air leaves were intermediate.
Oenanthe Phellandrium, Lamk.
v&r.fluviatilis, Colem.1 is very com-
mon in the Cam near Cambridge.
It has graceful, finely cut, pinnate
leaves with obcuneate segments,
and the plant is generally entirely
submerged; a shoot as long as
235 cms. has been recorded. Its
identity is liable to be puzzling at
first sight, since its aerial axes are
comparatively rarely to be found.
On one occasion, however, on
which the present writer found the
plant bearing both submerged and
aerial leaves, Oenanthe Phellan-
drium (proper) was noticed, at the
same time, growing magnificently
in a neighbouring ditch. It had
a very stout, lacunate stem, bearing
numerous aerial leaves and also a
relatively small number of sub-
merged leaves with capillary seg-
ments; the abundant lateral roots
were lacunate. A comparison of the
two plants suggested that Oenanthe
Phellandrium var. fluviatilis is a
mutation which has taken more
whole-heartedly to water life than
the type form of the species.
Polygonum amphibium is an example of a hydrophyte which
1 It is a matter of opinion whether this plant should be regarded as a
distinct species or as a variety. See Coleman, W. H. (1844).
FIG. 98. Sium latifolium, L. Sub-
merged leaf from a plant found at
Wicken Fen, June 27, 1914. Less
finely divided than leaf a in
Fig. 97. (Reduced.) [A. A.]
xi] SYMPETALAE AND MONOCOTYLEDONS 151
can produce either air leaves or water leaves with the utmost
facility. The floating leaves and air leaves differ in internal
anatomy and in the characters of the epidermis, and also show
obvious external differences (Figs. 99 and 100, p. 152); the
floating leaves are shiny, leathery and absolutely glabrous, while
the air leaves are wrinkled and covered with hairs1. The
lateral branches from a shoot with floating leaves, or even the
end of the branch itself, may rise into the air and develop the
characteristics of the land form2.
Certain Scrophulariaceae are heterophyllous, such as Ambulia
(Limnophila) hottonoides and Hydrotriche hottoniaefolia. In these
cases the submerged leaves are finely divided. Among the
Pedaliaceae, Trapella* has deltoid-rotundate floating leaves and
linear-oblong submerged leaves, while Limnosipanea Spruceana,
of the Rubiaceae, also shows a distinction between water and
air leaves4. Bidens Beckii* is an example of a Composite
showing heterophylly.
The heterophylly of the Alismaceae and Hydrocharitaceae
need not be reconsidered now, since it has been dealt with in
Chapters n and iv6. Two additional figures may, however, be
included here, to illustrate the effect of transferring to water a
small terrestrial seedling of Alisma Plantago found growing wild
(Fig. 101, p. 1 53). After between two and three months, it had
developed into the typical water plant shown in Fig. 102, p. 1 53.
There are many other cases of heterophylly among the
Monocotyledons. Certain Potamogetons, e.g. P. fluitans, have
air leaves, floating leaves and narrow submerged leaves7.
Potamogeton natans is also a particularly good example; the
narrow submerged leaves may attain a length of 50 cms. in
running water5. The result of planting a land form of P. natans
in water has been recorded5. The aerial leaves soon died, and
1 Costantin, J. (1886).
2 Schmidt, E. M. Inaug.-Diss. Bonn, 1879, quoted by Schenck, H.
(1885). 3 Oliver, F. W. (1888).
4 Hansgirg, A. (1903). 5 Goebel, K. (1891-1893).
6 See pp. 9-14, 19-23, 51-52, 57> and Figs- 3-6> 9-
7 Esenbeck, E. (1914).
152
HETEROPHYLLY
[CH.
B
FIG. 99. Polygonum amphibium, L. A , branch of aquatic plant with floating leaves.
B, branch of xerophilous plant inhabiting littoral dunes. [Massart, J. (1910).]
FIG. 100. Polygonum amphibium, L. A, upper epidermis, and B, lower epidermis of
floating leaf, cf. Fig. 99^. C, upper epidermis, and D, lower epidermis of xero-
philous leaf, cf. Fig. 99 B. The elements marked with a cross are reservoir cells.
[Massart, J. (1910).]
xi] SEEDLINGS OF WATER PLANTAIN 153
the next leaves formed had a smaller blade, a longer stalk, and
an upper epidermis with chlorophyll and but few stomates.
FIG. 101. Alisma Plantago, L. Seedlings found growing under the shade of a large
A, Plantago plant in a dry ditch, May 31, 1911. (Nat. size.) [A. A.]
FIG. 102. Alisma Plantago, L. One of the seedlings such as those shown in Fig. 101
which had germinated on dry land, but was planted in a pot on May 31, 191 1, and
submerged in shallow water until August 9, IQII (two months, nine days). In
this time it developed into a typical water form with three floating leaves (a, b, c)
and others showing transitions from the submerged type. (Reduced.) [A. A.]
The succeeding leaves were long and simple. Fig. 103, p. 154,
illustrates this experiment.
154 HETEROPHYLLY [CH.
The Pontederiaceae1 and some of the Aponogetons2 also
have band-shaped, submerged leaves in addition to those that are
aerial. Scirpus lacustris (Cyperaceae), in
which the aerial leaves are very poorly
developed, may produce strap-like
floating leaves. They were first re-
corded by Scheuchzer3 early in the
eighteenth century.
Some of the Pontederiaceae, e.g.
Eichhornia crassipes, present a curious
typeofheterophylly — the petioles being
swollen into bladder-like, floating
organs, when the plant grows in its
normal free-swimming manner, but
becoming slender and elongated when
it is thrown upon a muddy shore and
takes root there4. Experimental work
shows that not only a floating life, but
full light and low temperature, en-
courage the spherical form of petiole,
while heat, and poor illumination, tend
to reduce it to a more ordinary
shape5. The bladder-like swellings of
the leaves of Pistia also fail to develop
when the plant is stranded on mud6.
Examples of heterophylly in aquatics
might be multiplied almost without limit, but it is important to
remember that they are not unique, and that we often meet with
the same phenomenon in terrestrial plants. As Nehemiah Grew7
1Goebd,K. (1891-1893).
2 Krause, K. and Engler, A. (1906).
3 Scheuchzerus, J. (1719).
4 Spruce, R. (1908).
5 Treviranus, L. C. (1848*) and Boresch, K. (1912).
6 Hansgirg, A. (1903).
7 Grew, N. (1682).
FIG. 103. Potamogeton na-
tans, L. Land plant which
has been transferred to
water and has produced
narrow water leaves. (Re-
duced.) [Goebel, K. (1891-
1893)-]
xi] THE MEANING OF HETEROPHYLLY 155
wrote in the seventeenth century, "there are some, which have
Leaves (besides the two first Dissimilar ones1) of Two Kinds
or Two distinct Figures ; as the Bitter- Sweet, the common
Little Bell, Valerian, Lady-Smocks, and others. For the Under
Leaves of Bitter-sweet, are Entire; the Upper, with two Lobes ;
the Under Leaves of the Little Bell, like those of Fancy; the
Upper, like those of Carnation, or of Sweet-William''
We find parallels to the heterophylly of hydrophytes not only
among terrestrial Flowering Plants, but also in the case of the
distinct * youth forms* of Conifers, and even — more remotely
— in the Chantransia stage of such Algae as Batrachospermum.
The conclusion to be drawn from our very brief survey, which
only touches the fringe of the subject, is that heterophylly is so
widespread that no interpretation can be valid unless the con-
dition be treated broadly as a very general attribute of plant life,
rather than as a rare and exceptional phenomenon, for which
special and individual explanations will suffice.
(3) THE INTERPRETATION OF HETEROPHYLLY
To the earlier writers, such as Lamarck2, the problem of
heterophylly presented no difficulties. They regarded the sub-
merged or aerial type of leaf as representing a direct response,
on the part of the plant, to the medium. The work of the last
thirty years, has, however, rendered this simple conception
untenable; the theory that now holds the field accords a much
less prominent place to adaptation. The first observation that
cast doubt upon the idea that leaf form necessarily depended
directly on the milieu, was that of Costantin 3, who showed that,
in the case of Sagittaria, the aquatic and aerial leaves were
already distinguishable from one another in the submerged bud;
he noticed auricles on a leaf which was only 2 to 3 mm. long.
In Ranunculus aquatilis, also, the leaves destined to be aerial
are differentiated in the bud.
1 I.e. cotyledons. 2 Lamarck, J. B. P. A. (1809).
3 Costantin, J. (18852) and (1886).
156 HETEROPHYLLY [CH.
A large amount of experimental work has been published by
various authors on the effect of conditions upon the leaf forms
of heterophyllous plants, and, although some of the results are
confused and conflicting, a study of the literature seems to
justify one general conclusion — namely, that, in many cases,
the submerged type of leaf is, in reality, the juvenile form, but
can be produced later in the life-history in consequence of poor
conditions of nutrition ; the air leaf, on the other hand, is the
product of the plant in full vigour and maturity. This conclusion,
which is primarily due to Goebel1 and his pupils, is substantiated
not only by experiments but by observations in the field.
In many heterophyllous plants, the first leaves produced by a
seedling, whether it develops on land or in water, conform, more
or less, to the submerged type. This is the case for instance in
the Alismaceae. In Alisma Plantago (Fig. 101 yfand #, p. 153)
and Sagittaria sagittifolia (Fig. 90, p. 141), the first leaves
produced by the seedling, or the germinating tuber, are ribbon-
like, even when the young plant is terrestrial. The formation of
this type of leaf can be induced again, even in maturity, by
conditions which cause a general weakening of the plant.
Costantin2, thirty- four years ago, recorded that, when the leaves
of Alisma Plantago were cut off in the process of clearing out
a water-course, or in a laboratory experiment, the next leaves
produced were ribbon-like, thus representing a regression to
the submerged form. More recently, another worker3 tried
the experiment of cutting off the roots of healthy, terrestrial
plants of Sagittaria natans which bore leaves with differentiated
laminae; it was necessary to cut the roots away every week, as
they grew again so rapidly. The result of this treatment was that
the plants were found to revert to the juvenile stage, the new
leaves being band-shaped. When the experimenter ceased to
interfere with the roots, the plants again formed leaves with
laminae. Other plants, with uninjured roots, grown as water
cultures in distilled water, also produced the juvenile leaf form,
1 Goebel, K. (1896), etc. 2 Costantin, J. (1886)
3 Wachter, W.
xi] WATER LEAVES AND POOR NUTRITION [57
while those grown in a complete culture solution developed
their laminae normally.
The same observer recorded a case in which a plant of
Hydrocleis nymphoides, Buchenau (Butomaceae), which had
been bearing the mature form of leaf, was observed to revert
to the ribbon form. On examination it was found that most
of the roots had died off. When a fresh crop of roots was pro-
duced, the mature type of leaf occurred again.
Another writer1 demonstrated by a series of experiments upon
Limnobium Eoscii (Hydrocharitaceae) that, in this case also, the
heterophylly is not a direct adaptation to land or water life,
but that the floating leaves are " Hemmungsbildungen " due
to poor nutrition. In Stratiotes aloides^ also, he showed that the
stomateless leaves were primary, and that their production
could be induced at later stages by unfavourable conditions2.
An experiment tried by Goebel3 on Sagittaria sagitttfoHa
indicated that absence of light in this case inhibits the formation
of leaves of the aerial type. An observation of Gliick's on Alisma
graminifolium, Ehrh.4, also points to the same conclusion. But
it seems probable that the effect produced in these cases was not
due directly to the darkness, but to the state of inadequate
nutrition brought about by the lack of light for carbon assimi-
lation.
Among the Potamogetons 5, again, experimental work has
shown that reversion to juvenile leaves can be obtained under
conditions of poor nutrition. For example, when a land plant of
P. fluitanS) which had been transferred to deep distilled water,
had its adventitious roots repeatedly amputated, regression was
obtained to the floating type of leaf and then the submerged
type (Fig. 104, p. 158). A similar reversion to thin, narrow
leaves was brought about, in the case of P. natans^ by growing
the upper internodes of a shoot as a cutting (Fig. 105, p. 159).
Waterlily leaves respond to experimental treatment in just
1 Montesantos, N. (1913). 2 See pp. 51-52.
3 Goebel, K. (1891-1893). 4 See p. 280.
5 Esenbeck, E. (1914).
HETEROPHYLLY
CH
FIG. 104. Potamogetonfluitans, Roth. A land plant transferred for about a month
to distilled water with no substratum and the adventitious roots repeatedly re-
moved. The internodes marked I were formed during land life; fej, £>2 and 63 are
the surviving land leaves; the internodes i^ and «2 show some elongation as a
result of the changed conditions ; 64 and 65 are floating leaves ; bQ-bw are leaves of
the submerged type. [Esenbeck, E. (1914).]
xi] WATER LEAVES AND LOW VITALITY 159
the same way as the Monocotyledons already mentioned. In the
case of two species of Castalia, it has been found possible to
induce the mature plants to form submerged leaves, either by
removing the floating leaves or by cutting off the roots1. This
confirms an earlier suggestion, made by an Italian writer2, that
the development of the submerged leaves of Nymphaea lutea
FIG. 105. Potamogeton natans, L. The uppermost interned es of a normal plant
grown as a cutting. One floating leaf (s) survives, while the axillary shoots have
produced leaves with thin narrow blades, representing a transition between the
floating and submerged types. [Esenbeck, E. (1914).]
was due to "un indebolimento o diminuzione di energia
vitale." This suggestion has received independent, experi-
mental confirmation from another worker3, who estimated that
a well-developed floating lezfofNympkaea lutea was about eleven
times the dry weight of a submerged leaf of the same area.
Another Dicotyledon, Proserpinaca palustris^ which was in-
1 Wachter, W. (18972). 2 Arcangeli, G. (1890).
3 Brand, F. (1894).
1 60 HETEROPH YLLY [CH .
vestigated by Burns1, gave results pointing to the same general
conclusion as those observations already quoted. The primitive
type of leaf in this plant is always a " water" leaf, but this form
of leaf was also produced in the autumn by all the plants,
regardless of any external conditions which the experimenter
could control. On the other hand, at the time of flowering and
in the summer generally, almost every plant, whether growing
in water or air, produced the "land" type of leaf — the transi-
tion from the "water" to the "land" type taking place earlier
on strongly growing than on weak stems. The author considers
it evident that the aquatic environment is not the cause of the
division of the leaf, nor does it depend on light, temperature,
gaseous content of the water or contact stimulus. The only con-
clusion, which he considers justified by his experiments, is that
Proserpinaca -palustris has two forms — adult and juvenile; under
good vegetative conditions, it tends to produce the adult form
with the undivided leaf, the flower and the fruit, while, if the
vegetative conditions are unfavourably influenced, a reversion
can be induced to the primitive form with the submerged type
of leaf. These results are consistent with those of McCallum2,
who had dealt with the same species at an earlier date, but his
interpretation is slightly different. He is inclined to regard the
occurrence of the aquatic form as induced by the checking of
transpiration, and by the increased amount of water which hence
accumulates in the protoplasm. This explanation is not incon-
sistent with the more general view that any condition tending
to lower the vitality may be responsible for a reversion to the
submerged type of leaf.
In nature, the regression to the juvenile type of leaf some-
times occurs, not only in the case of an entire plant subjected
to adverse conditions, but also in the case of lateral shoots from
an individual which is otherwise producing the mature form of
leaf. Goebel3, for instance, examined an old example of Eichhor-
nia azurea (Pontederiaceae) which had wintered as a terrestrial
1 Burns, G. P. (1904). 2 McCallum, W. B. (1902).
3 Goebel, K. (1891-1893).
xi] REVERSION IN LATERAL SHOOTS 161
plant in a greenhouse ; the leaves were of the mature form —
differentiated into sheathing base, petiole and lamina — except
in the case of a lateral shoot, which bore the grass-like, simple,
leaves which characterise the young plant. Goebel1 also de-
scribes the occurrence of subdivided leaves of the water type
on lateral shoots of normal land plants of Limnophila hetero-
phylla. A corresponding reversion has been observed in the
case of the side branches of plants of Proserpinaca palustris*
developing in the air from a plant whose main stem was pro-
ducing the mature type of leaf; by removing the growing apex
of the stem in June, these side branches of the * water* type
were induced to develop.
The interest of these lateral shoots, which show a reversion
to an ontogenetically earlier type of leaf, is enhanced by the fact
that C. and F. Darwin3 have recorded a case of the occurrence,
on lateral shoots, of leaves whose characters are probably
phylogenetically earlier than those which the species normally
exhibits. Their observations related to the sleep habits of the
allied genera, Melilotus and Trifolium. They noticed, in Melilotus
Taurica, that leaves arising from young shoots, produced on
plants which had been cut down and kept in pots during the
winter in a greenhouse, slept like those of Trifolium^ with the
central leaflet simply bent upwards, while the leaves on the
fully-grown branches of the same plant afterwards slept accor-
ding to the normal Melilotus method, in which the terminal
leaflet rotates at night so as to present one lateral edge to the
zenith. They suggest that Melilotus may be descended from a
form which slept like Trifolium.
The idea that the * juvenile' leaves, produced on lateral
shoots, may in some cases represent an ancestral type, is con-
sistent with the facts in the case, for instance, of the Alismaceae,
provided that the ' phyllode theory ' of the Monocotyledonous
leaf be accepted in the sense advocated by Henslow and the
present writer. According to this theory, which will be dealt
1 Goebel, K. (1908). 2 Burns, G. P. (1904).
3 Darwin, C. and F. (1880).
A.W. P. II
1 62 HETEROPHYLLY [CH. xi
with in some detail in Chapter xxvm, the ancestral leaf of this
family was band-shaped, while the oval or sagittate blade,
or * pseudo-lamina/ is a later development — a secondary ex-
pansion of the distal region of the sheath or petiole. The
submerged youth-leaves of this family would thus represent a
reversion to phylogenetically older forms.
If the interpretation of heterophylly indicated in the present
chapter holds good at all widely, the teleological view of the
submerged leaf must be considerably modified. The present
writer would like to suggest that, for the old conception of
heterophylly as induced by aquatic life, we should substitute
the idea that such a difference between the juvenile and mature
forms of leaf as would render the juvenile leaf well suited to
life in water, has been in many cases one of the necessary pre-
liminaries to the migration from land to water, and that the
aquatic Angiosperms thus include, by a process of sifting1,
those plants whose terrestrial ancestors were endowed with a
strong tendency towards heterophylly2.
1 Guppy, H. B. (1906) first emphasized the fertile idea that the
habitats of plants were determined by their peculiarities of structure, and
not 'vice versa. In relation to the occurrence of plants with buoyant seeds
and fruits in water-side stations, he writes, " there are gathered at the
margins of rivers and ponds, as well as at the sea-border, most of the British
plants that could be assisted in the distribution of their seeds by the agency
of water. This great sifting experiment has been the work of the ages,
and we here get a glimpse at Nature in the act of selecting a station."
2 In addition to the references mentioned in this chapter, MacDougal,
D. T. (1914) and Shull, G. H. (1905) may also be consulted; the results
recorded in these papers emphasize the difficulty and complexity of the
problem.
[ 163 ]
/
CHAPTER XII
THE ANATOMY OF SUBMERGED LEAVES1
THE majority of submerged leaves have certain charac-
ters in common, the most obvious of which is their
delicacy of structure. On removal from the water they gene-
rally collapse rapidly, and in some cases, e.g. Hippuris vulgaris,
when they are plunged into alcohol the chlorophyll begins
visibly to pass into solution almost from the first moment. The
general tenderness of the leaves is due to the thinness of the
mesophyll and the absence of differentiation between spongy
and palisade parenchyma, and also to the relative lack of me-
chanical elements and the slight development of the cuticle2.
It is indeed the epidermal characters — such as the reduction
of cuticle — which most markedly distinguish submerged from
aerial leaves.
It will be remembered that, in general, the epidermal cells of
the leaves of Dicotyledons tend to be sinuous in outline, while
those of Monocotyledons are more rectangular. But in the case
of such a plant as Callitriche verna (Fig. 1 1 1, p. 1 70) which has
both aerial and submerged leaves, it is found that, though the
aerial leaves show the characteristic Dicotyledonous sinuosity
in the form of their epidermal cells, the corresponding elements
in the submerged leaves have straight walls, and hence approach
the Monocotyledonous type. An interesting hypothesis on this
subject was put forward long ago by Mer3. He drew attention
to the fact that the epidermis was the tissue most directly
affected by transpiration, and suggested that variations in that
function might exercise an influence upon the form of the
epidermal cells. According to his view, when transpiration is
1 For a comprehensive account of this subject see Schenck, H. (1886),
which has been largely drawn upon in the present chapter.
2 A cuticle, though thin, seems to be invariably present. See Geneau
de Lamarliere, L. (1906). 3 Mer, E. (iSSo1).
1 64 SUBMERGED LEAVES [CH.
feeble, as in the case of submerged plants, the epidermal cells
are kept in a constant state of turgescence, and hence their
growth takes a uniform course resulting in regularity of form.
But, on the other hand, when transpiration is active, as in
land life, the current is subject to great variations which react
upon the form of the epidermal cells and produce sinuosity. It
is scarcely possible to submit such a theory to direct proof, but
it seems to the present writer that it is at least consistent with
the fact, established at a much later date than Mer's work, that
Monocotyledons with their rectangular epidermal cells, are in
general, though with many exceptions, c sugar-leaved * and
weak transpirers, while Dicotyledons, with their epidermal cells
often resembling a Chinese puzzle, are * starch-leaved ' and
strong transpirers1.
The epidermal cells of submerged leaves differ from those
of air leaves not only in form but also in contents. Chlorophyll
grains, which are generally described as absent from the epi-
dermis of terrestrial plants, are often present in great abundance
in this tissue in submerged leaves2. Treviranus3, nearly a cen-
tury ago, alluded to the lack of distinctively epidermal charac-
ters— or, to use his own expression, the "absence of an epider-
mis " — in the case of the lower surface of the leaf of Potamogeton
crispus, while Brongniart4, a few years later, observed the pre-
sence of chlorophyll in the leaf epidermis of P. lucens. Subse-
quently, epidermal chlorophyll has been observed widely among
aquatic plants5, though there are certain exceptions, such as
Callitricht*. In some cases, e.g. Zoster a^ Cymodocea, Posidonia1,
the epidermis is actually the part of the leaf richest in green
corpuscles. The presence of chloroplasts does not constitute,
however, so absolute a difference from land plants as is some-
times assumed, since it has been shown that chlorophyll grains
can be found in the epidermis of the green organs of the
1 Stahl, E. (1900). 2 Schenck, H. (1886).
3 Treviranus, L. C. (1821). 4 Brongniart, A. (1834).
5 Chatin, A. (1855!), etc. 6 Schenck, H. (1886).
7 Sauvageau, C.
xn] CHLOROPHYLL AND STOMATES 165
majority of terrestrial Dicotyledons, though they are generally
absent in the case of terrestrial Monocotyledons1. They are
usually to be observed only in the lower epidermis of the leaf,
but it seems probable that this is due to the destructive action
of sunlight upon the chlorophyll in the upper epidermis. In
support of this view it may be mentioned that, in diffused light,
chlorophyll occurs in the upper epidermis of the leaves of Eellis
perennis, whereas under normal conditions there is chlorophyll
only in the lower epidermis. The presence of green plastids
in the epidermis of submerged plants may thus be regarded as
representing merely the elaboration of a character already
existing in terrestrial plants, which finds favourable oppor-
tunities for development in the relatively dim illumination
which submerged plants receive.
The statement, frequently made, that stomates are absent
from submerged leaves, and from the lower surface of floating
FIG. 1 06. Elodea canadensis, Michx. T.S. leaf; », intercellular air channels
[Schenck, H. (1886).]
leaves, needs considerable qualification2. It is, indeed, broadly
true that stomates are much less frequent in submerged than
in terrestrial leaves, and, moreover, in certain water plants,
such as Elodea (Fig. 106), Vallisneria^ Thalassia, and other
Hydrocharitaceae which always live entirely submerged, sto-
mates never occur3. Among the Cryptogams, Isoetes lacustris
is entirely free from stomates, and Goebel4 even found that it
failed to produce any when grown for two years as a land plant.
Submerged leaves in general are not only poor in stomates but
also in hairs ; it has been suggested by Mer5 that this — like the
^tohr, A. (1879).
2 Costantin, J. (I8851). See also Porsch, O. (1903) for citations of a
large number of cases in which the occurrence of stomates on submerged
organs is mentioned in the literature. 3 Solereder, H. (1913).
Goebel, K. (1891-1893). 5 Mer5 £ (jgSo1) and (1882^
4
1 66 SUBMERGED LEAVES [CH.
form of the epidermal cells — may be correlated with the feeble-
ness and uniformity of the transpiration stream. He supposed
that the active and variable flow of sap in land plants might
bring about the accumulation of nutriment at certain points
of the epidermis, thus favouring localised cell-multiplication
and the production of hairs and stomates. It seems possible to
the present writer that this suggestion contains an element of
truth. But on the other hand it must be remembered that
stomates have been observed in a large number of submerged
leaves, such as those of Lobelia Dortmanna1^ Villarsia ovata* and
Pontederia cor data?) and on the lower surfaces of certain floating
leaves, such as Limnocharis Humboldtii* and Hydrocharis Mor-
sus-ranae^. Porsch5, who has considered the subject compre-
hensively, concludes that the stomatal apparatus must have been
gradually evolved over a long period of time, so that its charac-
ters have become fixed with great tenacity; for, in cases where
its existence must be not only superfluous, but attended by a
certain danger to the plant, instead of being discarded, it is
often modified secondarily in such a way as to render it func-
tionless. He shows that, in the case of submerged plants which
retain their stomates, four different modifications are found,
each of which must have the result of preventing water entering
the tissues through the aperture between the guard cells :
(1) The guard cells may close on submergence, even in full
illumination, e.g. Callttriche verna and Hippuris vulgaris.
(2) The aperture may be permanently closed, as in the case
of Potamogeton natans (Fig. 1 07 B\ in which the whole stomatal
apparatus remains roofed in with cuticle.
(3) The development of each stomate may actually cease at
an early stage. This is rare, but such abortive stomates are found
in the submerged parts of a species of Oenanthe^.
1 Armand, L. (1912). 2 Costantin, J. (I8851).
3 Duchartre in discussion following Chatin, A. (1855*).
4 Goebel, K. (1891-1893). 5 Porsch, O. (1903) and (1905).
6 Porsch uses the specific name "Oenanthe aquatilis, L."; he is pro-
bably referring to Oe. Phellandrium^ Lamk. var. fluviatilisy Colem.
xn] WATER PORES AND AIR PASSAGES 167
(4) The stomates may develop normally, but the guard cells
remain pressed together
with their cuticular ridges
interlocked, e.g. Calla pa-
lustris (Fig. 107 A).
In addition to ordinary
stomates, which, in sub-
'. '. FIG. 107. A. Calla palustns, L. T.S. stomate
merged life, are incapable in submerged leaf stalk; the thickening bands
of pvprrkino- their normal fit closely together. B. Potamogeton natans ,
L. T.S. submerged stomate from leaf stalk
function, Submerged leaves of floating leaf. This stomate is entirely
! i i roofed in with cuticle. [Porsch, O. (1905).]
also very commonly bear
water stomates, which are probably of importance in keeping
up the 'transpiration' stream by exudation1. A longitudinal
section passing through the water pores of Pistia Stratiotes is
shown in Fig. 53, p. 82, while the apical
opening of Potamogeton densus — in which
the tracheids communicate directly with
the exterior without the intervention of
water stomates — is represented in Fig.
108.
The aerating system of submerged
leaves is a very conspicuous feature.
The mesophyll of such subcylindrical
radical leaves as those of Littorella and
Lobelia Dortmanna is traversed from end
to end by air passages, interrupted only ^ iog Pota**geton
by porous diaphragms, and the same densus, L. L.s. apex of
feature is markedly developed in the medi^ner^e InT showing
elongated petioles of such leaves as Sagit- the apical opening. (Upper
. ,T^. * N <-ni j- i surface of leaf to right
tana (Fig. 8, p. 19) Inese diaphragms hand.) fx 220<) [Sauva-
form points d'appui for the secondary 8eau> c- N*9**M
nerves connecting the longitudinal bundles2.
The mesophyll of submerged leaves shows, as has been
already indicated, little sign of differentiation into palisade and
1 This subject is considered more fully in Chapter xxi.
2 Duval-Jouve, J. (1872).
i68
SUBMERGED LEAVES
[CH.
spongy parenchyma. In many cases the assimilatory activity
seems, in great measure, confined to the epidermis, the meso-
phyll serving rather for storage
purposes. Myriophyllum^ shows
this distinction clearly; the
epidermis is rich in chloro-
phyll, while the mesophyll
contains large starch grains
(Fig. 109). This leaf is a good
example of the subdivided,
submerged type, each limb of
which exhibits a tendency to
a radial arrangement of the
T . 77 7-7- . 7 FIG. IOQ. Mvriophyllum spicatum. L.
tissues. Ltttorella, UtriCUlana T.S> through 'a segment of the leaf of
minor (Fig. 74, p. IO8) and the water form. The epidermis contains
^ \ „ , chloroplasts and the mesophyll is laden
Ler atop hy Hum all Show the Same with large starch grains, only indicated
approximately radial type of in a few cells- ^w) [Schenck, H
leaf anatomy. The effect of
environment upon this kind of leaf, is illustrated by a com-
parison between the land and water forms of Myriophyllum.
In the case of M. alter nifolium^ the land form, when growing
in sunny situations, has shorter and thicker leaf segments than
the water form; they are also dorsiventral and elliptical,
instead of radial and cylindrical, while the xylem is more
highly developed than in the water form. The epidermis
contains only a few small chlorophyll grains, and stomates
occur. The epidermal cells also have the sinuous outline which
is lacking in the water form. The absence of marked dorsi-
ventrality in the leaves of many submerged plants, such as
Myriophyllum, may in part be attributed to the fact that they
are perpetually being moved about by water currents, and thus
they do not retain any constant position in relation to the
incident light.
The very young submerged leaves of Myriophyllum vertidl-
latum and M. spicatum show a peculiarity which has^repeatedly
iSchenck, H. (1886).
xn] NON-RADIAL ANATOMY 169
attracted the attention of botanists1 — the occurrence, namely,
of little colourless cellular plates, arising generally at the apex
and base of each lobe, but sometimes elsewhere (Fig. 1 10 y/and
By p. 170). The cells at their base (c in Fig. no B) become
corky at an early stage, and the plates drop off. They are prob-
ably best interpreted as caducous trichomes; their function, if
they have one, is quite unknown.
As examples of the flat, non-radial type of submerged leaf,
Callitricfa Elodea and Alisma may be mentioned. In Fig. in,
p. 170, the contrast between the aquatic and aerial leaf of Cal-
litriche verna is indicated. The water leaf is thin, but still retains
some mesophyll ; the outlines of the epidermal cells in the two
forms show the distinguishing characters to which reference
has already been made. Callitriche autumnalis2, which lives and
flowers completely submerged, has a thinner leaf. The leaf of
Hottonia resembles that of Callitriche. The ribbon-leaf of
Alisma Plantago shows a slightly different type of structure.
The chlorophyll-containing epidermis forms the essential part
of the leaf, and the large air passages are bounded by it. There
is one main bundle, accompanied by two tiny laterals placed
close to the margins. In Elodea canadensis (Fig. 106, p. 165)
we reach almost the ultimate phase in reduction of the meso-
phyll, for here the entire assimilating tissue is reduced to the
two epidermal layers. The extremely delicate leaf is strength-
ened by some fibrous cells. Supporting sclerenchyma is cha-
racteristic of a certain number of submerged leaves such as
those of the Potamogetons (e.g. Fig. 38, p. 61).
There is a strong tendency, in submerged leaves, to the
reduction of the tracheal system. Among the Hydrocharitaceae,
for instance, though typical spiral tracheids occur in the sub-
merged leaves of Stratiotes^ the leaves of a number of other
genera show either no tracheids at all, or else more or less
ephemeral elements with annular thickenings, e.g. Elodea^
Halophila, Vallisneria and Thalassia*.
1 Irmisch, T. (1859!), Borodin, J. (1870), Magnus, P. (1871), and
Perrot, E. (1900).
2 Hegelmaier, F. (i 864). 3 Solereder, H. (i 9 1 3).
i yo
SUBMERGED LEAVES
[CH.
FIG. no. Trichomes of Myriopkyllum verticillatum, L. A, diagram of a young leaf
showing the arrangement of the trichomes. B, a single multicellular caducous
trichome at leaf margin with corky cells, c. at its base. [Perrot, £. (1900)-]
-I
FIG. in. Callitriche verna, L. A, T.S. submerged leaf, x 80; B, T.S. leaf of
land form, x 147; C, upper epidermis of submerged leaf, x 92; D, upper epi-
dermis of land leaf, x 88; E, lower epidermis of submerged leaf, x 92; F, lower
epidermis of land leaf, x 88. [Schenck, H. (1886).]
xn] 'ADAPTATION' TO WATER LIFE 171
A consideration of the structure of submerged leaves opens
up a series of perplexing theoretical problems. The idea that
the submerged type of leaf arises as an adaptive response to
the milieu^ proves on examination altogether inadequate. The
general form of these leaves seems attributable to poor nutri-
tion, while certain characters — thinness, lack of differentiation
of spongy and palisade parenchyma, and presence of chlorophyll
in the epidermis — are also common, in some degree, to terres-
trial plants growing in the shade, and seem intimately con-
nected with lack of sunlight1. We may perhaps suppose that the
dimness of the light which reaches a plant living below the
surface of the water may be directly responsible for these
characters; the green pigment, for instance, may be present
in the epidermis simply because the leaf is not exposed to direct
sunlight, which in the case of terrestrial plants destroys the
chlorophyll in the epidermis as fast as it is formed2. Now
there is little doubt that a thin leaf with an epidermis rich in
chlorophyll is particularly well adapted for the assimilation of
dissolved carbon dioxide; how then are we to account for the
singular coincidence that characters arising in this fortuitous
and mechanical fashion prove definitely advantageous to the
plant? It is perhaps conceivable that it is the very fact that
terrestrial plants under conditions of poor illumination tend to
develop this type of leaf, which has rendered possible the as-
sumption of the submerged habit, and that it is those plants
whose leaves happened under such conditions to develop on the
lines particularly suited to water life, which have accomplished
the transformation into thorough-paced aquatics.
1 Schenck, H. (1885). 2 Stohr, A. (1879).
CHAPTER XIII
THE MORPHOLOGY AND VASCULAR ANATOMY
OF AQUATIC STEMS1
THE stems of plants that pass the greater part of their
vegetative life entirely submerged, fall in general into
two categories. The less common type is the abbreviated axis
bearing a tuft of long narrow leaves (e.g. Stratiotes, Fig. 31,
p. 49 and Fig. 32, p. 53) while, on the other hand, the
majority of submerged plants are characterised by thin, elon-
gated, branched stems rising wholly or partially into the water,
clothed with leaves and often capable of rooting at the nodes
(e.g. Potamogeton, Fig. 37, p. 60 and Myriophyllum, Fig. 144,
p. 221). Owing to the high specific gravity of the water, and
the lightness of the stems, due to the air in the intercellular
spaces, each axis is to a large extent relieved of the task of
supporting the weight of its branches. In consequence there
seems to be no impulse to the relatively strong development of
a single main axis, and, in conformity with this, the general
system is often sympodial (e.g. Hippuris, Fig. 112). The plant
frequently grows actively in front while it dies away behind,
and may thus be regarded, to use Schenck's expression, as being
in a state of perpetual youth. The older regions tend to become
infested with a flora of epiphytic Algae and Fungi, among which
a microscopic fauna makes its appearance. This is an obvious
disadvantage, since no leaf thus laden can perform its functions
successfully. Possibly the rapid growth of fresh leafy shoots
at the apex serves as a compensation for a loss of activity in the
older regions, traceable to this cause.
The vascular system of submerged stems shows certain
modifications upon the terrestrial type, the most striking differ-
1 For a detailed treatment of this subject see Schenck, H. (1886),
which has been largely drawn upon in the present chapter.
CH. xm] MEANING OF LIGNIFICATION 173
ence being that the xylem tends to be reduced in amount, while
the lignification is often very poor. Spiral or annular vessels,
when present in the neighbourhood of the growing apex, may,
in some instances, be completely destroyed by the elongation of
theinternodes, and may survive only at the nodes, e.g. Potamogeton
lucens^^ Zannichellia patustris1, Althenia filiformis2, etc., while
in the case viEhdea canadensis^ the tracheal thickenings do not
even persist in the nodal tissues. Ceratophyllum (Fig. 56, p. 87)
is an example of a further degree of reduction, since here ligni-
fication is entirely lacking, even in the apical region. This loss
of lignification has been sometimes regarded as a corroboration
of the widely-held view that the transpiration stream has no
existence in submerged plants. But, as we shall show in Chapter
xxi, the idea that such a current is absent in these plants, seems
often to have been accepted on totally inadequate grounds. In
FIG. 112. Hippwis vulgaris, L. Diagram of the horizontal rhizome as seen from
above to show sympodial growth; a-A ; b-B; c-C\ d-D, E, represent successive
axes. [Irmisch, T. (1854).]
this connexion it appears to the present writer that, when xylem
and the part which it plays in water-conduction is being con-
sidered, too much stress is often laid — almost unconsciously
perhaps — on the question of lignification. It seems sometimes
to be assumed that the functional importance of the xylem is
proportional to its degree of lignification ; an idea which may
perhaps be interpreted partly as a hypnotic impression con-
veyed to the botanist's mind by the vividness of the xylem in
1 Caspary, R. (18582). 2 Prillieux, E. (1864).
174 AQUATIC STEMS [CH.
stained sections, and partly as a survival from the old days of
the 'imbibition theory/ when the ascent of water was sup-
posed to be due to some mysterious property peculiar to the
Signified membrane. But it is now universally recognised that
water travels in the cavities of the vessels and tracheids rather
than in the walls. What part then does lignification play in the
ascent of water? It must be remembered that the water-con-
ducting elements are dead and empty, and that in terrestrial
plants they often contain air, which is more or less rarefied,
and is thus at low pressure. These dead elements are generally
in contact with turgid living cells, which exert a strong pressure
against their walls. From the point of view of the ascent of
water, the only function of the lignified walls of vessels and
tracheids appears to be to prevent their being crushed by the
neighbouring living elements. The way in which tyloses force
themselves into vessels through the defenceless, thin places in
their walls, gives some idea of the pressure which living cells
are prepared to exert. In hydrophytes, however, the circum-
stances are very different. The vessels, instead of frequently
containing rarefied air, as in the case of land plants, are pre-
sumably more continuously full of liquid, and are therefore
less liable to be crushed and obliterated by the surrounding
living elements. The conduction of water is not, in their case,
conditioned by the possession of armoured walls. There is every
reason to suppose that the non-lignified conducting elements
of a submerged plant may be as effective in raising water as the
woody vessels of a terrestrial tree ; that water does, as a matter
of fact, travel freely in the non-lignified xylem spaces of the
submerged Potamogetons has been shown by experiment1.
Elongated, submerged stems, unless they grow in perfectly
still water, must be subjected to some amount of tension from
currents. It is probably more than a mere coincidence that the
vascular system of aquatics is so often condensed into a central
strand, recalling the central cylinder of roots and of climbing
stems, both of which are organs subjected to pulling forces.
1 Hochreutiner, G. (1896); see pp. 261-263, Chapter xxi.
xm] CONDENSED VASCULAR CYLINDER 175
The central strand, even when extremely simple as in the case
of Cattitriche*) the Hydrilleae, Aldrovandia^ Naias, Hippuris*,
etc., is not a single bundle, but represents an entire vascular
system, in which the strands are not differentiated as indi-
viduals. That the xylem reduction, to which we have already
referred, is not itself the cause of the union of the single bundles
into an axial strand, may be deduced from a comparison with
the stems of colourless saprophytes or parasites. In such plants
there is little transpiration and no assimilation and the xylem
is proportionately reduced. But the simplified bundles retain
their ancestral position and do not fuse into an axial strand3.
Among the Dicotyledons there are certain hydrophytes, e.g.
the Water Buttercups (Fig. 113, p. 176), in which the bundles
remain perfectly separate, but in the majority some degree of
condensation may be observed. The Potamogetons (Fig. 39,
p. 62 and Fig. 40, p. 64) provide an exceptionally interesting
series illustrating, within a single Monocotyledonous genus,
stages in the concentration of the vascular cylinder. It must
suffice here to draw attention to a few other typical examples,
showing various grades in the reduction of the vascular system.
In Pep Us For tula there is a well-marked axial strand, in
which individual bundles can no longer be distinguished. In
transverse section, an external ring of disconnected phloem
groups is seen to enclose a ring of xylem, consisting of short
radial rows of vessels separated by rows of parenchyma. The
internal phloem characteristic of the Lythraceae is developed
within the xylem, and a pith is formed. A cambial layer occurs,
but does little work.
The next stage of reduction may be illustrated by the stem
of Callitriche (Fig. 1 14 y^and #, p. 176) which shows in trans-
verse section a small ring of xylem surrounded by phloem;
there is no cambium. In the water forms (Fig. 1 14 5) the pith
is resorbed at an early stage and is represented by a space.
Hippuris has travelled still further upon the road of speciali-
1 Hegelmaier, F. (1864). 2 Sanio, C. (1865).
3Schenck, H. (1886).
1 76 AQUATIC STEMS [CH.
sation. The vascular tissue is concentrated into a definite cylin-
der, with external phloem and internal xylem, enclosing what
seems at first sight to be a pith. But Sanio1, who described the
.-v.b.
FIG. 113. Ranunculus trichophyllus, Chaix. T.S. young stem to show the numerous
air spaces, s, in the ground tissue, v.b. = vascular bundle; h = hair, (x 47.)
[A. A.]
B
FIG. 114. Callitriche stagnalis, Scop. Central cylinder of stem. A, land form.
(X475-) B, water form, (x 290.) [Schenck, H. (1886).]
anatomy of the stem, demonstrated that the central region,
which, if the mature structure alone were examined, would
1 Sanio, C. (1865).
xm] THE 'PITH' OF HIPPURIS 177
certainly be regarded as pith, is in reality to be interpreted as
xylem parenchyma. He described the occurrence of a number
of cauline tracheal elements in the 'pith' region of the embry-
onic vascular cylinder near the growing point. These cauline
elements were found by Sanio to be ephemeral and impersis-
tent; he observed their first appearance at levels above the entry
of the first lignified leaf traces. This account appeared to the
present writer so singular, that she repeated Sanio's observa-
tions in order to see whether the application of microtome
methods, by which the history of the tissue in question could
be traced element by element, would confirm or refute his
conclusions. The result was in all essentials to confirm Sanio's
description; the accuracy of his work is indeed remarkable,
when it is considered that he was obliged to rely entirely on hand
sections for the interpretation of this delicate piece of apical
structure. In one stem-apex examined by the present writer,
the first cauline xylem element appeared when the stele was only
0-08 mm. in diameter (Fig. 115 A^ p. 178). This harmonises
with Sanio's statement that in one preparation he observed the
first cauline element when the cylinder was about o-i mm.
across. The cauline elements gradually increased (Fig. 1 1 5 B)
and persisted for a distance of a few millimetres from the apex,
becoming gradually less lignified and thinner-walled until they
finally disappeared. At the level at which the first lignified leaf
trace began to pass in towards the stele (Fig. 115 B\ there were
twenty-one cauline tracheal elements. At a slightly lower level,
at which the tracheids belonging to eight leaf traces (L) had
entered and taken up a position at the periphery of the stele,
twenty-one cauline elements could still be identified (Fig. 1 1 5 C).
In this particular case, they were found to be just finally vanish-
ing at the level at which the seventh set of lignified leaf traces
(counting from the apex) entered the stele ; at this level the stele
was only 0-2 mm. in diameter. However, a few of the outermost
cauline elements were more persistent than the rest, and either
themselves became part of the xylem ring, or fused with the
leaf traces as they entered. That the lignified elements in the
A. W. P. I2
1 78 AQUATIC STEMS [CH.
'pith* are actually xyl em, and not merely altered pith cells, is
indicated by their possession of typical tracheal thickenings,
and also by their occasionally identifying themselves, as just
mentioned, with the xylem ring.
U L \ / I _A, . N'
/
L
I—
FIG. 115. Hippuris vulgaris, L. Series of transverse sections of stele of a stem near
apex to show relation of eauline and leaf trace xylem ; the dotted line in each case
represents the periphery of the stele, (x 280 circa.) A, appearance of first eauline
element when stele is 0-08 mm. in diameter. B, level at which first lignified leaf
trace begins to pass in towards the stele, which contains 21 eauline xylem elements,
but no leaf traces. C, the level at which eight lignified leaf traces (L) have taken
up a position at the periphery of the stele, in which 21 eauline elements can still
be counted. D, a lower level at which traces (I/) from a second node have entered.
Fusion of traces from the two nodes or of eauline elements with either is indicated
by (L + L'), (C + L), etc. [A. A.]
Myriophyllum (Figs. 1 1 6 and 117) closely resembles Hippuris
in vascular anatomy and has the same eauline tracheal elements
in the pith, but the xylem is more reduced1.
1 Vochting, H. (1872).
XI 1 1]
MILFOIL AND HORNWORT
179
Ceratophyllum (Fig. 56, p. 87), as we have already shown,
may be regarded as representing the extremest stage in the
simplification characteristic of the stem-anatomy of Dicotyle-
donous water plants. There is a central duct, surrounded by
FIG. 1 1 6. Myriophyllum spicatum, L. T. S. moderately old axis, (x 30.)
[Vochting, H. (1872).]
FIG. 117. Myriophyllum spicatum, L. T.S. stele of young axis showing the scat-
tered internal vessels and eight phloem groups near the periphery of the stele.
(x2i5.) [Vochting, H. (1872).]
elements whose walls are somewhat thickened, but consist of
cellulose only1. These thick-walled cells are again surrounded
by a broad zone of phloem2.
In connexion with the strong tendency shown by aquatic
1 Sanio, C. (1865). 2 Schenck, H. (1886).
180 AQUATIC STEMS [CH.
plants towards the condensation of the vascular system to a
single strand, devoid of secondary thickening, and in which
individual bundles cannot be distinguished, an interesting
suggestion, put forward some years ago by Scott1, may be con-
sidered. Expressed very briefly, this suggestion was that the
cases of polystely2 occurring among the Angiosperms may be
due to descent from aquatic ancestors, from which a reduced
type of vascular system without cambium has been derived.
If plants with this heritage at any stage of their phyletic history
returned to terrestrial life, they probably experienced the need
for an increase of vascular tissue; but the production of normal
secondary thickening possibly presented difficulties, owing to
the condensed nature of the vascular system and the loss of the
cambial apparatus, and this may have led to the alternative
expedient of multiplying the existing steles. Scott refers to two
genera of flowering plants containing polystelic species —
Auricula (Primulaceae) and Gunner a* (Haloragaceae). Both
these genera include polystelic and monostelic species. The
single steles of the monostelic species are exactly like the indi-
vidual steles of the polystelic species; they have the vascular
bundles crowded together and are almost devoid of pith and
1 Scott, D. H. (1891).
2 The word 'polystely' is used in this connexion in a descriptive sense,
as a matter of convenience, irrespective of the possible validity of the
objections to its use as a morphological term raised by Jeffrey, E. C.
(1899),
3 For the case of Gunnera a somewhat similar interpretation had been
proposed in 1 875 by Russow, who however did not perceive that a return
from water to land life might be the factor initiating the polystelic con-
dition. He suggested that the Gunneras were descended from ancestors
whose vascular system had been condensed into a single central strand,
and that in the course of generations this form of stele might have become
so far stereotyped that it could no longer separate into its original con-
stituents (collateral vascular bundles) when a more elaborate conducting
system was required j it thus adopted the alternative of branching, and
reproducing its structural peculiarities in each branch. (Russow, E.
('875)0
xm] POLYSTELY 181
secondary thickening. Both Auricula and Gunnera have near
relatives which are aquatic in habit. The reduced aquatic stele
of the submerged stem of Hottonia has much in common with an
individual stele of Auricula. This comparison between Hottonia
and Auricula has had its force greatly increased by Prankerd's1
subsequent discovery of a transient polystelic phase in Hottonia
palustris in the base of the inflorescence axis — that is to say,
in the region of transition from an aquatic to an aerial type of
stem.
It was observed by Scott that the stele of Myriophyllum or
Hippuris agrees closely in structure with that of the monostelic
Gunneras, or with a single stele from one of the polystelic
species. The comparison of the stele of Myriophyllum with that
of the Gunneras has been fully confirmed by more recent work2.
In the case of Gunnera — assuming a descent from an aquatic
ancestor — it is easy to realise how acute the need for increased
vascular tissue in the rhizome must have become when the
present type of habit was acquired, since the leaves grow in some
cases to an enormous size. Darwin3, in the Voyage of the
Beagle, describing the occurrence of Gunnera scabra on the
Island of Tanqui, off Chili, remarks — " I measured one [leaf]
which was nearly eight feet in diameter, and therefore no less
than twenty-four in circumference! The stalk is rather more
than a yard high, and each plant sends out four or five of these
enormous leaves, presenting together a very noble appear-
ance."
It should be noted that Scott had overlooked one previous
record of polystely due to Dangeard and Barbe4 — that of the
occurrence of four or five steles in the axis of Pinguicula vul-
garis. But this case introduces no difficulty so far as Scott's
hypothesis is concerned, for Pinguicula is related to Utricularia
1 Prankerd, T. L. (1911).
2 Schindler, A. K. (1904). This author takes the view that Hippuris
does not belong to the same cycle of affinity as Gunnera and Myrio-
phyllum.
3 Darwin, C. (1890). 4 Dangeard, P. A. and Barbe, C. (1887).
1 82 AQUATIC STEMS [CH. xm
with its numerous aquatic species. Further instances of poly-
stely have been subsequently discovered among the Nymphaea-
ceae1. Though the anomalous structures met with in this family
cannot perhaps be explained on quite the same lines as those
of Auricula and Gunnera, their existence does not invalidate
Scott's view; they are of interest as furnishing another example
of the tendency towards the development of distinct steles or
vascular zones in aquatic plants in which secondary increase
in thickness is lacking.
The present writer would like to suggest that there is possibly
some significance in the fact that nearly all the known cases of
polystely in Angiosperms occur in plants whose main vegetative
axis takes the form of a rhizome. This organ, not being sub-
jected to the same mechanical strains as an erect stem which has
to support leaves and branches, is not so irrevocably committed
to the * continuous cylinder* type of vascular system, which
is the best form of structure for withstanding bending forces.
That the polystelic type of anatomy does not make for strength,
is indicated by the recent observation, concerning a gigantic
Hawaian species of Gunner 'a, that "the rhizome is very soft,
and can be severed by a single machete stroke2."
One special point of interest connected with the hypothesis
of the origin of polystely through an aquatic ancestry, lies in the
fact that, if it be accepted, it forms a particularly salient in-
stance of the working of a certain principle of evolution which
the present writer proposes to call "the Law of Loss3'*; this
law will be discussed in Chapter xxvm.
1 Gwynne-Vaughan, D. T. (1897); see a^so Chapter in, p. 37.
2 MacCaughey, V. (1917). 3 Arber, A.
CHAPTER XIV
THE AERATING SYSTEM IN THE TISSUES
OF HYDROPHYTES
THE existence of a highly-developed system of inter-
cellular spaces, is one of the most marked anatomical
characters of water plants. It is generally assumed that this
lacunar system serves for the storage of the oxygen evolved in
assimilation, and its conveyance to the parts of the body that
stand in especial need of it, more particularly the roots and
rhizomes buried in the asphyxiating mud. The mesophyll of
the lamina, the ground tissue of the petiole, and the cortex
of the stem and root, are the regions in which the air spaces
reach their greatest development.
In the stem, the cortex, which is generally broad in propor-
tion to the stele, is penetrated by lacunae, which may be so
numerous as to render the whole organ extremely fragile in
texture. Two features in the arrangement of the cortical cells,
however, seem in some degree to obviate the dangers of this
fragility. The air spaces are, in the main, confined to the middle
cortex, while the outer cortex in many cases consists of elements
which are more closely placed and thus form a firmer peripheral
shell1; the septa, again, are radially arranged and thus are able
to withstand pressures acting at right angles to the axis, which
would otherwise be liable to crush the stem2. Support is also
obtained by diaphragms3, occurring chiefly at the nodes, which
divide the air spaces into sections; these diaphragms are not
air-tight, but are more or less water-tight, so that they form a
safeguard against the flooding of the entire aerating system in
the case of accidental injury. Fig. 1 1 8, p. 1 84, represents part
of a transverse section of a stem of Potamogeton natansy in which
1 Haberlandt, G. (1914). 2 Schenck, H. (1886).
3 Duval-Jouve, J. (1872), Blanc, M. le (19 12) and Snow, L. M. (1914).
i84 AERATING SYSTEM [CH.
the cortical lamellae are connected by a diaphragm (Z>) with
small intercellular spaces (m) at the angles of the cells. Fig. 119,
FIG. 118. Potamogeton natans, L. Part of T.S. of stem with diaphragm (D)
penetrated by intercellular spaces (m). f.l.b. = vascular bundle. [Blanc M. le
(1912).]
FIG. 119. Hippuris vulgaris, L. Three stages in the development of the nodal
diaphragms of the stem, seen in T.S. (all x 318). A, young stem, intercellular
spaces small and walls scarcely thickened. C, old stem, 7 mm. in diameter; inter-
cellular spaces so much enlarged that the cells are stellate, walls much thickened.
B, same stem as C, but from a region 3-5 mm. across, which shows intermediate
characters. [A. A.]
Ay 5, C, shows the development of the nodal diaphragm-tissue
in the case of Hippuris.
The air spaces may be either formed by the separation of
cells (schizogenous) or by their destruction (lysigenous). When
xiv] LACUNAE IN PITH AND CORTEX 185
the air spaces are schizogenous, they may be arranged in the
form of a single ring (e.g. Myriophyllum, Fig. 1 16, p. 179), or a
number of rings may occur, giving a lace-like appearance to the
stem, when seen in transverse section (e.g. Hippuris). The
development of the air spaces in the cortex of Hippuris vu/garis1
is illustrated by Fig. 120 A and B. The Water Crowfoot
forms a transition to those plants in which the air spaces are
lysigenous, for, in the young stem, irregularly placed schizo-
genous air spaces occur, especially in the pith (Fig. 1 1 3, p. 1 76),
FIG. 1 20. Hippuris vulgaris, L, Parts of transverse sections through a younger
stem (A) and an older stem (B) showing the origin of the cortical lacunae.
[Barratt, K. (1916).]
while, in the older stem, the whole of the central parenchyma
becomes torn and destroyed, leaving a large axial lacuna.
Pep Us Portu/a2 is an example of a plant whose air spaces are
mainly lysigenous. In transverse sections of the internodes,
four such spaces are visible, each containing the torn remains
of cells.
The aerating system of the roots of aquatics is to be found
in the cortex. In some cases, e.g. Vallisneria^ the intercellular
spaces may be small, but more frequently they are of con-
spicuous size, and arranged with a regularity that gives a notable
1 Barratt, K. (1916). 2 Schenck, H. (1886).
1 86 AERATING SYSTEM [CH.
symmetry of pattern to the transverse section. The process of
development of the intercellular spaces has been followed by the
present writer in the case of Stratiotes aloides'1 (Fig. 121). The
whole inner region of the cortex in the root of this plant must
be visualised as consisting of radially arranged plates, one cell
wide, which in the early stages are so placed as to leave no spaces
between. The cells composing the plates divide very rapidly,
and a number of new cell-walls are formed, almost all in planes
..Lac.
FIG. 121. Stratiotes aloides, L. Tangential section through middle cortex of a young
root to show the origin of the lacunae (lac.), (x 318.) [Arber, A. (1914).]
at right angles to the long axis of the root. The result is that the
plates elongate in the direction of growth of the root, but, owing
to the rapidity of their cell-divisions, the plates grow in length
faster than the rest of the root, and are thus forced into un-
dulations, since they become too long to retain their normal
vertical position. The possibility of their taking up this sinuous
form is due to the fact that the root enlarges in diameter and
thus allows room for the separation of the plates. It will readily
1 Arber, A. (1914).
xi v] SECONDARY AERENCHYMA 187
be seen that a series of plates, side by side, elongating indepen-
dently, and at the same time prevented from stretching to their
full length, will naturally become detached from one another
at certain points, leaving spaces between. The result of these
processes is that the middle cortex, as seen in transverse
section, consists of radial plates of cells, like the spokes of a
wheel, in contact or separated by lacunae, whereas in tangential
section the plates are found to meet their neighbours at intervals,
so as to form a network.
In some plants, e.g. Myriophyllum and Callitriche ver#a\ the
air spaces in the root cortex may be increased by the replace-
ment of small schizogenous air spaces by large cavities of a
partially lysigenous nature, due to the disruption of the septa.
Remarkable as is the aerating system developed in the pri-
mary tissues, that formed in the course of secondary growth is
often even more conspicuous. This secondary aerating system,
or aerenchyma, arises in some cases from a phellogen, in others
from a typical cambium. We will first consider that which is
produced by a phellogen, and may be regarded as a special
modification of an ordinary periderm. It is well known that in
land plants the impervious corky mantle, which so often covers
the older parts, is interrupted at intervals by lenticels, or patches
of powdery cork, in which the cells are slow in becoming
suberised, and are separated by intercellular spaces, instead of
being closely applied to one another as in normal periderm.
These lenticels form a channel by which gaseous exchange takes
place between the atmosphere and the interior of the plant.
We have thus, in the lenticel tissue, an example of an aeren-
chyma formed on a small scale by ordinary terrestrial plants,
and, moreover, this aerenchyma has a tendency to become
hypertrophied when the plant is submerged. The case has been
described, for instance, of a Poplar branch which had been a long
time under water, and in which masses of whitish tissue pro-
truded from the surface in many places. On examination these
protrusions proved to be due to a great development of the
iSchenck, H. (1886).
1 88 AERATING SYSTEM [CH.
aerenchyma of the lenticels1. Salix viminalis and Eupatorium
cannabinum, again, have been shown to develop spongy tissue
beneath the lenticels when grown in water or on marshy soil2.
In the course of evolution, this tendency to hypertrophy of the
lenticel tissue under the influence of water, may have formed
the starting point for the development of the special air-con-
taining phelloderm which is so marked a feature of a number
of plants to which we must now refer.
It was recorded more than forty years ago, by a Russian
observer, that the stems and roots of Epilobium hirsutum^ Lycopus
europaeus, and two species of Lythrum produced aerenchyma,
when grown in water3. In Lythrum Salicaria the aerenchyma,
which appears on the submerged parts when grown in shallow
water, enlarges the stem to as much as four times its normal
thickness2. It can be induced to occur in this and other cases
(e.g. Lycopus europaeus) by merely keeping the cut branches
in water for a few weeks1. The list of our native waterside plants,
in which aerenchyma occurs under suitable conditions, includes
Lysimachia, Lofus, Oenanthe, and Scutellaria, in addition to the
genera already named4. Schenck2, to whom our knowledge of
aerenchyma is largely due, showed that this tissue was particu-
larly characteristic of Onagraceae, where it occurred in twelve
species belonging to three genera; Leguminosae, where it was
found in six species representing five genera; and Lythraceae,
where it appeared in six species belonging to three genera. It
was Schenck who proposed the useful term 'aerenchyma' for
this non-suberised ventilating tissue produced by a phellogen.
The cells are not dead and empty, as in normal cork, but are
lined with a delicate protoplasmic pellicle and generally contain
clear cell-sap; they are separated by extensive lacunae. That
they are homologous with cork-cells is indicated by the fact
that, in the roots of Jussiaea, the cork, formed when the plant
grows on land, is replaced by aerenchyma when it grows in
1 Goebel, K. (1891-1893). 2 Schenck, H. (1889).
3 Lewakoffski, N. (I8731); on Epilobium see also Batten, L. (1918).
4Gluck, H. (1911).
xiv] JUSSIAEA AND NEPTUNIA 189
water1. It has been suggested1 that the stimulus that causes
the phellogen to develop aerenchyma in lieu of cork, is the lack
of oxygen in the inner tissues. The present writer would prefer,
however, to express the same idea somewhat differently, and to
say that the presence of some minimum of oxygen is possibly
a necessary condition for the process of suberisation, which is
inhibited when the oxygen-content of the cell-sap falls below a
certain point.
Some remarkable cases of aerenchyma development are found
in the tropical Onagraceous genus Jussiaea^\ in J. peruviana
(Fig. 1 22, p. 1 90), the submerged parts of the shoots are clothed
with this tissue, which is also developed on the normal roots
which enter the mud (m.r.'), and in certain erect roots which
seem to serve entirely for aeration (a.r.*). Fig. 1 22 B exhibits the
origin of the stem aerenchyma (a) from a phellogen (pg). Special
breathing roots also occur in the case of Jussiaea repens. They
show, in transverse section, a tiny stele, surrounded by a volu-
minous aerenchyma. That the modification of these roots is
directly related to the aquatic environment, is indicated by the
fact that Jussiaea grandiflora^ when cultivated for some years
in the botanical garden at Marburg as a land plant, produced
only normal adventitious roots, but when it was transferred to
water it developed roots with aerenchyma3.
The aerenchyma of certain members of the Leguminosae has
been recognised for many years. Humboldt and Bonpland 4, for
instance, more than a hundred years ago, recorded that in "Mi-
mosa lacustris" (Neptunia oleracea^ Lour.), the Floating Sensitive
Plant (Fig. 1 23, p. 19 1), the stems and branches were covered by
"une substance spongieuse, blanchatre." They made the mis-
take, however, of supposing that this tissue was a foreign body,
and not an integral part of the plant. More recent observations5
1 Schenck,H.(i889). 2 Martins, C.( 1866).
3Goebel,K. (1891-1893).
4 Humboldt, A. de, and Bonpland, A. (1808).
5 Rosanoff, S. (i 87 1 ). This author uses the name " Desmanthus natans "
for the plant now called Neptunia oleracea.
190 AERATING SYSTEM [CH.
have made it clear that the spongy mass (f in Fig. 123) is
an aerenchyma developed from a phellogen. That it also acts
B
FIG. 122. Jussiaea peruviana, L. A, habit drawing. The shoots are clothed with
aerenchyma up to the water level (s.w.). m.r., mud roots; a.r., air roots.
Aerenchyma occurs in both types of root. (Reduced.) B, Transverse section of
submerged part of a stem to show aerenchyma (a) developed from phellogen (pg).
The phloem (ph), normal cambium (c) and" xylem (xy] are also shown. [Adapted
from Schenck, H. (1889).]
as a float is indicated by Spruce's1 account of the plant as he
saw it growing in South America. He describes the buoyant
1 Spruce, R. (1908).
xiv] SESBANIA AND AESCHYNOMENE 191
"cottony felt" as serving to hold the delicate bipinnate leaves
and the heads of pale yellow flowers above the surface of the
water. In Sesbania^^ again, another Leguminous genus not at
all closely related to Neptunia, a similar air-tissue occurs, arising
from a cork-cambium in the inner cortex, just outside the
endodermis.
It is a curious fact that among the Leguminosae we not only
meet with the case just described, in which an aerenchyma arises
externally from a phellogen, but we also find instances in which
a tissue of somewhat similar nature is produced internally from
FIG. 123. Ncptuniaoleracea^our. Floating shoot. The two oldest internodes have
lost their floating tissue, /, while the three youngest have not yet developed it.
(Reduced.) [Adapted from Rosanoff, S. (1871).]
a normal cambium, and is thus of the nature of secondary wood.
In these cases, the air is contained within the xylem elements.
Aeschynomene aspera^ Willd.2 is a Leguminous shrub, frequent
in India on the margins of fresh waters, in which a pith-like
tissue, white and homogeneous, occupies the greater part of the
stem. This substance is, in fact, secondary xylem. It is so
extremely light in weight that it is collected to make toys,
floats for fishermen's nets, and 'pith' helmets. Another
member of the same genus which grows in Venezuela, Ae. his-
pidula, H. B. K.3, has remarkable swellings on the submerged
1 Scott, D. H. and Wager, H. (1888). * Moeller, J. (1879).
3 Ernst, A. (i8;22).
192 AERATING SYSTEM [CH.
parts of its stem, said to be due to aerenchyma. A third Legu-
minous plant, which has been described under the name of
Herminiera elaphroxylon, G. and P.1 but which is perhaps better
regarded as another member of the genus Aeschynomene^ also
has aerenchyma2. The floating wood of this plant, which is
known as the "Ambatsch," is employed on the Blue Nile to
make rafts. The pieces used are as thick as a man's arm, and
show under the bark a shining white woody mass, penetrated
by numerous rays. The wood is exceedingly light; a segment
of stem 2 1 feet long and about 4 inches in diameter, is described
as weighing less than \\ ounces. It has been shown that the
pits of the xylem are real perforations with no pit-closing mem-
branes, so that there is free passage for gases3.
The chief function served by the lacunar system of sub-
merged stems seems to be aeration4, but there are also instances
in which it plays a very important part in adding to the buoy-
ancy of the plant. In Trapa natans^ for instance, the aquatic
stem is formed exclusively of soft tissue, and would be unable,
if it depended on its own stiffness, to rear itself to the surface
of the water. It is entirely due to the increase of lacunae in the
upper part of the stem, and the swelling of the petioles of the
upper leaves, that the axis is enabled to raise the flowers into
the air. In the deeper regions, the pith is a compact tissue, and
there are only two circles of lacunae in the cortex, but in the
upper part of the stem the pith is lacunate and the number of
circles of air spaces increases to four or five5.
The secondary lacunar tissues were always assumed by the
earlier writers to serve for flotation alone ; in certain cases (e.g.
some of the Leguminosae already mentioned) it is quite pos-
sible that they were correct. Martins6, who long ago described
and figured the air roots of Jussiaea, regarded them merely
1 Also called Aedemone mtrabilis^ Kotschy.
2Kotschy, T. (1858), Hallier, E. (1859), Jaensch, T. (1884!) and
(i8842), Klebahn, H. (1891). See also Hope, C. W. (1902).
3 Goebel, K. (1891-1893). 4 Schenck, H. (1889).
5 Costantin, J. (1884). 6 Martins, C. (1866).
xi v] NESAEA 193
as floating organs. For this particular case, this view can scarcely
be maintained, since Goebel1 has shown that Jussiaea repens
floats quite well, even if the roots be all removed. A good case
has been made out, however, for regarding the aerenchyma of
Nesaea verticillata 2, one of the Lythraceae, as a true floating
tissue. Many of the wand-like stems of the plant, growing on
the borders of ponds in America, are described as reaching a
length of six to eight feet. In July and August they bend with
their own weight until the stem apex touches the water, when it
curves upwards again. In the region of contact between the
stem and the water a swelling occurs, and roots also arise from
b.w.
FIG. 124. Nesaea verticillata, H. B. and K. Plant at beginning of August; s.w.,
surface of water; b.w., bottom of water;/./., floating tissue. [Adapted from Schrenk,
J. (1889).]
this region, anchoring the floating part of the stem to the
ground (Fig. 124). The epidermis of the swollen region be-
comes fissured, disclosing a snowy white, soft, elastic, spongy
tissue, which arises from a pericyclic phellogen. Contraction
of the roots draws the swollen part down into the water, and
the spongy layer gradually extends over the submerged regions.
In the autumn the long slender stems die, except those portions
that have produced floating tissue around themselves, and have
rooted in the mud. A new root-stock is thus developed, some-
times at a considerable distance from the mother-plant. As
1 Goebel, K. (1891-1893). 2 Schrenk, J. (1889).
A. W. P. 13
194 AERATING SYSTEM [CH. xiv
evidence for the view that the aerenchyma in this plant is not
respiratory in function, Schrenk, who described it, points out
that in old stems the surface of this tissue is covered by a layer
which is air-tight and suberised, and that a similar layer is also
sometimes found separating it from the interior of the stem.
He accounts for its occurrence in regions where it cannot serve
for flotation, by supposing that the meristem spreads there
automatically from the floating parts.
To the present writer, however, the question whether the
secondary air-containing tissues of water plants serve mainly for
aeration or for flotation, seems to be a matter of minor import-
ance. It appears to her that the evidence as a whole points
rather to a fundamentally different interpretation — namely, that
the formation of the secondary air-tissues is directly induced by
environmental conditions, and that their serving any purpose
is to be regarded as quite fortuitous. In the case of the
-primary lacunar system, the position is somewhat different, and
it seems difficult to escape the conclusion that we have here an
example of the inheritance of acquired characters. There is
some experimental evidence tending to show that this system
was initiated as a direct response to the aquatic milieu; its
elaboration may either be attributed to natural selection or to
the inherited effects of use. There is no doubt that the habit
of developing an elaborate aerating system has now become in
many cases an inherited character, for though it can be modified
and reduced by terrestrial conditions, it cannot be altogether
eliminated.
[ 195 J
CHAPTER XV
LAND FORMS OF WATER PLANTS, AND THE
EFFECT OF WATER UPON LAND PLANTS
THE majority of water plants, with the exception of those
most highly specialised for aquatic life, are capable of
giving rise to land forms. Those plants which, when mature,
produce floating or air leaves, can obviously develop a land form
with less change in their structure and mode of life than those
which normally live entirely submerged. Limnanthemum nym-
phoides^) for instance, has been found growing on damp ground
with abbreviated internodes and petioles, and with reduced
laminae. Land forms ofHydrocharis*, and many Nymphaeaceae3
and Alismaceae4 are known, either in nature or in cultivation.
Successful terrestrial forms can also be produced by those
Potamogetons which possess coriaceous, floating leaves, or have
the power to develop such leaves on occasion. The land form
of Potamogeton natans is shown in Fig. 125, p. 196. P. varians,
a form allied to P. heterophyllus, Schreb., can exist for season
after season without being under water at all, tiding over the
winter by means of its bead-like tubers5. Even P. perfoliatus
has also been recently stated to produce a land form6, though
it is generally regarded as a typically submerged type, which
is incapable of terrestrial life7.
Myriophyllum, Callitriche* and the Batrachian Ranunculi
(Fig. 126, p. 196) agree in producing land forms which are
close-growing and tufted. When Myriophyllum spicatum1, for
1 Schenck, H. (1885). 2 Merj & (J8821).
3 Bachmann, H. (i 896), and Mer, £. (i 8821). See also p. 32, Ch. m.
4 See Chapter n and Gliick, H. (1905).
5 Fryer, A. (1887). « Uspenskij, E. E. (1913).
7 Fryer, A., Bennett, A., and Evans, A. H. (1898-1915).
8Lebel, E. (1863).
13—2
196 LAND FORMS OF WATER PLANTS [CH,
FIG. 125. Potamogelon natans, L. or possibly P. polygonifolius, Pourr. Land form
from a dried-up swamp, New Forest, September 2, 1911, after a very dry summer.
Only the blades of the leaves, and sometimes not even the whole of these, were
visible above ground. (Reduced.) [A. A.]
2.B.
FIG. 126. Ranunculus aquatilis, L. lA, seedling which germinated in water, and
which is shown in i B at a somewhat older stage. zA , seedling which germinated
on land, and which is shown in 2.B at a somewhat older stage. (Nat. size.) [Aske-
nasy, E. (1870).]
xv]
THE WATER VIOLET
197
instance, is left stranded, the water leaves are apt to dry up, but
the ends of the shoots grow into a land form entirely different
in habit from the water form. It develops as a minute turf, an
inch high; the stems are frequently branched, the internodes
are short instead of being elongated as in the water form,
and many adventitious roots are produced from the nodes.
The leaves are smaller than in the submerged form, and the
segments are fewer, broader and thicker.
A close connexion between submerged and aerial * forms *
has in recent years been demonstrated in the case of Hottonia,
the Water Violet. In this plant, which previous observers had
Inflortftceue •-•'•
FIG. 127. Hottonia palustris, L. Diagrammatic sketch of typical land and water
forms. [Prankerd, T. L. (1911).]
erroneously described as free-floating, it is now known1 that
the oldest part of the rhizome is generally embedded in mud,
and that from it arise vertical aerial branches, which may be-
come detached by the dying off of the older part of the stem,
thus giving rise to so-called 'land forms/ which are similar
in anatomical structure to the submerged parts of the aquatic
plant, rather than to the aerial inflorescence region (Fig. 127).
The differences between the land and water leaves of Poly-
gonum amphibium^ have already been mentioned, and are illus-
trated in Figs. 99 and 100, p. 1 52. It is notable that in this case
iPrankerdjT. L. (1911).
198 LAND AND WATER FORMS [CH.
the plant reaches its optimum development as an aquatic,
and flowers freely in water. As a land plant it rarely blossoms
and, indeed, under xerophilous conditions, flowering seems to
be entirely inhibited1.
In the case of amphibious plants, which can produce land
or water forms according to circumstances, the difference in
external appearance is often very
marked. Limosella aquatica, for
instance, produces a land form
with leaf-stalks half-an-inch to
one inch long, while the water
form may have petioles six inches
long, terminating in tender trans-
lucent blades2. Littorella lacustris
is another striking example. The
shallow water form, deep water
form, and land form are shown
in Fig. 128 A, B and C.
Various land plants can grow
and flower freely with their roots
and the lower parts of their stems
actually under water; Solanum
Dulcamara (Bittersweet) is a
species to which these condi-
tions seem especially favourable.
Such plants form a transition to
those which frequent the margins
of fresh waters, and are capable of responding to changes in the
water level by producing, at need, actual aquatic forms. Gliick3,
who has given great attention to this subject, has shown that, in
nature, submerged forms, often with reduced vegetative organs,
are produced not only by plants which normally inhabit damp or
marshy situations, such as Ranunculus Flammula (Figs. 1 34 and
1 35> P'2O3)> Ca/thapa/ustris(Fig. 129), Cnicuspratensis* (Fig. 1 30
FIG. 128. Littorella lacustris, L. (=L.
juncea, Berg.). A and B, water
forms; C, land form. A is from water
30 to 40 cms. deep ; B is from water
100 cms. deep; C shows three male
flowers one of which has lost its
stamens. (Reduced.) [After Gliick, H.
(1911), Wasser- und Sumpfgewachse,
Bd. in, Fig. 34, p. 346.]
1 Massart, J. (1910).
» Clack, H. (191 1).
2Schenck, H. (1885).
4 Gliick uses the name Cirsium anglicum> D.C.
xv] WATER FORMS OF LAND PLANTS 199
A and 5) and Menyanthes trifoliata^ but also by typically terres-
trial plants such as Achillea ptarmica, Trifolium resupinatum
(Fig. 131 5) and Cuscuta alba (Fig. 131 A), Gluck1 has also
produced experimentally a submerged form of Iris Pseudacorus.
Seeds of terrestrial plants may sometimes germinate and reach
a considerable development while entirely submerged. The
FIG. 129.
FIG. 130.
FIG. 131,
FIG. 129. Caltha palustris, L. The two leaves with long petioles belong to the sub-
merged form : the middle leaf is a corresponding air leaf of the land plant. (Re-
duced.) [After Gluck, H. (1911), Wasser- und Sumpfgewachse, Bd. in, Fig. 3, p. 65.]
FIG. 130. Cirsium anglicum, D.C. (=Cnicus pratensis, Willd.). A, land form,
B, water form. [After Gluck, H. (1911), Wasser- und Sumpfgewachse, Bd. in,
Figs, i a and 6, p. 16.]
FIG. 131. Cuscuta alba, J. and C. Presl, forma submersa. A, parasitic on water
form of Echinodorus ranunculoides, (L.) Engelm. B, parasitic on the form of Tri-
folium resupinatum, L. with floating leaves. (Reduced.) [After Gluck, H. (1911),
Wasserund Sumpfgewachse, Bd. in, p. 114, Figs. 7 A and B.~\
present writer has noticed Horse Chestnuts sprouting freely
in the mud at the bottom of a stream : one which was measured
had a plumular axis more than i inch in length, and a primary
root of 3! inches.
In connexion with Gliick's record of a submerged form of
1 Gluck, H. (1911).
200 LAND PLANTS IN WATER [CH.
Cnicus pratensis, it is interesting to note that a somewhat diffe-
rent water form has been described in the case of C. arvensis1.
The plant in question had suffered nine months' inundation in
a fenland flood; when observed in November, at first sight " the
leaf-rosette appeared normal ; . . . but on lifting it, it was found
to be attached to the ground by about 2 or 3 feet of slender
leafless stem of very soft and flexible consistency — exactly re-
sembling the woodless stem of a true aquatic. During the flood
Cnicus aruensis had evidently floated at the end of this aquatic
stem, much in the manner of, say, a Potamogeton or Callitriche"
The present writer has noticed Ranunculus repent* growing
by the water-side and putting out long runners into the water;
these runners bore leaves that were either submerged or rose
approximately to the level of the surface. Hydrocotyle vu/garis2
is also not infrequently seen either more or less submerged or
with a number of floating leaves (Fig. 132).
A considerable amount of work has been done on the
anatomical changes induced by growing terrestrial plants or
amphibious plants in water instead of air.
Among terrestrial plants, Vicia sativa, when grown in water,
does not develop aquatic characters in its epidermis, but the
xylem suffers marked diminution. This enfeeblement of the
xylem is characteristic of various other land plants when grown
in water, and, in the case of Ricinus and Lupinus, there is a
similar reduction in the thickening of the bast fibres 3. Rubus
fruticosuS) when grown in water, showed no change in the micro-
scopic structure of its sub-aquatic leaves and stem, except that,
in both organs, the chlorophyll was developed nearer the sur-
face than in the normal condition in air, while the hairs on the
stem tended to be unicellular instead of multicellular4; in the
shoots of Salix, also, little anatomical change was induced by
submergence5.
