LIBRARY
FACULTY OF FORESTRY
UNIVERSITY OF TORONTO
Minnesota Plant Diseases.
A Wound Parasite (Pleurotus ulmarius) on the Trunk of a Maple Tree.
Original.
MINNESOTA
PLANT DISEASES
E. M. Freeman, Ph. D.
Assistant Professor of Botany
University of Minnesota
Report of t h e S u r •;• e v
Botanical Series
r
Saint Paul, Minnesota
/;//»• ? / . / <><> 5
PUBLISHED BY AUTHORITY OF THE
BOARD OF REGENTS OF THE UNIVERSITY
FOR
THE PEOPLE OF MINNESOTA
Edition, 2,500 copies ,
Preface.
j|T is probably safe to say that millions of dollars are lost in Minnesota yearly
by the ravages of plant diseases. Agriculturists and horticulturists all over
the world have of late years directed a great deal of attention toward the
study of plant diseases and the methods of combating them. The Department of
Agriculture of the United States has done vastly more than any other institution in
the world along this line and the results have been well worth the efforts, for many
efficient methods of fighting these pests have been devised.
In many cases where cure is impossible an intelligent understanding of the con*
ditions and effects of a disease will aid in prevention. The dissemination of such
knowledge is of very great value. It is a very evident fact that all agricultural pur-
suits are taking great strides, and the education of those boys and girls* who are about
to cultivate or manage the cultivation of lands is becoming more and more impera-
tive.
The possession of an accurate knowledge of plant diseases and their causes is not
only of commercial use to the farmer, both in cure and prevention, but also, by
making him an intelligent observer, adds hosts of assistants to the small corps of men
who are devoting their time to this study of botanical science. The advantages of
such a condition amongst agriculturists would far surpass those where the mere
knowledge of present methods of prevention and cure obtains. In fact it is only with
the intelligent and hearty co operation of farmers that such work can successfully go
forward.
It is not the aim of this work therefore to catalogue all of the ills that Minnesota
plants are heir to, but its chkf object is to disseminate knowledge of the destructive
parasites of the useful plants of this state, to assist all concerned in the cultivation of
plants to a more intelligent and thorough understanding of the habits of these para-
sites, and to point out established methods of combating such diseases. Kecipes are
not the aim of such a work -- these are of value and as such are introduced ; but by
far the most valuable effort should be the inculcation of the knowledge of the habits
and life-stories of those organisms which are the causes of disease. Upon such
knowledge, widely disseminated, can be built a substantial system of disease preven-
tion. In short, the aim of this work is rather educational than immediately practi-
cal, for in the former feature the author hopes that it will be ultimately most useful.
viii Minnesota Plant Diseases.
It is to be regretted that a systematic survey of the plant diseases of the state,
sufficiently thorough to determine the full extent of the damage due to these diseases,
has not been possible. The Minnesota Agricultural Experiment Station has never
employed a special plant pathologist, and the records of the station on plant diseases
are therefore only fragmentary. The author has, in the pursuit of his studies on the
fungi of Minnesota under the Geological and Natural History Survey of the state, be-
come more or less acquainted with many of the plant diseases, and this volume is in
part the result of such observations as were made in that -work.
The omission of some diseases is naturally unavoidable, and on the other hand
it has been deemed advisable to include many diseases which are doubtfully of much
importance in this state. These have been added either because their prevalence is
to be expected on account of their existence in neighboring states, or on account of
their general importance in other parts of the country. While not wishing to borrow
trouble from the future, it is well to be forewarned. The old adage, "a stitch in time
saves nine," is peculiarly appropriate. Again, plant diseases are here described which
are economically of minor importance, but which are illustrative of certain impor-
tant classes of diseases, and, as it has been pointed out that this work pretends to be
chiefly educational, such diseases become, secondarily at least, of considerable im-
portance.
I wish to express my thanks to the following for assistance in various ways, as
in the use of plates, photographs, material or literature : Mr. F. K. Butters, Profes
sor E. W. D. Holway, Mr. H. Cuzner, Professor F. L. Washburn, Miss D. Hone and
Dr. H. L. Lyon of the Universit y of Minnesota ; Mr. C. J. Hibbard of Minneapolis ;
Dr, Francis Ramaley of the University of Colorado? Professor G. F. Atkinson of
Cornell University; Professor R. S. Macintosh of the Alabama Experiment Station;
Dr. G. P. Clinton of the Connecticut Agricultural College; Professor H. Marshall
Ward, F. R. S., of the University of Cambridge; Professor Roland Thaxter of Har-
vard University ; Professor F. C. Stewart of the New York Experiment Station ; Mr.
F. J. Seavers of the University of Iowa; Mr. M. A. Carleton of the United States
Department of Agriculture ; Professor H. L. Russell of the Wisconsin Agricultural
Experiment Station ; Professor B. M. Duggar of the University of Missouri ; Mr. S.
A. Sirrine of the New York Experiment Station ; Professor J. C. Blair of the Illinois
Agricultural Experiment Station ; Mr. C. G. Loyd of Cincinnati ; Dr. J. C. Arthur of
Purdue University; Dr. W. A. Kellerman of Ohio State University; Professor H. L.
Bolley of the North Dakota Agricultural College ; Professor B. D. Halsted of Rutgers
College ; Professor B. O. Longyear formerly of Michigan State Agricultural College ;
Minnesota Plant Diseases. ix
Professor L. F. Kinney of the Rhode Island Agricultural Experiment Station ; Mr.
J. B. Ellis of Newfield, New Jersey ; and Professor G. Massee of Ke w Gardens, Lon-
don. To my wife I am greatly indebted for assistance in proof reading and in pre-
paring the manuscript and index.
To the following Experiment Stations I am indebted for the loan of plates for
illustration: Kansas, Connecticut, New York (Geneva I, New York (Cornell), Illi-
nois, New Jersey, Massachusetts, Michigan, Rhode Island, Maryland. My thanks
are also due the Goulds Manufacturing Co. of Seneca Falls, N. Y., for the loan of
several electrotypes.
Amongst the many well-known general works consulted, the following have
proved particularly useful and have been freely used : I wish here to acknowledge my
indebtedness: Diseases of Plants, Tubeuf and Smith; Pflanzinkrankheiten, Hartig
Diseases of Trees, Hartig (translated by SomervUk and Ward ; Zerzetzungser
scheinungen des Holies, Hartig; Spraying of Plants, Lodeman ; A Textbook of Plant
Diseases, G. Massee ; Die Natiirlichen Pflanzenfamilien, Engler and Prantl ; and the
older general works of Sorauer, von Tavel. Frank, Zopf and De EUry.
I have made free use of the great literature of the bulletins and reports of the
United States Agricultural Experiment Stations and especially of Connecticut Experi-
ment Station Bulletin No. 142 and the Connecticut Report for 1903, both of which
were written by Professor G. P. Clinton.
Where illustrations have been taken from other works credit is given in the
proper place ; I desire here to acknowledge my indebtedness to the following publish
en, for permission to copy illustrations : Julius Springer, Berlin ; Eduard Trewendt,
Breslau; Gustav Fischer, Jena ; The Clarendon Press, Oxford; Longmans. Green &
Co., New York; The Botanical Gazette, Chicigo; Macmillun & Co., London and
New York ; Wilhelm Engelmann, Leipzig.
For the chapter arrangement of the descriptions of specific diseases in Part II,
I am indebted to the suggestion of Professor MacMillan.
All figures designated as original were made by Mr. C. J. Hibbard under th<
Geological and Natural History Survey of Minnesota. The great majority were
made under the direction and with the co-operation of the author; the remainder
under the direction of other members of the survey staff.
To the Board of Regents of the University of Minnesota is due the credit for
making financially possible the collection of material and illustrations and the publica-
tion of this work.
I am particularly indebted to Professor Conway MacMillan, at whose suggestion
thr work was undertaken, and without whose advice and assistance the publication
would h\v; b:en impossible.
Table of Contents.
M
PREFACE.
INTRODUCTION i
PART I General 5
CHAPTER I Fungi. Nutrition 7
CHAPTER II Fungi. Reproduction -M
CHAPTER III Fungi. Fungus Life Methods .15
CHAPTER IV Fungi. Plant Partnerships. Parasitism... 48
CHAPTER V Fungi. Parasites on Animals.. 66
CHAPTER VI Fungi. Parasites on Plants 77
CHAPTER VII Fungi Plant Disease. <A)
CHAPTER VIII Fungi Kinds of Fungi Algal Fungi.. 10.}
CHAPTER IX Fungi Kinds of Fungi Sac Fungi.. . 117
CHAPTER X Fungi Kinds of Fungi Sac Fungi . 1^5
CHAPTER XI Fungi. Kinds of Fungi Hasidmm bearing
Fungi i_sj
CHAPTER XII Fungi Kinds of Fungi Hasidumi bearing
Fungi 170
CHAPTER XIII Other Disease-causing Organisms .... iS<j
CHAPTER XIV Economics. Prevention and Cure.. joi
CHAPTER XV Fungicides and Spraying Apparatus .MI
PART II Special . j \ \
CHAPTER XVI Diseases of Timber and Shade Trees Timber
Rots _>^
CHAPTER XVII Diseases of Timber and Shade Trees Timber
Rots .... j<»)
CHAPTER XVIII Diseases of Field and Forage Crops. _.Sj
xii Minnesota Plant Diseases.
CHAPTER XIX Diseases of Garden Crops 316
CHAPTER XX Diseases of Orchards and Vineyards '347
CHAPTER XXI Diseases of Greenhouse and Ornamental
Plants 371
CHAPTER XXII Diseases of Wild Plants 385
INDEX . . 401
Index to Illustrations*
M
FRONTISPIECE. A wound parasite (Pleurotus ulmarius) on the trunk
of a maple tree. Original.
FIG. i. The mycelium of a food-mold fungus. After Zopf
FIG. 2. Various special absorptive or sucker threads of parasitic
fungi After Zopf n
FIG. 3, Fungus strands and storage organs. Original.. 13
FIG. 4. Storage organ of a cup-fungus with fruiting bodies. Original. 14
FIG. 5. Strands of mycelial threads of the dry-rot fungus. Original.. 15
FIG. 6. "Shoestring" strands of mycelial threads of the honey colored
mushroom. ( )riginal 1 7
FiG. /. Highly magnified view of section through the end of mycelial
strand of the honey-colored mushroom. Alter Zopf iH
FIG. 8. Fairy rings of a mushroom fungus. Photograph by Dr. F.
Ramaley JO
FIG. 9. Chief kinds of spores of fungi. Highly magnified. After vari-
ous authors
FIG. 10. Various kinds 01 common fruiting bodies of fungi. Alter
various authors -M
FIG. n. Kinds of spores produced by one ru>t lungus (wheat rust ) at
different times. Highly magnified. Alter various author*. -'5
FIG. I-'. A carrion fungus. Original £>
FIG. i.v A birds-nest iungus. Alter Kngler and I'rantl. and Sachs. $0
FIG. 14. Various explosive apparatuses i»r distributing spores. Mag-
nified. Alter various authors...
FIG. 15. A caterpillar-fungus spore, germinating. By the author..
FIG. 1 6. A dung-dwelling fungus oi the black mold group growing on
hor>e dung. Photograph \>\ F. K Butters
xiv Minnesota Plant Diseases.
FIG. 17. The same fungus as in figure 16, greatly enlarged. Micro-
photograph by F. K. Butters 38
FIG. 18. An earth-dwelling fungus of the gill fungi. Original 39
FIG. 19. A wood-dwelling fungus on a dead stick of wood. Original.. 40
FIG. 20. A wound parasite. Original 46
FIG. 21. A lichen. After Atkinson 48
FIG. 22. A large witches'-broom on white pine. Photograph by R. S.
Macintosh 52
FIG. 23. Witches'-broom on balsam fir, caused by a rust fungus.
Original 53
FIG. 24. Witches'-broom on white spruce, caused by a mistletoe.
Photograph by the author 54
FIG. 25. An enlarged view of the broom on the spruce shown in
Fig. 24. Photograph by the author 55
FIG. 26. Birds-nest witches'-broom on red cedar, caused by a rust
fungus. Original 57
FIG. 27. Oat smut. An accomplished parasite. After G. P. Clinton.. 59
FIG. 28. An enclophytic mycelium between the cells of a grass grain.
By the author 60
FIG. 29. Infection of a grass leaf by a rust fungus (wheat rust).
After Ward 61
FIG. 30. Beetle fungi attached to an insect. After Thaxter 68
FIG. 31. Various kinds of caterpillar fungi with fruiting bodies. Origi-
nal /o
FIG. 32. Dead minnow with fish mold. Original 71
FIG. 33. A spore-case of a fish mold, showing escaping swimming
spores. Highly magnified. After Zopf 72
FIG. 34. Damping-off of seedlings. After Atkinson 77
FIG. 35. Strawberry leaf spot. Original 79
FIG. 36. Larch tree killed by the parchment pore-fungus. Original.. 81
FIG. 37. Fungus galls on the leaves of Labrador tea. Original 83
Minnesota Plant Diseases. xv
FIG. 38. Two ways in which wood is destroyed by wood-rot fungi.
Highly magnified. After Hartig 86
FIG. 39. A good example of an epidemic. Potato-blight has within
a week entirely destroyed the potato plants in this field.
After Clinton 99
FIG. 40. An epidemic of mildew on cucumbers checked by spraying.
After F. C. Stewart 101
Fie. 41. A lowly algal fungus. Highly magnified. After Schroeter. . 105
FIG. 42. Water and fish molds. Highly magnified. After various
authors 106
FIG. 43. Sewer-pipe fungi. Highly magnified. After Pringsheim. ... 108
FIG. 44. Downy mildews. Highly magnified. After De Bary. ... 109
FIG. 45. A downy mildew with the aspect of a white rust. Original. . in
FIG. 46. A black mold. Highly magnified. After Zopf. . 113
FlG. 47. An insect mold. Highly magnified. After Brcfeld 115
FIG. 48. Yeast fungus cells. Highly magnified. After Rees. . 118
Fie. 49. Plum-pocket fungus and loose-weft fungus. Highly magni-
fied. Alter De Bary and Sachs I.M
FIG. 50. A powdery mildew on common plantain leaf. Original.. i-'-j
FIG. 51. The fruiting body of the powdery mildew of black haw. show-
ing the appendage-. Highly magnified. Microphoto-
graph by K. \V. I). Hoi way i .s
FIG. 52. The fruiting body of the powdery mildew of willows, show-
ing the appendages and spore-sacs. Highly magnified.
Micropholograph by K \V. D Holway ij6
FIG. 5.v Krgots of grasses. Original U7
FlC. 54. Krgot fungus on canary grass. Original.. u8
FIG. 55. Fruiting bodies and -porr- of thr t-rgot fungus. Variously
magnified. After I uhi-m- and Breield 130
FIG. 56. A caterpillar fungus. ( )riginal 131
FIG. 57. A strangling funuus .m ^r;»ss U-UM-S ainl ~u-inv ()riginal.. . I U'
xvi Minnesota Plant Diseases.