1 Compton, R. H. (1916).
2 The existence of these forms was noted by Gliick, H. (1911). On
Hydrocotyle see West, G. (1910). 3 Costantin, J. (1884).
4 Lewakoffski, N. (18732). * Lewakoffski, N. (1877).
xv] AMPHIBIOUS PLANTS IN WATER 201
In the case of amphibious plants, the comparison of air and
water shoots gives results of greater interest. Costantin1 de-
scribed the anatomy of a plant of Mentha aquatica growing on
dry land, which happened to have the apex of one of its shoots
plunged into water. The young part of the stem, which had thus
grown in an aquatic milieu, when compared with the older part
growing in air, was found to be glabrous and to have a greater
diameter and larger air spaces. The same increase in the air
FIG. 132. Hydrocotyle vulgaris, L. A branch sent out into water from a plant
growing on the bank ; w, water level. The under surfaces of the five expanded leaves
were examined for stomates, which were present on all. The petiole of the air leaf
was more hairy than that of the succeeding leaves. July 14, 1910. (£ nat. size.)
[A. A.]
spaces and of the diameter of the stem, was observed in sub-
merged shoots of Veronica Anagallis and Nasturtium amphibium.
Costantin notes that, in general, when submerged plants are
grown in deep water, the fibrous and tracheal elements diminish
markedly.
Cardamine fratensis is an example of an amphibious plant
which seems to pass with remarkable ease from the water to the
air condition. The present writer has found, on more than one
1 Costantin,J. (1884).
202
LAND AND WATER FORMS
[CH.
occasion, that an entirely submerged plant, when placed in soil
under ordinary aerial conditions, rapidly developed into a
typical land plant. Schenck1 has described the comparative
anatomy of submerged and aerial plants of this species. The
anatomy of the submerged stem showed several points of
interest. The intercellular spaces and the diameter of the cortex
were increased ; the vascular cylinder had approached nearer the
centre of the stem; all mechanical elements were absent, and
the xylem was reduced (Fig. 133, cf. A and 5). In the case of
FIG. 133. Cardamine pratensis, L. A, T.S. stem of land form. B, T.S. submerged
stem; rp = cortex, m = pith, mr = mechanical ring. C, T.S. leaf of land form. D,
T.S submerged leaf. [Schenck, H. (1884).]
the leaves, those that were submerged had developed no palisade
tissue (Fig. 133, cf. Cand Z>).
Such anatomical work as that briefly outlined above, leads
to the general conclusion that when amphibious plants are grown
in water they readily acquire the characters which we regard
as typical of aquatic plants, but that, when terrestrial plants are
grown under similar conditions, the changes which occur,
though trending in the same direction, are very much less
marked. There seem to be two possible, alternative explanations
of this difference of behaviour. On the one hand it may be that
1 Schenck, H. (1884).
xv] ORIGIN OF AQUATIC HABIT 203
amphibious plants were not originally gifted with any special
aptitude for aquatic life, but that they have gradually acquired,
and passed on to their descendants, the capacity for reacting
in an advantageous way to the stimuli of an aquatic environment,
and that we are thus dealing with a case of the inheritance of
acquired characteristics. But the second alternative, which
appears to the present writer to have most in its favour, is that,
in general, those species which are capable of a suitable response
to aquatic conditions have already been sifted out by nature,
and now inhabit situations where such conditions, at least
occasionally, arise; or, in other words, that the various species
of flowering plants were all endowed, from the first moment
of their appearance, with different constitutions which gave
them varying degrees of capacity for the adoption of water life;
and that their habitats have been determined by this capacity
and not vice versa1.
FIG. 134. Ranunculus Flammula, L.
A , form with floating leaves. B, land
form. (Reduced.) [After Gliick, H.
(1911), Wasser- und Sumpfgewachse,
Bd. in, Figs. 84 and 85, p. 494.]
FIG. 1 35 . Ranunculus Flammula, L.
Submerged form. The short up-
right stem replaces the inflor-
escence. (Reduced.) [ After Gliick,
H. (1911), Wasser- und Sumpfge-
wachse, Bd. in, Fig. 86, p. 496.]
1 See Footnote I, p. 162.
CHAPTER XVI
THE ROOTS OF WATER PLANTS
THE roots of certain of the more specialised water plants,
are extremely reduced or even in some cases entirely
absent, e.g. Ceratophyllum, Aldrovandia and Utricularia. In
other instances, such as Nymphaea, although the primary root
is very short-lived, a considerable system of adventitious roots
may be developed. As we shall show in Chapter xxi, among
aquatics, absorption by the roots is by no means of such negli-
gible importance as some writers have suggested; but at the
same time, when plants rooted at the bottom of water are
compared with those terrestrial herbaceous plants which they
most closely resemble in size and habit, it becomes clear that,
in the roots of the water plants, the function of anchorage has
assumed a greater importance, while the function of absorption
is less pre-eminent. A firm hold in the mud, and erectness of
the flowering stem, are often a sine qua non for aquatics, and
their roots help in various ways to bring this about. Some-
times we merely get a richly ramifying root system, e.g. Ranun-
culus aquatilis^. In other cases the type of arrangement of the
adventitious roots is such as to hold the stem in position. This
point is well illustrated in a description written more than
seventy years ago2, of a certain amphibious plant, Oenanthe
Phellandrium. "The flowering stem is remarkably fistulose,
furnished under water with frequent joints, which become more
distant upwards: it attains its greatest thickness two or three
internodes from the base, where it is often an inch or more in
diameter. From the joints proceed numerous whorled pecti-
nated fibres [adventitious roots], of which the lower ones are
as stout as the original fusiform root: these, descending in a
conical manner to the bottom of the water, form a beautiful
1 Hochreutiner, G. (1896). 2 Coleman, W. H. (1844).
CH. xvi] TENDRIL ROOTS 205
system of shrouds and stays to support the stem like a mast in
an erect position, while the pressure on the soft mud is lessened
by the buoyancy of the hollow internodes."
There are other cases, again, in which anchorage depends on
some modification of the adventitious roots. Brasenia Schreberi
(peltatay, for instance, is fixed by its well-developed root-caps,
which are of the nature of anchors, and prevent dislodgment
of the buoyant plant, when it is swayed about by the agitation
of the water surface. A still more remarkable method is the
production of spirally twisted roots, which in some cases fully
deserve the name of tendrils. Most of the known examples
occur in the Potamogetonaceae, but they have also been
recorded in the Hydrocharitaceae (Hydrilla)2, Fig. 136, and
FIG. 136. Hydrilla verticillata, Presl. Tendril roots. [Kirchner, O. von, Loew, E.
and Schroter, C. (1908, etc.).]
Gentianaceae (Menyanthes)^, while the present writer has
noticed them in Myriophyllum verticillatum (Haloragaceae).
The first case among the Potamogetonaceae in which spirally
twisted roots were observed, seems to have been Cymodocea
antarctica^. At a later date the corkscrew roots of Zannichellia
palustris were fully discussed by Hochreutiner5 (Fig. 137 A—F^
p. 206). He describes these roots as long, unbranched, and
twining about other objects like tendrils — to use his own ex-
iSchrenk,;. (1888).
2 Graebner, P., in Kirchner, O. von, Loew, E., and Schroter, C.
(1908, etc.). 3 Irmisch, T. (1861).
4 Tepper, J. G. O. (1882). 5 Hochreutiner, G. (1896).
206
ROOTS OF WATER PLANTS
[CH.
pression, " elles grimpent en bas." He adds that Potamogeton
densus (Fig. 137 G and //) shows the same peculiarity. A more
recent writer1 has recorded that, when the turions of Pota-
mogeton obtusifolius germinate, they produce spirally coiled roots,
which apparently serve to anchor the plantlets in the mud.
Twining roots are not confined to water plants; a case is
recorded by Darwin2, on the authority of Fritz Miiller, in
FIG. 137. Twining roots of Zannichellia palustris, L. (A—F) and of Potamogeton
densus, L. (G, H). [Hochreutiner, G (1896).]
which the aerial roots of an epiphytic Philodendron in the forests
of S. Brazil, twined spirally downwards round the trunks of
gigantic trees. That root tendrils merely represent a further
development of the general tendency to nutation common to
stems and roots, is indicated by C. and F. Darwin's3 record
1 Graebner, P., in Kirchner, O. von, Loew, E., and Schroter, C.
(1908, etc.). 2 Darwin, C. (1891). 3 Darwin, C. and F. (1880).
xvi] EQUILIBRIUM AND ASSIMILATION 207
of a slight and tentative circumnutation in the seedling roots
of several ordinary terrestrial plants. When the radicles of
Phaseolus, Vicia and Quercus "were compelled to grow and
slide down highly inclined surfaces of smoked glass, they left
distinctly serpentine tracks."
Hildebrand 1 has described a differentiation between absorb-
ing and anchoring roots in the case of Heter anther a zosteraefolia.
He states that from each leaf-base two roots arise, one of which
remains short and branches freely, while the other grows rapidly
in length and serves for anchorage. Plants cultivated in England
do not, however, so far as the present writer has been able to
observe, show this distinction ; it would be interesting to know
whether other botanists, who have seen this species growing
in Brazil, can confirm Hildebrand's description. In the case
of Phragmites communis 2, there is a similar differentiation be-
tween long, thick, unbranched mud-roots, and thin water-roots,
branched to the third degree.
The roots of free-floating plants obviously do not serve
for anchorage, but they seem sometimes to perform a corre-
sponding role in preserving equilibrium; this is particularly
obvious in the cases of Lemna and Stratiotes. Aquatic roots
often exercise another function, which is more remote from
those generally assumed in the case of terrestrial plants —
namely, that of assimilation ; their colour is sometimes quite
conspicuously green. In the Water Chestnut, Trapa natans*,
the later roots, developed adventitiously below the leaf-bases,
are free-floating and branched. These feathery structures have
been supposed by some authors to be of foliar nature ; this is
erroneous, although physiologically they correspond to the
divided leaves of Myriophyllum 4. It is an indication of the extra-
ordinarily acute mind of Theophrastus, the Father of Botany
(born B.C. 370), that he avoided the morphological pitfall which
has been fatal to so many subsequent writers, for in describing
Trapa he says, "quite peculiar to this plant is the hair-like
1 Hildebrand, F. (1885). 2 Pallis, M. (1916).
3 Barneoud, F. M. (1848). 4 Goebel, K. (1891-1893).
2o8 ROOTS OF WATER PLANTS [CH.
character of the growths which spring from the stalk ; for these
are neither leaves nor stalk1." We have already alluded to the thal-
loid roots of the Podostemaceae, which also serve for assimilation .
Like the stems of aquatics, the roots show certain anatomical
divergences from those of land plants2. Root hairs are occasion-
ally absent, e.g. Lemna trisulca. The roots of Ekdea bear no
absorbent hairs so long as they are immersed in water, but they
develop them freely on entering the soil3. In other hydrophytes,
e.g. Hydrocharis, the root hairs are unusually long. It is rather
curious that in the roots of water plants the piliferous layer,
and the layer immediately below it, are often cuticularised. The
aerating system, which occurs in the primary cortex, or as a
secondary formation, has been dealt with in Chapter xiv.
As in the case of submerged stems, the vascular system of the
roots tends to be very much reduced. The simplest root among
Dicotyledonous water plants is that of Callitriche stagnalis (Fig.
1 3 8), which has two protoxylems — each consisting of a single
tracheid — separated by a single median metaxylem element.
This simple xylem group is flanked on either side by a single
sieve-tube with companion-cells. In certain Monocotyledons,
a still more extreme degree of simplification is reached. Vallis-
neria spiralis (Fig. 139), for instance, has merely a central
channel, corresponding to the central vessel of other forms,
surrounded by a ring of cells, three of which are apparently
sieve-tubes, each accompanied by a companion-cell. Naias,
again, has a root of a very simple type, in which the phloem is
more conspicuously developed than the xylem4 (Fig. 140). The
reduction series in the roots of the Potamogetons is illustrated
in Fig. 41, p. 65.
Plasticity is certainly a marked feature of the roots of water
plants, for though they have to some extent given up the work
of absorption, they have assumed and developed various other
functions to which their terrestrial ancestors must have been
comparative strangers.
1 Theophrastus (Hort) (1916). 2 Schenck, H. (1886).
3 Snell, K. (1908). 4 Sauvageau, C.
XVI ]
ROOT ANATOMY
209
eni
FIG. 138. Callitnche
stagnatis, Scop. T.S.
central cylinder of ad-
ventitious root of water
form ( x 470) ; s, sieve
tube. ' [Schenck, H.
(1886).]
FIG. 139. Vallisneria spiralis, L. A, T.S. adventitious root
(x 240). B, T.S. central cylinder (x 470); end, endodermis,
5, sieve tubes of which three are present. The central vessel
is unthickened. [Schenck, H. (1886).]
FIG. 140. T.S. central region of roots of Naias, sieve tubes shaded. A, Naias
major, All., two central vessels. B and C, N. minor, All., one central vessel in B
and two in C. [Sauvagean, C. (iSSg1).]
A. w. P.
CHAPTER XVII
THE VEGETATIVE REPRODUCTION AND
WINTERING OF WATER PLANTS
THE conditions under which hydrophytes live — unlimited
water supply, abundant carbon-dioxide and protection
from sudden temperature changes — are favourable to acti-
vity of growth1, and the luxuriance which this vegetation often
attains is a matter of common note; indeed it sometimes
becomes such a hindrance to navigation as to compel the atten-
tion, not only of botanists, but also of those who normally take
no interest in plants. Even in the rivers of countries with a
temperate climate, such as our own, aquatics are liable to
multiply at a rate which renders them a great embarrassment in
boating. A letter, for instance, which appeared in the Morning
Post of July 1 6, 1914, refers to a locality in the Thames above
Whitchurch Weir, where the weeds were "20 ft to 30 ft long
and close under the surface of the stream from one bank to
another." The sluices of mills are liable to be choked, too, in
the autumn, by the countless detached fragments of Pofamo-
geton.
But the classic example in England of the extremely rapid
growth and multiplication of a water plant, is the behaviour of
Elodea canadensis*, the American Waterweed, in the first decade
or so after it made its debut in this country. Exactly when and
how it was introduced from America remains a mystery. Its
first appearance in Great Britain is said to have been in Ireland
in 1836, while its first recorded occurrence in England was in
Berwickshire in i8423. It travelled south, and by 1851 was so
. (1885).
2 Marshall, W. (1852) and (1857), Caspary, R. (18582), and Siddall,
J. D. (1885). For the continental history of the plant see Bolle, C.
(1865) and (1867). 3 Johnston, G. (1853).
CH.XVII] ELODEA IN BRITAIN 211
luxuriant at Burton-on-Trent — where it had been recorded in
I8491 — tnat it bid fair to block up one of the two streams into
which the Trent there divides. Unfortunately the Curator of
the Cambridge Botanic Garden, who had received the plant
from Professor Babington in 1 847, introduced it into a tribu-
tary of the Cam in 1 848. By 1 852 it had spread into the river,
and so completely choked it as to raise the water level several
inches, and to prevent fishing, swimming and rowing, and
greatly to hinder the towing of barges. At this date it first
invaded the fen district, and in a few years so choked the dykes
as seriously to impede drainage. The difficulties caused by the
presence of excessive quantities of the plant were so acute that
an adviser was sent down by the Government to consider the
best method of dealing with the pest. No successful plan for
coping with it was discovered, but in a few years the luxuriance
of the Elodea diminished without any apparent cause. Siddall2,
to whom we owe the most exhaustive treatment of the subject,
concludes that, "The experience of those who have had most
to do with it seems to indicate that if left alone, its habit is,
upon first introduction into a new locality, to spread with alarm-
ing rapidity; so much so as literally to choke other water plants
out of existence. But this active phase reaches a maximum in
from five to seven years, and then gradually declines, until at
last the Anacharis [Elodea] ceases to be a pest, and becomes an
ordinary denizen of the pond, river, or canal, as the case maybe."
As has been already stated in Chapter iv, Elodea canadensis
never reproduces itself sexually in this country, and the history
of the plant suggests that possibly the whole Elodea population
of England may be regarded, in one sense, as a single individual,
with an enormous vegetative output, mechanically sub-divided
into vast numbers of apparently distinct plants; in other words,
it is not improbable that it may represent the soma developed
from a single fertilised ovum. It would thus be a " major plant
unit," whose soma consists of a vast number of minor indivi-
duals. Pallis3, in a most suggestive study of the problem of
1 Caspary, R. (18582). 2 Siddall, J. D. (1885). 3 Pallis, M. (1916).
14—2
212 VEGETATIVE REPRODUCTION [CH.
individuality in the case of Phragmites communis, has brought
forward evidence which strongly suggests that the " major plant
unit/* i.e. the total vegetative output which one fertilised egg
is capable of initiating, is to be regarded as a constant for each
species, its mass being the measure of specific vital energy. She
has shown that, in the case of the reed swamps of the Danube,
there are distinct indications of a definite life-cycle of vegetative
growth, terminating in senescence and death, whose arrival is
not fortuitous or due to external conditions, but is a necessity
inherent in the very nature of the species itself. Such a thesis
is obviously very difficult to substantiate, but the history of
Elodea, outlined above, certainly seems to the present writer
to lend itself more readily to some such interpretation, than to the
accepted explanation, which sees in the aggressive phase of this
introduced plant, merely the direct stimulating effect of change
of environment. Elodea has passed through a period of great
luxuriance, followed by a gradual diminution in vigour, occur-
ring more or less contemporaneously in all the localities which
have been colonised by its rapid vegetative multiplication. By
1883 its period of maximum abundance was apparently over.
In 1 909 an enquiry1 was set on foot to determine the condition
of the species at that date, i.e. sixty-seven years from its first
recorded appearance in England. This enquiry resulted in reports
from many localities indicating that Elodea had sunk every-
where into the condition of a mere denizen, displaying no greater
luxuriance than the other water plants with which it was associa-
ted. Siddall, in this year, wrote that he had some difficulty
in finding a specimen of Elodea in a locality where in 1873 all
other vegetation was choked with it. He also made the extremely
interesting statement that the circulation of the protoplasm was
very feeble in 1909 as compared with its condition in 1873 —
a statement which the present writer feels must be accepted with
some reserve, for it is a point on which a really critical com-
parison would be attended with obvious difficulties.
The general history of Elodea seems at least to point towards
1 Walker, A. O. (1912).
xvn] WATER HYACINTH & RIVER LETTUCE 213
the conclusion that the " individual," which was introduced
into this country, has run its course, through an opulent
maturity, to a point approaching senility, which may ultimately
lead to complete extinction. Water plants certainly appear to
offer a favourable field for the study of the "major individual,"
since, in this biological group, reproduction by sexual means
is often deferred for long periods.
In warmer climates the rapidity of growth of water plants
is even more remarkable than in temperate regions. The way
in which Eichhornia speciosa, Kunth1, the Water Hyacinth, may
sometimes choke a wide river, forms a really startling example
of excessive quickness of growth and multiplication. About the
year 1890, this plant was accidentally introduced into the
St John's River in Florida, which, being a sluggish stream,
was particularly well-suited to serve as its home. After seven
years, two hundred miles of the river bank had become fringed
with a zone of Eichhornia from twenty-five to two hundred feet
in width. In the summer of 1896, a strong north wind drove
the plants up stream from Lake George, forming a solid mass
entirely covering the river for nearly twenty-five miles. The
growth was so dense that small boats with screw propellers
could not get through the mass. Formerly, when the stream
was clear, logs used to be rafted down the river, and it is esti-
mated that, at the time when the Water Hyacinth was at its
maximum, the lumber industry of the region suffered an
approximate annual loss of $55,000 from the difficulty of
rafting.
In Africa, the River Lettuce, Pistia Stratiotes^ plays a similar
part to the Water Hyacinth of America in hindering naviga-
tion. Miss Mary Kingsley2 gives a characteristically racy
description of its behaviour on the Ogowe and the neighbouring
rivers in the French Congo. " It is," she writes, " very like
a nicely grown cabbage lettuce, and it is very charming when
you look down a creek full of it, for the beautiful tender green
makes a perfect picture against the dark forest that rises from
1 Webber, H. J. (1897). » Kingsley, M. H. (1897).
2i4 VEGETATIVE REPRODUCTION [CH.
the banks of the creek. If you are in a canoe, it gives you little
apprehension to know you have got to go through it, but
if you are in a small steam launch, every atom of pleasure in its
beauty goes, the moment you lay eye on the thing. You dash
into it as fast as you can go, with a sort of geyser of lettuces
flying up from the screw; but not for long, for this interesting
vegetable grows after the manner of couch-grass. I used to
watch its method of getting on in life. Take a typical instance : a
bed of river-lettuces growing in a creek become bold, and grow
out into the current, which tears the outside pioneer lettuce
off from the mat. Down river that young thing goes, looking
as innocent as a turtle-dove. If you pick it up as it comes by
your canoe and look underneath, you see it has just got a stump.
Roots? Oh dear no! What does a sweet green rose like that
want roots for? It only wants to float about on the river and be
happy; so you put the precious humbug back, and it drifts
away with a smile and gets up some suitable quiet inlet and
then sends out roots1 galore longitudinally, and at every joint
on them buds up another lettuce; and if you go up its creek
eighteen months or so after, with a little launch, it goes and
winds those roots round your propeller2."
The luxuriance of hydrophytes as compared with other herba-
ceous plants can be demonstrated not only by examples of their
multiplication on a large scale, but also when the dimensions
of individuals are considered. A striking instance is afforded
by Caspary's3 measurements of the leaves of a plant of Victoria
regia cultivated in a hot-house; the maximum growth of the
lamina recorded in 24 hours was as much as 30-8 cms. in length
and 36*7 cms. in breadth. Even in our climate the growth of
aquatics must be rapid, to produce the length of stem some-
times observed; in the case of Ranunculus fluitam^ shoots twenty
or more feet in length have been recorded4, while floating
1 Botanically these " roots " are of course lateral stems.
2 For other cases of plant accumulations which are on a sufficient
scale to form serious obstructions, see Hope, C. W. (1902).
3 Caspary, R. (18562). 4 Schenck, H. (1885).
xvii] LUXURIANCE AND PERENNIATION 215
branches of Utricularia vu/garis may be six feet long1. The shoot
system, as a whole, sometimes attains a remarkable development.
The present writer examined, for instance, a plant of Polygonum
amphibium growing at Roslyn Pits, Ely, on June 30, 1913,
which showed at the surface of the water only one flowering
branch with seven foliage leaves. The plant was pulled up with
a boat-hook and inevitably somewhat mutilated in the process,
but, notwithstanding the breakages, the various axes forming the
shoot system were found to measure altogether approximately
forty-two feet. Besides the two visible leafy shoots, eight of the
branches terminated in leaf buds, which looked as though they
would probably have reached the surface in the course of that
season. The longest internode in the horizontal part of the stem
measured as much as sixteen inches.
The great development often reached by individual water
plants is no doubt an expression of the same tendency as that
which leads them so generally to perenniation. Annuals are
quite rare among hydrophytes ; only a few examples are known,
such as Naias minor, Naias flexilis and certain species of
Elatine*. There is of course no dry season to be spanned, and
many aquatics can continue their vegetation all the year round,
in some cases paying little regard to the passage from summer
to winter. Zannichellia palustris, for instance, may be found in
flower in November, while Aponogeton distachyus^ cultivated out-
of-doors in England, flowers sometimes in December and Janu-
ary. The strength of the tendency to perenniation may be illus-
trated by the fact that the following plants have at different
times passed successfully through one or more winters in so
unsympathetic a location as a rain-water tub in the present
writer's garden — Hydrocharis Morsus-ranaey Stratiotes aloides^
Spirodela polyrrhiza, Lemna trisulca, Myriophyllum sp., Qenan-
the Phellandrium v&r.fluviatiliS) CeratophyllumyHippuris,3.nd two
species of Potamogeton. That the perennial habit is directly
related to the environment, seems to be indicated by the fact
that, in the case of Callitriche2'^ the land forms are annual while
1 Burrell, W. H. and Clarke, W. G. (1911). 2 Schenck, H. (1885).
216 VEGETATIVE REPRODUCTION [CH.
the water forms are perennial. In the aquatic Callitriches,
rooted internodes bearing lateral buds may remain in the mud
and tide over the winter1. Montia fontana^ also, is biennial in
places where the water is liable to dry up, but, in springs and
permanent streams, it grows strongly and becomes perennial2.
Those water plants which have not adopted special methods
of perenniation, generally retain their leaves through the winter,
e.g. Peplis Portula^ Ceratophyllum, Hottonia^ and the submerged
species of Callitriche. In the case of such plants, any detached
shoot will generally grow into a new individual with extreme
readiness. In Hottonia the branches forming a whorl below the
inflorescence become separated from the axis and give rise to
new plants in the spring3. The present writer has noticed that,
in the case of Peplis Portula and Ceratophyllum, the submerged
stems are very brittle, and, in the early autumn, quantities of
detached floating shoots may be observed. The behaviour of
Callitriche* is particularly striking, for in this case new plants
can be formed from a node with only a very small piece of inter-
node attached. Lawia xeylanica^ Tul.5, one of the Podostema-
ceae of Ceylon, can recommence its growth from any portion
of the thallus, however small, if it be submerged under favour-
able conditions, and other members of the family have a similar
power. A very notable capacity for vegetative multiplication
is exhibited by some Cruciferae. In the case of the North
American Nasturtium lacustre^^ the pinnately dissected, sub-
merged leaves become detached about the middle of August
and float at the surface of the water ; an adventitious bud arises
at the base of each leaf and develops into a new plant. The same
production of buds from foliar tissue has long been known in
Cardamine pratensis^ the Lady's Smock, where it can easily be
observed at various times of year (Fig. 141). On May 21,
1919, the present writer saw countless plantlets growing from
detached leaflets in a dyke in the fens near Lakenheath Lode.
1 VaucherJ.P.(i84i)andLebel,E.(i863). 2 Royer,C. (1881-1883).
3 Prankerd, T. L. (1911). 4 Hegelmaier, F. (1864).
5 Willis, J. C. (1902). 6 Foerste, A. F. (1889).
xvn] AQUATIC GEOPHYTES 217
The caddice worms, which also abounded in this dyke, seemed
to have a great fancy for using the leaflets in constructing
their cases, and, in consequence, their
armour was often elegantly crested
with tiny adventitious plants of Lady's
Smock.
In addition to those aquatics which
retain their leaves through the winter,
there are others which perenniate in
or upon the substratum by means of
rhizomes or tubers. Plants which adopt
this habit, may be described as aquatic
geophytes. Limnanthemum (Figs. 22 and
23, p. 41), Castalia (Fig. 1 1, p. 26) and
Nymphaea (Figs. 10, p. 25 and 1 2, p. 27)
are rhizomatous. In some cases — e.g.
Sagittaria^ certain Potamogetons and
Nymphaeaceae — special tubers are
formed which outlast the winter These
afford a means of vegetative multipli-
cation, since an individual plant may submerged type growing
among Utricularia in shallow
in some cases give rise to numerous pooi, Commissioners' Pits,
tubers; a single plant of Sarittaria Upware, June 27, 1914- in
. .* ., c . each case the terminal leaflet
Saglttljoha^ for instance, may produce bears an adventitious plant-
as many as ten tuber-bearing stolons. let tVhe bfe: C',s!ngle»
' . much-decayed pinnule bear-
Another method of vegetative reproduc- ing a well-developed piantiet;
tion is illustrated by Littorella lacustris\ ^ ^af si^eTTl AJ
which puts out runners in the spring,
bearing at their apices young plants not easily distinguishable
from seedlings; these plantlets become independent by the
late summer or autumn. A plant of this species with a runner
is shown in Fig. 142, p. 218.
The most distinctive mode of wintering and of vegetative
reproduction found among hydrophytes, is, however, by means
of winter-buds or turions ; these specialised shoots, which are
1 Buchenau, F. (1859).
218
VEGETATIVE REPRODUCTION
[CH,
FIG. 142. Littorella lacustris, L. Plant drawn in February 1912. The
collapsed region at base of stem probably represents the part formed in
1910; r = runner arising in a leaf axil. (Reduced.) [A. A.]
xvn] TURIONS 219
stored with food material, and protected externally in some way,
become detached from the parent and pass the winter either
floating, or resting at the bottom of the water. In the spring
they expand, produce adventitious roots, and rapidly develop
into full-fledged individuals. Certain plants, also, which do not
actually produce independent turions of a specialised type,
show transitions towards such a development. If shoots of the
Greater Spearwort, Ranunculus Lingua^ •, are left in water over
the winter, they rise to the surface in the spring in a partly
decomposed state, but bearing healthy buds in the axils of their
leaves ; these become detached to give rise to new plants. Elodea
canademis (Fig. 34, p. 55) and Stratiotes aloides (Fig. 32, p. 53),
again, produce primitive reproductive buds, which do not imme-
diately become free, but germinate while attached to the parent
plant2. The apices of the shoots of Ceratophyllum are clothed
in autumn with leaves which are more crowded and of a deeper
green than those of the rest of the shoot, but, as we have already
pointed out3, they can scarcely be said to form definite winter-
buds.
Certain turions showing a high degree of specialisation have
already been mentioned, e.g. those of Hydrocharis (pp. 47-49),
Potamogeton (pp. 66-69), tne Lemnaceae (pp. 75-77), Aldro-
vandia (p. 1 10), and Utricularia (pp. 101-103). The difference
between the normal foliage leaf and the protective outer leaf of the
turion, in the case of U. intermedia^ is shown in Fig. 143, p. 220.
Among the British plants to whose wintering habits we have not
yet referred,Myriopky//um verticillatum^ affords a striking example
of turion formation. In August the plant may be found simul-
taneously producing flowers and winter-buds (Fig. 144, p. 22 1).
Early in October the ragged shoots may be seen floating, with
here and there a compact turion (T), distinguished against the
faded brownness of the parent plant by its vivid, dark-green hue.
These winter-buds become detached during the cold season, and
1 Belhomme, (1862). 2 Gluck, H. (1906). 3 See p. 87.
4 The winter-buds of Myriophyllum were noted by Vaucher, J. P.
220 WINTERING HABITS [CH.
in the spring they expand into graceful shoots (Fig. 145, p. 222).
The germination normally occurs in March or April, but it can be
induced at any time if the temperature is favourable ; if brought
indoors and kept warm, the turions will develop into new plants
in October, November, December or January1. Cold is ini-
mical to the winter-buds, and, if frozen for a few days, many of
them are killed. The turions of different aquatics vary very
widely in their capacity to withstand freezing1. Those of Utricu-
laria vulgaris are uninjured by inclusion in ice for as long as
twelve days, while Hydrocharis Morsus-ranae, according to
Gltick's experiments, is still more sensitive than Myriophyllum,
FIG. 143. Utricularia intermedia, Hayne. A, winter-bud leaf (enlarged).
B, summer leaf (less enlarged). [Goebel, K. (1891-1893).]
for, after three to ten days in ice, nearly all the turions were
killed. However, according to Guppy2, they are able to with-
stand inclusion in ice for a period of some weeks; the discre-
pancy between these results requires some explanation, which
may perhaps lie in the particular conditions of the experiments.
The turions of many hydrophytes are saved from the risk of
becoming frozen by their habit of wintering at the bottom of
fairly deep water.
For many years botanists were inclined to interpret the
development of * winter-buds ' on the simplest teleological
Glttck, H. (1906).
2 Guppy, H. B. (i 893).
XVII
WATER MILFOIL
221
FIG. 144. Myriophyllum verticillatum, L. August 15, 1911. A, the inflorescence
shows in succession female, hermaphrodite and female flowers. Three turions, T,
occur on the lower part of the axis. (Reduced.) For the further development of
one of these turions see Fig. 145, p. 222. B shows an hermaphrodite flower and its
subtending leaf. (Enlarged.) [A. A.]
222 WINTERING HABITS [CH.
lines. These turions were regarded as a definite adaptation
devised by the plant to tide over the cold season, and to ensure
vegetative propagation. But this position has been undermined
by experimental work originating with Goebel's1 discovery
that turion formation in Myriophyllum verticillatum is definitely
the result of unfavourable conditions. This observer, for ex-
ample, placed some of the buds in a glass vessel with water but
without earth, where they grew into richly rooted plants, more
than 30 cms. long. By April i, these plants had all formed
new turions terminating the main and lateral shoots, while in
the locality from which the original winter-buds had been
collected, their contemporaries remained still ungerminated !
FIG. 145. Myriophyllum verticillatum, L. One of the turions shown in Fig. 144,
p. 221, which had begun to germinate after the winter's rest and was found at the
bottom of the water in this condition on March 16, 1912 ; b, base. (Nat. size.) [A. A.]
Gliick2, who has carried Goebel's work on Myriophyllum fur-
ther, has shown that if the plant is grown in a vessel of water,
over-crowded with other aquatics so that there is much com-
petition for food, 'winter' bud formation may occur even in
the spring. He also planted turions of M. verticillatum in soil,
and cultivated them for an entire summer as land plants.
Numerous green shoots were formed, but, by the beginning of
August, each individual plant had also produced four to ten
pale green turions (Fig. 146 X), most of which were under the
soil. This early development of turions is attributed by Gliick to
the lack of water from which the plants suffered. On the other
1 Goebel, K. (1891-1893). 2 Gluck, H. (1906).
XVI l]
TURIONS
223
hand, luxuriant specimens growing in water in warm situations
may vegetate throughout the winter without forming turions.
It is most likely that, in normal life, it is
the lowering of the temperature in the
autumn which induces the formation of
winter-buds.
That it is unfavourable conditions
which bring about the development of
turions, seems to be true not only of the
Water Milfoil but of aquatics in general.
Some remarkable experiments on the effect
of starvation upon Utricularia have been
quoted on pp. 102—103. Similar results
have been obtained in the case of Sagittaria
sagittifolia^ in which, however, the vege-
tative multiplication is effected by tubers
and not by turions. Tuber formation in
the Arrowhead normally occurs when the
plant has exhausted itself by the forma-
tion of inflorescences, and when cooler
weather sets in. The land form, like that
of Myriophyllum, produces tubers several
weeks earlier than the form growing under
the optimum aquatic conditions. Gliick1,
one autumn, planted a tuber of the Arrow-
head in a pot of earth and left it there,
almost without water, until towards the
end of the following July. The plant, which
had failed to appear above the soil, was H. (1906), Wasser- und
then examined, and it was found that the
tuber had put out a few wretched-looking
little ribbon-leaves, which had not possessed strength to pene-
trate the earth. It had also formed four tiny stolons, 1-5 to
2 cms. long, each terminating in a small tuber, 8 to 10 mm. in
length. This tuber formation had apparently occurred as a
1 Gliick, H. (1905).
form with five subter-
ranean turions, two of
which are marked K.
still attached to the base
^ timber *5
adventitious roots. The
two lowest turions have
grown out of the axis
Sump&
226 VEGETATIVE REPRODUCTION [CH. xvn
There is good reason to suppose that, as Schenck1 long ago
suggested, the vegetative reproduction of water plants merely
illustrates the general rule that vegetation and fructification
stand in inverse ratio to one another. Orchards bear better
when the trees are pruned, while in wet years when leafage is
over-luxuriant, fruit formation diminishes. And thus the
excessive vegetative activity of water plants acts, in all probabi-
lity, as a deterrent to sexual reproduction.
1 Schenck, H. (1885).
CHAPTER XVIII
THE FLOWERS OF WATER PLANTS AND THEIR
RELATION TO THE ENVIRONMENT
THE most notable characteristic of the flowers of the
majority of aquatic Angiosperms is that they make sin-
gularly little concession to the aquatic medium, but display the
utmost conservatism in form and structure. The plants which
have, in the course of evolution, adopted water life, have, as
we have already shown, profoundly modified their vegetative
organs in connexion with their new environment, but their
methods of sexual reproduction in general depart little from
those which had already become stereotyped in their terrestrial
ancestors. This sharp distinction, between the degree of modi-
fication of the vegetative and reproductive parts, is particularly
well shown in the case of so highly specialised a water plant
as Utricularia vulgaris. Here the vegetative body is entirely
submerged, but the aerial inflorescence axis and the flowers,
which are adapted to entomophilous pollination, in no way differ
from those of a terrestrial plant. The extreme divergence in
mode of life, and even in internal structure, between the
aerial reproductive region and the submerged vegetative region
in this species, led an anatomist to speak of the plant as con-
sisting of "an aquatic being, vegetating horizontally without
roots," and "a vertical aerial being, producing flowers at its
apex, and implanted in the first, which serves it as soil, or
rather as roots1."
Those hydrophytes which still retain a type of flower adapted
for aerial life, are under the absolute necessity of raising their
inflorescence axis well above the water level, if cross-pollination
is to be secured. This is sometimes very incompletely achieved,
iTieghem, P. van (1868).
15—2
228 FLOWERS OF AQUATICS [CH.
and even within the same genus we find differing degrees of
success in the avoidance of submergence of the flower. Ranun-
culus fluitanS) for instance, which does not hold its peduncles
well erect and grows in rapidly flowing water, very often suffers
from the inundation of its flowers, and, in consequence, fails
to set seed1. Sometimes the attempt to rise above the water
surface seems to have been entirely given up. Ranunculus
trichophyllus is described as growing in the River Inn in enor-
mous masses, and frequently blooming under water, opening
its flowers at a depth of i to i J feet, but whether it can set
seed under these conditions does not seem to have been ob-
served2. Those Batrachian Ranunculi which flower successfully
in rapidly flowing water, prove to be species such as R. carinatus^
Schur. (R. confusus. Gen. et Godr.) which produce long flowering
stalks rising erect above the water, and not readily submerged
by slight changes in level1. In the case of the heterophyllous
Water Buttercups, the leaves associated with the flower are often
floating and relatively undivided; this must be an assistance in
maintaining the equilibrium of the pedicel3. In Heter anther a
zosteraefolia, also, the leaf next the inflorescence is described
as always being of the floating type4. The association of floating
leaf and flowers in Limnanthemum nymphoides, which is so close
that the inflorescence appears at first sight to spring from the
petiole, must also play a part in holding the flowers above water.
If any locality in which Limnanthemum grows freely be visited
in August, the way in which the fringed, yellow flowers are held
clear above the water will be found to be one of their most
striking characters.
The early development and whorled arrangement of the
branches springing from the base of the inflorescence axis in
Hottonia palustris*, the Water Violet, serve to support it on all
sides, and to keep it vertical, while the numerous adventitious
roots arising from the base of the erect shoot probably have a
1 Freyn, J. (1890). 2 Overton, E. (1899).
3 Askenasy, E. (1870). 4 Hildebrand, F. (1885).
5 Schenck, rf. (1885) and Prankerd, T. L. (1911).
xvm] INFLORESCENCE-FLOATS 229
similar effect (Fig. 127, p. 197). The part played by the roots
in holding the stem of Oenanthe Phellandrium in an upright
position has already been mentioned1, as well as the specialised
branches which in some Bladderworts keep the inflorescence
erect2. Fig. 150 shows the whorl of six branches surrounding
FIG. 150. Utricularia inflata, Walt. Part of swimming water shoot, with an
inflorescence axis bearing six floating organs. [Goebel, K. (1891-1893).]
the flowering axis in Utricularia inflata. Spruce3, in his account
of his travels in the Amazon region, mentions, as a general obser-
vation, that those hydrophytes which rear themselves erect and
thus raise the flowering part of their stem well out of the water,
prove on examination to have the sub-aquatic leaves grouped
1 See p. 204. 2 See p. 99. 3 Spruce, R. (1908).
230 FLOWERS OF AQUATICS [CH.
in whorls, even when their terrestrial relatives have a different
arrangement. He states that Jussiaea amaxonica has the narrow
submersed leaves so closely whorled as to resemble the Mare's-
tail of our ponds, while the emersed leaves are solitary.
Those water plants whose inflorescences rise into the air,
depend for cross-pollination upon insects or the wind. Those
which are entomophilous differ little from land plants in their
methods of attraction, except that, speaking very generally, a
blue colour perhaps occurs more rarely than in terrestrial plants,
while white or yellow are common1. The frequency of white
flowers among aquatics was noted long ago by Nehemiah Grew,
who, in his little book, An Idea of a Phytological History Pro-
pounded , published in 1673, wrote, "to Water-plants more
usually a White Flower/* The rarity of blue flowers among
hydrophytes may be accidental, but those who take a teleologi-
cal view of these matters prefer to attribute it to the fact that
blue does not contrast vividly with the colour of a water surface
with its sky reflections. It is possible that some water plants,
such as Lemna*, are pollinated by crawling insects, although
they possess no special means of attraction.
A certain number of aquatics appear to have given up insect
pollination and taken to anemophily, often with concomitant
simplification of the flower, e.g. Hippuris (Fig. 151) and Myrio-
-phyllum (Fig. 144, p. 221). This change of habit may be
associated with the fact that the number of insects flying over a
water surface is probably less, on an average, than the number
over a corresponding land surface. Peplis Portula (Fig. 152,
p. 232) seems to be actually in a state of transition from
entomophily to anemophily. There are six fugacious little white
petals, and a small amount of honey is secreted3. But the
flowers are very inconspicuous, and no insect visitors appear
to be attracted. The stigma becomes ripe a little sooner than
the stamens, but they bend inwards over it and pollinate it4.
Myriophyllum is an example of a wind-pollinated genus, in
1 Schenck, H. (1885). * See p. 80. 3 MacLeod, J. (1894).
4 Willis, J. C. and Burkill, I. H. (1895).
XVI 1 1]
MARE'S-TAIL
231
- a.L
FIG. 151. Hippuris vulgaris, L, A, shoot showing air^ leaves (a.?.), water leaves
(w.l.} and roots (r.}. Whorls of flowers at the upper nodes; nlt node with flowers
whose anthers have dehisced; n2, node with flowers whose anthers are still closed.
B, whorl of flowers enlarged, leaves (I) cut away. C, a single flower seen from
adaxial side; st = feathery style; an = anther; o = ovary. (Reduced.) [A. A.]
232 FLOWERS OF AQUATICS [CH.
which the long anthers swing on flexible filaments (B in Fig.
144, p. 221). In M. spicatum1 the upper flowers of the spikes
are generally staminate, and the lower pistillate, while perfect
flowers often occur in the intermediate region.
Littorella lacustris^ which is anemophilous, sets a full com-
plement of seeds by this means; it does not, like Myriophyllum
and Hippuris, raise its flowers out of the water, but is sterile
except when it grows as a land plant (Fig. 1 2 8 C, p. 1 98). When
submerged it develops no flowers, but reproduces itself by
FIG. 152. Peplis Portula, L. Land form, Forest of Wyre, September 13, 1911.
A , part of branch. (Nat. size.) B, flower and leaves. (Enlarged.) C, fruit with seeds
showing through transparent fruit coat. (Enlarged.) [A. A.]
runners (Fig. 1 28 y^and B, p. 198). Littorella has been described
as flowering so luxuriantly, in the height of summer in a
dried-up swamp, that the shaking of the white stamens in the
wind gave the whole area a silken sheen2, while another record
relates to a case of this plant flowering in a dry year, when it had
only attained ta such minute dimensions that the length of the
filaments actually exceeded that of the rest of the plant3! In
this genus we are probably not dealing with a case of loss of
1 Knupp, N. D. (191 1). 2 Buchenau, F. (1859).
3 Preston, T. A. (1895).
xvm] CLEISTOGAMY 233
entomophily associated with the water habit, since the immedi-
ate ancestors of Littorella were most likely closely related to the
typically wind-pollinated Plantagos.
The difficulty of keeping entomophilous or anemophilous
flowers above water seems to have led, in the case of certain
aquatics, to the formation of cleistogamic flowers which can
set seed even when submerged. But Prankerd's1 work has
suggested that records of cases of cleistogamy among water
plants ought to be received with some caution, unless they are
based on evidence of a highly critical nature. Concerning the
Water Violet, this author writes, "Cleistogamy has been attri-
buted to Hottonia, but I have found no trace of it during three
summers' field work. The idea is probably due to some small,
closed flowers, which occur sometimes among those fully
developed, but serial sections have shown that these are merely
abortive." It is possible that similar detailed investigations of
other water plants, which have the reputation of bearing cleisto-
gamic flowers, might considerably reduce the list ; Subularia for
instance, which has been called cleistogamic, seems to open its
flowers even if submerged2. There are however a certain number
of cases in which the existence of cleistogamy is adequately
established. Hooker3, for example, described the phenomenon
in detail in Limosella aquatica^ L. This plant in Kerguelen's
Land was, he writes, "found in the muddy bottom of a lake,
and probably flowers all the year round. I gathered it in the
month of July (mid- winter), beneath two feet of water, covered
with two inches of ice; even then it had fully-formed flowers,
whose closely imbricating petals retained a bubble of air, the
anthers were full of pollen and the ovules apparently impreg-
nated. The climate of Kerguelen's Land being such, that this
lake is perhaps never dried, it follows that the plant has here the
power of impregnation when cut off from a free communication
with the atmosphere, and supplied with a very small portion of
atmospheric air, generated by itself." Ranunculus fluitans^ Lmk.,
1 Prankerd, T. L. (1911). 2 Hiltner, L. (1886).
3 Hooker,}. D. (1847).
232 FLOWERS OF AQUATICS [CH.
which the long anthers swing on flexible filaments (B in Fig.
144, p. 221). In M. spicatum1 the upper flowers of the spikes
are generally staminate, and the lower pistillate, while perfect
flowers often occur in the intermediate region.
Littorella lacustris^ which is anemophilous, sets a full com-
plement of seeds by this means; it does not, like Myriophyllum
and Hippuris, raise its flowers out of the water, but is sterile
except when it grows as a land plant (Fig. 1 2 8 C, p. 1 98). When
submerged it develops no flowers, but reproduces itself by
FIG. 152. Peplis Portula, L. Land form, Forest of Wyre, September 13, 1911.
A , part of branch. (Nat. size.) B, flower and leaves. (Enlarged.) C, fruit with seeds
showing through transparent fruit coat. (Enlarged.) [A. A.]
runners (Fig. 1 28 y^and B, p. 198). Littorella has been described
as flowering so luxuriantly, in the height of summer in a
dried-up swamp, that the shaking of the white stamens in the
wind gave the whole area a silken sheen2, while another record
relates to a case of this plant flowering in a dry year, when it had
only attained to such minute dimensions that the length of the
filaments actually exceeded that of the rest of the plant3 ! In
this genus we are probably not dealing with a case of loss of
1 Knupp, N. D. (191 1). 2 Buchenau, F. (1859).
3 Preston, T. A. (1895).
xvm] CLEISTOGAMY 233
entomophily associated with the water habit, since the immedi-
ate ancestors of Littorella were most likely closely related to the
typically wind-pollinated Plantagos.
The difficulty of keeping entomophilous or anemophilous
flowers above water seems to have led, in the case of certain
aquatics, to the formation of cleistogamic flowers which can
set seed even when submerged. But Prankerd's1 work has
suggested that records of cases of cleistogamy among water
plants ought to be received with some caution, unless they are
based on evidence of a highly critical nature. Concerning the
Water Violet, this author writes, "Cleistogamy has been attri-
buted to Hottonia^ but I have found no trace of it during three
summers' field work. The idea is probably due to some small,
closed flowers, which occur sometimes among those fully
developed, but serial sections have shown that these are merely
abortive." It is possible that similar detailed investigations of
other water plants, which have the reputation of bearing cleisto-
gamic flowers, might considerably reduce the list ; Subularia for
instance, which has been called cleistogamic, seems to open its
flowers even if submerged2. There are however a certain number
of cases in which the existence of cleistogamy is adequately
established. Hooker3, for example, described the phenomenon
in detail in Limosella aquatica, L. This plant in Kerguelen's
Land was, he writes, "found in the muddy bottom of a lake,
and probably flowers all the year round. I gathered it in the
month of July (mid-winter), beneath two feet of water, covered
with two inches of ice; even then it had fully-formed flowers,
whose closely imbricating petals retained a bubble of air, the
anthers were full of pollen and the ovules apparently impreg-
nated. The climate of Kerguelen's Land being such, that this
lake is perhaps never dried, it follows that the plant has here the
power of impregnation when cut off from a free communication
with the atmosphere, and supplied with a very small portion of
atmospheric air, generated by itself." Ranunculus fluitans^ Lmk.,
1 Prankerd, T. L. (1911). 2 Hiltner, L. (1886).
3 Hooker,}. D. (1847).
234
FLOWERS OF AQUATICS
R. aquatiliS) L. and R. divaricatus,
Schr. are also said to flower under
water, pollination occurring in a
bubble of air formed within the
perianth1.
An Indian species of Podostemon,
P. Barberi, Willis2, has cleistogamic
flowers, with one stamen standing
close up against the stigmas (Fig. 82,
p. 121). Alisma natans* is described
as being cleistogamic in deep water,
while Echinodorus ranunculoides^ has
an entirely submerged form which
flowers under water at a depth of three
feet. Other recorded cases of cleisto-
gamy are Heteranthera dubia^ (Fig.
153) and Hydro thrix Gardner^ (Pon-
tederiaceae), Euryale ferox1 (Nym-
phaeaceae), Ilhcebrum verticillatunfi
(Caryophyllaceae), Tillaea aquatica*
(Crassulaceae), Trapella sinensis9 (Pe-
daliaceae), and a number of species
of Lythraceae with apetalous or sub-
apetalous flowers, belonging to the
genera Rotala^ Peplis and Nesaea10.
The pollination of cleistogamic
flowers, though it may occur beneath
1Royer, C. (1881-1883).
2 Willis, J. C. (1902). *
3Schenck, H. (1885).
4 West, G. (1910).
5Wylie, R. B. (^i;1).
6Goebel, K. (1913).
7Goebel, K. (1891-1893).
8Caspary, R. (1860).
9 Oliver, F.W. (1888).
10 Gin, A. (1909).
FIG. 153. Heteranthera dubia,
(Jacq.) MacM. A, L.S. through
an immature flower cut slightly
obliquely in the adaxial-abaxial
plane. The tip of the stigma lies
below the upper ends of the
anthers, and the style at this
stage is straight. B, upper por-
tion of an older flower cut in
the same general direction as A .
The stigma has been shoved up
into the upper end of the flower
in contact with the tips of the
anthers where the stigmatic
hairs touch the pollen grains
through the breaks in the sta-
mens. Pollen tubes are passing
from the anther into the stylar
chambers. The style is beginning
to fold on account of its exces-
sive elongation. [Wylie, R. B.
(I9I71)-]
xvm] HYDROPHILOUS POLLINATION 235
the water surface, is no more truly aquatic than are the vital
processes of a man in a diving bell, since, as Hooker points
out in the case of Limosella, the transference of the pollen
takes place within a bubble of gas. Certain plants, however,
present transitional methods of pollination, which without
being actually hydrophilous, show approaches to this state.
The oft-quoted case of Vallisneria spiralis (Hydrocharitaceae)
is perhaps the best instance of such a transitional method. The
male and female plants are distinct. The female flowers are
solitary within a spathe, and are carried up to the surface of the
water by the elongation of the peduncle below the spathe.
When mature they lie horizontally on the water surface1. The
submerged male spathes contain over 2ooo2 small flowers each
with two stamens; the perianths are hermetically sealed, each
enclosing a bubble of air. These male flowers become detached
and rise to the surface of the water, where they open. The float-
ing male flowers were figured early in the eighteenth century
by Micheli3, an Italian botanist. A later observer in India4
speaks of " seeing under a noonday sun the innumerable florets
freed from their spathes and ascending like tiny air-globules
till they reach the surface of the water, where the calyx quickly
bursts — the two larger and opposite sepals, reflex, forming tiny
rudders, with the third and smaller recurved as a miniature sail,
conjointly facilitating in an admirable manner the florets' mis-
sion to those of the emerging females. " The male flowers are
thus conveyed over the water surface by air currents, and some
of them get carried into the neighbourhood of the female flowers,
where the sticky pollen of the dehiscing anthers is likely to be
rubbed off against the exposed stigmas. Each female flower,
owing to its weight, is surrounded by a minute depression
in the surface film of the water; the male flowers easily slide
down the slope thus produced, and so approach the female2.
After pollination the spiral peduncle contracts, carrying the
maturing fruit deep down into the water; it is said that the
1 Chatin, A. (18552). 2 W7lie> R- B-
3 Micheli, P. A. (1729). 4 Scott, J. (1869).
236 FLOWERS OF AQUATICS [CH.
contraction does not actually bring it to the bottom of the water,
but that the last stages in the descent are accomplished by its
own weight, when it is ripe1. Other Hydrocharitaceae, e.g.
the marine genus Enhalus^^ possess a pollination mechanism
resembling that of Fallisneria. Others again, e.g. Elodea calli-
trichoides*, have, by a further modification, arrived at a type
of pollination which is strictly hydrophilous, for the pollen,
instead of being rubbed off against the stigmas, is shed explo-
sively and falls on to the surface film, reaching the stigmas by
flotation. The ultimate stage in the series of the Hydrocharita-
ceae is reached by the marine genus Halophila, in which neither
male nor female flowers emerge from the water, and the process
of pollination takes place in complete submergence4. The
stigmas are thread-like and the pollen-grains, being united into
strings, adhere readily to the stigmas, which present elongated
receptive surfaces.
The family Hydrocharitaceae is, indeed, of unique interest
from the standpoint of the evolution of submerged pollination,
since it includes within itself all stages in the transition from
entomophily to hydrophily5. It contains insect-pollinated
flowers, such as Hydrocharis Morsus-ranae and Elodea densa^ with
attractive perianths, and, sometimes, nectaries ; flowers in which
the unwetted pollen is conveyed over the water by the ' boat
mechanism/ e.g. Vallisneria; flowers in which the pollen floats
on the surface of the water, e.g. Elodea callitrichoides ; and, finally,
flowers with entirely submerged pollination, such as Halophila.
Callitriche^) among the Dicotyledons, provides another group
of species in which the transition from aerial to aquatic pollina-
tion can be followed. The genus is subdivided into two sections :
Eu-callitriche^ to which the ordinary amphibious species of
Water Starwort belong, and of which C. verna is the type, and
1 Royer, C. (1881-1883). 2 Delpino, F. and Ascherson, P. (1871).
3 Hauman-Merck, L. (i9i32). See p. 55. 4 See p. 130.
5 See pp. 55-57.
6 Hegelmaier, F. (1864), Jonsson, B. (1883-1884), and Schenck, H.
(1885).
3) flower. In the
case of the male flower both
bracts can be seen. (Enlarged.)
[A. A.]
xvm] HYDROPHILOUS POLLINATION 237
Pseudo-callitriche, which consists of submerged plants grouped
round the species C. autumnalis. C. autumnalis has no land form,
but vegetates, flowers and fructifies
below the level of the water surface.
Throughout the genus the simple
male and female flowers occur separ-
ately (Fig. 1 54) ; the female flowers
are commonly found lower down the
inflorescence than the male, but, in
C. autumnalis^ several male and female
regions may alternate with one another.
Insects, and possibly wind, carry the
pollen of the Eu-callitriches, which is
r . FIG. 154. Calhtnche verna, L.
of the terrestrial type and is clothed July 19, 1910. Flowering shoot
with an exine insoluble in sulphuric
acid. That of the Pseudo-callitriches,
on the other hand, is of the aquatic
type; it has no differentiated exine
and contains oil globules which render it lighter than water.
It is carried to the stigmas by water currents.
The aquatic pollination of Ceratofhyllum (Hornwort) has
already been considered1, as well as that of three members of the
Potamogetonaceae, Cymodocea^^ Zoster a* , and Zannichellia^. In
connexion with the submerged pollination of Naias graminea —
also belonging to the Pondweed family — a picturesque incident
which has been placed on record by Bailey5, suggests that
aquatic animals may occasionally play a part in the pollination
of submerged plants. He writes, " While . . . examining portions
of a living plant on which were ripe anthers, I noticed a colony
of Vorticellidae attached to one of the fascicles of leaves; the
grace and activity of its movements led me to watch it for a
considerable time, and whilst so watching it I witnessed grains
of pollen whirled in all directions, or drawn into the vortex of
the animal by its marginal cilia. The alternate contraction and
1 See pp. 84-85. 2 See p. 126. 3 See pp. 127-129.
4 See pp. 70-71. 5 Bailey, C. (1884).
238 FLOWERS OF AQUATICS [CH. xvm
elongation of the elastic and thread-like pedicles of the colony
kept the pollen-grains in constant motion, which left me no
doubt that at times the grains would be directly borne to the
stigmatoid appendages of the pistilliferous flowers/'
It seems to the present writer conceivable that, in future
phases of evolution, if more Angiosperms reach the highly
specialised stage of complete submergence, the water fauna may
come to play an important part in their pollination. There may
even arise a parallelism of development and an interdependence
between aquatic animals and submerged plants comparable with
that which has obtained in the case of aerial insects and the
flowers which they pollinate!
In general, the consideration of the flowers of hydrophytes
seems to lead to the conclusion that submerged pollination is a
relatively modern development. It is, from some points of view,
merely a further advance on lines similar to those already
marked out in the case of anemophily. The great majority of
hydrophilous plants have near relatives — sometimes even mem-
bers of the same genus — which retain anemophilous or entomo-
philous habits ; this may be regarded as a proof that plants with
submerged pollination have arisen in comparatively recent
times from ancestors with the aerial type of flower. Ceratophyl-
lum forms an exception, since it is entirely hydrophilous, and
has no intimate affinities with any other genus. It is probable,
from its extreme adaptation to aquatic conditions and its isolated
position in the relatively primitive Ranalean plexus, that it is a
genus whose ancestors took to aquatic life at a very early stage
in the race history of the Angiosperms.
[ 239 I
CHAPTER XIX
THE FRUITS, SEEDS AND SEEDLINGS OF
WATER PLANTS1
AS we have shown in the preceding chapter, submerged pol-
jt~\. lination represents an advanced stage in acclimatisation to
water life, to which only a small proportion of hydrophytes have
attained. But it is by no means so rare to find the events subse-
quent to pollination taking place beneath the water surface.
A great many aquatics — not only those which are hydrophilous,
but also a number of those which raise their flowers into the air
for pollination by wind and insects — after fertilisation draw
down their gynaeceum into the water where the ripening pro-
cesses take place. In fact, the water plants which retain an
entirely aerial method of fruit-ripening are relatively few;
examples of these exceptions are Utricularia, Hottonia and
Lobelia^ all of which lift their many-seeded capsules on long
infructescence axes above the water level. Numerous examples
of those aquatics which are pollinated in air but ripen their fruit
in water, might be quoted, but it will suffice to recall Aldro-
the Aponogetonaceae3, Limnanthemum Humboldtia-
Victoria regia5, the Batrachian Ranunculi (Fig. 93, p. 145),
Pontederia rotundifolitfi (Fig. 155, p. 240) and other members
of the Pontederiaceae4. Among the Hydrocharitaceae7, the
ripening ovary is conveyed down into the water by several
different methods; in Limnobium and Qttelia the flower-stalk
bends down, in Vallisneria it contracts spirally, while in Stratiotes
1 For a good general account to that date, see Schenck, H. (1885).
2 Caspary, R. (1859 and 1862).
3 Krause, K. and Engler, A. (1906).
* Muller, F. (1883). « See p. 34. '
6 Hauman-Merck, L, (I9I31). 7 Montesantos, N. (1913).
24o FRUITS OF AQUATICS [CH.
the fruit is carried down by the sinking of the entire plant. The
lowering of the fruit must not, however, be regarded as a special
innovation due to aquatic conditions, since countless examples
FWT!f-
FIG. 155. Pontederia rotundifolia, L. Branch bearing inflorescence (negatively
geotropic) and infructescences (positively geotropic). (Reduced.) [Hauman-
Merck, L. (191 3 1).]
occur among terrestrial plants, e.g. the spiral contraction of the
fruit stalk of Cyclamen and the downward curve of the peduncle
of Linaria Cymbalaria.
In those submerged fruits which are many-seeded, the
method of dehiscence is necessarily different from that obtain-
ing among terrestrial plants, since desiccation can play no part.
The irregular opening of the fruit ofNymphaea lutea has already
been described1. In the case of Limnanthemum nymphoides^
A 3
FIG. 156. Limnanthemum nymphoides, Hoffmgg. and Link. A, fruit from surface
of water, October i, 1914 (nat. size). B, fruit kept in water in unheated greenhouse
since October i, which had dehisced by November 23 (nat. size). C, seed, Novem-
ber 24, 1914 (x 2). [A. A.]
dehiscence takes place in a somewhat similar fashion. The
present writer found a number of infructescences of this plant
with green fruits (Fig. 156 A) floating on the surface of the
1 See p. 35.
xix] INDEHISCENT FRUITS 241
water at Roslyn Pits, Ely, on October i, 1914. At this stage
the seeds were unripe and white. The fruits were brought to
the laboratory and kept in water. After a considerable time
the pericarp split irregularly, after a fashion closely recalling
Nymphaea\ by November 24, the fruits were in this bursting
condition and the seeds, which had darkened in colour, had all
the appearance of being ripe. The embryos are said to be pro-
tected by the cuticularised epidermis of the testa1. The seeds
are flat and ciliated at the edge (Fig. 156 C). That these hairs
serve for flotation is indicated by the fact that if they are cut off
the least touch makes the seeds sink1. It has also been ascer-
tained that the seeds may become firmly attached to the downy
plumage of a bird's breast, by means of this fringe of hairs2.
The splitting of the ovary wall takes place mostly near the base
— the lobes that are thus produced curving up until the outer
epidermis of the pericarp, which was originally convex, becomes
concave. This curvature is due to decay and loss of tissue on the
inner surface of the fruit-wall, followed by swelling of the rest
of the tissues, with the exception of the outer epidermis and
adjacent layers (Fig. 157 A and J5, p. 242).
The fruits of Stratiotes aloides and Hydrocharis Morsus-ranae
are said to be burst open by the swelling of mucilage produced
from the testa of the enclosed seeds.
A remarkably large proportion of aquatics, on the other hand,
have fruits which are either one-seeded and indehiscent, or else
take the form of schizocarps or heads of achenes, separating
into one-seeded segments. The seeds are thus protected both by
pericarp and testa, which is possibly of value in enabling them
to resist the rotting effect of prolonged submergence3. It is
interesting in this connexion to compare, for instance, the fruits
of Plantago major and of the closely related aquatic, Littorella
/acustris1. The Plantain has a pyxidium capsule, with a thin
elastic wall, opening by means of a lid and containing a number
1 Fauth, A. (1903). 2 Guppy, H. B. (1906).
3 The protection of the embryo in certain aquatics is considered by
Marloth, R. (1883).
A.W.P. 16
242 FRUITS OF AQUATICS [CH.
of seeds. The fruit of Littorella on the other hand is reduced to
a nut developed from the two-celled gynaeceum. Only one
chamber is fertile and the embryo is protected by means of the
sclerised fruit wall, with its aperture closed by a stopper formed
from the funicular region of the seed. A protective endocarp,
with an opening closed by a plug, is also found in the four one-
seeded segments of the schizocarp of Myriophyllum spicatum^
B
FIG. 157. Limnanthemum nymphoides, Hoffmgg. and Link. A, T.S. wall of fruit
represented Fig. 156 A, p. 240, October i, 1914. B, T.S. wall of fruit represented
Fig. 156-6, November 23, 1914. (Both x 78 circa.} ep. = epidermis. [A. A.]
and in the drupe-like one-seeded nutlet of Hippuris vu/garis1.
The seeds of the latter species winter in mud at the bottom of
the water, protected by the stony endocarp. At germination
the radicle emerges from the stone through a foramen which
was previously filled by a cuticularised stopper, formed from
part of the funicle and integument. In Alisma Plantago the
embryo is protected by a chaffy carpel wall and a testa described
by different authors as suberised1 or as composed of pectic
substances2. In the case of the four nutlets into which the
1 Fauth, A. (1903). 2 Crocker, W. and Davis, W. E. (1914).
xix] DELAYED GERMINATION 243
schizocarp of Callitriche divides, the same function is performed
by the pericarp, which is thin, but tough and elastic. The well-
protected seeds of hydrophytes can in many cases withstand
inclusion for a considerable length of time in ice or frozen mud.
The fruits of Sagittaria sagittifolia^ Alisma Plantago and Myrio-
phyllum spicatum, and the seeds of Castalia alba and Nymphaea
lutea can tolerate freezing for a week or two, or, in some cases,
V \ much longer1.
^\ With the particularly effective protection of the embryo in
^hydrophytes, their characteristic habit of delayed germination
is probably to be associated. The sprouting of the seed may in
some cases be deferred until the third, fourth, or fifth year2,
the embryo remaining uninjured by this prolonged period of
dormancy.
Several investigators have studied the subject of delayed
germination, and the rather curious fact has emerged that this
delay only occurs if the seeds are continuously immersed in
water; if they are subjected to a period of drying, they germinate
promptly. It has been noted, for example, that the seeds of
MayacafluviatiliS) a Brazilian water plant, which were dried for
six weeks after gathering, germinated at once, while seeds
harvested at the same time, but put immediately into water,
showed no sign of sprouting at the end of three months3. The
seeds of some water plants can tolerate drying for a very long
period, e.g. thirty months in the case of Limnanthemum nymph-
oides*. The result of experimental work on the subject seems to
be to show that the delayed germination of undried seeds is due
to the mechanical pressure exerted by the seed coats5; if these
are artificially ruptured, the development of the embryo presents
no further difficulties. It has been found, for instance, that in
1 Guppy, H. B. (1893) and (1897).
2 Guppy, H. B. (1897) ; on delayed germination in Potamogetons
see pp. 71, 72, and in Nymphaea, p. 36.
3 Ludwig, F. (1886). " 4 Guppy, H. B. (1897).
5 Sauvageau, C. (1894), Crocker, W. (1907), and Crocker, W. and
Davis, W. E. (1914). For a somewhat different viewsee Fischer, A. (1907).
1 6— 2
244 SEEDLINGS OF AQUATICS [CH.
comparative cultures of the achenes of Alisma Plantago, ex-
amined at the end of ten days, those in which the protective
coats were intact, had not germinated at all, while 98 per cent,
of those whose walls had been ruptured, had begun to sprout.
The reason why preliminary drying favours germination, may
possibly be that it gives rise to some cracking of the seed coats;
a speeding-up of germination also occurs, in some cases, if the
seed passes through the alimentary canal of a bird1, a result
which again may be due to some disintegrating chemical or
mechanical action exerted on the wall. Freezing may also assist
germination by means of its effect on the outer covering of the
seed2.
It should be noted, that delayed germination, though
specially characteristic of water plants, is by no means peculiar
to them. That the causes which bring it about are of a similar
nature in aquatics and terrestrial plants, is indicated by the fact,
well known to gardeners, that a large proportion of such seeds
as those of Canna^ fail to germinate unless the shell is filed
through. The phenomena of delayed germination suggest that
Nature, in her solicitude for the protection of the embryo, is
liable to defeat her own ends by enclosing it in a prison from
which it can only escape with difficulty.
The germination and development of the seedling in aquatics
vary according to the natural affinities of the plants in question,
and are characterised by few peculiarities related to the environ-
ment, except a very frequent reduction of the primary root.
In Utricularia (Fig. 67, p. 100), Stratiotes aloides*, Hydrocharis,
Ruppia, Ceratophyllum (Fig. 55, p. 86), the Podostemaceae,
Nymphaea lutea, Aldrovandia*, Hippuris, Naias, Trapa5, etc.,
the radicle is either quite undeveloped or very short-lived. In
Aponogeton distachyus* the primary root does not attain to more
than 0-5 cms. in length, and eventually it disarticulates by
1 Guppy, H. B. (1897). 2 Guppy, H. B. (1893).
3 Irmisch, T. (1865). 4 Korzchinsky, S. (1886).
5 Queva, C. (1910); see also Fig. 160, p. 247.
6 Sergueeff, M. (1907).
xix] FIXATION OF SEEDLINGS 245
means of an absciss layer. There are exceptions, however, to the
general rule that the radicle of water plants is poorly developed :
in Lobelia Dortmanna, for example, it attains fair dimensions1.
In the case of those water plants which grow rooted in the
soil, the poor development of the radicle is often compensated,
at an early seedling stage, by the production of a garland of very
long root-hairs, which grow out from the 'collet,' or junction
of hypocotyl and root, e.g. Htppuris*) Elatine hexandra* (Fig.
158) and many Helobieae3'4, such as Zannichetlia (Fig. 159 C,
p. 246). This type of seedling is, however, by no means confined
to hydrophytes, but is also found in a number of land plants.
The weight of the large seed of Nelumbo 3, and of the achene
wall in the case of the small seedling of Zanxichellia* (Fig. 1 59),
are sufficient to keep the seedling steady at the bottom of the
water until the epicotyl and first leaves are produced. Other
FIG. 158. Elatine kexandra, D.C. Germination of seed; s, seed- s~*L^ ^f\
coat; h, wreath of hairs growing from collet and surrounding v^ C*S
the primary root which forms a minute conical structure.
[Klebs, G. (1884).]
seedlings are anchored for some time by the fruit wall and associ-
ated structures : the grappling apparatus of Cymodocea antarctica,
for instance, has been already described6. In Trapa natans1
(Fig. 1 60, p. 247) the fixation of the seedling is accomplished
in an unusual way, for here the heavy nut sinks to the bottom
of the water, where it is held by hooks derived from the calyx.
Two structures of very unequal size (Co1 and C02) are generally
interpreted as the two cotyledons, though possibly this view
is open to revision. The hypocotyl, including even its extreme
apex, which presumably is of root nature, is negatively geo-
tropic. The first lateral roots, borne by the hypotocyl, curve
downwards and anchor the plant in the soil, while many of the
1 Buchenau, F. (1866). 2 Irmisch, T. (I8591).
3 Klebs, G. (i 884). * Warming, E. ,(i 883!).
5 Hochreutiner, G. (1896). 6 See p. 127.
7Goebel, K. (1891-1893).
246 SEEDLINGS OF AQUATICS [CH.
later roots borne on the hypocotyl and plumule are negatively
geotropic.
An exceptional case is that of Littorella lacustris^^ in which
the seeds remain in situ. The gynaecea are borne close to the
axis, between the leaves, near the base of the little plant. On
FIG. 159. Zannichelliapolycarpa, Nolte. A, L.S. fruit (x 15) ; a = stigma; 6 = coty-
ledon; h = hypocotyl; A = vascular tissue; r = primary root; p = plumule.
B, cotyledon emerging from fruit (x 6). C, seedling (x 4); rh = root hairs.
[Raunkiaer, C. (1896).]
the death of the parent, the fruits are left surrounded by the
decaying remains; they germinate where they were produced,
only being dislodged in rare instances. The somewhat similar
behaviour of Cymodocea aequorea has been discussed on p. 127.
1 Fauth, A. (1903).
xix]
BULL NUT
247
FIG. 160. Trapa natans, L. i, L.S. through seed (Enlarged); Co^, the larger and
Co2 the smaller cotyledon; St, stalk of larger cotyledon. 2 and 3, seedlings (Re-
duced) ; A, shoot arising in axil of smaller cotyledon; W, roots arising in the region
of the leaf insertions. [Goebel, K. (1891-1893).]
248 SEEDS OF AQUATICS [CH.
In the case ofFarmeria metzgerioides, one of the Podostemaceae,
germination of the two-seeded, indehiscent fruit also occurs in
situ'1.
The seedlings belonging to certain floating plants owe their
station at the water surface to the early development of some
type of buoyant organ : in the case of Lemna, for instance, the
cotyledon itself acts as a float (Fig. 52, p. 81). The seedlings
of certain plants which are rooted at maturity, are capable of
developing to a considerable extent
while still unattached. Some seeds of
Limnanthemum nymphoides* were kept
in water over a winter by the present
writer, and on February 1 1 , one of
them was observed to have germinated
while floating.
It is a somewhat remarkable fact
that the large group of the Monocoty-
ledons which are known collectively as
the Helobieae or Fluviales — the Alis-
maceae, Butomaceae, Hydrocharita-
ceae, Juncaginaceae, Aponogetonaceae,
Potamogetonaceae and Naiadaceae —
are uniformly characterised by the
absence of endosperm and by a *ma-
cropodous ' embryo, in which the hypo-
cotyl reaches excessive proportions (e.g.
Zannichellia, Fig. 159, p. 246, Zostera,
Fig. 1 6 1, Ruppia, Fig. 1 66, p. 3 1 9) ; in
almost all other features the members
of the group show great range and
diversity. Except the Helobieae, the Monocotyledons may be
said, in general, to be characterised by the possession of endo-
sperm. The surmise suggests itself that possibly there may be
some connexion between water life and an exalbuminous seed
with an enlarged hypocotyl. The predominance among aquatics
1 Willis, J. C. (1902). 2 Fauth, A. (1903).
B
FIG. 161. Zostera marina, L.
Fruit in longitudinal section.
(XI5-) /£= fruit coat; fs=
seed coat; r= primary root;
rh= hypocotyl which at its
base enwraps the cotyledon a.
[Raunkiaer, C. (1896).]
xix] MACROPODOUS EMBRYOS 249
of seeds with elaborate and impervious coats, seems to indicate
that plants with imperfectly protected embryos have been unable
to enter upon aquatic life. Possibly there is a danger of rotting
if the contents of the seed are at all freely exposed to the water.
If this is so, it may be that an embryo which keeps its reserves
inside its own tissues is better adapted for water life than one
whose storehouse is outside its own body, even if it is enclosed
in a resistant coat; the food is probably more secure from the
depredations of Bacteria and from other harmful external in-
fluences, if it is incorporated within the cells of the embryo
instead of being merely surrounded by the testa. In the opinion
of the present writer, Monocotyledons have, in general, re-
duced their seed-leaves to a single cylindrical or tubular struc-
ture by means of the fusion of the petiolar or sheathing regions
and the loss of the blades. They are thus not in a position to
store food in the laminae of the cotyledons, as is done, for in-
stance, in the case of such Dicotyledons as the Pea or the Bean.
The radicles of aquatic seedlings are, as we have already shown,
markedly reduced, so a second possible location for food storage
is thus eliminated. In this connexion we may recall the fact
that, whereas mature Dicotyledons often store food in their
tap roots (e.g. Carrot, etc.) this method is unsuitable for Mono-
cotyledons, owing to the ephemeral nature of the primary
radicle, and they are hence almost wholly restricted to storage
in leaf structures, stem structures, or adventitious roots. We
are thus left with the fact that if a Monocotyledonous embryo
is to store its food in its own body, the only region where this
can be conveniently accomplished is the hypocotyl, since both
cotyledon and primary root have suffered reduction. From
these considerations we may perhaps conclude that the non-
endospermic type of seed with a macropodous embryo, whose
hypocotyl has become enlarged for food storage, represents a
form of Monocotyledonous seed which is particularly well fitted
for aquatic life.
PART III
THE PHYSIOLOGICAL CONDITIONS OF
PLANT LIFE IN WATER
" For the student of the conditions of aquatic life, the real inquiry has
yet to be begun."
H. B. Guppy, 1896.
253
CHAPTER XX
GASEOUS EXCHANGE IN WATER PLANTS
THE problems which a water plant has to solve, in
connexion with its assimilation and respiration, differ
widely from those which confront a terrestrial plant, since,
instead of being surrounded by atmospheric air, it passes its
life in water holding only a certain amount of air in solution.
Owing to the varying solubility of the atmospheric gases, the
dissolved air differs from free air in composition. At 15° C.,
the proportions in which the constituents should occur have
been calculated to be as follows1 :
FREE AIR DISSOLVED AIR
Carbon dioxide 0-04% 2-19%
Oxygen 2O-8o% 33-98%
Nitrogen 79- 1 6% 63-82%
In practice, however, the air dissolved in the surface layers of
the water of lakes and streams, under natural conditions, yields
varying figures when analysed, but all observers appear to agree
that, as regards carbon dioxide it is supersaturated, sometimes
highly so2. It seems clear that the excess cannot be obtained
by diffusion from the air, for an American writer3, who has
experimented with Elodea canadensis^ has shown that sufficient
carbon dioxide to keep this plant growing, or even alive, does
.not diffuse into water exposed to atmospheric air at Baltimore
during the winter months. He demonstrated that all the carbon
1 Devaux, H. (1889). The proportion of nitrogen given in this table
naturally includes the other inert gases which were not distinguished in
Devaux's time; the amount would be more correctly stated as including
approximately 78 per cent, of Nitrogen and I per cent, of Argon.
2 Forel, F. A. (1892-1904); Regnard, P. (1891).
3 Brown, W. H. (1913).
254 GASEOUS EXCHANGE [CH.
dioxide which a 3 -litre jar of water would absorb from the air
at ordinary temperatures, could be used up by ten shoots of
Elodea in two minutes. His view is that the substratum serves
as the chief source of carbon dioxide for submerged plants, the
amount of this gas given off into the water from soil containing
organic matter being greater than that obtained by diffusion
from the air.
Whether the excess of carbon dioxide is, in general, derived
from the substratum, or whether it is due to the oxidation of
carbonaceous substances in the water or to other causes, the
fact remains that hydrophytes growing under natural conditions
live in an environment particularly rich in carbon dioxide. This
advantage tends to be neutralised, however, by the slow diffusion
of gases in water. There is also the further drawback that the
absorption capacity of water sinks as the temperature rises, so
that, in warm weather, when the life processes of the plant are
proceeding most vigorously, the supply of carbon dioxide is
reduced1. Assimilation is nevertheless remarkably active among
water plants, several features which they commonly show being
well suited to the prevailing conditions ; one of these is the deve-
lopment of chlorophyll in the epidermal cells, so that the epi-
dermis forms part of the assimilating system, which is thus not
shut off from the surrounding medium by a layer whose func-
tion is purely protective, as in the case of terrestrial plants.
Cuticle is relatively little developed, and the cell-walls seem to
offer no more hindrance to the direct passage of dissolved gases
than if they were merely thin plates of water2. That the waxy
cuticle of such leaves as those of the submerged Potamogetons
is no obstacle to the entry of liquids, has been proved by plas-
molysis experiments in which the whole leaf was used3.
Submerged plants show various characteristics which have
the effect of increasing the surface relatively to the volume of the
leaf, and thus bringing a large proportion of the assimilating
cells into direct contact with the dissolved carbon dioxide. The
1 Goebel, K. (1891-1893). 2 Devaux, H. (1889).
3 Sauvageau, C. (iSgi1).
xx] LACK OF OXYGEN 255
leaves may, for instance, be very thin, but extensive in area, a<s
in the case of the submerged leaves of the Waterlilies, or they
may be sub-divided into hair-like segments, as in Myriofhyllurr. }
etc.1 In certain Podostemaceae belonging to the genus Oenone2,
curious hair-like outgrowths, rich in chlorophyll, are developed
on the leaves (Fig. 81, p. 119). These outgrowths, from their
presumed analogy with the breathing organs of water animals,
have been called gill-tufts (Kiemenbiischel), though it has not
been proved that they possess a respiratory function. The
negatively geotropic roots of Trapa natans^^ the Bull Nut (Fig.
1 60, p. 247), provide another example of a finely divided sub-
merged organ, by means of which gaseous exchange can readily
take place. The intimate contact achieved between these organs
and the water, probably assists not only assimilation but also
respiration.
It is true that dissolved air is richer in oxygen than atmo-
spheric air, about one-third of its volume consisting of this
element, but the essential point to bear in mind is that the
total volume of air held in solution in water at ordinary tempera-
tures is so extremely small that in a litre of water the maximum
amount of oxygen present is 10 cubic cms., as compared with
more than 200 cubic cms. in a litre of atmospheric air4. The
result is that water plants have considerably less oxygen at
their disposal in each unit volume of the surrounding medium
than is the case with land plants3; as far as hydrophytes are
concerned, oxygen is a rare and precious commodity.
Thus, on account of the poverty of the medium in this
element, no plant can be a successful aquatic unless it has a
special capacity either for obtaining an adequate oxygen supply,
or for husbanding it when obtained.
Every green plant forms oxygen as a by-product of carbon
1 See Chapters xi and xn.
2 Goebel, K. (1891-1893) and Matthiesen, F. (1908).
3Goebel, K. (1891-1893).
4 Regnard, P. (1891) ; see also Forel, F. A. (1901).
256 GASEOUS EXCHANGE [CH.
assimilation, through the disintegration of carbon dioxide1.
The greater part of the oxygen, in the case of terrestrial plants,
is at once returned, by means of the stomates, to the atmosphere
whence it came. But water plants show a marked tendency to
retain this element, and we find that their tissues are generally
penetrated by an elaborate system of intercellular lacunae, by
means of which the oxygen evolved in the assimilating cells
presumably finds its way to other parts of the plant, where it
may be used for respiration2. The aerating system arises very
early, as it also does, indeed, in many terrestrial plants; we
find, for instance, that, in the growing apex of the stem of
Elodea, there is a network of intercellular spaces reaching to
within two or three cells of the summit, while, in the winter-
buds of Myriophyllum, a complete ring of large air canals occurs
only i mm. from the stem apex3. In many water plants the
air system is so elaborately developed that almost all the cells
are in contact with the internal atmosphere by means of some
part of their surface. Unger4, who has measured the quantity
of air contained in various plant tissues, finds that 71-3 per cent.
of the volume of the leaves of Pistia Stratiotes^ L., the floating
River Lettuce, is occupied by air, while in land plants, especi-
ally xerophytes, the percentage is much lower; for instance,
the leathery leaves of Eucalyptus Preissiana^ Schauer, contain
9» 6 per cent, of air, and the succulent leaves of Begonia hydro-
cotylifoliay Hook., only 3-5 per cent.5
The exception that proves the rule that the tissues of water
plants are characterised by the unusual development of inter-
1 CloeZjS. and Gratiolet, P. (i 850); Cloez,S. (i 863); and later literature.
2 The gases bubbling from wounds in the green shoots of submerged
plants in sunlight have been described as containing about 90 per cent,
of oxygen. Tieghem, P. van (1866).
3 Devaux, H. (1889). 4 Unger, F. (18542).
6 Unger, F. (18542). The leaf of Pistia has no elongated stalk, while,
in the case of Eucalyptus and Begonia^ Unger includes the petioles in
the calculation. This might tend slightly to exaggerate the difference
in the percentages, but, even if corrected for this detail, the figures would
doubtless remain sufficiently striking.
xx] AERATING SYSTEM 257
cellular spaces, is provided by the Podostemaceae, which form
in other respects a highly anomalous group. The members of
this family, which we have discussed in Chapter ix, flourish in
rapidly moving water, even "at the sides of the waterfalls, with
the furious current rushing right over them1." The tissues are
found to include no large lacunae (Fig. 80, p. 1 1 8) and it is pro-
bably for this reason that these plants are confined to water
which, on account of its movement, is necessarily well aerated.
That the constitution of the Podostemaceae does actually
render them dependent on high aeration of the water, is shown
by the fact that, if, owing to a fall in the level of the stream, they
are left behind in a stagnant pot-hole, death quickly ensues1.
In ordinary hydrophytes, living in still or slowly moving
waters, there must be a liability to asphyxiation in the case of
the roots or rhizomes more or less buried in the saturated mud.
The elaborate air-system, developed in the long petioles of such
plants as the Waterlilies, probably plays some part in obviating
this danger. These petioles form the connecting link between
the submerged rhizome and the floating leaves, which not only
themselves produce oxygen in the process of assimilation, but
also have free access to the oxygen of the atmosphere. In many
cases, the air-canals traversing elongated organs, such as stems
and petioles, are crossed at intervals by diaphragms, which are
not, however, air-tight. Their structure is illustrated in Fig. 119,
p. 184, which shows phases in the development of the cells
forming the partitions that, at every node, cross the stem of
Hippuris vulgaris, the Mare's-tail. From these drawings it will
be recognised that intercellular spaces occur at the angles of the
cells, both in youth and age, so that gases can pass freely.
Although it seems to be generally agreed that oxygen is
conveyed by means of the internal air-passages from the assi-
milating organs to other parts of the plant, there is still much
obscurity with regard to the nature and causes of the movements
of gases in water plants. These movements have been studied
more particularly in the Nymphaeaceae. In Nelumbo, for in-
1 Willis,J. C. (1902).
A. W. P
258 GASEOUS EXCHANGE [CH.
stance, a remarkable bubbling of gas from the leaves of an intact
plant may sometimes be observed1, but there seems little agree-
ment among different observers as to the reasons for this curious
phenomenon, or even as to the actual facts of its occurrence2.
The whole subject needs to be reinvestigated by a botanist who
is also a competent physicist. The only point about which there
is some degree of certainty, seems to be that, at least, while
assimilation is actually proceeding, high gas pressures occur in
the air passages. This can be demonstrated by various direct
means, for instance by cutting into the plant beneath the water-
surface, when a stream of bubbles arises from the wound. A
curious piece of indirect evidence, bearing on the same point,
is perhaps worth recalling. It has been shown that, when a
Waterlily petiole suffers from a wound which involves any of the
air-canals, the cells bounding these cavities grow out in the form
of hairs, until they choke the channel3. The suggestion has been
made that this growth is induced by the temporary diminution
of the high pressure in the air-canals, due to their sudden
connexion with the external atmosphere4.
The cause of the high pressure in the canals during assimi-
lation is doubtless to be sought in the continual production
of oxygen, which accumulates in these intercellular spaces. In
the dark, when respiration is the only form of gaseous exchange
that persists, the high pressure is often replaced by a negative
pressure, since the relatively small quantity of carbon dioxide,
produced partly at the expense of the oxygen in the internal
atmosphere, diffuses away with considerable rapidity, in contrast
to the oxygen, which diffuses slowly. The high pressure of the
oxygen, in the lacunae adjoining the assimilating cells, may have
an effect in inducing movement towards regions of lower
pressure, such as the roots and rhizomes, where oxygen is
presumably in great request. Differences of temperature, be-
tween the sun-warmed upper parts of the plant and those in
the relatively cold lower layers of the water, may also have their
effect in causing currents in the internal atmosphere.
1 Raffeneau-Delile,A.(i84i),Ohno,N.(i9io). 2 Ursprung,A.(i9i2).
3 Mellink, J. F. A. (1886). 4 Schrenk, J. (i:
xx] AERATING SYSTEM 259
It has been suggested by Goebel1 that the origin of the
development of intercellular spaces in water plants may be
attributed to the direct action of the medium — an enlargement
of the air spaces resulting mechanically from the pressure of the
gases evolved, which are prevented by the surrounding water
from escaping freely. But he points out that the lacunar system,
thus initiated, has ultimately become hereditary. Some support
is given to Goebel's view by experimental work on amphibious
plants, and by the study of the comparative anatomy of speci-
mens growing under different conditions. It is found, for
instance, that if such a plant as the Water Speedwell, Veronica
AnagalliS) grows with one of its shoots submerged, while the
others develop in the air, the submerged shoot shows an in-
crease in intercellular spaces, as compared with the air shoots2.
But the presence of lacunae is something more than a mere
direct effect of environment, since they persist, even if in a di-
minished form, when aquatics are grown on land. For example,
stems of Peplis Portula^ when grown in water, are characterised
by four large lacunae in the cortex. On examination of plants
growing terrestrially, it has been found that they also show four
lacunae; the only difference between the aquatic and aerial
plant is that, in the former, the bands of tissue separating the
main lacunae are riddled by intercellular spaces, while, in the
latter, they are relatively solid2.
Whatever its origin may be, the aerating system in the stems,
leaves and roots of water plants belonging to the most divergent
cycles of affinity, is developed with a uniformity and an elabora-
tion which undoubtedly indicate that it is definitely related to
the milieu*. It is perhaps scarcely too much to say that the
difficulty of breathing is the principal drawback to life in water,
and that only those plants which have an inherent capacity for
coping with this difficulty, can make their home permanently
in an aquatic environment.
1 Goebel, K. (1891-1893). 2 Costantin, J. (1884).
3 For a consideration of the aerating system from the anatomical
standpoint see Chapter xiv, p. 183.
17—2
[ 260 ]
CHAPTER XXI
ABSORPTION OF WATER AND TRANSPIRATION
CURRENT IN HYDROPHYTES
ONE of the unfortunate results, which followed the
publication of The Origin of Species, was the acutely teleo-
logical turn thus given to the thoughts of biologists. On the
theory that every existing organ and structure either has, or has
had in the past, a special adaptive purpose and " survival value,'*
it readily becomes a recognised habit to draw deductions as
to function from structure, without checking such deductions
experimentally. Many points in connexion with the study of
aquatics, and, notably, the whole subject of the absorption of
water by such plants, have suffered profoundly from this ten-
dency. Two of the most conspicuous anatomical characters of
hydrophytes, as compared with land plants, are the relatively
small amount of cuticle1 on the surface of the epidermis, and
the poor development and lack of lignification of the xylem.
From these facts it has been lightly concluded that submerged
plants, being able to absorb water over their entire surface, have
simply dispensed with the transpiration current from root to
leaf which is universal among land plants, and that their roots
have lost all function except as attachment organs. These ideas
have become text-book platitudes, and may still be found even
in the writings of professed physiologists2, despite the fact that
they have been, to a large extent, refuted by a series of experi-
mental investigations by different observers, the first3 of which
1 Cuticle, though small in amount, is invariably present on the epi-
dermal walls of aquatics. See Geneau de Lamarliere, L. (1906).
2 See for example Hannig, E. (1912), where the author speaks of
submerged plants " bei denen kein Transpirationsstrom existiert."
3 Unger, F. (i 862). For a recent discussion of the subject see Snell, K.
(1908).
CH. xxi] TRANSPIRATION STREAM 261
appeared more than half a century ago. It may further be
recalled that, as early as 1858, a French botanist1 concluded,
from certain experiments, that the transpiration of a terrestrial
plant can continue when it is grown in a saturated atmosphere,
and even when the leafy portion is entirely immersed in water.
It is also known that emersed water plants transpire very freely2.
We shall only find it necessary here to refer to a few of the more
outstanding of the researches which bear directly upon the
transpiration of submerged plants.
The more modern work on the subject may be said to begin
with Sauvageau3, to whom we owe so much of our knowledge
of aquatics. He used for his experiments detached branches of
submerged plants, in which the cut end of the stem had been
sealed with cocoa butter, and all the roots had been removed.
He found that, even under these circumstances, the shoots
could live and prosper and develop fresh buds — thus, up to a
certain point, justifying the current view that water could be
absorbed through the surface of the stem and foliage. He also
performed a converse experiment, by means of which he at-
tempted to prove that, under normal conditions, a definite trans-
piration current, passing upwards to the leaves, occurs in sub-
merged plants. The apparatus used is shown in Fig. 162, p. 262.
It was essentially a form of potometer, modified for use with a
submerged shoot. This experiment, however, as has been pointed
out by a more recent worker4, is open to the criticism that water
may have been passively forced through the plant, owing to the
pressure exerted on the cut surface of the stem by the column
of water in the small tube. It seems as if some slight modifica-
tion of the apparatus might readily be contrived to obviate this
difficulty.
A number of further experiments were devised by Hoch-
reutiner5, of which the following example may be taken as
1 Duchartre, P. (1858).
2 Bokorny, T. (1890) and Otis, C. H. (1914).
3 Sauvageau, C. (iSgi1). 4 Weinrowsky, P. (1899).
5 Hochreutiner, G. (1896).
262
WATER ABSORPTION
[CH.
typical. He employed two branches of Potamogeton pectinatus,
L., arranging one of these branches so that its base, to a
depth of 2 cms., was immersed in eosin solution, while its
summit was in pure water; the second, he placed with its
summit in eosin and its base in pure water. After a couple of
days, sections of these two shoots were cut at various levels,
and it was found that, in the case of the first branch, the eosin
had mounted to a height of 1 5 cms. in the main axis, which was
itself 20 cms. long, and to 13—16 cms. in the lateral branches.
P. pectinatus possesses no vessels, but the xylem lacunae had
water
car
cotton-wool
— water
mercury
getatiKe-— -
Indlar ubber -
water
FIG. 162. Diagram illustrating experiment to show existence of 'transpiration'
current in a submerged plant. [Sauvageau, C. (iSgi1).]
evidently formed the path for the transpiration current, the cell
walls bounding them being alone coloured bright red. In the
case of the second branch, only the epidermis was stained, the
vascular tissue of the leaves and stem being unaffected.
Some experiments, similar in principle to those of Hoch-
reutiner, but more striking in result, were made some years ago
by two Cambridge botanists1. Their work had the advantage of
being carried on in situy so that the natural environment of the
plant was, as far as possible, retained. Potamogeton lucens was
1 Thoday, D. and Sykes, M. G. (1909).
xxi] TRANSPIRATION STREAM 263
chosen as the subject of the experiments, which were made in the
River Cam during July and August. The method adopted was
to attach a small glass bulb of aqueous eosin solution to the cut
end of a submerged branch. A flourishing, leafy stem was
selected, cut under water and left submerged for a short time.
A little cotton-wool was then wrapped round the stem near the
cut end, the small bulb of eosin brought down to the surface of
the water, and the cut end lifted for a moment above the surface
and inserted in the bulb. The plant was held beneath the water
for a recorded time, and, at the end of the experiment, the bulb
was removed and the stem at once examined. The rate of trans-
mission of the eosin solution was found to be surprisingly rapid
— the eosin travelling, in one case, at the rate of nearly 10 cms.
per minute. In these cut shoots, root-pressure is obviously
eliminated, and the upward stream was found to be due to the
action of the leaves ; the entire removal of the leaves rendered
the current almost negligible, while, when some were cut off,
the diminution in the rapidity of flow was roughly proportional
to the number removed.
Such experiments as these seem to leave little room for doubt
that an active water-current from base to apex, corresponding
to the 'transpiration' current of land plants, occurs even in
entirely submerged aquatics, or, in other words, that the absorp-
tion of water is polarised in the plant. Those who have denied
the existence of the transpiration stream, have been led to do so
rather on the a priori ground that such a current would be
a superfluous feature in the economy of a plant surrounded by
" water, water everywhere." This would in any case be a dan-
gerous method of argument, and it is based moreover upon a
misconception of the value of the transpiration current. Its use
is not merely to supply the tissues with water, but also to convey
to the assimilating and growing regions certain important ele-
ments of their food supply. Even the soil-water contains salts
in solution in quantities that are relatively minute, and the
only method whereby an adequate salt supply can be ensured
is by the passage of a proportionately large volume of water
264 ABSORPTION OF WATER [CH.
through the plant. Further, in the case of submerged aquatics,
the transpiration stream is, for two reasons, of even greater
importance than in the case of terrestrial plants. Firstly, it has
been shown that the water, in which submerged plants live, is
generally still poorer in saline matter than that which percolates
through the soil1, and, secondly, there seems some reason to
suppose that submerged plants depend upon their transpiration
stream, not only for their salts, but also, possibly, for some part
of their carbon dioxide supply. We have noted the possible
importance of the substratum as a source of carbon dioxide2
and, since this gas diffuses slowly, it is reasonable to suppose
that the water absorbed by the roots from the soil may be richer
in carbon dioxide than that in which the leaves are immersed.
Hence it is not impossible that the transpiration stream in
submerged plants may have its value in connexion with carbon
assimilation3.
The existence of a transpiration current throws light upon
the otherwise inexplicable fact that many submerged plants have
an elaborate system of roots, often bearing well-developed root-
hairs. In the case of some Potamogetons, for instance, the root-
hairs are said to survive and play their part after the death of the
other cells of the piliferous layer4. Such a root system could
scarcely be needed merely for purposes of anchorage, and, fortu-
nately, we now have direct experimental proof that it serves
also for absorption. An American observer, Raymond H.
Pond5, by means of an ingenious piece of apparatus, succeeded
in actually measuring the water taken up by an individual root
of one of the submerged Water Buttercups. The root in ques-
tion, which was 14 cms. long and clothed with root-hairs, was
found to absorb 5 cubic cms. of water in 24 hours.
Pond also carried out a number of indirect experiments on
1 Sauvageau, C. (iSgi1). 2 See pp. 253, 254.
3 The work of Brown, W. H. (1913), appears to support this view,
though the author does not himself draw these conclusions, but regards
the roots as mere organs of anchorage.
4 Sauvageau, C. (iSgi1). * Pond, R. H. (1905).
xxi] ROOTED AND ROOTLESS PLANTS 265
the same subject, of which the interpretation is a less simple
matter. He made comparative cultures of certain submerged
species (Vallisneria, Elodea, etc.) rooted in soil, rooted in washed
gravel, or anchored above the soil in such a way that the roots
were unable to penetrate it. He found, throughout, that the
rooted plants grew much better than those that were merely
anchored. Very similar results have been obtained more re-
cently by a German botanist1, whose experiments may be illus-
trated by means of a single example. A number of shoots of
Elodea canadensis were planted under water in soil in which they
were allowed to take root. Another set of shoots, equal in
number and approximately equal in size, were placed in the
same glass receptacle, but were supported above the bottom in
such a way that their roots were unable to penetrate the soil.
After 2 8 days the experiment was interrupted, and the two sets
of shoots were measured. It was found that the rooted shoots
had grown much more rapidly, their total length amounting to
308-0 cms., as compared with 177-5 cms. in the case of those
which had been prevented from taking root in the soil. The
interpretation of these and similar results has been the subject
of some controversy. Pond deduced that the primary cause of
the retarded growth of the non-rooted plants was their inability
to secure enough phosphorus and potassium and possibly
other elements. He found that such plants, in the case of
Vallisneria^ were not only stunted in growth, but had their tissues
loaded with an abnormal amount of starch; he came to the
conclusion that lack of certain salts inhibited proteid synthesis
and growth, though the conditions were favourable to photo-
synthesis. Another American author2 has recently published
results, bearing on this question, which it seems impossible to
reconcile with the views of Pond. He finds that the difference
in growth between rooted and unattached plants can be alto-
gether eliminated by passing carbon dioxide through the water
several times a day. He considers that the non-rooted plants
do not suffer at all from lack of salts, but chiefly from lack of
1 Snell, K. (1908). 2 Brown, W. H. (1913).
266 TRANSPIRATION CURRENT [CH.
the supply of this gas which is given off from soil containing
organic matter. The divergence of these workers* views indi-
cates a direction in which further experimental work of a critical
nature is markedly needed.
A piece of indirect evidence, which confirms, though it does
not actually prove, the existence of a transpiration current in
submerged vegetation, has recently been obtained in connexion
with certain studies on the relative osmotic strength of the cell-
sap in the leaves and roots of the same plant. In terrestrial
species, the osmotic pressure in the leaves has been shown to be,
as a general rule, less than that in the root, a result which is
entirely in harmony with the known facts relating to root-
pressure. In submerged plants (Elodea^ etc.), the same osmotic
relation has also been found to exist, a difference of as much as
four atmospheres being recorded, in one case, between the
pressures in leaf and root1. It seems impossible to explain these
results on the hypothesis that the transpiration current in such
plants is non-existent2.
If it be granted that a transpiration3 current occurs, even in
plants which are entirely submerged, and that this current is,
at least to some extent, dependent on the leaves4, we are at once
confronted with the problem of how the leaves eliminate the
water, since the discharge of water-vapour obviously cannot
occur in the manner characteristic of land plants. For a large
number of submerged plants, though by no means all, the
question has now been elucidated by the work of Sauvageau,
von Minden and other observers5. In many cases the mecha-
1 Hannig, E. (1912). 2 Snell, K. (1912).
3 The word " transpiration " is deliberately used throughout this
chapter, in lieu of " guttation," suggested by Burgerstein, A. (1904) as
more appropriate for submerged plants. The expression, "transpiration,"
is not likely to cause any confusion, and the word " guttation," though
perhaps more strictly accurate in many cases, is too awkward and ugly
to be readily admitted into our language.
4 Thoday, D. and Sykes, M. G. (1909).
5 Oliver, F. W. (1888), Schrenk, J. (1888), Sauvageau, C. (iSgi1),
Wachter,W. (i8971),Minden,M. von (i 899),Weinrowsky, P. (i 899), etc.
xxi] WATER STOMATES 267
nism employed is one which is already very general in terres-
trial plants, namely the development on the leaves of "water
pores" which are able to extrude water in the liquid state1.
These water pores, which occur singly or in groups in the
neighbourhood of the nerve-endings, both in submerged leaves
and on the under side of the floating leaves2, resemble large
stomates which remain permanently open. Beneath them, there
is a marked expansion of the tracheal termination of the bundle,
which is only separated from the epidermis by some layers of
thin-walled turgid cells, known as the epithem. The epithem
tissue is considerably developed in Dicotyledons, but less so in
Monocotyledons. The intercellular spaces between the cells of
this tissue are filled, normally, with water3; the epithem is
believed to act as a regulator, preventing the expulsion of the
drop until a certain root-pressure is reached4. Fig. 53, p. 82,
illustrates the relations of the water pores and associated struc-
tures in the case of a floating leaf — that of Pistia Stratiotes. In
this plant the vigorous excretion of drops of water maybe readily
seen, and we can scarcely doubt that, in the case of submerged
leaves furnished with the same mechanism, the expulsion of
drops also occurs, though it cannot be directly observed.
It is a curious fact — as yet unexplained — that the water pores
of aquatics are often highly ephemeral, being resorbed and
destroyed while the leaf is still quite young. This occurs, for
instance, in Callitriche^ in which the very young leaf bears two
groups of water stomates at the apex (Fig. 1 63 A^ p. 268). At an
early stage the epidermis in the neighbourhood of the water pores
becomes laden with a brownish, gummy or granular material,
and the cells eventually die. Similar substances are apt to choke
up the intercellular spaces of the epithem, and the mouths of the
1 Burgerstein, A. (1904), enumerates more than 200 genera of flower-
ing plants, belonging to nearly 100 families, in which the extrusion of
liquid water from the leaves, either by means of water pores or apical
openings, has actually been observed. The great majority of these are
land plants. * 2 Schrenk, J. (1888).
3 Volkens, G. (1883). * Gardiner, W. (1883).
268 TRANSPIRATION CURRENT [CH.
water pores, in other aquatics1. Possibly useless or poisonous
substances, carried by the ascending sap, which, in the case
of plants that get rid of their superfluous water through
innumerable stomates, are too much diffused to do damage,
may accumulate to a deleterious degree when they are localised
by the elimination of the water through a relatively small
number of pores. But, whatever its cause, the loss of the water
pores of Callitriche seems more than compensated by the result-
ing development of "apical openings" (Fig. 163 5). The
A
FIG. 163. Callitriche autumnalis, L. A, epidermis of apex of young leaf seen Irom
below with a group of stomates. B, apex of an older leaf seen from below. The
large opening in the epidermis is due to the resorption of five stomates ; below the
opening the small-celled parenchyma is exposed. [Borodin, J. (1870).]
destruction of the two groups of stomates exposes the sub-
stomatal chambers, which communicate directly with the apex
of the vascular bundle, and apparently, through these two
cavities, water is directly extruded.
In other cases the apical openings are said to have no con-
nexion with the destruction of water stomates. The entire tissue
clothing a bundle-end, including the epidermis, disappears,
leaving the tracheids actually emerging at the surface. In
Heteranthera zosterae/olla, water pores and an apical opening
exist side by side, while Fig. 108, p. 167, represents a longi-
tudinal section of the leaf-tip of Potamogeton densus^ in which, by
the death of the apical cells, the median nerve is brought into
direct contact with the water.
That the elimination of water does actually take place
1 Minden, M. von (1899).
xxi] APICAL OPENINGS 269
through the apical openings of submerged leaves, is indicated
by certain observations made independently by two different
workers at the end of the last century1. In the natural situation
of the leaves, it is not easy to devise a means of rendering this
elimination visible, but it is found that, if the level of the water
surface be lowered until the leaf apices emerge into the air,
drops of water appear in the region of the apical opening; if
wiped away they speedily re-form. This phenomenon has been
witnessed in a considerable number of cases — as, for instance,
the submerged leaves of Littorella and Potamogeton crispus — and
we shall probably not be guilty of too great an assumption in
supposing that the same thing goes on when the leaves are
beneath the water surface. The exudation of water from water
pores has been shown, in the case of land plants, to be dependent
upon root-pressure, and the existence of identical pores in
submerged species lends colour to the view that the roots of such
plants are not mere holdfasts, but have to some extent retained
their function as organs of absorption.
Notwithstanding the advances that have been made, many
problems connected with the absorption and elimination of
water by submerged plants remain to be solved. In Hydrocleis
nymphoides, for instance, by the disappearance of a special
transitory tissue at the leaf apex, the tracheids are left communi-
cating freely with an empty space, but this space remains separated
from the water by a persistent roof of cuticle, and can there-
fore play no part in the elimination of water (Fig. 1 64, p. 270)2.
Again, side by side with Zostera^ whose leaves are provided with
apical openings, we have two other marine genera of the Pota-
mogetonaceae, Cymodocea and Posidonia, in which no such open-
ings occur. It seems that we must either suppose that the
elimination of water from the apical openings is of relatively
little importance, or that, in related genera, the main physio-
logical activities of the plant may be differently performed.
In the case of such submerged, rootless plants as Cerato-
1 Minden, M. von (1899) and Weinrowskv, P. (1899).
2 Sauvageau, C. (1893).
270 TRANSPIRATION CURRENT [CH.
phyllum and Utricularia, we are still far from understanding the
mechanism of absorption and elimination. Here the liquid
exchange presumably takes place entirely by means of osmosis
and diffusion. But it should be noted that in both these un-
related genera, which are characterised by the total absence of
true roots, there is a tendency to the production of subterranean
shoots, which perform the function of roots1. This modification
of other organs for subterranean work, appears to suggest that,
in the course of evolution, some disadvantage has followed the
reduction and ultimate loss of the root system, and that an
attempt has been made to replace it.
The insectivorous habit of Utricularia may also perhaps be
correlated with the reduction of the transpiration stream, and
FIG. 164. Hydrocleis nymphoides, Buchen. T.S. leaf passing through the middle of
the apical cavity which remains roofed in with cuticle. [Sauvageau, C. (1893).]
the consequent limitation of the food supply2. This is rendered
more probable when it is remembered that the only other car-
nivorous genus among water plants, Aldrovandia, is also sub-
merged and rootless. The resemblance of the two genera, in
these respects, is the more remarkable since they belong to
widely separated cycles of affinity. Their common insectivorous
habit seems to indicate that a plant, which has dispensed with
an active transpiration stream, needs some compensation for
the loss of food materials involved.
In the present chapter, stress has been laid upon the diffi-
culties besetting a submerged plant in connexion with the
maintenance of a transpiration stream. In conclusion we must
glance for a moment at an embarrassment incurred by such
1 See pp. 88, 89, 96, 97, 2 Cohn, F. (1875).
xxi] MUCILAGE 271
plants, which is the very antithesis of the problem of keeping
up the water supply — namely, the danger that the osmotic
attraction of the cell-sap may draw an excess of water into the
young tissues. A certain feature, occurring widely among water
plants belonging to unrelated families, may possibly play some
part in obviating this risk; this is the development of an outer
layer of mucilage, clothing the young organs, whose epidermis
has not yet matured to a resistant coat1. This slime is secreted
by hairs or scale-like bodies, such as the "squamulae intra-
vaginales2 " occurring so frequently in the leaf axils of aquatic
Monocotyledons. A similar secretion exists in many land plants :
the young leaves of the Dock, for instance, are completely
invested by it. Here, again, its power of delaying the passage
of water, may be of some value to the plant, but, in acting as
a protection against excessive transpiration, it has exactly the
opposite influence to that exerted by the slimy coating of water
plants. It has also been suggested that in the aquatics the
mucilage may serve to prevent the soluble products of assimi-
lation diffusing into the water, or that it may form a protection
against animals and discourage parasitic and epiphytic growths.
These theories, regarding the possible function of the slimy
coating, are not easy to prove or to disprove, but there seems
to be some experimental evidence that, in the case of submerged
plants, the mucilage actually hinders the entry of water, while
the distribution and mode of occurrence of the slime in different
hydrophytes, furnish certain indications indirectly confirming
this view. In some cases the development of mucilage begins
very early, and it is thus present on the surface of the delicate
organs of the seedling: the hypocotyl of Callitriche stagnalis^
for instance, has scarcely emerged from the fruit before the
epidermis shows the first rudiments of the secretory trichomes3.
It has also been observed4 that plants of tender structure, such
as Limnanthemum nymphoides and Polygonum amphibium, retain
their slimy coat to a much later stage than plants of tougher
1 Goebel, K. (1891-1893). 2 Irmisch, T. (18582).
3 Fauth, A. (1903). * Schilling, A. J. (1894).
272 ABSORPTION OF WATER [CH. xxi
habit, such as Potamogeton natans. Again, it is found that all the
Nymphaeaceae have their young leaves clothed with mucilage,
with the one exception of Nelumbo, the Sacred Lotus. In this
plant, on the other hand, the epidermal cells become cuticula-
rised relatively early, and thus are able to exert a protective
function. The mucilage of the Waterlilies may reach extra-
ordinary proportions. In Brasenia Schreberi (pettata)1, for
instance, the thickness of the layer of slime coating the petioles
and flower-stalks may exceed the diameter of the organ itself.
Such an abnormal development can scarcely be regarded as a
useful adaptation, and it is probably safest to look upon the
production of mucilage, both in this and other aquatics, as a
mere by-product of the plant's metabolism, any useful purpose
that is served being purely secondary. There are certain cases
which are particularly difficult to explain on the adaptational
view. In Ceratophyllum^^ for instance, in which the growing
point and young leaves are cuticularised, curious mucilage hairs
occur, but do not seem to give rise to any protective layer. Again,
the trichome-diaphragms, formed across the intercellular spaces
in the petiole of Nymphaea lutea, are clothed with mucilage,
although they are not in contact with water but with the internal
atmosphere3.
The problems in relation to water which confront a terres-
trial plant, all hinge upon the difficulty of obtaining a constant
and adequate supply. In the case of submerged aquatics, on the
other hand, the supply is permanently excessive, and the plant
can only live successfully in this milieu if it possesses the knack
of controlling and regulating its absorption and elimination in
such a fashion that a steady upward stream is ensured, while
the tissues, especially those that are young and delicate, are
preserved from supersaturation.
1 For a detailed account of the mucilage of this plant see Schrenk, J.
(1888), and Keller, I. A. (1893). See Fig. 20, p. 38, for the structure
of the mucilage-secreting hairs.
2 Strasburger, E. (1902). 3 Raciborski, M. (18942).
CHAPTER XXII
THE INFLUENCE OF CERTAIN PHYSICAL
FACTORS IN THE LIFE OF WATER PLANTS
THE physical conditions, under which water plants have
their being, differ widely from those which affect land
plants. We have already considered the special features of the
gaseous exchange and the water supply due to life in a liquid
medium instead of in the atmosphere ; it now remains to discuss
the influence of certain other factors — especially temperature,
illumination and gravity — upon plants growing in water.
When the thermal conditions of land and water plants are
compared, the chief difference is found to be the smaller range
of temperature variation — both diurnal and seasonal — which
aquatics are called upon to endure. Though the truth of this
statement is universally recognised, it is based upon relatively
few exact observations, and further detailed field work is much
needed upon the temperature variation in different types of
waters, and the relation of this variation to vegetable life. A
notable beginning in this direction has been made by Dr
Guppy1, to whom we owe many original observations on the
bionomics of aquatics. He has shown that during a summer
day and night, when the range of shade temperature in the air
may be about 1 1 ° C., the range in the water of a river, such as
the Thames at Kingston, may be as little as about o 8 ° C. The
smaller the stream, the greater the range of variation ; a little
brook, two or three feet across and only three or four inches
deep, may show a variation in 24 hours of about 8° C., that is
to say, about three-quarters of the range in the air, but ten times
the range in the river. Irrespective of the size of the body of
1 Guppy, H. B. (I8941) ; the results in this paper are given on Fahren-
heit's scale, but in the present chapter they are quoted in Centigrade
terms for the sake of uniformity.
A. w. P. 18
274 PHYSICAL FACTORS [CH.
water, depth and velocity are important factors in determining
the extent of the variation ; the more rapid the current and the
shallower the stream, the greater is the daily range.
Besides the changes from hour to hour, the different tem-
peratures, which occur simultaneously at different depths in
the same body of water, must be noted. The heat received by a
water surface is said to be absorbed almost completely (94 per
cent.) by the topmost millimetre of liquid, warmth being con-
veyed to lower layers by means of currents only1. This explains
a curious fact, to which attention is drawn by Guppy2. He
points out that, in a river about 10 feet deep, the temperature
at the surface and bottom are much the same, but that ponds
and ditches differ from rivers in their liability to surface
heating; this becomes especially marked where the water is
crowded with plants, so that even the slight currents, that occur
in stagnant pools, are checked by the mass of vegetation. A
ditch full of plants, on a sultry afternoon, may exhibit a differ-
ence in temperature of 5° C. in nine inches, while a large pond,
4 or 5 feet deep, may be 6° C. to 7° C. warmer at the surface
than the bottom. The result is that, on sunny days, the tempera-
ture of the ponds in the neighbourhood of a river generally
stands some degrees above that of the river itself, and, in the
height of summer, the variation may be nearly 7° C. As
Guppy3 remarks, "Everything in plant-life is behindhand in
a river in comparison with a pond." This difference may pos-
sibly explain certain apparent anomalies in the distribution of
aquatic plants in a single neighbourhood.
Guppy's observations relate only to comparatively shallow
waters; in deep water the currents appear to be, as a rule,
unable to convey the daily heat of the sun to a greater depth
than about 10 metres. Beneath this level1 the temperature
sinks, until, at about 100 metres, it becomes constant at 4° or
5° C. Temperature is undoubtedly one of the principal factors
iMagnin, A. (1893).
2 Guppy, H. B. (1894!), (18943) and (1896).
3 Guppy, H.B. (1896).
xxn] TEMPERATURE 275
regulating the depth at which plants can grow. In deep lakes,
in which the thermometer at 10 metres below the surface
registers about 12° C. in summer, the higher plants are not
found at a greater depth than 6 metres. In peat-bog lakes,
however, the temperature of the lower layers is unusually high
(17° C. to 21° C. at i o metres) and, in these lakes, plants may
be found even at a distance of 1 3 metres from the surface.
When we compare the aquatics of hot and cold countries,
we do not find structural differences corresponding to the
differences of temperature; there is, in fact, a remarkable
uniformity in the general organisation of water plants, whether
they live in tropical or temperate climates. On the other hand,
they differ markedly in their life-cycles, since those in warm
surroundings vegetate continuously, while those which have to
pass through a cold season show the special features associated
with hibernation, which we have discussed in Chapter xvn.
We owe to Guppy the discovery that the rarity, in this
country, of the flowering and fruiting stages in the life-history
of certain hydrophytes, is due to thermal conditions. He has
shown, for instance, that Cer atop hy Hum* requires almost tropical
temperatures for the maturation of its fruit, and that Lemna
gibba^ does not flower except in water which is heated, during
the summer, to a degree unusual in this country. For many
water plants, however, the temperature of optimum vegetative
growth is decidedly low3. It has been recorded, for instance,
that, in the case of a certain canal near Manchester, which is
kept tepid by the entry of hot water from various mills, the
vegetation does not develop with any luxuriance. A Pondweed,
Potamogeton crispus, grows in this canal as a dwarfed variety,
especially near spots where warm water enters4; critical experi-
mental work would, however, be required before we could feel
certain of the fact that this result is due to temperature alone.
To some aquatics, the fact that lakes and rivers remain in
summer cooler than the surrounding atmosphere, may be a
i Guppy, H. B. (1894!). 2 Guppy) H B (j 894.2).
3 Goebel, K. (1891-1893). * Bailey, C. (1884).
18— 2
276 PHYSICAL FACTORS [CH.
drawback, and it has been suggested in this connexion that the
development of anthocyanin, which is so frequent in hydro-
phytes, may be an adaptation for heat absorption1. In con-
sidering the general question of the pigmentation of water
plants, however, it must be remembered that some of the most
striking examples may possibly represent pigmented races
derived from the normal specific form by the loss of an in-
hibiting factor; on this view, they are comparable with certain
coloured varieties well known among terrestrial plants, and
there is thus little reason to suppose that their pigmentation
bears any relation to the aquatic milieu. Nymphaea lutea, var.
rubropetala* for instance may perhaps be compared with the
chestnut-red variety of the Sunflower, while a form of Castalia
albaz^ which has been described as bearing rose-purple flowers,
may be analogous to the red variety of the white Hawthorn.
But, apart from such cases, there are certainly indications that
anthocyanin is formed by water plants with special facility. The
leaves of the Lemnaceae, Hydrocharis, Limnanthemum, and
certain Nymphaeaceae, are often more or less pigmented. The
Podostemaceae4 also, are apt to develop anthocyanin in their
surface cells.
There is, indeed, little room for doubt about the liability
of water plants to produce red and violet pigment, but the
attempt to explain this fact is fraught with difficulty and con-
fusion. The simple teleological explanation which assumes that
the development of anthocyanin is an adaptation for the absorp-
tion of heat rays, is probably far too facile; the fact that the
Podostemads, growing in the tropics, in water which maintains
a constant high temperature, very frequently produce these
pigments, seems to tell against such a view. The few observa-
tions which the present writer has been able to make, do not
seem to harmonise with any general statement about the adapta-
tional distribution of red and violet pigments in water plants.
For instance, in the Forest of Dean (September, 1910) Peplis
1 Ludwig, F. in Kirchner,O. von, Loew, E. and Schroter,C. (i 908, etc.).
2 Caspary, R. ( 1 86 1 ). 3 Fries, £.(1858). 4 See p. n 3.
xxn] ANTHOCYANIN 277
Portula was found growing at the bottom of a deep pool, and
entirely free from anthocyanin; but a number of shoots had
broken off, by the snapping of the brittle stems, and were
floating at the surface, and putting out adventitious roots. In
the case of these detached shoots, there was considerable pig-
mentation, and some of the leaves were quite red. Again, in an
extremely hot sunny summer (August, 1911) in the dykes at
Wicken Fen, many young Waterlily leaves of the floating type,
which were still rolled and had not reached the surface, were
noticed to be brilliantly red.
The whole subject of anthocyanin has recently been dealt
with comprehensively by Miss Wheldale (the Hon. Mrs Huia
Onslow)1. She puts forward the hypothesis that the pigment
arises from a chromogen formed from sugars in the leaf, and
that increase in the amount of carbohydrates leads to increased
formation of chromogen with the resultant production of antho-
cyanin, unless the chromogen be removed. If translocation be
slowed down for any reason, such as low temperature, produc-
tion of pigment tends to occur. This seems entirely consistent
with the facts so far as they relate to water plants. For instance,
in the case of the detached shoots of Pep Us mentioned above,
there would be little possibility of material being rapidly trans-
located from the leaves, because there is nowhere for it to go to ;
Miss Wheldale's theory thus explains the relatively high pig-
mentation of these shoots. In the case also of the Lemnas and
the Podostemads, practically the whole vegetative body con-
sists of assimilating organs. The excess sugar cannot, therefore,
be removed from those organs, and the theory thus fully explains
their liability to coloration. It is also confirmed by the known
fact that the Podostemaceae store large quantities of carbo-
hydrate, which is used up in their rapid flowering period. In
such cases as the Waterlilies, again, the relative coolness of
river or lake water may be a hindrance to rapid translocation
from leaves to rhizome. As regards the supposed functions
of anthocyanin, Miss Wheldale concludes that " For the time
1 Wheldale, M. (1916).
278 PHYSICAL FACTORS [CH.
being we may safely say that it has not been satisfactorily
determined in any one case whether its development is either
an advantage or a disadvantage to the plant." It is therefore
clear that the attractive theory that red coloration is developed
by water plants as an adaptation to their mode of life, must be
definitely abandoned, unless further evidence for its validity
can be produced.
Although water plants live, on the whole, in a more equable
and temperate climate than land plants, yet they are liable in
winter to one very severe ordeal — the freezing of the water in
which they occur. Some escape this trial by their habit of
sinking to the bottom in the cold season, while others are able to
withstand a temperature below freezing point for a long period,
especially when they are in the turion or seed phase1.
The illumination, to which submerged plants are exposed,
is as much affected by the medium as are the thermal con-
ditions. Free-swimming water plants and those with floating
or aerial leaves, on the other hand, receive light in much the
same way as land plants ; as a result of their situation, the leaves
are often exposed to all the available sunshine, mitigated by no
shade whatever. Such plants thus present no problems of
special interest in connexion with their light conditions, and
they may be disregarded in the present discussion, which will
be confined to those that are more or less completely sub-
merged.
The light which reaches a submerged shoot has been reduced
by four factors — reflexion from the water surface, absorption
by the water, and darkening due to certain substances in solu-
tion or to solid particles in suspension2. The absorption and
darkening may be very considerable in the less limpid waters.
It has been shown by experiments with a recording galvano-
meter that 60 per cent, of the light may be absorbed by the
first two metres3. Some observations made in the Lake of
Geneva4, with regard to the limit of visibility, show that a
1 See pp. 220, 243. 2 Goebel, K. (1891-1893).
3 Regnard, P. (1891). * Forel, F. A. (1892-1904).
xxn] ILLUMINATION 279
white disc lowered into the water remains visible to a depth
varying between 6-8 metres in summer and 14-6 metres in
winter. The annual mean was found to be 10-2 metres. This
method is a rough one, but it gives some idea of the penetrating
power of the luminous radiations. The results obtained har-
monise with the observation that chlorophyll may be developed
without loss of intensity by plants living at a depth of 10 metres.
In the Jura lakes, however, which are not very transparent,
some etiolation is produced even at 4 to 5 metres, in the case of
Naias and the submerged leaves of Nymphaea lutea^.
Some hydrophytes are dependent upon direct sunlight; the
Podostemaceae, for instance, are rarely to be found in shady
places where the water does not receive at least some hours
of sunshine during the day2. Certain water plants, on the other
hand, such as species of Utricularia and Ceratophyllum, perish
when exposed to strong illumination3; and, of submerged
plants in general, it is undoubtedly true that the conditions,
under which they live, approximate to those of * shade plants '
upon land4. Their response to these conditions is also similar,
and they share the characteristics of delicacy of lamina, absence
of a well-differentiated palisade-tissue and presence of chloro-
phyll in the epidermis 5. An attempt has been made to trace the
peculiarities of submerged plants to the direct etiolating action
of the obscurity in which they live6, just as it has been suggested
that the aerating system in their tissues was originally due to the
direct effect of the medium7. We may accept this view so far
as to acknowledge that the influences in question may, in both
cases, have played a part in the first initiation of the aberrant
structure of submerged plants, but such direct effects are
scarcely adequate to explain the structure of the most highly
modified forms which have lost the power to live on dry land.
In certain water plants showing heterophylly, the intensity
of the light is one of the factors concerned in determining which
1 Magnin, A. (1893). 2 Willis, J. C. (1902).
3 Goebel, K. (1891-1893). * Schenck, H. (1885).
5 Stohr, A. (1879). 6 Mer, £. (iSSo1). 7 See p. 259.
28o PHYSICAL FACTORS [CH.
type of leaf shall be produced. For example, the submerged
band-shaped leaves of Alisma graminifolium, Ehrh.1 require a
moderate illumination, while the air-leaves flourish in bright
light. In shallow water, in which the plants would, under
ordinary conditions, form air-leaves, the band-shaped leaves
continue to be produced, if the surface of the water happens
to be covered with a layer of Algae which reduces the light. The
influence of sunshine in this case is perhaps only indirect, the
activity of assimilation being probably the critical factor.
The effect of light upon the germination of the winter-buds
of Hydrocharis Morsus-ranae, the Frogbit, has been studied
experimentally2, and it has been shown that it is impossible
for these turions to develop into plantlets, unless they are
exposed to a minimum degree of illumination, which is far
removed from total darkness. The yellow and orange rays prove
to be the most active in promoting germination. But, marked
as is the effect of light on the vegetative growth of the Frogbit,
its influence in connexion with flowering is far more striking.
It has been shown 3 that a set of plants exposed daily from the
spring onwards to nine hours of direct sunlight, produced more
than a thousand flowers between the end of June and the end of
August, while a corresponding set of plants, which were insolated
daily for three hours only, produced no flowers at all. Indivi-
dual plants from this second set, removed and placed in bright
sunshine at the end of June, began to flower in four weeks. By
artificially cooling the water in which the insolated plants grew,
it was shown that these effects were produced by differences of
illumination, and not by the heating influence of the sun's rays.
Darkness seems to inhibit the germination of certain water
plants ; this has been shown in the case of the achenes of Ra-
nunculus aquatilts and the nutlets of Callitriche. The seeds of
Nymphaea lutea^ also, though they are able to germinate in the
dark, do so in far greater numbers in diffuse light. In other
cases, e.g. Potamogeton natans^ darkness favours germination 4.
1 Gluck, H. (1905). 2 Terras, J. A. (1900).
3 Overton, E. (1899). * Guppy, H. B. (1897).
xxn] TROPISMS AND SLEEP MOVEMENTS 281
On the subject of heliotropism, we do not appear, in the case
of water plants, to possess much experimental evidence. The
work of one observer seems to suggest that the heliotropism
of stems is less intense in the case of submerged than of terres-
trial plants1. Positive heliotropism has been recorded for the
leaves of Aponogeton distachyus and A. fenestralis2", the floating
leaves of Trapa natans*, on the other hand, are described as
transversely heliotropic and as owing their horizontal position
on the surface of the water to their response to light. It was
shown, in certain experiments, that, after a week in darkness,
the new leaves, which had unfolded, stood upright out of the
water. In this connexion it has been recalled that, among the
near relations of Trapa, there are land plants with transversely
heliotropic leaves.
The leaves of the water form of Myriophyllu m proserpinacoides
exhibit * sleep ' movements when living submerged. The young
leaves, which, normally, are spreading, rise up at night and
cover the growing point, thus returning more or less to the
position they occupied in the bud. Sleep movements also occur
in Limnophila heterophylla*. The leaves of Myriophyllum and
Ceratophyllum — excluding those of the apical bud — are said
to have the peculiarity of bending downwards on darkening5.
As regards geotropism, aquatic plants seem to be generally
comparable with land plants. In Aponogeton^ for instance, it has
been observed that the leaves are negatively, and the adventi-
tious roots positively, geotropic2. The present writer has, how-
ever, noticed in the case of the seedlings otNymphaea lutea, that
the short-lived primary root, after the earliest stages are past,
shows little response to gravity, sometimes pointing vertically
upwards. But this is probably merely a sign of its early de-
generation and decay. There are also instances of the stems of
water plants, in certain specialised cases, responding to gravity
in the reverse of the usual way. For instance, the lateral
1 Hochreutiner, G. (1896). 2 Sergueeff, M. (1907).
3 Frank, A. B. (1872). 4 Goebel, K. (1908).
5 Mobius, M. (1895).
282 PHYSICAL FACTORS [CH.
branches of Potamogeton pectinatus, when swelling up to form
tubers, become positively geotropic. They bend towards the
soil and bury themselves in it to pass the winter. This has an
important result, because, being lighter than water, these winter-
buds would otherwise be liable to rise to the surface when set
free by the decomposition of the parent plant1. Again, there are
many cases of fruiting peduncles bending downwards and thus
allowing the ovary to ripen under water; a similar curvature
occurs not infrequently in terrestrial plants. Positive geotro-
pism of the fruit stalk is characteristic of the Pontederiaceae2
(Fig. 155, p. 240). Limnobium Boscii is a similar case; here it
has been shown that the geotropic curvature is independent of
fertilization3.
Hochreutiner 4, who has paid special attention to the response
of water plants to certain physical stimuli, has made some obser-
vations on 'rheotropism5,' or reaction to current. He noticed
that, in the case of Zannichellia palustris, where the water was
still, the stem-branches rose erect, as would be expected of a
negatively geotropic organ, but that, where there was a current,
the axes adopted its direction. Hochreutiner observed this in
the case of a current of such slight force that he was convinced
that no mechanical compulsion was exerted, but that the stems
responded to the stimulus by their own activity and might
thus be called positively rheotropic. Roots, on the other hand,
seem to show a tendency to grow against the current. It is
suggested that this sensibility would be useful to the plant,
since it would lead to the roots and stems taking up a position
in which they would be unlikely to be damaged by the pulling
force of the current. Further experimental work on rheotropism
is obviously needed, however, before the subject lends itself
to generalisation. The question is complicated by the fact that
a rapid current alters the conditions of life of the plant very
materially. Differences between the morphology of the same
1 Hochreutiner, G. (1896). 2 Miiller, F. (1883).
3 Montesantos, N. (1913). 4 Hochreutiner, G. (1896).
5 This term was suggested by Jonsson, B. (1883).
xxn] PETIOLE LENGTH 283
species, when grown in still or moving water, are possibly due,
in some cases, to the better aeration of water which is in motion.
Such differences are markedly exhibited by Myriophyllum^^
which in still, small pools may have leaves whose segments are
very tender and almost hair-like, while in strongly flowing
water they are shorter and firmer.
One of the most interesting problems connected with the
tropisms of water plants, is the question of the influences which
regulate the length of the petiole in the case of floating leaves.
It is a matter of common observation that, in plants such as
the Waterlilies, the length of the petiole varies with the depth
of the water. The accommodation begins at the youngest stages,
for, if the seeds of Castalia alba* are planted at different levels
in the mud, the length of the first internode, the acicular first
leaf, and the petiole of the second leaf, adapt themselves most
remarkably to their circumstances, elongating until they are
long enough to raise the leaves well into the water (Fig. 13,
p. 28).
In free-floating plants, such as the Frogbit (Hydrocharis
Morsus-ranae\ this power of accommodation to depth is also in
evidence, though it is naturally less conspicuous. The Frogbit
has gained notoriety in the present connexion, since it was the
subject of an oft-quoted series of experiments by Frank3. Its
petioles are normally 6 to 8 cms. long, but when grown in
shallow water they may not exceed i cm. If the plant is
attached to the bottom of a deep glass vessel, on the other hand,
very long petioles may be produced, a length of nearly 14 cms.
being recorded in one case. Frank obtained a sensational con-
trast in petiole length, by growing a plant in a deep jar until its
youngest leaf had succeeded in reaching the surface by elon-
gating its petiole to 1 1 cms. It was then transferred to a shallow
vessel in which the terminal bud was only just covered. The
next leaf produced a petiole 1-5 cms. long, i.e. less than 14 per
cent, of the length of the preceding leaf-stalk.
1 Schenck, H. (1885). 2 Massart, J. (1910).
3 Frank, A. B. (1872).
284 PHYSICAL FACTORS [CH. xxir
Both common observation, and critical experiments such as
these, leave no room for doubt about the fact that accommodation
of petiole-length to water-depth does actually occur; but when
we pass on to the question of the factors which bring about this
accommodation, by causing cessation of growth at the appro-
priate moment, we find ourselves on controversial ground. One
point seems to be uncontested — namely that, in the case of
Hydrocharis, the regulation is not due to the change in light
intensity, for even in darkness the petioles grow only to exactly
the right length to bring the blade to the surface. Frank's
experiments led him to the conclusion that, when the lamina
reached the water-surface, the lowering of pressure, due to the
absence of a superincumbent layer of water, was the physical
factor which gave the signal to the petiole to cease growth.
However, the repetition and critical analysis of Frank's experi-
ments seem to have shown clearly that his deductions cannot
be accepted. Karsten1, using Ranunculus sceleratus^ Marsilea
and HydrochariS) showed that if tubes of oxygen-free air were
inverted over individual leaves, the growth of the petiole con-
tinued after the lamina had come in contact with the gas, in-
stead of ceasing, as it did under normal conditions, as soon
as the lamina reached the surface. His experiments seem to
justify the conclusion that it is contact with the oxygen of the
atmosphere which checks the further growth of the petiole,
but we have no conception of the exact nature of the process by
which this inhibition is brought about.
1 Karsten, G. (1888) ; see also Vries, H. de (1873).
285
CHAPTER XXIII
THE ECOLOGY OF WATER PLANTS
THE study of the relation of plants to their habitats,
of their different forms of association with one another,
and of their applied physiology in general, is at the present
day commonly included under the name of 'Ecology/ around
which a complicated system of other technical terms has grown
up. But, though the ecological language is new, the ecological
standpoint and even the special ecology of water plants, are as
old as the science itself. Theophrastus (370 B.C.— 285 B.C.),
whose writings form our earliest botanical classic, distinguishes
water and marsh plants as a biological group and classifies them
according to their varieties of habitat1.
In a country such as Great Britain, where cultivation of the
land, grazing of flocks and herds, and the numberless activities
of man, have reduced the terrestrial plant population to a mere
disheartening semblance of its former self, the vegetation of the
waters has preserved, in many cases, a closer approximation to
its original condition. Despite periodical disastrous clearances,
ponds and streams, even in highly cultivated regions, some-
times show a fairly natural grouping of their inhabitants, while,
on dry land, such a grouping can often only be discovered in
remote districts, such as our few remaining areas of virgin fen
and forest.
At the present day a voluminous literature has come into
existence dealing with ecological topics, but it must be confessed
that, as regards water plants, the results attained are, on the
whole, scarcely of first-rate importance. On analysing the work
in question, one is led to the conclusion that the chief service,
which Ecology has rendered to the study of water plants, has
probably been in emphasizing the influence of the substratum
1 Greene, E. L. (1909).
286 ECOLOGY [CH.
and of the degree of aeration of the water in determining the
distribution of aquatics1. It might have been supposed that the
nature of the soil, underlying the water in which hydrophytes
grow, would be relatively unimportant, but, on investigation, it
proves to be a factor of almost as much significance as in the
case of terrestrial plants. It is true that there are certain ex-
ceptions, such as the Podostemaceae, which seem indifferent
to the chemical composition of the naked rocks on which they
live2, but this case may perhaps be explained by the fact that
the rapidly flowing waters, to which they are confined, probably
owe little of their dissolved constituents to the particular rocks
over which they are passing at any given moment. The majority
of hydrophytes, however, show definite preferences and aver-
sions in the matter of the soil underlying the water in which
they grow, and of the resulting differences in the nature of the
solution in which they are immersed.
A case has been described in America, in which the depen-
dence of water plants upon the substratum is shown with dia-
grammatic lucidity3. Lake Ellis in North Carolina is an area
of shallow water, 2 J by 3 miles across, and seldom more than
two feet in depth ; the entire floor is clothed with plants. Three
distinct assemblages of vegetation occur in the Lake, the differ-
entiation apparently depending wholly on the nature of the soil.
The central region, where the soil is sandiest, is characterised
by Eriocauloti) E I eo charts und. Myriophyllum \ a number of different
plants, including one or two Waterlilies, frequent the inter-
mediate muddy belt, while the marginal area of muddiest soil
is chiefly clothed with Grasses and Sedges. The observation,
made long ago by a German writer4, that the variety of Hydrilla
verticillata found in Pomerania is intolerant of sandy soil and
is confined to muddy clay, is comparable with the facts just
cited concerning Lake Ellis.
The two classes of substratum which offer the most marked
contrast, as regards the flora which they support, are the cal-
1 Tansley, A. G. (1911). 2 Willis, J. C. (iQH1).
3 Brown, W. H. (191 1). 4 Seehaus, C. (1860).
ZONATION 287
careous and the peaty. Certain water plants are decidedly
calcophil; Stratiotes aloides^ is one of these cases, while another
is Scirpus /acusfris2, which has been recorded as absent or rare
in the Vosges, while it becomes common when the streams from
this mountain region reach the Loess alluvium. When the
substratum is peaty, on the other hand, the humous acids break
up the calcium carbonate, thus rendering the water untenable
for lime-loving plants but favourable for others, which are able
to live in a solution poor in mineral salts, such as Lobelia^
Littorella and Isoefes*. Those plants which can tolerate peaty
water, enjoy the great advantage of freedom from the ravages
of Water-snails4.
Lists have been drawn up of the hydrophytes frequenting
stagnant and slowly flowing waters in this country, showing
that a different assemblage of plants is characteristic of each of
these habitats5. This difference is probably due primarily to
variations in thejieration. In extremely stagnant waters, which
contain mucIT decaying organic matter and are poorly aerated,
the higher plants rarely appear. The Lemnaceae, however, form
an exception to this rule, since they not only tolerate, but
actually require, certain soluble products of organic decom-
position. It has been shown that normal growth and multi-
plication cannot be sustained in Lemna minor for any length
of time in the absence of certain organic, growth-promoting
substances, or auximones6.
A subject on which great stress is laid in descriptive eco-
logical studies, is the "zonation" of the hydrophytes which
characterises very many water areas. As a typical example we
may refer to Magnin's 7 description of the Jura Lakes, where the
plants are distributed with great regularity. Passing inwards
from the shore, the following order is generally observed. There
is, firstly, a littoral zone of plants standing out of the water —
1 Davie, R. C. (1913). 2 Kirschleger, F. (1857).
3 West, G. (1905), (1908), and (1910). 4 West, G. (1908).
5 Tansley, A. G. (1911).
6 Bottomley, W. B. (1917); see also p. 81. 7 Magnin, A. (1893)
288
ECOLOGY
[CH.
Phragmites followed by Sdrpus lacustris\ next, a belt of plants
with floating leaves, among which Nymphaea lutea is the domi-
nant species, and, still farther from the shore, a zone of plants
with leafy shoots reaching to the water surface, or nearly, con-
sisting mainly of Potamogetons. To this succeeds a region in
which the upper layers of the water are free from vegetation,
while the grappling iron brings to light various plants which
grow on the bottom, such as Ceratophyllum, Naias, Chara and
Nitella. Fig. 165 shows, in the form of a section, the essentially
similar zones of vegetation in the White Moss Loch in Perth-
shire1.
AIRA WESPITOSA
'SPIRAEA
; ICALICJM PALUSTRE
C.AMPULLACEA
PHRApMITES
C./1HPULLACEA
. FIUFOI?MI5i POT/IMOCETpN HETEROPHVLLUS
J HEWANTHES
PiTRICHO{DES P PEWOLMTUS
•NITELLA
FIG. 165. Section nearly N. and S. across White Moss Loch, Perthshire, showing
relations of plants to water environment. [Matthews, J. R. (1914).]
One of the chief reasons determining this zonation seems to
be that plants with floating leaves can only flourish if guarded
from the wind. For this reason they generally do not occur at
a great distance from the shore, except in very sheltered basins,
and often obtain the necessary protection by growing among
reeds. It has been pointed out that in the larger English Broads,
the "floating-leaf association" is almost coterminous with the
"open reed-swamp2," while in Lake St Clair (Michigan) pre-
cisely the same thing occurs, the plants with large floating leaves
all belonging to the " Phragmitetum3." In the case of the White
1 For recent views on ecological classification of aquatics, see
Pearsall, W. H. (1917-1918) and (1918).
2 Pallis, M. inTansley, A. G. (191 1). 3 Pieters, A. J. (1894).
xxm] COLONISATION 289
Moss Loch, it has been recorded that the floating leaves of
Potamogeton natans cover the surface in the parts of the loch
which are protected from the prevailing winds; where the
water is much exposed, however, such broad-leaved plants are
absent, their place being taken by Myriophyllum^ whose highly
divided foliage is uninjured by wave-motion1. Submerged
plants, as a rule, form a special zone farther from the shore than
the floating-leaf association, because the latter shades the lower
layers of the water so much that the subdued sunlight, that
penetrates it, is insufficient to supply a deeper flora. An ex-
ception to this rule is afforded by Aldrovandia vesiculosa, a
typical shade plant, which grows among reeds, or protected
by the leaves of Waterlilies, in order to secure the dim light
which suits its requirements2.
In addition to the examination of well-established aquatic
floras, another branch of the ecology of aquatics consists in
the study of the process of colonisation of newly formed waters.
We shall return in the next chapter to the methods by which
this colonisation is achieved, but we may mention here an
account, recently published by a Cambridge botanist3, of an
ecological experiment on a large scale which was carried out in
the fen country, by Nature herself, not long ago. In January,
1915 an area of about 24 square miles became inundated, and
remained under water for nine months, until re-drainage was
accomplished; it was thus temporarily restored to something
like its original aquatic conditions. Even in the brief period
in question, water plants invaded the area, but, somewhat un-
expectedly, the new flora was confined mainly, as far as flower-
ing plants were concerned, to two species, Alisma Plantago and
Polygonum amphibium. Those were present in abundance and
tended locally to form "closed associations."
The effect of altitude above sea level upon the water vege-
tation, may be considered as coming within the purview of
1 Matthews, J. R (1914). 2 Hausleutner, (I85O1).
3 Compton, R. H. (1916).
A. W. P. IQ
290 ECOLOGY [CH.
ecology1. It is a matter of common knowledge that the land
flora suffers great changes in the passage from the lowlands to
the mountains, until an Alpine flora is reached, whose facies is
totally different from that of the plains below. The hydrophytes,
on the other hand, show singularly little change, though the
number of species diminishes rapidly as high altitudes are
approached. In Scotland, West2 has pointed out that, if a high-
land loch is well sheltered and possesses a good shore and water
not too poor in mineral salts, its flora may scarcely be distin-
guishable from that of a lowland basin. In the Jura, to take a
Continental example, sixty lakes were investigated by Magnin3,
who showed that out of thirty species of hydrophytes, twenty-
four were common to all these basins, whose heights ranged
from 200 to 1000 metres above sea level. Tansley4, again, has
drawn attention to the fact that the plants recorded by Graebner5
from sandy pools in the barren heaths of North Germany —
Isoetes, Littorella, Lobelia^ etc. — are the same as those occurring
in Britain in mountain lochs, and suggests that this indicates
that the poverty in mineral salts, common 'to both types of
locality, has more influence than the actual altitude in deter-
mining the flora.
In the Alps many aquatics reach considerable heights. In
the Upper Engadine6, Ranunculus trichophyllus has been found
at above 2500 metres, and a Potamogeton, a Callitriche and
Hippuris vulgaris at above 2000 metres. These plants have thus
an astonishing range of altitude, since they abound, on the
other hand, almost at sea level in the English fens. Outside
Europe, the same great range is also observed. In South
America near Chimborazo7, Myriophyllum, Lemna and Calli-
triche have been recorded at a height of above 2400 metres. The
1 Overton, E. (1899) has shown that the data on this point given by
Schenck, H. (1885) have little value, since the altitudes which he names
are, in reality, much exceeded.
2 West, G. (1908). 3 Magnin, A. (1893).
4 Tansley, A. G. (191 1). 5 Graebner, P. (1901).
6 Overton, E. (1899). 7 Spruce, R. (1908).
xxm] ALTITUDE 291
genus Isoetes, like the flowering plants just mentioned, shows
great indifference to altitude. One species, /. amazonica, Mgg.,
was found on the river margin at Santarem in the lowlands,
while another occurred at about the same latitude on the cold
Paramos of the Andes at nearly 3700 metres1. In India, Lemna
minor has been recorded at Laboul at a height of above 2900
metres2. In Venezuela and Tibet, Potamogetonpectinatus, which
flourishes at sea level in England, has been found at heights of
above 5000 metres3.
The term Ecology is used by some botanists in a sense so
wide that it becomes almost co-extensive with out-of-door
Botany in general. But, if we limit our consideration to that
branch of plant study which strictly deserves the name, it does
not appear, as far as the present writer is able to judge, that
any general ideas of the first importance, bearing upon the
study of water plants, have emerged from it, beyond those to
which allusion has been made in this chapter. At present
Ecology has scarcely passed the stage of a merely descriptive
branch of the science; indeed one of its chief promoters4 de-
scribed it, a decade ago, as "still in its infancy." When it has
become more closely linked up with Physiology, we may look
to it for further help in solving the complex problems presented
by the life of hydrophytes 5.
In conclusion, it may be suggested that there is room, in the
case of aquatic plants, for ecological work of a rather different
character from that usually attempted — namely, a study of the
changes occurring from year to year in the Angiospermic flora
1 Spruce, R. (1908). 2 Kurz, S. (1867).
3 Ascherson, P. and Graebner, P. (1907).
4 Warming, E. (1909).
5 In addition to the references given in the course of this chapter, see
Bruyant, C. (1914), Massart, J. (1910), Moss, C. E. (1913), Nakano, H.
(1911), Pieters, A. J. (1902), Preston, T. A. (1895), Roux, M. le
(1907), Schorler, B., Thallwitz, J. and Schiller, K. (1906), Schroter, C.
and Kirchner, O. (1902), Thiebaud, M. (1908). On the cultivation of
water plants see Monkemeyer, W. (1897).
19 — 2
292 ECOLOGY [CH. xxm
of the same waters. These changes seem to be much more
notable and rapid than those occurring among terrestrial plants
in corresponding periods. In certain dykes and ditches, which
the present writer has had under more or less continuous obser-
vation for some years, various species appear, disappear, and
reappear, in a fashion which seems at first glance wholly erratic,
but which might, on thorough study, yield results which would
throw some light upon the problems of dispersal and distribu-
tion.
PART IV
THE STUDY OF WATER PLANTS FROM THE
PHYLOGENETIC AND EVOLUTIONARY
STANDPOINTS
" The theorem of Organic Evolution is one thing; the problem of
deciphering the lines of evolution, the order of phylogeny, the
degrees of relationship and consanguinity, is quite another. Among
the higher organisms we arrive at conclusions regarding these things
by weighing much circumstantial evidence, by dealing with the
resultant of many variations, and by considering the probability
or improbability of many coincidences of cause and effect; but
even then our conclusions are at best uncertain, our judgments
are continually open to revision and subject to appeal, ..."
D'Arcy Wentworth Thompson, Growth and Form, 1917.
295
CHAPTER XXIV
THE DISPERSAL AND GEOGRAPHICAL
DISTRIBUTION OF WATER PLANTS
THE most striking character of the geographical dis-
tribution of water plants is, in general, their remark-
ably wide range1. Countless instances might be cited, but it
may perhaps suffice to refer, as examples, to Potamogeton crispusy
which occurs in Europe, Asia, Africa, America and Australia,
and to Ceratophyllum demersum and Lemna minor, which are also
found almost all over the world. Of the twenty-two genera of
Lythraceae, again, only five are common to both hemispheres
— Rotala, Ammania^ Pep/is, Lythrum and Nesaea — and these
five all characteristically frequent water or marshy ground2. The
wide distributions of aquatics often include occurrences on
islands which are some distance from other land surfaces; Lemna
trisuha, for example, which is found in Europe, Asia, North
and South America, Australia and Africa, penetrates to Mauri-
tius, Madeira, the Azores and the Canary Islands. The most
marked exception to the rule of the wide distribution of hydro-
phytes is furnished by the Podostemads3, many of which inhabit
extremely restricted areas. The Brazilian river Araguay, for
instance, has three sets of cataracts, each of which is populated
by an almost entirely different group of species belonging to
this family. Seven species of Castelnavia occur in this river,
although the genus is almost unknown elsewhere.
If we except the Podostemads, the generalisation certainly
holds good that aquatic Angiosperms have, as a rule, a wider
distribution than the terrestrial members of the group. This
1 Schenck, H. (1885), gives the ranges of a long series of aquatic
plants, as far as they were known at that date.
2 Gin, A. (1909). s Weddell, H. A. (1872).
296 DISTRIBUTION [CH.
is by no means what one would expect at first glance, since it
might reasonably be supposed that salt-water areas, mountain
ranges, and wide tracts of arid country would prove insuper-
able barriers to the migration of plants of fresh water1. This
difficulty was so keenly felt by Alphonse de Candolle2 that he
was forced to the conclusion that the facts of the distribution
of aquatic species were scarcely explicable except on the theory
that there had been multiple centres of creation.
For the sake of simplicity we may first consider the distri-
bution of hydrophytes within a single country such as our own,
which, on a small scale, presents the same difficulties. A partial
solution of the problem might be reached, if former con-
nexions between the existing river basins could be postulated,
in order to account for the uniformity of their floras. But the
history of the land surfaces at once disposes of this possibility.
In the words of Clement Reid3, whose labours disinterred so
much of the geological history of our present flora, "Each
year's work at the subject makes it more clear, that ever since
our climate became sufficiently mild to allow of the existence
of our present fauna and flora, many of the river-basins of
Britain have formed isolated areas." It is no doubt possible
that floods may, in some cases, give a species the opportunity
of introducing itself into fresh situations; an extension on a
small scale, of the area of distribution of certain aquatic plants
was induced by the great floods in East Anglia in 1912.
Furthermore, floods may even, as Guppy4 has suggested, oc-
casionally bring about an exchange between plants belonging
to different rivers traversing extensive level regions. But such
effects can never be more than partial and they will not explain
the passage of any species over a well-defined watershed 5.
1 This paradox was noted by Darwin, C. (1859).
2 Candolle, A. P. de(i855).'
3 Reid, C. (1892). 4 Guppy, H. B. (1906).
5 Dr Guppy has suggested to the writer " that the permanent head-
springs of rivers in elevated regions where the sources of rivers may lie
in proximity would serve as centres of dispersion for the same plants in
xxiv] SEED DISPERSAL 297
Even within a single river basin, the question of the seed-
dispersal of aquatic plants is by no means a simple one. The
expectation might perhaps be formed that aquatics would be
characterised by floating seeds or fruits, capable of being water-
borne for considerable distances. But, as is often the case,
Nature fails to conform to the preconceived notions of the
teleologist, and we find, as a matter of actual fact, that although
many plants with water-side stations possess buoyant seeds, such
seeds are relatively rare among true aquatics. Guppy1, who gives
the results of experiments on the floating powers of the seeds
of more than 300 British plants, records that sinking occurred
within a week in the case of 26 aquatics, e.g. Ranunculus aqua-
tilis, Hottonia palustris. Lobelia Dortmanna, Lemna gibba, Calli-
triche, and others. He found that the seeds of Limnanthemum
nymphoides would float for i to 4 weeks, while Lemna minor,
Sagittaria sagittifolia, Alisma Plantago and certain species of
Potamogeton were the only hydrophytes whose seeds and fruits
were capable of floating for months at a time, and, of these,
the Alismaceae should perhaps be reckoned, in this connexion,
as water-side rather than as aquatic plants.
It is true that the seeds of those aquatics that sink very
rapidly may yet sometimes be carried a short distance by the
wind. For instance, the slender infructescences of Hippuris
vulgaris are swayed to and fro by the breeze, and the fruits may
be jerked a little way2, but the migrations thus achieved can
never be extensive.
If the dispersal of hydrophytes within a single river basin
can only be explained with difficulty, this is still more the case
when we come to consider migration from one country to
another. As Guppy3 has pointed out, Ceratophyllum demersum
different river-basins, and if that is right then the species held in common
ought to include all those growing in the head-springs, e.g. in England,
Callitriche aquatica, Nasturtium officinal t, Ranunculus aquatilis, etc., etc."
(By letter, February 3rd, 1918.)
1 Guppy, H. B. (1906). See also Praeger, R. L. (1913).
2 Fauth, A. (1903). 3 Guppy, H. B. (1893).
298 DISPERSAL [CH.
possesses a fruit which sinks like a stone, and the plant is soon
killed by sea water — yet it has established itself nearly all over
the globe, reaching such islands as the Bermudas and Fijis. The
Potamogetons, again, present little or no obvious capacity for
dispersal by sea — yet such a species as Potamogeton densus^
whose fruits sink at once in fresh or salt water, flourishes in
Europe, Asia, Africa and America.
Water plants, as we have already pointed out, are particu-
larly prone to reproduction by vegetative means, and any theory
attempting to account for their dispersal must take into con-
sideration the conveyance of detached fragments, and of various
types of winter-buds or turions, which are probably more
effective than fruits and seeds in the process of dissemination.
The hypothesis has been proposed that water-fowl are the
' chief agents in the dispersal of hydrophytes. This theory cer-
tainly explains a large proportion of the observed facts, and a
considerable amount of indirect and circumstantial evidence
has accumulated in its favour. Darwin1 pointed out how readily
wading birds, which are great wanderers, might convey seeds
from one water basin to another, in the mud adhering to their
feet. Clement Reid2 came to conclusions bearing on this ques-
tion in the course of his study of the colonisation of isolated
ponds — such as pools which collect in old brick yards, quarries,
etc., and the dew ponds dug on dry chalk downs to provide
water for cattle and sheep. He found, in general, that the water
plants which colonise isolated ponds are essentially the floating
species with finely divided leaves. Their seeds and fruits are
commonly such as would be digested and destroyed if eaten by
birds, but their stems are brittle, and their leaves, on removal
from the water, collapse and cling closely to any object they may
touch. He therefore concluded that it was probable that these
plants are transported in fragments that adhere to the feet of
wading birds. This would also account for the constant presence
of Limnaeids in these ponds, since their eggs might easily be
carried, clinging to pieces of leaves or stems.
1 Darwin, C. (1859). 2 Reid, C. (1892).
xxiv] WATER-FOWL AND WATER PLANTS 299
An interesting experiment in the colonisation of a pond was
made at Garstang in Lancashire some years ago1. The pond in
question was dug in a grass field and carefully railed off to
prevent access of cattle. After about eighteen months certain
aquatic Angiosperms had appeared in the pond — Alisma
Plantago, Callitriche and Glyceria fluitans^ as well as species of
Juncus. In the course of the next five years no new hydrophytes
appeared, but Alisma^ Glyceria and Juncus conglomerates deve-
loped so freely as practically to exclude any intruders. In con-
nexion with the Garstang experiment, it is significant that
fragments of Alisma Plantago^ Glyceria fluitans and Juncus sp.
were observed by a French botanist2 many years ago attached
to the feet and feathers of migrating birds. The only water birds,
actually seen to visit the Garstang pond, were Moorhens, but
other aquatic species were numerous in the district.
That water birds convey hydrophytes from place to place,
is so far an accepted fact that it has been stated that it is "vain
to make a shallow reservoir in the line of the constant migration
of water fowl (i.e. between their resorts), and expect it to main-
tain a freedom from water plants3." On the other hand we
occasionally meet with an apparent exception. A case was re-
corded in Germany4 in which Utricularia Bremii grew in one
locality, while in another, less than a mile away, U. minor
found. These marshes had been under observation for a century,
and, during that time, no exchange of species had taken place,
though, throughout the summer, numbers of Ducks and other
water-fowl flew daily between the localities in question.
There is obviously no doubt that hydrophytes and water-fowl
are constantly brought into intimate relations. One has only to
watch Moorhens in summer, running for long distances over
Waterlily leaves without wetting their feet, to realise that plant
1 Wheldon, J. A. and Wilson, A. (1907). Information relating to
this experiment has been most kindly supplied to me by letter by the
authors, to supplement that recorded in their Flora of West Lancashire.
2 Duval-Jouve, J. (1864). 3 West, G.
4 Meister, F. (1900).
300 DISPERSAL [CH.
and bird play some part in one another's life. In British Guiana,
Im Thurn1 noticed Spurwings (Parra jacana) running about
over the leaves of Victoria regia ; one of them had even nested on
a leaf. In the case of Lawia zeylanica, a Podostemad belonging
to Ceylon, Willis2 records that wading birds are often seen
walking over the thalli. Very numerous fruits are produced,
each containing a large number of seeds, whose epidermis
swells up and becomes mucilaginous on wetting. This mucilage,
when it dries, serves to fix the small seeds firmly to any object
with which they come in contact, and Willis points out that
in this way they may easily adhere to the feet of wading birds.
When we come, however, to the question of the first-hand
evidence as to the part played by water-fowl in the dispersal
of aquatic plants, we find that the facts actually recorded are
relatively few. Our ignorance on this point was emphasized by
Caspary3 in 1 870, and though almost half a century has elapsed
since he propounded the question — " Welche Vogel verbreiten
die Samen von Wasserpflanzen?" — very few observers have
stepped into the breach. It is a question which might well en-
gage the attention of local natural history societies, since it
requires the co-operation of botanists and zoologists: an investi-
gation conducted over a number of seasons could scarcely fail
to produce interesting results.