FIG. 58. A strangling fungus. Fruiting bodies and spores. Variously
magnified. After Winter and Brefeld 133
FIG. 59. Black knot of plum. After Clinton 135
FIG. 60. Two common types of "burnt-wood" fungi: a dung fungus
(Sordariaceae), and a somewhat closely related fungus (of
the family Chaetomiaccae). Magnified. Microphotographs
by F. K. Butters 137
FIG. 61. A common cup-fungus growing on sunken sticks and appear-
ing abundantly in the spring. Original 140
FIG. 62. A single sac and sterile threads from the palisade of sacs of
the fungus shown in Fig. 61. Highly magnified. After
Seavers MI
FIG. 63. A cluster of cup fungi showing cups just appearing above the
ground. Original 143
FIG. 64. A cup fungus on the bark of a fallen tree. Original 144
FIG. 65. Cup fungus on decaying wood. Original 145
FIG. 66. Morel fungi. Original 147
FIG. 67. Saddle fungi. Original 148
FIG. 68. Truffles. Photograph by F. K. Butters 149
FIG. 69. Truffles. Fruiting bodies and spores, variously magnified.
After F. K. Butters 159
FIG. 70. Two types of imperfect fungi. Magnified. After Tulasne... 151
FIG. 71. Smut spores, germinating. Highly magnified. After Brefeld 155
FIG. 72. Loose smut of wheat. Original 157
FIG. 73. Spores of rust fungi. Highly magnified. After Ward and
Carleton 159
FIG. 74. Spores of rust fungi. Highly magnified. After Tavel 161
FIG. 75. Cluster-cups of ash-leaf rust fungus, on an ash twig. Mag-
nified. Microphotograph by E. W. D. Holway 162
FIG. 76. Cluster-cup spores from the rust fungus of Fig. 75. Highly
magnified. Microphotograph by E. W. D. Holway 163
Minnesota Plant Diseases. xvii
FIG. 77. Spores of a grass rust fungus (Puccinia vexans). Highly mag-
nified. Microphotograph by E. W. D. Holway 165
FIG. 78. Various basidia and spores of the lower basidium-bearing
fungi. Highly magnified. After Brefeld 166
FIG. 79. Jew's ear fungus fruiting bodies on a dead branch of a balsam
fir. Original 167
FIG. 80. A trembling fungus on the end of a log. Original 168
FIG. 81. Basidia and basidiospores of the higher basidium-bearing
fungi. Highly magnified. After Brefeld and Schroeter. .. i/o
FIG. 82. A smothering fungus growing on the ground. Original 17-
FIG. 83. Club fungi on a decaying log. Original 1/3
Fie. 84. The coral fungus on the under side of a log. Original. . 174
FIG. 85. A pore fungus, growing on the ground. Original 176
FIG. 86. A stick-dwelling gill fungus, on a dead branch of a birch.
Original >77
FIG. 87. The shaggy-mane fungus. Original 1/8
FIG. 88. The shaggy-mane fungus— a later stage than that shown in
Fig. 87. Original 1 79
FIG. 89. The common wild mushroom fruiting body. Original iHo
FIG. 90. A group of the common gemmed puff-balls, just before open-
ing. Original 181
FIG. 91. The same group as in Fig. 90, taken two weeks later. Origi-
nal iSj
FIG. 9.2. Stalked puff-balls. Original |S^
FIG. 93. Karth Mars. Original 185
FIG. 94. A carrion fungus. Original 187
Fir.. 95. A carrion fungus, photographed just alter the breaking of
the "egg," and while the cap was being lifted. Original. iKS
Fir.. 96. Bacteria of the black n>t <>i cabbage. Highly magnified.
Alter H. I.. Kus>cll ify
FIG. 97. Bacteria of fire-blight <>i appli-v Highly magnified. Alter
B. M. Duggar. i<>?
xviii Minnesota Plant Diseases.
FIG. 98. Bacterial nodules on root of common bean. Original 195
FIG. 99. The bacteria of such root nodules of the pea family as are
shown in Fig. 98. Highly magnified. After Atkinson... 196
FIG. loo. Slime molds. Variously magnified. After De Bary and
Cienkowski 197
FIG. 101. Twig of a witches'-broom of spruce, showing the parasitic
plants of the mistletoe, which cause the brooming of the
branches. Photograph by the author 199
FIG. 102. A bucket pump. (The Deming Co.) 211
FIG. 103. A knapsack pump. (The Goulds Mnfg. Co.) 212
FIG. 104. A barrel pump. (The Deming Co.) 213
FIG. 105. A simple type of barrel pump us«d in the horticultural de-
partment of the University of, Minnesota Experiment Sta-
tion. Photograph by R. S. Macintosh 214
FIG. 106. A gear-power force pump. (Victor Spraying Machine) 216
FIG. 107. A barrel pump in action, on the farm of B. Hoyt, St
Anthony Park, Minn 217
FIG. 108. A powerful type of spray pump for orchard spraying.
(Goulds Mnfg. Co.) 220
FIG. 109. A complex type of spray pump used at the New York Ex-
periment Station for spraying several rows of asparagus at
once. After S. A. Sirrine 222
FIG. no. The apparatus shown in Fig. 109 in action. After F. A. Sir-
rine 224
FIG. in. Various fixings, tools and appliances for spraying apparatus.
After J. C. Blair 228
FIG. 112. A convenient nozzle for spraying the under side of leaves.
(Deming Co.) 230
FIG. 113. Nozzle for spraying plants in rows. (Goulds Mnfg. Co.).... 230
FIG. 114. An effective nozzle for mist-like sprays. (Goulds Mnfg. Co.) 231
FIG. 115. Powder gun, with attachments. (Leggett) 231
Minnesota Plant Diseases. xix
FIG. 116. Fungus fruiting boaies of a gill fungus, on street railway ties.
Photograph by Dr. F. Ramaley 236
FIG. 117. A Stereum wound parasite. Original 241
FIG. 1 18. Partridge wood rot. Original 242
FIG. 119. The coral fungus, on the under surface of a log. Original. . 246
FIG. 120. The fruiting body of the dry-rot fungus. Original 245
Fie. 121. The dry-rot fungus on a pine board. Original 248
FIG. 122. The dry-rot fungus on pine boards, showing later stages, of
decay than that in Fig. 121. Original 249
FIG. 123. The fruiting body of the flattened pore-fungus, on a standing
dead tree trunk. Original 252
FIG. 124. Fruiting bodies oi the sulphur pore-fungus, on a dead oak
stump. Original 253
FIG. 125. Fruiting bodies of the scaly pore-fungus seen from both sur-
faces. After Loyd .'5 j
FIG. 126. Fruiting body of the birch pore-fungus, on a branch of a
white birch. Original 255
FIG. 127. Fruiting bodies of an undetermined pore fungus on a bass-
wood log. Original 257
FIG. 128. Fruiting bodies of the honey-colored mushroom, at the base
of a tree. Original 261
FIG. 129. Fruiting bodies of the fatty Pholiota in a wound of an oak
tree trunk. Original 263
FIG. 130. The velvet-stemmed Collybia on a decaying log. Original. .'(14
FIG. 131. Fruiting bodies of the sapid Pleurotus on a standing yellow
birch trunk. Original .'65
FIG. 132. Fruiting bodies of the pine Leti/itc*. common on soft woods
Original i«,
Fir,. 133. Tar spots of willow and maplr. ( )ri^in;il ... _>6o
FlG. 134. Powdery mil. lew of willow leal. Original.
FIG. 135. Powdery mildew of elms on ;in dm leal. < )riginal .'74
Fir.. 136. Pine knot on Scotch pine. Original ^~tt
xx Minnesota Plant Diseases.
FIG. 137. Poplar leaf rust. Original 278
FIG. 138. Willow leaf rust. Original 280
FIG. 139. Wheat rust. Stems of wheat, showing opened and unopened
black clusters of winter spores. Slightly magnified.
Original 283
FIG. 140. Wheat rust. A section of such a stem as is shown in Fig. 139,
highly magnified. Microphotograph by E. W. D. Holway 284
FIG. 141. Oat stems and leaf bases, with clusters of summer spores of
the oat rust. Original 285
FIG. 142. Spores of the common "black rust" of wheat. After Arthur
and Holway 286
FIG. 143. Spores of the crown rust of wheat. Highly magnified. After
Arthur and Holway 287
FIG. 144. Cluster-cups of the crown rust of wheat, on swollen cushions
of the stem of the alder-leaved buckthorn. Photograph by
Arthur and Holway 288
F'iG. 145. Cluster-cups of the black or stem rust of wheat, on sfems and
leaves of the barberry. Photograph by Arthur and Hol-
way 290
FIG. 146. Loose smut of oats. Original 293
FIG. 147. Stinking smut of wheat, showing smutted grains and spores.
Variously magnified. After Tubeuf 296
FIG. 148. Smut of corn. On the leaves and tassels. After Clinton. .. . 298
FIG. 149. Corn smut on an ear of corn. Original 299
FIG. 150. Head smut of sorghum. After Kellerman 301
FIG. 151. Grain smut of sorghum. After Kellerman 302
FIG. 152. Powdery mildew of grasses on wild grass-plant leaves.
Original 304
FIG. 153. "Black mold" of clover on leaves of white clover. Original 305
FIG. 154. The ergot fungus on rye. After Clinton 307
FIG. 155. Storage organs or ergots of ergot fungi on various grasses.
Original 308
Minnesota Plant Diseases. xxi
FIG. 156. Flax wilt; wilted seedlings. After Bolley 311
FIG. 157. Spores of the flax wilt fungus, highly magnified. After Bol-
ley 312
FIG. 158. Flax wilt; the fungus threads around the root of an attacked
flax plant. Highly magnified. After Bolley 312
FIG. 159. Flax wilt; a section of a flax root, with fungus threads and
spores at the surface. Magnified. After Bolley 313
FIG. 160. Orange rust of raspberry and blackberry. Original 316
FIG. 161. Winter spores of the asparagus rust. Highly magnified.
Microphotograph by E. W. D. Hoi way 318
FIG. 162. Rust of bean. After Clinton 319
FIG. 163. Pore-fungus root-rot of currant. Original 3-'
FIG. 164. Potato scab. After Clinton.. 3-'6
FIG. 165. Anthracnose of bean. After Halsted.. 3-"*
FlG. 166. Potato blight. Karly stages of the blight on the loaves
After Clinton 33-'
FlG. 167. Potato blight. Later stages on the leaves. After Clinton.. 333
FIG. 168. Downy mildew of nniskim-lon. Blighted vine in the field.
After Clinton 333
Fie. 1(19. Downy mildew of muskmelon. showing the under surface of
an attacked leal. Alter Clinton. . 33''
FIG. 170. Downy mildew of nuiskindon. I'nder surface of an attacked
leaf. Alter F. C. Stewart 337
FIG. 171. Downy mildew of melon> and cucumbers. Spores and spore-
bearing threads. Highly magnified Alter Humphrey
and F. C. Stewart.
FIG. l/.'. Bacterial rot of potato After Clinton.. 34"
FIG. 173. Bacterial rot oi squash. Alter Clinton.. 34'
FlG. 174. Black rot of cabbage. A badly inicMed field. Alter H. 1..
Russell .'•»-'
FIG. 175. Black rot of cabbage. Artificial infection of cabbage plants.
Alter H. L Unveil. . J43
xxii Minnesota Plant Diseases.
FIG. 176. Black rot of cabbage. Bacteria, highly magnified. After
H. L. Russell 343
FIG. 177. Black rot of cabbage. Cabbage heads, apparently sound, are
attacked by the rot. After H. L. Russell 344
FIG. 178. Black rot of cabbage. A cabbage leaf showing the manner
of infection. After H. L. Russell 344
FIG. 179. Club root of turnips. After Halsted 345
FIG. 180. Club root of cabbage. After Clinton 346
FIG. 181. Cedar apples of red cedar. Original 348
FIG. 182. Rust of apple leaves. After Clinton 349
FIG. 183. Apple scab on the fruit. After Clinton 351
FIG. 184. Apple scab on the fruit. After Longyear 351
FIG. 185. Apple scab on a twig. After Clinton 352
FIG. 186. Apple scab on the leaf. After Longyear 353
FIG. 187. Spores of the apple scab fungus. Highly magnified. After
Longyear 354
FIG. 188. Blue-mold fruit rot of apple. After L. F. Kinney 355
FIG. 189. Blue-mold fruit rot of apple. Accessory spores of the fun-
gus, highly magnified. After L. F. Kinney 356
FIG. 190. Bitter rot of apple. After Clinton 357
FIG. 191. Black knot of wild cherry, showing various stages in the de-
velopment of the knots. Original 359
FIG. 192. Powdery mildew of plums and cherries. Variously magni-
fied. After Ellis 3^°
FIG. 193. Plum Pockets. Photograph by H. Cuzner 362
FIG. 194. Black rot of apple. After Clinton 364
FIG. 195. Fire blight of apples. Bacteria which cause the disease.
Highly magnified. After B. M. Duggar 364
FIG. 196. Downy mildew of grape. Under surface of an attacked grape
leaf. Original 368
FIG. 197. Downy mildew of grape. A healthy and an attacked bunch
of grapes. Original 369
Minnesota Plant Diseases. xxiii
FIG. 198. Downy mildew of grape. Spores and spore-bearing threads.
Highly magnified. After Millardet 370
FIG. 199. Leaf rust of roses. The cluster-cup stage on the stems and
leaves. Photograph by H. Cuzner 374
Fie. 200. Leaf rust of roses. Stem with groups of cluster-cups. Origi-
nal 375
FIG. 201. Leaf rust of roses. Variously magnified. After Massee 376
FIG. 202. Powdery mildew of lilac. Original 377
Fie. 203. Powdery mildew of roses. A leaf of the rose attacked by the
disease. After Clinton 378
FIG. 204. Powdery mildew of roses, showing the superficial mycelium
and summer spores on the leaves. After Tulasne 379
Fie. 205. Golden-rod rust. Original 388
FIG. 206. Sunflower rust. Original 3X9
FIG. 207. The stem rust of the cowberry. Highly magnified After
Hartig 390
FIG. 208 Rust of wild sarsaparilla. Original 391
FIG. 209. Mint rust. Original 393
FIG. 210. Powdery mildew of composites, on the leaf of the great rag-
weed. Original 396
FIG. 211. Gall fun gu< on the wild peanut. Original.. 3<>S
Introduction*
The diseases of plants and their causes may be grouped as
follows :
Organic diseases, i. e., those caused by living organisms
such as:
Fungi.
Bacteria.
Slime molds.
Flowering plants.
Insects and other animals.
Inorganic diseases, i. e.. those due to other causes than living
organisms :
Unfavorable conditions of soil. etc.
Unfavorable conditions of weather, etc.
It is not the purpose of this work to consider nil of the dis-
eases of Minnesota plants. The attack of insects furnishes a
vast field of research which is best left to the entomologist. By
far the most widely distributed and most destructive of Minne-
sota plant diseases are organisms belonging to the plants known
as fungi. Bacteria are responsible for a considerable number
and the fungus-like animals, known as slime-molds, are respon-
sible for a few. In addition the flowering plants cause several
diseases. There are also to be considered those diseases which
are caused by inorganic agencies as drought, heat. wind. hail,
lightning, frost-cracks, sunscalds. etc. This work will not ad-
mit of a discussion of the latter group.
It is well at the outset to note that disease cannot be easily
defined. ( )ne might consider any variation due to the derange-
ment from the most favorable conditions of the life of a plant
as a disease. The most favorable conditions in all respects are
seldom, if ever, realized. When the favorable conditions of life
are so seriously interfered with by any agency, so that the life
i
2 Minnesota Plant Diseases.
of a part of a plant or of the whole plant is threatened, we rec-
ognize disease in that plant. The change in favorable condi-
tions may be so slight that the shortening of the life of the plant
or its parts is not apparent. One does not recognize disease
in such a case, although it is essentially similar to that of well-
recognized diseases. There are, then, between health and dis-
ease in plants imperceptible gradations and no sharp lines of
demarcation. A farmer who intelligently strives for all of the
most favorable conditions of his crop is in reality combating
disease. A great loss to agriculture annually occurs which d'oes
not usually pass for disease. When the grower of plants real-
izes this, and when he joins his efforts with those who are seek-
ing methods of combating diseases, then more rapid strides will
be possible in methods of investigation and prevention. The
more knowledge a farmer possesses of the conditions favorable
and unfavorable to the numerous diseases which affect his crop,
just so much more successful will he be in his efforts toward
preventing disease. Agriculture really resolves itself into one
great problem, the prevention of plant disease in the broader
sense.
There are three factors to be considered in a plant disease :
(1) The immediate cause of a disease, e. g., fungi, bacteria,
insects, etc., as enumerated above.
(2) The immediate effect in the anatomy, form and physi-
ology of the host plant and the effect in inheritance.
(3) The previous condition and disposition of plants which
may seriously affect the susceptibility of those plants to a cer-
tain disease ; in other words, the predisposition of plants toward
disease.
It is therefore apparent that one must study not only the
immediate cause of a disease but the predisposition or immu-
nity of plants toward that disease. An appreciation of these
principles finds expression in the selection of varieties for spe-
cific purposes and in the more detailed study of the life-histories
of diseases. By such study an exact knowledge of the habits
of a parasite are obtained and it is only by means of this knowl-
edge that we can intelligently devise methods of prevention.
Too much stress cannot be placed on the necessity for accurate
work in the observations of the habits of a parasite and of its
Minnesota Plant Diseases. 3
life-history. All of those diseases which ure at present success-
fully combated have been dealt with only after a thorough
knowledge of their habits. The treatment of oat smut, for in-
stance, is based on the knowledge that infection of the oat plant
takes place when the plant is in the seedling stage and from
spores found usually clinging to the oat grains.
The predisposition of plants toward disease is a subject
which at this point is to be dealt with only in passing, and will
receive more detailed attention in later chapters.
Part I. of this work will deal in general with those groups of
plants, particularly the fungi, which furnish the causes of dis-
eases in plants and with general methods of combating diseases,
etc. Part II. will be given up to a consideration of specific dis-
eases of Minnesota plants.
PART I.— GENERAL.
Chapter I.
Fungi. Nutrition.
jr
What the fungi are. As understood today, the plants known
as fungi do not include the bacteria and the slime molds. The
bacteria are plants which find their closest affinities with the
blue-green algae. Slime-molds possess fructifications which
have at least great superficial resemblance to those of the fungi,
but their vegetative life is similar to that of the lowest order of
animals. They are therefore known appropriately as fungus-
animals.
The fungi are all devoid of leaf-green. They hold this char-
acter in common with bacteria, slime-molds and many flower-
ing plants. The lack of leaf-green is the result of a different
habit and nutrition method from that of leaf-green-bearing
plants. The latter can utilize constituents of the air and water,
together with mineral salts from the soil, and build them up.
with the power of sunlight, first into starch and then into the
more complex substance known as protoplasm or living sub-
stance. The loss of leaf-green indicates that a plant has no
longer any use for a starch-forming apparatus, but since it still
needs starch it must obtain such material in a manufactured
condition. Fungi are therefore dependent upon other plants or
animals or upon the products of these organisms for food. Al-
though lack of leaf-green is not characteristic of fungi alone
but is shared by certain other plants or groups of plants, we find
that the fungi do possess a distinguishing mark in the structure
of the vegetative portion of their bodies.
That portion of the plant which is concerned with the build-
ing up of the individual plant itself is known as the vegetative
portion, while that which is concerned with the production of
cells for the development of offspring is reproductive. The
vegetative portion of a fungus is known as a mycelium and has
8
Minnesota Plant Diseases,
a characteristic structure and method of growth. This myce-
lium is composed of fine microscopic threads, more or less
branched and densely interwoven to form loose, woolly masses,
as in bread mold, or may even be compacted to form solid
bodies. All fungi reproduce in some form by means of micro-
scopic cells, more or less spherical in shape, and often as small
as 1/2000 of a millimeter in diameter. They are usually, how-
ever, larger. These tiny cells are known as spores and have
various forms and methods of production, which are character-
FIG. 1. — The mycelium of a food-mold fungus (Penicillium). A. Mycelium which is
entirely absorptive and tufts (t) of spores (reproductive tract). The original spore
from which the mycelium grew is seen at a. B. Highly magnified view of spore tuft.
After Zopf.
istic for different groups of fungi. There is, however, no spore
form or spore receptacle which is common to all fungi, nor are
spores themselves confined to fungus plants.
Plants as well as animals can usually be best understood by
their ancestry. The fungi have all descended from the algae,
probably not, however, from one, but from several groups, e. g..
Minnesota Plant Diseases. 9
from the flower-pot algae, the green felts and the pond scums,
and possibly from the red sea-weeds.
The fungi therefore comprise low forms of plant life which
have descended from algal stock and which by a change in their
nutritive methods have lost their leaf-green and have come to
possess a vegetative mechanism, composed of more or less
branched threads known as a mycelium.
The number of fungi in Minnesota is undoubtedly very
large. It has been estimated at between 2,500 and 3,000, out
of a total number of 7,000 Minnesota plants. The minute size of
many of these fungi, — some of the entire plants cannot be seen
without the aid of a hand-lens. — the difficulty of observation,
the great resemblances of forms and the complex methods of
life make the determination of these plants a slow task, and the
exact number of Minnesota fungi will probably not be known
for some years. The rate of constant additions of new forms is
sufficient indication of the very large number which exists in
the state and points towards a confirmation of the above esti-
mate.
The fungus method of obtaining nutrition. It was stated
above that fungi had lost the leaf-green of their algal ancestors
and were therefore unable to make starch from water, soil and
air constituents but compelled to derive their elaborated food
from other sources. Two methods have been adopted. In one
the fungus derives its nutritive material directly from living
plants. Such are parasites, and the plants upon which they
feed are known as host plants. In the other method the fungus
derives its prepared food from the dead products or remains of
animals or plants, as leaf-mold, broad, preserves, etc. Such
plants are known as saprophytes. In both of these cases the
food obtained is at least partially prepared.
How the nutritive method is expressed in structure. It is a
law which covers all living things, plants as well as animals,
that the complexity of the structure of an organism depends on
the amount and kinds of work which it can perform. When
an organism has its food prepared by no effort of its own, it
soon shows the loss of power to do that work. This loss of
power is usually expressed in loss of certain structures, or in
the simplifying of such structures. Such an effect is commonly
I0 Minnesota Plant Diseases.
described as degeneration. It is a noteworthy fact that such a
plant may be very well adapted for obtaining food in its own
way, and in this respect may be highly specialized. The wheat-
rust, for instance, is very highly organized and is very closely
adapted to its own manner of life. The fungi are specialists
along certain lines of obtaining food and are in these lines more
highly specialized than leaf-green-bearing plants. Plants with
such a -habit of life do not need the elaborate starch-making
machinery of higher plants, as of ferns and flowering plants.
It is easier and more economical for fungi to reduce their vege-
tative areas and hence to simplify their structure. It is a case
of economy on the part of the plant. In general, all plants,
whether fungi or flowering plants, when devoid of leaf-green,
are efficient specialists in their absorptive methods while at the
same time the vegetative area may be comparatively simple. It
must therefore be understood that when these plants are called
degenerate it is only in this one aspect of vegetative structure
that they are correctly so called. In absorptive power and in
reproduction they may be fairly complex.
It is also well known that parasitism in animals also results
in degeneration of structure. There are a large number of
worms, such as tapeworms and thread worms, numerous insects,
such as fleas and bird lice, and even vertebrates, as the hag
fishes, which are parasitic in their habits. In all of these cases
simplification or degeneration of the animal body results. Or-
gans of locomotion, sense organs, digestive tracts are all pro-
foundly affected; either very much reduced or lost entirely.
Many flowering plants have also adopted either parasitic or
saprophytic habits. Familiar examples are found in the dodder
and coral-root orchid. The dodder is usually found in swampy
places or in clover fields and is a confirmed parasite. It has
lost its leaf-green except in very early life and is consequently
in later life yellowish in color. The coral-root orchid grows on
leaf mold in the deep woods and is a saprophyte in habit ; it has
also lost its leaf-green ; and its leaves, as in the case of the
dodder, are reduced to small scales, useless for starch-making
purposes. On the other hand, all parasites and saprophytes,
whether plants or animals, have well developed systems of ab-
sorption and reproduction. The fungus system of absorption,
Minnesota Plant Diseases.
1 1
at least in higher forms, is highly organized. In lowly forms of
fungi, where the plant body is but a single, small, more or less
rounded cell of microscopic size, absorption takes place" over
the entire surface of the little plant and there is no specialized
region for the performance of this function. In all of the higher
forms absorption takes place through a system of much-
branched, fine threads of microscopic size.
In a mushroom, for instance, these threads penetrate the
soil for a considerable distance, often for feet and even vards.
I'lC. 2. — Various special absorptive or sucker threads of parasitic fungi, in. The mycclial
threads. The sucker threads (I!) are teen in the host plant cells. I. A downy
mildew. II. Rust fungus. III. Protoniyces (a fungus with a doubtful systematic
position). Highly magnified. After Zopf.
The absorptive area is built upon a similar physiological prin-
ciple to that of the root system of flowering plants, for in these
absorption takes place at the surface of very fine hairs, which
are borne on the surface of the younger roots. True root hairs
and fungus absorption threads embody the same advantage in
the presentation of a large absorbing area. In the fungus the
threads branch profusely and are of great length, and thus a
1 2 Minnesota Plant Diseases. .
greater area of soil is drained of its nourishment. Root hairs
of flowering plants never branch, but new ones are constantly
being formed near the tip of the growing rootlets, thus effect-
ing a similar result to that of the branched mycelium of the
fungus. The absorptive system of parasites often consists of a
similarly branched mycelium which runs between the cells of
the plant upon which it feeds. Some of the branches of these
fungus threads are of a special kind and penetrate into the cells
of the host plant. Parasitic plants may not have such a richly
developed absorptive system as a mushroom, but in other re-
spects may be more highly specialized. The mycelium of a
highly organized parasite is usually only able to obtain nour-
ishment from certain species or groups of species of plants.
For instance, certain rusts are capable of getting nourishment
only from one kind of grass plant. It will be seen from these
considerations that the absorptive system of this group of
plants, whether parasites or saprophytes, is, in general, well de-
veloped.
Parasitism and saprophytism. Parasites are usually de-
scribed as those plants which obtain their nourishment directly
from living plants or animals. They are so organized that,
when their nourishing threads come into close contact with cer-
tain living plants or parts of plants, they answer to certain im-
pulses, sending special branches directly into the living tissues
and there absorbing nutrition. Saprophytic plants, on the
other hand, are not reacted upon by living plants and are com-
pelled to get their nourishment from the dead products of
plants or animals. The real substances which are absorbed by
parasites and saprophytes may not be different in their chem-
ical natures but the methods of obtaining them differ. The
parasite has learned to respond to certain impulses, which it re-
ceives when it conies near to another plant, and by this response
obtains nutrition. True saprophytes never respond to such an
impulse. They live on ground rich in leaf mold or in decaying
wood, or on dung of animals, on remains of animal life or on
still other products of living plants or animals, but never
upon the organism when the latter is still alive.
Parasites are limited in their size by the size of their host-
plant, hence they are usually very small — often microscopic in
Minnesota Plant Diseases. 13
size. Being limited in size, they often live for a long period
through which they produce their reproductive bodies and thus
compensate for lack of size. In some cases they produce dif-
ferent kinds of spores at different seasons. Such is the case in
the fungus which causes rust diseases of grains. The sapro-
phyte, on the other hand, has often an unlimited supply of mate-
PlC. 3.— Strand* ami storage- organs. 1. Straixl
young fruiting Iw <lu s anac'iol. J. Straiuli
(Dictyopbura ravi nrlliii. Original.
|>utT-l>all ( Tylostmuu) with
rgans' of a c::rrio:i finiK'US
rial at its disposal. Moreover. tlii> food material is easilv a\'ail-
ahle and large plant bodies can thus be built up. Such is the
case with a great many saprophytes, especially those of the
mushroom group, puff-balls, etc. ( )nly one effort a season may
14 Minnesota Plant Diseases.
be made by the plant to produce reproductive bodies and then
one grand effort is made. A single mushroom may produce mil-
lions of spores arid shed them all in a single day. Not all para-
sites, however, are small; but in some cases, as in the wound
parasites, they may produce large shelf-like fruiting bodies.
These plants are often saprophytic at first, becoming parasitic
later.
Storage organs. Most fungi use the food materials which
have been absorbed from their various sources, for the immedi-
ate production of fruiting bodies. Consequently the fungus con-
sists almost entirely of these two regions, the absorptive myce-
I'iG. 4. — Storage organ of a cup fungus (Sclerotinia) with fruiting bodies
(stalked cups) which have grown from the storage organs. Original.
Hum and the reproductive organs. Some fungi, however, have
learned to store food for future use and are thus able to collect
considerable material, before attempting the formation of
spore-bearing organs. The ergot of rye is such a storage or-
gan, formed by a fungus parasitic on the rye. The fungus ap-
propriates the nutrient material of the young grain and builds
up a solid elongated or roundish body which, when mature, be-
comes dark violet colored or blackish. This body is composed
of parallel threads of the fungus tightly compacted together and
Minnesota Plant Diseases.
contains nutrient mate-
rial in the form of oils
and other compounds.
This ergot remains dor-
mant through winter
and in the spring pro-
duces reproductive bod-
ies. Certain carrion fun-
gi form storage organs.
They are found under the
ground, developed on
strands of the mycelium.
In this case the storage
organ has packed up its
food material in the form
of a starch peculiar to
fungi and known as fun-
gus starch. Certain pore
fungi produce very large
underground storage or-
gans. Such is probably
the "Tuckahoe Indian
Bread" of the southeast-
ern states. This storage
organ is often about the
size of a small cantaloupe
and of heavy doughy
consistency. A certain
pore fungus of Australia
produces storage organs
of immense size and these
are used by the natives
for food. The caterpillar
fungus furnishes an ex-
ample of a storage organ
of some interest. The
fungus attacks living cat-
erpillars and the myceli-
l-'lC. 5. — Str?.nds of mycclial threads of the dry-
rot fungus ( Mcrulius lacryinans). See also
I'iKS. 120, r_'l and I.:.'. Oriuinal.