Such direct evidence as we at present possess, relates partly
to the unintentional conveyance of water plants attached to a
bird's feet or feathers, and partly to the presence of undigested
seeds and fruits in the alimentary canal. With regard to the
Lemnaceae, Weddell4 records that, when shooting in Brazil,
he killed a water bird called "Camichi"; its feathers were
soiled with greenish matter, and closer examination revealed
the presence of a minute Duckweed, Wolffia brasiliensis, in full
flower! At a later date Darwin5 stated that, in this country, he
had twice observed Duckweed adhering to the backs of Ducks
1 Im Thurn, E. F. (1883). 2 Willis, J. C. (1902).
3 Caspary, R. (18702). 4 Weddell, H. A. (1849).
5 Darwin, C. (1859).
xxi v] WATER-FOWL AND WATER PLANTS 301
on their suddenly emerging from the water. Guppy1 found that
a week in sea water killed the seeds of Lemna minor, while a day
generally killed the fronds, but he considers that in damp
weather the plants might, for a day or two, withstand exposure
to the atmosphere and thus might be carried a few hundred
miles entangled in a bird's plumage — a supposition to which the
observations of Weddell and Darwin lend colour.
That seeds and fruits may be conveyed in mud, adhering to
the beaks, feet, or feathers of birds, has long been known. Most
of the records on this point relate to plants which are not strictly
aquatic, but Kerner2 mentions Elatine hydropiper, Glyceria
fluitam and Limosella aquatica among the species which he has
himself found in this situation. Duval-Jouve3, who also paid
attention to this subject, observed at different times the debris
of twelve plant species adhering to the feet and breasts of the
migrating web-footed birds exposed for sale in a market.
Our knowledge of the internal conveyance by birds of the
seeds of aquatics, rests almost entirely on the work of Guppy4,
whose remarkable observations on the life-histories of water
plants have been frequently cited in the foregoing chapters.
Guppy dissected and examined thirteen wild Ducks purchased
in the London markets, and found altogether 828 seeds
and fruits, including those of Sparganium and Potamogeton.
Seeds obtained from this source sprouted with such greatly
increased rapidity that Guppy describes the wild Ducks
as "flying germinators." He adds the observation that, of a
large number of nutlets of Potamogeton natans which were eaten
and passed by a domestic Duck in December, 60 per cent,
germinated in the following spring, whereas, at the same date,
sprouting had only occurred in the case of i per cent, of the
nutlets left over in the vessel from which the Duck had been fed.
It is possible that, in certain cases, the seeds of water plants
1 Guppy, H. B. (1893).
2 Kerner, A. and Oliver, F. W. (1894-1895).
3 Duval-Jouve, J. (1864).
4 Guppy, H. B. (18941), (1897) and (1906).
302 GEOGRAPHICAL DISTRIBUTION [CH.
may — accidentally as it were — offer some lure to birds. When
a fruit of Castalia alba bursts, some 1600 to 1700 seeds rise to
the surface, where they float for a day or two in a mass, looking
like a patch of fish spawn1 and perhaps on this account attract-
ing the attention of birds.
Ascherson2, who has given much study to the distribution
of marine Angiosperms, argues, from the occurrence of Zostera
nana in the Caspian Sea, that this water area must have been
in comparatively recent times connected with the Black Sea,
where this species is also found. However, in the light of the
part played by birds in the distribution of water plants, it is
probable that little stress can be laid upon such evidence. It has
been observed3 in Britain that Brent Geese feed on Zostera^
and that these birds are almost confined to the parts of the coast
where the Grass-wrack is to be found. It is quite conceivable
that they may occasionally carry seeds or fragments of the plant
which would be able to take root on reaching salt water again :
by analogy we may suppose that birds might also be competent
to convey Zostera nana over the three hundred miles or so which
separate the Black Sea from the Caspian.
Problems of plant distribution are often a good deal com-
plicated by the interference of man. This is less the case with
aquatic than with terrestrial vegetation, because, on the whole,
water plants are of no great utility to the human race, and are
seldom introduced intentionally. But the present distribution
of certain aquatics cannot be understood unless allowance be
made for the influence of mankind in their dispersal. Trapa
natans^ the Bull Nut or Water Chestnut, is an instance.
This plant now occurs over a considerable part of Europe, the
Caucasus and Siberia4. It has been used from early times for
food, medicine and magic, and is supposed to have been intro-
duced into Switzerland as long ago as the period of the lake
dwellings 5. It is now nearly exterminated in that country, and
1 Guppy, H. B. (1893). 2 Ascherson, P. (1875).
3 Walsingham, Lord and Payne-Gallwey, R. (1886).
* Areschoug, F. W. C. (1873*). 5 jaggi, J. (1883).
xxiv] AQUATIC ALIENS 303
has vanished from various localities in Belgium, Holland and
Sweden, where there are records of its occurrence in compara-
tively recent times. It certainly seems to be a plant which is in
process of extinction in various parts of its range, since it
occurs in peat in a semi-fossil condition in places where
it has never been known alive within the memory of man1.
The exact reason for its disappearance is hard to find.
Probably the lowering of the mean temperature has some
bearing on the question, but it evidently does not provide
a complete explanation, since the Bull Nut can live in the
north of Scania, although that region is colder than Belgium
and the Swiss lowlands, where the plant is now almost, if not
entirely, extinct2.
Just as certain terrestrial plants penetrate as weeds with
the seeds of cereals into alien localities, so aquatics find a con-
genial home in swampy rice fields, and are disseminated to other
countries in company with the rice. Thus the Lythraceous
Rotala indica and several species of Ammania^ belonging to the
same family, have penetrated into Kurdestan, Transcaucasia and
Astrakhan3, while Naias gramme a has reached Upper Italy4 in
the same fashion. The latter species has even been introduced
into England, probably with Egyptian cotton, and grew at one
time in a canal near Manchester, where the temperature hap-
pened to be artificially raised by the discharge of hot water
from various mills5. Cotton is probably also responsible for
the introduction into Yorkshire of Potamogeton pennsyfoanicus,
which is the only non-native Pondweed recorded from Britain 6.
In the Tropics, e.g. Fiji, a number of edible tubers, such as
Colocasia and Alocasia, are cultivated at the borders of ponds
and ditches. It has been suggested7 that aboriginal man, in
taking such moisture-loving food plants with him on his
1 Reid, C. (1899). 2 Areschoug, F. W. C. (18732).
3 Gin, A. (1909). 4 Ascherson, P. (1874).
5 Bailey, C. (1884) and Weiss, F. E. and Murray, H. (1909).
6 Fryer, A., Bennett, A., and Evans, A. H. (1898-1915).
7 Guppy, H. B. (1906) and (1917).
3o4 GEOGRAPHICAL DISTRIBUTION [CH.
migrations, may often have assisted unintentionally in the
dispersal of associated aquatics.
Turning from the detailed question of the modes of dispersal
of hydrophytes, to the more general problem of their geographi-
cal distribution, we find that these plants furnish certain data
bearing on the theories put forward in recent years by Guppy
and Willis. The views of these two authors, though wholly
independent, and in many ways quite distinct, seem in some
respects to supplement one another.
The nature of Guppy's hypothesis — which he names the
Differentiation Theory1 — may be briefly indicated as follows.
He supposes that the history of our present flora is " essentially
the history of the differentiation of primitive world-ranging
generalised types in response to the differentiation of their con-
ditions." He expressly points out that his view does not attempt
to explain the origin of these primitive generalised families,
and he is careful to note that the present distribution is also
" an expression of the influence of the arrangement of the con-
tinents during secular fluctuations of climate." For lack of
space it is impossible here to do justice to Guppy's theory, but
we may consider two cases among water plants, to each of which
he draws attention as illustrating differentiation and distri-
bution within a single genus. One of these is the genus Naias2,
which he treats in the light of Rendle's monograph3. Guppy
considers that the polymorphic Naias marina^ which occurs
almost all over the whole area of the genus, is the primitive type,
representing the stock from which the other species are derived.
None of the remaining species are so widely distributed, and
though some of them have a considerable range, others are
extremely localised. In Limnanthemum^^ again, Guppy re-
gards nearly all the tropical species as reducible to varieties
of L. indicum, which he takes to be another typical poly-
morphic species of wide range; it has played a role^ in the
warm fresh waters of the globe, comparable with that of
1 Guppy, H. B, (1917), etc. 2 Guppy, H. B. (1906).
3 Rendle, A. B. (1901).
xxiv] THE DIFFERENTIATION THEORY 305
Naias marina, giving birth to new species in various parts of
its range.
There is another case among water plants which, though
Guppy does not allude to it, seems to the present writer to be
readily interpreted on the differentiation theory. The case in
question is that of the family Aponogetonaceae, with its one
genus Afonogeton^ the Arrowgrass, often cultivated in England1.
Africa and Madagascar appear to be the headquarters of the
genus; the species in this region consist almost entirely of
plants with forked inflorescences, while the I ndo- Australian
species have simple inflorescences. The species can be placed,
according to their geographical position, in a series extending
from west to east which also represents their affinities. The
African species lead on to the Madagascan ; these show affinity
with the Indian, while the North Australian are the most
remote. It seems that we must interpret the genus Aponogeton
as having reached a more advanced stage of differentiation than
such genera as Naias and Limnanthemum. Afonogeton no longer
contains any species whose range is approximately coterminous
with that of the genus, but the original area has become
"divided up into a number of smaller areas each with its own
group of species2." However it must not be overlooked that
this case might be interpreted in other ways by those who hold
different views on plant evolution.
Willis3 has in recent years put forward a remarkable hypo^
thesis which is in many ways easily related to Guppy's theory
— namely, the " Law of Age and Area," according to which the
relative size of the geographical territory occupied by each
species within a genus (or genus within a family) is, in general,
proportional to the age of that species. According to this
hypothesis, the most widely distributed genera and species —
instead of being the best adapted, as is maintained by orthodox
Darwinians — are in reality the most primitive, while those occu-
pying limited areas are relatively modern. It is impossible here
1 Krause, K. and Engler, A. (1906). 2 Guppy, H. B. (1906).
3 Willis, J. C. (i9i42), and a number of earlier and later papers.
A. W. P. 20
306 GEOGRAPHICAL DISTRIBUTION [CH.
to enter upon any discussion of the grounds upon which Willis
bases his view, or of the criticisms to which it has been sub-
jected. It must suffice to see whether it can be applied to any
aquatic plants, and, if so, with what result. The only hydrophytes
with which Willis himself deals are the Tristichaceae and Podo-
stemaceae. He points out that, owing to the peculiar morphology
of these plants, it seems possible to say with some degree of
certainty which are the older forms. Tristkha and Podostemon
are almost radially symmetrical, and do not diverge greatly
from the ordinary type of submerged plant. Lawia and Cas-
telnavia, on the other hand, show the most extreme dorsi-
ventrality of structure and have highly modified flowers ; most
botanists would probably agree that Tristicha and Podostemon are
the older types, while Lawia and Castelnavia represent a more
recent evolutionary development. If this view be accepted, the
families in question form a striking illustration of the principle
of Age and Area, for Tristicha and Podostemon cover the whole
range of distribution of the families, while Lawia and Castel-
navia are both limited to comparatively small regions1.
The difficulty of applying a morphological test to Willis's
or to Guppy's theory lies in the fact that botanists seldom agree
as to which members of any given family or genus are to be
considered primitive and which are more specialised. The Water
Starworts (Callitriche\ however, seem to the present writer to
present a case which is, in this regard, less problematical than
most. Within Callitriche we have two sub-genera, one of which,
Eu-callitriche, has the upper leaves floating and k characterised
by aerial pollination, while the other, Pseudo-callitriche^ is com-
pletely submersed throughout life. Most botanists would pro-
bably admit that the genus is descended from terrestrial
ancestors, and that the submerged Pseudo-callitriche is hence a
more highly specialised and recent type. In distribution, Eu-
callitriche is almost cosmopolitan, while Pseudo-callitriche is
confined to the North Temperate regions. The distinction holds
even within our own country, where C. verna and its sub-species
1 Willis,J. €.(1917).
xxiv] THE LAW OF AGE AND AREA 307
representing Eu-callitriche, are abundant, whereas C. autumnalis
(Pseudo-callitriche) is rare and local. The two sub-genera of
Starworts are thus related to one another, as regards their dis-
tribution, in exactly the way that would be predicted, from their
degree of specialisation, either on the Differentiation Theory,
or on the Law of Age and Area. Further, it may be suggested
that the Duckweeds afford another case in point. Lemna minor,
which is the most widespread member of the family, also shows
indications of being the least specialised. These instances are
obviously too few for generalisation, but, as far as they go, they
show that the evidence from hydrophytes is decidedly favour-
able to the views of Willis and Guppy. It is greatly to be wished
that more test cases may come to light, in which certain species
within a genus, or genera within a family, can be accepted with
some degree of confidence as relatively primitive.
20 2
[ 308 ]
CHAPTER XXV
THE AFFINITIES OF WATER PLANTS AND THEIR
SYSTEMATIC DISTRIBUTION AMONG THE
ANGIOSPERMS
(i) THE AFFINITIES OF CERTAIN AQUATIC ANGIOSPERMS
IT is generally recognised that the primaeval forms of
vegetable life were probably aquatic, and that it is only in
the highly evolved group of Seed Plants that a terrestrial habit
has become firmly established. It follows that any aquatics met
with among the higher plants must be regarded as descendants
of terrestrial ancestors, which have reverted in some degree
to the hydrophytic habits of their remote forbears. That this
view is tenable, and that the Aquatic Angiosperms cannot trace
their ancestry in an unbroken aquatic line from some far-away
algal progenitor, is demonstrated by the fact that their floral
organs, in the vast majority of cases, belong to a decidedly
terrestrial type1.
Before discussing any significance which may be attributed
to the systematic distribution of aquatics among the families
and genera of terrestrial Angiosperms, it will be necessary
briefly to review the natural affinities of various members of this
biological group — affinities which are still in some cases "deci-
dedly problematical. The present writer accepts the theory that
the Ranalean plexus includes the most primitive forms among
the living Angiosperms2, and also the view that from this plexus
the Monocotyledons have been derived3; these theories provide
the basis for the general order in which the plants are dealt with
in this chapter, and they also form the bed-rock for the dis-
cussion arising out of the facts -enumerated.
1 See Chapter xvm. 2 Arber, E. A. N. and Parkin, J. (1907).
3 Sargant, E. (1908) and earlier papers.
CH. xxv] RANALES AND CRUCIFERS 309
Dealing first with those more primitive members of the
Archichlamydeae, which are known as the Polypetalae, we find
that, in the Ranalean plexus, the Nymphaeaceae offer a striking
example of a family rich in genera and species, and consisting
entirely of water and marsh plants. There is great variation in
the structure of the flower, and the carpels range from superior
to inferior. The variety of form occurring in the family suggests
that it is an old one which has had a long time to evolve, since
it adopted aqua tic life. It should be noted that various observers1 ,
have regarded the Nymphaeaceae as Monocotyledons, but it
seems more reasonable to suppose that they are truly Dicoty-
ledonous, though descended from a stock closely related to that
which gave rise to the Monocotyledons.
The curious genus Ceratophyllum, on whose affinities the
most divergent claims have been made, seems best regarded
as a reduced form, closely related to the Nymphaeaceae 2 and es-
pecially the Cabomboideae3. Thus this genus, which on account
of its extreme specialisation is reasonably relegated to a distinct
family, may be regarded as the ultimate term in the Nymphaea-
ceous series ; its rootlessness, reduced anatomy and submerged
pollination indicate how completely it has identified itself with
aquatic life.
The Ranunculaceae are typically terrestrial, but the genus
Ranunculus contains, besides purely terrestrial species, the sub-
genus Batrachium which is definitely aquatic, and also a number
of species such as R. Flammula, which are amphibious.
The Cruciferae include certain types, e.g. Nasturtium amphi-
bium and Cardamine pratensis, which are capable of living either
in damp places or actually submerged. These form a link
between the terrestrial Crucifers and such definitely aquatic
forms as Subularia aquatica. This plant, which superficially
resembles a tiny Juncus, lives entirely submerged and has been
described as cleistogamic.
1 Trecul, A. (1845) and (1854), Henfrey, A. (1852), Seidel, C. F.
(1869), Schaffner, J. H. (1904), Cook, M. T. (1906).
2 Brongniart, A. (1827), Strasburger, E. (1902). 3 Gray, A. (1848),
3io AFFINITIES [CH.
The Droseraceae possess one curious little floating water
plant, Aldrovandia vesiculosa. Its flowers are aerial and of the
type characteristic of the family, but it is rootless, and its
anatomy is much simplified.
The Podostemaceae have been placed in the most various
systematic positions, but botanists seem now to regard them
as showing some affinity with such forms as Nepenthes1 and the
Saxifragaceae. The carpels present numerous points of simi-
larity with those of the latter family, e.g. the gynaeceum is
hypog'ynous, with a bicarpellary ovary, two free styles and a
number of ovules on a thick placenta connected with the outer
wall by a thin septum, while the ovule is anatropous, with a
straight embryo and no endosperm2. The most modern view is
to regard the Podostemads as an old phylum lying near the
Resales and Sarraceniales3.
The Crassulaceae, which presumably belong to the same
plexus as the Podostemaceae, though typically xerophytic,
include certain aquatic forms belonging to the genus Tillaea
(Bulliarda).
Several families containing a few aquatic plants are to be
found in the same cycle of affinity as the Caryophyllaceae ; the
plants in question are characterised by their inconspicuous
flowers, which suggest reduction from a more highly deve-
loped type. Montia fontana (Portulacaceae), which occurs in
Britain, generally lives submerged. In the heat of summer,
however, the shoots often become exposed, but the thickish
stem and leaves do not collapse in drought in the manner
characteristic of submerged plants. The Portulacaceae include
many succulent xerophytes, and it has been suggested that
Montia is descended from ancestors of this type, and that, in
spite of adopting the water life, it has retained — to its own
advantage — certain xerophytic characters4. As a water plant
descended from a xerophilous stock, it may perhaps be compared
with Tillaea aquatica. The Elatinaceae, which show affinities
1 Gardner, G. (1847). 2 Warming, E. (1888).
3 Willis, J. C. (1902). 4 Focke, W. O. (1893!).
xxv] POLYPETALAE 3 1 1
both with the Caryophyllaceae and Hypericineae1, contain
the British species Elatine hexandra and E. hydropiper — small
submerged herbs with minute flowers. Illecebrum (Illecebraceae),
again, is so near to the Caryophyllaceae, that it is perhaps best
included in this family.
Polygonum amphibium is an example of an aquatic species
belonging to a terrestrial genus and family (Polygonaceae).
It is amphibious, but only reaches its optimum growth in water.
The affinities of the little family Callitrichaceae have been
much disputed. Robert Brown2, followed by Hooker3 and
Hegelmaier4, included it in the Haloragaceae. But it is better
related to the Euphorbiaceae ; in this family itself, aquatics
are not unknown, e.g. the SaMnia-like Phyllanthu s fluitans 5.
Richard6 was the first to compare Callitriche with Mercurialis,
and more recent work on the relation of its reduced flowers to
those of various Euphorbiaceae has rendered it highly pro-
bable that he was right7.
The Lythraceae contain a number of marsh plants, such as
Lythrum Salicaria, the Water Loosestrife, and also a certain
proportion of true aquatics, such as Peplis Portula, with its
inconspicuous flowers.
The Onagraceae include genera occupying very varying
habitats; some, such as the Willow Herbs, contain typically
terrestrial species, while Ludwigia and Jussiaea are aquatic. A
closely related group, generally separated under the name of
Haloragaceae, includes Myriophyllum, the Water Milfoil and
Trapa, the Bull Nut; Trapa is however sometimes placed in
a distinct family, the Hydrocaryaceae 8. The most problematic
genus associated with the Onagraceae is Hippuris. By some
1 Cambessedes, J. (1829) and Mailer, F. (1877).
2 Brown, R. (1814) 3 Hooker, J. D. (1847).
4 Hegelmaier, F. (1864). 5 Spruce, R. (1908).
6 Richard, L. C. (1808). ' Baillon, H. (1858) and Lebel, E. (1863).
8 The distinctness of Trapa from the Onagraceae has recently been
emphasized by Tackholm, G. (1914) and (1915) on the ground of its
embryo-sac characters.
312 AFFINITIES [CH.
authors it has been placed. in the Haloragaceae1, but it is ex-
cluded by others, and a remote position near the Santalaceae
has even been assigned to it2. The most reasonable view seems
to be the non-committal one of Juel3, whose investigations led
him to believe that the position of the genus must still be treated
as uncertain, since it is by no means even proved that it belongs
to the Archichlamydeae. So it is best, provisionally, to relegate
it to a separate family, the Hippuridaceae, possibly allied to the
Haloragaceae. The geographical distribution of the two fami-
lies, as Schindler2 has pointed out, lends colour to the idea of
their distinctness. He shows that the Haloragaceae (including
the two tribes Haloragideae and Gunnereae) form an "ant-
arctic" group of plants, a few of which by virtue of their
special dispersal-capacity as aquatics, extend into the north
temperate zone ; while the Hippuridaceae, on the contrary, are
an "arctic" family, confined to the Northern Hemisphere.
At different times in the last century, botanical writers have
grouped the following genera in pairs as members of the same
family — Ceratophyllum with Callitrichey Callitriche with Myrio-
phyllum, and Myriophyllum with Hippuris — but more recent
research has led to the belief that these four genera may even
belong to four different Cohorts; this example indicates
the degree to which homoplastic convergence may prevail
among aquatics, and the confusion which it is apt to introduce
into systematic botany.
The Umbelliferae are primarily terrestrial, but certain genera
and species have, to a greater or less degree, taken to aquatic
life. In some, e.g. Oenanthe Phellandrium^ var. fluviatilis, the
vegetative organs are completely submerged.
Among the Sympetalae, water plants are more scattered, and
there is a notable absence of wholly hydrophytic families.
In the Primulaceae there is the single aquatic genus, Hottonia,
with one European and one American representative.
The Gentianaceae are mainly terrestrial, but such marsh
1 Parmentier, P. (1897). 2 Schindler, A. K. (1904).
3 Juel, O. (1910) and (1911).
xxv] SYMPETALAE AND MONOCOTYLEDONS 313
plants as Menyanthes, the Bog Bean, form a transition to the
typically aquatic genus Limnanthemum.
The Scrophulariaceae include several hydrophytic genera;
heterophyllous species are found in Ambulia (Limnophila) and
Hydrotriche. In Britain the water Scrophulariaceae are re-
presented by Limosella aquatica^ a small plant whose corolla
scarcely exceeds the calyx in length, while its capsule sometimes
fails to dehisce ; these features are no doubt symptoms of the
reduction so often associated with aquatic life.
The Bladderworts ( Utricularia\ belonging to the Lenfibularia-
ceae, contain a number of species which are aquatic, besides
others which live on dry land. The terrestrial Plantagos, whose
anemophilous flowers are generally regarded as reduced from
the Scrophulariaceous type, form a transition to the aquatic
genus Littorella in which floral reduction has reached a still
higher pitch; the flowers are unisexual with a one-seeded in-
dehiscent fruit. Limnosipanea is an example of a Rubiaceous
hydrophyte.
Among the otherwise terrestrial Campanulaceae, we find the
submerged Lobelia Dortmanna, while the Compositae include
a few hydrophytes1 such as Bidens Beckii — a heterophyllous
water plant from North America — and Cotula myriophylloides.
Passing to the Monocotyledons — which the present writer
regards as a phylum comparable with the Dicotyledons in being
ultimately derived from ancestral forms of the dicotylar Rana-
lean plexus — we are at once struck with the relatively high
number of aquatic families. The Helobieae (or Fluviales) con-
sist of a series of families which are generally grouped together,
chiefly on account of the enlarged hypocotyl of their embryo,
which forms a remarkable common character. The aquatic and
marsh families generally included in the Cohort are the Alisma-
ceae, Butomaceae, Hydrocharitaceae, Aponogetonaceae, Junca-
ginaceae, Potamogetonaceae and Naiadaceae. The Alisma-
ceae, which appear to be the most primitive of the group, show
striking similarities to the Ranunculaceae, which they re-
1 Hutchinson, J. (1916).
3 14 AFFINITIES [CH.
semble in polycarpy, polyandry and the insertion of the ovules1.
The scattered arrangement of the ovules on the carpellary wall
of Butomus and Vallisneria is similar to that observed in certain
Nymphaeaceae, while coalescence and epigyny occur in both
Hydrocharitaceae and Nymphaeaceae2. The view that these
resemblances are not indicative of affinity, and that the develop-
ment of a similar type of flower in the two families is mere coin-
cidence3, seems to the present writer to have little to support it,
except the fact that the flowers of the Ranunculaceae are gene-
rally more or less acyclic, while those of the Alismaceae have
the parts whorled. This argument scarcely seems to carry much
weight, when it is recalled that certain genera which are un-
doubtedly members of the Ranunculaceae, e.g. Aquilegia^ have
flowers which are verticillate throughout.
The Helobieae as a whole appear to be more nearly related
to the Spathiflorae (Araceae and Lemnaceae) than to any other
Cohort of Monocotyledons4 — the Aponogetonaceae forming,
in some respects, a link between the two Cohorts. This family
recalls the Araceae in its sympodial growth and tuberous stem,
its laticiferous tissue and its flower spike with a fleshy axis. In
the perforation of the leaves, Aponogeton fenestralis may be
compared with Monstera 5. But the Aponogetonaceae show, in
addition, certain distinctively Helobian characters^ which have
led to their association with the Alismaceae, Juncaginaceae and
Potamogetonaceae 6.
The Potamogetonaceae and Naiadaceae seem to form a co-
herent group, while their affinity with the other mejnbers of the
Cohort is by no means a close one. The Potamogetonaceae share
with the Hydrocharitaceae one curious little character, which/
may be of systematic importance, the occurrence, namely, of
peculiar teeth at the edge of the leaf, formed from elongated cells
1 Buchenau, F. (I9O31). 2 Schaffner, J. H. (1904).
3 Rendle, A. B. (1904).
4 Hegelmaier, F. (1868) and Engler, A. (1892).
5 Sergueeff, M. (1907).
6 Planchon, J. E. (1844) and Krause, K. and Engler, A. (1906).
xxv] NAIAS 315
with thickened walls1. The Potamogetonaceae, like the Apono-
getonaceae, show certain features which suggest the Araceae.
Zostera, in particular, was actually included among the Aroids
by de Jussieu2, while, nearly a century later, Engler3 suggested
that the carpels and anthers of this genus might possibly each
represent a male or female flower, the arrangement thus being
comparable with that prevailing in the Aroid Spathicarpa.
The position of the Naiadaceae is obscure, owing to the
difficulty of interpreting the extremely simple flower. Rendle,
in his authoritative work on Naias, regards it as an "appa-
rently primitive type of Monocotyledon4.'* Such a view is of
course entirely irreconcilable with the belief that the Mono-
cotyledons are derived from some early member of the Ranalean
plexus, and that the primitive Angiospermous flower was of the
1 Eu-anthostrobilus ' type5, with a petaloid perianth of numerous
members, and numerous free stamens and carpels. On this view
Naiasmust be interpreted as a highly reduced form, representing
perhaps the ultimate term of reduction in the Potamogetona-
ceae series. The female flower consists of a single ovule, around
which a carpellary wall and integuments grow up in a rather
belated fashion. The flower is sometimes naked, but sometimes
surrounded by a membranous bottle-shaped envelope. The
male flower consists of a single stamen, enclosed in most cases
in two such envelopes, but sometimes in one only. According
to Rendle, the outer envelope of the male flower, and the corre-
sponding envelope which occasionally invests the female flower,
are of the nature of spathes, comparable with the spathes
occurring in other submerged water plants, e.g. Hydrilla^ and
with the membranous cup enclosing the female flowers of
Zannichellia. The probabilities are perhaps in favour of this
interpretation, but it is more difficult to agree with Rendle's
explanation of the inner envelope of the male flower, which
he regards as a perianth. The present writer would like to
1 Ascherson, P. and Graebner, P. (1907) ; see also p. 133.
2 Jussieu, A. L. (^(1789). 3 Engler, A. (1879).
4 Rendle, A. B. (1899). * Arber, E. A. N. and Parkin, J. (1907).
3i6 AFFINITIES [CH.
suggest that this envelope — and possibly the ' spathes ' also —
may be, not foliar organs at all, but structures more closely
comparable with such outgrowths from the floral axis as the
membranous cup which surrounds the essential organs in the
male and female flower of the Poplar, and, more remotely, with
the arillus of the seed of the Yew-tree. The Potamogetonaceae
are characterised throughout by the absence of a perianth ; if
Naias be descended from the Pondweed stock, any ' perianth '
which it possesses must have been acquired de novo and hence
it is highly improbable that any such organ which it might form
would be morphologically a normal perianth1. In Althenia, the
' perigonium ' of the male flowers and the scarious * bracts'
associated with the female flowers, and, in Zannichellia, the
membranous cup surrounding the female flowers (m.c. in Fig.
45, p. 70) may also be mere cupules of no phylogenetic import-
ance, but in the case of the female flowers of these genera, the
possibility that we are dealing with spathes is not excluded. The
variable occurrence of the floral envelopes in different sections
of the genus Naias, harmonises well with the theory that they
are recently acquired organs of no historical significance. On
this view we are absolved from making the forlorn attempt to
recognise in this genus the counterparts of all the organs which
characterise the typical Angiospermic flower.
The Lemnaceae have long been regarded as connected with the
Arum family. More than eighty years ago Schleiden2 propounded
the view that Pistia and Lemna both belong to the Aroideae and
are related to one another. He showed that in Pistia the axis is
abbreviated instead of being elongated as in most Aroids, and
he regarded the River Lettuce as forming, in this respect, a
transition to the Duckweeds3. Certain dissimilarities between
Lemna and Pistia have, however, been emphasised by Koch 4.
The aquatic family Pontederiaceae (Farinosae) is somewhat
1 This follows from the ' Law of Loss ' which will be discussed in
Chapter xxvm.
2Schleiden, M. J. (1838!).
3 See also Arber, A. (1919*); and p. 74. 4 Koch, K. (1852).
xxv] THEORETICAL DEDUCTIONS 317
remote in affinity from those hitherto considered, and is pro-
bably best interpreted as ultimately descended from the stock
from which the Liliiflorae were also derived. Solms-Laubach1
regarded the genus Eichhornia as of older origin than Pontederia,
an opinion which accords well with the fact that Eichhornia has
a trilocular ovary with numerous ovules, while in Pontederia
the ovary is reduced to a single loculus containing one ovule.
Among the Farinosae we also find another entirely aquatic
family in the small group of the Mayacaceae.
No other families among the Monocotyledons are exclusively
aquatic, but there remain certain cases of hydrophytic genera
and species, occurring among families which consist otherwise
of terrestrial or marsh plants. Examples from the British flora
are Scirpus lacustris and S.fluitans (Cyperaceae), Glyceria aquatica
and G. fluitans (Gramineae) and Sparganium natans (Spargania-
ceae). The resemblance of Sparganium to the Pandanaceae is
so great that we may perhaps regard S. natans as representing
an aquatic off-shoot from the stock which also gave rise to the
Screw Pines.
(2) THEORETICAL CONSIDERATIONS2
From the foregoing section of this chapter certain general
conclusions may be deduced. The most obvious and striking
feature is the relative paucity of hydrophytes in comparison
with terrestrial plants. Contrasted with those that live on land,
the number of aquatic families is so small as to be almost
negligible, and even when all the individual hydrophytic genera
and species are added, the sum total is relatively insignificant.
This result is however hardly surprising when we consider that
the Phanerogams are essentially a terrestrial stock and are dis-
tinguished from the Cryptogams by their aerial mode of polli-
nation, which has won for them the freedom of the land. Under
these circumstances, the reversion to aquatic life could hardly
be expected to occur on any great scale. It must also be remem-
1 Solms-Laubach, H. Graf zu (1883).
2 This section of the present chapter is based on a recent paper by the
writer in the Journal of Botany. See Arber, A.
3i8 SYSTEMATIC DISTRIBUTION [CH.
bered that the entire area of the fresh waters of the globe is very
small as compared with the land surfaces, and that thus the
aquatic Angiosperms occupy a much more restricted field than
their terrestrial compeers.
The mode of systematic distribution of aquatics among the
Angiosperms shows every possible variety. In the earlier part
of this chapter we have pointed out that among the Dicotyledons
there are cases in which one species of a terrestrial genus is
aquatic (e.g. Polygonum amphibium\ and others in which a num-
ber of species in a genus are hydrophytic while some are terres-
trial (e.g. Ranunculus with its aquatic sub-genus Batrachium).
Again, an entire genus of an otherwise terrestrial family may be
aquatic (e.g. Hottonia among the Primulaceae) or several genera
of a land family may be aquatic (e.g. Jussiaea, Ludwigia, etc.
among the Onagraceae, and Limosella, Hydrotriche, etc. among
the Scrophulariaceae). Finally, an entire family may be aquatic
and contain no terrestrial forms (e.g. Podostemaceae). A family
given over wholly to aquatic life may include a number of
genera (e.g. Nymphaeaceae and Podostemaceae) or a single
genus (e.g. Ceratophyllaceae and Callitrichaceae). Among the
Monocotyledons, on the other hand, we meet with more cases
of entire families leading a water life (e.g. Lemnaceae, Pontede-
riaceae, and various families belonging to the Helobieae), but
there are fewer instances of individual aquatic genera and
species belonging to families which are mainly terrestrial, though
these occasionally occur (e.g. Glyceria aquatica of theGramineae).
When one genus or species in an otherwise terrestrial family
has taken to aquatic life, this may well be held to indicate that
the habit is a recent one; but when a whole family, containing
a number of genera, is found to be hydrophytic, it is hardly
possible to avoid the conclusion that the differentiation of the
genera has occurred since the adoption of the aquatic habit,
which, on this view, must be very ancient. The only other alter-
native, namely that all the genera have been evolved in the
course of terrestrial life, and that they have all subsequently
and independently taken to the water, seems too far-fetched to
xxv]
HELOBIEAE
be considered seriously. A scrutiny of the characters of those
aquatic families which contain a number of highly individua-
lised genera, confirms the notion that such families adopted
aquatic life at a relatively early stage in the course of evolution
of the Angiosperms. The Nymphaeaceae show characters that
are markedly primitive among the Dicotyledons, and the Podo-
stemaceae, though not standing so low in
the scale of floral evolution, yet appear to
be a very old phylum related to the Resales
and Sarraceniales. That is to say, the only
Dicotyledonous families which are both ex-
clusively aquatic and also contain a number
of distinct genera, belong to the more primi-
tive groups among the Polypetalae, and
hence may be regarded as ancient lines
which took to the water before they had
diverged widely from the ancestral type.
Among the Helobieae, the Alismaceae
are probably nearest to the ancestral stock.
This family shows characters which are
in many ways decidedly Ranalean, and
which^L suggest that the Helobieae re-
present a branch that took to the water at a very early stage
in the evolution of the Monocotyledons, while they still re-
tained features recalling the Ranalean plexus from which they
sprang. That they are descended from a geophytic ancestor
is suggested by the characteristically abbreviated main axis,
which in many cases does not elongate except to form the stalk
of the inflorescence. It is also perhaps conceivable that the
enlarged hypocotyl of the embryo (Fig. 166) recalls an ancestor
which possessed a hypocotyledonary tuber, resembling that of
Eranthis hiemalis, the chief difference being that in the Helo-
bieae the storage of food in the hypocotyl has been shifted back
to a pre-germination stage, owing perhaps to the exigencies of
aquatic life1. It may be recalled, in this connexion, that tuberous
1 See pp. 248, 249.
FIG. 1 66. Ruppia bra-
chypus, J. Gay. Longi-
tudinal section of fruit.
(xi5.) a, cotyledon;
b, first leaf following
cotyledon ; h, hypo-
cotyl; r, primary root.
[Raunkiaer, C. (1896).]
320 SYSTEMATIC DISTRIBUTION [CH.
hypocotyls are common among Ranunculaceae with concrescent
cotyledons, that is to say, among forms which supply indica-
tions of the characters of the original Monocotyledonous stock1.
The idea that the Helobieae are descended from a very
ancient group of Angiosperms, and have inhabited the water
for a correspondingly long period, is ratified by the fact that
this series consists of a whole plexus of related families, some
of which have departed widely from the original type ; it con-
tains forms as far asunder, for instance, as Alisma with its many
Ranalean features and Naias which represents the very acme
of floral reduction. One minor piece of evidence favouring the
antiquity of the water habit in the case of the Helobieae, is the
fact that this Cohort includes all the marine Angiosperms — a
biological group which probably originated through the further
modification of fresh- water forms.
That the Nymphaeaceae and the related Ceratophyllaceae
on the one hand, and the Helobieae on the other, have taken
to aquatic life with such conspicuous success, suggests that the
original Ranalean stock, from which they both sprang, may
have been particularly well adapted to water life. In the Ranun-
culaceae the tendency to aquatic habits in the case of the genus
Ranunculus is obvious ; besides the definitely aquatic sub-genus
Batrachium, the Buttercups include a number of forms, such
as R. sceleratus and R. F/ammu/a,Vfrhich are capable both of
land and water life. The singularly slight difference in general
anatomy, between the terrestrial and aquatic species of Ranun-
culus^ suggests that the land forms are of a type which does
not require great changes of structure in order to succeed in
water life.
It is a remarkable fact that the Sympetalae — the most highly
evolved group of Angiosperms — has produced no entirely
aquatic family, nor any single aquatic species which has become so
far adapted to water life as to have acquired submerged hydro-
philous pollination. The very large family of the Compositae,
which may perhaps be classed as the ultimate term of the
1 Sargant, E. (1903) and (1908).
xxv] AQUATICS, NEW AND OLD 321
Sympetalous series, contains apparently only four aquatic mem-
bers1. Exactly the same is true of all the earlier Cohorts of
Engler's Archichlamydeae, which, on the present writer's view,
represent the more advanced and reduced forms of the Series.
The families which are generally known as Polypetalae (the
later Cohorts of Engler's Archichlamydeae), and which, on the
view here adopted, include all the more primitive Dicotyledons,
are markedly richer in aquatic types. It would hardly be going
too far to say that independent aquatic families are chiefly
characteristic of the Ranalean plexus, and of its derivatives —
both Dicotyledonous and Monocotyledonous — while among the
more advanced Polypetalae, and the Sympetalae, the sporadic
occurrence of aquatic types and their close relation to terrestrial
forms, indicate that the water-habit has been acquired com-
paratively recently. It is always possible that those individual
genera and species among the Sympetalae which are hydro-
phytic at the present day, may each, in some future age, be
represented by an entire aquatic family; for such groups as the
Helobieae, Nymphaeaceae and Podostemaceae may owe their
richness in genera and species partly to their ancient birth and to
the length of time that has elapsed since they took to the water.
But, on the other hand, a member of the Sympetalae embarking
at the present day upon an aquatic career, may possibly be
handicapped, as a potential ancestor, by the high degree of
specialisation it has attained in its previous terrestrial life. The
members of the primaeval Ranalean plexus may have possessed
a greater plasticity in correlation with their lower degree of
specialisation. It must also be remembered that the more pri-
mitive Angiosperms, which entered the water at an early period,
had merely to take possession of a field undisputed by other seed
plants, whereas species embarking on an aquatic life at the
present day are exposed to acute competition from the numerous
well-established hydrophytes with which the fresh waters of the
world are already so fully stocked2.
1 Hutchinson, J. (1916).
2 Since this chapter was written, I have learned that some of my
conclusions were anticipated by Boulger, G. S. (1900).
CHAPTER XXVI
THE THEORY OF THE AQUATIC ORIGIN OF
MONOCOTYLEDONS
THE high proportion of aquatic species among Mono-
cotyledons, as compared with Dicotyledons, has been
noticed in the preceding chapter. This, and other considera-
tions, suggested to Professor Henslow his interesting theory of
the aquatic origin of Monocotyledons1, the broader aspects of
which we may now briefly consider. He discusses the number
of aquatic families to be found in each of the great groups, and
concludes that only 4 per cent, of the Dicotyledonous families
are aquatic, as compared with 33 per cent, of the Monocotyle-
donous. These figures probably have little absolute value — since
it is difficult to decide, to begin with, exactly what we are to
understand by the expression * aquatic family ' — but they serve
a useful purpose in showing how much more numerous
aquatics are among Monocotyledons than among Dicotyledons.
This is indeed a matter of common observation. It is recorded2
for instance, that in the case of the Bodensee, the plants living
in the water or on the margin include forty Monocotyledons
and thirty-eight Dicotyledons; this proportion is remarkable
when we realise that the total number of species of Monocoty-
ledons now existing on the face of the earth, bears to the total of
Dicotyledons the ratio3, very roughly, of i : 4-5. Henslow's
general conclusion, with which most botanists will probably
agree, is that marked numerical contrasts of this type "show
that there is some decidedly important connexion between an
1 Henslow, G. (1893) and (1911). It should be recalled that Gardiner,
W. (1883) also regards Monocotyledons as essentially aquatic.
2 Schroter, C. and Kirchner, O. (1902).
3 The figures from which this ratio is deduced are taken from Coulter,
J. M. and Chamberlain, C. J. (1904).
CH. xxvi] AQUATIC GEOPHYTES 323
aquatic habit and endogenous structures." Further, Henslow
points out that Monocotyledons and aquatic Dicotyledons have
many characters in common, and he explains these resem-
blances, and the numerical preponderance of aquatic Mono-
cotyledons, on the theory that Monocotyledons have arisen
from a Dicotyledonous stock through "self-adaptation to an
aquatic habit."
Henslow's theory has been criticised in some detail by Miss
Sargant1, who has shown that a large proportion of the charac-
teristic features of Monocotyledons can be more readily inter-
preted on the supposition that the group was evolved through
adaptation to a geophilous habit, than on the view that it was
originally aquatic. The resemblances between aquatic plants and
Monocotyledons are, on her view, largely due to the fact that
both have suffered some reduction and degradation of structure,
not necessarily arising from the same cause. It is true that the
type of plant reconstructed by Miss Sargant, as representing the
ancestral Monocotyledonous stock, would be, as she has pointed
out, well adapted for subsequent aquatic life. Many aquatic
Dicotyledons are formed more or less upon the geophilous
plan, e.g. Nymphaea (Fig. 10, p. 25), Castalia (Fig. 1 1, p. 26),
Limnanthemum (Fig. 22, p. 41), Littorella (Fig. 142, p. 218).
It is worthy of note that, in an instance in which an aquatic
flora — that of the Jura lakes — was analysed from this point of
view2, of the forty aquatic Phanerogams and Vascular Crypto-
gams recorded, thirty-one proved to have rhizomes.
The main lacuna in Henslow's theory appears to be that it
treats the reduction of the cotyledons, from two to one, merely
as a symptom of the general degeneracy of Monocotyledons,
whereas Miss Sargant's theory of the geophilous origin of
Monocotyledons offers a specific and convincing explanation
of this peculiarity.
If Henslow's theory be not accepted, the onus rests upon his
opponents of explaining the existence of so large a proportion
of aquatic families within the Monocotyledons. Miss Sargant
1 Sargant, E. (1908). 2 Magnin, A. (1893).
21 — 2
324 ORIGIN OF MONOCOTYLEDONS [CH.
suggests as an explanation that Monocotyledons are on the
whole a decadent race, of which some branches may have been
driven to an aquatic habitat to escape the severer competition
on land. She regards the existence of a large proportion of small
families among the Monocotyledons as suggesting that the
modern members of the group are survivals from a period when
they were more numerous and widely spread, and she supposes
that they have chiefly maintained themselves in such situations
as fresh-water areas, in which competition is less keen than
under more genial conditions. This view is obviously bound up
with the assumption that the adoption of an aquatic life is a
device by which a poorly equipped species may escape from
the competition of its more favoured compeers1, saving itself
from extinction by retirement into a quiet back-water of exist-
ence. In other words, water life is regarded as a refuge for the
destitute among plants. The present writer, having begun the
study of aquatics ten years ago with a full conviction of the
truth of this picturesque theory, has gradually and reluctantly
been forced to the conclusion that there is no sound evidence
in its favour. On the hypothesis in question, water plants are
more or less comparable with the remnant of a defeated race
among mankind, which preserves its existence by retreating into
some forbidding and inaccessible region, into which its con-
querors have little temptation to pursue it. But this analogy is
probably quite misleading; it would perhaps be more illumin-
ating to compare water plants with the pioneers who are to be
found leading hard and difficult lives in barbaric regions on the
frontiers of civilisation — not forced thereto by failure to ' make
good* in the excessive competition prevailing in regions more
anciently inhabited, but impelled to the frontiersman's life by
a natural, inborn affinity for the adventurous conditions which
it offers. In the same way, water plants appear to the present
writer to have adopted this mode of life, not as a last resource,
but because it happened to suit their particular constitution and
1 Darwin, C. (1859), Goebel, K. (1891-1893), Hutchinson, J.
(1916), etc.
xxvi] THE WATERS AS A REFUGE 325
character. There is little doubt that, after they had once entered
upon an aquatic career, they must have evolved along lines
which gradually harmonised them more and more completely
with their surroundings, but the initial step or steps, which led
to the adoption of the water-habit, must have been due to an
innate affinity for the environment, rather than to the negative
quality of incapacity for success in terrestrial life; to pursue
our metaphor — the man, who fails in the struggle for existence
at home, is not of the type that makes the successful colonist.
West's1 critical study of the vegetation of certain Scottish
lakes, led him to a similar conclusion, which is best expressed
in his own words. "It seems to me," he writes, "that aquatic
plants have not always had their origin from terrestrial forms
that had been forced into the water by more robust competitors
on the land, as is sometimes stated, but, more probably, because
certain suitable forms have exhibited a tendency, as some do even
now, to take on the aquatic habit, that mode of living being
more agreeable to their requirements, . . . never have I observed
the case of a plant being forced into the water by a stronger
competitor."
If the preponderance of aquatic families among Monocoty-
ledons is neither to be explained as due to the aquatic origin
of the Class, nor to the part played by the waters in offering a
harbour of refuge to a decadent and unsuccessful race, it
remains to be seen whether any other interpretation can be
offered. In scrutinising more closely the numerical preponder-
ance of aquatic Monocotyledonous families, it becomes obvious
that this does not depend so much upon the constitution of the
group in general, as upon the existence of the very large and
highly differentiated Cohort of the Helobieae. Apart from the
Helobieae, there is no particular disparity between the propor-
tion of aquatic families in the two Classes, and, if the number
of species is to be taken into consideration, the theory that there
is a decided aquatic tendency among the Monocotyledons be-
comes hard to maintain. It has been pointed out2, for instance,
1 West, G. (1910). 2 Coulter, J. M. and Chamberlain, C. J. (1904).
326 ORIGIN OF MONOCOTYLEDONS [CH. xxvi
that the half-dozen purely hydrophytic families of Monocoty-
ledons, though they have a world-wide distribution, contain
altogether less than two hundred species, whereas the four
great world-wide terrestrial families — Gramineae, Cyperaceae,
Liliaceae and Iridaceae — contain ten thousand species.
As we attempted to show in Chapter xxv, the Helobieae
carry every indication of being an ancient group which took
to the water very early in the history of the Monocotyledons,
and in which the existence of the macropodous embryo has
possibly played a considerable part in favouring aquatic life.
The Cohort seems in the main monophyletic, though it is
conceivable that certain families, therein included, are really
offshoots from other Cohorts, which have come by secondary
modification to resemble the true Helobieae.
The two factors that have led to the great development of the
Helobieae, and hence to the prevailing impression that there
is a strong aquatic tendency among Monocotyledons in general,
may be held to be — firstly, the long period which has elapsed
since the ancestral stock of the Cohort became aquatic1, thus
allowing time for its differentiation into a wide variety of forms
— and secondly, the fortunate provision of an embryo with its
food stored in the swollen hypocotyl, which has possibly been
one of the chief instruments in determining the remarkable
success of the group in aquatic life2.
1 See pp. 319, 320. 2 See pp. 248, 249.
CHAPTER XXVII
WATER PLANTS AND THE THEORY OF NATU-
RAL SELECTION, WITH SPECIAL REFERENCE
TO THE PODOSTEMACEAE1
FROM a study of the Podostemaceae, Dr Willis2 has
arrived at certain views as to their evolution which, if
accepted, have a peculiarly wide bearing. The great variety and
anomalous character of the features exhibited by this family
have been touched upon in Chapter ix. There is little doubt that
these plants have been derived from some terrestrial group,
since the structure of the flower and fruit is typically adapted to
land life. Willis suggests that a possible origin for the family
is from plants already growing on the banks of mountain
streams, with creeping adventitious roots, upon which secon-
dary shoots were regularly developed; these secondary shoots
might provide the opportunity for an entrance into aquatic life.
Most of the peculiarities of the group, as Willis points out, can
be traced to the remarkable plasticity of the skeletonless root,
and to the parallel dorsiventrality of the vegetative organs and
flowers. This dorsiventrality is associated with "their plagio-
tropic method of growth, forced upon them by the fact that they
live only upon an unyielding substratum; they have not, and
can never have had, primary roots going downwards into the
rock, and are thus, one might almost say, cut in half, or deprived
of one-half of their polarity3." "No other family above the
liverworts shows so marked and far-reaching a dorsiventrality
in organisation4." The dorsiventrality of the flowers, Willis
1 For the sake of brevity the term Podostemaceae will be used in this
chapter in the old sense, to include both the Podostemaceae proper, and
the closely related Tristichaceae.
2 Willis, J. C. (1902), (I9H1), and (i9i52).
3 Willis, J. C. (I9H1). 4 Willis, J. C. (1902).
328 NATURAL SELECTION [CH.
regards as forced upon them, so to speak, by that of the vege-
tative organs, "without any reference to advantages or dis-
advantages to be derived from it in the performance of the
functions of the floral organs themselves1." He believes that
the dorsiventrality was first impressed upon the vegetative
organs, whence it spread, as it were, to the reproductive regions,
affecting the bracts, spathe and flower. The stamens most
commonly exhibit it, but, in the cases in which it is carried
furthest, the gynaeceum also conforms to it. The zygomorphy of
the flower develops concurrently with a tendency towards
anemophily and autogamy, whereas in most families it is associ-
ated with adaptation to entomophily. Willis looks upon the
zygomorphy of the more specialised Podostemaceae as a cha-
racter without survival-value, which thus cannot owe its pre-
sence to Natural Selection, but which originates as an inevitable
corollary to the dorsiventrality of the vegetative organs. In fact,
he even goes so far as to regard the zygomorphy of the flower
as a positive disadvantage, whose influence the plant seems to
attempt to neutralise. "However dorsiventral the flower be-
comes it still stands erect as long as it possesses a stalk, and
when at last we come to the forms without the stalk we find
the flower curving its ovary and stamens so as to get them as
erect as possible. It seems as if the flower were, so to speak,
struggling against the dorsiventrality to the last1."
The aspect of the zygomorphy of the Podostemad flower
upon which Willis dwells with the greatest emphasis, is its
apparent uselessness. This is one of the points which he
brings forward to show that, though the family as a whole is
probably more completely transformed than almost any other
from the average mesophytic type, the great variety in morpho-
logical structure presented by the individual members cannot
be explained as due to adaptation to their individual surround-
ings. For, though the family has become differentiated into at
least thirty genera and one hundred species of the most varied
morphological structure, the conditions under which they live
1 Willis,J. €.(1902).
xxvn] SPECIFIC DIFFERENCES 329
are uniform in the extreme. " By no stretch of imagination can
the variety in the conditions of life be made to fit one quarter
of the variety of structure1." Even the dorsiventrality, which
is obviously associated with the mode of growth, must not,
according to Willis, be interpreted as an advantageous adapta-
tion, for he points out that the least modified species, in which
dorsiventrality hardly occurs at all, can and do live in nearly
all the places occupied by the family. As a conspicuous ex-
ample of the lack of adaptation among these plants, Willis1
instances the fact that, in the great majority of species, there is
no device to enable the seeds to cling to the rocks upon which
they find themselves shed; he thinks it probable that it often
takes from five hundred to one thousand seeds to produce three
or four seedlings.
The Podostemaceae thus exhibit great variety and marked
specific differentiation, but the features in which the genera
and the species differ from one another cannot, according to
Willis, be explained as adaptational. Further, the particular
situations in which they thrive are such as almost to preclude
competition with other plant forms, and there is also relatively
little struggle for existence even between members of the same
species. On these grounds Willis concludes that the evolution
of the group cannot be explained as due to the natural selection
of infinitesimal variations.
- In scrutinising Willis's criticism of selectionist views, no
progress can be made unless Natural Selection be analysed in
accordance with the two distinct claims which have been made
on its behalf — firstly, that it is the cause of the origin of species,
and secondly, that it is one of the factors conditioning adapta-
tion. Unfortunately the distinctness of these two functions is
not clearly recognised in Darwin's own work, and the con-
fusion thus initiated has given rise to much obscurity in later
writings. Willis's observations certainly strike a severe blow
at Natural Selection considered from the first point of view,
i.e. as the originator of specific types. In the Podostemaceae we
1 Willis, J. C. (I9H1).
330 NATURAL SELECTION [CH.
undoubtedly have a case in which Natural Selection can scarcely
be a factor of any great importance, and yet there is a quite
extraordinary variety of specific forms, many of which are
confined to extremely limited areas.
That specific forms may be markedly definite and distinct,
and that yet the differences between them may be such that it
is scarcely possible to imagine that they have any special sur-
vival value, is also indicated in the case of a number of aquatics
outside the Podostemaceae. Water plants in general have the
character of being Protean, and there is undoubtedly great
individual variability associated with varying conditions of life,
but, at the same time, the opinions of those best qualified to
judge, tend to the conviction that there is great fixity rather than
plasticity of specific characters. It is probable that the general
impression as to the specific variability of aquatics is partly
attributable to the fact that, owing to the prevalence of vegeta-
tive reproduction, local races readily come into being, since any
variation may be perpetuated by this means for a considerable
time. But there is no reason to suppose that such local races
would come true from seed. In the case of the Eu-callitriches,
great variation may often be observed in the form of the leaves
and the size of the floating rosette. Little groups of plants
growing together often conform to one type in these respects ;
but it is probable that such homogeneous groups are merely
the vegetative progeny of one individual. The Potamogetons
are proverbially variable, and their specific identification pre-
sents almost insuperable difficulties to the tyro, yet a great
authority on this group was led, by a critical study of some of
these puzzling forms, to write: "All I have observed during
the past summer induces me to believe that, at the present time,
each form of the lucens group is so far constant that seed of each
form produces its like. Their imitation of one another under
variation, induced by abnormal circumstances, may betray a
comparatively recent common origin, but at the present day
our fenland pondweeds certainly seem to be ' fixed quantities1/ '
1 Fryer, A. (1887).
xxvn] SPECIFIC DIFFERENCES 331
The idea that the specific distinctions among the Potamogetons
are somewhat fluid, may be partly attributed to a too exclusive
use of external features in systematic work; there is no logical
reason for the exclusion of anatomical characters from taxo-
nomic study and their importance is fortunately now becoming
recognised1. It has been demonstrated, for instance, that,
though the flower and fruit characters of the Potamogetons
show very small differences in the different species, and the
external characters of the vegetative parts which can be used
in diagnosis are few and variable, the anatomical characters of
the vegetative organs prove to be much more constant2. That
the majority of specific differences observed among the Pond-
weeds could be of any survival-value, seems almost incompre-
hensible, and the lack of any apparent utility in certain specific
characters is seen almost more clearly when we turn to the
marine Potamogetonaceae. In the case of these plants, the
anatomy of the leaves, taken by itself, furnishes data for exact
specific determination3. Dealing with Cymodocea and Halodule^
Sauvageau4 remarks, " It is an interesting fact that plants which
in general are of relatively simple structure, present such a
variation from one species to another, and, at the same time, such
constancy in specific anatomical characters." It can scarcely
be imagined that the majority of the specific differences, ob-
served in the anatomy of the vegetative organs of the marine
Potamogetonaceae, can serve any purpose in connexion with
the relatively uniform conditions of their submerged life, and,
unless these differences are advantageous, it is impossible to
suppose that they are due to Natural Selection. It is most re-
markable that in so simple a genus as Naias, in which some, at
least, of the external specific differences can hardly, by any
stretch of imagination, be supposed to fit their possessors in
1 The excellent method advocated by R. C. McLean (New Phyt.
Vol. xv, 1916, p. 103) for rendering herbarium material available for
anatomical work, makes the use of internal characters in systematic study
more practicable than hitherto. 2 Raunkiaer, C. (1903).
3 Sauvageau, C. (iSgi1); see also p. 131. 4 Sauvageau, C.
332 NATURAL SELECTION [CH.
any special way for their environment, these specific or varietal
characters are exceedingly constant. Naias graminea, var. Delilei,
for example, has been known in Egypt to have the same cha-
racters for about a century, and when introduced into England
these characters remain wholly unchanged1. These considera-
tions seem to the present writer to confirm the conclusion
drawn by Willis from his study of the Podostemaceae — a con-
clusion which has also been arrived at by various workers in
other fields — that Natural Selection is incompetent to explain
the origin of the sharply defined entities which we call
species.
But when we turn to Natural Selection in its second aspect —
as one of the various factors to which adaptation may be due —
Willis's conclusions seem to need some revision. Accepting the
view that we have, among the Podostemaceae, a case of evolu-
tion untrammelled by the limiting influence of Natural Selec-
tion, we find associated with this freedom, the development of a
large number of well-defined species, remarkable for their lack
of definite adaptation to the conditions of their life. The view
may well be taken that the lack of adaptation which Willis
finds so striking, is actually in part attributable to the absence of
competition and hence to the elimination of Natural Selection.
From this point of view, the Podostemaceae furnish evidence —
negative but forcible — for the importance of Natural Selection
in the development of adaptation, since here we have a case of
the absence of Natural Selection correlated with the absence of
special adaptations. Among the Podostemads, presumably, all
variations — good, bad, or indifferent — have had an almost equal
chance of perpetuation, provided they did not interfere with
those general features which gave the group its special capacity
for growth in the rapidly running water, which is so inimical to
most forms of plant life. Perhaps the present condition of the
Podostemaceae may be broadly compared with that of certain
of our domestic animals, consisting at the present day of many
sharply defined breeds, which could not have survived the
1 Magnus, P. (1883).
xxvn] ADAPTATION 333
stringent ordeal of Natural Selection, to which they would have
been subjected in the feral state.
But Natural Selection is, after all, merely a negative force.
That in the struggle for existence the less fit go to the wall, is
a truism which all must admit ; but, curiously enough, we do not
seem to possess many records among aquatics of this process
having been observed in actual operation. It has been noticed,
however, that, in the lake district of Pico in the Azores, Potamo-
geton polygonifolius is playing the part of an aggressive species
and is ousting such plants as Littorella and Isoetes from the
ponds1. Possibly the chief work of Natural Selection consists in
sorting out species into the environments most suited for them ;
it has, for instance, suffered plants which can tolerate aquatic
conditions to embrace that mode of life, while annihilating
any others, with a constitution unfavourable for the purpose,
which may also have attempted it. In the same way a Labour
Exchange may distribute men into appropriate situations, and
may also be responsible for the elimination of the unfit, by
setting some of them to tasks not within their capacity, but yet it
has no claim to be the originator of any skill which they display
in their respective crafts.
If we can no longer whole-heartedly accept the facile Dar-
winian explanation, we must be content to confess that adapta-
tion remains one of the outstanding mysteries of biology. It
seems impossible to arrive at any glimmer of a comprehension
of its nature, without accepting, in some form, the notion of
the inheritance of acquired characters, with which the inherit-
ance of unconscious memory is probably bound up. Many
biologists to-day seem disposed, at the best, to regard the in-
heritance of acquired characters as both unproven and im-
probable, but it seems to the present writer to be an almost
inevitable article of belief, if it is understood in a broad and
general sense. Whether the offspring of a mutilated Guinea-pig
derives abnormal characters from its injured parent, is quite
beside the point. If we suppose that the whole organic world
334 NATURAL SELECTION [CH.
has arisen from a single primaeval form of life, those complex
powers of reaction to the environment, and the structures
subserving them, which distinguish man from the primordial
speck of protoplasm, must, in a broad sense, be regarded as
* acquired characters,' and, unless such characters were herit-
able, we should not have advanced to-day beyond the uni-
cellular stage. This contention remains true even if we accept
the suggestion, which Bateson has recently made, that the course
of evolution may conceivably be represented by "an unpacking
of an original complex which contained within itself the whole
range of diversity which living things present." This striking,
and at first sight paradoxical, notion contains fundamentally
nothing new. Erasmus Darwin, for instance, who believed in
the origin of the whole animal and vegetable world from "one
living filament, which the great First Cause endued with ani-
mality," must have had in mind, as the essential attribute of this
primordial living stuff, its inherent potentiality of development.
Every evolutionist must suppose that, as the descendants of the
primaeval speck of protoplasm multiplied and advanced along
diverse lines of development, what they gained in specialisation
they lost in plasticity. In other words, while the original living
matter contained within itself the power of development in the
direction of any and every class of the organic world as we now
know it, one of its descendants which has gone far along the
path towards becoming, let us say, an Angiosperm or a Rodent,
has only done so by closing the gates upon itself in countless
other directions : it no longer retains the power of developing,
for instance, into a Bryophyte or a Bird. In this sense all evolu-
tion is accompanied by a succession of losses, and the highly
evolved descendant of the original "living filament" pays the
price of its specialisation in losing the power to develop in
countless other directions. A human analogy, though obviously
imperfect, may perhaps make this point clearer. The future of
a new-born infant presents a wide variety of possibilities. In one
case, for instance, he may contain within himself the powers —
at this stage, necessarily, in a latent form — for ultimately
xxvn] PERFORMANCE FERSUS PROMISE 335
becoming, let us say, an artist, a bishop, or a stock-broker. But
we know that if he achieves any one of these aims in later life,
it will almost inevitably be at the expense of the power to arrive
at the other two. If, in the course of his ontogeny, the stock-
broker triumphs, we may regard him as built up upon the
ashes of the potential bishop and artist. The man, though
superior to the baby in actual achievement, is inferior to it in
the qualities which may be summed up in the word "promise,"
just as the Angiosperm, though its degree of differentiation so
greatly exceeds that of the primordial protoplasmic speck, is
inferior to it when judged by its power to produce descendants
of widely varying types.
L 336 ]
CHAPTER XXVIII
WATER PLANTS AND THE 'LAW OF LOSS'
IN EVOLUTION1
IT is a well-known fact — indeed almost a truism — that
structural reduction is one of the most marked charac-
teristics of water plants. In the preceding chapters of this book
we have alluded to numerous cases in which aquatics are
reduced, both in their vegetative and reproductive organs, as
compared with their terrestrial relations. The consideration of
this reduction, and of some of its sequels, led the present writer
to formulate, under the name of the 'Law of Loss/ a certain
minor principle which seems to be operative in various phases
of plant evolution. The expression ' Law of Loss ' is meant to
indicate the general rule that a structure or organ once lost in
the course of phylogeny can never be regained; if the organism
subsequently has occasion to replace it, it cannot be repro-
duced, but must be constructed afresh in some different mode.
In the very nature of the case, such a law is not susceptible
of formal proof. We can only here consider whether, if accepted
as a working hypothesis, it throws any light on structural
features observed among water plants, which would otherwise
be obscure. We may begin with a case which happened to be
the first to arrest the present writer's attention in connexion
with the ' Law of Loss,' and to which allusion has already been
made2. Ceratophyllum demersum and certain species of Utricu-
laria are entirely rootless at all stages of their life-history — even
the primary root of the seedling being either altogether absent
1 The greater part of this chapter has already appeared in two papers
by the present writer, Arber, A. (1918) and (19192), to which reference
can be made for a fuller treatment of the subject. The ' Law of Loss ' is
closely related to Dollo's c Law of Irreversibility.'
2 See pp. 88, 89, 96, 97.
CH. xxvm] PHYLLODE THEORY 337
or remaining quite rudimentary. These plants are undoubtedly
descended from ancestors of the normal Angiospermic type,
characterised by possessing a root system ; but they have them-
selves entirely lost the ancestral capacity for producing roots.
Nevertheless, in both these unrelated genera, the need for an
absorbing organ seems to have re-asserted itself, and to have
been met, not by the re-establishment of root-formation, but
by the development of special subterranean shoots which —
though not of the morphological nature of roots — perform
root-like functions. This behaviour, in the case of Cera top hy Hum
and Utricularia^ may be interpreted to mean that a plant which
has entirely given up root-formation and afterwards again
experiences the need of roots, cannot re-acquire them, but can
only press some existing organ into the service, modifying it as
best it may. It is possible that the root-like water leaves of
Salvinia indicate a similar history.
As another instance of the working of the 'Law of Loss/
we may take the phylogenetic history of the leaves of the
Alismaceae, Pontederiaceae, or Potamogetonaceae — or indeed
of any other Monocotyledons which possess ' laminae.* But
whether or no this illustration be accepted, depends upon the
standpoint adopted regarding the general morphology of the
leaves of Monocotyledons. The typical Monocotyledonous leaf
is of simple, linear to ovate form, with a sheathing base and
parallel veins ; how is such a leaf to be compared with that of
a Dicotyledon, consisting, in its fullest expression, of leaf-base
and stipules, petiole, and net-veined lamina? This question has
naturally attracted the attention of morphologists, and an inter-
pretation, which has become known as the ' phyllode theory '
was first put forward with some reservations by de Candolle1,
not much less than a century ago. According to this view, the
typical Monocotyledonous leaf does not correspond to the
complete Dicotyledonous leaf, with its leaf-base and stipules,
petiole and lamina, but is merely the equivalent of a petiole
with a sheathing base. It seems to the present writer probable
1 Candolle, A. P. de (1827).
A. W. P. 22
338 ' LAW OF LOSS ' [CH.
that in many cases reduction may have gone yet further, so that
the leaf-base alone is represented.
The phyllode theory is supported by the existence of a
number of examples among Dicotyledons, in which organs not
dissimilar to typical Monocotyledonous leaves can be shown
to be equivalent either to leaf-bases, or to leaf-bases and petioles.
Such cases are numerous and familiar — those in which the
reduced leaves correspond to leaf-bases alone, being decidedly
the commoner. In Cabomba caroliniana'1, to take an instance
from among aquatics, two or three pairs of lanceolate simplified
leaves with no laminae are followed by transitional forms in which
a lamina occurs but is much reduced. These are succeeded by
the normal submerged leaves with finely divided laminae.
It is a commonplace of every text-book that one of the most
distinctive features of Monocotyledons is the parallel venation
of the leaves. But no theory hitherto propounded regarding
the origin of Monocotyledons has offered any satisfactory
explanation of this well-marked character of the Class. To the
present writer it appears that one of the chief merits of de Can-
dolle's theory is that it explains the parallel venation of Mono-
cotyledonous leaves in a perfectly unstrained way. For some
form of parallel veining is one of the most obvious characters
of Dicotyledonous leaf-bases, petioles and phyllodes. Hence,
on de Candolle's theory, the venation of the Monocotyledonous
leaf ceases to present any problem; it shows precisely those
characters which might have been anticipated from the morpho-
logical nature of the organ.
So far we have only considered those Monocotyledonous
leaves in which no lamina is differentiated, but we must now
return to the question with which we started — what are the
homologies of the lamina in the Alismaceae and other families
with a corresponding foliar morphology? If the Monocotyle-
dons are monophyletic, two explanations are open to us; it is
either a revival of the lamina as it occurs among the Dicoty-
ledons, or an organ which has arisen de novo as a modification
iRaciborskf, M. (18942).
xxvm] PHYLLODE THEORY 339
of the distal region of a pre-existing phyllode. In deciding
between these two alternatives, the Law of Loss comes to our
assistance. On this law, the blade once lost cannot be regained^
and it is therefore clear that the * lamina ' of the Monocotyle-
don is, as Henslow1 has suggested, an expansion of the petiole,
imitative of, but not identical with, the blade of a Dicotyledon :
the present writer proposes to distinguish such a blade as a
* pseudo-lamina.' This interpretation certainly accords well
FIG. 167. Potamogeton
lucens, L. Apical part
of a shoot showing range
of leaf form. (Reduced.)
[Raunkiaer, C. (1896).]
£\
FIG. 1 68. Potamogeton natans, L. Series of leaf forms including
A, the normal floating 'lamina.' (A and B, reduced; C-E, nat.
size.) [Raunkiaer, C. (1896).]
with the venation of many Monocotyledonous leaves. The
transitional leaf forms produced in Sagittaria between the band
and arrow-shaped types (Fig. 5, p. 14) have all the appearance
of merely representing different degrees of expansion of the
upper region of the petiole, with correspondingly varying
degrees of outward curvature and apical detachment of the
veins. A somewhat similar series can be traced in certain
Potamogetons (Figs. 167 and 168). These series afford an
1 Henslow, G. (1911).
22 — 2
340 ' LAW OF LOSS ' [CH.
illustration of the way in which the development of the * pseudo-
lamina * may have occurred in the course of phyletic history.
The phyllode theory has met with lively opposition at the
hands of Goebel1. He discusses the question chiefly in con-
nexion with Sagittaria^ and takes the view that the band-like
submerged leaves of this plant are not reduced leaves in which
the lamina has disappeared, but rudimentary leaves in which no
differentiation of blade from petiole has occurred. He supports
this view by recalling that, in the ontogeny of the individual
arrow-head leaf, stages are passed through corresponding, firstly,
to the band-shaped submerged leaf, and secondly to the oval
floating leaf. It is true that these developmental facts are not
easy to reconcile precisely with the phyllode theory as enun-
ciated by de Candolle, but they fall readily into place when
considered in the light of Henslow's extension of de Candolle's
view. If the blade of Sagittaria be merely the expansion and
development of the apical region of the petiole, the band-shaped
leaf is indeed, as Goebel says, comparable with a complete air-
leaf and not merely with its petiole. Where Henslow would
part company with Goebel would be in regarding both the
simple band-leaf and the highly differentiated air-leaf as homo-
logous with the leaf -base and -petiole alone of a typical Dicoty-
ledon.
The present writer had felt for many years that it ought to be
possible to apply anatomical evidence to the phyllode theory,
and at length a path leading in this direction was disclosed.
Solereder2, in the course of a general anatomical study of the
Hydrocharitaceae, reported the discovery of vascular bundles
of inverted orientation in the leaves of various members of the
family (Fig. 28, p. 46). He compared the structure thus re-
vealed to that of petioles, Acacia phyllodes and Iris leaves, but
he did not, apparently, attach any theoretical importance to it.
It seemed, however, to the present writer that these inverted
bundles were an indication of the phyllodic nature of the leaves
in question. In the light of this idea, a general examination of
1 Goebel, K. (1891-1893). 2 Solereder, H. (1913).
XXVI 1 1]
PONTEDERIACEAE
the leaves of Monocotyledons was undertaken, with the result
that * phyllodic ' anatomy was found to occur frequently in this
Class. In many cases the existence of this type of structure
had already been recognised, but it had not been interpreted
as ' phyllodic.' In other instances the existence of inverted
bundles had apparently been overlooked. This was the case in
the Pontederiaceae — an aquatic family belonging to the Fari-
nosae; it may therefore be worth while to describe the leaf
structure of this group in some detail. The leaves, as a rule,
have a sheathing leaf-base, a petiole, which is sometimes much
FIG. 169. A, 'lamina' of Pontederia cor data, L.; B, small 'lamina' of Eichhornia
speciosa, Kunth. (Reduced.) [Arber, A. (1918).]
swollen, and a * lamina.' In external appearance and venation
the leaves of Pontederia (Fig. 169^ and Eichhornia (Fig. 1 69 B)
distinctly suggest that the * laminae ' are produced by expansion
of the apical region of the petiole, and that they are thus
* pseudo-laminae ' and not equivalent to the blades of Dicoty-
ledonous leaves. The anatomy confirms this idea in a striking
fashion. Fig. lyo-D, p. 342, shows the transverse section of a
petiole of Pontederia cordata, L. with inverted bundles towards
the upper side. When the ' lamina ' is cut transversely, its
structure is found to be exactly such as might have been
anticipated on the theory that it is produced by extreme
342
' LAW OF LOSS '
[CH.
Phyllodic Anatomy inPontederiacea?
^y-'^-X^Jvb.o.b _ob__ n-b
$ c/ 9 3 c $ QJ« <» o O »_j_^
PP-sTPontederia mc
p.p.
fx
n.b
xy P:P- r
-^Pontederia
lib. HeterantKera reniforrrus
HeterantKera zosteraefoUa
m.b.
FIG. 170. Leaf anatomy of Pontederiaceae. A, Eichhornia speciosa, Kunth, T.S.
lateral vein of 'lamina.' One small normal bundle (n.b.). One larger inverted
bundle (i.b.) higher in leaf is giving off a branch, also inverted. B, Pontederia coy-
data, L., half T.S. lamina near apex. All bundles inverted (i.b.) or oblique (o.b.)
except the median bundle (m.b.) and the three bundles n.b., n.b/, and n.b.". Fibres
(/) at margin; h.b. — horizontal branch. C, Pontederia cordata, L., the part of the
T.S. shown in B which is included between the dotted arrows. One normal bundle
(n.b.) and two inverted bundles (i.b.), one with an inverted branch, m.c. = cells
containing a secretion, probably myriophyllin. D, Pontederia cordata, L., T.S.
petiole near its upper end, outlines of lacunae dotted. E, Heteranthera reniformis,
Ruiz, and Pav., part of T.S. of lamina, including midrib (m.b.). All the bundles
shown are inverted, except the midrib and main lateral. F, Heteranthera zoster ae-
folia, Mart., T.S. part of ribbon-leaf to show one normal and one inverted bundle
[Arber, A. (1918).]
xxvm] PONTEDERIACEAE 343
flattening and expansion of the petiole in the horizontal plane
(Fig. 170 B and C). For, instead of the normal arrangement of
bundles, all orientated with the xylem upwards, which we are
accustomed to find in laminae, the vascular strands in this case,
though in a single series, are orientated, some normally (#.£.),
including the median bundle (m.b.\ the majority inversely (/.£.)>
and a few obliquely placed (0J.), A small part of the transverse
section is shown in greater detail in Fig. 1 70 C. In this drawing,
the central and largest bundle is seen to be normally orientated,
but the bundles on either side of it have the xylem below and
phloem above.
In the heart-shaped * lamina ' of Heter anther a reniformis,
Ruiz, arid Pav., a very similar bundle arrangement is found
(Fig. 170^). Here, only the midrib and main laterals are
normally placed, the remaining bundles being inverted.
The ' lamina ' of Eichhornia speciosa, Kunth (Fig. 170^)
differs from that of the other members of the family here con-
sidered, in its much greater thickness. Inverted bundles occur, '
not only in the thick basal region in which the transition from
petiole to ' lamina ' takes place quite gradually, but also near
the margin. Here, there is only a single series of vascular
strands, among which inversely orientated bundles are very
numerous. Some of the lateral veins in the ' lamina ' consist of
a single, normally orientated bundle, while others include a pair
of bundles, one normal and one inverted.
Among the Pontederiaceae, we not only find leaves, such as
those just described, in which there is a differentiation between
petiole and * lamina/ but others, which are ribbon-like, with no
distinction of blade and stalk. For comparison with the more
highly differentiated leaves, sections were cut of the ribbon-leaf
of Heter anther a zoster aefolia^ Mart. Here the midrib and main
laterals proved to be normal, but the others — i.e. the majority
of the laterals — were inverted. Fig. 1 70 F shows two adjacent
bundles orientated in opposite ways. The structure of this
ribbon-leaf is closely similar to that of the * lamina ' in H. reni-
f or mis.
344 ' LAW OF LOSS ' [CH.
It may be worth noting that a peculiar submerged member
of this family, Hydrothrix Gardner^ Hook, f., described by
Goebel1, has leaves with a sheathing base and hair-like upper
region, whose external morphology distinctly suggests a
phyllodic origin. In this case anatomical evidence cannot be
sought, since the extremely slender leaves are said to be tra-
versed by a single bundle only.
The presence of inverted bundles in all species of Pontederia-
ceae of which material has been available to the present writer,
is a remarkable anomaly which calls for some explanation. It
is difficult to see how such a structural peculiarity can be ex-
plained as an adaptation, since it is common to leaves otherwise
differing notably in type and mode of life. It is equally con-
spicuous in the very delicate ribbon-leaf of Heteranthera zos-
teraefolia and in the well-defined, thick * lamina * of Eichhornia
speciosa; it occurs both in Heteranthera reniformis, in which
palisade parenchyma is confined to the upper side and in
Pontederia cordata, in which this tissue occurs towards both
surfaces. In the present writer's opinion, this anatomical ano-
maly is best interpreted on the view that the * laminae ' of the
Pontederiaceae, instead of being homologous with the blades
of Dicotyledons, are merely the expanded apices of pre-
existing phyllodes : the inverted bundles are thus an indication
of the petiolar nature of the organ, and are regarded as an
ancestral feature rather than as an adaptation.
The Pontederiaceae are not the only family in which we
meet with phyllodic anatomy of the 'lamina/ The present
writer has found, in the arrow-head blade of Sagittaria monte-
vidensis, Cham, and Schlecht. (Fig. 171 B\ that, besides the
normal main bundles (n.b^) and a series of smaller bundles
running near the lower surface (n.b^ there is a third series
of small inverted bundles near the upper surface (/.£.). In
Sagittaria sagittifolia, L., inverted bundles are a less striking
feature, but the lateral ribs, one of which is represented in
Fig. 171 A) show both normal and inverted bundles.