1 6 Minnesota Plant Diseases.,
um finally gains entrance to the interior of the insect body. By
continued growth of the fungus the caterpillar is killed. Its
substance is absorbed and appropriated by the parasite, which
finally replaces all insect parts with densely woven threads
packed with nourishment. There is thus produced a complete
cast of all parts of the caterpillar, life size, composed of the
threads of the fungus. After a rest period, this mummy or
storage organ produces a stalked reproductive body. In New
Zealand certain very large caterpillars are thus attacked and
the resulting storage organs are used as a food by the natives.
Thev are known as vegetable worms.
Fungus Shoestrings or Strands. One often finds in decaying
logs or in soil where an abundance of woody material is present,
cord-like strands, often whitish in color, or in other cases very
dark. By tracing them along one finds them connected with
puff-ball fruiting bodies, or carrion fungi or gill fungi. Those
strands formed by the puff-ball or carrion fungus are whitish
in color and branch considerably ; some of the branches are very
small and occasionally meet each other, fusing together to form
a network. These threads are not absorptive in their function,
although the smaller branches connect directly with the ab-
sorptive mycelium. They serve probably in part to store up a
certain amount of nourishment, but their chief purpose is to
distribute as widely as possible the fruiting bodies and to enlarge
the territory from which the fungus draws its nutrition. In re-
spect to the enlargement of the spore distribution such strands
function as do the runner stems of higher plants.
Perhaps the most common of these strands and those to
which the name shoestring more properly applies, are the gill-
fungus strands, particularly those of the honey mushroom,
which is abundant everywhere in the fall. These strands are
found both in the ground and under the bark of trees. They
are dark-colored exteriorly and branch profusely and, like those
of the puff-balls, may form elaborate networks. The older
strands look somewhat like shoestrings. They may attack
roots of trees, penetrate the bark and spread under the latter
to form an absorptive mycelium which is parasitic, and which
may finally kill the tree. Under the bark of such dead trees
one finds large networks of shoestring strands and at the base
Minnesota Plant Diseases. 17
of the trunks will arise the honey-colored mushroom, which
usually occurs in great clusters.
Fie. 6. — "Shoestring" str.vids of myctlial threads of tne honey-colored mushroom
(Armillaria nicllca). (See als > I'ijf. 113*. > Orini"al.
Physiology of the Mycelium. The mycelium arises from
the spore by the germination of the latter. The spore sends
1 8
Minnesota Plant Diseases.
out one or more little tubes which elongate and finally, by
branching, produce numerous threads; the spore is then seen
at the center of a system of radiating threads, like the hub
of a wheel and its spokes. These threads soon branch pro-
fusely and now a circular, densely interwoven network is
produced which keeps on enlarging, thus encroaching upon
new- areas of nu-
trition. If the
spore should be
placed in nutrient
jelly, where its'
environments in
all directions are
alike, the result-
ing mycelium
would be ball-
shaped in outline ;
but if the myceli-
um is nrodnrerl FIG. 7.— Highly magnified view of section through end of
mycelial strand of honey-colored mushroom, showing
in cii^1i n n1arp> nc compactness of central portion (c and d) and loose
threads at the surface (a and b). Highly magnified.
the mold soil on After zopf.
the forest floor, the symmetry of the form is interfered with
by various obstacles. In general, a mycelium would tend to
become circular in outline as seen from above. Such a myce-
lium is often seen in the production of what are called fairy
rings. Many gill-fungus mycelia grow from year to year and
at the proper season of each year produce a crop of fruiting
bodies at the surface of the ground. These are formed at the
end of the mycelium and hence come to stand in a circle. One
circle appears each year, becoming larger year by year.
The peculiar life habits of many fungi bring with them
peculiarities in the development. Many fungus spores will ger-
minate between temperatures a little above freezing, i.5°-2°C.,
and 40°-43°C., but best at about 25°C. Such as are required
to pass through the alimentary canal of certain animals before
germinating demand, in general, higher temperatures. One
of the gaseous constituents of the air, oxygen, is necessary to
the germination of spores of fungi. Every housewife knows
Minnesota Plant Diseases. 19
that if all of the air is excluded from a jar of preserves no molds
will develop.
The spores of parasitic fungi will usually germinate if placed
in water. They often require to be kept for a certain time and
are often adapted for certain seasons. For instance, the black
rust spores of wheats and grasses usually will, not germinate
until the following spring. A germinating spore of a true par-
asite must be brought into contact with its proper host, or it
will soon die for lack of food. When brought into contact it
commences very soon its parasitic life. The spores of many
saprophytes, on the other hand, require nutrient substances
before they will germinate. It is often a matter of very exact
requirements as, for instance, in the case of the common com-
mercial mushroom. It is only within the last few years that
the commercial mushroom spore has been observed germinat-
ing. The continuation of the growth of the mycelium takes
place at about the temperature of the germination. Light is
not a necessary condition for growth, for it is not an essential
in the building up of starch in fungi, as it is in the case of any
of the leaf-green-bearing plants. Hence one finds fungi devel-
oping luxuriantly in caves and cellars. Light, however, some-
times influences the formation of the fruiting bodies. The
food material of most saprophytic fungi is required to be of a
slightly acid composition. The concentration of compounds
found in the nutritive substances affect profoundly the develop-
ment of the fungus. Certain fungi which develop well in' a
weak solution of sugar, cannot grow in a very concentrated
solution, a principle which is utilized in the preserving of fruits.
Such fungi as the wood-inhabiting and insect-inhabiting
forms illustrate well the method of attack of many fungi. The
timber parasites and saprophytes exude from their threads a
chemical substance which attacks the wood tissues and destroys
the woody properties. The wood is thereby reduced to punk.
Insect-inhabiting forms exude a substance which attacks and
disintegrates the chitinous coverings of the insect, thus gain-
ing entrance for the fungus to the soft parts of the insect.
The age of a mycelium varies considerably in different fungi.
Some live for but a few days, some live indefinitely, being lim-
ited only by the absence of nutrition, and others again are reg-
2O
Minnesota Plant Diseases.
ularly perennial. The latter include both saprophytes and
parasites. The fairy-ring mushrooms are good examples of the
former, while of the latter, illustrations are found in those rust
fungi which attack balsam fir and other cone-bearing plants
and form witches' brooms. The mycelium of the fungus caus-
ing smut of grains is of a peculiar kind. It often finds its way
into the host plant when the latter is very young and tender,
and continues to grow in the delicate growing parts and dies
FIG. 8. — Fairy rings of a mushroom fungus (probably a Lepiota). Photographed by Dr. F.
Ramaley.
behind in the mature tissues. The examination of such a plant
would show a mycelium only in the growing part of the stem.
When the young grains are formed the mycelium develops in
their tissues, completely destroying them and forming smut
spores in their stead.
The mycelia of many fungi are capable of resisting many
unfavorable conditions, reviving again immediately upon the
return of propitious surroundings. Evidence of such power is
seen in any woods when a heavy rain follows on a long period
of drought. On all sides one finds fungi improving to the full-
est their opportunity of favorable weather.
Chapter II.
Fungi. Reproduction.
The fungus method of reproduction. Fungi reproduce by
means of very small bodies of microscopic size, which are
known as spores.* All of the spores of fungi are not similar in
origin, structure or appearance, but differ in these respects
very considerably. Some spores are pinched off. as it were, of
special fungus threads, often in rows, as in the summer spores
of mildews. Others, again, are formed in cases, as in the small
black heads of black molds; or in sacs, as in the morels and
cup fungi. Again, a spore may be formed as the result of a
breeding act — i. e.. the fusion of two sexual elements which
may be both alike or may be male and female. Some spores
are provided with fine thread-like processes and by whipping
these about can swim around in the water. Such spores are
found in the potato-blight and in many water-inhabiting forms,
as fish-molds. Many spores are capable of germinating im-
mediately while others require a long rest period and are there-
fore provided with thick protective coats. The summer or
red-rust spores of grass rusts commence to grow as soon as
they are ripe, if the conditions are otherwise favorable, and this
fact accounts in part for the rapid spread of rust in certain
seasons. The winter spores of rust, or black rust. ha\v thick
protective coats and usually rest over until the following
spring, when they continue their further development.
In the bread-mold and its allies, in the fish molds and in the
potato-blight relatives, no complex organs are formed upon
which the spores, whether pinched off or in cases, may be ag-
*The term Sjiore migiit U-.-tUr. as is adv
equivalents of the spore of the moss sp >n'H<
tion would exclude the term from the rt-aln
«ac st>ores if the sac funtii an.l certain v
sporidia of tl1? rusts. Convenience and cstal li
letention of this teiin in the older and c-.inn
led Sy many botanists, lie retained for the
mi and all other sporophytes. This restric-
f fun^i with the exception of perhaps the
I th<- aln.il fun^i. and perhaps also lite
hcd ii.-t.iKe would si-cm to counsel here the
ly accepted sense.
22
Minnesota Plant Diseases.
gregated together. They are found on threads more or less
loosely scattered about. In many higher fungi, however, the
spore cases or sacs are borne on special structures, called fruit-
ing bodies, though, of course, this term does not imply that
they are at all similar or equivalent to fruits, as the gardener or
horticulturist understands that term, when applied to parts of
FIG. 9. — Chief kinds of s >ores of fungi. 1. Sac with spores. 2. Basidia with basidio-
spores; a, b and c stages in s;>ore formation. 3. Spore case of mold containing numer-
ous spores. 4. Tuft of pinched-off spores of blue mold. 5. Swimming spores of an
algal fungus. 6. Spores of a black mold produced by a breeding act — stalks of the
breeding cells are seen below the spore. 7. Spores of an insect mold. 1, 2 and 5 after
DeBary; 3 after Sachs; 4, 6 and 7 after Tirefeld.
flowering plants. The best known of such fruiting bodies are
the common structures known as mushrooms and toadstools,
which in typical forms are composed of a stalk and an umbrella-
like cap, on the under surface of which are leaf-like plates, run-
ning from the edge to the top of the stalk. The spores are
Minnesota Plant Diseases. 23
borne all over the surface of the plates, or gills, as they are
termed, and the spore area is thus very greatly increased in
size. Such fungi are known as gill fungi. Again, shelf fruit-
ing bodies are produced, which have holes all over the under
surface, as though pricked with a needle. The spores are
formed over the entire surface of these holes or pores. These
fungi are known as pore fungi. The fruiting bodies of other
fungi, again, may be more or less club shaped and branched or
unbranched. or they may be provided with numerous teeth as
in the bear's-head fungus. The puff balls are very common ob-
jects, especially towards the fall of the year; they are closed
fruiting bodies, with one or more enclosing membranes, which
open by a definite hole at the top, to allow of the escape of the
ripe spores. By pressing such a puff ball a dust of spores is
thrown out to the wind and scattered considerable distances.
Many relatives of the puff ball form fruiting bodies under-
ground, which look somewhat like truffles. The curious little
beaker-shaped structures containing egg-like objects are
fruiting bodies of the "birds-nest" fungi and the fruiting bodies
of the carrion fungi arc still more remarkably elaborated.
Here the spores are borne on the top of a very elastic stalk and
are found in a sticky mass which has an odor of carrion and
is much sought after by insects. The whole is enclosed in an
elastic covering which ruptures only when the spores are ripe
and then the stalk, previously held under pressure, is released
and lifts the spore area up very quickly into the air. In the
mildews, such as the common mildew on lilacs, in addition to
the loosely scattered summer spores, fruiting bodies are found
in the fall. They are usually very much smaller than a pin-
head. L'nder a microscope they are seen to be little, hard,
black-walled, capsule-like objects with curious appendages and
containing one or more sacs of spores. The black-knots on
cherry trees are fruiting bodies which contain, scattered over
the surface, numerous minute, pear-shaped depressions, which
are partially lined with sacs of spores. Very common in most
places, on wood or on the ground, are the cups of the cup-
fungi. These are fruiting bodies of various sixes with, in gen-
eral, a cup or beaker shape and are often brightly colored.
The inside of the cup is lined with sacs which burst open and
Minnesota Plant Diseases.
FIG. 10. — Various of the most common kinds of fruiting bodies of fungi. 1. Birds-nest
fungus. 2. A gil! fungus. 3. Caterpillar fungus, one on grub and other on fly. 4.
Club fungus. 5. Carrion fungus. 6. Pore fungus. 7. A morel. 8. Puff-ball. 9. Truffle.
10. Cup fungus. 11. Sac-spore-capsulc of powdery mildew (highly magnified). 1-8.
After Engler and Prantl; 10, After Rehm; 9 and 11, after Tulasne.
Minnesota Plant Diseases.
forcibly eject their spores. Often by a change in the atmos-
pheric conditions a large number of sacs burst at once and
clouds of spores can be seen to ascend from the cup. The truf-
fles have underground closed fruiting bodies which are related
to the cups but never open except by decay of the walls. The
morels and their allies have cups which are turned inside out.
as it were, and are furthermore usually much wrinkled, and
borne on stalks. Another very important phase of reproduc-
tion in fungi lies in the kinds of spores produced by a given
fungus. One and the same fungus may often produce more
than one kind of spore. In fact, some fungi produce as many
as five or six kinds.
The wheat-rust, for
example, forms one or
more, commonly
two, — kinds of spores
in the spring, another
in summer and anoth-
er in the autumn and
the autumn
grow in early
still another
produced.
*
is
when
spores
spring
kind
These spore forms fol-
low in a certain way
the seasons. The mil-
dew, for instance, has
summer spores and
winter spores. In oth-
er fungi the various
forms may be called
forth by differences in the substances upon which tlu- fungus
grows. In some fish-molds the production of the different
spores can be exactly controlled by changing the food sub-
stances. Sometimes a fungus which is <>r has been capable of
producing several spore-forms continues under certain condi-
tions to produce only one kind of spore. Our knowledge of
such a fungus is incomplete until we know the other spore-
forms which it is capable of producing. There is a vast num-
FIG. 11. — Kinds of s|>orc» produced bv one rust
fungus (a wheat rust) at different times. 1.
Winter s|«>rc. 'J. Itasidiospore. 3. Cluster-cup
s.K»rc. 4. I'ycnidial sj>ore (probably a function-
let* relic of a male sexual cell). 6. Summer
spore. 1. 2. 4 and 5, after Ward; 3, after Ar-
thur and Hi >1 way.
26 Minnesota Plant Diseases.
ber of such imperfectly known fungi, many of them being of
great economic importance. They are usually designated as
"Imperfect Fungi" and are classified temporarily according to
a very artificial system under what are usually termed "form
genera."
This selection of fungi for special substances, for the pro-
duction of certain spores, and the production of different spores
according to seasons, has given rise to a very remarkable phe-
nomenon in the succession of spores. Not only may some
parasitic fungi form different kinds of spores but these spores
may be formed on widely different plants. The wheat rusts
furnish us with the most familiar examples. The spring spores
are formed on barberry or on buckthorn, or on some other
plant, according to the kind of rust, while the summer and
winter spores are formed on grasses. If one sows spring
spores on barberry they will not develop but they must be con-
veyed to a grass plant before infection takes place. In a simi-
lar manner, when the winter spores germinate, the little spores
which are produced on the germ threads must be borne to a
barberry or buckthorn leaf before they can cause infection.
Spore distribution. Just as the seed plants utilize many
agencies for the purpose of distributing their seeds over as
wide an area as possible, just so do fungi utilize the same agen-
cies for the dissemination of their spores. The fungi in gen-
eral may be said to be very prodigal of their spores, so that
these are produced usually in great numbers. This may be
accounted for in the peculiar requirements of the spore for ger-
mination and for further development. Hundreds or thou-
sands usually fail to develop where one or two find suitable
conditions and give rise to a mature plant. A mushroom or a
puff-ball produces literally millions of spores, yet from the
abundance of any given kind we know that very few germinate
and come to maturity. Again spores are microscopically small
and hence in general cannot contain a great deal of nourish-
ment. They cannot therefore withstand unfavorable condi-
tions of germination for such protracted periods as can many
seeds of seed-bearing plants. Many spores can pass through a
very long resting period and are capable of germination at the
end of this period, but after germination is begun the spore
Minnesota Plant Diseases. 27
cannot usually resist unfavorable conditions; this is an impor-
tant principle commonly made use of in combating fungus
diseases. The spraying of fungi is most effective if carried out
just after the spores germinate. Under the natural conditions
of the sowing of spores, unfavorable dry periods may follow
closely on a damp season, in which the spores have just ger-
minated, and in this way undoubtedly myriads of spores come
to grief.
Distribution by water. There is a great group of fungi
which always live in the water or. if not actually in the water,
in very moist conditions; or, as parasites of seed plants, they
pass long periods in the resting condition and revive during
very moist seasons, as after a rain or heavy dew. Such fungi
have spores, with special mechanisms for dissemination through
the water. Each little spore is provided with one or two ex-
ceedingly delicate whip-like processes which protrude from the
end or side of the spore. These lashes whip about and propel
the spore with comparatively great speed through the water,
until it finally comes to rest and then germinates into a new
plant. In this way potato blight is spread and this disease be-
comes epidemic only during very wet seasons. In the so-
called white rust which so commonly attacks almost, if not
all, of the plants of the mustard family, an enormous number
of spores is found in white rust-like patches which give the com-
mon name to the fungus. These spores are formed in chains
and when ripe are blown about by the wind, and are thus borne
to the surface of other plants. Here they remain until very
moist weather brings about their further development. They
then divide up internally into numerous little swimming spores
provided, as in the fish and water molds, with propelling lashes,
and the chances of infection of the host plant leaves by these
swimming spores are thereby many times increased. The white-
rust therefore uses both the wind and water in the dissemina-
tion of its spores.
Distribution by wind. The great majority of fungi utilize
the wind as an agent for carrying spores. The spores of rusts
and smuts are shaken out into the wind by the movement of
the plants on which they grow. Their position is of advantage
just as is the elevated position of the wind-distributed seeds
28 Minnesota Plant Diseases.
and fruits — their radius of distribution is proportionately in-
creased by increase of height from ground. Rust spores can
be blown for great distances and still retain their power to in-
fect plants. In this connection one sees in the structure of
these spores a certain adaptation which assists in the wind
sowing. The food material packed up in the spore is usually
oily and is therefore light in weight. The spore-coat, more-
over, has often spiny projections which enable the spore to ad-
here to objects with which it comes in contact. Moreover,
the summer spores of rusts are often formed continuously for
a long period, — throughout the summer, — that is to say, the
fungus scatters its chances over a long period rather than con-
centrate the production into one effort. The mildews are like-
wise parasites with a similar habit of spore distribution. The
mushrooms and their allies have learned to use the wind in
sowing their spores. The stalked, unbrella-like, fruiting body
raises the spores into the air and at maturity sheds them where
the wind can take them up. Many shelf fungi on the trunks
of trees have acquired especially elevated positions. Such
fungi can be said to concentrate their efforts upon the produc-
tion of an enormous number of spores for distribution in a
comparatively short time and a favorable period is of course
sought for this effort. The spores of mushrooms are in gen-
eral smooth-coated, as they usually come to the ground before
they germinate and require no special means of attachment.
Puff-balls also form myriads of spores but do not shed them
all at once or in such a short time. Gusts of winds, or a jar by
some falling object, may force out little clouds or puffs of
spores and such a puffing goes on intermittently for a long
period.
Distribution by insects. Again some fungi have learned to
use insects as an aid in spore distribution. A very effective de-
vice has been invented by the fungus which forms ergot of rye.
Previous to the formation of the storage organ known as the
ergot, the fungus forms a soft mass of much branched threads
in the young grain and from these are formed summer spores.
These are accompanied by an attractive sugary solution which
is luring to insects and with this sugar food the latter carry
off the spores, sowing them on other flowers and thus rapidly
Minnesota Plant Diseases. 29
spreading the disease. The early spring spores of rusts are
often accompanied by structures exuding sweet fluids that are
attractive to insects and may be materially beneficial in the sow-
ing of spores. There is a certain group of fungi, often known as
the honey-dew fungi, which grow chiefly on the leaves of
higher plants. They are not parasites but live on insect secre-
tions and excreta which are deposited upon the leaves of
plants. In this rich pabulum the fungi grow luxuriantly and
often form very black sooty coats on the leaves. Such fungi
are often specialized to the secretions of certain specific insect
forms. A very curious device has been developed among the
so-called birds-nests fungi — a device which has to do with the
utilization of insects for the spreading of spores. The fruiting
FIG. 12. — A carrion fungus. The black head at the top of the fruiting body ( lying on
the leaf) is covered with a sticky solution in which spores are found. Insects, at-
tracted by the odor, carry off this solution and thus scatter the spores. Original.
body is beaker-shaped and in the little beaker are tiny flattened
egg-like bodies, in reality closed cases, the interior of which
contains numerous spores. The "eggs-stalks" become gelat-
inous and very elastic when wetted and can be pulled out to a
comparatively enormous length. These stalks probably serve
to attach the "eggs" to insects' legs and later, becoming en-
tangled in twigs or leaves, fasten the "eggs" to these objects.
Germination of the spores follows immediately under favorable
conditions.
Undoubted and remarkable examples of insect aid to spore
sowing occurs in the so-called carrion fungi. Here the spores
are found in a stickv, usuallv brownish mass, which is at matu-
Minnesota Plant Diseases.
FIG. 13. — A birds-nest fungus. To the
left are unopened fruiting bodies;
to the right a section of the same;
the eggs are chambers, carrying
spores, and the chamber stalks be-
come sticky when moist and prob-
ably catch in the legs of insects and
are thus distributed. After Engler
and Prantl, and Sachs.
rity very qiuckly elevated by a Sponge-like stalk to a conspicu-
ous height. The spore-mass contains substances that emit a
very strong odor as of carrion; hence the common name of
these plants. This odor is very attractive to many insects and
apparently the spore mass contains abundant food material
for it very soon disappears as a result of the numerous visits
of flies and other insects. In some forms of these carrion
fungi pure white veil-like or lace-like mantles — in appearance
much like a large-meshed Wels-
bach mantle — are produced.
Certain tropical forms, more-
over, add a phosphorescence to
these mantles so that they at-
tract nocturnal insects, and such
forms open usually at or just be-
fore dusk. Certain molds inha,b-
it the bodies of larvae of insects,
living parasitically on them. An
insect thus infected may carry
the fungus to a considerable distance and after death numerous
spores will be formed which may infect new larvae. The si^k-
worm is often preyed upon by these fungi.
Distribution by other animals. Vertebrate animals are also
occasionally agents of spore distribution. Squirrels often feed
on certain mushrooms thereby carrying the spores off into
their holes. These fungi are the so-called wound parasites
which start life as saprophytes in the dead heart-wood of trees
and finally grow out into the sap-wood and kill the tree. In
the well-protected shelter of such squirrel holes a wound para-
site can get a good start. Rabbits and other burrowing ani-
mals often brush up against the fungus fruiting bodies of root-
inhabiting forms and carry the spores in their furry coats.
Truffles are probably distributed by those animals which feed
on them. There is a very large class of fungi which inhabit
the dung of certain animals. Such fungi often grow from
spores which have passed through the alimentary canals of
these animals. The near relatives of the shaggy-mane mush-
room are good examples of these fungi. The common com-
mercial mushroom also regularly inhabits dung and is there-
Minnesota Plant Diseases. 31
fore raised in caves from beds of manure. Many molds and
many black knot allies are also constantly found upon dung.
Animals are thus very potent factors in the distribution of the
spores of such fungi. Woodpeckers play the same role as do
squirrels, for they open holes in the bark of trees by which
fungi gain entrance to a tree and boring insects are similar
abettors in the attack of wound parasites.
Man is an important agent in spore distribution. In all
of his commercial transactions, such as shipments of grains,
introduction of plants and moving of commodities, fungi of
many kinds may be introduced and spread over vast areas.
The mallow rust furnishes a good example. This rust was in-
troduced from South America less than twenty-five years ago
and has since spread over nearly the whole world, becoming a
great destroyer of many kinds of plants of the mallow family.
The spores of many fungi lurk on the seeds of other plant
parts and develop with the advent of favorable conditions.
Smut spores are .very good examples of such fungi for they
often attach themselves to grains of grasses and when the
grain germinates attain conditions favorable for their germi-
nation. This, at the same time, is precisely the best period
for the infection of the grain-plant. Fungus spores or myceha
may be present in bulbs or underground parts of plants which
are transported from one place to another and thus are spread
over wider areas.
Explosive apparatus. In addition to these external factors
of wind, insects, etc.. some fungi have developed special meth-
ods of their own for hurling out spores so that these shall be
scattered over larger areas or may better be caught by the
wind. The cup fungi have one such device. Here the spores
are formed in long cylindrical sacs. These sacs have lids at
the apex and when ripe throw off the lids ami spurt out the
spores, together with a little drop of rtuid material. Often
numerous sacs blow off at once so that one sees little clouds of
spores arise from the cup. The little mold fungus which
causes tly cholera has also a shooting device to thrust off its
spores. Each little spore is formed on the end of a thread and
is finally snapped off by the prolusion of the wall just under-
neath the spore. One sees these spores as a little halo around
Minnesota Plant Diseases.
the fly on panes of window glass in the autumn. A very com-
mon dung-inhabiting mold has also an explosive apparatus.
FIG. 14. — Various explosive apparatuses for distributing spores. 1. Sac fungus — spores are
blown out of the sac when the lid is also blown out. 2. A black mold — the whole top
of the spore case with spores is blown off; on right unopened case— on left, case is
being blown off. 3. Sphere-throwing puff-ball — showing a longitudinal section with the
spore mass ready to be thrown out. 4. The spore mass is ejected by the inversion of
the fruiting-body coats. 5. The fly cholera fungus (an insect mold). To the right a
spore has been snapped off with a small surrounding mass of sticky fluid which serves
to fasten the spore to another insect. 1, after Engler and Prantl; 2, 3, 4 and 5, after
Zopf.
This fungus forms numerous spores in a case on the end of a
fungus thread. The thread just beneath is much swollen and
under pressure, until at the ripening of the spores the whole
Minnesota Plant Diseases. 33
mass of the latter breaks away and is shot off with considera-
ble force. One of the most interesting devices is that found
in the ball-throwing fungus. This is a very tiny puff-ball, little
larger than a pin head. The spores are not released in a pow-
der as is usual in the puff-balls, but cling together in a ball-like
mass. The outer coats of the puff-ball burst open in star-
shaped fashion and the inner coats suddenly invert, throwing
the ball a yard or more into the air, reminding one of the simi-
lar methods which certain seed plants, as the common touch-
me-not, utilize to cast their seeds abroad.
Spore resistance. Just as one finds great diversity in the
form and method of production of fungus spores, so also may
one find great differences in their powers of resistance. The
presence of moisture is often a crucial factor in determining
the life of a spore. The spores of many of the algal-fungi,
most of which are aquatic in habit, cannot endure a dry atmos-
phere for any considerable length of time. This is particularly
true of the swimming spores, which are peculiarly adapted to
the water habit. When such spores are dried they lose their
power of germination — they are dead. The great majority of
fungus spores can. however, endure desiccation with perfect
impunity. Such spores as smut spores have been known to
retain their vitality for eight years or more in an air-dried con-
dition. The spores of the ordinary green molds are also capa-
ble of living in dry atmospheres for a very long time. That the
atmosphere of an ordinary room contains many such spores in
full vigor of life can readily be demonstrated by exposing nutri-
ent gelatine to the air. when colonies of green or blue molds
will be produced in a few days. Such spores are always, after
their maturity, ready for germination.
Moreover, the air-dried spores of fungi are in general capa-
ble of resisting high and low temperatures, much more so than
spores in moist conditions. Blue mold spores can survive dry
temperatures of several degrees above the boiling point of wa-
ter. Rut under moist conditions they never survive this tem-
perature; in fact, they succumb at temperatures considerably
below it. The common treatment for smuts is based on this
fact, for smut spores perish in water considerably below boiling
water temperature. On the other hand, dry spores can endure
34
Minnesota Plant Diseases.
very much lower temperatures. Very many spores of our
fungi must be able to endure forty degrees below zero Fahr. to
pass the winter. In fact many can undergo still lower temper-
atures and survive.
Conditions of spore germination. When a spore is placed
under proper conditions of moisture, temperature and of other
factors, it germinates, i. e., grows out into a fine thread which,
if conditions remain favorable, develops directly into the fun-
gus mycelium. By far the largest majority of fungus spores
are capable of germination as soon as they are ripe, provided,
of course, that such
external conditions
as light, moisture,
etc., are favorable.
Many so-called rest-
ing spores are forced
to undergo a cer-
tain resting period
after maturity be-
fore they can germi-
nate. Such spores
are provided with
thick coats for pro-
tection. This resting period is often connected with the suc-
cession of seasons. For instance most of the rust winter
spores germinate best in the following spring and cannot be
made to germinate before that time. Moreover, they retain
but a decreasing vitality as the following summer passes, and
are usually incapable of growth in the fall. Such spores are
adapted closely to the seasons. Not only resting spores but
other non-resting spores may also evince such conditions.
Rust summer spores are generally incapable of germination
after the summer in which they are formed, though some are
probably capable of surviving the winter in vigorous condition.
Such adaptations are of course especially bound up in the pe-
culiar habits of the fungus.
FIG. 15. — A caterpillar-fungus (Cordyceps) spore. A
germinating spore at different successive stages of
several hours apart. The small resulting mycelium
is seen below. Highly magnified. By the author.
Chapter III.
Fungi. Fungus Life Methods.
jr
Parasitism and saprophytism. \Ve have already seen how
fungi have adopted two methods of nutrition, the parasitic and
the saprophytic. It may now be pointed out that there is asso-
ciated with these methods of nutrition a further difference, viz. :
that of reaction to certain impulses. When a certain parasite
comes into close contact with a suitable host plant, it is at-
tracted or reacted upon by that plant. In other words, it re-
ceives an impulse from that plant which results in certain pecul-
iarities of growth, e. g., the sending out of sucker threads or
organs, and the final result is the parasitic mode of nutrition.