1 Goebel, K. (1913).
xxvm] SUBMERGED POLLINATION 345
If the view here advocated regarding the nature of the blades
of Monocotyledonous leaves be accepted, it forms a particularly
salient instance of the working of the * Law of Loss/ since we
have here an instance of a discarded organ (the lamina) being
replaced by a modification of another (the petiole) in lieu of
being re-acquired.
FIG. 171. A, Sagittaria sagittifolia, L., T.S. lateral vein of lamina, next but one to
midrib. B, Sagittaria montevidensis, Cham, and Schlecht., small part of T.S. of
leaf near margin. The lower of the two bundles belonging to the normal series
(n.b2) is irregularly placed, (n.b^ = bundle of main normal series; i.b. = inverted
bundle; xy = xylem; ph = phloem; a.t. = assimilating tissue; st = stomate;
o.d. = oil duct.) [Arber, A. (1918).]
The pollination methods of submerged Angiosperms may
also possibly be regarded as illustrating the Law of Loss. The
ciliation of the male gamete in the great group of the Pterido-
phyta — from which it is supposed that Flowering Plants are
ultimately derived — is associated essentially with aquatic fertili-
sation ; with the adoption of terrestrial life this feature was lost,
and is now unknown either in the higher Gymnosperms or the
346 'LAW OF LOSS ' [CH.
Angiosperms. It might well have been expected that when
certain Angiosperms adopted water-life so completely as even
to revert to the remotely ancestral habit of submerged fertili-
sation, they would also simultaneously revert to ciliated sperms,
associated with a broad stylar canal and open micropyle. Such
a trumpet-shaped stigma as that possessed by Zannichellta
seems, indeed, exactly adapted for the entry of swimming
sperms. But no such ciliated Angiospermic gametes have come
into existence; those Flowering Plants which are pollinated
beneath the water, go through all the processes of making
pollen-grains as for aerial pollination, with such slight modifica-
tions as will permit them to be carried passively to the stigma
by gravity or water currents. It seems that cilia once lost
cannot be recovered, even when the circumstances in which
they were formerly of use again recur, and the plant has, as it
were, to patch up some substitute.
If the Law of Loss be accepted as of general application,
it furnishes a clue to certain phylogenetic problems. We have
already alluded to the light which it throws on the difficult
question of the interpretation of the flower of Naias1. Again it
is highly unlikely, on the Law of Loss, that a naked unisexual
flower could evolve into a hermaphrodite flower with a peri-
anth, and hence the law points to the primitiveness of such
floral types as those found among the Ranales and Alismaceae.
We have already2 considered Dr Scott's suggestion that the
anatomical peculiarities of the polystelic genus Gunnera might
lie in an ancestral history in which an original terrestrial period,
followed by an aquatic phase, has been succeeded by a second
terrestrial period. Expressing this example in terms of the
Law of Loss, we may say that the cambial system, once dis-
carded under the influence of water-life, could not be regained
even when the plant reverted to terrestrial conditions; the
expedient of adding to the number of the existing reduced steles
represents a device for repairing this irrevocable loss of means
by such substitutes as are to hand.
1 See p. 315. 2 See p. 180.
xxvm] 'LAW OF IRREVERSIBILITY ' 347
Some time after the present writer had deduced the Law of
Loss from a consideration of the structure of the water plants
living to-day, she learned that zoologists had already arrived, on
fossil evidence, at very similar conclusions regarding animals.
The Law of Loss covers part of the same ground as Dollo's 'Law
of Irreversibility.' That this law should have been arrived at
independently for plants and for animals is perhaps an indica-
tion of its probable validity.
With current Mendelian conceptions, the ' Law of Loss '
harmonises without apparent difficulty. If evolution has pro-
ceeded by variations due to successive losses of factors, we
should certainly expect that the complete loss of an organ might
be associated with inability to recall it, even when circum-
stances seem to put a premium upon its reappearance.
If we accept the views of Samuel Butler so far as to admit that
there is at least an analogy of a highly intimate nature between
heredity and unconscious memory, each example of the ' Law
of Loss ' may perhaps be visualised as representing a lapse or
failure of memory. If an organ be lost, the remembrance of it
presumably in course of time becomes more and more remote,
until finally, even if circumstances renew the need for it, the
memory has so entirely faded that the plant cannot, as it were,
recall how to reconstruct it. It is thrown, so to speak, on its
own resources, and is thus compelled to discover for itself some
method of responding upon new lines to the ancient need.
[ 349 ]
ALPHABETICAL LIST OF BOOKS AND MEMOIRS
BEARING ON THE STUDY OF AQUATIC
ANGIOSPERMS
[This list is far from exhaustive, being merely intended to indicate the principal
sources. Each title is followed by a brief note on the contents and scope of the
memoir. In the case of works cited in the body of the text, or from which figures
have been reproduced, references to the pages in question will be found beneath
the authors' names.]
Agardh, C. A. (1821)
[P 123]
Anon., (1828)
[P- i?]
Anon., (1895)
[P- 17]
Arber, A. (1914)
[pp. 50, 1 86 and
Figs. 31, p. 49 and
121, p. 186]
Arber, A. (1918)
[PP- 52, 336 and
Figs. 169, p. 341, 1 70,
p.342andi7i,p.345]
Arber, A. (I9I91)
[P-
Arber, A. (I9I92)
[pp. 182, 336]
Arber, A. (I9I93)
[P. X43]
Arber, A. (i9i94)
[pp. 74, 82, 316]
Species Algarum, Vol. I. 1821, 531 pp. Gryphis-
waldiae.
(Amphibolis zoster aefolia [ — Cymodocea antarctica] included
under the Algae.)
Honzo Zuju (Phonzo Zoufou). Yedo, 1828.
(A large series of volumes with fine illustrations of Japanese
plants. Vols. 69-76 contain coloured figures of Nymphaeaceae,
Trapa, Trapella and other water plants. There is a copy in the
Library of the Kew Herbarium.)
Useful Plants of Japan, described and illustrated.
Agricultural Society of Japan, Tokyo, 1895.
(Trapa, Nelumbo, Euryale, Sagittaria and Scirpus tuber osus are
figured and their uses described.)
On Root Development in Stratiotes aloides L. Proc.
Camb. Phil. Soc. Vol. xvn. 1914, pp. 369-379, 2 pis.
(The development of the adventitious roots is discussed in this
paper, and attention is called to the frequently bi-lobed character
of the nuclei in their stelar tissues.)
The Phyllode Theory of the Monocotyledonous Leaf,
with Special Reference to Anatomical Evidence.
Ann. Bot. Vol. xxxn. 1918, pp. 465-501, 32 text-figs.
(In this paper the nature of the leaves in the Pontederiaceae,
Sagittaria and other aquatic Monocotyledons is discussed.)
Aquatic Angiosperms and their Systematic Distri-
bution. Journ. Bot. Vol. 57, 1919, pp. 83-86.
(See Chapter 25 of the present book.)
The 'Law of Loss' in Evolution. Proc. Linn. Soc.
Session 131, 1918-1919, pp. 70-78.
(See the last chapter of the present book.)
Heterophylly in Water Plants. Amer. Nat. Vol. 53,
1919, pp. 272-278.
(A general discussion of this question.)
On the Vegetative Morphology of Pistia and the
Lemnaceae. Proc. Roy. Soc. B, Vol. 91, 1919, pp.
96-103, 8 text-figs.
(It is here shown that the leaf of Pistia is phyllodic in anatomy,
and that its sheath forms a lateral pocket in which a bud is
produced, in a position comparable with that of a young frond
of Lemna.)
350
Arber,E. A.N.)
and
Parkin, J. j
[PP- 308, 315]
Arcangeli, G. (1890)
[pp. 27, 159]
Areschoug, F. W. C.
(I8731)
Areschoug, F. W. C.
(i8732)
[pp. 302, 303]
Armand, L. (1912)
[p. 166]
Ascherson, P. (1867)
[pp. 123, 124]
Ascherson, P. (1870)
[P- 135]
Ascherson, P. (1873)
[p. 146]
Ascherson, P. (1874)
[P- 3033
BIBLIOGRAPHY
On the Origin of Angiosperms. Linn. Soc. Journ. Bot.
(1907) Vol. 38, 1907, pp. 29-80, 4 text-figs.
(This paper is partly devoted to a reconstruction of the primitive
type of Angiospermic flower. Among aquatics, the Nym-
phaeaceae, Alismaceaeand Butomaceae are regarded as showing
certain primitive features of flower structure.)
Sulle foglie delle piante acquatiche e specialmente
sopra quelle della Nymphaea e del Nuphar. Nuovo
Giornale Botanico Italiano, Vol. xxn. 1890, pp. 441-
446.
(A study of heterophylly in these genera.)
Om Trapa natans L. och dess i Skane annu lefvande
form. Ofversigt af k. vet. akad. Forhandl. xxx.
1874 (for 1873), No. i, pp. 65-80, i pi.
[An account of this Swedish paper was given in the same year
in the Journ. of Bot. See Areschoug, F. W. C. (i8732).]
On Trapa natans L., especially the form now living
in the southernmost part of Sweden. Journ. Bot.
Vol. xi. N.S. Vol. ii. 1873, pp. 239-246, i pi.
[This paper is a translation, revisedby the author, of Areschoug,
F.W.C.(i873').]
Recherches morphologiques sur le Lobelia Dortmanna
L. Revue gen. de Bot. T. xxiv. 1912, pp. 465-478,
1 8 text-figs.
(A description of the anatomy of this species, and, for com-
parison, of the terrestrial species, L. urens and L. erinus.}
Vorarbeiten zu einer Uebersicht der phanerogamen
Meergewachse. Linnaea, Bd. 35, N.F. Bd. i. 1867-
1868, pp. 152-208.
(A systematic account of the marine Hydrocharitaceae and
Potamogetonaceae, the synonymy and distribution being dealt
with in detail.)
t)ber die Phanerogamen des rothen Meeres, besonders
Schizotheca Hemprichii Ehrb., Phucagrostis rotundata
Ehrb. und Phucagrostis ciliata. Sitzungs-Berichte
d. Gesellsch. naturforsch. Freunde zu Berlin, Dec. 20,
1870, pp. 83-85.
[This brief descriptive account of the marine Phanerogams of
the Red Sea should be read in conjunction with Magnus, P.
(iSyo2).]
Ueber Schwimmblatter bei Ranunculus sceleratus.
Sitzungs-Ber. d. Gesellsch. naturforsch. Freunde zu
Berlin, May 20, 1873, pp. 53-55.
(The first record of the occurrence of floating leaves in this
species.)
Vorlaufiger Bericht iiber die botanischen Ergebnisse
der Rohlfs'schen Expedition zur Erforschung der
libyschenWiiste. (Schluss.) Bot. Zeit. Jahrg.32, 1874,
pp. 641-647.
(In this paper mention is made of the occurrence of Naias
graminea, Del. in the rice fields both of Egypt and Upper Italy.)
Ascherson, P. (1875)
[PP- i35» 302]
Ascherson, P. (1883)
Ascherson, P.I
and V (1907)
Graebner, P. )
[pp. 133, 291, 315]
Ascherson, P.j
and V (1889)
Gurke, M. )
Ascherson, P.
Askenasy, E. (1870)
[pp. 144, 228 and
Fig. 126, p. 196]
Aublet, F. (1775)
[P-
Auge de Lassu (1861)
[p. 109]
Bachmann, H. (1896)
[pp. 32, 195]
BIBLIOGRAPHY
Die geographische Verbreitung der Seegraser, in
Dr G. von Neumayer's Anleitung zu wissenschaft-
lichen Beobachtungen auf Reisen, 1875, pp. 358-373
(also later editions).
(A detailed and suggestive account of the distribution of the
marine members of the Potamogetonaceae and Hydrochari-
taceae.)
Bemerkungen iiber das Vorkommen gefarbter
Wurzeln bei den Pontederiaceen, Haemodoraceen
und einigen Cyperaceen. Ber. d. deutsch. Bot.
Gesellsch. Bd. i. 1883, pp. 498-502.
(The author describes the blue or pale lilac colouring of the
roots of several genera of Pontederiaceae.)
Potamogetonaceae, in Das Pflanzenreich, iv. n
(herausgegeben von A. Engler), 184 pp., 221 text-figs.
Leipzig, 1907.
(An authoritative account of all the species, Ascherson being
responsible for the marine forms.)
Hydrocharitaceae, in Die Natiirlichen Pflanzen-
familien, n. i (Engler, A. and Prantl, K.). Leipzig,
1889, pp. 238-258, ii text-figs.
(A systematic treatment of the family.)
See Delpino, F. and Ascherson, P. (1871).
Ueber den Einfluss des Wachsthumsmediums auf die
Gestalt der Pflanzen. Bot. Zeit. Jahrg. 28, 1870, pp.
193-201, 209-219, 225-231, 2 pis.
(An account of the structure and development of Ranunculus
aquatilis, L. and R. divaricatus, Schr. The chief feature of the
work is the experimental investigation into the effect of land
or water conditions on these two species.)
Histoire des plantes de la Guiane Fran£oise, T. i.
London and Paris, 1775.
(On pp. 582-584 there is the first account of the Podoste-
maceous genus Mourera. The author notes that the plant
grows on rocks in rapidly running water and is entirely sub-
merged with the exception of the flowers.)
Analyse du memoire de Gaetan Monti sur I'Aldro-
vandia, suivie de quelques observations sur 1'irrita-
bilite des follicules de cette plante. Bull, de la Soc.
bot. de France, T. vm. 1861, pp. 519-523.
(An analysis of Monti's original memoir on this plant, published
between 1737 and 1747, followed by the first record of the
closure of the leaves when irritated.)
Submerse Blatter von Nymphaea alba. Landformen
von Nymphaea alba. Ber. d. Schweiz. bot. Gesellsch.
Heft vi. 1896 (Jahresber. d. ziircher. bot. Gesellsch.),
pp. [n] and [12].
[The author describes certain cases of the occurrence of the
submerged leaves of Castalia (Nymphaea) alba, and also of a
land form which he found in three locali ties in the dry summer
of 1895.]
Bailey, C. (1884)
[pp. 237, 275, 303]
Bailey, C. (1887)
[P-
Baillon, H. (1858)
[P-
Balfour, I. B. (1879)
[p. 129 and
Fig. 87, p. 130]
Barbe, C. (1887)
BIBLIOGRAPHY
Notes on the Structure, the Occurrence in Lancashire,
and the Source of Origin, of Naias graminea Delile,
var. Delilei Magnus. Journ. Bot. Vol. xxn. 1884,
PP- 3°5~333> 47 text-figs., 4 pis.
[This account of an Egyptian species, which has been introduced
into Lancashire, in some points supplements Magnus, P.
(I8701). Magnus, P. (1883), Ascherson, P. (1874) andWeiss,
F. E. and Murray, H. (1909) deal with the same plant.]
Forms and Allies of Ranunculus Flammula L. Journ.
of Bot. xxv. 1887, pp. 135-138.
(In this paper the existence of a form of Ranunculus Flammula
with floating leaves is recorded.)
Recherches sur 1'organogenie du Callitriche et sur ses
rapports naturels. Bull, de la Soc. bot. de France,
T. v. 1858, pp. 337-341.
(A defence of the Euphorbiaceous affinity of Callitriche, based
upon the structure and development of the gynaeceum.)
On the Genus Halophila. Trans, and Proc. Bot. Soc.
Edinburgh, Vol. xm. 1879, pp. 290-343, 5 pis.
[A full account of two species of this genus collected by the
author on the reefs surrounding the island of Rodriguez;
Solereder, H. (1913), pp. 46, 47, discusses Balfour's material
from the systematic standpoint.]
See Dangeard, P. A. and Barbe, C. (1887).
Barber, C. A. (1889) On a change of Flowers to Tubers in Nymphaea
[pp. 36, 225 and Lotus, var. monstrosa. Ann. Bot. Vol. iv. 1889-
Fig. 19, p. 37] l89i. PP- I05-H6, i pi.
(An account of a case of the replacement — under cultivation —
of flowers by tubers, which, when detached were capable of
reproducing the plant.)
Barneoud,F. M. (1848) Memoire sur Tanatomie et 1'organogenie du Trapa
[p. 207] natans (Linn.). Ann. d. sci. nat. Ser. in. Bot. T. ix.
1848, pp. 222-244, 4 pis.
(This early description of Trapa natans includes a study of
the germination, anatomy and floral development.)
Barratt, K. (1916)
[p. 185 and Fig.
120, p. 185]
in the Stem of
1916, pp. 91-99,
The Origin of the Endodermis
Hippuris. Ann. Bot. Vol. xxx.
6 text-figs.
(The author's results regarding the apical anatomy of the stem
of Hippuris are in general agreement with those of Schoute.)
Barthelemy, A. (1883) Sur la respiration des plantes aquatiques ou des
plantes aquatico-aeriennes submerges. Comptes
rendus de 1'acad. des sciences, Paris, T. 96, 1883,
pp. 388-390.
(An account of experiments on the assimilation and respiration
of aquatic plants, from which the author concludes that "la
respiration speciale des organes verts ne peut a voirl' importance
cosmique qu'on lui attribue. ")
BIBLIOGRAPHY
353
Batten, L. (1918)
[p. 188]
Bauhin, G. (1596)
[p- 9]
Bauhin, G. (1620)
[p. 9 and Fig. 3, p. u]
Bauhin, G. (1623)
[P- 27]
Belhomme, (1862)
[p. 219]
Benjamin, L. (1848)
[PP- 97, 99, 101]
Bennett, A. (1896)
Bennett, A. (1913)
Bennett, A. (1914)
[P- 551
Bennett, A.
Observations on the Ecology of Epilobium hirsutum.
Journ. Ecology, Vol. 6, 1918, pp. 161-177, 15 text-
ligs.
[A fully illustrated account of the "aerenchyma" of this
species — a tissue whose existence had previously been recorded
by Lewakoffski, N. (I8731) and Schenck, H. (1889).]
Phytopinax seu Enumeratio Plantarum...Basileae
per Sebastianum Henricpetri 1596.
(Bauhin describes the germinating tuber of Sagittaria *as
"Gramen bulbosum," p. 21.)
Prodromes Theatri Botanici...Francofurti ad Moe-
num, Typis Pauli Jacobi, impensis Joannis Treudelii,
1620.
[Bauhin gives a figure (p. 4) of " Gramen bulbosum aquaticum"
to which he has already referred in Bauhin, G. (1596).]
Pinax Theatri Botanic! . . .Basileae Helvet. Sumptibus
et typis Ludovici Regis, 1623.
[The submerged leaves of Nymphaea (Castalia) alba are
described on p. 193.]
Note sur les bourgeons reproducteurs du Ranunculus
Lingua. Bull, de la Soc. bot. de France, T. ix. 1862,
p. 241.
(A note on the wintering of this species.)
Ueber den Bau und die Physiologic der Utricularien.
Bot. Zeit. Jahrg. 6, 1848, pp. 1-5, 17-23, 45-50,
57-61, 81-86.
(This paper, which contains some interesting observations, was
written before the insectivorous nature of the bladders was
recognised.)
Fortschritte der schweizerischen Floristik. Potamo-
geton. Ber. d. Schweiz. bot. Gesellsch. Heft vi. 1896,
PP- 94-99-
(A systematic enumeration of the results obtained by the
author in the course of a revision of the principal Swiss
herbaria.)
Remarks on Some Aquatic Forms and Aquatic
Species of the British Flora. Trans. Bot. Soc. Edinb.
Vol. xxvi. 1917 (for 1911-1915), Part n. 1913, pp.
21-27.
(Notes relating to the occurrence and nomenclature of some of
the aquatic forms and species described by West, Gliick, etc.)
Hydrilla verticillata Casp. in England. Journ. Bot.
Vol. LII. 1914, pp. 257-258, i pi.
(This plant, which is new to the British flora, has been found
growing at Estwaite Water associated with Naias flexilis, etc.)
See Fryer, A., Bennett, A. and Evans, A. H. (1898-
A. w. P.
23
BIBLIOGRAPHY
Geologic History indicated by the Fossiliferous
Deposits of the Wilcox Group (Eocene) at Meridian,
Mississippi. U.S. Geol. Survey. Professional Paper
1 08 E. Shorter contributions to general geology,
1917, Washington, pp. 61-72, 3 pis., i text-fig., i map.
(This memoir contains an account with map of the past and
present distribution of the genus Nelumbo.)
The Prickle-pores of Victoria regia. Ann. Bot. Vol. i.
1887-1888, pp. 74-75.
[The author criticises the account of these structures given by
Trecul, A. (1854), and concludes that the function of the
spines is probably merely protective.]
Sur les diaphragmes des canaux aeriferes des plantes.
Revue gen. de Bot. T. 24, 1912, pp. 233-243, i pi.
(In this paper the diaphragms crossing the intercellular spaces
of the stems aad leaves of certain aquatics are described, and
they are figured in the cases of Sagittaria sagittifolia, Pontederia
cor data and Potamogeton natans.)
Ueber die durchsichtigen Punkte in den Blattern.
Flora, N. R. Jahrg. XLII. (G. R. Jahrg. LXVII.) 1884,
PP- 49-57, 97-H2, 136-144, 204-210, 223-225, 275-
283, 291-299, 339-349, 355-37°, 37I~386-
(The transparent dots on the leaves of Nymphaeaceae are
referred to on pages 100-102.)
See Paillieux, A. and Bois, D. (1888).
Weitere Mittheilung iiber die wasserleitenden Gewebe.
Pringsheim's Jahrb. f. wissen. Bot. Bd. xxi. 1890,
PP. 505-519.
(An account of an experimental investigation of the transpira-
tion stream in Myriophyllum proserpinacoides, when the plant
is growing with its leafy shoots above water.)
Bolle, C. (1861-1862) Notiz iiber die Alismaceenformen der Mark. Ver-
handl. d. bot. Vereins Provinz Brandenburg, Heft.
in. and iv. 1861-1862, pp. 159-167.
[An account of certain forms of Sagittaria andAlisma found by
the author. A more modern discussion of the subject will be
found in Gliick, H. (1905).]
Bolle, C. (1865) Eine Wasserpflanze mehr in der Mark. Verhandl. d.
[p. 210] bot. Vereins Provinz Brandenburg, Jahrg. 7, 1865,
pp. 1-15.
[See note on Bolle, C. (1867).]
Bolle, C. (1867) Weiteres iiber die fortschreitende Verbreitung der
[p. 210] Elodea canadensis. Verhandl. d. bot. Vereins Provinz
Brandenburg, Jahrg. 9, 1867, pp. 137-147.
[This paper and Bolle, C. (1865) record the way in which
Elodea, at that date a comparative rarity, was spreading over
Germany.]
Bonpland, A. See Humboldt, A. de, and Bonpland, A. (1808).
354
Berry, E. W. (1917)
[p. 38 and Fig. 21,
P- 39]
Blake, J. H. (1887)
Blanc, M. le (1912)
[p. 183 and Figs. 8,
p. 19, and 1 1 8, p. 184]
Blenk, P. (1884)
[P- 37]
Bois, D.
Bokorny, T. (1890)
[p. 261]
BIBLIOGRAPHY
355
Boresch, K. (1912)
[P- 154]
Bornet, E. (1864)
[p. 125 and Fig. 83,
p. 124]
Borodin, J. (1870)
[pp. 86, 169 and
Fig. 163, p. 268]
Bottomley, W. B.
(1917)
[p. 287]
Boulger, G. S. (1900)
[P- 321]
Brand, F. (1894)
[pp. 27, 159]
Brongniart, A. (1827)
[P- 309]
Brongniart, A. (1833)
[P- 76]
Brongniart, A. (1834)
[p. 164]
Die Gestalt der Blattstiele der Eichhornia crassipes
(Mart.) Solms in ihrer Abhangigkeit von verschie-
denen Faktoren. Flora, N.R. Bd. 4 (Ganze Reihe, Bd.
104), 1912, pp. 296-308, i pi., 3 text-figs.
(This paper describes a series of experiments which show that
the inflated form of petiole in Eichhornia crassipes can be
induced by full light, low temperature and a free-swimming
life, whereas the converse conditions tend to be associated with
the elongated form of petiole.)
Recherches sur le Phucagrostis major Cavol. Ann.
d. sci. nat. Ser. v. Bot. T. i. 1864, pp. 5-51, n pis.
(This finely illustrated memoir gives a singularly complete
account of the structure and life-history of the plant now called
Cymodocea aequorea, Kon.)
Ueber den Bau der Blattspitze einiger Wasser-
pflanzen. Bot. Zeit. Jahrg. 28, 1870, pp. 841-851, i pi.
[A description of the stomates which occur in small numbers
near the apices of the submerged leaves of Callitriche and
Hippuris. Mention is also made of the peculiar oil-containing
processes at the tips of the leaves of Myriophyllum and Cerato-
phyllum. For a criticism of this paper see Magnus, P. (1871).]
Some Effects of Organic Growth-Promoting Sub-
stances (Auximones) on the Growth of Lemna minor
in Mineral Culture Solutions. Proc. Roy. Soc. B,
Vol. 89, 1917, pp. 481-507, 2 pis.
(By means of comparative cultures it is shown that Duckweed
cannot be kept healthy in solutions with only mineral salts —
soluble organic matter is essential.)
Aquatic Plants. Journ. Roy. Hort. Soc. Vol. 25,
1900, pp. 64-77.
(A suggestive general account of hydrophytes, with a systematic
appendix showing the independent origin of the aquatic habit
in a comparatively small number of Cohorts.)
Ueber die drei Blattarten unserer Nymphaeaceen.
Bot. Centralbl. Bd. LVII. 1894, pp. 168-171.
(A brief account of the submerged, floating and air leaves of
Nymphaea lutea and Castalia alba.)
Memoire sur la Generation et le DeVeloppement de
1'Embryon dans les vegetaux phan6rogames. Ann.
des sci. nat. Vol. 12, 1827, pp. 14-53, 145-172,
225-296, ii pis.
(On p. 253 et seq. the author compares the embryo of Cerato-
phyllum with that of Nelumbo.)
Note sur la structure du fruit des Lemna. Archives
de Botanique, T. n. 1833, pp. 97-104.
(An account of the structure of the seed and fruit in Lemna
minor and L. gibba.)
Nouvelles recherches sur la structure de 1'^piderme
des Ve"ge"taux. Ann. d. sci. nat. Ser. n. T. i. Bot.
1834, pp. 65-71, 2 pis.
[On p. 68 the author records the discovery of chlorophyll in
the epidermis of the leaves of Potamogeton lucens and the
existence of "une pellicule tout-a-fait incolore" (=cuticle) on
the surface of the epidermal layer. In PL III, Fig. 5, the
characters of the epidermis are clearly demonstrated.]
23—2
356
Brown, C. Harrington
(1876)
Brown, R. (1814)
[P-
Brown, W. H. (1911)
[p. 286]
Brown, W. H. (1913)
[pp. 253, 264, 265]
Bruyant, C. (1914)
[p. 291]
Buchenau, F. (1857)
Buchenau, F. (1859)
[pp. 217, 232]
Buchenau, F. (1865)
Buchenau, F. (1866)
[P- 245]
Buchenau, F. (1882)
[P- i?]
BIBLIOGRAPHY
Canoe and Camp Life in British Guiana, xi + 400 pp.,
10 pis. and map. London, 1876.
(On p. ii some Podostemaceae occurring in the Cuyuni River
are described under the name of Lads spp.)
General remarks on the Botany of Terra Australis.
89 pp. Reprinted in the Miscellaneous Botanical
Works of Robert Brown, Vol. I. 1866.
(The author includes CaUitriche in the Halorageae; see p. 22.)
The Plant Life of Ellis, Great, Little, and Long Lakes
in North Carolina. Contributions from the U.S.
National Herbarium, Vol. 13, Part 10 (Misc. Papers),
Washington, 1911, pp. 323-341, i text-fig.
(An account from the ecological standpoint of the plant life of
these lakes, special attention being paid to the relation of soils
to aquatic vegetation.)
The Relation of the Substratum to the Growth of
Elodea. The Philippine Journal of Science, C, Botany,
Vol. vin. 1913, pp. 1-20.
(An important experimental study on the factors affecting the
growth of Elodea, especially the CO8 supply.)
Les Tourbieres du massif Mont-Dorien. Annales de
Biologic Lacustre, T. vi. Fasc. 4, 1914, pp. 339-391,
i map, 14 text-figs.
(This memoir contains an ecological study of the peat bogs of
this region.)
Ueber die Bliithenentwickelung von Alisma und
Butomus. Flora. N.R. Jahrg. xv. (G.R. Jahrg. XL.)
1857, pp. 241-254, i pi.
(A description of the development of the parts of the flower in
Alisma Plantago and Butomus umbellatus, with a briefer
mention of Sagitlaria sagittifolia.)
Zur Naturgeschichte der Littorella lacustris L. Flora,
N.R. Jahrg. xvn. (G.R. Jahrg. XLII.) 1859, pp.
81-87, 464, 705-706, i pi.
(A study of the external morphology of the flowering land form
and the sterile water form of this species.)
Morphologische Studien an deutschenLentibularieen.
Bot. Zeit. Jahrg. 23, 1865, pp. 61-66, 69-71, 77-80,
85-91, 93-99, 2 pis.
(In the 3rd and later parts of this memoir the branching and
flower development of Utricularia are dealt with.)
Morphologische Bemerkungen uber Lobelia Dort-
manna L. Flora, N.R. Jahrg. 24 (G.R. Jahrg. 49),
1866, pp. 33-38, i pi.
(An account of the germination and general morphology of this
species.)
Beitrage zur Kenntniss der Butomaceen, Alismaceen
und Juncaginaceen. Bot. Jahrbucher (Engler's),
Bd. n. 1882, pp. 465-510.
[This paper is intended to supplement and correct Micheli's
monograph of the same group; see Micheli, M. (1881).]
BIBLIOGRAPHY 357
Buchenau, F. (I9031) Alismataceae, in Das Pflanzenreich, iv. 15 (heraus-
[PP- 9. 3*4] gegeben von A. Engler), Leipzig, 1903, 66 pp., 19
text-figs.
(The standard systematic account of this family.)
Buchenau, F. (i9<>32) Butomaceae, in Das Pflanzenreich, iv. 16 (heraus-
gegeben von A. Engler), 12 pp., 5 text-figs. 1903.
(An authoritative account of the species of this family which
includes water plants such as Hydrocleis nymphoides.)
Burgerstein, A. (1904) Die Transpiration der Pflanzen. x + 283 pp., 24
[pp. 266, 267] text-figs. Jena, 1904.
[This critical compilation contains a chapter (xxvi. " Guttation,
Hydathoden") dealing with the elimination of liquid water
from the leaves. The case of water plants is discussed on
pp. 195-197.]
Burkill, I. H. See Willis, J. C. and Burkill, I. H. (1895).
Burns, G. P. (1904) Heterophylly in Proserpinaca palustris. L. Ann.Bot.
[pp. 160, 161] Vol. xvm. 1904, pp. 579-587, i pi.
[An account of experimental work on the conditions deter-
mining the formation of leaves of the "land- type" and "water-
type." This paper should bereadin conjunction withMcCallum,
W. B. (1902), on which it is based.]
Burrell, W. H.I Botanical Rambles in West Norfolk, with notes on
and >• (1911) the genus Utricularia. Trans. Norfolk and Norwich
Clarke, W. G.) Naturalists' Society, Vol. ix. 1914 (Pt n. 1911),
[p. 215] pp. 263-268.
(These notes contain a reference to remarkably luxuriant
growth observed in Utricularia.)
Biisgen, M. (1888) Ueber die Art und Bedeutung des Thierfangs bei
[pp. 93, 94, 95] Utricularia vulgaris L. Ber. d. deutsch. bot. Gesellsch.
Bd. vi. 1888, pp. Iv-lxiii.
(The author discusses the function of the bladders in this
species and shows experimentally that the carnivorous habit
is an advantage.)
Caldwell, O. W. (1899) On the Life-history of Lemna minor. Bot. Gaz. Vol.
[p. 76] xxvn. 1899, pp. 37-66, 59 text-figs.
(In this memoir special attention is paid to the gametophytes
and fertilisation.)
Cambessedes,J. (1829) Note sur les filatinees, nouvelle famille de plantes.
[p. 311] Mem. du museum d'histoire nat. T. xvm. 1829,
pp. 225-231.
(The author proposes to remove Elatine, Bergia and Merimea
from the Caryophyllaceae and to place them in a separate
family. He remarks on certain resemblances which they show
to the Hypericineae.)
Campbell, D.H. (1897) A Morphological Study of Naias and Zannichellia.
Proc. Cal. Acad. Sci. Ser. in. Botany, Vol. i. 1897—
1900, pp. 1-70, 5 pis.
(In this memoir special attention is paid to the anatomy and
the gametophytes.)
358
Candolle, Alphonse
P. de (1855)
[p. 296]
Candolle, Auguste P.
de (1827)
[pp. 12, 337]
Cario, R. (1881)
Caspary, R. (1847)
Caspary, R.
Caspary, R. (1856 2)
[p. 214]
Caspary, R. (1857)
Caspary, R. (I8581)
Caspary, R. (i8s82)
[PP-55,56, 173, 210,
211]
Caspary, R. (i8s83)
BIBLIOGRAPHY
Geographic Botanique. Paris, T. n. 1855.
(Pages 998-1006 deal with the distribution of aquatic species.
After showing how widely these plants are distributed, the
author concludes that the facts are scarcely explicable except
on the ground that there have been multiple centres of
creation.)
Organographie vegetale. Paris, 1827.
(Vol. i. Book 2, Chap. in. contains the first enunciation of the
phyllode theory of the Monocotyledonous leaf.)
Anatomische Untersuchung von Tristicha hypnoides
Spreng. Bot. Zeit. Jahrg. 39, 1881, pp. 25-33, 41-48,
57-64> 73-82, i pi.
[The author obtained material of this plant in Guatemala. The
present paper forms an anatomical monograph of the species
which was incompletely treated in Tulasne, L. R. (1852).
The part of the plant which Cario describes as the "thallus"
is now generally regarded as representing the root-system.]
Ueber Elatine Alsinastvum und Trapa natans, Ver-
handl. des naturhistorischen Vereines der preuss.
Rheinlande, Jahrg. 4, 1847, pp. in, 112.
(A brief note on a new locality for Elatine, and on the absence
of Trapa in the neighbourhood of Bensberg.)
Les Nympheacees fossiles. Ann. des sci. nat. Ser.
iv. Bot. T. vi. 1856, pp. 199-222, 2 pis.
(An account of the remains of this family found in Tertiary beds.)
Ueber die tagliche Periode des Wachsthums des
Blattes der Victoria regia Lindl. und des Pflanzen-
wachsthums iiberhaupt. Flora, N.R. Jahrg. xiv.
(G.R. Jahrg. xxxix.) 1856, pp. 113-126, 129-143,
145-160, 161-171.
(A detailed study of the growth of the leaves of Victoria regia
in a hot-house. The maximum growth in 24 hrs was 30-8 cms.
in length, and 36-7 cms. in breadth.)
Note sur la division de la famille des Hydrocharidees,
proposee par M. Chatin. Bull, de la Soc. bot. de
France, T. iv. 1857, pp. 98-101.
[A criticism of views expressed in Chatin, A. (1856).]
Eine systematische Ubersicht der Hydrilleen. Mon-
atsber. d. Konig. Preuss. Akad. d. Wiss. Berlin, 1858
(for 1857), pp. 39-5 1-
(A systematic account of the tribe of the Hydrocharitaceae
which includes Elodea, etc.)
Die Hydrilleen (Anacharideen Endl.). Pringsheim's
Jahrb.'f. wiss. Bot. Bd. i. 1858, pp. 377~5I3, 5 Pls-
(A very important monograph of that tribe of the Hydro-
charitaceae which includes Hydrilla, Elodea and Lagarosiphon.
The standpoint is systematic, but a good deal of anatomical
work is included.)
Die Bliithe von Elodea canadensis Rich. Bot. Zeit.
Jahrg. 16, 1858, pp. 313-317, J P1-
(A description of the female flower based on living material.)
BIBLIOGRAPHY 359
Caspary, R. (1858*) Sur YAldrovanda vesiculosa. Bull, de la Soc. hot. de
[p. in] France, T. v. 1858, pp. 716-726.
[The observations in this paper are expanded and illustrated
in Caspary, R. (1859 and 1862).]
Caspary, R. (1859 Aldrovanda vesiculosa Monti. Bot. Zeit. Jahrg. 17,
and 1862) 1859, pp. 117-123, 125-132, 133-139, 141-150, 2 pis.
[pp. no, 239 and Aldrovandia vesiculosa. Bot. Zeit. Jahrg. 20, 1862,
Fig. 75, p. in] pp. 185-188, 193-197, 201-206, i pi.
[These papers form a monograph of this species. An abstract
of part of Caspary's work on the subject is also to be found in
Flora, N.R. Jahrg. xvn. (G.R. Jahrg. XLII.) 1859, pp. 140-143.]
Caspary, R. (1860) Bulliarda aquatica D.C. Schriften d. konig. phys.-6k.
[p. 234] Gesellsch. zu Konigsberg, Jahrg. i. 1861 (for 1860),
pp. 66-91, 2 pis.
(A monograph of this aquatic member of the Crassulaceae,
now known as Tillaea aquatica L.)
Caspary, R. (1861) Nuphar luteum L. var. rubropetalum. Schriften d.
[p. 276] konig. phys.-6k. Gesellsch. zu Konigsberg, Jahrg. n.
1862 (for 1861), pp. 49-50, i pi.
(A description, illustrated with a coloured plate, of a variety
of Nymphaea lutea with red petals.)
Caspary, R. (iSyo1) Neue und seltene Pflanzen Preussens. Schriften d.
konig. phys.-6k. Gesellsch. zu Konigsberg, Jahrg. xi.
1871 (for 1870), pp. 61-64.
(These field notes include an account of certain varieties of
Castalia alba.)
Caspary, R. (iSyo2) Welche Vogel verbreiten die Samen von Wasser-
[p. 300] pflanzen? Schriften d. konig. phys.-6k. Gesellsch. zu
Konigsberg, Jahrg. xi. 1871 (for 1870), Sitzungsber.
p. 9.
(This note emphasizes our ignorance of the part played by
water birds in the distribution of water plants.)
Caspary, R. (1875) Die geographische Verbreitung der Geschlechter von
[p. 54] Stratiotes aloides L. Sitzungs-Ber. d. Gesellsch. Natur-
forsch. Freunde zu Berlin, 1875, pp. 101-106.
(An account of the distribution of this species, supplementing
and criticising previous work, and showing that though in
some regions female plants alone are present, no region is
known in which male plants appear exclusively.)
Cavolini, F. j, ^ Zosterae Oceanicae Linnei AN0H2IS. Contem-
(Caulinus,P.)J ' ' platus est Philippus Caulinus Neapolitanus. Annis
[p. 125] 1787 et 1791, 20 pp., i pi. Neapoli, 1792.
[An account of the flowering and vegetative organs of Posidonia
Caulini = " Zoster a oceanica." This paper and Cavolini, F.
(1792 2) are analysed in Delpino, F. and Ascherson,P. (1871).]
Cavolini, F. \ , 2> Phucagrostidum Theophrasti AN®H^I2. Contem-
(Caulinus,P.)j ^'^ ' platus est Philippus Caulinus Neapolitanus. Anno
[p. 125] 1792, 35 pp., 3 pis. Neapoli, 1792.
(An account with good figures of the vegetative and flowering
structure of Cymodocea aequorea = " Phucagrostis major" and
Zostera nana = " Phucagrostis minor.'")
36°
Chamberlain, C. J.
Chatin, A. (1855*)
[pp. 164, 1 66]
BIBLIOGRAPHY
See Coulter, J. M. and Chamberlain, C. J. (1904).
Note sur la presence de matiere verte dans 1'epiderme
des feuilles de I'Hippuris vulgaris, du Peplis portula,
des Jussiaea longifolia et /. lutea, de I'lsnardia
palustris et du Trapa natans. Bull, de la Soc. bot.
de France, T. n. 1855, pp. 674-676.
(The object of this note is to draw attention to the existence
in many water plants of an epidermis supplied with stomates
and also containing chlorophyll. The author points out that
this type of epidermis is well adapted to amphibious life.)
Memoire sur le Vallisneria spiralis, L. 31 pp., 5 pis.
Paris, 1855.
(The morphology, anatomy and floral structure are dealt with
in detail, and there is a habit drawing showing male and
female plants.)
Anatomic comparee des vegetaux, Livraison i and 2,
pp. 1-96, 20 pis. Paris, 1856.
(The first part of this work deals with Monocotyledonous
water plants. It is fully illustrated but singularly inaccurate.)
Note sur le cresson de fontaine (Sisymbrium Nastur-
tium. L., Nasturtium officinale R. Br.) et sur sa culture.
Bull, de la Soc. bot. de France, T. v. 1858, pp.
158-166.
(This economic paper deals with the cultivation of the Water-
cress.)
Faits d'anatomie et de physiologic pour servir a
1'histoire de I'Aldrovanda. Bull, de la Soc. bot. de
France, T. v. 1858, pp. 580-590.
(This paper is of less importance than those of Caspary dealing
with the same subject. Chatin and Caspary obtained the main
part of their material from the same source.)
Chrysler, M. A. (1907) The Structure and Relationships of the Potamo-
[pp. 63, 65, 135 and getonaceae and allied Families. Bot. Gaz. Vol. XLIV.
Fig- 39, P- 62] 1907, pp. 161-188, 3 text-figs., 5 pis.
(A discussion of the affinities of these families is based upon
a study of the anatomy of Potamogeton, Ruppia, Zostera,
Phyllospadix, Cymodocea and Zannichellia, etc.)
Chatin, A. (i8552)
[pp. 134, 235]
Chatin, A. (1856)
Chatin, A.
Chatin, A. (i8s82)
Clarke, W. G.
Clavaud, A. (1876)
[P- 78]
Clavaud, A. (1878)
[p. 127]
See Burrell, W. H. and Clarke, W. G. (1911).
Sur une particularite du Lemna tvisulca L. Actes de
la Soc. Linn, de Bordeaux, T. xxxi. (Ser. iv. T. i.)
1876, pp. 300-311.
(A note on the occurrence of raphides in this species and their
possible biological significance.)
Sur le v6ri table mode de fecondation du Zostera
marina. Actes de la Soc. Linn, de Bordeaux,
T. xxxn. (Ser. iv. T. n.) 1878, pp. 109-115.
(An account of the pollination of Zostera growing in situ, from
observations made from a boat.)
BIBLIOGRAPHY 361
Cloez, S. (1863) Observations sur la nature des gaz produits par les
[p. 256] plantes submergees sous I'influence de la lumiere.
Comptes rendus de 1'acad. des sciences, Paris, T. LVII.
1863, pp. 354-357-
(The author describes experiments showing that the gas given
off by aquatic plants exposed to light is a mixture of oxygen
and nitrogen: he holds that this nitrogen is produced by
decomposition of the substance of the plant.)
Cloez, S. and) , g , Recherches sur la vegetation. Comptes rendus de
Gratiolet, P. j Vfr5»J r academic des sciences, Paris, T. xxxi. 1850, pp.
[p. 256] 626-629.
(An early account of the gaseous exchange in submerged
plants.)
Clos, D. (1856) Mode de propagation particulier au Potamogeton
[p. 67] crispus L. Bull, de la Soc. bot. de France, T. in.
1856, pp. 350-352.
(The first account of the peculiar turions of this plant.
According to the author, they are unique among organs of
vegetative reproduction in their horny consistency, and also
in the fact that the detached shoot grows no further, but its
whole vitality is concentrated in its axillary buds.)
Cohn, F. (1850) UeberAldrovandavesiculosaMonti. Flora, N.R.Jahrg.
[p. no] vin. (G. R. Jahrg. xxxm.) 1850, pp. 673-685, i pi.
[A description of the anatomy and morphology of this species,
less detailed than that of Caspary, R. (1859 and 1862).
A brief account of early references to the plant is given in an
appendix.]
Cohn, F. (1875) Ueber die Function der Blasen von Aldrovanda und
[PP- 93, 96, no, 270] Utricularia. Cohn's Beitrage zur Biologic der
Pflanzen, Bd. i. Heft 3, 1875, pp. 71-92, i pi.
(The earliest memoir in which the existence of the carnivorous
habit in these two genera is fully established.)
Coleman, W. H. (1844) Observations on a new species of (Enanthe. Annals
[pp. 150, 204] and Mag. of Nat. Hist. Vol. xm. 1844, pp. 188-191,
i pi.
(The author makes out what appears to be a good case for
regarding Oenanthe fluviatilis as a species distinct from Oe.
Phellandrium, Lamk., instead of as a mere variety of it.)
Compton, R. H. (1916) The Botanical Results of a Fenland Flood. Journ. of
[pp. 200, 289] Ecology, Vol. iv. 1916, pp. 15-17, 2 pis.
(This paper gives an account of the effect of a nine months'
period of submergence upon the flora of an area of fenland in
E. Anglia, 24 square miles in extent.)
Cook, M. T. (1906) The Embryology of some Cuban Nymphaeaceae.
[p. 309] Bot. Gaz. Vol. 42, pp. 376-392, 3 pis.
(The author's study of several genera leads him to the con-
clusion that the Nymphaeaceae are anomalous Monocotyledons.)
Costantin, J. (1884) Recherches sur la structure de la tige des plantes
[pp. 192, 200, 201, 259] aquatiques. Annales des sci. nat. vi. Ser. Bot.
T. xix. 1884, pp. 287-331, 4 pis.
(A comparison of the anatomy of stems of different individuals
of the same species, or of different parts of the same stem,
grown in water, in air, or embedded in soil beneath water
A very important contribution to the experimental anatomy
of water plants.)
362
Costantin, J. (1885
[pp. 165, 1 66]
Costantin, J. (i88s2)
Costantin, J. (i88s3)
Costantin, J. (1886)
[pp. 12, 28, 30, 51,
145, 151, 155, 156]
Coster, B. F. (1875)
[P- 67]
Coulter, J. M.)
and ,
Chamberlain, [(I9°4)
C.J. J
[pp. 322, 325]
Coulter, J.M. )
and
Land,W.J.G.)
[P- 15]
Crocker, W. (1907)
[P- 243]
BIBLIOGRAPHY
Observations critiques sur I'dpidenne des feuilles des
vegetaux aquatiques. Bull, de la Soc. hot. de France,
T. xxxii. (Ser. n. T. vii.) 1885, pp. 83-88 (followed
by an account of a discussion in which £. Mer and
P. Duchartre took part, pp. 88-92).
(The author attempts to show that the influence of the aquatic
medium is one of the causes of the loss of stomates in sub-
merged leaves. He also maintains that submerged plants
possess a true epidermis, even if stomates are absent and
chlorophyll present in this layer.)
Recherches sur la Sagittaire. Bull, de la Soc. bot. de
France, T. xxxii. (Ser. n. T. vn.) 1885, pp. 218-223.
(Observations on the heterophylly of Sagittaria sagittifolia and
a comparison of the anatomy of the submerged and aerial
leaves.)
Influence du milieu aquatique sur les stomates. Bull,
de la Soc. bot. de France, T. xxxii. (Ser. n. T. vn.)
l885> PP- 259-264.
[This paper forms a continuation of Costantin, J. (I8851).
The author criticises Mer's view that the presence or absence
of stomates is partly an hereditary character and partly due
to variations in illumination and nutrition, and brings forward
further evidence to show that the milieu has a great influence
on the distribution of stomates.]
Etudes sur les feuilles des plantes aquatiques. Ann.
d. sci. nat. Ser. vn. Bot. T. 3, 1886, pp. 94-162,
5 pis.
(A memoir on the morphology and anatomy of the leaves of
water plants, with special reference to the effect of the environ-
ment upon their structure.)
Om Potamogeton crispus L. och dess groddknoppar.
Botaniska Notiser, Lund, 1875, pp. 97-102, i text-fig.
[This paper, which deals with the winter buds of Potamogeton
crispus, is reviewed in Bot. Jahresber. (Just) Jahrg. in. 1877
(for 1875), p. 425.]
Morphology of Angiosperms. x + 348 pp., 113 text-
figs. London and New York, 1904.
(This general work contains a number of references to water
plants.)
The Origin of Monocotyledony. Bot. Gaz. Vol. 57,
1914, pp. 509-519, 2 pis., 2 text-figs.
(In this paper the seedling of Sagittaria variabilis is described.)
Germination of Seeds of Water Plants. Bot. Gaz.
Vol. 44, 1907, pp. 375-380.
[The author shows experimentally that the delay in "germination
of the seeds of water plants, which have not been subjected
to a period of desiccation, is due to the impossibility of absorbing
sufficient water through the intact seed coats. Drying followed
by a soaking seems to induce rupture of the coats, and thus to
allow growth to begin. The paper contains a criticism of
Fischer, A. (1907).]
BIBLIOGRAPHY
363
Crocker, W.
and
Davis, W. E.
[pp. 242, 243]
Cunnington, H. M.
(1912)
[P- 135]
iard, |
and >
>,C. )
Dangeard,
P. A.
Barbe,
[P- 181]
1887)
Delayed germination in seed of A lisma Plantago. Bot.
(1914) Gaz. Vol. 58, 1914, pp. 285-321, 8 text-figs.
(A detailed study of one case, A lisma Plantago, illustrating the
delay in germination so common among water plants; the
dormancy of the achenes is here due to the mechanical restraint
exercised by the seed coats.)
Crouan (Freres) (1858) Observations sur un mode particulier de propagation
[P- 93] des Utricularia. Bull, de la Soc. bot. de France, T. v.
1858, pp. 27-29.
(These notes on U. minor are written without knowledge of
the previous literature.)
Anatomy of Enhalus acoroides (Linn, f.), Zoll. Trans.
Linn. Soc. Lond. Ser. n. Bot. Vol. vn. Pt 16, 1912
(1904-1913), pp. 355-371, i pi., 13 text-figs.
(A detailed account of the anatomy of this marine Angio-
sperm, in which special attention is paid to the development
of the various tissues.)
La Polystelie dans le genre Pinguicula. Bull, de la
Soc. bot. de France, T. 34, ^1887, pp. 307-309.
(The authors show that the old axes of Pinguicula vulgaris
may contain four or five steles, each surrounded by a well-
marked endodermis.)
Darwin, C. (1859) On the Origin of Species, ix + 502 pp. London,
[pp. 296, 298, 300, 324] 1859.
(Chapter xn. contains a section dealing with the distribution
of fresh-water animals and plants, pp. 383-388.)
Insectivorous Plants, x + 462 pp. 30 text-figs.
London, 1875.
(Chapter xiv. deals with Aldrovandia and Chapters xvu. and
xvin. with Utricularia.)
Insectivorous Plants. Second Edition revised by
Francis Darwin, xiv + 377 pp., 30 text-figs. London,
1888.
[This edition contains a certain number of additional facts and
references not found in Darwin, C. (1875).]
Journal of Researches into the Natural History and
Geology of the... voyageof...H. M.S. 'Beagle.' London,
1890.
(See reference to Gunnera on p. 298.)
The Movements and Habits of Climbing Plants.
ix + 2o8 pp., 13 text-figs. London, 1891.
(Darwin's references to climbing roots are of interest in con-
nection with the tendril roots of certain water plants.)
The Power of Movement in Plants, x + 592 pp.,
196 text-figs. London, 1880.
[On p. 21 1 the observations made by Rodier on the movements of
Ceratophyllum are discussed. See Rodier, 6. (i877x) and
(18772).]
Darwin, C. (1875)
[PP- 93. 95, in]
Darwin, C. (1888)
[P- 95]
Darwin, C. (1890)
[p. 181]
Darwin, C. (1891)
[p. 206]
Darwin, C. and F.
(1880)
[pp. 90, 161, 206]
364
Davie, R. C. (1913)
[pp. 50, 287]
Davis, W. E.
Delpino, F. (1870)
[P- 135]
Delpino, F. (1871)
[p. no]
Delpino, F. and)
Ascherson, P. J(I87I)
[pp. 84, 135, 236]
Desmoulins, C. (1849)
[P- 27]
Devaux, H. (1889)
[pp. 253, 254, 256]
Dodoens, R. (1578)
[p. 144]
Dollo, L. (1912)
[P- 39]
BIBLIOGRAPHY
Stratiotes Aloides, Linn., near Crieff . Trans, and Proc.
Bot. Soc. Edinb. Vol. xxvi. 1913, pp. 180-183, x pi-
(The author regards this plant as introduced in all Scottish
localities. Water more or less richly charged with lime seems
to suit it best.)
See Crocker, W. and Davis, W. E. (1914).
Ulteriori osservazioni et considerazioni sulla dico-
gamia nel regno vegetale n. Atti della Soc. Ital. di
Scienze Naturali, Vol. xin. 1870, pp. 167—205.
[Pp. 168-187 deal with hydrophilous plants, giving a resume
of the work on their pollination up to 1870. For a German
version with some additions see Delpino, F. and Ascherson,
P. (1871).]
Sulle Piante a Bicchieri. Nuovo Giornale Botanico
Italiano, Vol. in. 1871, pp. 174-176.
(A footnote on p. 175 deals with the carnivorous habits of
Aldrovandia.)
Federico Delpino 's Eintheilung der Pflanzen nach
dem Mechanismus der dichogamischen Befruchtung
und Bemerkungen iiber die Befruchtungsvorgange
bei Wasserpflanzen. Mitgetheilt und mit einigen
Zusatzen versehen von P. Ascherson. Bot. Zeit.
Jahrg. 29, 1871, pp. 443-445, 447-459, 463-467.
(This paper is based on Delpino, F. (1870) with certain
additions: it consists of a critical compilation from the literature
dealing with the pollination of Posidonia, Cymodocea, Halodule,
Zostera, Halophila, Ruppia, Vallisneria, CcratopKyllum and
Enhalus.)
Feuilles du Nymphaea et du Scirpus lacustris. Actes
de la Soc. Linneenne de Bordeaux, T. xvi. (Ser. n.
T. vi.) 1849, pp. 63-64.
(A record of the fact that the submerged leaves of Castalia
were known to Gaspard Bauhin, and that the floating leaves of
Scirpus lacustris were described by Scheuchzer.)
Du mecanisme des echanges gazeux chez les plantes
aquatiques submergees. Ann. d. sci. nat. Ser. vii.
T. 9, 1889, pp. 35-179, 8 text-figs.
(This may be regarded as the classic memoir on the physics of
the gaseous exchange in submerged plants. It includes a dis-
cussion of earlier works on the subject.)
A Nievve Herball, or Historic of Plantes:... no we
first translated out of French into English, by Henry
Lyte Esquyer. At London by me Gerard Dewes...
1578.
(This herbal contains an account of the heterophylly of the
Water Buttercup.)
Les Cephalopodes adaptes a la Vie Nectique Secon-
daire et a la Vie Benthique Tertiaire. Zool. Jahrb.
Suppl. 15, Bd. i. 1912, pp. 105-140.
[In this paper Dollo applies the Law of Irreversibility to certain
aquatic plants; see also Arbor, A. (1919 2).]
BIBLIOGRAPHY
365
Douglas, D. (1880)
[P- 55]
Duchartre, P. (1855)
Duchartre, P. (1858)
[p. 261]
Duchartre, P.
[P-
[1872)
Notes on the Water Thyme (Anacharis alsinastrum,
Bab.). Science Gossip (Hardwicke's), Vol. xvi. 1880,
pp, 227-229, 4 text-figs.
(The male flowers of Elodea canadensis, hitherto unknown in
Britain, are here recorded from Scotland and are described and
figured.)
Quelques mots sur la fecondation chez la Vallisnerie.
Bull, de la Soc. bot. de France, T. n. 1855, PP-
289-293.
(An historical account of the different views which have been
held on the question whether the male flowers of Vallisneria
do or do not become detached from their pedicels and float to
the surface of the water.)
Recherches experimentales sur la transpiration des
plantes dans les milieux humides. Bull, de la Soc. bot.
de France, T. v. 1858, pp. 105-111.
(The author concludes from his experiments that the transpira-
tion of a terrestrial plant can continue when it is grown in
a saturated atmosphere or even when it is completely immersed
in water.)
Quelques observations sur les caracteres anatomiques
des Zostera et Cymodocea, a propos d'une plante
trouvee pres de Montpellier. Bull, de la Soc. bot. de
France, T. xix. 1872, pp. 289-302.
[The author shows that, in the absence of the organs of
fructification, Zostera and Cymodocea can be distinguished by
their anatomy. This analysis of the anatomical characters of
marine Angiosperms was carried much further by another
French observer about twenty years later; see Sauvageau, C.
and following titles.]
Dudley, W. R. (1894) Phyllospadix, its systematic characters and distribu-
[p. 123] tion. Zoe, San Francisco, Vol. iv. 1894, No. 4, pp.
381-385-
(A revised diagnosis of this genus, and of the two species,
P. Scouleri, Hook, and P. Torreyi, Wats.)
Sur la nature reelle de la " fronde " et du " cotyledon "
des Lemna. Bull. mens. de la Soc. Linneenne de
Paris, T. i. 1874-1889, No. 19, 1878, pp. 147-149.
(This author regards the thallus of Lemna as "un sympode
d'embryons disposes a la suite les uns des autres.")
La fecondation chez les Ceratophyllum. Bull. mens.
de la Soc. Linneenne de Paris, No. 132, 1892, p. 1056.
(The author describes the rising to the surface of the detached
anthers, and the descent of the pollen through the water.)
Duval-Jouve, J, (1864) Lettre sur la de"couverte du Coleanthus subtilis en
[pp. 299, 301] Bretagne. Bull, de la Soc. bot. de France, T. xi.
1864, pp. 265, 266.
(Notes on the part played by birds in the dispersal of aquatic
plants.)
Dutailly, G. (1878)
[P- 73]
Dutailly, G. (1892)
[P. 85]
366 BIBLIOGRAPHY
Duval-Jouve, J. (1872) Diaphragmes vasculiferes des monocotyledones aqua-
[pp. 167, 183] tiques. Academic des Sciences et Lettres de Mont-
pellier. Mem. de la section des sciences, T. vm.
1872-1875, pp. 157-176, i pi.
(The author of this paper shows that the occurrence of dia-
phragms crossing the lacunae of the leaves of aquatic Angio-
sperms is more general than has hitherto been supposed, and
that transverse vascular connexions between the longitudinal
veins are commonly associated with such diaphragms.)
Ehrhart, F. (1787) Wiedergefundene Bliite der dicken Wasserlinse
(Lemna gibba L.). Ehrhart's Beitrage zur Natur-
kunde, Bd. I. 1787, pp. 43-51.
[An account of the finding of the flowers of Lemna gibba which
had not been seen since they were described in Micheli, P. A.
(1729).]
Engler, A. (1877) Vergleichende Untersuchungen iiber die morpho-
[pp. 74, 82] logischen Verhaltnisse der Araceae. n. Theil. Ueber
Blattstellung and Sprossverhaltnisse der Araceae.
Nova Acta der Ksl. Leop. -Carol. Deutschen Akad.
der Naturforscher, Bd. 39, No. 4, 1877, PP- x59-232»
6 pis.
(The author explains the nature of the shoot of the Lemnaceae
on the basis of a close comparison with Pistia, after an
exhaustive discussion of the morphology of the Araceae in
general.)
Engler, A. (1879) Notiz iiber die Befruchtung von Zoster a marina und
[pp. 135, 315] das Wachsthum derselben. Bot. Zeit. Jahrg. 37,
1879, pp. 654-655.
[A criticism of Hofmeister, W. (1852), with remarks on the
method of pollination, the branching of the sterile and fertile
shoots, etc.]
Engler, A. (1892) Die systematische Anordnung der monokotyledoneen
[?• 3*4] Angiospermen. Abhandl. d. k. Akad. d. Wiss. Berlin,
1892, Abh. ii. 1892, 55 pp.
(The systematic relationships of the Helobieae are dealt with on
pp. 11—20.)
Engler, A. See Krause, K. and Engler, A. (1906).
Ernst, A. (I8721) Ueber Stufengang und Entwickelung der Blatter von
Hydrocleis nymphoides Buchenau (Limnocharis Hum-
boldtii C. L. Richard). Bot. Zeit. Jahrg. 30, 1872,
pp. 518-520.
(A brief account of heterophylly in this species.)
Ernst, A. (1872*) Ueber die Anschwellung des unter Wasser befind-
[p. 191] lichen Stammtheiles von Aeschynomene hispidula
H. B. K. Bot. Zeit. Jahrg. 30, 1872, pp. 586-587.
(A description of the aerenchyma found in this Leguminous
shrub — a native of Venezuela.)
BIBLIOGRAPHY
36?
Esenbeck, E. (1914)
[pp. 151, 157 and
Figs. 104, p. 158,
and 105, p. 159]
Evans, A. H.
Fauth, A. (1903)
[pp. 15, 18, 241, 242,
246, 248, 271, 297]
Fenner, C. A. (1904)
[p. in]
Ferrero, F.
Fischer, A. (1907)
[P- 243]
Fischer, G. (1907)
Beitrage zur Biologie der Gattungen Potamogeton
und Scirpus. Flora, N.F. Bd. 7 (G.R. Bd. 107), 1914,
pp. 151-212, 59 text-figs.
(An account of experimental and anatomical work on the land
forms of Potamogeton and on leaf development in Scirpus
lacuster and other Cyperaceae which are normally leafless. The
author follows Goebel in regarding the water leaves of all these
plants as youth leaves, to which the plant reverts under con-
ditions of poor nutrition, rather than as direct adaptations to
the medium.)
See Fryer, A., Bennett, A. and Evans, A. H. (1898-
1915).
Beitrage zur Anatomic und Biologie der Friichte und
Sarnen einiger einheimischer Wasser- und Sumpf-
pflanzen. Beihefte zum Bot. Centralblatt, Bd. xiv.
1903, pp. 327-373> 3 p!s-
(The fruit and seeds of Alisma, Elisma, Sagitlaria, Butomus,
Callitriche, Hippuris, Myriophyllum, Limnanthemum, Meny-
anthes and Littorella are dealt with, and certain land plants are
included for comparison.)
Beitrage zur Kenntnis der Anatomic, Entwicklungs-
geschichte und Biologie der Laubblatter und Driisen
einiger Insektivoren. Flora, Bd. 93, 1904, pp. 335-
434, 16 pis.
(One section of this paper is devoted to Aldrovandia.}
See Gibelli, G. and Ferrero, F. (1891).
Wasserstoff- und Hydroxylionen als Keimungsreize.
Ber. d. deutsch. Bot. Gesellsch. Bd. xxv. 1907, pp.
108-122.
[A study of the delayed germination characteristic of many
water plants, which the author attributes to the lack of certain
chemical stimuli. For a criticism see Crocker, W. (1907).]
Focke, W. 0. (1893!)
[p-
Die bayerischen Potamogetonen und Zannichellien.
Ber. d. Bayer. Bot. Gesellschaft, Mimchen, Bd. xi.
1907, pp. 20-162.
(A detailed systematic monograph of the Bavarian Potamo-
getonaceae, without illustrations.)
Eihe Fettpflanze des siissen Wassers. Abhandl.
naturwiss. Vereine zu Bremen, Bd. xn. Heft in.
1893, p. 408.
(This paper deals with Montia rivularis Gm. and its possibly
xerophytic ancestry.)
Focke, W. O. (i8932) Fehlen der Schlauche bei Utricularia. Abhandl.
naturwiss. Vereine zu Bremen, Bd. xn. 1893, P- 5^3.
(In this brief note the author reports the discovery of a form
of Utricularia vulgaris without bladders. He considers that it
cannot be a hybrid between U. vulgaris and U. intermedia
because it resembles U. vulgaris in all points except the absence
of bladders.)
368
Foerste, A. F. (1889)
[p. 216]
Forel, F. A. (1901)
[p. 255]
Forel, F. A. (1892-
1904)
[pp. 253, 278]
Frank, A. B. (1872)
[pp. 281, 283]
Freyn, J. (1890)
[p. 228]
Fries, E. (1858)
[p. 276]
Fryer, A. (1887)
[PP- 195, 330]
Fryer, A., Bennett, A.
and Evans, A. H.
(1898-1915)
[pp. 58, 195, 303]
BIBLIOGRAPHY
Botanical Notes. Bull. Torr. Bot. Club, Vol. xvi.
1889, pp. 266-268, i pi.
(On p. 266 there is a note on the adventitious buds which arise
from the base of the submerged leaves in Nasturtium lacustre.
In this species marked heterophylly occurs, the submerged
leaves being pinnately dissected and the air leaves simple.)
Handbuch der Seenkunde. Allgemeine Limnologie
(Bibl. Geog. Handbiicher herausgegeben von F.
Ratzel). Stuttgart, 1901.
[This general treatise on Limnology contains a chapter (pp.
161-241) on the biology of lakes.]
Le Leman. Monographic limnologique. 3 vols.
Lausanne, 1904.
(This elaborate monograph of the Lake of Geneva throws much
light on the physics and chemistry of fresh waters. The Biology
of the Lake is dealt with in Vol. in. pp. 1-408.)
Ueber die Lage und die Richtung schwimmender
und submerser Pflanzentheile. Cohn's Beitrage zur
Biologie der Pflanzen, Bd. i. (1870-1875) Heft 2,
1872, pp. 31-86.
[This memoir is the record of a series of experiments which the
author undertook in order to examine the influences which
regulate the position and direction of floating and submerged
leaves. He chiefly employed Hydrocharis, Trapa and Callitnche.
For criticisms of the work see Karsten, G. (1888) and Vries, H.
de(i873).]
Beitrage zur Kenntniss einiger Arten der Gattung
Ranunculus. Bot. Centralbl. Bd. XLI. 1890, pp. 1-6.
(On p. 5 the author gives some observations on the pollination
of the aquatic species of Ranunculus.)
Kiirzere briefliche Mittheilungen. Ueber A vena,
Datura und Nymphaea. Bot. Zeit. Jahrg. 16, 1858,
P- 73-
[These notes contain the record of the occurrence in a lake in
Sweden (Fagersjo in Nerike) of a (Nymphaea) Castalia with
rose-purple flowers, which is regarded by the author as a
variety of C. alba.]
Notes on Pondweeds. 6. On Land-forms of Potamo-
geton. Journ. of Bot. Vol. xxv. 1887, pp. 306-310.
(This paper forms one of a series of contributions made by
the author to the study of this group, the majority of which
are not included in this bibliography, as their interest is almost
exclusively systematic. In the present paper the land forms
of Potamogeton natans, P. fluitans, P. plantagineus, P. hetero-
phyllus and P. Zizii are described.)
The Potamogetons (Pond Weeds) of the British Isles,
x + 94 pages, 60 pis., 2 text-figs. London, 1898-1915.
(A systematic monograph of the genus, as far as it is represented
in Britain, with fine coloured plates by R. Morgan.)
BIBLIOGRAPHY
369
Gardiner, W. (1883) On the Physiological Significance of Water Glands
[pp. 267, 322] and Nectaries. Proc. Camb. Phil. Soc. Vol. v. 1886
(for 1883-1886). Paper read, Nov. 12, 1883, pp. 35-
50, i pi.
[In the course of this paper the author suggests (p. 43) that
Dicotyledons are typically land plants while Monocotyledons
are of an essentially aquatic nature.]
Travels in the Interior of Brazil, xvi + 562 pp.,
i map, i pi. London, 1846.
(This volume of travels by the .Superintendent of the Royal
Botanic Gardens of Ceylon contains an account on pp. 527,
528 of the curious Utricularia nelumbi folia.)
Observations on the Structure and Affinities of the
Plants belonging to the natural order Podostemaceae,
together with a Monograph of the Indian species.
Calcutta Journ. of Nat. Hist. Vol. vn. 1847, pp. 165-
189.
(This paper is chiefly systematic, but points connected with the
life-history are also touched upon. The author suggests that
there is an affinity between the Podostemaceae and Nepenthes.)
Gaudichaud, C. (1826) Voyage autour du monde, par Louis de Freycinet.
[p. 130] Botanique. vii + 522 pp.
[On p. 430 the filamentous pollen of Halophila ovata and
Ruppia antarctica (=Cymodocea antarctica) is mentioned.]
Gardner, G. (1846)
[p. 108]
Gardner, G. (1847)
[pp. 112, 310]
Geldart, A. M. (1906)
[pp. 50, 54]
Stratiotes A hides L. Trans. Norfolk and Norwich
Naturalists' Society, Vol. vm. 1905, pp. 181-200,
i pi.
[This paper forms a useful account of the Water Soldier, partly
drawn from Nolte, E. F. (1825) and other sources, but also con-
taining original observations on the life-history of the plant.]
Geneau de Lamarliere, Sur les membranes cutinisees des plantes aquatiques.
Revue gen. de Bot. T, 18, 1906, pp. 289-295.
(A micro-chemical study of the epidermis and of the cells in
contact with the internal lacunae in the cases of Ranunculus
fluitans, Caltha palustris, Castalia alba, Myriophyllum spicatum,
Hottonia palustris, Elodea canadensis, Potamogtton densus
Glyceria spectabilis and Equisetum limosum.)
L. (1906)
[pp. 163, 260]
Gibelli, G. )
and j- (1891)
Ferrero, F.j
Gin, A. (1909)
[pp. 234, 295, 303]
A. W. P.
Intorno allo sviluppo dell' ovolo e del seme della
Trapa natans L. Ricerche di anatomia e di morfologia.
Malpighia, v. 1891, pp. 156-218, n pis.
(An elaborate and fully illustrated monograph dealing with the
ovary, ovule and seed of Trapa natans. The vascular anatomy
of the ovary is fully described, and the development of the
embryo. The authors regard the embryo as a degraded
structure which cannot be homologised with normal embryos.)
Recherches sur les Lythracees. 166 pages, 13 pis.,
28 text-figs. These Doct. Univ. Paris, 1909.
(This memoir contains information about the structure, dis-
tribution, etc. of the aquatic Lythraceae.)
24
Gliick, H. (1901)
[P- 44]
Gluck, H. (1902)
Gluck, H. (1905)
[pp. 9, 19, 195. 223,
280 and Figs. 147,
p. 224, 148 and 149,
P- 225]
Gluck, H. (1906)
[Passim and Figs. 44,
P. 69, 57, P- 89, 58,
P. 89, 59, p. 92, 63,
p. 96, 64, p. 96, 66,
P- 99, 69, p. 102, 146,
p. 223]
Gliick, H. (1911)
[pp. 145, 188, 198,
199, 200, and Figs.
95, p. 147, 128, p.
198, 129, 130 and
131, p. 199, 134 and
135. P- 203]
Gliick, H. (1913)
BIBLIOGRAPHY
Die Stipulargebilde der Monokotyledonen. Verhandl.
d. Naturhist.-Med. Vereins zu Heidelberg, N.F. Bd. 7,
Heft i, 1901, pp. 1-96, 5 pis., i text-fig.
(In this work the morphology and biology of the stipular
structures of many Monocotyledons are described, including
those found in a number of aquatic forms such as Potamoge-
tonaceae, Hydrocharitaceae, etc.)
Ueber die systematische Stellung und geographische
Verbreitung der Utricularia ochroleuca R. Hartman.
Ber. d. deutsch. bot. Gesellsch. Bd. xx. 1902, pp.
141-156, i pi.
(This paper contains a good deal of information about the
submerged species of Utricularia in general.)
Biologische und morphologische Untersuchungen
iiber Wasser- und Sumpfgewach.se. I. Die Lebens-
geschichte der europaischen Alismaceen. xxiv + 312
pp., 7 pis., 25 text-figs. Jena, 1905.
[The species studied were Alisma Plantago, (I..) Michalet,
A . graminifolium, Ehrh., Elisma natans, Buchenau, Echinodorus
ranunculoides, (L.) Engelm., E. ranunculoides var. repens,(Lam.) ,
Caldesia parnassifolia, (Bassi) Par!., Damasonium stellatum,
(Rich.) Pers., and Sagittaria sagittifolia, L. An elaborate series
of culture experiments was carried out, to determine the effect
of external conditions upon these plants.]
Biologische und morphologische Untersuchungen
uber Wasser- und Sumpfgewachse. II. Untersuchun-
gen iiber die mitteleuropaischen Utricularia- Arten,
iiber die Turionenbildung bei Wasserpflanzen, sowie
iiber Ceratophyllum. xvii + 256 pp., 28 text-figs.,
6 pis. Jena, 1906.
(An admirable account of the genus Utricularia, of 'winter-
bud' formation in general, and of the biology of the genus
Ceratophyllum, with special reference to the formation of
'rhizoids.')
Biologische und morphologische Untersuchungen
iiber Wasser- und Sumpfgewachse. III. DieUferflora.
xxxiv + 644 pp., 8 pis., 105 text-figs. Jena, 1911.
[A detailed study of the manner of life of those plants which
grow on the margin of fresh waters and have adopted an
amphibious habit. As in his previous work, the author com-
bines cultural experiments with observations in the field. He
shows that a large number of shore plants have aquatic forms
which have remained hitherto undescribed. Like Gliick, H.
(1905) and (1906) the book is beautifully illustrated and pro-
vided with a useful index.]
Contributions to our Knowledge of the Species of
Utricularia of Great Britain with Special Regard to
the Morphology and Geographical Distribution of
Utricularia ochroleuca. Ann. Bot. Vol. xxvu. 1913,
pp. 607-620, 2 pis., 7 text-figs.
(The author records Utricularia ochroleuca from a number of
stations in Great Britain and discusses the morphology, biology
and distribution of this species.)
BIBLIOGRAPHY
Goebel, K. (1879)
[P- 225]
Goebel, K. (1880)
[p. 12]
Goebel, K. (I8891)
Goebel, K. (18892)
[PP- 93, 99]
Goebel, K. (i8893)
[P-
Goebel, K. (1891)
[pp. 40, 100, 103,104,
106, and Fig. 68, p.
100]
371
Bot. Zeit.
Ueber Sprossbildung auf Isoetesblattern.
Jahrg. 37, 1879, pp. 1-6, 4 text-figs.
(A record of the replacement of sporangia by young plants in
the case of certain examples of Isoetes lacustris and /. echinospora
from the Vosges.)
Beitrage zur Morphologic und Physiologic des
Blattes. (Schluss.) Bot. Zeit. Jahrg. 38, 1880, pp.
833-845, i pl-
(On pp. 833-836 the heterophylly of Sagittaria sagittifolia is
described. In opposition to de Candolle, Goebel takes the view
that the band-shaped leaf of Sagittaria represents the entire
leaf, not merely a modified petiole.)
Ueber die Jugendzustande der Pflanzen. Flora, Neue
Reihe, Jahrg. 47, 1889, pp. 1-45, 6 text-figs., 2 pis.
(Pp. 40-43 contain an account of the germination of Utricularia
montana.)
Der Aufbau von Utricularia. Flora, Neue Reihe,
Jahrg. 47 (G. R. Jahrg. 72), 1889, pp. 291-297, i pi.
(This paper forms a continuation of the author's previous work
on Utricularia', U. affinis, U. longifolia, and U. bryophila are
figured.)
Pflanzenbiologische Schilderungen. Teil i. 239 pp.,
9 plates, 98 text-figs. Marburg, 1889.
(Pp. 166-169 deal with one of the Podostemaceae, a species of
Terniola.)
Morphologische und Biologische Studien. V. Utricu-
laria. VI. Limnanthemum. Ann. du Jardin Bot. de
Buitenzorg, Vol. ix. 1891, pp. 41-126, n pis.
(In these papers certain extra-European species of Utricularia
and Limnanthemum are dealt with; the vexed question of the
morphology of the Utricularia shoot receives special considera-
tion.)
Goebel, K. (1891-1893) Pflanzenbiologische Schilderungen. Teilu. iv + 386
[Passim and Figs. 1 4, pp., 31 pis., 121 text-figs. Marburg, Lief, i, 1891,
Lief. 2, 1893.
[This work contains sections dealing with Utricularia (pp. 127-
160, 173-181, pis. XIV, XV) and the Podostemaceae (pp.
331-354, pis. XXVI-XXX). There is also a very important
general discussion of water plants from the biological stand-
point (pp. 217-373, pis. XXIV, XXV, etc.).]
p. 29, 20, p. 38, 60,
p. 92, 65, p. 98, 92,
p. 144, 103, p. 154,
143, p. 220, 150, p.
229, 160, p. 247]
Goebel, K. (1895)
Ueber die Einwirkung des Lichtes auf die Gestaltung
der Kakteen und anderer Pflanzen. Flora, Bd. 80,
1895, PP- 96-116, 5 text-figs.
[This paper includes a short account (pp. no, in) of certain
experiments upon Sagittaria which show that want of light
induces this plant to return to the 'youth form' in which
only band-shaped leaves are developed. Its behaviour is thus
analogous to that of Phyllocactus which, under similar con-
ditions, also reverts to the youth form.]
24—2
372
Goebel, K. (1896)
[p- 156]
Goebel, K. (1904)
[p. 104 and Fig. 70,
p. 104]
Goebel, K. (1908)
[pp. 161, 281]
Goebel, K. (1913)
[PP. 234, 344]
Goppert, H. R. (1847)
Goppert, H. R. (1848)
[p. 86]
Graebner, P. (1901)
[p. 290]
Graebner, P.
Gratiolet, P.
Gray, A. (1848)
[P- 309]
BIBLIOGRAPHY
Ueber Jugendformen von Pflanzen und deren
kiinstliche Wiederhervorrufung. Sitzungsber. d.
math.-phys. Classe d. k. b Akademie d. Wissensch.
zu Miinchen, Bd. xxvi. 1897 (f°r I^96), pp. 447-497,
1 6 text-figs.
(Pp. 487-491 are devoted to heterophylly in water plants.
The author regards the band-shaped submerged leaves of many
Monocotyledons, not as representing a direct adaptation to
the medium, but as a juvenile form of leaf which may also be
produced at later stages in the life of the plant, if the external
conditions are unfavourable.)