The saprophyte cannot respond to this impulse, no matter how
closely its threads may be associated with another plant. It
has not learned to respond and so is forced to obtain nutriment
in other ways. i. e.. in the saprophytic mode. Some plants,
however, seem to have partially or imperfectly learned to avail
themselves of the parasitic habit, while during the greater part
of their lives they are true saprophytes. That is to say, at
times in their development they may become parasitic, though
they are nominally saprophytic. Such are known as half-
saprophytes. Some of the blue molds and especially the wound
parasites of trees furnish good examples. Again there are cer-
tain fungi which are for the greater part of their lives parasites,
but which are capable of passing, even for a considerable period
of time, to a saprophytic habit. Some smuts are able to do
this. Such plants are known as half-parasites. True sapro-
phytes are those whose whole life is saprophytic. e. g.. most
mushrooms; while a true parasite draws nourishment from its
host plant throughout the life of the latter. < )f true parasites
the rusts furnish excellent examples.
Saprophytes. True saprophytes cannot in any way obtain
their nutriment directlv from living cells. But since, on account
36 Minnesota Plant Diseases.
of lack of leaf-green, they are unable to manufacture starch for
themselves they are forced to depend on the products of other
plants or animals. Such elaborated food stuff is found in many
different forms both in animal and plant remains. Saprophytes
which are adapted to growth on special substances often re-
quire such materials both for development of the mycelium and
also for the germination of spores. The following are the more
common habits of saprophytes :
The yeast habit. The yeast are fungi which grow luxuri-
antly in sugar solutions of one kind or another. In nature they
occur, for instance, on the ripe berries of grapes, especially
where a berry has broken open and the sugary juice exudes.
In this 'juice the yeast plant thrives. Again in the slimy fluxes
of tree trunks, yeasts often grow well. The yeast plant is
microscopic in size and propagates with great speed. This
speed is often facilitated by the fluid condition of the medium
in which the yeast is placed, because the new plants when bud-
ded off from the old can easily separate. This is not true of
yeast growing in solid starch paste. The yeast usually exerts
a peculiar effect upon the medium in which it lives. It exudes
at the surface of its cells a chemical substance known as a fer-
ment and this substance has the power of splitting up the
sugar into two substances, carbonic acid gas, which escapes as
tiny bubbles, and alcohol, which remains in the solution. The
escape of these bubbles is the well known effect which is pro-
duced in fermentation, though not all yeasts cause fermenta-
tion. Preserved fruits sometimes "work," gas bubbles arising
to the surface. Such may be caused by yeast plants which were
allowed to get into the preserves before sealing. Two great
industries are founded upon this fermenting power of yeasts.
The raising of dough in bread-making is caused by the produc-
tion of gas bubbles in the action of growing yeast plants upon
sugary solutions, and thus bread-making is dependent upon
this process. The second is the process of brewing. The abil-
ity of yeast to break up sugars into alcohol and carbonic acid
gas is again utilized, but the alcohol is here the chief object of
the employment of the yeast.
Water-mold habit. .Almost all water molds and fish molds
live in a submerged condition. Manv of the fish molds are
Minnesota Plant Diseases. 37
half-saprophytes, since they are capable of attacking living fish
or other water animals. As saprophytes, however, the water
molds obtain their nourishment from the water in which they
are continuously bathed and in which organic food stuff is
found in solution. In stagnant pools or ponds they may be
particularly abundant. They are often sensitive to the amount
of acid in the water, preferring very slightly acid water. Such
plants have their food material easily accessible, absorbing it
at all points of the mycelium.
Dung-dwelling habit. Very many fungi are constantly
found on the dung of certain animals. Particular fungi are
often to be met with only on the dung of certain species of
animals and on the other hand some are almost constantlv to
FlC. 16.— A dung-dwelling fungus (I'ilobolu*) >•( the black r.mM itrnui, on horse <|IIIIK.
The threads, hrariiiK spore-cases, are seen pointing in parallel directions. Pli..t<.Ki;t|>li
l>y 1". K. Huttcrs.
be found on the dung of these animals if placed under proper
conditions. For instance, certain molds grow on fresh horse
dung and almost without exception one will find this fungus
if the horse dung is placed under favorable conditions of
moisture and heat. There are two ways in which the fungus
spores get into the dung of animals. They may fall on the
dung from the air or they may be deposited with the dung.
having previously passed through the alimentary canal. In
the latter case thev arj of course taken in with the food of
jjr ^^s.
38 Minnesota Plant Diseases.
the animal. Many of the latter fungi have so become adapted
to this passage through the canal that they require the higher
temperature and the previous action of the digestive fluids of
certain animals before they will germinate. Such are some
of the little black "burnt-wood" fungi which always appear on
horse dung when the latter is allowed to remain for several
weeks under a bell jar in moist
conditions. Besides these burnt
wood fungi, the common inhab-
itants of the dung of our ordi-
nary herb-eating animals are
members of the mushroom
group, the molds and the cup
fungi. The specialization of
many forms to the dung of cer-
tain species of animals is, of
course, explained in the prefer-
FIG. 17. — The same fungus as in Fig. r , 1 • 1 r
16, greatly enlarged. The spore case CnCC OI tllC ailimal for Certain
has a svringe-bulb thread-end, below, r , , . r 1 • i •
which 'throws off the spore mass, foods, the remains of which in
usesp°onrees°n %£&££?& R the animal dung are most favora-
K- Butters- ble for the fungus.
Earth-dwelling habit. On the forest floor or on the ground,
in fields, from the thaw of early spring until snow flies in fall,
one sees fungi of one sort or another. Such fungi appear to
take their substance from the soil since their mycelium is
branched and scattered in the earth. However, if these fungi
were removed and placed in pure sand where no plant or ani-
mal remains were present, or where no substances had been
leached out of dead wood, leaves or roots, and diffused through
the soil, they would be utterly unable to develop. That is to
say, they are unable to live in plant-free or animal-free soil, and
so-called earth-inhabiting fungi in reality draw their nourish-
ment from substances deposited in the soil or in solutions in
the soil water. It is very noticeable that one finds numerous
fungi in the neighborhood of old, partially decayed stumps or
tree trunks, where bits of the wood have been scattered about
and where the water has long been soaking through the wood.
The forest floor is of course usually a humus soil, one which
has been built up for inches, or even feet, by the deposit of
Minnesota Plant Diseases.
39
plant debris from year to year. Often apparently earth-inhabit-
ing fungi can be traced back to their attachment to wood lying
buried in the soil, and many plants which may apparently live
both on the soil and on the wood belong to this category.
FIG. IS. — An earth-dwelling fungus (Lri>i»ta pmocrai of the «ill luiiui. Original.
Among the earth-inhabiting fungi the mushroom group is per-
haps most prominent, but a host of other fungi have a similar
habit. Club fungi, many pore fungi, puff balls, carrion fungi,
cup fungi, and saddle fungi are found among the commoner
forms.
4o
Minnesota Plant Diseases.
Wood-dwelling habit. A great host of saprophytic fungi
grow upon wood — on sawed timber, fallen logs and on the ex-
posed heart wood of living trees. They constitute the great
timber diseases — the chief agents of the rot of wood. Railroad
ties, mine timbers, house foundation timbers, in fact, wood,
wherever it is placed in continuously moist, dark places, quickly
undergoes a rotting which is caused by these fungi. The wood
of all our trees is subject to the attack of some of these fungi,
but one kind of fungus is often confined to one kind of tree
timber. For instance, the birch pore fungus is found only on
birches. As a general rule, these fungi are not able to live in
the bark of trees, hence they can gain entrance to the wood of
living trees only through wounds in the bark. When once such
an entrance has been obtained, the fungus remains in the heart-
wood — which is of course dead even in healthy trees — and sets
up a decay which may finally cause the tree to become hollow.
Such a hollow tree may live for years, since the attacking fungi
may be unable to injure the sap wood in which the living
cells are found. Wood-inhabit-
n
fungi obtain their nourish-
F ic,. 111. — A \v(!()(l-(hvcllin«; funuus d>;il-
dinia vernicosa) on a dead stick of
wood. This is a burnt-wood fungus.
Original.
ment from the wood in which
the mycelium is buried. The
"woody" character of wood is
largely given to it by a substance
known as lignin. The timber
saprophyte is able to secrete a
chemical which can break down
this lignin just as the ferment of
the yeast cell breaks down sugar.
When the lignin is broken down
the wood no longer gives the
characteristic chemical tests for
lignin. The wood has then been
converted into "punk," is brittle
and soft and crumbles readily.
This action of the fungus is in
all probability often aided by the
.
aCtlOll of baCtCHa. \\ OUlKl Sap-
ropilvtcs gain entrance to the
Minnesota Plant Diseases. 41
heart-wood through a wound in the bark but never attack the
sap wood. Some half-saprophytes are capable of attacking the
sapwood after an established saprophytic life — thus becoming
parasitic in habit. Such fungi are known as wound parasites.
They live most of their lives as saprophytes and are capable of
living for an indefinite time as such. The wound parasites are
dangerous enemies to forest and shade trees. The injuries and
wounds through which fungi gain entrance to a living tree may
be caused in numerous ways which will be more fully discussed
later. Storms, hail, insects and rodents are among the more
common agencies.
Leaf-dwelling habit. There is a great host of very minute
fungi found on dead leaves, while the latter are still on the tree
or after they have fallen. For the most part they are "burnt
wood" fungi but one often finds among them small fungi of
the mushroom group. In fact, most of those fungi found on
the leaf mold of our forest floor are in reality leaf saprophytes.
The number of such plants is very large and includes fungi of
very different kinds. Most conspicuous, perhaps, are the fleshy
fungi of the mushroom group which, on the undisturbed floor
of the hard-wood forests in the northern part of the state, often
occur in astonishing abundance. The burnt wood fungi are
also very abundant.
The leaf saprophytes, as well as the wood saprophytes, are
of great importance in nature's economy, for they are the
agents through which the dead plant structures are gradually
disintegrated or broken down until finally the constituents are
again mingled with those of the soil and air. The substances
are actually burned by this process until they arc reduced t»»
soil and air constituents. If this fungus and bacterial disinte-
gration of wood and leaves were suddenly to cease all over the
world the earth's surface would quickly be cove-red with the
debris of leaf-green plants and its physiognomy would be vastly
changed. Many of the plants of this day would require impor-
tant alterations in their habits and form to survive such a
change, as they would at present be unable to exist among the
fast accumulating debris. Plants of low stature on the fores!
floor would probably succumb first and if one imagines the
process to continue indefinitely only the taller plants would
42 Minnesota Plant Diseases.
survive. These saprophytes are therefore of great economic
importance in two ways. In man's narrower economy they
are directly injurious in the enormous losses sustained in the
decay of woods and timbers. In the broader economy of
nature they are of inestimable value for they are the garbage-
destroyers which keep down the accumulation of plant debris.
As such their use vastly outweighs those effects detrimental to
man's interest.
Bees-nest-dwelling habit and others. Certain fungi, whose
near relatives are the blue molds, are often found on nests of
bees and wasps. They have learned to utilize for their nourish-
ment the material of which the nest is made and so well have
they learned this method that they are unable to thrive on
any other material. One therefore finds certain fungi confined
to such material. Other fungi also related to the blue molds
are found on horn. They are able to produce a horn-destroy-
ing substance which makes the horn material available for the
fungus food. One finds such fungi on old cattle horns, or
horses' hoofs, and it is only on such substances that they are
found. Again, certain fungi occur on bones and still others
on feathers. One of the most common of the feather-inhabit-
ing fungi is also a blue mold relative.
Fungus-dwelling habit. A very common habit among
fungi is that of living on other fungi. This is especially the
case among those molds which live on plants of the mushroom
group. A mushroom placed in a closed moist chamber will
soon be covered with mold-growths of various kinds. These
molds are for the most part, truly saprophytic, though some are
capable of parasitism during a part of their life history.
Honey-dew-dwelling habit. There is a great group oi
fungi which are known as "honey-dew" fungi and for the most
part belong to the "burnt wood" groups. They are true sapro-
phytes and live on the excretions and secretions deposited by
various insects upon the surfaces of leaves and twigs. They
often show an exact selection for the secretion of certain kinds
of insects. A fungus of spongy appearance, for instance, al-
ways appears on the woolly aphis secretions. After the death
of the insect the dead remains of the body become incorporated
with the secretions and the whole forms a mass in which the
Minnesota Plant Diseases. 43
fungus thrives. The mycelium of such honey-dew fungi is usu-
ally black in color and looks like partially burnt wood. These
fungi are usually true saprophytes and do not attack the living
leaves or plant parts on which they develop. They may, how-
ever, grow in such abundance on the surface of the leaves that
they cut out the light and hence injure the plant by prohibiting
the leaf in its starch-making function. The secretions of in-
sects, especially when the latter are abundant, are often evenly
distributed over leaf surfaces and hence the fungus may be-
come very evenly and abundantly distributed over the foliage.
Food-mold habit. Jt is the common experience of every
housewife that bread and cake, and starchy material in general,
is subject to molding. Such molding is due to the presence of
certain fungi known as black or bread molds. They develop on
all kinds of starch foods and especially where these are kept
moist, as often happens in improperly ventilated bread boxes.
Such fungi will commonly grow in sugar solutions. The molds
of preserves are also common enemies of the housewife. These
are for the most part fungi of the blue or green mold group.
\Yhen fruit is preserved in jars spores of such molds are intro-
duced with the fruit and those near the lid have access to the
included air or to air which leaks in through imperfectly fitting
covers. These spores develop into the blue or green mold
plants and produce the scum which is so often found under the
jar covers. When paraffin is poured on preserves it forms a
close-fitting, air-tight cover and does not allow any molds to
develop. It is well known how cheese when allowed to remain
under moist conditions for any length of time will produce,
especially on the rind surface, green patches of mold which,
unless removed, increase in size until they cover the whole
cheese. This mold is a saprophytic fungus and the green color
is due to the millions of spores produced on much-branched
threads. Green molds are purposely cultivated in certain kinds
of cheese to which they impart peculiar flavors.
"Mildew" of clothes. When moist clothes are left in closed,
badly ventilated receptacles for any length of time they "mil-
dew" or get moldy. This condition is due to the growth of
fungi which feed on the cotton or wool fibers. It is only under
moist and undisturbed conditions that such will grow. An air-
44 Minnesota Plant Diseases.
ing dries out the cloth and the fungus perishes. Moldy clothes
have usually lost their firmness because the fibers have been
partially disintegrated and weakened by the fungus.
Egg-inhabiting fungi. Not all rotting of eggs is caused by
fungi, as bacteria are chiefly responsible for these processes.
Mold fungi, however, do occasionally penetrate, especially
through the cracks in the shells, and live saprophytically upon
the albumen. The latter makes an excellent nutrient material
and the fungus usually thrives here though it cannot form any
spores unless air is admitted. The keeping of eggs in lime or
in cold storage serves the same purpose — the prevention of the
development of fungi and bacteria.
Half-saprophytes. Intermediate between pure saprophytes
and pure parasites are those fungi which can live under either
conditions of life. Some are, however, typically saprophytes
and are usually found growing under saprophytic conditions,
but are capable of parasitic life under other conditions. As a
rule, such fungi do not show any great specialization or exact
selection in their parasitism. They are not confined in their
parasitic life to certain specific kinds of host plants but often
attack plants of widely related groups.