Morphologische und biologische Bemerkungen. 15.
Regeneration bei Utricularia. Flora, Bd. 93, 1904,
pp. 98-126, 17 text-figs.
(Includes an account of the formation of adventitious shoots
from the leaves of the water Utricularias.)
Einleitung in die experimentelle Morphologic der
Pflanzen. viii + 260 pp., 135 text-figs. Leipzig and
Berlin, 1908.
(In this book heterophylly in amphibious plants is dealt with
at some length, with special reference to Myriophyllum pro-
serpinacoides and Limnophila heterophylla.)
Morphologische und biologische Bemerkungen. 22.
Hydrothrix Gardneri. Flora, N.F. Bd. 5 (Ganze
Reihe, Bd. 105), 1913, pp. 88—100, 9 text-figs.
(An investigation of a peculiar submerged member of the
Pontederiaceae with 'long' and 'short' shoots and cleisto-
gamic flowers.)
Ueber die Schlauche von Utriculavia vulgaris und
einen Farbestoff in denselben. Bot. Zeit. Jahrg. 5,
1847, pp. 721-726.
(An account of the structure and development of the bladder,
which the author regards as a metamorphosed "Fiederblatt-
chen." He records the occurrence of blue pigment in the cells
of the bladder.)
Ueber den rothen Farbestoff in den Ceratophylleen.
Bot. Zeit. Jahrg. vi. 1848, pp. 147, 148.
(A record of the occurrence of a violet colouring matter, turning
brown with age, in the cellular processes at the tips of the leaf
segments in Ceratophyllum.)
Die Heide Norddeutschlands. (Engler, A. und
Drude, O. Die Vegetation der Erde, V.) xii + 320
pages, i map. Leipzig, 1901.
(This book contains some information about the flora of low-
land heath pools.)
See Ascherson, P. and Graebner, P. (1907).
See Cloez, S. and Gratiolet, P. (1850).
Remarks on the Structure and Affinities of the Order
Ceratophyllaceae. Annals of the Lyceum of Nat.
Hist., New York, Vol. iv. 1848, pp. 41-50 (read
Feb. 20, 1837).
(The author regards Ceratophyllum as allied to the Cabombaceae
and Nelumbiaceae and supports this conclusion by a com-
parison of the seed characters.)
BIBLIOGRAPHY
373
Greene, E. L. (1909)
[P- 285]
Grew, Nehemiah
(1682)
[P- 154]
Griset, H. E. (1894)
Gronland, J. (1851)
[p. 127]
Guppy, H. B. (1893)
[pp. 35, 220, 243, 244,
297, 301, 302]
Guppy, H. B. (I8941)
[pp. 85, 88, 273, 274,
275, 301 and Fig. 55,
p. 86]
Guppy, H. B. (18942)
[PP- 75, 77, 275]
Guppy, H. B. (i8943)
[P- 274]
Guppy, H. B. (1896)
[P- 274]
Landmarks of Botanical History. Part I. Prior to
1562 A.D. Smithsonian Misc. Coll. Vol. 54, 1909,
pp. 1-329.
(On pp. 126, 127, attention is drawn to the opinions of Theo-
phrastus upon the ecology of water plants.)
The Anatomy of Plants. 1682. 304 pp., 83 pis.
(This classic account of structural botany contains occasional
references to aquatics or to subjects bearing on their study.)
Circulatory Movements of Protoplasm. Science-
Gossip, Vol. i. New Series, 1894, PP- 132-133, 2 text-
figs.
(The author draws attention to the stipules of Hydrocharis
Morsus-ranae and the diaphragms of the petiole and peduncle
of Alisma Plantago as affording excellent material for the
observation of intracellular protoplasmic movements.)
Beitrag zur Kenntniss der Zostera marina L. Bot.
Zeit. Jahrg. ix. 1851, pp. 185-192, i pi.
[This account of the ovules and anthers of Zostera is supple-
mented and corrected by Hofmeister, W. (1852).]
The River Thames as an Agent in Plant Dispersal.
Journ. Linn. Soc. Bot. Vol. xxix. 1893, pp. 333-346.
(An account of observations upon river drift in the Thames,
Lea and Roding, with a discussion of the part played by birds
in the dispersal of aquatic plants.)
Water-Plants and their Ways. Science-Gossip, Vol.
i. New Series, 1894. Their Dispersal and its Observa-
tion, pp. 145-147. Their Thermal Conditions, pp.
178-180. Ceratophyllum demersum, pp. 195-199,
i text-fig.
(These short papers, though published in a popular journal,
contain original observations of great importance.)
On the Habits of Lemna minor, L. gibba, and L.
polyrrhiza. Journ. Linn. Soc. Lond. Bot. Vol. xxx,
1895 (for 1894), pp. 323-330.
[Observations on the life-history of these forms, including a
detailed study of the temperature conditions necessary for
germination, flowering, etc. The paper may be regarded as
supplementary to Hegelmaier, F. (1868).]
River Temperature. Part I. Its Daily Changes and
Method of Observation. Proc. Roy, Phys. Soc.
Edinburgh, Vol. xn. 1892-1894, pp. 286-312.
[A more detailed consideration of the subject than in Guppy,
H. B. (I8941)-]
River Temperature. Part III. Comparison of the
Thermal Conditions of Rivers and Ponds in the
South of England. Proc. Roy. Phys. Soc. Edinb.
Vol. xin. 1894-1897, pp. 204-211.
[The comparison of the temperatures of ponds with that of the
Thames is treated more fully in this paper than in Guppy, H. B.
(I8941)-]
BIBLIOGRAPHY
On the Postponement of the Germination of the
Seeds of Aquatic Plants. Proc. Roy. Phys. Soc.
Edinburgh, Vol. xm. 1894-1897, pp. 344-359.
(An account of experimental work on delayed germination of
the seeds of water plants kept in water, with notes on the
effect of drying, freezing and exposure to light or darkness.)
Observations of a Naturalist in the Pacific between
1896 and 1899. Vol. n. Plant-dispersal, xxviii +627
pp., i pi. London, 1906.
(The water-side plants of the British flora are considered in
Chapters in. and iv. Note 10, pp. 535-538, records the degree
of buoyancy of the seeds and seed vessels of more than 300
British plants, including a large number of aquatics. The book
also contains numerous other notes on water plants, e.g. dis-
tribution of Naias, p. 367.)
Plants, Seeds, and Currents in the West Indies and
Azores, x + 531 pages, 3 maps, i pi. London, 1917.
(This book contains further developments of the author's
"differentiation" hypothesis. A number of references to water
plants are included.)
See Ascherson, P. andGiirke, M. (1889).
On some Points in the Morphology and Anatomy of
the Nymphaeaceae. Trans. Linn. Soc. Lond. Ser. II.
Vol. v. 1895-1901, Part 7, 1897, pp. 287-299, 2 pis.
(The most important discovery recorded in this paper is that
of the occurrence of clear cases of polystely in certain stem
structures of the Nymphaeaceae.)
Haberlandt, G. (1914) Physiological Plant Anatomy, translated from the
[pp. 45, 183] fourth German edition by Montagu Drummond.
xv + 777 pages, 291 text-figs., 1914.
(This standard work contains many references to the structure
of water plants and its interpretation.)
374
Guppy, H. B. (1897)
[pp. 243, 244, 280,
301]
Guppy, H. B. (1906)
[pp. 88, 162, 241, 296,
297. 301, 303, 304,
305]
Guppy, H. B. (1917)
[PP. 303, 304, 333]
Giirke, M.
Gwynne-Vaughan,
D. T. (1897)
[PP- 33, 37. 38, 182]
Hall, J. G. (1902)
Hallier, E. (1859)
[p. 192]
Hannig, £. (1912)
[pp. 260, 266]
An Embryological Study of Limnocharis emarginata.
Bot. Gaz. Vol. xxxin. 1902, pp. 214-219, i pi.
(An account of the embryo-sac and embryo in this species.)
Aedemone mirabilis Kotschy. Ein neues Schwimm-
holz vom weissen Nil, anatomisch bearbeitet. Bot.
Zeit. Jahrg. 17, 1859, pp. 153-156, i pi.
[The anatomy of Aedemone mirabilis, Kotschy (=Herminiera
Elaphroxylon, Guill. et Perr.) is described and its close resem-
blance is pointed out to that of Aeschynomenepaludosa, Roxb.
(=Sesbania aculeata, Poir.).]
Untersuchungen iiber die Verteilung des osmotischen
Drucks in der Pflanze in Hinsicht auf der Wasser-
leitung. Ber. d. deutschen bot. Gesellsch. Jahrg. xxx.
1912, pp. 194-204.
[On p. 200 the author gives an account of the differences
between the osmotic pressure in leaf and root in certain water
plants. For a criticism of his interpretation of his results see
Snell, K. (1912).]
BIBLIOGRAPHY 375
Hansgirg, A. (1903) Phyllobiologie. xiv + 486 pp., 40 text-figs. Leipzig,
[pp. 143, 151, 154] 1903.
[This book includes (pp. 52-84) a summarised account, chiefly
based upon previous work, of the various types of leaf met with
among aquatic plants.]
Hauman-Merck, L. Sur un cas de geotropisme hydrocarpique chez
(19131) Pontederia rotundifolia L. Recueil de 1'Institut Bot.
[p. 239 and Fig. 155, Leo Errera, T. ix. 1913, pp. 28-32, i text-fig.
P- 240] (The author shows that after fertilisation the inflorescences of
this plant, which have been previously held erect above the
water, bend down through an angle of 180° and dip into the
water where the fruits ripen.)
Hauman-Merck, L. Observations ethologiques et syst6matiques sur deux
(19132) especes argentines du genre Elodea. Recueil de
[PP- 55. 57> 236] 1'Instit. Bot. Leo Errera, T. ix. 1913, pp. 33-39.
(An account of the morphology and mode of pollination of
Elodea densa and E. callitrichoides .)
Hauman, L. (1915) Note sur Hydromystria stolonifera Mey. Anales del
(formerly Hauman- Museo Nac. de Hist. Nat. de Buenos Aires, T. 27,
Merck) 1915, pp. 325-331.
[p- 57] (The author draws attention to root dimorphism and hydro-
anemophily in this species.)
Hausleutner, (I85O1) Ueber Aldrovanda vesiculosa. Bot. Zeit. Jahrg. vm.
[pp. in, 289] 1850, p. 600. Nachtrag zu Aldrovandia. Bot. Zeit.
Jahrg. vm. 1850, pp. 831, 832.
(These notes describe certain occurrences of this plant in the
wild state, and give directions for its cultivation. The author
shows that, in nature, it grows among reeds or protected by
the leaves of Waterlilies, and that it can only be cultivated
successfully if these shade conditions are reproduced.)
Hausleutner, (i85O2) Ueber eine neue Nymphaea aus Schlesien. Bot. Zeit.
Jahrg. vm. 1850, pp. 905-908.
(This is the record of the occurrence of a new species of Castalia,
called by the author Nymphaea neglecta.)
Hausleutner, (1851) Ueber die Aldrovanda in Schlesien. Bot. Zeit. Jahrg.
[p. in] ix. 1851, pp. 301-304.
(A discussion of the anomalous distribution of Aldrovandia.
It has been found in Schlesia in two lakes alone. The author
thinks that it is improbable that it is distributed by water-
fowl, since it perishes so rapidly on being removed from the
water.)
Hegelmaier, F. (1864) Monographie der Gattung Callitriche. 64 pp., 4 pis.
[pp. 169, 175, 216, Stuttgart, 1864.
236* 31 J] (In this memoir the anatomy and floral structure of the genus
are fully treated and all the species are described. The geo-
graphical distribution and affinities are also discussed. The
author returns to Robert Brown's opinion that this genus
belongs to the Halorrhagideae, and he does not accept the
newer view which relates it to the Euphorbiaceae.)
376
Hegelmaier, F. (1868)
[PP- 73, 74, 75, 77, 80,
314 and Figs. 48,
p. 76, 50, P- 79, 52,
Ml]
Hegelmaier, F. (1870)
[P- 70]
Hegelmaier, F. (1871)
[PP- 73, 74, 80
and Fig. 47, p.
74]
Hegelmaier, F. (1885)
[P. 73]
Henfrey, A. (1852)
[P- 309]
Henslow, G. (1893)
[pp. 142, 322]
Henslow, G. (1911)
[pp. 322, 339]
Hentze, W. (1848)
Hiern, W. P. (1872)
[P- 30]
BIBLIOGRAPHY
Die Lemnaceen. Eine Monographische Untersuch-
ung. 169 pp., 16 pis. Leipzig, 1868.
(This monograph deals with the family systematically and also
discusses its affinities and distribution. The vegetative and
floral morphology of the different genera and species, and their
anatomy and biology, are also treated in detail.)
Ueber die Entwicklung der Bliithentheile von Pota-
mogeton. Bot. Zeit. Jahrg. 28, 1870, pp. 281-289,
297-305, 313-319, i pi.
(An account of the morphology and development of the flowers
and fruit of this genus, P. crispus being studied in the greatest
detail.)
Ueber die Fructifikationstheile von Spirodela. Bot.
Zeit. Jahrg. 29, 1871, pp. 621-629, 645-666, i pi.
(After writing his monograph of the Lemnaceae, the author
obtained some of the very rare flowers of Spirodela polyrrhiza
from N. America, on which the present illustrated account is
based.)
Wolffia microscopica. Bot. Zeit. Jahrg. 43, 1885, pp.
241-249.
(A description of some material of this species from India.)
On the Anatomy of the Stem of Victoria Regia. Phil.
Trans. Roy. Soc. Lond. 1852, pp. 289-294, 2 pis.
(An early account of the structure of this plant, which suffers
from the fact that the only specimen available for study was
partially decayed.)
A Theoretical Origin of Endogens from Exogens,
through Self -Adaptation to an Aquatic Habit.
Journ. Linn. Soc. Bot. Vol. xxix. 1893, pp. 485-528.
[An exposition of the author's theory of the aquatic origin of
Monocotyledons. For a criticism of this paper see Sargant, E.
(1908).]
The Origin of Monocotyledons from Dicotyledons,
through Self-Adaptation to a Moist or Aquatic
Habit. Ann. Bot. Vol. xxv. 1911, pp. 717-744.
[A further development of the views put forward in Henslow,
G. (1893) with a reply to the criticisms contained in Sargant, E.
(1908).]
Beschreibung einer neuen Nymphaea. Bot. Zeit.
Jahrg. 6, 1848, pp. 601-603. Weitere Mittheilung
iiber die Untersuchung deutscher Seerosen. Bot.
Zeit. Jahrg. 6, pp. 697-702, 1848.
(These papers deal with several distinct forms of Castalia alba.
The author leaves open the question whether these are, or are
not, true species.)
A Theory of the Floating Leaves in certain Plants.
Proc. Camb. Phil. Soc. Vol. n. 1876 (for 1864-1876),
Part XIII, read March 13, 1871, pp. 227-236.
(A mathematical paper, demonstrating the advantages con-
ferred on a floating leaf by a circular form.)
BIBLIOGRAPHY
377
Hildebrand, F. (1861)
[P- 67]
Hildebrand, F. (1870)
Hildebrand, F. (1885)
[pp. 207, 228]
Hiltner, L. (1886)
[P- 233]
Hochreutiner, G.
(1896)
[pp. 174, 204, 205,
245, 261, 281, 282
and Fig. 137, p. 206]
Hochreutiner, G.
(1897)
Hoffmann, J.F. (1840)
[P- 78]
Hofmeister,W.(i852)
Einige Beobachtungen aus dem Gebiete der Pflanzen-
Anatomie. Herrn Professor L. C. Treviranus zur
Feier seines... Doctor- Jubilaums...dargebracht. 30
pp., 2 pis. Bonn, 1861.
(These miscellaneous notes include an account of the winter-
buds of Potamogeton crispus, pp 24-26, with i figure.)
Ueber die Schwimmblatter von Marsilia und einigen
anderen amphibischen Pflanzen. Bot. Zeit. Jahrg.
28, 1870, pp. 1-8, 17-23, i pi.
(A record of the occurrence of floating leaves in Marsilia
quadrifolia, M. data and M. pubescens, and a comparison of
the anatomy of the floating and aerial leaves in these cases,
and also in Sagittaria sagittifolia and Polygonum amphibium.)
t)ber Heteranthera zosterifolia. Engler's Bot. Jahr-
biich. Bd. vi. 1885, pp. 137-145, i pi.
[Observations on living plants of this species grown from
Brazilian seed. The author draws attention to the floating
leaves, which were not noticed in Solms-Laubach, H. Graf zu
(1883).]
Untersuchungen iiber die Gattung Subularia. Engler's
Bot. Jahrbuch. Bd. 7, 1886, pp. 264-272, i pi., i
text-fig.
(The author concludes, from a study of their morphology and
anatomy, that Subularia monticola and the forms of S. aquatica
are not true species, but owe their differences to their varying
environments.)
fitudes sur les Phanerogames aquatiques du Rhone
et du Port de Geneve. Rev. gen. de Bot. T. vm.
1896, pp. 90-110, 158-167, 188-200, 249-265, i pi.,
15 text-figs.
[The first part of these studies consists of a detailed account of
the morphology, anatomy and development of Zannichellia
palustris (pp. 90—110). The remaining instalments deal with
the following branches of the physiology of submerged plants: —
the ascent of water (pp. 158-167), geotropism (pp. 188-200,
249-258), hydrotropism (pp. 258-263), rheotropism (pp. 263-
264) and heliotropism (pp. 264-265).]
Notice sur la Repartition des Phanerogames dans le
Rhone et dans le Port de Geneve. Bull, de 1'Herbier
Boissier, Annee v. No. i, 1897, pp. 1—14, i pi.
(A study of the distribution and ecology of the water plants of
this region.)
Beitrage zur naheren Kenntniss von Lemna arrhiza
nebst einigen Bemerkungen iiber L. polyrrhiza, gibba,
minor und trisulca. Wiegmann's Archiv fur Natur-
geschichte, Berlin, Jahrg. 6, 1840, pp. 138-163, 2 pis.
(A translation of this memoir by Buchinger appeared in Ann.
d. Sci. nat. Ser. n. T. xiv. Bot. pp. 223-242.)
Zur Entwickelungsgeschichte der Zostera. Bot. Zeit.
Jahrg. x. 1852, pp. 121-131, 137-149, i pi.
[An account of the development of the pollen, ovule and
embryo of Zostera, which supplements and corrects Gronland,
J . ( 1 85 1 ) . Some account of Ruppia is also given. For criticism
see Engler, A. (1879).]
378
BIBLIOGRAPHY
Hofmeister, W. (1858) Neuere Beobachtungen iiber Embryobildung der
[p. 82] Phanerogamen. Pringsheim's Jahrbiich. f. wissen-
schaft. Bot. Bd. I. 1858, pp. 82-188, 4 pis.
[This memoir contains some account of the ovule and embryo
of the following water plants: — Alisma, p. 147, Lemna, p. 152,
Naias, p. 145, Nelumbium, p. 85, Nuphar (Nymphaea), p. 83,
Pistia, p. 152, Pontederia, p. 166, Trapa, p. 105, Zannichellia,
p. 147.]
Holm, T. (1885)
[p. 129]
Recherches anatomiques et morphologiques sur deux
monocotyledones submergees (Halophila ' Baillonii
Asch. et Elodea densa Casp.). Bihang till k. Svenska
Vet.-Akad. Handlingar, Bd. 9, No. 13, 1885, 24 pp.,
4 pis.
[These two species are described in some detail. In the case
of Halophila, this paper may be regarded as supplementary to
Balfour, I. B. (1879).]
The Botany of the Antarctic Voyage of H.M. Dis-
covery Ships Erebus and Terror. I. Flora Antarctica.
Part II. 364 pp., 198 pis. London, 1847.
(On p. 334 there is an account of cleistogamy in Limosella.)
Hooker, J. D. (1887) On Hydrothrix, a new genus of Pontederiaceae. Ann.
Bot. Vol. i. 1887-1888, pp. 89-94, i Pi-
[This paper is chiefly of systematic interest. Hydrothrix is a
reduced and aberrant member of the family. See also Goebel,
K. (1913).]
Hooker, J. D. (1847)
[PP- 23
Hope, C. W. (1902)
[pp. 192, 214]
The ' Sadd ' of the Upper Nile : its Botany compared
with that of similar Obstructions in Bengal and
American waters. Ann. Bot. Vol. xvi. 1902, pp.
495-516.
(An account of the plants which play a part in the great
vegetable accumulations that form barriers on the Nile, the
floating vegetation of Bengal, etc.)
Horen, F. van (1869) Observations sur la physiologic des Lemnacees.
[pp. 74, 75, 76] Bull, de la Soc. Roy. de Bot. de Belgique, T. vni.
1869, pp. 15-88, i pi.
[These observations, which deal largely with the hibernation
of the Lemnaceae, are intended by the author to supplement
Hegelmaier, F. (1868). For an English version of this paper
see Horen, F. van (1870).]
Horen, F. van (1870) On the Hibernation of Lemnaceae. Journ. Bot. Vol.
vin. 1870, pp. 36-40.
[This is an abridged translation by A. W. Bennett of Horen, F.
van (1869).]
Hovelacque, M. (1888) Recherches sur 1'appareil veg6tatif des Bignoniacees,
[pp. 104, 107] Rhmanthacees, Orobanchees et Utriculari6es. Paris,
1888.
(The fourth part of this book — pp. 635-745, 126 text-figs. —
deals with the anatomy of the Utriculariaceae.)
BIBLIOGRAPHY
379
Humboldt, A.\ Plantae Aequinoctiales. T. i. vii + 232 pp., 65 pis.
de, and I (1808) Paris, 1808.
Bonpland, A. ) [The aerenchyma of Mimosa lacustris (Neptunia oleracea, Lour.)
[p. 189] is noticed on p. 56, but it is mistakenly described as a foreign
body.]
Hutchinson, J. (1916) Aquatic Compositae. Card. Chron. Vol. 59, 1916,
[PP- 3!3> 321, 324] P- 3°5, 4 text-figs.
(An account of Bidens Beckii, Cotula myriophylloides, Pectis
aquatica and Erigeron heteromorphus.)
Im Thurn, E. F. (1883) Among the Indians of Guiana, xvi + 445 pp., 10 pis.,
[pp. 118, 120, 300] 43 text-figs., i map. London, 1883.
(This book contains references to the Podostemaceae and
Victoria regia living in Guiana waters.)
Im Thurn,
E. F. and
Oliver, D.
[p. 109]
(1887)
The Botany of the Roraima Expedition of 1884:
being Notes on the Plants observed, by Everard F.
im Thurn; with a list of the Species collected, and
Determinations of those that are new, by Prof.
Oliver, F.R.S., F.L.S., and others. Trans. Linn. Soc.
Lond. Ser. n. Vol. n. Bot. 1881-1887, Part XIII.
1887, pp. 249-300, 10 pis.
(This memoir contains an account of the curious mode of life
of Ulricularia Humboldtii, which lives in the water collected in
the leaf axils of a Bromeliad.)
Kurze botanische Mittheilungen. 6. Nymphaea alba
und Nuphar luteum, 7. Potamogetondensus. 8. Dauer
der Ceratophyllum-Arten. Flora, N.R. Jahrg. xi. (G.R.
Jahrg. xxxvi.) 1853, pp. 527-528, i pi.
Fin these notes attention is called to the stipula axillaris of
Nymphaea (Cistalia) alba — the fact that the apparently
opposite leaves of Potamogeton densus are really alternate —
and the fact that the shoots of Ceratophyllum may vegetate
through the winter.]
Irmisch, T. (1854) Bemerkung iiber Hippuris vulgaris L. Bot. Zeit.
[Fig. 112, p. 173] Jahrg. 12, 1854, pp. 281-287, J P1-
(A detailed account of the mode of branching of the sympodial
stems.)
Irmisch, T. (1853)
[pp. 26, 87]
Irmisch, T.
Irmisch, T. (i8582)
[pp. 52, 271]
Botanische Mittheilungen. i. Ueber Utricularia
minor. Flora, Neue Reihe, Jahrg. xvi. (Ganz. Reihe,
Jahrg. XLI.) 1858, pp. 33-37, i pi.
(An account of the morphology of this species; the author
interprets the branching in connexion with the inflorescence
axis as sympodial.)
Ueber das Vorkommen von schuppen- oder haar-
formigen Gebilden innerhalb der Blattscheiden bei
monokotylischen Gewachsen. Bot. Zeit. Jahrg. 16,
1858, pp. 177-179.
(This paper records the occurrence of "squamulae intra-
vaginales" in a number of Helobieae.)
380
Irmisch, T. (i8s83)
[P- 59]
Irmisch, T. (iSS
[pp. 169, 245]
Irmisch, T. (i8592)
Irmisch, T. (1861)
[P- 2°5]
Irmisch, T. (1865)
[P- 244]
Ito, T. (1899)
[P- 83]
Jaensch, T. (I8841)
[p. 192]
Jaensch, T. (i8842)
[p. 192]
Jaggi, J. (1883)
[p. 302]
BIBLIOGRAPHY
Ueber einige Arten aus der natiirlichen Pflanzen-
familie der Potameen. Abhandl. d. naturwiss.
Vereines f. Sachsen und Thiiringen in Halle, Bd. n.
Berlin, 1858 (Vol. published 1861), pp. 1-56, 3 pis.
(The morphology and life-history of Potamogeton natans L.,
P. lucens L., P. crispus L., P. obtusifolius M. et K., P. pectinatus
L., and also of Zannichellia and Ruppia, are described and
illustrated with the thoroughness characteristic of the author.)
Bemerkungen iiber einige Wassergewach.se. Bot.
Zeit. Jahrg. 17, 1859, pp. 353-356.
(Notes on the morphology of Myriophyllum, Callitriche,
Potamogeton trichoides, Hydrocharis and Stratiotes.)
Zur Naturgeschichte des Potamogeton densus L.
Flora, N.R. Jahrg. xvn. (G.R. Jahrg. XLII.) 1859,
pp. 129-139, i pi.
[This paper is supplementary to Irmisch, T. (i8583).]
Ueber Polygonum amphibium, Lysimachia vulgaris,
Comarum palustre und Menyanthes trifoliata. Bot.
Zeit. Jahrg. 19, 1861, pp. 105-109, 113-115, 121-123,
i pi.
(A description of the seedlings and of the development and
morphology of the mature plant in the four species named.)
Beitrag zur Naturgeschichte des Stratiotes A hides.
Flora, N.R. Jahrg. xxm. (G.R. Jahrg. XLVIII.) 1865,
pp. 81-91, i pi.
(The fruit, seed and seedling of Stratiotes aloides, the seedling
of Naias major and the axillary shoots of Hydrocharis Morsus-
ranae, and Vallisneria spiralis are described and figured in this
paper.)
Floating-apparatus of the Leaves of Pistia Stratiotes,
L. Ann. Bot. Vol. xm. 1899, p. 466.
(Notes on the structure and mode of flotation of the leaves of
this plant which was studied in its native habitat.)
Nachtrag zur Kenntniss von Herminiera Elaphroxy-
lon G.P.R. Ber. d. deutsch. bot. Gesellsch. Bd. n.
1884, pp. 233-234.
(A note on the occurrence of Aedemone mirabilis, Kotschy, in
Senegambia.)
Zur Anatomic einiger Leguminosenholzer. Ber. d.
deutsch. bot. Gesellsch. Bd. n. 1884, pp. 268-292,
i pi.
[This memoir includes an account of the structure of the wood
in Herminiera Elaphroxylon (Aedemone), Aeschynomene and
Sesbania. For a criticism see Klebahn, H. (1891).]
Die Wassernuss, Trapa natans L., und der Tribulus
der Alten. Zurich, 34 pp., i pi., 1883.
(This paper deals mainly with the history of Trapa, its distri-
bution and uses, and the causes which are leading to its
extinction in Switzerland and elsewhere. The author regards
it as a plant of Southern Europe introduced into other
localities at a very early period as a food plant.)
BIBLIOGRAPHY
t)ber Schwimmblatter. Funfstiick's Beitrage zur
Wissens. Botanik, Bd. i. 1897, PP- 281-294, i pi.
(A general consideration of floating leaves, especially of the
manner in which they are supposed to be adapted to their
mechanical needs.)
The Morphology of the Central Cylinder in the
Angiosperms. Trans. Canad. Inst. Vol. vi. 1899,
pp. 599-636, 5 Pis-
[The section of this paper relating to polystely should be read
in connexion with Scott, D. H, (1891).]
The Botany of the Eastern Borders, London, 1853.
xii + 336 pp., 13 pis.
(Pp. 191-192 give an early account of the spread of Elodea
canadensis in this country.)
Der richtende Einnuss stromenden Wassers auf
wachsende Pflanzen und Pflanzentheile (Rheotro-
pismus). Ber. d. deutsch. Bot. Gesellsch. Bd. i. 1883,
pp. 512-521.
(The author proposes the term "Rheotropismus" for the
directive influence exerted upon plants by a water current.)
Om befruktningen hos slagtet Najas samt hos
Callitriche autumnalis. Lunds Univ. Ars-skrift, Tom.
xx. Part IV. 1883-1884, 26 pages, i pi.
(A Swedish paper with a resume in German dealing with the
pollination of Naias and Callitriche.)
Cynomorium und Hippuris. Svensk. Bot. Tidskrift,
Bd. 4, 1910, pp. 151-159, 6 text-figs.
(A comparison of these two genera leads the author to the
conclusion that there is little ground for assuming a relation-
ship between them. He shows that it is not even certain that
Hippuris belongs to the Choripetalae, but if placed in this
group it is best treated as representing a distinct family allied
to Halorrhagideae.)
Studien iiber die Entwicklungsgeschichte von Hip-
puris vulgaris. Nova Acta Regiae Societatis Scien-
tiarum Upsaliensis, Ser. iv. Vol. 2, N. n, 1907-1911,
26 pp., 3 pis.
(The author's study of the development of the ovule and
embryo leads him to the conclusion that the systematic
position of the genus is still uncertain.)
Jussieu, A.L.de (1789) Genera Plantarum. Ixxii + 499 pp. Paris, 1789.
[P- 3T5l (In this work Zoster a is included among the Aroids, see p. 24.)
Das Bliihen der Wasserlinsen. Zeitschrift. f. Natur-
wissenschaften, Bd. 68 (Folge v. Bd. 6), 1895, pp.
136-138.
(The author's observations suggest certain minor corrections
in the accounts hitherto published of the flowering of Lemna
minor.)
Jahn, E. (1897)
[pp. 30, 31]
Jeffrey, E. C. (1899)
[p. 1 80]
Johnston, G. (1853)
[p. 210]
Jonsson, B. (1883)
[p. 282]
Jonsson, B.
(1883-1884)
[P- 236]
Juel, O. (1910)
[P- 312]
Juel, O. (1911)
[P- 312]
Kalberlah, A. (1895)
[p. 76]
382
BIBLIOGRAPHY
Kamienski, F. (1877) Vergleichende Untersuchungen iiber die Entwickel-
[pp. 100, 103 and ungsgeschichte der Utricularien. Bot. Zeit. Jahrg.
Fig. 67, p. 100] 35, 1877, pp. 761-776, i pi.
(This paper is concerned with the embryology, germination
and anatomy of Utricularia vulgaris.)
Karsten, G. (1888)
[pp. 146, 284]
Keller, I. A. (1893)
[p. 272]
Kerner, A. and
Oliver, F. W.
(1894-1895)
[P- 301]
Ueber die Entwickelung der Schwimmblatter bei
einigen Wasserpflanzen. Bot. Zeit. Jahrg. 46, 1888,
PP- 565-578, 581-589-
[The author has repeated and extended the experiments on
the regulation of growth of the petiole in floating leaves
recorded by Frank, A. B. (1872) and he comes to conclusions
differing from those of the latter author. He employed
Hydrocharis, Marsilea and Ranunculus sceleratus.}
The Glandular Hairs of Brasenia peltata Pursch.
Proc. Acad. Nat. Sci. Philadelphia, 1894 (for 1893),
pp. 188-193, J pl-
(The author shows that the mucilaginous coat covering the
younger parts of this member of the Nymphaeaceae is due to
the secretory activity of ephemeral hairs.)
The Natural History of Plants. 2 vols., 1760 pp.,
1000 figs., 16 pis.
(This well-known book includes a good deal of information
about water plants.)
Kingsley, M. H. (1897) Travels in West Africa, xvi + 743 pp., 47 illustra-
[p. 213] tions. London, 1897.
(Pp. 378-380 contain an account of the rapid multiplication of
Pistia Stratiotes in the river Ogowe.)
Kirchner, O. von, Lebensgeschichte der Bliitenpflanzen Mitteleuropas.
Loew, E. and Bd. i. Abth. i. and in., and Bd. 11. Abth. in. Stutt-
Schroter,C. (1908, etc.) gart, 1908, 1909 and 1917.
[PP. 5°. 59, 74» 8l, (The life-history of the following aquatic groups is dealt with:
123, 205, 206, 276 Helobieae, Abth. i. pp. 394-714, 195 text-figs.; Lemnaceae,
and Figs. 49, p. 79, Abth> m- PP- 57-8o, 23 text-figs.; Ceratophyllaceae, Bd. n.
136, p. 205]
Abth. in. pp. 51-73, 16 text-figs.)
Kirchner, O.
See Schroter, C. and Kirchner, O. (1902).
Kirschleger, F. (1856) Etwas iiber fluthende Pflanzen (Plantae fluitantes)
[p. 12] und sonstige Notizen in Bezug auf die rheinische
Flora. Flora, N.R. Jahrg. xiv. (G.R. Jahrg. xxxix.)
1856, pp. 529-536-
(Observations on the forms of Sagittaria sagittifolia, Scirpus
lacustris and Sparganium simplex with floating leaves.)
Kirschleger, F. (1857) Nachtrag zu der Notiz iiber fluthende Pflanzen.
[p. 287] Flora, N.R. Jahrg. xv. (G.R. Jahrg. XL.) 1857,
pp. 193-194.
[A continuation of Kirschleger, F. (1856) giving further
references, and an account of the dependence of Scirpus
lacustris upon the nature of the soil.]
BIBLIOGRAPHY
383
Klebahn, H. (1891)
[p. 192]
Klebs, G. (1884)
[p. 245 and Fig. 158,
P- 245]
Klinge, J. (1881)
[pp. 15, 1 8]
Klinsmann, F. (1860)
[P- 54]
Knoch, E. (1899)
[p- 34]
Knupp, N. D. (1911)
[p. 232]
Koch, K. (1852)
[pp. 82, 316]
Koehne, E. (1884)
Ueber Wurzelanlagen unter Lenticellen bei Her-
miniera Elaphroxylon und Solanum Dulcamara.
Nebst einem Anhang iiber die Wurzelknollchen der
ersteren. Flora, N.R. Jahrg. 49 (G.R. Jahrg. 74),
1891, pp. 125-139, i pi.
[The author shows, in opposition to Jaensch, T. (i8842) that
the lenticels of Herminiera Elaphroxylon, G.P.R. (Aedemone
mirabilis, Kotschy) are not " Markstrahlrindenporen," but are
lenticels of normal structure. He also describes, both in this
plant and in Solanum Dulcamara, the occurrence beneath the
lenticels of rudimentary adventitious roots, which may develop
under favourable circumstances.]
Beitrage zur Morphologic und Biologic der Keimung.
Unters. bot. Inst. Tubingen, Bd. i. Heft 4, 1884
PP- 536-635> 24 text-figs.
(In this paper the seedlings of certain water plants come under
consideration.)
Ueber Sagittaria sagittaefolia L. Sitzungsber. d.
Naturforscher-Gesellsch. bei d. Univ. Dorpat, Bd. v.
Heft in. 1881 (for 1880), pp. 379-408.
(A description of the morphology and anatomy of this species
and of the different forms in which it occurs.)
Ein Beitrag zur Entwickelungsgeschichte von Stra-
tiotes aloides. Bot. Zeit. Jahrg. 18, 1860, pp. 81-82,
i pi.
(The author succeeded in germinating the seeds of this plant
and describes and figures the seedling.)
Untersuchungen iiber die Morphologic, Biologic und
Physiologic der Bliite von Victoria Regia. Bibliotheca
Botanica, Bd. ix. 1899, Heft 47, 60 pp., 6 pis.
(In this memoir the anatomy and morphology of the flower of
Victoria regia are dealt with, and special attention is paid to
the development of heat at the flowering period.)
The Flowers of Myriophyllum spicatum L. Proc.
Iowa Acad. Sci. (Des Moines), Vol. xvm. 1911,
pp. 61-73, 4 pis.
(A study of the development and general structure of the
flowers of this species.)
Ueber Pistia in Allgemeinen und Pistia Turpini
Blume insbesondere. Bot. Zeit. Jahrg. 10, 1852,
PP- 577-585. i pl-
(The author describes the germination of Pistia, which he
regards as differing from that of Lemna. He also emphasizes
the dissimilarity of Pistia and the Aroids. He describes the
flowers of Pistia Turpini which he observed in the living state.)
Ueber Zellhautfalten in der Epidermis von Blumen-
blattern und deren mechanische Function. Ber. d.
deutsch. bot. Gesells. Bd. n. 1884, pp. 24-29, i pi.
(The author shows that the folds in the lateral walls of epidermal
cells of petals serve a mechanical purpose in strengthening the
organ. This conclusion may have some bearing on the loss of
folding in the epidermal cells of water leaves.)
384
BIBLIOGRAPHY
Kotschy, T. (1858)
[p. 192]
[pp. 62,142,143,154,
239, 305, 314]
Kurz, S. (1867)
[PP- 73, 291]
Lamarck, J. B. P. A.
(1809)
[P- 1.55]
Land, W. J. G.
Lebel, E. (1863)
[pp. 134, 195, 216,
Korzchinsky, S. (1886) Ueber die Samen der Aldrovandia vesiculosa L. Bot.
[p. 244] Centralbl. Bd. xxvu. 1886, pp. 302-304, 334-335, i pi.
(An account of the structure of the ripe seed and the germina-
tion of this plant.)
Eine neue Leguminose vom weissen Nil. Oester-
reichische Bot. Zeitschrift, Jahrg. vm. 1858, No. 4,
pp. 113-116, i pi.
(The first scientific description of Aedemone mirabilis, Kotschy —
Herminiera Elaphroxylon, G.P.R.)
Aponogetonaceae, in Das Pflanzenreich, iv. 13
(herausgegeben von A. Engler), 24 pp., 71 text-figs.
Leipzig, 1906.
(A monograph of this family of hydrophytes.)
Enumeration of Indian Lemnaceae. Journ. Linn.
Soc. Bot. Vol. ix. 1867, pp. 264-268, i pi.
(A systematic paper with some general notes on distribution of
the group.)
Philosophic Zoologique. 2 vols. Paris, 1809.
(The heterophj'lly of the Water Crowfoot is discussed in Vol. i.
Chapter vn. p. 230.)
See Coulter, J. M. and Land, W. J. G. (1914).
Callitriche. Esquisse Monographique. Mem. de la
Soc. Imp. des Sci. Nat. de Cherbourg, T. xi. 1863,
pp. 129-176.
(A systematic monograph of the genus, dealing also with its
anatomy, relationships, etc. — a most vividly written and
interesting memoir.)
Ueber den Einfluss des Wassers auf das Wachsthum
der Stengel und Wurzeln einiger Pflanzen. (Gelehrte
Schriften der k. Universitat in Kasan, 1873.)
Abstracted in Just's Bot. Jahresbericht, Jahrg. i.
1873, P- 594-
(According to the abstract, this Russian paper deals with the
development of aerenchyma in the stems and roots of Epilobiunt
hirsutum, Lycopus europaeus and two species of Lythrum, when
grown in water.)
Zur Frage iiber den Einfluss des Mediums auf die
Form der Pflanzen. (Gelehrte Schriften der k.
Universitat in Kasan, 1873.) Abstracted in Just's
Bot. Jahresbericht, Jahrg. i. 1873, pp. 594, 595.
(According to the abstract this Russian paper deals with the
effect of an aquatic life on Rubus fruticosus .)
Lewakoffski,N. (1877) Ueber den Einfluss des Wassers auf die Entwickelung
[p. 200] einiger Arten von Salix (Beilage zu dem Protocolle
der 91. Sitzung der Naturforsch. an der Universitat
zu Kazan). Abstracted in Just's Bot. Jahresber.
Jahrg. v. 1879 (for 1877), pp. 575, 576.
(According to the abstract, this Russian paper deals chiefly
with the effect of submergence on Salix shoots and demon-
strates that very little effect is produced on their anatomy by
water life.)
Lewakoffski, N.
(I8731)
[p. 188]
Lewakoffski, N.
(i8732)
[p. 200]
BIBLIOGRAPHY
385
Lindberg, S. 0. (1873)
[P- 46]
Lister, G. (1903)
[P-
Loeselius, J. (1703)
[pp. II, 20]
Loew, E.
Loew, O. (1893)
Ludwig, F. (1881)
[pp. 80, 84]
Ludwig, F. (1886)
[P- 243]
Luetzelburg, P. von
(1910)
[pp. 91, 96, 102, 105
and Fig. 71. p. 105]
Lundstrom, A. N.
(1888)
[p. 62]
Lyte, H.
A. W. P.
Is Hydrocharis really Dioecious? Trans, and Proc.
Bot. Society, Edinburgh, Vol. xi. 1873, p. 389.
(The author suggests that Hydrocharis, instead of being
dioecious as is commonly supposed, is really monoecious or
monoico-female.)
On the Occurrence of Tristicha alternifolia, Tul., in
Egypt. New Phyt. Vol. n. 1903, pp. 15-18, I pi.
(The author discovered Tristicha alternifolia Tul. var. pulchella
Warmg. in rushing water below the first cataract on the Nile ;
this is the first record of the family Podostemaceae from Egypt.)
Flora Prussia, sive Plantae in Regno Prussiae sponte
nascentes. . .Curantejohanne Gottsched. . .Regiomonti
...Sumptibus Typographiae Georgianae, 1703.
[Plantago aquatica (—Alisma graminifolium, Mich.), PI. 62 and
p. 199, and Sagittaria aquatica foliis variis (=Sagittaria
sagittifolia, L.), PI. 74 and p. 234, represented in both cases with
the ribbon type of leaf and bearing an inflorescence.]
See Kirchner, O. von, Loew, E. and Schroter, C.
(1908, etc.).
Worauf beruht die alkalische Reaction, welche bei
Assimilationsthatigkeit von Wasserpflanzen beo-
bachtet wird? Flora, Bd. 77, 1893, pp. 419-422.
(The red coloration obtained, when phenolphthalein is added
to the water in which aquatic plants are living and assimilating,
is attributed by the author to calcium carbonate held in a
colloidal state by the presence of organic matter.)
Ueber die Bestaubungsverhaltnisse einiger Siiss-
wasserpflanzen und ihre Anpassungen an das Wasser
und gewisse wasserbewohnende Insekten. Kosmos
(Stuttgart), Jahrg. v. Bd. x. 1881, pp. 7-12, 17 text-
figs.
(Observations on the pollination of Lemna, Callitriche, Myrio-
phyllum and Ceratophyllum.)
Ueber durch Austrocknen bedingte Keimfahigkeit
der Samen einiger Wasserpflanzen. Biol. Centralbl.
Bd. vi. No. 10, 1887 (for 1886), pp. 299, 300.
(A note on the effect of drying on the seeds of Mayaca fluvia-
tilis.)
Beitrage zur Kenntnis der Utricularien. Flora, Bd.
100, 1910, pp. 145-212, 48 text-figs.
(This paper is concerned, in part, with the aquatic Utricularias.
The secretions of the bladders are investigated, and a number
of cultural experiments are described.)
Ueber farblose Oelplastiden und die biologische
Bedeutung der Oeltropfen gewisser Potamogeton-
Arten. Bot. Centralbl. Bd. xxxv. 1888, pp. 177-181.
(A discussion of the cause and significance of the oily surface
possessed by the leaves of some submerged Potamogetons.)
See Dodoens, R. (1578).
25
386
McCallum, W. B.
(1902)
[p. 160]
MacCaughey, V.
(1917)
[p. 182]
MacDougal, D. T.
[p. 162]
MacLeod, J. (1893
and 1894)
[pp. 9, 230]
Magnin, A. (1893)
[pp. 274, 279, 287,
290, 323]
Magnus, P.
Magnus, P. (i
[P- 135]
Magnus, P. (1871)
[p. 169]
BIBLIOGRAPHY
On the nature of the stimulus causing the change of
form and structure in Proserpinaca palustris. Bot.
Gaz. Vol. xxxiv. 1902, pp. 93-108, 10 text-figs.
[Experimental work on the "land type" and "water type" of
leaf in Proserpinaca palustris. This paper should be read in
conjunction with Burns, G. P. (1904).]
Gunner a petaloidea Gaud., a remarkable plant of
the Hawaian Islands. American Journ. Bot. Vol. iv.
1917, pp. 33-39.
(A "titanic herbaceous-perennial" belonging to a genus whose
anatomy is of interest in relation to that of certain water
plants.)
The Determinative Action of Environic Factors upon
Neobeckia acquatica Greene. Flora, N.F. Bd. vi.
^G.R. Bd. 106), 1914, pp. 264-280, 14 text-figs.
(A study of the heterophylly of this plant under a variety of
conditions.)
Over de bevruchting der bloemen in het kempisch
gedeelte van Vlaanderen. Bot. Jaarboek, Vol. v.
1893, pp. 156-452, 58 text-figs.; Vol. vi. 1894, pp.
119-511, 65 text-figs.
(The second part of this elaborate memoir on the pollination of
the plants of Flanders, concludes with an index and a summary
in French.)
Recherches sur la vegetation des lacs du Jura. Rev.
g6n. de Bot. T. v. 1893, pp. 241-257, 303-316,
8 text-figs.
(An ecological survey of 62 out of the 66 lakes which occur in
the Jura region.)
Beitrage zur Kenntniss der Gattung Najas L.
viii + 64 pages, 8 pis. Berlin, 1870.
(This monograph of the genus contains an historical account
of the literature, a description of the germination, general
morphology, apical development and anatomy, and a discussion
of the interpretation of the peculiar floral structure.)
Ueber die Anatomic der Meeresphanerogamen.
Sitzungs-Berichte d. Gesellsch. naturforsch. Freunde
zu Berlin, Dec. 20, 1870, pp. 85-90.
[An anatomical account of some marine Phanerogams, which
should be read in connexion with Ascherson, P. (1870).]
Einige Bemerkungen zu dem Aufsatze des Herrn J.
Borodin "Ueber den Bau der Blattspitze einiger
Wasserpflanzen." Bot. Zeit. Jahrg. 29, 1871, pp.
479-484.
[A criticism of Borodin, J. (1870). The author points out the
analogy of the ephemeral stomates described by Borodin at
the leaf apex of Callitriche with the stomates found at the
nerve endings of the leaves of such land plants as Crassula.
He shows, on the other hand, that the analogy, suggested by
Borodin, with the outgrowths at the leaf apices of Myriophyllum
and Ceratophyllum does not hold.]
BIBLIOGRAPHY
387
Magnus, P. (1872)
[P- 135]
Magnus, P. (1883)
[P- 332]
Magnus, P. (1894)
Magnus, W.
and
Werner, E.
[p. 121]
(1913)
Maisonneuve, D. de
(1859)
[p. no]
Marloth, R. (1883)
[p. 241]
Marshall, W. (1852)
[pp. 55, 210]
Untersuchungen iiber die Anatomic der Cymodoceen.
Sitzungs-Ber. d. Gesellschaft naturforsch. Freunde zu
Berlin, 1872, pp. 30-33.
(These notes are chiefly devoted to the occurrence of " Schlauch-
gefasse" in Cymodocea.)
Ueber eine besondere geographische Varietat der
Najas graminea Del. und deren Auftreten in England.
Ber. d. deutsch. bot. Gesetlsch. Bd. i. 1883, pp.
521-524-
[This paper on a form of Naias graminea which grows in the
Egyptian rice fields should be read hi connexion with
Ascherson, P. (1874) and Bailey, C. (1884).]
Ueber die Gattung Najas. Ber. d. deutsch. bot.
Gesellsch. Bd. xn. 1894, pp. 214-224, i pi., 3 text-
figs.
[A reply to the criticisms on Magnus, P. (I87O1) contained in
Schumann, K. (1892).]
Die atypische Embryonalentwicklung der Podoste-
maceen. Flora, N.F. Bd. 5 (G.R. Bd. 105), 1913,
pp. 275-336, 4 pis., 41 text-figs.
(A detailed comparative account of the embryo-sac and embryo
in the Podostemaceae, with a general discussion of the ecological
and morphological significance of the peculiarities observed.)
Aldrovandia. Bull, de la Soc. bot. de France, T. vi.
l859, PP- 399-401-
(The author of this note shows that many plants of Aldrovandia
may remain at the bottom of the water even in June, weighted
down by the remnant of the turion.)
tfber mechanische Schutzmittel der Samen gegen
schadliche Einfliisse von aussen. Engler's Bot.
Jahrb. Bd. iv. 1883, pp. 225-265, i pi.
(A detailed account of the protective layers in seed coats,
including references to certain water plants. The paper con-
cludes with an index of the species studied.)
Excessive and noxious Increase of Udora Canadensis
(Anacharis Alsinastrum). Phytologist, Vol. iv. 1852,
PP- 705-7I5-
(An historical account of the introduction of this plant.)
Marshall, W. (1857) The American Water-weed. Anacharis Alsinastrum.
[pp. 55, 210] Phytologist, Vol. n. N.S. 1857-8, pp. 194-197.
[An additional note on the nuisance caused by this weed; see
Marshall, W. (1852).]
Martens, G. von (1824) Reise nach Venedig. Ulm, 1824.
[?• I35] [This book contains (p. 623) an early reference to the hetero-
phylly of Sagittaria sagittifolia. There is also a mention (p. 550)
of the part played by Zostera marina in the Venetian lagoons,
and its use from time immemorial in packing Venetian glass.]
25—2
388 BIBLIOGRAPHY
Martins, C. (1866) (i) Sur les racines aeriferes ou vessies natatoires des
[pp. 189, 192] especes aquatiques du genre Jussiaea L. (2) Sur
la synonymie et la distribution geographique du
Jussiaea repens de Linne. Memoires de la section d.
sci. Acad. des Sci. et Lettres de Montpellier, Vol. vi.
1866, pp. 353-381, 4 pis.
(An account of the air roots of Jussiaea. Habit drawings of
three species are given. The same papers appeared without
illustrations in Bull. Soc. bot. de France, T. xui. pp. 160-189,
1866.)
Massart, J. (1910) Esquisse de la Geographic botanique de la Belgique.
[pp. 198, 283,291 and Recueil de 1'Inst. bot. Leo Errera, Tome supp!6men-
Figs. 13, p. 28, 99 taire vn. bis. xi + 332 pp., 101 text-figs. Brussels,
and 100, p. 152]- 1910.
(This work, which deals exhaustively with the ecology of
Belgium, contains a certain amount of information about
aquatics — see especially pp. 115-123. There is also a separate
"annexe" with numerous photographs of the vegetation,
including a number of pictures of water plants.)
Matthews, J. R. (1914) The White Moss Loch : A Study in Biotic Succession.
[p. 289 and Fig. 165, New Phyt. Vol. xin. 1914, pp. 134-148, 2 text-figs.
p. 288] [An ecological study in which the aquatic formation of the
Loch is dealt with (pp. 137-140).]
Matthiesen, F. (1908) Beitrage zur Kenntnis der Podostemaceen. Bibl.
[pp. 112, 114, 117, Bot. Bd. xv. Heft 68, 1908, 55 pp., 9 pis., i text-fig.
122, 255 and Fig. 8l, (This memoir is chiefly occupied with a description of certain
p no] species of Podostemaceae from Venezuela, but it also includes
a general account of the morphology and anatomy of the
group.)
Meierhofer, H. (1902) Beitrage zur Anatomic und Entwickelungsgeschichte
[p. 103 and Figs. 61, der Utricularia-Blasen. Flora, Bd. 90, 1902, pp. 84-
p. 93, 62, p. 95, 73, 114, 9 pis.
p. 107] (The author describes the structure and development of the
bladders of the European aquatic Utricularias and comes to
the conclusion that these organs are foliar in nature.)
Meister, F. (1900) Beitrage zur Kenntnis der europaischen Arten von
[pp. 100, 1 01, 299] Utricularia. Memoires de 1'Herbier Boissier, No. 12,
1900, 40 pp., 4 pis.
(A systematic account with biological notes.)
Mellink,J.F.A.(i886) Zur Thyllenfrage. Bot. Zeit. Jahrg. 44, 1886, pp.
[p. 258] 745-753, i pl-
[An account of a petiole of Nymphaea (Castalia) alba which
had at some time been wounded at various points. It was
found that, in the neighbourhood of the wounds, the air canals
were choked by hairs, which had grown out from the surrounding
parenchyma cells in a thylose-like manner into the canals.]
Mer, £. (iSSo1) Des modifications de forme et de structure que
[pp. 163, 165, 279] subissent les plantes, suivant qu'elles vegetent a 1'air
ou sous 1'eau. Bull, de la Soc. bot. de France, T.
xxvu. (Ser. n. T. n.) 1880, pp. 50-55.
(An analysis of the differences in morphology and structure
exhibited by the land and water forms of Ranunculus aquatilist
R. Flammula, Littorella lacustris, etc. The author suggests a.
comparison between etiolated and submerged plants.)
BIBLIOGRAPHY
389
Mer, £. (i88o2)
Mer, £. (1881)
Mer, E. (I8821)
[pp. 32, 42, 165, 195]
Mer, £. (1882*)
Merz, M. (1897)
[p. i oo]
Micheli, M. (1881)
Micheli, P. A. (1729)
[pp. 76, 235]
Milde, (1853)
Miller, G. S. \
and [-(1912)
Standley, P. C.)
Des causes qui modifient la structure de certaines
plantes aquatiques vegetant dans 1'eau. Bull, de la
Soc. bot. de France, T. xxvu. (Se"r. n. T. n.) 1880,
pp. 194-200.
(This paper is concerned with the differences between the forms
of Littorella and Isoetes growing under different conditions.)
Observations sur les variations des plantes suivant
les milieux. Bull, de la Soc. bot. de France, T. xxvm.
(Se"r. n. T. m.) 1881, pp. 87-90.
(Brief notes on the submerged and aerial forms of Callitriche
Littorella, etc.)
De la vegetation a 1'air des plantes aquatiques.
Comptes rendus de 1'acad. des sciences, Paris, T. 94,
1882, pp. 175-178.
(An account of the experimental production of land forms in
the case of certain aquatic plants.)
De quelques nouveaux exemples relatifs a 1'influence
de 1'heredite et du milieu sur la forme et la structure
des plantes. Bull. Soc. bot. de France, T. xxix. 1882,
pp. 81-87.
(A study of the leaf characters of Potamogeton rufescens growing
in deep or shallow water.)
Untersuchungen iiber die Samenentwickelung der
Utricularieen. Flora, Bd. 84 (Erganzungsband zum
Jahrg. 1897), 1897, pp. 69-87. 34 text-figs.
(A detailed account of the embryo-sac and seed in ten species
of the genus, which is characterised by the early disappearance
of the nucellus and the development of endospermic haustoria
at both ends of the sac.)
Alismaceae, Butomaceae, Juncagineae. A. and C. de
Candolle's Monographiae Phanerogamarum, Vol. in.
1881, pp. 7-112.
(A systematic account of these families with a discussion of
their affinities, etc.)
Nova Plantarum Genera.... Florentiae, 1729.
(The flowers of Lemna gibba are figured on PI. u under the
name of " Lenticula," and the sterile plants of L. minor,
L. trisulca, Wolffia arrhiza and Spirodela polyrrhiza under the
name of " Lenticularia." Vallisneria with its floating $ flowers
and spiral peduncles is shown on PI. 10.)
Wolffia Michelii Hork. (Lemna arrhiza L.). Bot. Zeit.
Jahrg. xi. 1853, pp. 896, 897.
(A note on the occurrence of this plant in Germany.)
The North American Species of Nymphaea. Con-
tributions from the U.S. National Herbarium, Vol.
16, Pt 3, 1912. Smithsonian Institution. U.S.
National Museum, viii + 109 pp., 39 text-figs.,
13 pis.
(This systematic monograph is fully illustrated, especially with
photographs of fruits and with maps showing the distribution,
of the various species in N. America.)
390 BIBLIOGRAPHY
Minden,M. von (1899) Beitrage zur anatomischen und physiologischen
[pp. 83, 266, 268, 269 Kenntnis Wasser-secernierender Organe. Bibliotheca
and Fig. 53, p. 82] Botanica, Bd. ix. Heft 46, 1899, 76 pp., 7 pis.
(Pp. 1-30 deal with the secretion of watery solutions from
water pores and apical openings in the leaves of water plants,
and form an exhaustive account of the subject so far as it had
been worked out by the end of the nineteenth century.)
Mo bius, M. (1895) Ueber einige an Wasserpflanzen beobachtete Reizer-
[p. 281] scheimmgen. Biol. Centralbl. Bd. 15, 1895, pp. 1-14,
33-44, 8 text-figs.
(Observations on the effect of light and darkness on water
plants.)
Moeller, J. (1879) Aeschynomene aspera Willd. (Papilionaceen) . Bot.
[p. 191] Zeit. Jahrg. 37, 1879, pp. 720-724, i text-fig.
(An account of the anatomy of the floating wood of this plant.)
Monkemeyer, W. Die Sumpf- und Wasserpflanzen. Ihre Beschreibung,
(1897) Kultur und Verwendung. iv + 189 pp., 126 text-
[p. 291] figs. Berlin, 1897.
(A useful compendium of water and marsh plants arranged on
Engler and Prantl's system, with notes on their cultivation.
It is by the Inspector of the Leipzig Botanic Garden, and is
primarily intended to help those who wish to grow water
plants in an aquarium or water garden.)
Montesantos,N.(i9i3) Morphologische und biologische Untersuchungen
[pp. 50, 51, 52, 157, iiber einige Hydrocharideen. Flora, N.F. Bd. v.
239, 282] (Ganze Reihe, Bd. 105), 1913, pp. 1-32, 5 pis.
(This paper deals with the genera Limnobium, Blyxa, Ottelia
and Stratiotes. Certain experiments are described showing that
the heterophylly of Limnobium and Stratiotes is not due to the
direct action of the medium, and that the sinking of Stratiotes
in the autumn is due to the increase of weight brought about
by a deposition of chalk on the leaves.)
Monti, Gaetano(i747) De Aldrovandia novo herbae palustris genere. De
[p. 109] Bononiensi Scientiarum et Artium Institute atque
Academia Commentarii. Tomi secundi Pars tertia,
i747> PP- 404-4H. i Pi-
[This old and rare memoir on Aldrovandia is analysed in
Aug6 de Lassu (1861).]
Mori, A. (1876) Nota sull' irritabilita delle foglie dell' Aldrovandia
[p. no] vesiculosa. Nuovo Giornale Botanico Italiano, Vol.
vm. 1876, p. 62.
. (The author shows that the irritability of the Aldrovandia leaf
is confined to the central glandular region.)
Moss, C. E. (1913) Vegetation of the Peak District, x + 235 pp., 36 figs.,
[p. 291] 2 maps. Cambridge, 1913.
(Chapter vi. contains an account of the marsh and aquatic
associations of the district.)
Muller, F. (1877) Untersuchungen iiber die Struktur efhiger Arten von
[p. 311] Elatine. Flora, N.R. Jahrg. xxxv. (G.R. Jahrg. LX.)
1877, pp. 481-496, 519-526, i pi.
(A description of the anatomy and flower structure of Elatine
and a discussion of the affinities of the genus.)
Miiller, F. (1883)
[pp. 239, 282]
Miinter, J. (1845)
[P- 15]
Murray, H.
Nakano, H. (1911)
[P- 291]
Nolte, E. F. (1825)
[pp. 15,50/52,54
and Fig. 32, p. 53]
Ohno, N. (1910)
[P- 258]
Oliver, D.
Oliver, F. W. (1888)
[pp. 151, 234, 266]
Oliver, F. W. (1889)
Oliver, F. W. (1894)
Onslow, The Hon.
Mrs Huia
Osbeck, P. (1771)
[P- i?]
BIBLIOGRAPHY
Einige Eigenthiimlichkeiten der Eichhornia crassipes.
Kosmos, Jahrg. vn. Heft iv. 1883, pp. 297-300.
(Notes on the floral biology of this species.)
Beobachtungen iiber besondere Eigenthiimlichkeiten
in der Fortpflanzungsweise der Pflanzen durch
Knospen. III. Ueber die Knospen der Sagittaria
sagittaefolia L. Bot. Zeit. Jahrg. 3, 1845, pp. 689-697.
[An account of the tuber formation in this species, with a
mention of certain early references to the subject. The author
discusses the statement in Nolte, E. F. (1825), that tuber
formation was once found by him in Alisma Plantago, and
decides that this is undoubtedly an error.]
See Weiss, F. E. and Murray, H. (1909).
The Vegetation of Lakes and Swamps in Japan. I.
Teganuma (Tega-Swamp) . Bot. Mag. Tokyo, Vol.
xxv. 1911, pp. 35-51, 6 text-figs.
(The first ecological survey of a Japanese lake and swamp.)
Botanische Bemerkungen iiber Stratiotes und Sagit-
taria. Kopenhagen, 44 pp., 2 pis., 1825.
[An admirable account of the life-history of these two genera,
in which special attention is paid to their methods of vegetative
reproduction, and, in the case of Stratiotes, to the distribution
of the sexes and the structure of the fruit. For a criticism see
Miinter, J. (1845).]
Ueber lebhafte Gasausscheidung aus den Blattern
von Nelumbo nucifera Gaertn. Zeitschrift f. Bot.
Jahrg. ii. 1910, pp. 641-644, 4 text-figs.
(In this paper — from a Japanese laboratory — the author draws
the conclusion that the pressure which produces the streaming
of gas bubbles from the leaves of Nelumbo can be explained
on purely physical grounds, but that it also has a physiological
significance.)
See Im Thurn, E. F. and Oliver, D. (1887).
On the Structure, Development, and Affinities of
Trapella, Oliv., a new Genus of Pedalineae. Ann.
Bot. Vol. n. 1888-1889, PP- 75-H5, 5 pis., i text-fig.
(A monograph of Trapella sinensis, Oliv., a Chinese water plant
discovered by Dr Henry.)
On a new form of Trapella sinensis. Ann. Bot.
Vol. in. 1889-1890, p. 134.
[A brief account of a land form of this species. This note is
supplementary to Oliver, F. W. (1888).]
See Kerner, A. and Oliver, F. W. (1894).
See Wheldale, M. (1916).
A Voyage to China.... Translated... by John Reinhold
Forster. Vol. i. xx + 367 pp., 4 pis. London, 1771.
(The author mentions on pp. 334, 335 that a species of Sagittaria
is cultivated by the Chinese as a food plant.)
392
BIBLIOGRAPHY
Osborn, T. G. B. (1914) Botany and Plant Pathology. Reprinted from Hand-
[p. 127] book of South Australia. British Association Visit.
Adelaide, 1914, 27 pp., 7 figs.
(On p. n there is a brief reference to the marine Angiosperms
of S. Australia, and a mention of the curious seedlings of
Cymodocea antarctica.)
OstenfeldjC. H. (1908) On the Ecology and Distribution of the Grass-Wrack
[pp. 123, 134]
Otis, C. H. (1914)
[p. 261]
Overton, E. (1899)
[pp. 228, 280, 290]
Paillieux, A.)
and V (1888)
Bois, D. )
[pp. 17, 24]
Pallis, M. (1916)
[pp. 207, 211]
Parkin, J.
Parmentier, P. (1897)
[P- 312]
Payne-Gallwey, R.
(Zoster a marina) in Danish Waters. Report of the
Danish Biological Station to the Board of Agriculture.
XVI. Translated from Fiskeri-Beretning for 1907,
Copenhagen, 1908, 62 pp., 9 text-figs.
(The distribution of this plant is dealt with in detail, and
special attention is paid to the algae and marine animals with
which it is associated.)
The transpiration of emersed water plants: its
measurement and its relationships. Bot. Gaz. Vol.
58, 1914, pp. 457-494, 3 text-figs, and 14 charts.
(An extremely elaborate study of the transpiration of water
plants whose leaves are in contact with the atmosphere, e.g.
Castalia, Sagittaria and Pontederia.)
Notizen iiber die Wassergewachse des Oberengadins.
Vierteljahrsschrift der Naturforschenden Gesellschaft
in Zurich, Jahrg. 44, 1899, pp. 211-228.
(A record of certain experiments on the effect of light and
temperature on the flowering of Hydrocharis and Elodea,', and
of the vertical distribution of the water plants of the Upper
Engadine.)
Les plantes aquatiques alimentaires. Bull, de la Soc.
nat. d'acclimatation de France, Ser. iv. T. 5, Annee
35, 1888, pp. 782-793, 924-929, 1028-1035, 1 102-
1108.
(An account of a number of aquatic plants which are used for
food, including Aponogeton, Trapa, Eleocharis, Sagittaria and
various Nymphaeaceae.)
The Structure and History of Plav: the Floating Fen
of the Delta of the Danube. Journ. Linn. Soc. Bot.
Vol. 43, 1916, pp. 233-290, 15 pis., i text-fig.
(This paper deals with Phragmites communis, Trin., fiflavescens,
Gren. & Godr.)
See Arber, E. A. N. and Parkin, J. (1907).
Recherches anatomiques et taxinomiques sur les
Onotheracees et les Haloragacees. Ann. des sci. nat.
Ser. vin. Bot. T. in. 1897, PP- 65-149, 6 Pls-
(A discussion, based on the anatomical characters of stem and
leaf, of the relation of the Onothereae, Ludwigieae, Halorageae
and Gunnereae.)
See Walsingham, Lord, and Payne-Gallwey, R.
(1886).
BIBLIOGRAPHY
393
Pearsall, W. H. The Aquatic and Marsh Vegetation of Esthwaite
(1917-1918) Water. Journ. of Ecology, Vol. v. 1917, pp. 180-202
[p. 288] arid Vol. vi. 1918, pp. 53-74, 12 text-figs.
(A detailed ecological survey of a Lancashire lake.)
Pearsall, W. H. (1918) On the classification of Aquatic Plant Communities,
[p. 288] Journ. of Ecology, Vol. vi. 1918, pp. 75-83.
(The author regards aquatic, fen and moor successions as
together forming a unit and leading up to the one formation
moor.)
Perrot, £. (1900) Sur les organes appendiculaires des feuilles de
[p. 169 and Fig. no, certains Myriophyllum. Journ. de Bot. T. xiv. 1900,
p. 170] pp. 198-202, 5 text-figs.
(An account of the peculiar processes borne by the leaf of
Myriophyllum verticillatum and M. spicatum, which the author
regards as pluricellular caducous trichomes.)
Ueber einige deutsche Nymphaen. Bot. Zeit. Jahrg.
12, 1854, pp. 172-175.
(A critical article in which special stress is laid on the import-
ance for systematic purposes of ascertaining the characters of
the ripe fruit.)
Pieters, A. J. (1894) The Plants of Lake St Clair. Bull. Michigan Fish
[p. 288] Commission, No. 2, 1894, 12 pp., i map.
[An ecological study in which the zonation of the plants
observed in Lake St Clair is compared with that recorded by
Magnin, A. (1893) for the Jura lakes.]
Pfeiffer, L. (1854)
Pieters, A. J. (1902)
[p. 291]
Contributions to the Biology of the Great Lakes.
The Plants of Western Lake Erie, with Observations
on their Distribution. Bull. United States Fish
Commission, Vol. xxi. 1902 (for 1901), pp. 57-79,
10 pis., 9 text-figs.
(An ecological study.)
Planchon, J. E. (1844) Observations sur le genre Aponogeton et sur ses
[p. 314] afnnites naturelles. Ann. d. sci. nat. Ser. in. Bot.
T. i. 1844, pp. 107-120, i pi.
(The author describes Aponogeton distachyus and brings
forward evidence for removing it from the neighbourhood of
Saururus and placing it in a sub-order between the Alismaceae
and Juncaginaceae.)
Planchon, J. E. (1853) fitudes sur les Nympheacees. Ann. des sci. nat.
Ser. in. T. xix. 1853, pp. 17-63.
(A systematic account of this family.)
Pond, R. H. (1905)
[p. 264]
Contributions to the Biology of the Great Lakes.
The Biological Relation of Aquatic Plants to the
Substratum. University of Michigan. Inaug. Diss.
Ann Arbor, 1905, 43 pp., 6 text-figs.
(This paper contains important experimental work relating to
the function of the roots in aquatic plants.)
394
Porsch, O. (1903)
[pp. 165, 1 66]
Porsch, O. (1905)
[p. 1 66 and Fig. 107,
P-
Praeger, R. L. (1913)
[p. 297]
Prankerd,T. L. (1911)
[pp. 181, 197, 216,
228, 233 and Fig.
127, p. 197]
Preston, T. A. (1895)
[pp. 232, 291]
Prillieux, E. (1864)
[pp. 63, 173]
Pringsheim, N. (1869)
[pp. 97, 1 06 and Fig.
72, p. 106]
Pringsheim, N. (1888)
Queva, C. (1910)
[p. 244]
BIBLIOGRAPHY
Zur Kenntnis des Spaltofmungsapparates submerser
Pflanzenteile. Sitzungsber. d. Math.-naturwiss.
Klasse d. k. Akad. d. Wissens. Wien, Bd. cxn. Abt. i.
1903, pp. 97~I38> 3 PJs.
(An account of the means by which the flooding of the inter-
cellular spaces through the stomata of submerged organs is
prevented.)
Der Spaltoffnungsapparat im Lichte der Phylogenie.
xv + 196 pp., 4 pis. and 4 text-figs. Jena, 1905.
[Pp. 83-87 deal with the stomates of water plants and form
a resume of Porsch, 0. (1903).]
On the Buoyancy of the Seeds of some Britannic
Plants. Sci. Proc. Royal Dublin Soc., N.S., Vol. xiv.
I9i3~19i5, PP- 13-62.
[This memoir is supplementary to the parts of Guppy, H. B.
(1906) which relate to seed buoyancy.]
On the Structure and Biology of the Genus Hottonia.
Annals of Bot. Vol. xxv. 1911, pp. 253-267, 2 pis.
and 7 text-figs.
(A general account of H. palustris and H. inflata. The author
shows that the mature plant of H. palustris is not rootless as
generally supposed. Traces of polystely occur at the base of
the inflorescence axis in both species.)
The Flora of the Cropstone Reservoir. Trans. Leic.
Lit. and Phil. Soc. Vol. in. 1895, pp. 430-442.
(An account of the flora of a reservoir which had been in
existence twenty-four years.)
Recherches sur la vegetation et la structure de
I'Althenia filiformis Petit. Ann. d. sci. nat. Se"r. v.
Bot. T. ii. 1864, pp. 169-190, 2 pis.
(A general account of this Mediterranean member of the
Zannichellieae.)
Uber die Bildungsvorgange am Vegetationskegel von
Utricularia vulgaris. Monatsber. d. k. preuss. Akad.
d. Wissens. Berlin, 1869, pp. 92-116, i pi.
(The classic account of the apical development of Utricularia
and its bearing on the morphological perplexities presented by
the genus.)
Ueber die Entstehung der Kalkincrustationen an
Siisswasserpflanzen. Pringsheim's Jahrb. f . wiss. Bot.
Bd. xix. 1888, pp. 138-154.
(The author shows experimentally that the chalk incrustation
on the surface of so many fresh-water plants is due to the
abstraction, during the process of assimilation, of CC>2 which
has held the calcium carbonate in solution.)
Observations anatomiques sur le " Trapa natans L."
Association Fran£aise pour Tavancement des sciences.
Compte rendu de la 38e session, Lille, 1909 (1910),
pp. 512-517, 2 text-figs.
(The author's anatomical study of the seedling leads him to
the conclusion that the primary root is entirely unrepresented.
The anatomy of the hypocotyl is modified by the insertion of
numerous adventitious roots which are localised on the same
side of the axis as the large cotyledon.)
BIBLIOGRAPHY
395
Raciborski, M. (1893)
Raciborski,M. (1894^
Raciborski, M. (i8942)
[PP. 29, 35, 272, 338]
Raciborski, M. (1895)
Raffeneau-Delile, A.
(1841)
[pp. 38, 258]
Raunkiaer, C. (1896)
[Figs. 34, p. 55, 159,
p. 246, 161, p. 248,
166, p. 319, 167,
p. 339, 168, p. 339]
Ueber die Inhaltskorper der Myriophyllumtrichome.
Ber. d. deutsch. bot. Gesellsch. Bd. xi. 1893, pp.
348-35I-
(The highly refractive bodies present in the trichomes of
Myriophyllum are considered to be of the nature of a glucoside,
and to be related to substances found in the trichomes of the
leaves of Ceratophyllum, Elatine, etc.)
Die Morphologic der Cabombeen und Nymphaeaceen.
Flora, Bd. 78, 1894, pp. 244-279, 9 text-figs.
(In this memoir special attention is paid to the ontogeny of the
flower and the vegetative shoots.)
Beitrage zur Kenntniss der Cabombeen und Nym-
phaeaceen. Flora, Bd. 79 (Erganzungsband), 1894,
pp. 92-108, i pi.
[This paper is supplementary to Raciborski, M. (I8Q41) and
includes a reply to the criticisms on the latter contained in
Schumann, K. (1894).]
Die Schutzvorrichtungen derBluthenknospen. Flora,
Bd. 8 1 (Erganzungsband), 1895, pp. 151-194, 30
text-figs.
(This paper contains a section, pp. 190—192, dealing with the
protection of the flower-bud among water plants.)
Evidence du mode respiratoire des feuilles de
Nelumbium. Ann. d. sci. nat. Ser. n. T. xvi. Bot.
1841, pp. 328-332.
(This paper on the emission of air from the leaves of the Lotus
is followed by nine pages of controversy on the subject with
Dutrochet.)
De Danske Blomsterplanters Naturhistorie. Bd. i.
Enkimbladede i. Helobieae, 1896, 138 pp., 240 text-
figs.
(This fully illustrated account of the biology of the Helobieae
native to Denmark is in Danish.)
Raunkiaer, C. (1903)
[pp. 62, 65, 331 and
Fig. 38, p. 61]
Ravn, F. K. (1894)
Regnard, P. (1891)
[pp. 253/255, 278]
Anatomical Potamogeton-Studies and Potamogeton
fluitans. Botanisk Tidsskrift, Vol. 25, 1903, pp. 253-
280, 9 text-figs.
(In this paper, which is written in English, the author shows
the value of anatomical characters of the leaf and stem in
classifying the genus Potagometon.)
Om Flydeevnen hos Fr^ene af vore Vandog Sump-
planter. Botanisk Tidsskrift, Vol. 19, 1894, pp.
143-188, 26 text-figs.
(This Danish paper on the floating power of the seeds of aquatic
and marsh plants concludes with a French resume.)
Recherches experimentales sur les conditions phy-
siques de la vie dans les eaux. vii + 500 pp., 236
text-figs., 4 pis. Paris, 1891.
(This book consists of a series of lectures on aquatic biology.
The physical aspect is fully treated; the applications relate
chiefly to animals, but plants are not excluded.)
Reid, C. (1892)
[pp. 296, 298]
Reid, C. (1893)
[P- 54]
Reid, C. (1899)
[P- 303]
Reinsch, P. (1860)
Rendle, A. B. (1899)
[P- 315]
Rendle, A. B. (1900)
Rendle, A. B. (1901)
[P- 304]
Rendle, A. B. (1904)
IP-
Richard, L. C. (1808)
[P-
BIBLIOGRAPHY
On the Natural History of Isolated Ponds. Trans.
Norfolk and Norwich Nat. Soc. Vol. v. 1894 (for
1889-1894), Part 3, 1892, pp. 272-286.
(This paper is chiefly based on a study of the dew ponds of
the South Downs. It forms an important contribution to the
subject of the methods of dispersal of water plants.)
On Paradoxocarpus carinatus, Nehring, an extinct
fossil plant from the Cromer Forest-bed. Trans.
Norfolk and Norwich Nat. Soc. Vol. v. 1894 (for
1889-1894), Part 4, 1893, pp. 382-386, i text-fig.
[An account of a fossil fruit which was eventually discovered
to belong to Stratictes aloid.es L. (vide note by same author in
Trans. Norfolk and Norwich Nat. Soc. Vol. vi. Pt 3, 1897,
P. 328).]
The Origin of the British Flora, vi + 191 pp. London,
1899-
(This classical study, based on the flora of the Newer Tertiary
beds, contains many references to water plants.)
Morphologische Mittheilungen. 5. Ueber die dreierlei
Arten der Blatter der Sagittaria sagittaefolia L.
Flora, N.R. Jahrg. xvm. (G.R. Jahrg. XLIII.) 1860,
pp. 740-742, i fig.
(An account of the heterophylly of Sagittaria including a
mention of the distribution of the stomates in the different
types of leaf. The arrow-head leaves are distinguished as
" Bluthezeitblatter.")
A Systematic Revision of the Genus Najas. Trans.
Linn. Soc. Lond. Ser. n. Vol. v. 1895-1901, Part xn.
1899, pp. 379-436. 4 Pls-
(This monograph includes a general introduction dealing with
the morphology, structure and distribution of the genus.)
Supplementary Notes on the Genus Najas, Trans.
Linn. Soc. Lond. Ser. n. Vol. v. 1895-1901, Part xm.
1900, pp. 437-444-
[This paper supplements Rendle, A. B. (1899).]
Naiadaceae, in Das Pflanzenreich, iv. 12 (heraus-
gegeben von A. Engler). 21 pp., 71 text-figs. Leipzig,
1901.