Ripe rots of fruits. Many of the fruit rots are due to fungi
of this class. Some of the green molds and also of the bread
molds are able to penetrate the thin skin of some fruits and
attack the living cells within in the manner of a parasite. In
the killed portions the fungus continues to live as a saprophyte.
The living substance in most fruits is at the time of ripeness
practically dormant and contains a great deal of food material,
both of which conditions serve to make it easier for those fungi,
which have not yet learned thoroughly, but only in an amateur-
ish way, the parasitic life, to obtain nourishment. The low vital-
ity of the fruit-cell protoplasm is insufficient to ward off the at-
tack and the large amount of nourishment is an alluring reward.
Hence these molds may live for a short time as parasites and
then continue their saprophytic life. In fruits a great deal of
sugar is stored up and this furnishes the nutrition. The fungus
gains entrance through thin-skinned fruits or through cracks in
the skins. Those with thick skins are capable of warding off
such fun<ri. Bruisine: or crushing of berries or fruits mav not
Minnesota Plant Diseases. 45
only injure them so that the fungus can gain entrance, but ex-
uding juices will often furnish nutrition where the fungus can
build up a strong mycelium from which the attack upon the
uninjured parts may be better carried on.
Damping-off fungi. Another half-saprophytic habit is that
of the damping-off fungi. These fungi are usually found under
very moist conditions and feed upon plant and animal debris
in the water. One of the most common of these fungi (Pythi-
um debaryanum) requires a very considerable amount of water
for its development. When it comes into contact with seed-
lings, especially of the mustard family, it is capable of attacking
the young plant at about the surface of the ground and kills
the tissues. The plant falls over and dies. In this way whole
beds of seedlings may be destroyed in a few days. This fungus
is never able to attack old plants. The weakness of the seed-
lings lies in the fact that the living substance is not yet pro-
tected by thick coats of cork and cuticle as it is in the older
plants. When the seedlings have been killed, the damping-off
fungus continues to live as a saprophyte. The fungus is not a
highly proficient professional in its parasitism for two reasons:
First, just as do the mold fruit rots, it exercises no particular
selection for special kinds of hosts, but will attack almost any
plant in the seedling stage; and. second, it kills its host as soon
as it penetrates, thus preventing any further service which the
host might pay to its parasite. Rusts and smuts, as we shall
see later, are much more proficient in this habit of life than is
the damping-off fungus.
Wound parasites. Perhaps the most important of all half-
saprophytes are those which have already been mentioned un-
der wood-inhabiting fungi as wound parasites. These fungi
are usually found on dead wood. The bark of trees ordinarily
refuses to them entrance to the tree trunk, since the fungus
threads are incapable of forcing their way through layers of
cork. When, however, a wound occurs which lays bare the
wood, this difficulty is overcome and the fungus thrives in the
heart-wood. \fter building up cons:derable mycelial strength
in its saprophytic life it proceeds to attack the growing zone
of the trunk, i. e.. where the sap wood joins the bark and where
the living substance is protected by very thin walls. The host
46
Minnesota Plant Diseases.
I'lG. 20. — A wound parasite (young specimen of Pleurotu:
are formed in a knot-hole of an unprune
ulniarius). The fruiting bodies
tree. Original.
Minnesota Plant Diseases. 47
is thus slowly killed and the fungus continues to live on in its
saprophytic way. The wounds, through which these fungi
penetrate, may be caused in many ways: the breaking of
branches in storms, or the wounds by falling trees, the rubbing
together of trees swayed by the wind ; injury by cattle and
deer; lightning strokes; frost cracks; hailstones, sun scalds,
holes of woodpeckers, squirrels, boring insects : injury to roots
by burrowing animals. Moreover, man himself is responsible
for many such opportunities for wound parasites, chief among
which are the wounds of shade and orchard trees in pruning.
Such wounds should be covered with tar or some other sub-
stance which will prevent the development of the fungus myce-
lium. Of the wood parasites by far the greater number are allies
of the mushroom group. Gill fungi and pore fungi and a few
burnt-wood fungi are also found in this class. The best known
is the common fall- or honey-mushroom which occurs in clus-
ters at the bases of stumps and trees in the autumn. Many of
the very common "shelf fungi" are also in this class. Xot all
half-saprophytes are dependent upon wounds for their entrance
to the tree trunk. A few such, as the honey-mushroom, may
gain entrance by attacking the smaller roots with a shoestring-
like strand composed of thousands of threads. The latter pene-
trate the bark to the growing layer just beneath. They then
enter upon a parasitic life and make their way up through the
roots to the stem. In this way the fungus can proceed from
one living tree to another and cause epidemics.
Chapter IV.
Fungi. Plant Partnerships. Parasitism.
Equal partnerships of plants. Plants often live in very inti-
mate relationship with each other. Sometimes this intimacy
works out to the injury of one and to the benefit of the other.
It may result in benefit to both partners or in what may be
called an equal partnership of plants. When two plants find
such an intimacy beneficial they may learn to modify their
FIG. 21. — A lichen. A plant with equal partnership of fungus and alga. After Atkinson.
habits and even their structure in such a way that both may re-
linquish the fulfillment of some duties and will depend on the
partner for the accomplishment of that work. In this way the
Minnesota Plant Diseases. 49
two plants may work as one individual, one unit, though really
composed of two plants. Such are the organisms known as
lichens, which occur in abundance as flattened crusts on rock
surfaces or on the trunks of trees. Each lichen is composed
of a fungus and an alga. The algae are for the most part rela-
tives of the flower-pot algae, while the fungi are almost all rela-
tives of the cup fungi. The little green algal spheres are en-
closed in dense wefts of the fungus threads. To the former is
assigned the task of starch-making on account of the leaf
green, to the latter the task of protection and also of the ab-
sorption of mineral salts from the soil. Together the two
plants thrive, while, if separated, the fungus at least would
perish and the alga would probably not thrive so well. This
partnership is therefore of benefit to both plants and the result
has been a unifying of two organisms into one. A somewhat
similar living together is also encountered among certain
plants and animals, e. g.. the little wheel animalcule which is
always found in the small cup-shaped portions of certain leaves
of one of our common liverworts. The cup furnishes a pro-
tected harbor for the wheel animal and the plant probably de-
rives nitrogenous food from the animal, and thus a living to-
gether on equal terms is effected.
Unequal partnership host dominant. The number of
equal partnerships among plants is of comparatively rare oc-
currence. In a vast majority of cases one partner becomes
dominant and the benefits are shared unequally, if not entirely
appropriated by the dominant party. In a very few of those
very numerous cases when a fungus and a leaf-green plant en-
ter an unequal partnership the leaf-green plant is dominant,
and what might be termed nutrient parasitism arises. In such
cases the fungus derives nourishment from the soil and trans-
mits it to the host plant, getting, as far as one can see. no bene-
fit in return. In other words, these fungus partners of leaf-
green plants behave much as do the tiny absorbent root hairs
which are commonly found on the roots of leaf-green plants.
Most of our native orchid plants as well as many foreign mem-
bers of the same family possess such a fungus partner. Some
of these orchid plants show no external evidence of the pos-
session of fungus partners, still retaining their leaf-green in
50 Minnesota Plant Diseases.
undiminished quantity. In other cases, where the orchid plant
has learned to derive more of its nutrition from the fungus
partner, it may economize in its own structure and labor and
dispense with some or all of its leaf-green. As a matter of
course, the leaf-green organ would also be reduced. Such
plants have a yellowish appearance with little or no green color
and the leaves are mere bracts. The well-known coral-root
orchid is an excellent example of such a plant. The little plant
known as Indian-pipe is an even more conspicuous example.
It is a little forest-floor plant, whose relatives are members of
the blueberry family, and has formed a very effective fungus
partnership. So great have its profits become that it has entire-
ly dispensed with leaf-green and derives all its nutrition through
the fungus in its roots. The leaves consequently are reduced
to mere colorless scales and the whole plant has a pure white
appearance. There are many other plants, however, which
have fungus root-hairs but which have not yet abandoned their
leaf-green apparatus for starch-making. They may also pos-
sess ordinary root hairs in addition to the fungus. For in-
stance, many oak trees, and perhaps most plants of the heath
family, possess a subservient fungus root partner. Further in-
vestigation will probably show many more plants with this
same device, as the list is constantly increasing.
Bacteria and bacteria-like plants are also met with as sub-
servient root partners of the green plants. Such are the or-
ganisms of the root tubercles which are so commonly found on
the roots of plants of the pea family. These bacterioids are
capable of converting nitrogen, one of the unavailable gaseous
constituents of the air, into an available compound, and thus
prove of great benefit to the host plant. Often special struc-
tures are formed upon the roots by the stimulation of the fun-
gus or bacteria and in them these organisms are found. Such
structures are usually tubercle-like bodies, as in the clover
roots; or they may be dense, grape-like clusters of tubercles,
as 'are found in the roots of alder trees.
In recent years it has been asserted by a French botanist
that the well-known potato tubers, which are swellings of the
underground stem of our common potato plant, are due to an
infection bv a certain fungus. This infection is said to be fol-
Minnesota Plant Diseases. 5 i
lowed by the excessive growth of the stem at the infected
points. In many of these unequal partnerships we find again
the welding together of two organisms into one individual, a
phenomenon comparable with that in lichens, but with a differ-
ent final result, at least as far as nutrition is concerned.
Unequal partnership — fungus dominant. Parasites. An
overwhelming majority of the partnerships between fungi and
leaf-green plants result in exclusive benefit to the fungus, and
this condition is usually designated as parasitism. The host is
subservient and the fungus is dominant. It may not be the
entire host, though this is so in some cases, that is robbed of
nutrition, but special parts only may be attacked and forced to
nourish the fungus. From the standpoint of the host plant it
may be termed destructive parasitism or simply parasitism in
the narrower sense. The destructive effect is the ultimate
effect received by the host plant as a unit. The immediate
effect of such parasitism may be very local and may be in the
nature of a stimulation. Moreover, the living together of a
parasite with special parts of its host often produces again, as
in the lichen, an essentially new individual composed of the
fungus and the host plant-part.
Witches'-brooms. Such "individuation" is best shown by
the structures known as witches'-brooms. Many of our com-
mon trees are attacked by certain fungi, the latter chiefly rusts,
whose mycelium becomes confined to a certain well-marked re-
gion of the host plant. This part of the host behaves in a
peculiar manner. The branches are usually larger than nor-
mal, are more numerous, and often, again, profusely branched.
The whole mass of branches looks like a little bush growing
parasitically on the host. Moreover, the bush usually arises
from one point on the host plant and the main branch of the
bush, although it may be a lateral branch of the tree, behaves
as though it were the leader and grows straight up in the air.
This brings the bush still more into prominence and demon-
strates the individualistic character of the broom. Such bu>hes
are known as witches'-brooms. The branches usually bear
leaves which fall early and arc often yellowish, having lost
some or all of their leaf green. This serves to point out an-
other important feature of the broom, vi/.. that, as an individ-
Minnesota Plant Diseases.
Minnesota Plant Diseases.
53
ual, it is living parasitically on the remainder of the host plant.
That the broom itself is not injured, but rather stimulated, in
its growth is seen by the production of such numerous and
large-sized branches. But the ultimate effect upon the whole
I'IG. 13. — Witches'-broom on balsam fir, caused by a rust fungus (. \ecidium rla(imiin).
The branches of the broom arc vertical instead of horizontal, as are the normal, un-
diseascd branches in the ni;ht of the picture. <hiiMti.il.
plant is injurious because the normal balance of nutrition and
work has been interfered with for the rapid production of a
group of larger but worthless branches. In a word, therefore,
the witches'-broom mav be described as a bush- or broom-like
54
Minnesota Plant Diseases,
individual, formed by the partnership of a fungus and certain
branches of the host, and living at least partially as a parasite
upon the remainder of the host plant. It behaves as does a par-
asitic mistletoe plant and is not unlike it in appearance. Most
of the witches'-brooms of Minnesota trees are due to rust fungi.
One of the most common is the birds-nest broom upon red
FIG. 24. — Witches'-broom on white spruce, caused by a mistletoe (Razoumofskya pusilla).
The spruce is badly affected. Numerous brooms are seen below and the whole upper
part of the tree is broomed. (See also Fig. 25 and Fig. 101.) Photograph by author.
cedars. These brooms occur in great numbers in many parts
of the state and look like crows' nests in the distance. The
branches are very numerous and the broom stands on a lateral
branch like an independent plant. The leaves are not like the
Minnesota Plant Diseases.
55
ordinary leaves but are larger and very spiny, and stand out
from the branches just as do the leaves on a very young plant
of red cedar or in a similar fashion to those of the common
juniper. At the bases of the leaves may be found in spring the
brown cushions of spores. Another very common broom, espe-
cially in the northern part of the state, is that on the balsam fir.
This broom is much larger than that of the red cedar and the
branches are often very long and wavy and are thicker than
their sister unbroomed branches. The leaves are thickish, and
are yellowish in color and fall very early, never lasting as long
Mi;. -."). — An nilar^f! view of a broom on the spruce shown in hi;. in -i. The distorted
hush-like appearance of the broom is very marked. The mistleti>e plants can IK- wren
on the smaller branches. (Set Fig. 101. ) Photograph bv author.
as the ordinary leaves. It is clear that the broom must derive
most if not all of its nourishment from the neighboring parts
of the fir tree. Such brooms may l>ecome ten feet or more in
diameter. The fungus partner of this broom is also a rust fun-
gus and the spores are produced in great abundance in late
spring or early summer. Another common broom is found on
56 Minnesota Plant Diseases.
cherry trees. Almost any kind of cherry is subject to broom-
ing. The broom branches are usually very numerous and the
leaves do not acquire the usual regularity of form but are often
distorted. This is especially noticeable where the fungus part-
ner forms its spores. The latter are produced usually on the
lower surfaces of the leaves over which a grayish filmy coat
spreads. This fungus belongs to the sac fungi and is a relative
of the cup fungi. Although it produces no cups yet the spores
and sacs are arranged in a similar fashion. Birch trees some-
times carry brooms which are caused by fungi of the same
group.
Witches'-brooms are not always caused by fungus attacks.
Insects are sometimes also able to produce them, but in many
cases the origin of the broom is unknown. In the latter
category stand the brooms which are sometimes found on pine
trees, occasionally attaining a diameter of over ten feet.
Other examples of individuation. Witches'-brooms are not
the only cases of the building up of a physiological individual
from a fungus and a part of its host. Swellings are often pro-
duced on pine trunks which are five times the thickness of the
adjacent part of the trunk. Such swellings are caused by a
parasitic fungus and may be considered again as individuals
which are living luxuriantly at the expense of the host tree.
Burls on trees are by no means uncommon though their origin
from a fungus infection is not always clear. In many cases
their origin is unknown. Again, such tubercular swellings as
are found on Indian corn, where smut later arises, are in reality
favored individualized parts of the corn with a fungus partner.