(An authoritative account of all the species of the genus Naias ;
the general description of the group is in English.)
The Classification of Flowering Plants. Vol. i.
Gymnosperms and Monocotyledons, xiv + 403 pp.,
187 text-figs. Cambridge, 1904.
(This instalment of a text book of systematic botany gives a
very useful account of the Helobieae and other Monocoty-
ledonous aquatics.)
D6monstrations Botaniques ou Analyse du Fruit.
Paris, 1808. xii + in pp.
(On p. 33 the author makes the suggestion that Callitriche is
related to the Euphorbiaceae by its seed structure.)
BIBLIOGRAPHY
397
Rodier, £. (1877*)
[p. 90]
Rodier, £. (18772)
[p. 90]
Rohrbach, P. (1873)
Roper, F. C. S. (1885)
[p. 146]
Rosanoff, S. (1871)
[p. 189 and Fig. 123,
p. 191]
Rossmann, J. (1854)
[p. 144]
Roux, M. le (1907)
[p. 291]
Roxburgh, W. (1832)
[p. no]
Royer, C. (1881-1883)
[pp. 24, 27, 87, 216,
234, 236]
Sur les mouvements spontanes et re"guliers (Tune
plante aquatique submergee, le Ceratophyllum de-
mersum. Comptes rendus de 1'acad. des sciences,
Paris, T. 84, 1877, pp. 961-963.
[For an English account of this work see Rodier, 6. (i8772).]
The Movements of a Submerged Aquatic Plant.
Nature, Vol. xvi. 1877, pp. 554-555, i text-fig.
(This brief paper is translated from an article by the author
in "La Nature" and contains substantially the facts recorded
in Rodier, £. (1877*) with the addition of a text-figure showing
the successive positions assumed in the course of two days by
a branch of Ceratophyllum demersum.)
Beitrage zur Kenntniss einiger Hydrocharideen.
Abhandl. d. naturforsch. Gesellschaft zu Halle, Bd.
xii. 1873, pp. 53-114, 3 pis.
(This memoir deals chiefly with the morphology and anatomy
of Hydrocharis Morsus-ranae, Stratiotes aloides and ValUsncria
spiralis. Special attention is paid to the shoot and inflorescence
systems and to the development of the flower.)
Note on Ranunculus Lingua, Linn. Journ. Linn. Soc.
Bot. Vol. xxi. 1886, pp. 380-384, 2 pis.
(An account of the submerged leaves of this species. The two
types of leaf are clearly figured, and there is an historical
account from the literature of the records of their occurrence.)
Ueber den Bau der Schwimmorgane von Desmanthus
natans Willd. Bot. Zeit. Jahrg. 29, 1871, pp. 829-838
i pi.
[A study of the aerenchyma of Desmanthus natans, Willd.
(Neptunia oleracea, Lour.).]
Beitrage zur Kenntniss der Wasserhahnenfusse,
Ranunculus sect. Batrachium. vi + 62 pp. Giessen,
1854.
(This memoir is divided into two parts; the first deals generally
with the Water Buttercups, and discusses their heterophylly,
while the second consists of descriptions of the species recognised
at this date.)
Recherches biologiques sur le lac d'Annecy. Annales
de Biologic Lacustre, T. n. Fasc. i and 2, 1907,
pp. 220-387, 6 pis., 14 text-figs.
(This memoir includes an ecological study of the flora of the
lake.)
Flora Indica. Vol. n. vi + 691 pp. Serampore, 1832.
(On p. 112 the author mentions that Aldrovandia verticillata is
" Found swimming on ponds of water over Bengal during the
cold and hot season.")
Flore de la Cote-d'Or avec determinations par les
parties souterraines. 2 vols., 693 pp. (2 vols. paged
as one). Paris, 1881-1883.
(This flora, of that Departement of France which includes Dijon,
is unusual in paying special attention to the biology and life-
history of the plants enumerated. It contains a good many
useful notes on water plants.)
398
Roze, E. (1887)
[P- 7i]
Roze, E. (1892)
[P- 85]
Russow, E. (1875)
[pp. 107, 1 80]
Sanio, C. (1865)
[pp. 65, 86, 175, 176,
179]
Sargant, E. (1903)
[p. 320]
Sargant, E, (1908)
[pp. 308, 320, 323]
BIBLIOGRAPHY
Le mode de fecondation du Zannichellia palustris L.
Journ. de Bot. T. i. 1887, pp. 296-299, i text-fig.
(Observations on the submerged pollination of this species.)
Sur le mode de fecondation du Najas major Roth et
du Ceratophyllum demersum L. Bull, de la Soc. bot.
de France, T. xxxix. (Ser. n. T. xiv.) 1892, pp.
361-364.
[The pollination of Naias is described, and, in the case of
Ceratophyllum, the observations of Dutailly, G. (1892) are
confirmed.]
Betrachtungen iiber das Leitbiindel- und Grundge-
webe (Jubilaumschrift Dr Alexander von Bunge).
78 pp. Dorpat, 1875.
(The anatomy of water plants is dealt with in this memoir in
some detail.)
Einige Bemerkungen in Betreff meiner iiber Gefass-
biindelbildung geausserten Ansichten. Bot. Zeit.
Jahrg. 23, 1865, pp. 165-172, 174-180, 184-187,
191-193, 197-200.
[This paper forms a reply to the criticism of the author's
anatomical views by R. Caspary in Prings. Jahrb. Bd. 4,
1865-6, pp. 101-124. It includes an account of the anatomy
of certain water plants — Hippuris (pp. 184-186), Myriophyllum
(p. 186), Elodea (pp. 186, 187 and 191-192), Ceratophyllum
(pp. 192, 193), Trapa (p. 193), and Potamogeton (p. 193).]
A Theory of the Origin of Monocotyledons, founded
on the Structure of their Seedlings. Ann. Bot. Vol.
*7» 1903, PP- 1-92, 7 pis., 10 text-figs.
[This paper does not deal with water plants, but should be
read in connexion with the theory of the aquatic origin of
Monocotyledons proposed in Henslow, G. (1893).]
The Reconstruction of a Race of Primitive Angio-
sperms. Ann. Bot. Vol. xxn. 1908, pp. 121-186,
21 text-figs.
(This memoir contains a criticism (pp. 175-178) of Henslow's
theory of the aquatic origin of Monocotyledons.)
Sauvageau, C. (I8891) Sur la racine du Najas. Journ. de Bot. Vol. in. 1889,
[p. 208 and Fig. 140, pp. 3-11, 7 text-figs.
p. 209] (A detailed account of the extremely reduced anatomy of the
roots of Naias.)
Sauvageau, C. (i8892) Contribution a 1' etude du systeme mecanique dans
[p. 66] la racine des plantes aquatiques; les Potamogeton.
Journ. de Bot. Vol. in. 1889, pp. 61-72, 9 text-figs.
(A full comparative study of the root anatomy of the genus,
bringing out the interesting point that lignin is as abundant
in the roots of Potamogeton as in those of many land plants.)
BIBLIOGRAPHY
399
Sauvageau, C. (i8893)
[P- 135]
Sauvageau, C.
[pp. 124, 131, 164]
Sauvageau, C.
[p.
Sauvageau, C.
[pp. 124, 131]
Sauvageau, C.
[pp. 123, 131, 254,
261, 264, 266, 331
and Figs. 84, p. 125,
85 and 86, p. 128, 88
and 89, p. 132, 108,
p. 167, 162, p. 262]
Sauvageau, C. (i89i2)
Sauvageau, C.
[PP- 135, 33i]
Sauvageau, C. (1893)
[p. 269 and Fig. 164,
p. 270]
Contribution a 1'etude du systeme mecanique dans
la racine des plantes aquatiques; les Zostera, Cymo-
docea et Posidonia. Journ. de Bot. Vol. in. 1889,
pp. 169-181, 5 text-figs.
(A continuation of the author's detailed study of the roots of
submerged plants. In Zostera and Cymodocea the mechanical
tissue is of the nature of collenchyma, while in Posidonia it is
sclerised.)
Observations sur la structure des feuilles des plantes
aquatiques; Zostera, Cymodocea et Posidonia. Journ.
de Bot. T. iv. 1890, pp. 41-50, 68-76, 117-126,
128-135, 173-178, 181-192, 221-229, 237-245, 38
text-figs.
(The author's elaborate study of these three genera leads to
the conclusion that anatomical data serve here to distinguish
species.)
Sur la feuille des Hydrocharidees marines. Journ. de
Bot. T. iv. 1890, pp. 269-275, 289-295, 3 text-figs.
(This memoir deals with the leaf structure of Enhalus, Thalassia
and Halophila.)
Sur la structure de la feuille des genres Halodule et
Phyllospadix : Journ. de Bot, Vol. iv. 1890, pp. 321-
332, 7 text-figs.
(This paper forms the conclusion of the author's study of the
leaves of marine Angiosperms, and includes a summary of his
results.)
Sur les feuilles de quelques monocoty!6dones
aquatiques. Ann. d. sci. nat. Ser. vii. Bot. T. xm.
1891, pp. 103-296, 64 text-figs. (Also published as
Theses presentees a la faculte" des sciences de Paris,
Se"r. A, No. 158, No. d'ordre 720, 1891.)
[An exhaustive account of the leaf structure of forty-eight
species of the Potamogetonaceae (as denned by Ascherson),
incorporating the results published in Sauvageau, C. (1890*)
and (iSQO3). The memoir contains some experimental work on
the transpiration current in submerged plants.]
Sur la tige des Zostera. Journ. de Bot. T. v. 1891,
PP. 33-45. 59-68, 9 text-figs.
(A description of the anatomy and morphology of the stems of
the five species of Zostera, showing that the stem anatomy gives
even better criteria for distinguishing the species than those
deduced from the author's study of the leaves.)
Sur la tige des Cymodocees Aschs. Journ. de Bot.
T. v. 1891, pp. 205-211, 235-243, 6 text-figs.
(The author shows that the different species of Cymodocea and
Halodule can be distinguished by the anatomy of their stems
just as they can by that of their leaves.)
Sur la feuille des Butomees. Ann. des sci. nat. Ser. 7,
Bot. T. 17, 1893, pp. 295-326, 9 text-figs.
(Certain of the plants dealt with in this paper are aquatic, e.g.
Hydrocleis nymphoides, whose leaf anatomy is fully described.)
400
Sauvageau, C. (1894)
[PP. 59, 63, 71, 243
and Figs. 37, p. 60,
43, P. 68]
Schaffner,J.H.(i896)
[P- 19]
Schaffner,J.H.(i897)
[P- 9]
Schaffner,J.H.(i904)
[PP- 309, 314]
Schenck, H. (1884)
[p. 202 and Fig. 133,
p. 202]
Schenck, H. (1885)
[Passim]
Schenck, H. (1886)
[Passim and Figs. 40,
p. 64, 41, p. 65, 51,
P- 79, 56, p. 87, 74,
p. 108, 106, p. 165,
109, p. 168, in, p.
170, 114, p. 176, 138
and 139, p. 209]
Schenck, H. (1887)
BIBLIOGRAPHY
Notes biologiques sur les Potamogeton. Journ. de
Bot. T. vni. 1894, pp. 1-9, 21-43, 45-58, 98-106,
112-123, 140-148, 165-172, 31 text-figs.
[An account of the anatomy and life-history of Potamogeton
crispus L., P. trichoides Ch. et Schl., P. pusillus L., P. gemnti-
parus (Robbins) Morong, P. acutifolius Link, P. perfoliatus L.,
P. polygonifolius Pourr., P. lucens L., P. pectinatus L.,
P. natans L., P. densus L.]
The embryo-sac of Alisma Plantago. Bot. Gaz. Vol.
xxi. pp. 123-132, 2 pis., 1896.
[An account of fertilisation and embryo development in this
species.)
Contribution to the Life History of Sagittaria varia-
bilis. Bot. Gaz. Vol. xxm. 1897, pp. 252-273, 7 pis.
(This paper is confined to an account of the gametophytes,
fertilisation and embryology of this species.)
Some Morphological Peculiarities of the Nym-
phaeaceae and Helobiae. The Ohio Naturalist, Vol.
iv. 1904, pp. 83-92, 3 pis., 2 text-figs.
(The author attempts to show that the Nymphaeaceae are
Monocotyledons . )
Ueber Structuranderung submers vegetirender Land-
pflanzen. Ber. d. deutsch. bot. Gesellsch. Bd. n.
1884, pp. 481-486, i pi.
(An account of the differences observed between the structure
of the normal terrestrial form of Cardamine pratensis, and of
the same species when growing submerged.)
Die Biologic der Wassergewachse. Verhandl. des
naturhist. Vereines d. preuss. Rheinlande, Westfalens
und des Reg.-Bezirks Osnabriick, Jahrg. 42 (Folge v.
Jahrg. 2), 1885, pp. 217-380, 2 pis.
[This memoir, in conjunction with Schenck, H. (1886), forms
one of the most important general contributions ever made to
the study of water plants ; it summarises the state of knowledge
of a generation ago. Many of the more recent accounts of this
biological group are based on Schenck's work.]
Vergleichende Anatomic der submersen Gewachse.
Bibliotheca Botanica, Bd. i. Heft i. 1886, 67 pp.,
10 pis.
(A detailed and fully illustrated account of the anatomy of
those water plants which are most completely specialised for
an aquatic life.)
Beitrage zur Kenntniss der Utricularien. Utricularia
montana Jacq. und Utr. Schimperi nov. spec.
Pringsheim's Jahrb. Bd. xviu. 1887, pp. 218-235,
3 Pis.
(The two species described in this paper are terrestrial, but
they are compared with the aquatic members of the genus.)
BIBLIOGRAPHY 401
Schenck, H. (1889) Ueber das Aerenchym, ein dem Kork homologes
[pp. 188,189, 192 and Gewebe bei Sumpfpflanzen. Pringsheim's Jahrb. f.
Fig. 122, p. 190] wissen. Bot. Bd. xx. 1889, pp. 526-574, 6 pis.
(A detailed account of the occurrence of aerenchyma in
Onagraceae, Lythraceae, Melastomaceae, Hypericaceae, Cap-
paridaceae, Euphorbiaceae, Labiatae and Leguminosae. The
aerenchyma is regarded as primarily a breathing tissue.)
Scheuchzerus, J. Agrostographia sive Graminum, Juncorum, Cypero-
(1719) rum, Cyperoidum, iisque affinium Historia. . . .Tiguri,
[p. 154] Typis et Sumptibus Bodmerianis, 1719.
(This book contains an early reference to the floating leaves of
Scirpus lacustris; see "Scirpus paniculatus," p. 354.)
Schiller, K. See Schorler, B., Thallwitz, J. and Schiller, K. (1906) .
Schilling, A. J. (1894) Anatomisch-biologische Untersuchungen iiber die
[p. 271] Schleimbildung der Wasserpflanzen. Flora, Bd. 78,
1894, pp. 280-360, 17 text-figs.
(A full account of the mucilage organs of water plants; the
author shows that they are all of the morphological nature of
hairs. He believes that the function of the mucilage, which is
formed in all cases at the expense of the cell wall, is to prevent
excess of water from passing into the young tissues.)
Schindler, A. K. (1904) Die Abtrennung der Hippuridaceen von den Halor-
[pp. 181, 312] rhagaceen. Beiblatt zu den Bot. Jahrb. (Engler) Bd.
xxxiv. Heft 3, 1904, pp. 1-77.
[A detailed study of the anatomy and morphology of these
families from which the author concludes that Halorrhagaceae
(Halorrhagideae + Gunnereae) and Hippuridaceae are entirely
unrelated.]
Schlechtendal, D. F. L. Einige Worte iiber Nymphaea neglecta und biradiata.
von (1852) Bot. Zeit. Jahrg. 10, 1852, pp. 557-559.
(The author shows that these two species of Castalia tend to
approach one another, but he leaves open the question as to
whether transitional forms exist.)
Schlechtendal, D. F. L. Betrachtungen iiber die Limosella-Arten. Bot. Zeit.
von (1854) Jahrg. 12, 1854, pp. 909-918.
(A critical account of the species and varieties.)
Schleiden, M. J. (1837) Beitrage zur Kenntniss der Ceratophylleen. Linnaea,
[pp. 63, 84, 86] Bd. n, 1837, pp. 513-542, i pi.
(A very thorough account of the family ; the author includes
all the known forms under the single species Ceratophyllum
vulgare, Schl.)
Schleiden, M. J. ( 1 8381) Bemerkungen iiber die Species von Pistia. Allge-
[p. 316] meine Gartenzeitung, Jahrg. 6, No. 3, 1838, pp. 17-20.
(A systematic account of the genus, with a discussion of its
affinities.)
Schleiden, M.J.( 1 8382) Berichtigungen und Nachtrage zur Kenntniss der
Ceratophylleen. Linnaea, Bd. 12, 1838, pp. 344-346,
i pi.
[Supplementary to Schleiden, M. J. (1837). The germination
of the seeds is described, and attention is drawn to the suppres-
sion of the primary root and the absence of adventitious roots.]
A. W. P. 26
4O2
Schleiden,M.J.(i839)
[P- 73]
Schoenefeld, W. de
(1860)
[p. no]
Schorler, B.,
Schiller, K. ]
[p. 291]
Schrenk, J. (1888)
[pp. 30, 205, 258,
266, 267, 272]
Schrenk, J. (1889)
[p. 193 and Fig.
124, p. 193]
Schroter, C. \
and I (1902)
Kirchner, 0. J
[pp. 291, 322]
Schroter, C.
Schuchardt, T. (1853)
Schultz, F. (1873)
[p. 101]
Schumann, K. (1892)
[P- 70]
BIBLIOGRAPHY
Prodromus Monographiae Lemnacearum oder Con-
spectus Generum atque Specierum. Linnaea, Bd. xin.
1839, pp. 385-392.
(A systematic account of the Lemnaceae which are treated as
a tribe of the Aroideae.)
Sur le mode de vegetation de I' A Idrovanda vcsiculosa
en hiver et au printemps. Bull, de la soc. bot. de
France, T. vii. 1860, pp. 389-392.
(The author shows that when kept indoors the turions of this
plant may float all the winter and then germinate in the spring.)
Pflanzen- und Tierwelt des Moritzburger Grossteiches
bei Dresden. Annales de Biologic Lacustre, T. i.
Fasc. 2, 1906, pp. 193-310.
(This work includes an ecological study of the vegetation of
this lake by B. Schorler.)
On the Histology of the Vegetative Organs of
Brasenia peltata, Pursch. Bull. Torr. Bot. Club,
Vol. xv. 1888, pp. 29-47, 2 pis.
(The points to which special attention is paid in this paper
are the nature and origin of the surface layer of mucilage, the
internal hairs, and the submerged leaves.)
On the Floating-tissue of Nesaea verticillata (L.),
H.B.K. Bull. Torr. Bot. Club, Vol. xvi. 1889, pp.
315-323, 3 Pis.
(An account of the biology and anatomy of the "aerenchyma"
in a member of the Lythraceae. The author regards it primarily
as a floating tissue which serves only secondarily, if at all, for
purposes of aeration.)
Die Vegetation des Bodensees. T. n. Der " Bodensee-
Forschungen"neunter Abschnitt. 86 pp., 3 pis., i map,
15 text-figs. Lindau i. B. 1902.
[In this book the water and marsh vegetation (higher plants)
of the Bodensee is discussed from an ecological standpoint.]
See Kirchner, O. von, Loew, E. and Schroter, C.
(1908, etc.).
Beitrage zur Kenntniss der deutschen Nymphaeen.
Bot. Zeit. Jahrg. xi. 1853, pp. 497-510.
[A critical account of the species and varieties of Nymphaea
(Castalia) native to Germany.]
Beitrage zur Flora der Pfalz (Schluss). Flora, Neue
Reihe, Jahrg. xxxi. (Ganz. Reihe, Jahrg. LVI.) 1873,
pp. 247-251.
(The author mentions that Utricularia intermedia, had at that
time existed in Pfalz for forty years without flowering.)
Morphologische Studien. Heft i. x + 206 pp., 6 pis.
Leipzig, 1892.
[Pp. 119-186 contain an account of the ontogeny of the flowers
of the Potamogetonaceae, Zannichelliaceae and Naiadaceae.
The author criticises the views on the flower ofNaias expressed
by Magnus, P. (iSyo1).]
BIBLIOGRAPHY
4°3
Schumann, K. (1894) Die Untersuchungen des Herrn Raciborski iiber die
Nymphaeaceae und meine Beobachtungen iiber diese
Familie. Ber. d. deutsch. bot. Gesellsch. Bd. xn.
1894, pp. I73-I78-
[A criticism of Raciborski, M. (I8941).]
Scott, D. H. (1891)
[p. 180]
Scott, D. H.)
and > (1888)
Wager, H. J
Scott, J. (1869)
[P- 235]
Seehaus, C. (1860)
[p. 286]
Seidel, C. F. (1869)
[PP- 34, 309]
Sergueeff, M. (1907)
[pp. 142, 244, 281,
314 and Fig. 91, p.
142]
Shull, G. H. (1905)
[P- 162]
Origin of Polystely in Dicotyledons. Annals of Bot.
Vol. v. 1890-1891, pp. 514-517.
(In this paper the hypothesis is put forward that the cases of
polystely known to occur among Angiosperms maybe associated
with an aquatic ancestry.)
On the Floating-Roots of Sesbania aculeata, Pers.
Ann. Bot. Vol. i. 1887-1888, pp. 307-314, i pi.
(An account of the aerenchyma developed on the roots of this
Leguminous plant. The spongy tissue is produced by a cortical
phellogen.)
Note on the Isoetes capsularis, Roxb. Journ. Linn.
Soc. Bot. Vol. x. 1869, pp. 206-209, i pi.
(In this note, the curator of the Calcutta Botanic Garden shows
that Roxburgh's so-called "Isoetes capsularis" is the detached
male flower of Vallisneria spiralis, L.)
Hydrilla verticillata (L. fil.) Casp. var. pomeranica
(Rchb.) Casp. Verhandlung. d. bot. Vereins f. d.
Provinz Brandenburg, Heft n. 1860, pp. 95—102.
(Observations on the life-history of this species.)
Zur Entwickelungsgeschichte der Victoria regia
Lindl. Nov. Act. Acad. Caes. Leopoldino-Carolinae
Germanicae Naturae Curiosorum (Verhandl. d. Kais.
Leop.-Car. deutschen Akad. d. Naturforscher), T. 35,
1870 (for 1869), No. 6, 26 pp., i table, 2 pis.
(A general account of Victoria regia with a discussion of its
affinities. The author regards the Nymphaeaceae as Mono-
cotyledons related to the Hydrocharitaceae.)
Contribution a la morphologic et la biologic des
Aponogetonacees. Universite" de Geneve. Thdse...
docteur es sciences, Institut de Botanique. Prof.
Dr Chodat, 7me serie, vmme fasc. 1907, 132 pp., 5 plsM
78 text-figs.
[A detailed study of Aponogeton (Ouvirandra) fenestralis, and A.
distachyus. A general account of the family and a discussion of
its affinities are included.]
Stages in the Development of Slum cicutae folium.
Carnegie Institution of Washington, Publication No.
30. Papers of Station for Experimental Evolution at
Cold Spring Harbor, New York, No. 3, 1905, 28 pp.,
7 pis., ii text-figs.
(A study of heterophylly in this species.
26 — 2
404
Siddall, J. D. (1885)
[pp. 55, 210, 211]
Snell, K. (1908)
[pp. 208, 260, 265]
BIBLIOGRAPHY
The American Water Weed, Anacharis Alsinastrum,
Bab. : Its Structure and Habit ; with some Notes on
its introduction into Great Britain, and the causes
affecting its rapid spread at first, and apparent
present diminution. Proc. Chester Soc. Nat. Sci.
No. 3, 1885, pp. 125-134, i pi.
(This paper gives the early history of Elodea canadensis, Michx.
in this country.)
Untersuchungen iiber die Nahrungsaufnahme der
Wasserpflanzen. Flora, Bd. 98, 1908, pp. 213-249,
2 text-figs.
(The author's main conclusion is that, in the case of rooted
submerged plants, the greater part of the water supply is
taken in by the roots, but that the leaves may also absorb
water.)
Der Transpirationsstrom der Wasserpflanzen. Ber.
d. deutschen bot. Gesellsch. Jahrg. xxx. 1912, pp.
361, 362.
[A note which should be read in connexion with Snell, K.
(1908) and Hannig, E. (1912).]
Contributions to the knowledge of the diaphragms
of water plants. I. Scirpus validus. Bot. Gaz. ¥01.58,
1914, pp. 495-51?. l6 text-figs.
(This paper contains a comprehensive review of the records in
the literature relating to the occurrence of diaphragms in
various groups of the higher plants.)
Systematisch-anatomische Untersuchung des Blattes
der Hydrocharitaceen. Beihefte zum Bot. Central bl.
Bd. xxx. Abth. i. 1913, pp. 24-104, 53 text-figs.
(A highly detailed comparative study of the leaves of the
Hydrocharitaceae. The author has examined all the genera
belonging to this family.)
Zur Anatomie und Biologic der neuen Hydrocharis-
Arten aus Neuguinea. Mededeelingen van's Rijks
Herbarium Leiden, No. 21, 1914, 2 pp.
(A description of the leaf structure of H. parnassifolia and
H. parvula — the former has typical air leaves like H. asiatica,
and the latter, swimming leaves like H. Morsus-ranae.)
Solms-Laubach, H. Pontederiaceae. A. andC.de Candolle'sMonographiae
Graf zu (1883) Phanerogamarum, Vol. iv. 1883, pp. 501-535.
[p. 31?] (A systematic account of this group with a discussion of the
geographical distribution, etc.)
Spenner, F. C. L. (1827) Ueber Nuphar minima Smith. Flora, Jahrg. x. Bd. i.
[p. 28] 1827, pp. 113-119, 2 pis.
[In his account of this plant, the author describes the submerged
leaves and figures them (PI. I). He suggests that leaves of this
type probably occur in other Nymphaeaceae, but that they
have been overlooked.]
Snell, K. (1912)
[p. 266]
Snow, L. M. (1914)
[P- 183]
Solereder, H. (1913)
[pp. 42, 46, 52, 135,
165, 169, 340]
Solereder, H. (1914)
[p. 42]
BIBLIOGRAPHY
405
Spruce, R. (1908)
[pp. 3i, 99, I54> 190,
229, 290, 291, 311]
Stahl, E. (1900)
[p. 164]
Standley, P. C.
Stein, B. (1874)
[p. in]
Stohr, A. (1879)
[pp. 165, 171, 279]
Strasburger, E. (1884)
[P- 37]
Strasburger, E. (1902)
[pp. 85, 86, 272, 309]
Sykes, M. G.
Sylven, N. (1903)
Tackholm, G. (1914)
[P-
Notes of a Botanist on the Amazon and Andes...
during the years 1849-1864, edited by A. R. Wallace.
2 vols. London, 1908.
(These volumes contain a number of notes on the aquatic plants
observed by Spruce in S. America.)
Der Sinn der Mycorhizenbildung. Pringsheim's
Jahrbuch. Bd. 34, 1900, pp. 539-668, 2 text-figs.
(The author does not deal with aquatics, but his classification
of plants into "starch leaved" strong transputers and "sugar
leaved" weak transpirers seems to have a bearing upon the
nature of the epidermis of submerged leaves.)
See Miller, G. S. and Standley, P. C. (1912).
t)ber Reizbarkeit der Blatter von Aldrovanda vesicu-
losa. Zweiundfiinfzigster Jahres-Ber. d. Schlesischen
Gesellsch. 1875 (1874), pp. 83-84.
(The author records the sensitiveness of the Aldrovandia leaf
to contact.)
Cfber Vorkommen von Chlorophyll in der Epidermis
der Phanerogamen-Laubblatter. Sitzungsberichte
der math.-naturwissens. Classe d. k. Akad. d. Wissens.
Wien, Bd. LXXIX. Abth. i. 1879, pp. 87-118, i pi.
(In opposition to the current opinion, the author shows that
chlorophyll is frequently present in the epidermis of the lower
side of the leaf in terrestrial Dicotyledons, while it is absent hi
the case of terrestrial Monocotyledons.)
Das Botanische Practicum. xxxvi + 664 pp., 182
figs. Jena, 1884.
[This well-known text-book contains many references to the
anatomy of water plants, e.g. Vallisneria, p. 54; Nymphaea
(Castalia), p. 171; Potamogeton,p.i82; Hippuris,pp. 185 and
249; Elodea, p. 187.]
Ein Beitrag zur Kenntniss von Ceratophyllum sub-
mersum und phylogenetische Erorterungen. Prings.
Jahrb. f. wiss. Bot. Bd. 37, pp. 477-526, 3 pis., 1902.
(This investigation supports the view that Ceratophyllum is
allied to Nymphaeaceae. The development of embryo-sac and
pollen-grain are described in detail. There is a discussion of
the use of mucilage in water plants.)
See Thoday, D. and Sykes, M. G. (1909).
Studier ofver organisationen och lefnadssattet hos
Lobelia Dortmanna. Arkiv for Botanik utgifvet af
K. Svenska Vetenskaps-Akad. Bd. 1. 1903-1904, i pi.,
PP- 377-388.
(This Swedish paper is reviewed in the Bot. Centralbl. Bd. 93,
1903, pp. 613-614).
Zur Kenntnis der Embryosackentwicklung von
Lopezia coronata Andr. Svensk Bot. Tidsk. Vol. 8,
1914, pp. 223-234, 5 text-figs.
(The author is in favour of removing Trapa from the Onagraceae
on account of its embryo-sac structure.)
406 BIBLIOGRAPHY
Tackholm, G. (1915) Beobachtungen iiber die Samenentwicklung einiger
[p. 311] Onagraceen. Svensk Bot. Tidsk. Vol. 9, 1915, pp.
294-361, 1 6 text-figs.
(It is pointed out on p. 354 that in the true Onagraceae and in
Tvapa we have two highly differentiated and widely separated
embryo-sac types.)
Tansley, A. G. (1911) Types of British Vegetation, by Members of the
[pp. 286, 287, 288, Central Committee for the Survey and Study of
290] British Vegetation, edited by A. G. Tansley.
Cambridge, 1911.
(The following sections of this book deal with the ecology of
British water plants: pp. 187-203, Aquatic Vegetation; pp.
223-229, The Aquatic Formation of the River Valleys of East
Norfolk.)
Tapper, J. G. O. (1882) Some Observations on the Propagation of Cymodocea
[pp. 127, 205] antarctica (Endl.). Trans, and Proc. and Rep. of the
Royal Society of South Australia, Vol. iv. 1882 (for
1880-81), pp. 1-4, i pi. Further Observations on the
Propagation of Cymodocea antarctica. Ibid. pp. 47-
49, i pi.
(The first account of the viviparous growth of this plant.)
Terras, J. A. (1900)
[pp. 48, 280]
Thallwitz, J.
Theophrastus (Hort)
(1916)
[p. 208]
Thiebaud, M. (1908)
[P- 291]
ay, D. )
md V
J, M. G.)
Thoday, D.
and
Sykes
[pp. 262, 266]
(1909)
Thurn, E. F. Im
Notes on the Germination of the Winter Buds of
Hydrocharis Morsus-Ranae. Trans, and Proc. of the
Bot. Soc. of Edinburgh, Vol. xxi. 1900 (for 1896-
1900), Part iv. 1900, pp. 318-329.
(An account of experiments upon the germination of winter
buds of this species, with special reference to conditions of
illumination.)
See Schorler, B., Thallwitz, J. and Schiller, K. (1906).
Enquiry into Plants, with an English translation by
Sir Arthur Hort. 2 vols. London, 1916.
(Book iv. Chapter 9 contains an exceedingly clear description
of Trapa natans.)
Contribution a la Biologic du Lac de Saint-Blaise.
Annales de Biologic Lacustre, T. in. Fasc. i, 1908,
pp. 54-140, 5 pis.
(This work contains a short section dealing with the plants of
the Lake.)
Preliminary Observations on the Transpiration
Current in Submerged Water-plants. Ann. Bot.
Vol. xxin. 1909, pp. 635-637.
(The authors have demonstrated by experiments on plants of
Potamogeton lucens, in situ in the River Cam, that an unex-
pectedly rapid water current occurs in detached, rootless stems,
and that this current is to a great extent dependent on the
leaves.)
See Im Thurn, E. F.
BIBLIOGRAPHY
407
Tieghem,P.van(i866)
[P- 256]
Tieghem, P. van (1867)
Tieghem,P.van(i868)
[pp. 107, 108, 227]
Tieghem, P. van
(1869!)
[p. 107]
Tieghem, P. van
(1869s)
Tittmann,J.A.(i82i)
[P- 34]
Trecul, A. (1845)
[PP- 37, 309]
Trecul, A. (1854)
[PP- 33, 37, 38, 309]
Treviranus, L. C.
(1821)
[p. 164]
Recherches sur la respiration des plantes submerges.
Bull, de la Soc. bot. de France, T. xm. 1866, pp.
411-421.
[An account of some experiments dealing with assimilation
(not respiration in the modern sense). The author claims to
show that if, in the case of certain submerged plants, the
decomposition of CO2 is initiated in direct sunlight, it may
continue actively for some hours after the plant has been placed
in darkness; see, however, Tieghem, P. van (iS6gz).]
Note sur la respiration des plantes aquatiques.
Comptes rendus de Tacad. des sciences, Paris, T. 65,
1867, pp. 867-871.
[A further communication dealing with the same results as
Tieghem, P. van (1866).]
Anatomic de I'Utriculaire commune. Bull, de la Soc.
bot. de France, T. xv. 1868, pp. 158-162.
(An account of the anatomy of the submerged and aerial parts
of Utricularia vulgaris.)
Anatomic de 1'Utriculaire commune. Ann. d. sci.
nat. Ser. v. Bot. T. x. 1869, pp. 54-58.
[See Tieghem, P. van (1868).]
Sur la respiration des plantes submergees. Comptes
rendus de 1'acad. des sciences, Paris, T. 69, 1869,
PP- 531-535-
[In this paper the author withdraws his previously expressed
opinion (Tieghem, P. van (1866) and (1867) that assimilation
in submerged plants continues after the removal of the light.]
Die Keimung der Pflanzen. viii + 200 pp., 27 pis.
Dresden, 1821.
[The seedlings of a number of water plants are described and
figured: Alisma Plantago, Nymphaea (Castalia) alba and Nuphar
luieum (Nymphaea lutea), Potamogeton natans, Trapa natans.]
Recherches sur la structure et le developpement du
Nuphar luteum. Ann. des sci. nat. Ser. in. Bot. T. iv.
1845, pp. 286-345, 4 Pis.
(The anatomy of the stem, roots and leaves, and the structure
of the reproductive organs, are described in detail. Attention
is drawn to the points in the anatomy and mode of germination
which recall the Monocotyledons.)
fitudes anatomiques et organogeniques sur la
Victoria regia, et anatomic compared du Nelumbium,
du Nuphar et de la Victoria. Ann. d. sci. nat. Ser.
iv. Bot. T. i. 1854, pp. 145-172, 3 pis.
[From his study of Victoria regia and other Waterlilies the
author concludes that the Nelumbiaceae differ widely from.
the Nymphaeaceae. Among the points to which he draws
attention are the operculum of the seed of Victoria and Nuphar
( Nymphaea) and the succession of leaf types in the seedling of
Victoria. For a criticism see Blake, J. H. (1887).]
Vermischte Schriften. Bd. 4. ii + 242 pp., 6 pis.
Bremen, 1821.
(The "absence of an epidermis" on the lower side of the iea
of Potamogeton crispus is alluded to on p. 76.)
408
Treviranus, L. C.
(1848^)
[PP. 93, 99, 154]
Treviranus, L. C.
(1848*)
Treviranus, L. C.
(i853)
Treviranus, L. C.
(1857)
[P- 67]
Tulasne, L. R. (1852)
[p. 112]
Unger, F. (1849)
Unger, F. (1854!)
Unger, F. (1854*)
[P- 256]
BIBLIOGRAPHY
Noch etwas iiber die Schlauche der Utricularien.
Bot. Zeit. Jahrg. 6, 1848, pp. 444-448.
(Notes on the bladders of Utricularia which the author regards
as of foliar nature.)
Observationes circa germinationem in Nymphaea et
Euryale. Abhandl. d. Math.-Phys. Classe d. konig.
bay. Akad. d. Wiss. Bd. v. Abt. n. 1848, pp. 397-403,
i pi.
[A description in Latin of the germination of Nymphaea
(Castalia) caerulea and Euryale ferox. In the latter case the
author figures the four outgrowths which were later described
by Goebel as breathing organs.]
De germinatione seminum Euryales. Bot. Zeit.
Jahrg. xi. pp. 372-374, 1853.
[This short paper should be read in connexion with Treviranus,
L. C. (l8482) since it consists of corrections of the latter, based
on a better supply of material of Euryale ferox.]
Vermischte Bemerkungen. i . Hybernacula des Pota-
mogeton crispus. 2. Hybernacula der Hydrocharis
Morsus Ranae L. Bot. Zeit. Jahrg. 15, 1857, pp.
697-702, i pi.
[As regards Potatnogeton crispus Treviranus confirms the
observations recorded by Clos, D. (1856). He also gives a
short description of the winter buds of Hydrocharis.]
Podostemacearum Monographia. Archives du Mu-
seum d'hist. nat. T. vi. 1852, 208 pp., 13 pis.
(This highly important Latin monograph is illustrated with
a series of exquisite plates, giving a clear idea of the peculiarities
of this anomalous family.)
Die Entwickelung des Embryo's von Hippuris
vulgaris. Bot. Zeit. Jahrg. 7, 1849, pp. 329-339, 2 pis.
(A description of the embryology of Hippuris. The spherical
multicellular embryo becomes sunk in the endosperm by means
of a long suspensor.)
Einiges iiber die Organisation der Blatter der
Victoria regia Lindl. Sitzungsber. d. k. Akad. d.
Wissenschaften, Math.-Naturwissens. Classe, Bd. xi.
Wien, 1854 (for 1853), pp. 1006-1014, i pi.
(The author describes the minute perforations which are
characteristic of the leaves of Victoria regia.)
Beitrage zur Physiologic der Pflanzen. I. Bestim-
mung der in den Intercellulargangen der Pflanzen
enthaltenen Luftmenge. Sitzungsber. d. k. Akad. d.
Wissenschaften, Math.-Naturwissens. Classe, Bd. xii.
Wien, 1854, pp. 367-378.
(The author shows experimentally how much air is contained
in various plant tissues. One of the organs investigated was
the leaf of Pistia.)
BIBLIOGRAPHY
409
linger, F. (1862)
[p. 260]
Ursprung, A. (1912)
CP. 258]
Uspenskij,E.E.(i9i3)
[pp. 139, 195]
Vaucher, J. P. (1841)
[pp. 216, 219]
Vochting, H. (1872)
[p. 178 and Figs.
1 16 and 1 17, p. 179]
Volkens, G. (1883)
[p. 267]
Vries, H. de (1873)
[P- 284]
Wachter, W. (1897!)
[pp. 12, 117, 156,266]
Beitrage zur Anatomic und Physiologic der Pflanzen.
XII. Neue Untersuchungen iiber die Transspiration
der Gewachse. Sitzungsberichte der math. -naturwiss.
Classe der k. Akad. der Wissens. Wien, Bd. XLIV.
Abth. n. 1862, pp. 327-368, i text-fig.
(Pp. 364-367 contain an account of experiments on water
plants demonstrating the existence of a definite transpiration
stream even in submerged plants.)
Zur Kenntnis der Gasdiffusion in Pflanzen. Flora,
N.F. Bd. 4 (G.R. Bd. 104), 1912, pp. 129-156.
(The greater part of this memoir is occupied with a critical
account of the literature dealing with the bubbling of gas
which takes place, under certain conditions, from the leaves of
the Nymphaeaceae. The writer also brings forward some fresh
experimental evidence.)
Zur Phylogenie und Ekologie der Gattung Potamo-
geton. I. Luft-, Schwimm- und Wasserblatter von
Potamogeton perfoliatus L. Bull, des Naturalistes de
Moscou, N.S., Vol. 27, 1913, pp. 253-262, 3 text-figs.
(An account of the land form of this species, followed by
a general comparison between dissected and thin flat laminae,
regarded as adaptations to aquatic life.)
Histoire physiologique des plantes d'Europe. T. n.
743 PP- Paris, 1841.
(On p. 358 the winter buds of Myriophyllum are described.
Observations on other water plants are also included.)
Zur Histologie und Entwickelungsgeschichte von
Myriophyllum. Nova Acta Acad. Caesareae Leo-
poldino-Carolinae Germanicae Naturae Curiosorum.
T. xxxvi. 1873, 18 pp., 4 pis.
(An account of the anatomy and apical development of this
genus.)
Ueber Wasserausscheidung in liquider Form an den
Blattern hoherer Pflanzen. Jahrb. d. k. bot. Gartens
und d. bot. Museums zu Berlin, Bd. n. 1883, pp.
166-209, 3 pis.
(This paper is the earliest general account of the excretion of
water in liquid form from the leaves of the higher plants. The
structure and development of the apical opening in the leaf of
Alisma Plantago are described and figured, p. 206 and PL VI,
figs. 5 and 6.)
Die vitalistische Theorie und der Transversal-
Geotropismus. Flora, N.R. Jahrg. xxxi. (G.R.
Jahrg. LVI.) 1873, pp. 305-315-
[A criticism of Frank, A. B. (1872).]
Beitrage zur Kenntniss einiger Wasserpflanzen. I.
and II. Flora, Bd. 83, 1897, pp. 367-397, 21 text-figs.
(The first part of this paper deals with the results of experi-
mental work on the production of the different forms of leaves
in Sagittaria natans, Michx., S. chinensis, Sims, Eichhornia
azurea, Kth., Heteranthera reniformis, R. et P., Hydrocleis
nymphoides, Buchenau. The second part deals with the
morphology and anatomy of Weddellina squamulosa, Tul., one
of the Podostemaceae.)
4io
Wachter, W. (18972)
[P- 159]
Wager, H.
Wagner, R. (1895)
[p. 39 and Fig. 23,
p. 41]
Walker, A. O. (1912)
[p. 212]
Walsingham, Lord,
and Payne-Gallwey,
R. (1886)
[PP- I35, 302]
Walter, F. (1842)
[PP- 15, i?]
Warming, E. (1871)
IP- J35]
Warming, E. (1874)
[p. 100]
Warming, E. (1881,
1882, 1888, 1891)
[pp. 112, 118, 310]
BIBLIOGRAPHY
Beitrage zur Kenntniss einiger Wasserpflanzen. III.
Flora, Bd. 84, Erganzungsband zum Jahrgang 1897,
PP- 343-348.
[This paper is a continuation of the first part of Wachter, W.
(I8971). It contains an account of experiments upon the
heterophylly of Castalia, showing that the production of the
different forms of leaf in this genus is dependent upon external
conditions, just as in the case of the Monocotyledons previously
investigated;]
See Scott, D. H. and Wager, H. (1888).
Die Morphologic des Limnanthemum nymphaeoides
(L.) Lk. Bot. Zeit. Jahrg. 53, Abt. i. 1895, pp.
189-205, i pi., 1895.
(A general descriptive paper dealing with the development,
branching, etc. of this species.)
The Distribution of Elodea canadensis, Michaux, in
the British Isles in 1909. Proc. Linn. Soc. London,
I24th session, 1912, pp. 71-77.
(This paper gives the result of enquiries made in 1909 among
local natural history societies as to the degree of success
attained by Elodea in establishing itself in this country.)
Shooting (Moor and Marsh). Badminton Library,
xiii + 348 pp. London, 1886.
(The authors mention, pp. 158 and 165, that Brent Geese feed
on Zostera, and that these birds are almost confined to those
parts of the coast where Zostera occurs.)
Bemerkungen liber die Lebensweise einiger deutschen
Pflanzen. Flora, Jahrg. xxv. Bd. n. 1842, pp. 737-
748, i pi.
(A picturesque account of Walter's discovery of tuber-formation
and heterophylly in Sanitaria sagittifolia.)
Forgreningen hos Pontederiaceae og Zostera. Viden-
skab. Meddel. fra den naturhist. Forening i Kjoben-
havn for Aaret 1871, pp. 342-346, i text-fig.
(This Danish paper deals with the nature of the shoot system
in the plants mentioned.)
Bidrag til Kundskaben om Lentibulariaceae. Viden-
skab. Meddel. fra den naturhist. Forening i Kjoben-
havn for Aaret 1874 (1874-5), PP- 33-58, 3 pis.
(This paper, which is in Danish, deals with Genlisea and
Utricularia. The germination of Utricularia is described.)
Familien Podostemaceae. Kongel. Dansk. Videnskab.
Selskabs Skrifter. Sjette Raekke. i. Vol. n. 1881,
pp. 1-34, 6 pis. 2. Vol. ii. 1882, pp. 77-130, 9 pis.
3. Vol. iv. 1888, pp. 443-514, 12 pis. 4. Vol. vn.
1891, pp. 133-179, 185 text-figs.
(This important monograph is in Danish, but each part is
followed by a French resume.)
BIBLIOGRAPHY
411
Warming, E. (1883!)
[P- 245]
Warming, E. (i88s2)
[Figs. 76 and 77,
p. 115, 79, p. 116]
Warming, E. (1909)
[p. 291]
Webber, H. J. (1897)
[p. 213]
Botanische Notizen. Bot. Zeit. Jahrg. 41, 1883, pp.
193-204.
(In section 2, "Zur Biologic der Keimpflanzen," pp. 200-203,
the author refers to the development of long root-hairs, at the
junction of root and hypocotyl, which attach the seedlings of
certain water plants to the substratum.)
Studien iiber die Familie der Podostemaceae.
Engler's Bot. Jahrbiich. Bd. iv. 1883, pp. 217-223,
5 figs.
(A German version of part of the author's work on this family.)
(Ecology of Plants, xi + 422 pp. Oxford, 1909.
(This English version of the author's well-known book contains
sections dealing with aquatic and marsh plants; see especially
pp. 97-100 and 149-190.)
The Water Hyacinth, and its relation to navigation
in Florida. U.S. Depart, of Agriculture. Division of
Botany. Bulletin, No. 18, 1897, 20 pp., i pi., 4 text-
figs.
[An account of the excessive luxuriance of Piaropus crassipes,
(Mart.) Britton, — Eichhor.nia speciosa, Kunth, = Eichhornia
crassipes, (Mart.) Solms.]
Observations sur une espece nouvelle du genre
Wolffia (Lemnacees). Ann. des sci. nat. Ser. in.
Bot. T. 12, 1849, pp. 155-173, i pi.
(The author discovered in Brazil a minute species of Wolffia,
which he named W. brasiliensis. Twelve of the flowering plants
could be accommodated on one frond of Lemna minor.)
Weddell, H. A. (1872) Sur les Podoste"macees en general, et leur distribution
[pp. 113, 295] geographique en particulier. Bull, de la Soc. bot. de
France, T. xix. 1872, pp. 50-57.
(This paper is based upon the author's own observations in
Brazil. Stress is laid upon the very local distribution of many
of the Podostemaceae.)
Weinrowsky , P. ( 1 899) Untersuchungen iiber die Scheiteloff nung bei Wasser-
[pp. 261, 266, 269] pflanzen. Fiinfstiick's Beitrage zur Wissensch. Bot.
Bd. in. 1899, pp. 205-247, 10 text-figs.
(An extremely important account of the apical openings of the
leaves of water plants.)
Weddell, H. A. (1849)
[pp. 80, 300]
Weiss, F. E.)
and
Murray, H. )
[P- 303]
On the Occurrence and Distribution of some Alien
(1909) Aquatic Plants in the Reddish Canal. Mem. and
Proc. of the Manchester Lit. and Phil. Soc. Vol. 53,
1909, No. 14, 8 pp., i map.
[The authors show that Naias graminea (Del.) var. Delilei
(Magnus), recorded in Bailey, C. (1884) as occurring in the
warm water of this canal, has now disappeared. Certain alien
Algae are also discussed, and the distribution of Vallisneria
spiralis, which was planted here forty years ago.]
412
Went, F. A. F. C.
(1910)
[pp. 114, 122]
Werner, E.
West, G. (1905)
[p. 287]
West, G. (1908)
[pp. 287, 290]
West, G. (1910)
[pp. 20, 87, 145, 200,
234, 287, 299, 325]
Wettstein, R. von
(1888)
[p- 38]
Wheldale, M. (The
Hon. Mrs Huia
Onslow) (1916)
[p. 277]
BIBLIOGRAPHY
Untersuchungen ueber Podostemaceen. Verhande-
lingen d. Konin. Akad. van Wetenschappen te
Amsterdam, Tweede Sectie, Dl. xvi. No. i, 1910,
88 pp., 15 pis.
[In this memoir, based upon the results of the author's travels
in Surinam, the following members of the Podostemaceae are
described: 6 sp. of Oenone of which 3 are new, 3 new species of
Apinagia, Lophogyne (i sp.), Mourera (i sp.) and Tristicha
(i sp.). The anatomy, and the development of the ovules, are
treated, as well as the general morphology.]
See Magnus, W. and Werner, E. (1913).
A Comparative Study of the dominant Phanerogamic
and Higher Cryptogamic Flora of Aquatic Habit, in
Three Lake Areas of Scotland. Proc. Roy. Soc.
Edinb. Vol. xxv. Part n. 1906 (for 1905), pp. 967-
1023, 55 pis.
(A general ecological survey of certain Scottish Lakes.)
Notes on the Aquatic Flora of the Ness Area.
Bathymetrical Survey of the Fresh-water Lochs of
Scotland. VIII. The Geogr. Journal, Vol. xxxi.
1908, pp. 67-72.
[This brief paper, which is of a general nature, should be read
in conjunction with the author's detailed studies of the Scottish
lakes— West, G. (1905) and (1910).]
A Further Contribution to a Comparative Study of
the dominant Phanerogamic and Higher Crypto-
gamic Flora of Aquatic Habit in Scottish Lakes.
Proc. Roy. Soc. Edinb. Vol. xxx. 1910 (Session
1909-10), pp. 65-181, 62 pis.
[A continuation of West, G. (1905).]
Beobachtungen iiber den Bau und die Keimung des
Samens von Nelumbo nucifera Gartn. Verhandl. d.
k. k. zool.-bot. Gesellsch. in Wien, Bd. 38, 1888,
pp. 41-48, i pi.
(The structure and germination of the seed of this plant,
which has no endosperm or perispenn, is figured with great
clearness.)
The Anthocyanin Pigments of Plants, x + 318 pp.
Cambridge, 1916.
[Chapter vi. (Physiological Conditions and Factors Influencing
the Formation of Anthocyanins) and Chapter vm. (The
Significance of Anthocyanins), may be consulted in connexion
with the red coloration so prevalent in water plants.]
Wheldon, J. A.J The Flora of West Lancashire. 51 1 pp., 15 pis., i map.
and ["(1907) Eastbourne, 1907.
Wilson, A. ) (On p. 339 a reference is made to a pond which was dug
[p. 299] experimentally in order to see what water plants would
colonise it.)
BIBLIOGRAPHY
413
Wigand, A. (1871)
[P- 37]
Wight, R. (1849)
[P- 99]
Willdenow, C. L.
(1806)
[P- 85]
Willis, J. C. (1902)
[Passim and Figs. 78,
p. 115, 80, p, 118, 82,
p. 121]
Willis, J. C. (I9I41)
[pp. 112, 286, 327,
329]
Willis, J. C. (I9I42)
[P- 305]
Willis, J. C. (I9I51)
[p. 112]
Willis, J. C. (I9i52)
[pp. 112, 327]
Willis, J. C. (1917)
[p. 306]
Nelumbium sped osum, W. Bot. Zeit. Jahrg. 29, 1871,
pp. 813-826, i text-fig.
(An account of the development, morphology, anatomy and
starch distribution in this member of the Nymphaeaceae.)
Conspectus of Indian Utriculariae. Hooker's Journal
of Botany and Kew Garden Miscellany, Vol. i. 1849,
PP- 372-374-
(The author records the occurrence of a whorl of floats below
the flower in U. stellaris.)
Determination of a new aquatic vegetable Genus,
called Caulinia, with general Observations on Water-
plants. Annals of Botany (edited by C. Konig and
J. Sims), Vol. ii. 1806, pp. 39-51.
(A translation of a paper by this author who was the first to
suggest that the pollination of Ceratophyllum was hydro-
philous.)
Studies in the Morphology and Ecology of the
Podostemaceae of Ceylon and India. Ann. Roy. Bot.
Gard. Peradeniya, Vol. i. 1902, pp. 267-465, 34 pis.
(An important general work dealing with the structure and
biology of this group.)
On the Lack of Adaptation in the Tristichaceae and
Podostemaceae. Proc. Roy. Soc. Vol. 87, B. 1914,
PP- 532-550.
(The detailed development of a thesis, to which the author has
been led in the course of seventeen years' study of these families
in India, Ceylon and Brazil — namely, that the natural selection
of infinitesimal variations is quite incompetent to explain their
evolution.)
The Endemic Flora of Ceylon, with Reference to
Geographical Distribution and Evolution in General.
Phil. Trans. Roy. Soc. London, Ser. B, Vol. 206,
1914, pp. 307-342.
(This paper does not deal with water plants, but is quoted
here because it is the first of the series of contributions in
which the author has developed his " Age and Area " hypothesis,
which has an important bearing on the study of aquatics.)
A New Natural Family of Flowering Plants —
Tristichaceae. Linn. Soc. Journ. Bot. Vol. 43, 1915,
pp. 49-54-
(A proposal to separate the Podostemaceae into two families —
Tristichaceae = Chlamydatae, and Podostemaceae = Achlamy-
datae.)
The Origin of the Tristichaceae and Podostemaceae.
Ann. Bot. Vol. xxix. 1915, pp. 299-306.
(A reconstruction of the type of ancestor from which these
groups are probably derived.)
The Relative Age of Endemic Species and other
Controversial Points. Ann. Bot. Vol. xxxi. 1917, pp.
189-208.
(See pp. 201, 202 for a consideration of the Podostemaceae and
Tristichaceae from the point of view of the author's "Age and
Area" Law of plant distribution.)
414
Willis, J. C. )
and L (1895)
Burkill, I. H.j
[p. 230]
Wilson, A.
Wilson, W. (1830)
[P- 76]
Wydler, H. (1863)
Wylie, R. B. (1904)
[PP. 55, 57]
Wylie, R. B. (1912)
[PP- 55, 86 and Fig-
35, P- 56J
Wylie, R. B. (I9I71)
[p. 234 and Fig. 153,
P- 234]
Wylie, R. B. (I9I72)
[P- 235]
Zacharias, O. (1891)
BIBLIOGRAPHY
Flowers and Insects in Great Britain. Ann. Bot.
Vol. ix. 1895, pp. 227-273.
(This paper includes observations on the pollination of Peplis
and Mentha aquatica.)
See Wheldon, J. A. and Wilson, A. (1907)
Lemna gibba. Remarks on the Structure and Ger-
mination. Hooker's Botanical Miscellany, Vol. i.
1830, pp. 145-149, i pl.
(A description, with clear figures, of the seedlings of this
species.)
Morphologische Mittheilungen. Alisma Plantago, L.
Flora, N.R. Jahrg. xxi. (G.R. Jahrg. XLVI.) 1863,
pp. 87-90, 97-100, 2 pis.
(A detailed study of the shoot relations and the inflorescence
of Alisma Plantago, L.)
The Morphology of Elodea canadensis. Bot. Gaz.
Vol. xxxvu. 1904, pp. 1-22, 4 pis.
(An account of the gametophytes, pollination, etc. in this
species.)
A long-stalked Elodea flower. Bull, from the Labs.
of Nat. Hist. State University Iowa, Vol. vi. 1912,
PP- 43-52, 2 pis.
(A description of a new species of Elodea, E. ioensis, in which
the male flower reaches the surface through great elongation of
its stalk.)
Cleistogamy in Heteranthera dubia. Bull, from the
Labs, of Nat. Hist. State University Iowa, Vol. vn.
No. 3, 1917, PP- 48-58, i pl.
(The cleistogamy of this species, which is very thoroughly
described, is considered by the author to be ' largely accidental.')
The Pollination of Vallisneria spiralis. Bot. Gaz.
Vol. 63, 1917, pp. 135-145, i pl. and 6 text-figs.
(The author corrects a number of errors in earlier accounts of
this plant, and lays great stress upon the part played in
pollination by the surface film.)
Die Tier- und Pflanzenwelt des Siisswassers, Vol. i.
x + 380 pp., 79 text-figs. Leipzig, 1891.
(F. Ludwig contributes a section, pp. 65-134, dealing with the
Phanerogams of fresh waters.)
[ 415 ]
INDEX TO BIBLIOGRAPHY
GENERA AND FAMILIES NAMED IN THE BIBLIOGRAPHY,
EITHER IN TITLES OR ABSTRACTS
Aedemone. Hallier, E. (1859) ; Jaensch, T. (I8841) and (18842) > Klebahn,
H. (1891); Kotschy, T. (1858).
Aeschynomene. Ernst, A. (18722); Hallier, E. (1859); Jaensch T (1884*)'
Moeller, J. (1879).
Aldrovandia. Auge de Lassu (1861) ; Caspary, R. (1858*), (1859 and 1862) ;
Chatin, A. (18582); Cohn, F. (1850) and (1875); Darwin, C.
(1875) and (1888); Delpino, F. (1871); Fenner, C. A. (1904);
Hausleutner, (1850!) and (1851); Korzchinsky, S. (1886);
Maisonneuve, D. de (1859); Monti, G. (1747); Mori, A.
(1876); Roxburgh, W. (1832); Schoenefeld, W. de (1860);
Stein, B. (1874).
Alisma. Bolle, C. (1861-1862); Buchenau, F. (1857); Crocker, W.
and Davis, W. E. (1914) ; Fauth, A. (1903) ; Gliick, H. (1905) ;
Griset, H. E. (1894); Hofmeister, W. (1858); Loeselius, J.
(1703); Miinter, J. (1845); Nolte, E. F. (1825); Schaffner,
J. H. (1896); Tittmann, J. A. (1821); Volkens, G. (1883);
Wydler, H. (1863).
ALISMACEAE. Arber, E. A. N. and Parkin, J. (1907) ; Bolle, C. (1861-1862) ;
Buchenau, F. (1882) and (1903!); Gliick, H. (1905); Micheli,
M. (1881); Planchon, J. E. (1844).
Althenia. Prillieux, E. (1864).
Amphibolis. Agardh, C. A. (1821).
ANACHARIDEAE. (See HYDRILLEAE.)
Anacharis. (See also Elodea.) Douglas, D. (1880); Marshall, W. (1852) and (1857);
Siddall, J. D. (1885).
Apinagia. Went, F. A. F. C. (1910).
Aponogeton. Paillieux, A. and Bois, D. (1888); Planchon, J. E. (1844);
Sergueeff, M. (1907).
APONOGETONACEAE. Krause, K. and Engler, A. (1906); Sergueeff, M. (1907).
ARACEAE. Engler, A. (1877); Jussieu, A. L. de (1789); Schleiden, M. J.
(1839).
Bergia. Cambessedes, J. (1829).
Bidens. Hutchinson, J. (1916).
BIGNONIACEAE. Hovelacque, M. (1888).
Blyxa. Montesantos, N. (1913).
Brasenia. Keller, I. A. (1893); Schrenk, J. (1888).
Bulliarda. Caspary, R. (1860).
BUTOMACEAE. Arber, E. A. N. and Parkin, J. (1907); Buchenau, F. (1882)
and (19032); Micheli, M. (1881); Sauvageau, C. (1893).
Butomus. Buchenau, F. (1857); Fauth, A. (1903).
CABOMBEAE. Gray, A. (1848); Raciborski, M. (1894!) aQd (18942).
Caldesia. Gluck, H. (1905).
Callitviche. Baillon, H. (1858); Borodin, J. (1870); Brown, R. (1814);
Fauth, A. (1903); Frank, A. B. (1872); Hegelmaier, F.
(1864); Irmisch, T. (1859!); Jonsson, B. (1883-1884); Lebel,
E. (1863); Ludwig, F. (1881); Magnus, P. (1871); Mer, £.
(1881); Richard, L. C. (1808).
416
INDEX TO BIBLIOGRAPHY
Caltha.
CAPPARIDACEAE.
Cardamine.
CARYOPH YLLACEAE .
Castalia.
Caulinia.
CERATOPH YLLACEAE .
Ceratophyllum.
Coleanthus.
Comarunt.
Cotula.
Crassula.
Cymodocea.
Cynomorium.
CYPERACEAE.
Damasonium.
Desmanthus.
Diplanthera.
Echinodorus.
Eichhornia.
ELATINACEAE.
Elatine.
Eleocharis.
Elisma.
Elodea.
Enhalus.
Epilobium.
Equisetum.
Erigeron.
EUPHORBIACEAE.
Euryale.
Genlisea.
Glyceria.
Gunnera.
GUNNEREAE.
Geneau de Lamarliere, L. (1906).
Schenck, H. (1889).
Schenck, H. (1884).
Cambessedes, J. (1829).
(See Nymphaea.)
Willdenow, C. L. (1806).
(See Ceratophyllum.}
Borodin, J. (1870); Brongniart, A. (1827); Darwin, C. and F.
(1880); Delpino, F. and Ascherson, P. (1871); Dutailly, G.
(1892); Gliick, H. (1906); Goppert, H. R. (1848); Gray, A.
(1848); Guppy, H. B. (1894!); Irmisch, T. (1853); Kirchner,
O. von, Loew, E. and Schroter, C. (1908, etc.) ; Ludwig, F.
(1881); Magnus, P. (1871); Raciborski, M. (1893); Rodier, £.
(1877!) and (18772); Roze, E. (1892); Sanio, C. (1865);
Schleiden, M. J. (1837) and (18382); Strasburger, E. (1902);
Willdenow, C. L. (1806).
Duval-Jouve, J. (1864).
Irmisch, T. (1861).
Hutchinson, J. (1916).
Magnus, P. (1871).
Agardh, C. A. (1821) ; Bornet, E. (1864) ; Cavolini, F. (1792*) ;
Chrysler, M. A. (1907) ; Delpino, F. and Ascherson, P. (1871) ;
Duchartre, P. (1872); Gaudichaud, C. (1826); Magnus, P.
(1872); Osborn, T. G. B. (1914); Sauvageau, C. (1889*),
(1890*) and (1891 3); Tepper, J. G. O. (1882).
Juel, O. (1910).
Ascherson, P. (1883); Esenbeck, E. (1914).
Gliick, H. (1905).
Rosanoff, S. (1871).
(See Halodule.)
Gluck, H. (1905).
Boresch, K. (1912); Miiller, F. (1883); Wachter, W. (1897!) •
Webber, H. J. (1897).
Cambessedes, J. (1829).
Cambessedes, J. (1829); Caspary, R. (1847)- Muller, F.
(1877); Raciborski, M. (1893).
Paillieux, A. and Bois, D. (1888).
Fauth, A. (1903); Gliick, H. (1905).
Bolle, C. (1865) and (1867); Brown, W. H. (1913); Caspary,
R. (1858!), (18582) and (1858"); Douglas, D. (1880); Geneau
de Lamarliere, L. (1906); Hauman-Merck, L. (i9i32)»
Holm, T. (1885); Johnston, G. (1853); Overton, E. (1899);
Sanio, C. (1865); Siddall, J. D. (1885); Strasburger, E.
(1884); Walker, A. O. (1912); Wylie, R. B. (1904) and
(1912).
Cunnington, H. M. (1912); Delpino, F. and Ascherson, P.
(1871); Sauvageau, C. (iSgo2).
Batten, L. (1918); Lewakofifski, N. (I8731).
Geneau de Lamarliere, L. (1906).
Hutchinson, J. (1916).
Baillon, H. (1858); Hegelmaier, F. (1864); Richard, L. C.
(1808); Schenck, H. (1889).
Anon. (1895); Treviranus, L. C. (18482) and (1853).
Warming, E. (1874).
Geneau de Lamarliere, L. (1906).
MacCaughey, V. (1917).
Schindler, A. K. (1904).
INDEX TO BIBLIOGRAPHY
HAEMODORACEAE. Ascherson, P. (1883).
Halodule (Diplanthera) . Delpino, F. and Ascherson, P. (1871); Sauvageau, C.
(iSgo3) and (iSgi3).
Halophila. Balfour, I. B. (1879); Delpino, F. and Ascherson, P. (1871);
Gaudichaud, C. (1826); Holm, T. (1885); Sauvageau, C.
(i89o2).
HALORRHAGIDEAE (HALORAGEAE) . Brown, R. (1814); Hegelmaier, F. (1864);
Juel, O. (1910); Parmentier, P. (1897); Schindler, A. K.
(1904).
Herminiera. Hallier, E. (1859) ; Jaensch, T. (1884 J) and (18842) '> Klebahn,
H. (1891); Kotschy, T. (1858).
Heteranthera. Hildebrand, F. (1885); Wachter, W. (1897*); Wylie, R. B.
(I9I71)-
HIPPURIDACEAE. Schindler, A. K. (1904).
Hippuris. Barratt, K. (1916); Borodin, J. (1870); Chatin, A. (I8551);
Fauth, A. (1903); Irmisch, T. (1854); Juel, O. (1910) and
(1911); Sanio, C. (1865); Strasburger, E. (1884); Unger, F.
(1849).
Hottonia. Geneau de Lamarliere, L. (1906); Prankerd, T. L. (1911).
Hydrilla. Bennett, A. (1914); Caspary, R. (18582); Seehaus, C. (1860).
HYDRILLEAE. Caspary, R. (1858!) and (18582).
Hydrocharis. Frank, A. B. (1872) ; Griset, H. E. (1894) ; Irmisch, T. (1859^
and (1865); Karsten, G. (1888); Lindberg, S. O. (1873);
Overton, E. (1899); Rohrbach, P. (1873); Solereder, H.
(1914); Terras, J. A. (1900); Treviranus, L. C. (1857).
HYDROCHARITACEAE. Ascherson, P. (1867) and (1875); Ascherson, P. and
Giirke, M. (1889); Caspary, R. (1857), (1858!) and (1858');
Gliick, H. (1901); Montesantos, N. (1913); Rohrbach, P.
(1873); Sauvageau, C. (iSgo2); Solereder, H. (1913).
Hydvocleis. Buchenau, F. (19032); Ernst, A. (I8721); Sauvageau, C.
(1893); Wachter, W. (I8971).
Hydromystria. Hauman, L. (1915).
Hydrothrix. Goebel, K. (1913); Hooker, J. D. (1887).
HYPERICACEAE. Cambessedes, J. (1829); Schenck, H. (1889).
Isnardia. Chatin, A. (1855!).
Isoetes. Goebel, K. (1879); Mer, E\ (i88o2); Scott, J. (1869).
JUNCAGINACEAE. Buchenau, F. (1882); Micheli, M. (1881); Planchon, J. E.
(1844).
Jussiaea. Chatin, A. (1855!); Martins, C. (1866).
LABIATAE. Schenck, H. (1889).
Lacis. Brown, C. Barrington (1876).
Lagarosiphon. Caspary, R. (18582).
LEGUMINOSAE. Ernst, A. (18722); Schenck, H. (1889).
Lemna. Arber, A. (1919*); Brongniart, A. (1833); Caldwell, O. W.
(1899); Clavaud, A. (1876); Dutailly, G. (1878); Ehrhart, F.
(1787); Guppy, H. B. (18942); Hoffmann, J. F. (1840);
Hofmeister, W. (1858); Kalberlah, A. (1895); Koch, K.
(1852); Kurz, S. (1867); Ludwig, F. (1881); Micheli, P. A.
(1729); Milde, (1853); Weddell, H. A. (1849); Wilson, W.
(1830).
LEMNACEAE. Arber, A. (1919*); Engler, A. (1877); Hegelmaier, F. (1868)
and (1871); Horen, F. van (1869) and (1870); Kirchner,
O. von, Loew, E. and Schroter, C. (1908, etc.); Kurz, S.
(1867); Schleiden, M. J. (1839); Weddell, H. A. (1849).
LENTIBULARIACEAE. Buchenau, F. (1865).
Limnanthemum. Fau^h, A. (1903); Goebel, K. (1891); Wagner, R. (1895).
Limnobium. Montesantos, N. (1913).
A. w. P.
27
4i8
INDEX TO BIBLIOGRAPHY
Limnocharis. Ernst, A. (I8721); Hall, J. G. (1902).
Limnophila. Goebel, K. (1908).
Limosella. Hooker, J. D. (1847); Schlechtendal, D. F. L. von (1854).
Littovella. Buchenau, F. (1859); Fauth, A. (1903); Mer, E. (iSSo1)
(i88o2) and (1881).
Lobelia. Armand, L. (1912); Buchenau, F. (1866); Sylven, N. (1903).
Lopezia. Tackholm, G. (1914).
Lophogyne. Went, F. A. F. C. (1910).
LUDWIGIEAE. Parmentier, P. (1897).
JLycopus. Lewakoffski, N. (I8731).
Lysimachia. Irmisch, T. (1861).
LYTHRACEAE. Gin, A. (1909); Schenck, H. (1889); Schrenk, J. (1889).
Lythrum. Lewakoffski, N. (I8731).
Marsilea. Hildebrand, F. (1870); Karsten, G. (1888).
May oca. Ludwig, F. (1886).
MELASTOMACEAE. Schenck, H. (1889).
Mentha. Willis, J. C. and Burkill, I. H. (1895).
Menyanthes. Fauth, A. (1903); Irmisch, T. (1861).
Merimea. Cambessedes, J. (1829).
Mimosa. Humboldt, A. de and Bonpland, A. (1808).
Montia. Focke, W. O. (I8931).
Mourera. Aublet, F. (1775); Went, F. A. F. C. (1910).
Myriophyllum. Bokorny, T. (1890); Borodin, J. (1870); Fauth, A. (1903);
G6neau de Lamarliere, L. (1906) ; Goebel, K. (1908) ; Irmisch,
T. (I8591); Knupp, N. D. (1911); Ludwig, F. (1881);
Magnus, P. (1871); Perrot, E. (1900); Raciborski, M. (1893);
Sanio, C. (1865); Vaucher, J. P. (1841); Vochting, H. (1872).
NAIADACEAE. Rendle, A. B. (1901); Schumann, K. (1892).
Naias. Ascherson, P. (1874); Bailey, C. (1884); Bennett, A. (1914);
Campbell, D. H. (1897); Guppy, H. B. (1906); Hofmeister,
W. (1858); Irmisch, T. (1865); Jonsson, B. (1883-1884);
Magnus, P. (I87O1), (1883) and (1894); Rendle, A. B. (1899),
(1900) and (1901); Roze, E. (1892); Sauvageau, C. (iSSg1);
Schumann, K. (1892); Weiss, F. E. and Murray, H. (1909).
Nasturtium. Chatin, A. (1858*); Foerste, A. F. (1889).
NELUMBIACEAE. Gray, A. (1848).
Nelumbo (Nelumbium). Anon., (1895) ; Berry, E. W. (1917) ,* Brongniart, A. (1827) ;
Hofmeister, W. (1858); Ohno, N. (1910); Raffeneau-Delile,
A. (1841); Trecul, A. (1854); Wettstein, R. von (1888);
Wigand, A. (1871).
Neobeckia. MacDougal, D. T. (1914).
Nepenthes. Gardner, G. (1847).
Neptunia. Humboldt, A. de and Bonpland, A. (1808); Rosanoff, S.
(1871).
Nesaea. Schrenk, J. (1889).
Nuphar(Nymphaea). Arcangeli, G. (1890); Brand, F. (1894); Caspary, R. (1861);
Hofmeister, W. (1858); Irmisch, T. (1853); Spenner, F. C. L.
(1827); Tittmann, J. A. (1821); Trecul, A. (1845) and (1854).
Nymphaea(Castalia). Arcangeli, G. (1890); Bachmann, H. (1896); Barber, C. A.
(1889); Bauhin, G. (1623); Brand, F. (1894); Caspary, R.
(iSyo1); Desmoulins, C. (1849); Fries, E. (1858); Geneau de
Lamarliere, L. (1906); Hausleutner, (18502); Hentze, W.
(1848); Irmisch, T. (1853); Mellink, J. F. A. (1886); Miller,
G. S. and Standley, P. C. (1912); Otis, C. H. (1914);
Schlechtendal, D. F. L. von (1852); Schuchardt, T. (1853);
Strasburger, E. (1884); Tittmann, J. A. (1821); Treviranus,
L. C. (i8482); Wachter, W. (i8972).
INDEX TO BIBLIOGRAPHY
419
NYMPHAEACEAE.
Anon., (1828); Arber, E. A. N. and Parkin, J. (1907);
Blenk, P. (1884); Brand, F. (1894); Caspary, R. (1856*) ;
Cook, M. T. (1906); Gwynne-Vaughan, D. T. (1897); Keller,
I. A. (1893); Paillieux, A. and Bois, D. (1888); Pfeiffer, L.
(1854); Planchon, J. E. (1853); Raciborski, M. (1894!) and
(1894 2); Schaffner, J. H. (1904); Schuchardt, T. (1853);
Schumann, K. (1894); Spenner, F. C. L. (1827); Strasburger,
E. (1902); Ursprung, A. (1912); Wigand, A. (1871).
Coleman, W. H. (1844).
Went, F. A. F. C. (1910).
Parmentier, P. (1897).
Schenck, H. (1889); Tackholm, G. (1914) and (1915).
Hovelacque, M. (1888).
Montesantos, N. (1913).
Sergueeff, M. (1907).
Reid, C. (1893).
Hutchinson, J. (1916).
Oliver, F. W. (1888).
Chatin, A. (1855!) ; Willis, J. C. and Burkill, I. H. (1895).
Pallis, M. (1916).
Phucagrostis (see also Cymodocea). Ascherson, P. (1870); Bornet, E. (1864);
Cavolini, F. (i7922).
Goebel, K. (1895).
Chrysler, M. A. (1907); Dudley, W. R. (1894); Sauvageau, C.
(1890").
Webber, H. J. (1897).
Dangeard, P. A. and Barbe, C. (1887).
Arber, A. (1919*) ; Engler, A. (1877); Hofmeister, W. (1858);
Ito, T. (1899); Kingsley, M. H. (1897); Koch, K. (1852);
Schleiden, M. J. (1838!) ; Unger, F. (18542).
Aublet, F. (1775); Brown, C. Barrington (1876); Gardner, G.
(1847) ; Goebel, K. (i8893) and (1891-1893) ; Im Thurn, E. F.
(1883) ; Lister, G. (1903) ; Magnus, W. and Werner, E. (1913) ;
Matthiesen, F. (1908); Tulasne, L. R. (1852); Wachter, W.
(1897*); Warming, E. (1881, 1882, 1888, 1891) and (18832);
Weddell, H. A. (1872) ; Went, F. A. F. C. (1910) ; Willis, J. C.
(1902), (I9I41). (I9I51), (i9i52) and (1917)-
Hildebrand, F. (1870); Irmisch, T. (1861).
Blanc, M. le (1912); Hauman-Merck, L. (I9I31); Hofmeister,
W. (1858); Otis, C. H. (1914).
Arber, A. (1918); Ascherson, P. (1883); Goebel, K. (1913);
Hildebrand, F. (1885) ; Hooker, J. D. (1887) ; Solms-Laubach,
H. Graf zu (1883); Warming, E. (1871).
Focke, W. O. (1893!).
Cavolini, F. (1792*) ; Delpino, F. and Ascherson, P. (1871);
Sauvageau, C. (i8Sg9) and (iSgo1).
Bennett, A. (1896); Blanc, M. le (1912); Brongniart, A.
(1834); Chrysler, M. A. (1907); Clos, D. (1856); Coster, B. F.
(1875); Esenbeck, E. (1914); Fryer, A. (1887); Fryer, A.,
Bennett, A. and Evans, A. H. (1898-1915); Geneau de
Lamarliere, L. (1906) ; Hegelmaier, F. (1870) ; Hildebrand, F.
(1861); Irmisch, T. (1853), (1858*), (1859!) and (i8592);
Lundstrom, A. N. (1888); Her, E. (i8822); Raunkiaer, C.
(1903); Sanio, C. (1865); Sauvageau, C. (i88g2) and (1894);
Strasburger, E. (1884); Thoday, D. and Sykes, M. G. (1909);
Tittmann, J. A. (1821); Treviranus, L. C. (1821) and (1857);
Uspenskij, E. E. (1913).
Oenanthe.
Oenone.
OENOTHERACEAE.
ONAGRACEAE.
OROBANCHACEAE.
Ottelia.
Ouvirandra.
Paradoxocarpus.
Pectis.
PED ALINE AE.
Peplis.
Phragmites,
Phyllocactus.
Phyllospadix.
Pi ar opus.
Pinguicula.
Pistia.
PODOSTEMACEAE.
Polygonum.
Pontederia.
PONTEDERIACEAE.
PORTULACACEAE.
Posidonia,
Potamogeton.
27 — 2
420
INDEX TO BIBLIOGRAPHY
POTAMOGETONACEAE. Ascherson, P. (1867) and (1875) ; Ascherson, P. and Graebner,
P. (1907); Chrysler, M. A. (1907); Fischer, G. (1907); Cluck,
H. (1901); Irmisch, T. (i8583); Sauvageau, C. (iSgi1);
Schumann, K. (1892).
Burns, G. P. (1904); McCallum, W. B. (1902).
Ascherson, P. (1873) ; Askenasy, E. (1870) ; Bailey, C. (1887) ;
Belhomme, (1862); Dodoens, R. (1578); Freyn, J. (1890);
Geneau de Lamarliere, L. (1906); Karsten, G. (1888);
Lamarck, J. P. B. A. (1809) ; Mer, E. (iSSo1) ; Roper, F. C. S.
(1885); Rossmann, J. (1854).
Hovelacque, M. (1888).
Lewakoffski, N. (18732).
Chrysler, M. A. (1907) ; Delpino, F. and Ascherson, P. (1871) ;
, C. (1826); Hofmeister, W. (1852); Irmisch, T.
Proserpinaca.
Ranunculus.
RHINANTHACEAE.
Rubus.
Ruppia.
Sagittaria.
Salix.
Saururus.
Schizotheca.
Scirpus.
Sesbania.
Sisymbrium.
Sium.
Solanum.
Sparganium.
Spirodela.
Stratiotes.
Subularia.
Terniola.
Thalassia.
Tillaea.
Trapa.
Trapella.
Tristicha.
TRISTICHACEAE.
Udora. (See also
Anon., (1895) ; Arber, A. (1918) ; Bauhin, G. (1596) and (1620) ;
Blanc, M. le (1912); Bolle, C. (1861-1862); Buchenau, F.
(1857); Costantin, J. (18852); Coulter, J. M. and Land, W.
J. G. (1914); Fauth, A. (1903); Gliick, H. (1905); Goebel, K.
(1880) and (1895); Hildebrand, F. (1870); Kirschleger, F.
(1856); Klinge, J. (1881); Loeselius, J. (1703); Martens, G.
von (1824); Hunter, J. (1845); Nolte, E. F. (1825); Osbeck,
P. (1771); Otis, C. H. (1914); Paillieux, A. and Bois, D.
(1888); Reinsch, P. (1860); Schaffner, J. H. (1897); Wachter,
W. (I8971); Walter, F. (1842).
Lewakoffski, N. (1877).
Planchon, J. E. (1844).
Ascherson, P. (1870).
Anon., (1895); Desmoulins, C. (1849); Esenbeck, E. (1914);
Kirschleger, F. (1856) and (1857); Scheuchzerus, J. (1719);
Snow, L. M. (1914).
Hallier, E. (1859); Jaensch, T. (18842); Scott, D. H. and
Wager, H. (1888).
Chatin, A. (iSsS1).
Shull, G. H. (1905).
Klebahn, H. (1891).
Kirschleger, F. (1856).
Hegelmaier, F. (1871); Micheli, P. A. (1729).
Arber, A. (1914); Caspary, R. (1875); Davie, R. C. (1913):
Geldart, A. M. (1906); Irmisch, T. (1859!) and (1865);
Klinsmann, F. (1860); Montesantos, N. (1913); Nolte, E. F.
(1825); Reid, C. (1893); Rohrbach, P. (1873).
Hiltner, L. (1886).
Goebel, K.
Sauvageau, C.
Caspary, R. (1860).
Anon., (1828); Anon., (1895); Areschoug, F. W. C.
(1873!) and (18732); Barneoud, F. M. (1848); Caspary, R.
(1847); Chatin, A. (1855*); Frank, A. B. (1872); Gibelli, G.
and Ferrero, F. (1891); Hofmeister, W. (1858); Jaggi, J.
• (1883); Paillieux, A. and Bois, D. (1888); Queva, C. (1910);
Sanio, C. (1865); Tackholm, G. (1914) and (1915); Theo-
phrastus (Hort) (1916); Tittmann, J. A. (1821).
Anon., (1828); Oliver, F. W. (1888) and (1889).
Cario, R. (1881); Lister, G. (1903); Went, F. A. F. C. (1910).
Willis, J. C. (I9I41), (igis1), (i9i52) and (1917).
Elodea.) Marshall, W. (1852).
INDEX TO BIBLIOGRAPHY
421
Utricularia.
UTRICULARIACEAE.
Vallisneria.
Victoria.
Weddellina.
Wolffia,
Zannichellia.
ZANNICHELLI ACE AE .
Zostera.
Buchenau, F. (1865); Burrell, W. H. and Clarke, W. G.
(1911); Biisgen, M. (1888); Cohn, F. (1875); Crouan (Freres)
(1858); Darwin, C. (1875) and (1888); Focke, W. O. (18932);
Gardner, G. (1846); Gliick, H. (1902), (1906) and (1913);
Goebel, K. (1889*), (18892), (1891), (1891-1893) and (1904);
Goppert, H. R. (1847); Im Thurn, E. F. and Oliver, D.
(1887); Irmisch, T. (1858!) ; Kamienski, F. (1877); Luetzel-
burg, P. von (1910); Meierhofer, H. (1902); Meister, F.
(1900) ; Merz, M. (1897) '> Pringsheim, N. (1869) ; Schenck, H.
(1887); Schultz, F. (1873); Tieghem, P. van (1868) and
(I8691) ; Treviranus, L. C. (1848*); Warming, E. (1874);
Wight, R. (1849).
Benjamin, L. (1848); Hovelacque, M. (1888).
Chatin, A. (18552); Delpino, F. and Ascherson, P. (1871);
Duchartre, P. (1855); Irmisch, T. (1865); Micheli, P. A.
(1729); Rohrbach, P. (1873); Scott, J. (1869); Strasburger,
E. (1884); Weiss, F. E. and Murray, H. (1909); Wylie, R. B.
(I9i72).
Blake, J. H. (1887) ; Caspary, R. (18562) ; Henfrey, A. (1852) ;
Im Thurn, E. F. (1883); Knoch, E. (1899); Seidel, C. F.
(1869); Trecul, A. (1854); Unger, F. (1854!).
Wachter, W. (1897!).
Hegelmaier, F. (1885); Micheli, P. A. (1729); Milde, (1853);
Weddell, H. A. (1849).
Campbell, D. H. (1897) ; Chrysler, M. A. (1907) ; Hochreutiner,
G. (1896); Hofmeister, W. (1858); Irmisch, T. (1858'); Roze,
E. (1887).
Fischer, G. (1907) ; Prillieux, E. (1864) ; Schumann, K. (1892).
Cavolini, F. (I7921) and (17922); Chrysler, M. A. (1907);
Clavaud, A. (1878); Delpino, F. and Ascherson, P. (1871);
Duchartre, P. (1872) ; Engler, A. (1879) ; Grdnland, J. (1851) ;
Hofmeister, W. (1852) ; Jussieu, A. L. de (1789) ; Martens, G.
von (1824); Ostenfeld, C. H. (1908); Sauvageau, C. (iSSg3),
(iSgo1), (18912); Walsingham, Lord, and Payne-Gallwey, R.
(1886); Warming, E. (1871).
[ 422 ]
INDEX
[The names of authors which occur in the bibliography are not included in the following
index, since page references are given in connexion with the titles in the bibliography,
which thus also serves as an index of authors' names]
Acacia phyllode, 340
Achillea ptarmica, 5, 199
Acquired characters, inheritance of,
333. 334
Adaptation, 171, 332-335
Aedemone mirabilis. See Herminiera
elaphroxylon
Aerating system, in tissues of hydro-
phytes, 183-194, 256-259; of root,
185-187; of stem, primary, 183-185;
of stem, secondary, 187-194
Aerenchyma, 187-194; from cambium,
191-192; from phellogen, 187-191,
193-194
Aeschynomene, aerenchyma, 191, 192
Aeschynomene aspera, 191
Aeschynomene hispidula, 191-192
Affinities of hydrophytes, 308-321
Africa, 213, 295, 298, 305
"Age and Area" in plant distribution,
305-307
Air spaces, lysigenous, 184, 185
Air spaces, schizogenous, 184, 185
Aldrovandia, affinities, 310; carnivorous
habit, iio-in, 270; embryo, no;
fruit ripening under water, 239; roots,
absence of, 109, no, 204, 244; seed,
no; sensitive leaves, no, in (Fig.
75) ; shade plant, 289; stem anatomy,
175; turions, no, 219
Aldrovandia vesiculosa, 8, 109-111 (Fig.
75), 289, 310
Algae, 113, 114, 123, 124, 142, 155, 172
Aliens, 303
Alisma, effect of freezing on fruit, 243;
fruit, 242; germination and rupture
of seed coats, 244; heterophylly, 19,
20; land and water plants, 153 (Figs.
101 and 102) ; ranalean features, 320
Alisma graminifolium, 19, 20, 23, 157,
280
Alisma natans, 234
Alisma Plantago, 19, 20, 23, 151, 153
(Figs. 101, 102), 156, 169, 242, 243,
244, 289, 297
Alisma ranunculoides. See Echinodorus
ranunculoides
Alismaceae, 5, 9-23, 24, 33, 151, 156,
195, 224, 248, 297, 313, 314, 319, 337,
346
Alocasia, 303
Aloe, Water. See Stratiotes aloides
Alps, 290
Althenia, bracts, 316; in brackish water,
134; perigonium, 316; reduced stem
anatomy, 63, 173
A Ithenia filiformis, 1 73
Altitude above sea-level, 289-291
Amazons, 31, 99, 113, 229
"Ambatsch," 192
Ambulia, affinities, 313; heterophylly,
151
Ambulia hottonoides, 151
America, 61, 108, 120, 190, 193, 210,
216, 286, 290, 295, 298, 312, 313
American Indians, 17, 118
Ammania, 303
Amphibious plants, effect of water
upon, 20 1, 202
"Amphibolis zosteraefolia," 123
"An Idea of a Phytological History," 230
Anacharis. See Elodea
Andes, 291
Anemophily. See Pollination, anemo-
philous
Anemophytes, 143
Angiosperms, Marine. See Marine An-
giosperms
Anthocyanin, 15, 17, 113, 276-278
Apical openings in leaves, of Callitriche,
268 (Fig. 163); Heteranthera, 268;
Littorella, 269; Pistia, 82 (Fig. 53);
Potamogeton, 167 (Fig. 108), 268, 269-
Potamogetonaceae, 133; Zostera, 269
Aponogeton, affinities, 314; disarticula-
tion of primary root, 244; distribu-
tion, 305; fenestration, 142 (Fig. 91),
143; geotropism, 281; heliotropism,
281; heterophylly, 154; undulated
leaf, 62
Aponogeton angustifolius, 143
Aponogeton Bernerianus, 142
Aponogeton distachyus, 215, 244, 281
Aponogeton fenestralis, 142 (Fig. 91),
143, 281, 314
Aponogeton ulvaceus, 62
Aponogetonaceae, 239, 248, 305, 313,
314. 315
Aquilegia, 314
Araceae, 74, 82, 314, 315
INDEX
423
Araguay, River, 295
Argentine, 55
Aroideae, 316
Arrowgrass. See Aponogeton
Arrowhead. See Sagittaria sagittifolia
Asia, 295, 298
Astrakhan, 303
Auricula, polystely in, 180, 181, 182
Australia, 295, 305
Awlwort. See Subularia aquatica
Azores, 295, 333
Bacteria, 142
Baltic, 123
Baltimore, 253
Bananas, 143
Band leaves, n (Fig. 3), 12, 13 (Fig. 4),
14 (Fig. 5), 19, 20, 22, 23, 140, 141
(Fig. 90), etc.
Bar clay a, 33
Bateson, W., on evolution, 334
Batrachian Ranunculi. See Ranunculus
sect. Batrachium, Ranunculus aqua-
tilis, etc..
Batrachospermum, 155
Bean, 249
Beetles, as pollinators of Lemnaceae,
80; in utricle of Utricularia, 93
Begonia hydrocotylifolia, 256
Belgium, 303
Bellis perennis, 165
Bengal, no
Bermudas, 298
Bidens Beckii, 151, 313
Biological classification of hydrophytes,
4-8, 42
Birds and dispersal, 35, 298-302
Bittersweet. See Solanum dulcamara
"Bitter-sweet," Grew on heterophylly
in, 155
Black Sea, 302
Bladderwort. See Utriculavia
Bladderwort, Common. See Utricularia
vulgaris
Blue Nile, 192
Bodensee, 322
Boottia, 57
Bostrychia Moritziana, 114
Brasenia peltata. See B. Schreberi
Brasenia Schreberi, 38 (Fig. 20), 205,
272
Brazil, 206, 207, 243, 295
Brent Geese, 302
Broads, 288
Brocchinia cordylinoides , 109
Bromeliaceae, 108, 109
Bruch-Eicheln, 17
Brunfels, Otto, 27
Bull Nut. See Trapa natans
Bulliarda (Tillaea). affinities, 310; aqua-
tic with xerophilous ancestry, 310;
cleistogamy, 234
Bulliarda (Tillaea) aquatica, 234, 310
Burton-on-Trent, 211
Butler, Samuel, 347
Butomaceae, 157, 248, 513
Butomus, 314
Buttercup, Water. See Ranunculus
aquatilis, Ranunculus sect. Batra-
chium, etc.
Cabomba, anatomy, 37,38; heterophylly,
29 (Fig. 14), 146; polystely, 37; re-
duced leaves, 338
Cabomba caroliniana, 338
Cabomboideae, 38, 309
Caddice worms, 217
Calcareous substratum, 286, 287
Caldesia, heterophylly, 23; turions, 22,
225 (Figs. 148, 149)
Caldesia parnassifolia, 22, 23, 224, 225
(Figs. 148, 149)
California, 123
Calla palustris, 167 (Fig. 107)
Callitrichaceae, 134, 311, 318
Callitriche, affinities, 311, 312; altitude,
290; annual and perennial forms, 215,
216; as coloniser, 299; chlorophyll,
absence in epidermis, 164; distribu-
tion, 306, 307; flowers, 237 (Fig. 154);
fruit, 242, 243; germination, 280;
heterophylly, 146, 147 (Fig. 94); land
form, 170 (Fig. in), 195; leaf
anatomy, 163, 169, 170 (Fig. in);
local races, 330; mucilage trichomes,
271; pollination, 236, 237; roots, air
spaces in, 187; root anatomy, 208,
209 (Fig. 138); seeds, 297; stomates,
166; vascular strand of axis, 175, 176
(Fig. 114); vegetative reproduction,
216; water pores, 267, 268 (Fig. 163)
Callitriche autumnalis, 6, 134, 169, 237,
268 (Fig. 163), 307
Callitriche stagnalis, 176 (Fig. 114), 208,
209 (Fig. 138), 271
Callitriche verna, 6, 146, 147 (Fig. 94),
163, 1 66, 169, 170 (Fig. in), 187,236,
237 (Fig. 154), 306
Caltha palustris, 198, 199 (Fig. 129)
Cam, River, 150, 211, 263
Cambridge, 150
Cambridge Botanic Garden, 211
"Camichi," 300
"Cammomill," 144
Campanulaceae, 313 .
Canadian Waterweed. See Elodea
canadensis
Canary Islands, 295
Canna, 244
Carbon dioxide, derived from sub-
stratum, 254; excess of, available for
hydrophytes, 254; proportion of, in
free and dissolved air, 253
Cardamine, adventitious budding from
leaves, 216, 217 (Fig. 141); land and
water forms, 201, 202 (Fig. 133)
424
INDEX
Cardaminepratensis, 201, 202 (Fig. 133),
216, 217 (Fig. 141), 309
Carnation, 155
Carolina, 286
Carrot, 249
Caryophyllaceae, 234, 310, 311
Caspian Sea, 302
Castalia, air leaves, 32; effect of frost
on seeds, 243; floating leaves, 30, 146,
159; geophytic habit, 217, 323; length
of peduncle and petiole, 31 (Fig. 15),
40; pigmented variety, 276; rhizome,
24-26 (Fig. n), 39, 217; seedlings, 28
(Fig. 13), 29; seeds, 302; stipules, 25,
26 (Fig. n); submerged leaves, 29,
146, 159; terjrestrial form, 32
Castalia alba, 24, 25, 26 (Fig. 11), 27,
28 (Fig. 13), 29-31 (Fig. 15), 32, 243,
276, 302
Castalia flav a, 37
Castalia Lotus, 34, 36, 37 (Fig. 19), 225
Castalia pygmaea, 33
Castelnavia, 117, 295, 306
Caucasus, 302
Ceratophyllaceae, 84-90, 318, 320
Ceratophyllum demersum, 84-90; affini-
ties, 84, 309, 312; cuticularisation,
86; distribution, 295, 297, 298; effect
of strong illumination, 279; epiphytic
fauna, 88; flowers, 84, 85 (Fig. 54);
freezing, effect of, 88, 89; hairs con-
taining mucilage, 86, 272; high
temperatures necessary for fruiting,
88, 275; in biological classification, 8;
in deep water, 86, 288; leaf, anatomy
of, 1 68, dimensions of, 140, juvenile, 86
(Fig. 55); luxuriance, 87; monoecism,
84, 85; movements, 90, 281 ; mucilage
hairs, 86, 272; perenniation, 215;
pollination, hydrophilous, 84, 85, 134,
237, 238; rhizoid branches, 88, 89
(Figs. 57 and 58), 98, 336, 337; roots,
absence of, 85, 204, 244; seedling, 85,
86 (Fig. 55); stem anatomy, 86, 87
(Fig. 56); vegetative reproduction,
87, 216, 219; water absorption, 269,
270; water content, 86
Ceylon, 112, 216
Chalky incrustation on leaves of
aquatics, 51
Chantransia, 155
Chara, 288
Chili, 181
Chimborazo, 290
China, 17
Chlorophyll, in epidermis of aquatics,
164, 168 (Fig. 109), 169, 254; in epi-
dermis of terrestrial plants, 164, 165
Chydorus sphaericus, as food of Utri-
eularia, 94
Cirsium anglicum, 198, 199 (Fig. 130)
Classification, biological, of hydrophytes,
4-8, 42
Cleistogamy, 233, 234; in Alisma, 234;
Bulliarda (Tillaea), 234; Echinodorus,
234; Euryale, 34, 234; Heteranthera,
234 (Fig. 153); Hydrothrix, 234; Ille-
cebrum, 234; Limosella, 233, 235;
Nesaea, 234; Peplis, 234; Podostemon,
121 (Fig. 82), 234; Ranunculus, 233,
234; Rotala, 234; Tillaea, 234; Tra-
pella, 234
Climate and life-cycles, 275
Cnicus arvensis, 200
Cnicus pratensis, 198, 199, 200
Codium tomentosum, 123
"Collet." development of root-hairs
from, 245
Colocasia, 303
Colonisation of waters, 289, 298, 299
Commissioners' Pits, Upware, 217
Competition, aquatic life as a refuge
from, 324, 325
Compositae, 151, 313, 320, 321
Conifers, "Youth forms" of, 155
Copepods, as food of Uiricularia, 94
Cotton, aliens accompanying, 303
Cotula myriophylloides, 313
Crassulaceae, 234, 310
Cruciferae, 216, 309
Crustacea, as food of Utriculana, 93,
94
Cuscuta alba, 5, 199 (Fig. 131)
Cuticle, slight development of, in
hydrophytes, 163, 254, 260
Cuyuni River, 119
Cyclamen, 240
Cymodocea, absence of apical openings
in leaves, 269; anatomy, 125 (Fig. 84),
131, 331; chlorophyll in epidermis,
164 ; flowers, 126 ; grappling apparatus
of fruit, 127, 245; habit, 124 (Fig. 83),
125; leaf form, 124; life-history, 124
(Fig. 83)-127; pollination, hydro-
philous, 126, 237; regarded as Alga,
123; spiral roots, 205; squamulae
intravaginales, 126; vivipary, 127, 246
Cymodocea aequorea, 124 (Fig. 83), 125
(Fig. 84), 126, 127, 246
Cymodocea antarciica, 123, 127, 205, 245
Cymodocea isoetifolia, 124
Cyperaceae, 154, 317, 326
Cypris, as food of Utricularia, 94
Damasonium stellatum, 23
^Danube, 212
Daphnidae, as food of Utricularia, 94
Darwin, Erasmus, on evolution, 334
Delayed germination in aquatics, 36,
71, 72, 243-244
Delesseria Leprieurii, 114
"Dents nageoires," 133, 314, 315
Depth to which plants can grow, 86,
123, 275
Desmanthus natans. See Neptunia
oleracea
INDEX
425
Diaphragms, 18, 19 (Fig. 8), 183, 184
(Figs. 118, 119), 257
Dicotyledonous families, proportion of
among aquatics, 322
Dicraea elongata, 115 (Fig. 77)
Dicraea stylosa, 114, 115 (Fig. 78), 116
(Fig. 79), 118
Dictyota dichotoma, 123
"Differentiation Theory" of plant dis-
tribution, 304-307
Dionaea, m
Diplanthera, 123
Distribution, geographical, 73, 112,
295-307
Dock, 271
Dodder. See Cuscuta alba
Dodoens' Hiswire des Plantes, 144
Dollo's "Law of Irreversibility," 336,
347
Droseraceae, 109, in, 310
Duckweed. See Lemna, Lemnaceae,
Spirodela, Wolffia
Duckweed, Rootless. See Wolffia
East Anglia, flood of 1912 in, 296
Echinodorus ranunculoides, cleistogamy,
234; heterophylly, 23; inflorescence
and vegetative shoots, 224 (Fig. 147);
land and water forms, 21 (Fig. 9)
Ecology, 285-292
Egypt, 332
Egyptian cotton, aliens accompanying,
303
Eichhornia, affinities, 317; air tissue in
petioles, 154; heterophylly, 154, 160,
161; phyllodic interpretation of leaf,
341 (Fig. 169), 342 (Fig. 170), 343,
344; vegetative multiplication, 213
Eichhornia azurea, 160, 161
Eichhornia crassipes, 154
Eichhornia speciosa, 213,' 341 (Fig. 169),
342 (Fig. 170), 343, 344
Elatinaceae, 310, 311
Elatine, affinities, 311; annual species,
215; conveyance by birds, 301; root-
hairs from "collet/' 245 (Fig. 158)
Elatine hexandra, 245 (Fig. 158), 311
Elatine hydropiper, 301, 311
Eleocharis, 286
Elisma, heterophylly, 23; relation of
inflorescence and vegetative shoot, 20
Elisma natans, 20, 23
Ellis, Lake, 286
Elodea, aerating system, 256; circula-
tion of protoplasm, 212 ; experimental
cultures, 265 ; history in Britain, 55,
210-213; leaf anatomy, 165 (Fig,
106), 169; leaf form, 141; pollination
mechanism, 55, 56 (Fig. 35), 57, 134,
236; root-hairs, 208; vegetative re-
production, 55, 210—213; wintering
shoots, 55 (Fig. 34), 219
Elodea callitrichoides, 55, 56, 236
Elodea canadensis, 6, 7, 55 (Fig. 34), 57,
165 (Fig. 106), 169, 173, 210-213, 219,
253. 254, 265, 266
Elodea densa, 57, 236
Elodea ioensis, 55, 56 (Fig. 35)
Embryo, macropodous, 246 (Fig. 159),
248 (Fig. 161), 249, 319 (Fig. 166),
326; protection of, 242, 243; vivi-
parous, 127
Engadine, 290
Enhalus, 57, 123, 124, 131, 236
Enter omorpha, 123
Entomophily. See Pollination, ento-
mophilous
Epidermis of aquatics, chlorophyll in,
164, 168, 169, 254; form of cells of,
163, 164
Epilobium hirsutum, 188
Epithem, 267
Eranthis hiemalis, 319
Eriocaulon, 286
' ' Eu-anthostrobilus, "315
Eu-callitriche, 236, 237, 306, 307, 330
Eucalyptus Preissiana, 256
Eupatorium cannabinum, 188
Euphorbiaceae, 311
Europe, 290, 295
Euryale, affinities, 38; cleistogamy, 34,
234
Euryale fer ox, 34, 234
Farinosae, 316, 317, 341
Farmeria metzgerioides, 114, 248
Fenestration of leaves, 142 (Fig. 91)
Fijis, 298, 303
Flagellates, 142
"Floating-leaf association," 288
Floating leaves, 30-32, 44-46, et passim
Floating Sensitive Plant. See Neptunia
oleracea
Floating wood of Herminiera, 192
Florida, 213
"Flossenzahne," 133, 314
Flowers of water plants, 227-238, etc
Fluviales. See Helobieae
Fly pollinating Sagittaria, 9
"Flying germinators," Water-fowl as,
301
Fontinalis, 225
Food plants, Alismaceae, 17; Alocasia,
303; Colocasia, 303; Nymphaeaceae,
24; Trapa, 302
Forest of Dean, 276
Freezing, effect of, 220, 243, 278
Frogbit. See Hydrocharis Morsus-ranae
Fruits of water plants, 239-249, etc.
Fruits, ripening under water, 239, 240
Fungi, 172
Gaseous exchange, 253-259
Geneva, Lake of, 278
Gentianaceae, 39, 205, 312
Geographical distribution, 295—307, etc.
27—5
426
INDEX
Geophytes, aquatic, 217, 323
Geotropism, 281, 282
Germany, 17, 53, 290, 299
Germination, delayed, 36, 71, 72, 243,
244; in situ, So, 127, 246, 248; of
various genera, see heading, Seedlings
Giant Waterlily. See Victoria regia
Gill-tuftsof00«<we,ii8,ii9(Fig.8i), 255
Glechoma hederacea, 5
Glyceria, aquatic grass, 317, 318; dis-
tributed by birds, 301
Glyceria aquatica, 317, 318
Glyceria fluitans, 301, 317
"Gramen bulbosum aquaticum," n
Gramineae, 317, 318, 326
Grass-wrack. See Zostera
Grasses in Lake Ellis, 286
Grew, Nehemiah, on flower colour of
aquatics, 230; on heterophylly, 154,
155
Griffithiella Hookeriana, 114
Ground Ivy. See Glechoma hederacea
Guiana, British, 109, 118, 119, 300
Guiana, French, 113
Gunner a, gigantic herb, 181; polystely,
180-182, 346
Gunner a scabra, 181
Gunnereae, 312
Hairs, absence in submerged leaves, 165,
1 66 ; absence in water forms of amphi-
bious plants, 151, 152 (Fig. 99); change
in character of hairs of Rubus when
submerged, 200 ; growth of hairs due
to wounding of Waterlily petiole, 258 ;
loss of hairs of Mentha when sub-
merged, 201 ; mucilage-containing
hairs of Ceratophyllum, 86, 87, 272;
mucilage-secreting hairs of Nymphae-
aceae, 38 (Fig. 20), 272 ; Myriophyllum
trichomes, 168, 169, 170 (Fig. no);
Polygonum amphibium, hairs on air
leaves only, 151, 152 (Fig. 99); Utricu-
laria, hairs of bladders, 92 (Fig. 60), 93
(Fig. 61), 94, 95 (Fig. 62); Utricularia,
protective hairs of turions, 101, 102,
220 (Fig. 143 A ) ; sensitive hairs of Al-
drovandia, in; stipular hairs of Nym-
phaea lutea, 26; see also under Root-
hairs and Squamulae intravaginales
Halodule, anatomy of vegetative organs,
132 (Fig. 88), 331; marine Angio-
sperm, 123
Halodule uninervis, 132 (Fig. 88)
Halophila, anatomy, 131, 169; in bio-
logical classification, 6; leaf form,
124; marine Angiosperm, 57, 123;
pollen-grains in strings, 130; pollina-
tion, hydrophilous, 130, 236 ; structure
and life-history, 129, 130 (Fig. 87);
styles filiform, 130
Halophila ovalis, 129, 130 (Fig. 87)
Halophila ovata, 129
Halophila stipulacea, 129, 130
Haloragaceae, 180, 205, 311, 312
Haloragideae, 312
Haptera of Podostemaceae, 114; of
Tristichaceae, 113
Hawthorn, pigmented variety, 276
Heliotropism, 281
Helobieae, 52, 123, 124, 245, 248, 313,
314, 318, 319, 320, 321, 325, 326
Herbarium material, use in anatomical
work, 331
Herbarum vivae eicones of Brunfels, 27
and Frontispiece
Herminiera elaphroxylon, 192
Heteranthera, cleistogamy, 234 (Fig.
153); phyllodic leaf anatomy, 342
• (Fig. 170), 343, 344 ; root differentia-
tion, 207; support of inflorescence,
228 ; water pores and apical opening,
268
Heteranthera dubia, 234 (Fig. 153)
Heteranthera renifotmis, 342 (Fig. 170),
343, 344
Heteranthera zosteraefolia, 207, 228, 268,
342 (Fig. 170), 343, 344
Heterophylly, 143-162, et passim
Himanthalia lorea, 114
Hippuridaceae, 312
Hippuris vulgaris, affinities, 311, 312;
altitude, 290; anemophily, 230, 232;
diaphragms of stem, 184 (Fig. 119),
257; flowers, 230, 231 (Fig. 151); fruit
dispersal. 297 ; heterophylly, 141, 146,
147 (Fig. 95), 148 (Fig. 96), 231 (Fig.
151); in biological classification, 6;
nutlets, 242; perenniation, 215; re-
duction of primary root, 244 ; rhizome,
173 (Fig. 112); root-hairs from
"collet," 245; stem, 172, 173; stem
anatomy, 175-178 (Fig. 115), 181,
184 (Fig. 119 ), 185 (Fig. 120); sto-
mates, 166; tenderness of leaves, 163
Holland, 303
Horned Pondweed. See Zannichellia
Hornwort. See Ceratophyllum demersum
Horse Chestnut, submerged germina-
tion, 199
Hottonia palustris, affinities, 312, 318;
in biological classification, 6, 7 ; land
and water forms, 197 (Fig. 127); leaf
anatomy, 169; non-cleistogamic, 233;
polystely, 181 ; ripening of fruit in air,
239; sinking of seeds, 297; support of
inflorescence, 228; vegetative repro-
duction, 216
Hyacinth, Water. See Eichhornia
speciosa
Hydrilla, in Britain, 54, 55; leaves. 57;
spathe. 3 15; tendril roots,2O5 (Fig. 136)
Hydrillaverticillata, 54, 55, 205 (Fig. 136)
Hyclrilleae, 175
Hydrobryum, 114, 115 (Fig. 76)
Hydrocaryaceae, 311
INDEX
427
Hydrocharis, anthocyanin, 276; buds,
summer, 43 (Fig. 24); buds, winter,
47 (Fig. 29), 48, 49 (Fig. 30); de-
hiscence, 47, 241 ; dioecism or monoe-
cism, 46; flowers, 46; fruits, 46, 47,
241; freezing, 220; germination of
turions, 48, 49 (Fig. 30), 280; in
biological classification, 7; inverted
bundles of leaf, 46 (Fig. 28) ; land form,
42, 49; leaf anatomy, 44 (Fig. 25), 45
(Figs. 26, 27), 46 (Fig. 28); light,
effect of, 280; petiole length, experi-
ments on, 283, 284; pollination, 236;
root-hairs, 42, 43; roots, 42, 43, 244;
stipules, 43 (Fig. 24), 44; stomates, 45
(Fig. 26) ; submerged form, 45 ; turions,
47 (Fig. 29), 48, 49 (Fig. 30); winter-
buds, 47 (Fig. 29), 48, 49 (Fig. 30)
Hydrocharis asiatica, 42
Hydrocharis Morsus-ranae, 7, 32, 42,
43 (Fig. 24), 44 (Fig. 25), 45 (Figs.
26, 27), 46 (Fig. 28), 47 (Fig. 29),
48, 49 (Fig. 30), 53, 54, 57, 166, 195,
215, 219, 220, 236, 241, 280, 283
Hydrocharis parnassifolia, 42
Hydrocharitaceae, fresh-water, 42-57,
84, 151, 157, 248; marine, 123, 129-
131, 133, 134; other references, 169,
205, 235, 236, 239, 314, 340
Hydrocleis, apical cavity of leaf, 269,
270 (Fig. 164); heterophylly, 157
Hydrocleis nymphoides, 157, 269, 270
(Fig. 164)
Hydrocotylevulgaris, 200, 201 (Fig. 132)
Hydromy 'stria, 57
Hydrophilous pollination. See Pollina-
tion, hydrophilous
Hydrothrix, cleistogamy, 234; phyllode
leaf, 344
Hydrothrix Gardneri, 234, 344
Hydrotriche, affinities, 313, 318; hetero-
phylly, 151
Hydrotriche hottoniae folia, 151
Illecebraceae, 311
Illecebrum, affinities, 311; cleistogamy,
234
Illecebrum verticillatum, 234
Illumination, 157, 278-280
"Imbibition theory," 174
Indehiscent fruits of aquatics, 241-244
India, 112, 191, 291, 305
Infusoria, as food of Utricularia, 94
Inn, River, 228
Ireland, 210
Iridaceae, 326
Iris, phyllodic anatomy, 340
Iris Pseudacorus, 199
Isoetes, altitude, 291 ; in peaty water,
287; in mountain lochs and heath
pools, 290; ousted by Potamogeton,
333; replacement of sporangia by
plantlets, 225
Isoetes amazonica, 291
Isoetes echinospora, 225
Isoetes lacustris, 225
Italy, 303
Ivy-leaved Duckweed. See Lemna
trisulca
Japan, 17
Juncaginaceae, 248, 313, 314
Juncus, 299, 309
Juncus conglomerate, 299
Jura lakes, 279, 287, 290, 323
Jussiaea, aerenchyma from phellogen,
189, 190 (Fig. 122); affinities, 311,
318; breathing roots, 189; replace-
ment of cork by aerenchyma, 188,
189; roots not floats, 192, 193; sub-
mersed leaves whorled, 230
Jussiaea amazonica, 230
Jussiaea grandi flora, 189
Jussiaea peruviana, 189, 190 (Fig.
122)
Jussiaea repens, 189, 193
Kaieteur, 109
Kerguelen's Land, 233
" Kiemenbiischel " (gill-tufts) of Oenone,
118, 119 (Fig. 81), 255
Kingston, 273
Kurdestan, 303
Laboul, 291
Lace-plant of Madagascar. See Apono-
geton fenestralis
Lads alata, 120
"Lady-Smocks," Grew on heterophylly
in> 155
Lady's Smock. See Cardamine pratensis
Lake dwellings, 302
Lake Ellis, North Carolina, 286
Lake George, Florida, 213
Lake St Clair, Michigan, 288
Lakenheath Lode, 216
Land forms, of water plants, 195-198;
of Alismaceae, 20, 21 (Fig. 9), 153
(Fig. 101), 195; Cattitriche, 195;
Cardamine, 202 (Fig. 133); Hottonia,
197 (Fig. 127); Hydrocharis, 42, 49,
195; Lemnaceae, 77, 78; Limnan-
themum, 19*5 ; Limosella, 198 ; Littorella
198 (Fig. 128); Myriophyllum, 195,
223 (Fig. 146); Nymphaeaceae, 32,
195; Polygonum, 152 (Figs. 99 and
i oo), 197, 198; Potamogeton, 195, 196
(Fig. 125); Ranunculus, 195, 196 (Fig.
126), 203 (Fig. 134)
Land plants, effect of water upon, 200,
201 (Fig. 132)
"Law of Age and Area," 305-307
"Law of Irreversibility, " 336, 347
"Law of Loss," 182, 3~36-347
Lawia, germination, 117; mucilaginous
seeds, 300; shoot thallus, 117; special-
428
INDEX
ised Podostemad, 306 ; starch storage,
120; vegetative reproduction, 216
Lawia foliosa, 117
Lawia zeylanica, 117, 120, 216, 300
Leaves, band or ribbon, n (Fig. 3), 12,
13 (Fig. 4). J4 (Fig. 5), *9, 20, 22, 23,
140, 141, 343, 344, etc.
Leaves, floating, 30-32, 44-46, etpassim
Leaves, submerged, 139-143, 163-171 ;
"adaptation" in, 171; aerating sys-
tem, 167; diaphragms, 167; epidermal
cells, form of, 163, 164; epidermis,
chlorophyll in, 164; fenestration, 142
(Fig. 91); mesophyll for storage, 168
(Fig. 109); non-radial anatomy, 165
(Fig. 1 06), 169; radial anatomy, 168
(Fig. 109); ratio of surface to volume,
1 40; reduction of cuticle, 1 63 : stomates
and hairs, 165-167 (Fig. 107); un-
differentiated mesophyll, 167, 168
(Fig. 109); water pores, 167
Leguminosae, 188, 189, 191, 192
Lemnagibba, 7, 76 (Fig. 48), 77, 78, 81,
275. 297
Lemna minor, 7, 76, 77, 78, 80, 291, 295,
297, 301, 307
Lemna trisulca, 8, 78, 79 (Figs. 49, 50,
51), 80, 81 (Fig. 52), 208, 215, 295
Lemnaceae,73— 82 ; aerenchyma, 76 (Fig.
48); affinities, 74, 82, 314, 316; alti-
tude, 290, 291; anatomy, 78, 79 (Fig.
51); anthocyanin, 276, 277; cotyledon
as float, 81 (Fig. 52), 248; dispersed
by water birds, 300, 301 ; distribution,
73, 112, 295, 307; entirely aquatic,
318; entomophily, 80, 230; flowers,
74 (Fig. 47), 79 (Fig. 50), 80; land
forms, 77, 78; life in impure water,
81, 287; number of genera, 84; pro-
tandry, 80; range, 73, 112, 295, 307;
rarity of seeds, 75; reduced inflores-
cences, 73, 74 (Fig. 47); root-caps, 74,
76 (Fig. 48); roots for equilibrium,
74, 207; seedlings, 80, 81 (Fig. 52);
seeds, 80, 297; turions, 74-77; vegeta-
tive morphology, 73-74; vigour of
vegetative growth, 77, 81, 83
Length, of axes, of Oenanthe, 150, of
Polygonum, 215, of Ranunculus, 214,
of Utricularia, 215; of petiole, ped-
uncle, etc., in Nymphaeaceae, 28
(Fig. 13), 31 (Fig. 15), 283; of petiole
in Hydrocharis, Marsilea, Ranunculus,
283, 284; of submerged leaves of
Sagittaria, 12, of Vallisneria, 140
Lentibulariaceae, 91, 104, 313
Lenticels, effect of submergence on, 187
Lesser Water Plantain .See Echinodorus
ranunculoides
Lignification, poor, in aquatics, 260
Liliaceae, 326
Limnanthemum, 39—41; affinities, 313;
anthocyanin, 276; dehiscence, 240
(Fig. 156), 241, 242 (Fig. 157); dis-
tribution, 304, 305; effect of drying
on seeds, 243 ; fruit ripening in water,
239; geophytic habit, 41 (Figs. 22 and
23), 217, 323; germination, 248; land
form, 195; mucilage, 271; rhizome,
39, 41 (Figs. 22, 23), 217, 323; seeds,
240 (Fig. 156), 241, 297: support of
inflorescence, 228
Limnanthemum Humboldtianum, 239
Limnanthemum indicum, 40, 304
Limnanthemum nymphoides,3Q— 41 (Figs.
22, 23), 195, 228, 240 (Fig. 156),' 241,
242 (Fig. 157), 243, 248, 271
Limnobium, geotropic curvature of fruit-
stalk, 239, 282; heterophylly, 157
Limnobium Boscii, 157, 282
Limnocharis Humboldtii, 166
Limnophila, heterophylly, 151, 161;
sleep movements, 281; systematic
position, 313
Limnophila heterophytta, 161, 281
Limnophila hottonoides, 151
Limnosipanea, heterophylly, 151; af-
finities, 313
Limnosipanea Spruceana, 151
Limosella, affinities, 313, 318; cleisto-
gamy, 233, 235; distributed by birds,
301; flowers, 313; land and water
forms, 198
Limosella aquatica, 198, 233, 301, 313
Linaria Cymbalaria, 240
"Little Bell," Grew on heterophylly in,
155
Littorella, aerating system of leaf, 167;
affinities, 313; anemophily, 232;
apical openings of leaves, 269; flowers
and fruit, 313; fruit, 241, 242;
funicular plug in fruit wall, 242;
geophytic habit, 323 ; germination in
situ, 246; in peaty water, 287, 290;
land and water forms, 198 (Fig. 128);
ousted by Potamogeton, 333; radial
leaf, 1 68; runners, 217, 218 (Fig. 142)
Littorella lacustris, 7, 141, 198 (Fig. 128),
217, 218 (Fig. 142), 232, 241, 242, 246
Liverworts, 327
Lobelia Dortmanna, aerating system of
leaves, 167; affinities, 313; fruit
ripening in air, 239; in biological
classification, 7; in peaty water, 287;
in sandy pools and mountain lochs,
290; leaves, 141; root, 245; sinking of
seeds, 297; stomates, 166
Lobelia, Water. See Lobelia Dortmanna
Loess alluvium, 287
Loosestrife, Water. See Lythrum Sali-
caria
Lotus, 1 88
Lotus, Sacred. See Nelumbo Nelumbo
Low countries, 9
Ludwigia, 311, 318
Lupinus, 200
INDEX
429
Luxuriance of vegetative growth, 210-
215
Lycopus europaeus, 188
Lysimachia, 188
Lyte's Herbal, 144
Lythraceae, 175, 188, 193, 234, 303, 311
Ly thrum Salicaria, 188, 311
McLean, R. C., on treatment of her-
barium material, 331
Macropodous embryo, 246 (Fig. 159),
248 (Fig. 161), 249, 319 (Fig. 166),
326
Madagascar, 305
Madeira, 295
"Major plant individual," 211-213
Manchester, 275, 303
Marathrum utile, 113
Marburg, 189
Mare's-tail. See Hippuris vulgaris
Marine Angiosperms, 123-135; affini-
ties, 123, 320; association with Algae,
123; flowers, 126, 127, 129, 130 (Fig.
87); fruits, 126, 127, 248 (Fig. 161);
leaf anatomy, 125 (Fig. 84), 128 (Figs.
85, 86), 130, 131, 132 (Figs. 88, 89);
leaves, 124 (Fig. 83), 130 (Fig. 87),
133; origin of the group, 133-135;
pollen-grains, Conferva-like, 124, 125,
126; pollen-grains in strings, 130;
pollination, hydrophilous, 124-127,
129; seed-coats, 130; vegetative
habit, 124 (Fig. 83), 130 (Fig. 87);
vivipary, 127
Marsilea, 284
Mauritius, 129, 295
Mayaca fluviatilis, 243
Mayacaceae, 317
Mediterranean, 123, 125
Melilotus Taurica, sleep habits of, 161
Memory, unconscious, 333
Mentha aquatica, 201
Menyanthes, affinities, 313; submerged
form; 199; tendril roots, 205
Menyanthes irifoliata, 199, 313
Mercurialis, 311
Michigan, 288
Milfoil, Water. See Myriophyllum
Mimosa lacustris. See Neptunia oleracea
Mirabilis, 121
Monocotyledonous families, proportion
of, among aquatics, 322
Monocotyledons, aquatic origin of, 322-
326
Monstera, 142, 314
Montia, affinities, 310; biennial and
perennial forms, 216; submerged
xerophyte, 310
Montia fontana, 216, 310
Mosses, 113
M our era, anthocyanin, 113; flowering,
120; haptera, 114
M our era fluviatilis, 113, 114, 120
Mucilage, 38 (Fig. 20), 47, 271-272, 300
Mucilage-secreting trichomes, 13, 15,
38 (Fig. 20)
Myriophyllum, affinities, 311, 312; air
spaces in roots, 187; in stem, 179
(Fig. 116), 256; altitude, 290; ane-
mophily, 230, 232; effect of freezing
on fruits, 243; on turions, 220; fruits,
242; germination of turions, 222 (Fig.
145) ; growth in still or moving water,
283; habit, 172, 221 (Fig. 144); in
biological classification, 6; land form,
195, 223 (Fig. 146); on sandy sub-
stratum, 286; relation of turions to
inflorescence, 224; sleep movements,
281; stem anatomy, 178, 179 (Figs.
116, 117), 181; submerged leaves,
form, 255, structure, 168 (Fig. 109);
trichomes, 168-170 (Fig. no) ; turions,
219, 220, 221 (Fig. 144), 222 (Fig.
145), 223 (Fig. 146), 224; wave
motion, 289
Myriophyllum alternifolium, 168
Myriophyllum proserpinacoides, 281
Myriophyllum spicatum, 134, 140, 168
(Fig. 109), 179 (Figs. 116, 117), 195,
197, 232, 242, 243
Myriophyllum verticillatum, 6, 168-170
(Fig. no), 219, 220, 221 (Fig. 144),
222 (Fig. 145), 223 (Fig. 146)
Naiadaceae, 248, 313, 315
Naias, alien weed with rice and cotton,
303; annual, 215; distribution, 304,
'305; effect of depth, 279; flower, 315,
316, 320, 346; in biological classifica-
tion, 6; in deep water, 279, 288;
pollination, hydrophilous, 237; re-
duction of primary root, 244; root
anatomy, 208, 209 (Fig. 140) ; specific
differences, 331, 332; stem anatomy,
175 ; submerged vegetative organs, 134
Naias flexilis, 215
Naias graminea, 237, 303
Naias graminea, var. Delilei, 332
Naias major, 209 (Fig. 140)
Naias marina, 304, 305
Naias minor, 209 (Fig. 140), 215
Nasturtium, affinities, 309; air and
water shoots, 201; budding from
leaves, 216
Nasturtium amphibium, 201, 309
Nasturtium lacustre, 216
Nelumbium. See Nelumbo
Nelumbo, absence of mucilage, 257, 272;
affinities and structure, 38, 39;
geologic distribution, 38, 39 (Fig. 21);
movements of gases, 257, 258 ; possible
case of reversion from aquatic to
terrestrial life, 39; stability of seed-
ling, 245
Nelumbo Nelumbo, 38, 39 (Fig. 21)
Nelumbonoideae, 38
430
INDEX
Nepenthes, 93, 310
Neptunia oleracea, 189-191 (Fig. 123)
Nesaea, aerenchyma, 193 (Fig. 124),
194; cleistogamy, 234; distribution,
295
Nesaea verticillata, 193 (Fig. 124), 194
Nile, 113
Nile, Blue, 192
Nitella, 288
Nitrogen, proportion in free and dis-
solved air, 253
Nuphar luteum. See Nymphaea lute a
Nuphar minima, 28
Nuphar pumilum, 32
Nymphaea, dehiscence, 35, 36; effect of
frost on seeds, 243; etiolation with
depth, 279; floating leaves, 30, 31,
146, 159; fruit, 34 (Fig. 17), 35, 36,
240; general habit, Frontispiece;
geophytism, 217, 323; length of
petiole and peduncle, 31 (Fig. 15), 40;
operculum of seed, 35 (Fig. 18), 36;
pigmented variety, 276; reduction of
primary root, 244, 281; rhizome, 24,
25 (Fig. 10), 26, 27 (Fig. 12), 36, 39,
217; roots, 25 (Fig. 10), 204, 281;
seedlings, 34, 35 (Fig. 18), 36, 280;
submerged leaves, 27 (Fig. 12), 28,
29, 146, 159, 279; trichome dia-
phragms, 272
Nymphaea alba. See Castalia alba
Nymphaea lutea, 6, 24, 25 (Fig. 10), 26.
27 (Fig. 12), 28-31, 34 (Fig. 17), 35
(Fig. 18), 36, 159, 243, 244, 272, 279,
280, 281, 288, see also Frontispiece
Nymphaea lutea, var. rubropetala, 276
Nymphaea pumila, 32
Nymphaeaceae, 24-39; affinities, 309,
314, 318-320; air system in petioles
and peduncles, 37, 257; anatomy,
36-38, 182; ancient aquatic habit,
321; and water fowl, 299, 300;
anthocyanin, 276, 277; cleistogamy,
234 '> geophytic habit, 217; hetero-
phylly, 27 (Fig. 12), 28, 29 (Fig. 14),
146; in Lake Ellis, 286; land forms,
32, 195; leaf and flower, 40; leaf,
floating, 30, 31; leaf, submerged, 27
(Fig. 12), 28 (Fig. 13), 29 (Fig. 14),
255; mucilage, 35, 36, 38 (Fig. 20),
272; wound effects, 258
Nymphaeoideae, 32, 38
Oenanthe, aerenchyma, 188; hetero-
phylly, 150; perenniation, 215; root
system, 204, 205, 229; stomates, 166;
submergence, 312
Oenanthe Phellandrium, 150, 204, 205,
229
Oenanthe Phellandrium, var. fluviatilis,
150, 166, 215, 312
Oenone, gill-tufts, or Kiemenbiischel,
119 (Fig. 81), 255
Oenone multibranchiata, 119 (Fig. 81)
Onagraceae, 188, 189, 311, 318
"Open reed-swamp," 288
Organ Mountains, 108
Origin of Species, The, 260
Osmotic pressure of sap in leaves and
roots, 266
Ottelia, geotropism of peduncle, 239;
heterophylly, 57
Ouvirandra. See Appnogeton fenestralis
Oxygen, proportion in free and dissolved
air, 253; scarcity in water life, 255
Pacu myletes, 118
Padina pavonia, 123
Palms, 143
"Fancy," 155
Pandanaceae, 317
Parallel veining of Monocotyledonous
leaves, 338
Parra jacana, 300
Parsnip, Water. See Sium latifolium
Pea, 249
Peat-bog lakes, 275
Peaty substratum, 287
Pedaliaceae, 151, 234
Peplis, aerating system, 185, 259;
affinities, 311; anthocyanin, 276, 277;
cleistogamy, 234; detached shoots,
216, 276, 277; flowers and fruit, 230,
232 (Fig. 152); pollination, 230; vas-
cular anatomy, 175; vegetative re-
production, 216; winter state, 216
Peplis Portula, 175, 185, 216, 230, 232
(Fig. 152), 259, 276, 277, 311
Perenniation among hydrophytes, 215
Perthshire, 288
Phaseolus, 207
Phelloderm, air-containing, 187-191
Phellogen producing aerenchyma, 187-
191
Philodendron, 206
Phragmiies, in Jura Lakes and White
Moss Loch, 287, 288 (Fig. 165);
"major plant unit," 212; root differ-
entiation, 207
Phragmites communis, 207, 212
"Phragmitetum," 288
" Phucagrostis major," 125
" Phucagrostis minor," 125
Phyllanthus fluitans, 311
Phyllode theory of Monocotyledonous
leaf, 52, 161, 162, 337-345
Phyllospadix, 123, 124
Pico, 333
Piliferous layer, cuticularised, 208;
death of, before death of root-hairs,
264
Pilularia, 225
Pinguicula, insectivorous habit and
relation to Utricularia, in; polystely,
181
Pinguicula vulgaris, 181
INDEX
Pistia Stratiotes, air tissue of leaves, 82,
154, 256; comparison with Lemna-
ceae, 74, 82, 316; hairs, 82, 83; vigour
of vegetative growth, 83, 213, 214;
water pores, 82 (Fig. 53), 83, 167, 267
"Pith" helmets, 191
Plantago, 233, 313
" Plantago aquatica," 20
Plantago major, 241
Plantain, Lesser Water. See Echino-
dorus ranunculoides
Plantain, Water. See Alisma Plantago
Podostemaceae (including Tristicha-
ceae), 112-122, 327-333; affinities,
310, 319; anatomy, 117, 118 (Fig. 80);
ancient aquatics, 321; and natural
selection, 327-333; and wading birds,
300; anemophily, 120, 121 ; anthocya-
nin, 112, 113, 276, 277; cleistogamy,
121 (Fig. 82) ; dependence on aeration,
257; distribution, 295, 306; dorsi-
ventrality, 121, 122, 327-329; en-
tirely aquatic, 318; flowers, 120, 121
(Fig. 82); germination in situ, 248;
"gill-tufts," 118, 119 (Fig. 81), 255;
habit, 114, 115 (Figs. 76, 77), 116
(Fig. 79), 117; haptera, 113, 114. 121;
in biological classification, 7; inhabit
rapids, 112, 113, 119, 257; "Kiemen-
biischel," 118, 119 (Fig. 81), 255;
lack of adaptation, 328-333; lack of
intercellular spaces, 118 (Fig. 80),
257; morphology, 73, 121, 122;
mucilaginous seeds, 300; polymor-
phism of thallus, 114-117; rarity
outside tropics, 112, 113; reduction
of primary root, 244; root thallus,
114, 115 (Figs. 76, 77, 78), 116 (Fig.
79), 117, 208; secondary shoots, 114;
seedling, 114, 115 (Fig. 78), 117;
seeds, 121, 300; shoot thallus, 117;
silica, 117; simulation of lower plants,
114-117; vegetative reproduction,
216; water reservoir in nucellus, 121
Podostemon, Alga-like form, 114 ; cleisto-
gamy, 121 (Fig. 82), 234; distribution,
306
Podostemon Barberi, 121 (Fig. 82), 234
Podostemon subulatus. 114
Pollination, anemophilous, 57, 120, 121,
230, 232, 233
Pollination, aquatic. See Pollination,
hydrophilous
Pollination, cleistogamic. See Cleisto-
gamy
Pollination, entomophilous, 9, 57, 80, 230
Pollination, hydrophilous, i, 6, 8, 55-
57, 70, 71, 84, 85, 124, 127, 129, 130,
134, 235-238, 345, 346
Polygonaceae, 311
Polygonum, affinities, 311, 318; colonis-
ing new waters, 280; land and water
forms, 150, 151, 152 (Figs. 99, 100),
I97, 198; heterophylly, 150, 151, 152
(Figs. 99, 100); length of shoot
system, 215; mucilage, 271; vegeta-
tive reproduction, 225
Polygonum amphibium, 150-152 (Figs.
99, 100), 197, 198, 215, 271, 289, 311,
3i8
Polygonum viviparum, 225
Polypetalae, 309-312, 319
Polystely, 37, 180-182, 346
Pond weed. See Polamogeton
Pond weed, Horned. See Zannichellia
Pontederia, geotropic curvature of fruit
stalk, 239, 240 (Fig. 155); phyllodic
leaf anatomy, 341 (Fig. 169), 342
(Fig. 170). 343,344; specialised genus,
317; stomates, 166
Pontederia cordata, 166, 341 (Fig. 169),
342 (Fig. 170), 343, 344
Pontederia rotundifolia, 239, 240
Pontederiaceae, affinities, 316, 317;
cleistogamy, 234 (Fig. 153); entirely
aquatic, 318; geotropic curvature of
fruit stalk, 239, 240 (Fig. 155), 282;
heterophylly, 154, 1 60, 161; phyllodic
leaf structure, 337, 341 (Fig. 169),
342 ( Fig. 170)-344 ; vegetative multi-
plication, 213
Poplar, 187, 316
Portulacaceae, 310
Posidonia, apical openings absent, 269;
chlorophyll in epidermis, 164; fibres
in leaf sheath, 133; habit, 124; leaf
anatomy, 132 (Fig. 89); marine
Angiosperm, 123; pollen thread-like,
124, 125
Posidonia Caulini, 125, 132 (Fig. 89)
Potamogeton, 58-72; air tissue in fruit
wall, 71, 72 (Fig. 46); altitude, 290,
291; anatomy of inflorescence axis,
65; anatomy of root, 65 (Fig. 41), 66,
208; anatomy of stem, 62 (Fig. 39),
63, 64 (Fig. 40), 65, 175; apical
openings of leaves, 167 (Fig. 108),
268; chlorophyll in epidermis, 164;
choking mill sluices, 210; cortical
bundles, 65; cuticle, waxy, 254; de-
layed germination, 71, 72; dia-
phragms, 65, 184 (Fig. 118); dispersal
by ducks, 301, 302; distribution, 295,
297, 298; dwarfing due to heat, 275;
exudation of water drops, 269; fibres
in leaves, 61 (Fig. 38), 169; flowers,
69-71; fruits, 71, 72 (Fig. 46), 297;
germination, 280; heterophylly, 151,
153, 154 (Fig. 103), 157, 158 (Fig.
104), 159 (Fig. 105), 339 (Figs. 167 and
1 68); in biological classification, 6;
land forms, 61, 195, 196 (Fig. 125);
leaf forms, 61,339 (Figs. 167 and 168);
oil drops, 62 ; perenniation, 215 ; phyl-
lodic interpretation of leaf, 339 (Figs.
167, 168), 340
43
INDEX
Potamogeton crispus, 61, 62 (Fig. 39)-64
(Fig. 40), 67 (Fig. 42), 68 (Fig. 43), 69,
71, 164, 269, 275, 295
Potamogeton densus, 65 (Fig. 41), 71,
167 (Fig. 108), 206 (Fig. 137), 268, 298
Potamogeton fluitans, 69, 151, 157, 158
(Fig. 104)
Potamogeton heterophyllus, 61, 195
Potamogeton lucens, 61-64 (Fig. 40), 164,
173, 262, 330, 339 (Fig. 167)
Potamogeton natans, 6, 31, 32, 61, 62
(Fig. 39), 63, 65 (Fig. 41), 66, 70, 72,
151, 157, 159 (Fig. 105), 166, 167 (Fig.
i07),i84(Fig.n8),i95,i96(Fig.i25),
272, 280, 289, 301, 339 (Fig. 168)
Potamogeton obtusifolius, 206
Potamogeton pectinatus, 62-64 (Fig. 40),
65 (Fig. 41), 66, 70, 134, 262, 282, 291
Potamogeton pennsylvanicus, 303
Potamogeton perfoliatus, 58, 59 (Fig. 36),
61, 63, 69, 71, 140, 195
Potamogeton polygonifolius, 196 (Fig.
125), 333
Potamogeton praelongus, 62
Potamogeton pulcher, 61, 62 (Fig. 39), 63,
65
Potamogeton pusittus, 63, 64 (Fig. 40),
66, 71
Potamogeton rufescens, 69 (Fig. 44)
Potamogeton trichoides, 62, 66, 71
Potamogeton varians, 195
Potamogeton zosterifolius, 61 (Fig. 38)
Potamogetonaceae, fresh- water, 58-72;
marine, 123-129, 131-135, 237, 331;
other references, 205, 248, 314-316,
Primulaceae, 180, 312, 318
Proserpinaca palustris, heterophylly,
159-161
Protection of embryo in aquatics, 242,
243
Pseudo-callitriche, 134, 237, 306, 307
Pseudo-lamina, 339, 340, 341
Quercus, 207
Rafts of wood of Herminiera, 192
Ranales, 146, 238, 308, 319, 320, 321, 346
Range, wide, of aquatics, 295
Ranunculaceae, 309, 313, 314, 320
Ranunculus, affinities, 318; air spaces,
1 76 (Fig. 113), 185; altitude, 290; am-
phibious, aquatic and terrestrial types,
200, 309, 320; dimensions of dissected
leaves, 140; geotropic curvature of
peduncle, 145 (Fig. 93), 239; germina-
tion, 280; heterophylly, 144 (Fig. 92),
145, 146, 155; in biological classifica-
tion, 6; land and water forms, 195,
196 (Fig. 126), 198, 203 (Figs. 134,
135); luxuriance, 214; non-hetero-
phyllous form, 145 (Fig. 93); root-
system, 204, 264; sinking of seeds,
297; stem anatomy, 175, 176 (Fig
113); sub-aquatic flowering, 233, 234;
submerged leaves, 29, 140, 142; sub-
mergence of inflorescence, 228; sup-
port of inflorescence, 228; toleration
of salt, 134; winter-buds, 219
Ranunculus aquatilis, 144, 145, 155, 196
(Fig. 126), 204, 234, 280, 297
Ranunculus Baudotii, 134
Ranunculus carinatus, 228
Ranunculus circinatus, 145
Ranunculus confusus, 228
Ranunculus divaricatus, 234
Ranunculus Flammula, 145, 198, 203
(Figs. 134, 135), 309, 320
Ranunculus fluitans, 145, 214, 228, 233
Ranunculus hederaceus, 145 (Fig. 93)
Ranunculus heterophyllus, 145
Ranunculus Lingua, 146, 219
Ranunculus Purschii, 144 (Fig. 92)
Ranunculus repens, 200
Ranunculus sceleratus, 146, 284, 320
Ranunculus trichophyllus, 140, 176 (Fig,
113), 228, 290
Ranunculus sect. Batrachium, 6, 29, 142,
144-145, 175, 185, 195, 228, 239, 264,
309, 318, 320
Rheotropism, 282
Rhizomatous plants of Jura Lakes, 323
Rhizome, and polystely, 182; rhizome
of Castalia, 24—26 (Fig. n), 217;
Gunner a, 182; Hippuris, 173 (Fig.
112); Hottonia, 197 (Fig. 127); Lim-
nanthemum, 39-41 (Figs. 22, 23), 217;
Nymphaea, 24, 25 (Fig. 10), 27 (Fig.
12), 217; Potamogeton, 58-60 (Fig. 37)
Rhizopods, as food of Utricularia, 94
Rhyncolacis macrocarpa, 120, 121
Ribbon leaves, n (Fig. 3), 12, 13 (Fig.
4), 14 (Fig. 5), 19, 20, 22, 23, 140,
141, etc.
Riccia, 225
Rice, aliens accompanying, 303
Ricinus, 200
River-basins, isolation of, 296
Rodriguez, 129
Root-caps, of Brasenia, 205 ; of Lemna-
ceae, 74
Root-hairs, absence of, in Lemna tri-
sulca, 208, in water roots of Elodea,
208; in Hydrocharis, length of, 42, 43,
208; protoplasmic rotation, 43
Rootless Duckweed. See Wolffia
Roots of water plants, 204-209 ; aeren-
chyma, secondary, 188, etc.; air
tissue, 185, 186 (Fig. 121), 187;
anatomy, 65 (Fig. 41), 208, 209 (Figs.
138-140); assimilation, 207; differen-
tiation, 207; equilibrium, 207; im-
portance in life of aquatics, 264-266;
reduction of, 208, 244; spiral or
tendril, 127, 205 (Fig. 136), 206 (Fig.
137)
INDEX
433
Roraima, 109
Resales, 310. 319
Roslyn Pits, Ely, 147, 215, 241
Rotala, alien accompanying rice, 303;
cleistogamy, 234
Rotala indica, 303
Rotifers, 94, 142
Rubiaceae, 151, 313
Rubus jruticosus, 200
Ruppia, in brackish water, 134; macro-
podous embryo, 319 (Fig. 166);
pollination, 70; reduction of primary
root, 244
Ruppia brachypus, 319 (Fig. 166)
Sacred Lotus. See Nelumbo Nelumbo
Sagittaria, band or ribbon leaves, 9, n
(Fig. 3), 12, 13 (Fig. 4), 140, 141 (Fig.
90); diaphragms, 19 (Fig. 8), 167;
effect of freezing on fruit, 243 ; floating
of fruit, 297; flowers, 10 (Fig. i);
fruits, 10 (Fig. 2); heterophylly, 9,
ii (Fig. 3), 12, 13 (Fig. 4), 14 (Fig. 5),
1 6 (Fig. 6), 22, 23 ; in biological classifi-
cation, 5; leaf anatomy, 344, 345 (Fig
171); mericarps and seeds, 17, 18;
phyllodic interpretation of leaf, 161,
162, 339, 34.0, 344, .345 (Fig-
squamulae intravaginales, 13, 15;
stolons, 15, 16 (Fig. 6), 18 (Fig. 7);
tubers, 11 (Fig. 3), 13 (Fig. 4), 15, 1 6
(Fig. 6), 17, 18 (Fig. 7), 217, 223, 224
Sagittaria montevidensis, 344, 345 (Fig.
171)
Sagittaria natans, 12, 156
Sagittaria sagittifolia, 5, 9, 10 (Figs. 1,
2), 11 (Fig. 3), 12, 13 (Fig. 4), 14
(Fig. 5), 15, 16 (Fig. 6), 17, 18 (Fig.
7), 19 (Fig. 8), 23, 32, 34, 61, 141
(Fig. 90), 156, 157, 217, 223, 224, 297,
344, 345 (Fig- i?i)
Sagittaria sagittifolia f. v alii snerii folia,
II, 12
Sagittaria teres, 7, 22
Sagittayia variabilis, 17
St John's River, Florida, 213
Salix, development of aerenchyma, 188 ;
effect of submergence, 200 "
Salix viminalis, 188
Salt, toleration of, by certain hydro-
phytes, 133, 134
Salvinia, 311, 337
Santalaceae, 312
Santarem, 291
Sarracenia, 93
Sarraceniales, 310, 319
Saxifragaceae, 310
Scania, 303
Scirpus, affinities, 317; heterophylly,
154; in Jura lakes, 287, 288
Scirpus fluitans, 317
Scirpus lacustns, 154, 288, 317
Scotland, 290
Screw Pine, 317
Scrophulariaceae, 151, 313, 318
Scutellaria, 188
Sedges in Lake Ellis 286
Seed dispersal, 17, 18, 35, 71, 72 (Fig.
46), 297-303
Seedlings, 243-249; oiAlisma, 151, 153
(Fig. 101); Castalia, 28 (Fig. 13), 29;
Ceratophyllum, 85, 86 (Fig. 55);
Dicraea, 114, 115 (Fig. 78); Elating,
245 (Fig. 158); Hippuris, 245 ; Lawia,
H7;Lemna, 80, 81 (Fig. 52); Limnan-
themum, 248; Nymphaea, 35 (Fig. 18),
36; Rhyncolacis, 121; Trapa, 245-
247 (Fig. 160); Utricularia, 100 (Figs.
67, 68); Victoria, 32, 33 (Fig. 16), 34;
Zannichellia, 245, 246 (Fig. 159)
Seeds, 239-249; of Aldrovandia, no;
Alisma, 242, 297; Callitriche, 297;
Castalia, 243; Hippuris, 242, 297;
Hottonia, 297; Hydrocharis, 241;
Lemnaceae, 80, 297; Limnanthemum,
240 (Fig. 156), 241, 243, 297; Litto-
rella, 242 ; Lobelia, 297 ; Mayaca, 243 ;
Myriophyllum, 242; Nymphaea, 243;
Potamogeton, 297; Ranunculus, 297;
Sagittaria, 17, 18, 297; Stratiotes,
241 ; Utricularia, 99, 100
Sensitive Plant, Floating. See Neptunia
oleracea
Sesbania, 191
"Shade leaf" characters of submerged
leaf, 45 (Fig. 27), 164, 165, 171, 279
Siberia, 302
"Sifting" in evolution, 162, 203
Sium latifolium, heterophylly, 147, 149
(Fig. 97), 150 (Fig. 98); in biological
classification, 5
Sleep movements, 281
Snails, as food of Utricularia, 93
Snails, water, absence in peaty water,
287; as pollinators of Sagittaria, 9;
unable to eat turions of Utricularia,
101
Sneezewort. See Achillea ptarmica
Solanum Dulcamara, 198
Soldier, Water. See Stratiotes aloides
Sparganium, fruits eaten by wild ducks,
301; resemblance to Pandanaceae,
317
Spargamum natans, $ij
Spathicarpa, 315
Spathiflorae, 314
Spearwort, Greater. See Ranunculus
Lingua
Spearwort, Lesser. See Ranunculus
Flammula
Specific characters, constancy of ana-
tomical, 131, 331; lack of utility of,
I31, 330, 33i
Specific vital energy, 212
Speedwell, Water. See Veronica Ana-
gallis
434
INDEX
Spirodela polyrrhiza, 7, 74 (Fig. 47),
75, 76, 78, 80, 215
Spurwing, 300
" Squamulaeintravaginales," 15, 126,271
"Starch-leaved" plants, 164
Starwort, Water. See Callitriche
Stems, aquatic, condensation of vascular
tissue, 174-180; morphology and
anatomy, 172-185, 187-194; poly-
stely, 180—182; reduction of xylem,
172, 173; sympodial growth, 172, 173
Stomates, on submerged leaves, 165,
166, 167 (Fig. 107); water stomates,
30, 267, 268 (Fig. 163), 269
Stratiotes, calcophil, 287; chalky in-
crustation on leaves, 51; dehiscence,
241; dioecism, 54; flowers, 54 (Fig.
33); fruit, 239; geographical distribu-
tion of sexes, 54; habit, 53 (Fig. 32);
in biological classification, 7; in-
versely orientated leaf bundles, 52;
leaves, 49~53, 57. I4I. J57> J69;
mechanism of rising and sinking, 50,
51 ; Pleiocene and Pleistocene records,
54;roots, 50, 185, 186 (Fig. 121), 187,
207, 244; stem, 49 (Fig. 31), 172;
stomates, 51, 52; winter-buds, 53
(Fig. 32), 54
Stratiotes aloides, 7, 49 (Fig. 31), 50-53
(Fig. 32), 54 (Fig. 33), 185-187, 215,
219, 241
Submerged leaves. See Leaves, sub-
merged
Substratum, influence of, 286—287
Subularia, affinities, 309; in biological
classification, 7 ; submerged flowering
233
Subularia aquatica, 7, 309
"Sugar-leaved" plants, 164
Sundew, in
Surface-heating of ponds, 274
"Swan's Potatoes," 17
Sweden, 46, 303
Sweet William, 155
Switzerland, 302, 303
Sympetalae, 312, 313, 320
Tanqui, 181
Temperature, 273-275
Tendril roots, of Gentianaceae, 205;
Haloragaceae, 205 ; Hydrocharita-
ceae, 205 (Fig. 136); Philodendron,
206; Potamogetonaceae, 205, 206
(Fig- 137)
Terrestrial forms. See Land forms
Thalassia, leaf anatomy, 131, 169;
marine Angiosperm, 57, 123
Thallus of Podostemads, 7, 114, 115
(Figs. 76, 77, 78), 116 (Fig. 79), 117
Thames, 210, 273
Theophrastus, on ecology of aquatics,
285; on Trapa, 207
Thyme, Water. See Elodea canadensis
Tibet, 291
Tillaea. See Bulliarda
Tillandsia, 108, 109
Tornelia, 142
Transcaucasia, 303
Transpiration current, 260-272
Trapa natans, affinities, 311; assimila-
tory roots, 207, 255; buoyancy due to
lacunae, 192; changes in distribution,
302, 303; cotyledons, 245; fixation of
seedling, 245; fossil records, 303;
hypocotyl, negatively geotropic, 245;
reduction of primary root, 244 ; seed-
ling, 247 (Fig. 160); transverse helio-
tropism, 281; use in magic and
medicine, 302
4 ; heterophylly,
Trap ell a sinensis, 234
Trianea, 45
Tri folium, sleep habits of, 161
Trifolium resupinatum, 199 (Fig. 131)
Tristicha, dorsiventral root, 113; primi-
tive Podostemad, 306
Tristicha ramosissima, 113
Tristichaceae (see also Podostemaceae),
7, 112, 113, 120, 306
Turions, 217-225; and unfavourable
conditions, 222-224 ; m relation to in-
florescences, 224, 225 ; oiAldrovandia,
no, 219; of Caldesia, 22, 225 (Figs.
148, 149) ; oiHydrocharis, 47 (Fig. 29),
48, 49 (Fig. 30), 219; of Lemnaceae,
75-77, 219; of Myriophyllum, 219,
220, 221 (Fig. 144), 222 (Fig. 145),
223 (Fig. 146); of Potamogeton, 66, 67
(Fig. 42), 68 (Fig. 43), 69 (Fig. 44);
of Utricularia, 101, 102 (Fig. 69), 103,
219, 220 (Fig. 143)
Ulva, 27, 146
Umbelliferae, 5, 147, 312
Unconscious memory, 333, 347
Upware, 216
Utricularia, 91-109; absence of roots,
91, 204, 244; affinities, 313; "air
shoots," 96-98 (Fig. 65); anatomy,
107, 108 (Fig. 74), 22 7; apical develop-
ment, 106 (Fig. 72), 107 (Fig. 73);
benzoic acid in utricles, 96; capsule,
239; carnivorous habit, 93-96, in,
270; comparison with Aldrovandia,
no; dispersal, 299; "earth shoots,"
96 (Figs. 63, 64), 97, 270, 336, 337;
effect of strong light, 279 ; epiphytism,
108, 109; floats on inflorescence axis,
99, 229 (Fig. 150); freezing, 220;
hairs inside utricle, 92 (Fig. 60), 93
(Fig. 61), 95 ; hairs on valve of utricle,
92 (Fig. 60), 94, 95; land forms, 91;
morphology, 73, 103-107; position
in biological classification, 8 ; regene-
ration, 104 (Fig. 70), 105 (Fig. 71),
INDEX
435
1 06; relation to Pinguicula, 181;
"rhizoids," 96, 98, 99 (Fig. 66); seed-
lings, 100 (Figs. 67, 68); seeds, 99,
100; turions, 101-103, 219, 220;
utricles, 91, 92 (Figs. 59, 60), 93
(Fig. 61), 94, 95 (Fig. 62), 96 (Figs.
63, 64), 97, 98 (Fig. 65); vegetative
luxuriance, 215 ; water absorption, 2 70
Utricularia Bremii, 93 (Fig. 61), 95 (Fig.
62), 97, 299
Utricularia exoleta, 100 (Fig. 68)
Utricularia flexuosa, 92 (Fig. 60), 93
Utricularia Hookeri, 93
Utricularia Humboldtii, 109
Utricularia inflata, 99, 229 (Fig. 150)
Utricularia inflexa, 99
Utricularia intermedia, 91, 94, 97, 101,
219, 220 (Fig. 143)
Utricularia minor, 91, 96 (Figs. 63, 64),
97, 100, 102 (Fig. 69) 108 (Fig. 74),
168, 299
Utricttlaria neglecta, 92 (Fig. 53), 93, 97,
99 (Fig. 66), 104
Utricularia nelumbi folia, 108, 109
Utricularia ochroleuca, 97
Utricularia quinqueradiata, 99
Utricularia stellaris, 99
Utricularia vulgar is, 91, 93, 94, 97, 98
(Fig. 65), 100 (Fig. 67), 101, 102, 104
(Fig. 70), 105 (Fig. 71), 106 (Fig. 72),
107 (Fig. 73), 215, 220, 227
Valerian, Grew on heterophylly in, 155
Vallisnerta, contraction of peduncle,
235. 239; experimental cultures, 265;
leaves, 57, 140, 169; ovules, 314;
pollination, 57, 235, 236; root
anatomy, 208, 209 (Fig. 139); tolera-
tion of salt, 134
Vallisneria spiralis, 134, 140, 209 (Fig.
139), 235, 236
Vegetative reproduction, 210-226, etc.
Venezuela, 113, 122, 191, 291
Veronica, anatomy of submerged and
air shoots, 201, 259
Veronica Anagallis, 201, 259
Vicia, effect of water, 200; nutation of
roots, 207
Vicia sativa, 200
Victoria regia, affinities, 38; evocation
of heat from flower, 34; in shallow
water, 31; leaf succession, 32-34;
peltate leaf, 30; rate of growth, 214;
ripening of fruit under water, 300;
seedlings, 32, 33 (Fig. 16), 34; size,
80; Spurwing nesting on leaf, 300
Villarsia. See Limnanthemum
Villarsia ovata, 166
Violet, Water. See Hottonia palustris
Vorticellidae, 237
Vosges, 225, 287
""Wapatoo," 17
Water Aloe. See Stratiotes aloides
Water Buttercup. See Ranunculus sect.
Batrachium, R. aqualilis, etc.
Water Chestnut. See Trapa natans
Water Crowfoot. See Ranunculus sect.
Batrachium, Ranunculus aquatilis, etc.
Water forms, of Achillea, 199; Caltha,
198, 199 (Fig. 129); Cirsium (Cnicus),
198, 199 (Fig. 130), 200; Cuscuta,
199 (Fig. 131); Hydrocotyle, 200, 201
(Fig. 132); Menyanthes, 199; Ranun-
culus, 198, 200, 203 (Figs. 134, 135);
Trifolium, 199 (Fig. 131), etc.
Water-fowl and dispersal of hydro-
phytes, 35, 298-302
Water Hyacinth. See Eichhornia spe-
ciosa
Water Lobelia. See Lobelia Dortmanna
Water Loosestrife. See Lythrum Sali-
caria
Water Milfoil. See Myriophyllum
Water Parsnip. See Sium lati folium
Water Plantain. See Alisma Plantago
Water Plantain, Lesser. See Echino-
dorus ranunculoides
Water pores, 267-269, etc.
Water-shield. See Cabomba
Water-snails. See Snails, water
Water Soldier. See Stratiotes aloides
Water Speedwell. See Veronica Ana-
gallis
Water Starwort. See Cattitriche
Water stomates. See Stomates, water
Water Thyme. See Elodea canadensis
Water Violet. See Hottonia palustris
Waterlily, Giant. See Victoria regia
Waterlily, White. See Castalia alba
Waterlily, Yellow. See Nymphaea lutea
Waterweed, American, or Canadian.
See Elodea canadensis
Weddelina squamulosa, 113
Whitchurch Weir, 210
White Moss Loch, Perthshire, 288 (Fig.
165), 289
White Waterlily. See Castalia alba
Wicken Fen, 20
Willow Herb, 311
Wolffia, conveyance by birds, 300; in
biological classification, 7; member
of Lemnaceae, 74; size, structure,
wintering habits, 80
Wolffia brasiliensis, 80, 300
Wolffia Michelii, 80
Xerophyte, aquatic, 310
Xylem and water conduction, 173, 174
Yellow Waterlily. See Nymphaea lutea
Yew-tree, 316
Yorkshire, 303
"Youth forms" of Conifers, 155
Zannichettia, anatomy, 62, 63, 173;
436
INDEX
flowers, 70 (Fig. 45), 71, 215, 315, 316; of leaves, 269; association with Algae,
fruit and seedling, 246 (Fig. 159), 123; distribution, 302; food of Brent
248; hydrophilous pollination, 70, 71, Geese, 302; fruit, 248 (Fig. 161);
134, 346; in biological classification, habit, 124, 140; in biological classi-
6; rheotropism, 282; root-hairs from fication, 6; leaf anatomy, 128 (Figs
"collet," 245; stability of seedling, 85, 86), 131, 164; macropodous
245; twining roots, 205, 206 (Fig. 137) embryo, 248 (Fig. 161); pollen,
Zannichettia palustris, 134, 173, 205, thread-like, 125; pollination, 127,
206 (Fig. 137), 215, 282 129, 237
Zannichettia polycarpa, 70 (Fig. 45), 71, Zostera marina, 123, 127, 128 (Figs. 85,
246 (Fig. 159) 86), 129, 248
Zonation, 287-289 Zostera nana, 125, 302
Zostera, affinities, 315; apical openings "Zostera ocean-ica." 125
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