Large galls form in allies of the blueberry plant upon leaves
and stem, and these galls are also of fungus origin. A larger
number of examples might be cited but enough have been
mentioned to illustrate the individuation of fungus with plant
parts in a parasitism which is ultimately detrimental to the host
plant. In most cases of parasitism of fungi the host plant does
not in any way show a stimulation of the affected parts and the
absence of any difference in the action of the affected and nor-
mal parts indicates a low degree or absence of individuation.
It is worthy of mention here, however, that parasitic fungi in
general thrive best on healthy plants rather than on weaklings.
Minnesota Plant Diseases.
57
though some weak points in the plant organization may be re-
sponsible for the successful attack of the parasite, as has been
experimentally proven within the last year. In other words, the
most successful parasitic fungi are those which can stimulate
the affected parts of host plants to extraordinary effort, or at
least do not immediately injure those parts.
:
FIG. 26.— "Ilirds-nest" wilchcc'-broom on red cidar caused by the birds nest rust fungus
(GymnOSporangium nidus-avis). The hush like hriMiin stands vertical on the horizontal
branch of the host. The difference between the diseased and healthy leaves is very
marked. The former are very similar to those of the common juniper. Original.
Degrees of proficiency in parasitism. The simplest modes
of parasitism are undoubtedly to be met with in those half-
saprophytes which are just learning the methods of parasites.
Some of these have already been described in certain mold fruit-
rots. Such a beginner can only obtain its food from living
58 Minnesota Plant Diseases.
substance which is in a resting state and which approaches
most nearly the condition of dead proteid material. More-
over, such protoplasm contains much nutrient material. The
fungus kills as soon as it comes into contact. It has not acquired
any particular choice for specific kinds of hosts but attacks al-
most indiscriminately. The damping-off fungus is another
amateur parasite, though it has carried a little farther its ability
to kill. It is able to attack vigorously growing parts, as seed-
lings, but, like the fruit molds, does not exercise any well-
marked preferences in its selection of hosts, i. e., it may attack
almost any seedling. The beginnings of such a preference are
indicated in the great frequency with which it attacks seedlings
of the mustard family. The wound parasites of trees show
likewise a low degree of parasitic efficiency. They require a
mycelium well established by previous growth in the heart-
wood before they can successfully attack the living part of the
tree.
When, now, we examine the powdery mildews, e. g., the
powdery mildew of lilac bushes, we find an improved method of
parasitism. The fungus does not noticeably injure the host,
though it is of course detrimental to it even when the results
are not evident, and in some mildews the results are obviously
disastrous to the host. Moreover, the parasite requires special
hosts and a given mildew is found only on one kind of host,
or only on plants which are very close relatives and so furnish
very similar materials. In other words, the mildew is more
select in its choice of food than the damping-off fungus, and its
method of attack is more complicated and exact in its detail.
Now, if one considers the parasitism of the smut fungus,
e. g., the smut of corn, one sees again an improvement in para-
sitic methods. In the first place the fungus has refined very
much its selective power for food and can now only exist as a
parasite on corn, and is unable to live on any other plant even
of the same family. But when it has once established itself
upon its host it does not immediately destroy the attacked
portion of the plant, as would the damping-off fungus; neither
is it a passive passenger, as is the mildew ; on the contrary, it
stimulates the part of the corn plants on which it lives and
causes that part to grow abnormally larger at the expense of
Minnesota Plant Diseases. 59
the rest of the plant. Then arise the carbuncle-like swellings
of the leaves. If a kernel of the cob is attacked it increases
perhaps tenfold in size. During this increase of size the fungus
is also gaining strength and keeping pace with its partner
plant-part, and when the proper moment has arrived for the
formation of its spores it proceeds rapidly and utilizes all the
extra food stored up by the swollen host plant-parts and de-
stroys the latter rapidly. Such a parasite stimulates its host
to unusual activity for a long time and at the same time pre-
pares to use to best advantage all of the nutrient material laid
up by the host, delaying its destruc-
tive effects until the most advanta-
geous moment. Sometimes, as in oat
smuts, the presence of the fungus is
not determinable until harvest-time,
when the fungus forms its smutty
powder of spores in place of the
grain. This is a very efficient meth-
od of parasitism but, in some respects
at least, the fungi producing grain
rusts are even more capable. The
smut produces but one kind of spore
on its host plant and that is a resting
spore for tiding the fungus plant over
I he winter season. The rust fungus
can produce spores from early spring
to autumn and is able to do this by
forming different kinds of spores at
different seasons. Such a rust will
produce a spring spore, a summer
*pore. and in autumn a so-called win-
ter spore, the latter having the same
function as the spore of the smuts.
This continuous production of spores
Fic.27.-oai imut-a a,c,.,n js of Coursc a vcrv efficient device.
plishol parasitr. Aftrr d. 1 .
t'ii"«"»- In addition t<> the multiplicity of
spores the rust fungi often possess the stimulating powers al-
ready mentioned for smuts. Such have also been described in
witches'-brooms of red cedar and balsam fir. In the simpler
6o
Minnesota Plant Diseases.
cases of rusts all of the spore forms are found on the same kind
of host plant and it is now a well-known fact that the rusts are
extreme specialists in the selection of their hosts. So exact
has this selction become that certain rusts will attack one grain
plant and are unable to attack other even closely related
grasses. In this respect they are among the most proficient
of all known parasitic fungi. Still further complications may,
however, arise. A rust fungus may increase its distribution
by selecting in the spring time another earlier plant for a host,
and produce upon this plant its spring spores. This migration
is the expression of one phase of the education of the most
highly educated plant, parasites known to botanists of today.
In view of these and other accomplishments of these fungi one
has little hesitation in pronouncing them the most proficient
parasites amongst the fungi.
The modes of life of parasitic fungi. In general, there are two
methods of life. The fungus may live on the surface or it may
live within the tissues of the host plant. The powdery mildew
of lilacs lives on the surface of the leaves while the smut of
oats lives inside the tis-
sues of the oat plant.
Those fungi living in the
tissues of their host, how-
ever, come to the surface
when they are about to
produce spores. The sur-
face-dwelling fungus may
derive its nutrition in one
of two ways : it may
send special threads into
the living substance of
the host and through
these sucker-threads
draw nourishment, or
may merely attach itself
to the surface of the
plant and never send
threads into the living-
substance. It is clear
FIG. 28. — An endophytic (internal) mycelium be-
tween the cells of a grass grain. (Fungus of
Lolium temulentum.) Highly magnified. ]!y
the author.
Minnesota Plant Diseases.
61
that in the latter case the nutrient material must first pass
through the walls of the host plant before it can be taken up
by the fungus thread. The interior-dwelling fungi may get
their nourishment in several ways. In many, special sucker-
threads are sent into the living substance of the plant. In
other cases the fungus threads run between the cells of the tis-
sues without ever coming into direct contact with the living
substance. On the other hand, fungi may gain entrance to
the cells arid live entirely within them. Such is the common
method of many very minute water fungi. The sucker-threads
of the various fungi differ considerably in shape and often fur-
nish important marks of distinction, since each fungus may
FIG. i9.— Infection of a tirass leaf by a rust fungus (wheat rust). Above is a summer
spore showing germ-tube*. Itelow it a germ-tube entering through the |>ore of the leaf
and is reaching down in the internal part of the leaf where it soon becomes well
established. After Ward.
have its own peculiar form of sucker. The simplest are little
cylindrical unhranched threads. Again, they may be small
tubercular hyphae; others are branched to form a stubby-fin-
gered, hand-like system of threads. In still other cases the
suckers may be very much branched and the branches may be
coiled up into dense mats entirely filling the cell of the host.
Methods of attack. When the spore of a parasitic fungus
falls on the leaf of a host, it awaits favorable conditions for fur-
ther development. When the moisture and temperature and
other conditions are most favorable the spore sends out a
62 Minnesota Plant Diseases.
thread which in many cases grows directly to a ventilating pore
of the leaf and enters through this pore. In many cases, how-
ever, it is able to bore its way through the walls and thus pene-
trate to the interior. Special threads may be developed to
fasten the germinating spore to the host plant. This is accom-
plished by minute disk-like ends similar to little rubber vacuum
cups. Abundant hairs on the surface of a host plant, or a very
thick cuticle, may lessen the danger to the host of fungus at-
tacks. Some fungi select certain periods in the growth of the
host during which the latter is less able to ward off the attack.
Such is seen in the oat smut and damping-ofJf fungi, which at-
tack seedlings, or again in the wounded trees where a fungus
gains entrance before the tree has had time to close a wound in
the normal manner. Since the selection for a time for attack
is in many cases of great importance to the fungus, the latter
usually forms its spores to coincide with this favorable time.
Fungi which attack the trunks of trees are usually unable to
penetrate the bark unless aided by wounds of some sort, but
they may occasionally penetrate through the ventilating holes.
Mention has already been made of those fungi which require
previous preparation for attack, as is the case in many of the
wound parasites.
The living together with special plant-parts. Parasitic fungi
do not usually live together with all parts of their host plants
but confine themselves to certain organs, or at least show pref-
erence for certain plant-parts.
Leaf-inhabiting parasites. Perhaps the most conspicuous
and common are those which prefer the partnership with
leaves. Most .rust fungi are of this class; most mildews,
blights, leaf-curls and that great group of imperfectly known
fungi which commonly form the so-called leaf spots. The
foliage leaf is usually selected by the fungus, though more
rarely the scale leaves or floral leaves may also be attacked.
Sometimes, as in the leaf-spot, the fungus only inhabits a small
portion ; in others it may pervade or cover the whole leaf. The
leaf-dwelling parasites are perhaps the most destructive of all
fungus parasites, both on account of their number and their
effect upon the starch-making machinery of the plant. The
ease with which the fungi develop in the leaf-tissues is perhaps
Minnesota Plant Diseases. 63
explained by the fact that, on account of the great air-spaces
inside of the leaf, the fungus can easily obtain the air gases
which are necessary for its development; secondly, that
these spaces are always more or less moist on account of the
water vapor given off by the leaf tissues; and, lastly, they are
not too highly illuminated by sunlight. The interior of a leaf,
therefore, furnishes excellent opportunities for fungus develop-
ment and many fungi have availed themselves of these oppor-
tunities. Moreover, the fungus can often gain easy entrance
through the air pores on the leaf surface. When a leaf-fungus
dwelling in the interior is about to produce spores, it forms the
latter usually at the surface of the leaf. Sometimes, as in the
potato-blight allies, it shoves the spore-bearing threads out
through the air pores, but this is not the method in the rusts
Here the leaf surface is broken open, splits out, and the interior-
ly formed spores reach the air through the split. Of course
such an injury, minute though it may be. really injures the leaf
by the interference with the leaf control of water vapor. A
large numl>er of such wounds, together with the injury by loss
of nutrition to the fungi, may cause the death of the leaf. The
spores of the fungi usually appear as a powder or cake uncov-
ered by the upheaval of the leaf surface tissues. In some few
leaf-fungi the spores are formed internally and are only released
by the decay of the leaf.
Stem-inhabiting parasites. The stems of plants furnish an-
other favorite abode for parasitic fungi. In the stems of herb-
like plants the fungus problems of entrance and life are not
very different from those of the leaf except that the tissues are
firmer. Hence we find many rusts capable of living either on
the leaves or stems of a given host plant. But in woody plants,
as in shrubs and trees, the fungus meets with new difficulties
in the nature of a thick layer of bark which must l>e jxMietrated
before the living part of the stem can be reached. Moreover,
the compactness of the tissues and the resultant absence of
larger air-spaces do not make the stem such a congenial dwell-
ing place as is the leaf. In such woody stems, therefore, we
find almost exclusively those fungi which are capable of break-
ing down woody tissues and feeding on them. It has already
been stated that these fungi must usually depend for entrance
64 Minnesota Plant Diseases.
to the stem upon some wound, which will remove the protect-
ing cork layer from the wood. Many burnt wood fungi in-
habit stems both herbaceous and woody. On the latter are
very often found the gill fungi or mushroom allies and the
pore fungi. These fungi are in general long-lived, living from
year to year on a tree trunk and storing up nourishment in
their mycelia. Months and even years of preliminary growth
are often required of such fungi before the spore-bearing or-
gans are produced. Enormous numbers of spores are then
formed and a new crop may be shed every year until the nour-
ishment in the tree trunk is exhausted.
Root- inhabiting parasites. The root is not as popular a
resort for parasitic fungi as either the leaf or the stem, but not
a few find a congenial abode in these parts. They have similar
difficulties to meet as the stem dwellers and are in fact mostly
members of the same groups of fungi. Often the same fungus
is capable of growing up into the tree trunk. The spore-bear-
ing organs are always found either at the surface of the ground
or in air-spaces in the soil, such as in the burrows of rabbits.
In certain grass-like plants a smut is found in the roots and
causes the formation of swollen pear-shaped bodies.
Fruit-inhabiting parasites. A very large group of fungi
inhabit the fruits of flowering plants. The fruits, whether
they be fleshy, like apples, or hard, like nuts, have always some
protective coat, which is a serious obstacle against an invading
fungus. Some fruits are better protected than others in this
respect and the weaker may prove vulnerable to fungus attacks,
e. g., when thin-skinned apples are invaded by mold rots. The
smuts, which are commonly found in the grains of grass-
plants, have devised an ingenious method for a successful at-
tack upon the fruit of the grasses. The fungus gains entrance
to the stem of the plant when the latter is in the seedling stage
and then keeps pace with the growing plant without appar-
ently affecting it at all detrimentally, until the grains are com-
mencing to fill. Then the fungus permeates all of the grain
tissues, appropriates the food material and forms its smut
spores. The ergot of rye and other grains has still another
device for attacking the grass fruit. It does not, as the smut,
live in the point of the stem until the fruit is formed, but at-
Minnesota Plant Diseases. 65
tacks the grain from without while the latter is still very young.
It seems to be able to penetrate the grain coats at this stage
and immediately proceeds to convert the grain into storage
material, packing it up in the dark-coated storage organ known
as the ergot. This is used in the following spring to produce
the spore-bearing organs. The fruit-inhabiting fungi include
members of almost every group of fungi. Fruit-mold rots,
smuts and ergots have already been mentioned. There are
many other burnt-wood fungi beside ergot. Plum-pocket
fungi, cup fungi and algal fungi are also among the inhabitors
of fruits.
Anther-inhabiting parasites. Among the smut fungi are to
be found forms which have developed very strange habits. One
of the most remarkable cases is that of the smut which forms its
spores only in the anthers of particular kinds of plants. The
latter are members of the pink family. The fungus gains en-
trance to the plant before the flower is completely formed and
in the young flower it selects for its abode only the stamens,
and particularly the pollen-bearing part or anthers. It gives
no external evidence of its presence until the flower opens.
When this happens one finds that, in place of pollen, the an-
thers give forth a violet dust of smut spores, ami few, if any.
pollen grains are produced. To the casual observer such
flowers appear to throw off purple pollen while other flowers
of the same kind of plant give off yellow pollen. The fungus
has formed its spores in place of the host's pollen, and when
the anthers open they shed the spores. When insects visit
these flowers they carry smut spores in place of pollen from
plant to plant, thus aiding in the spread of the fungus. These
fungi often prove troublesome pests on plants of the pink fami-
ly, such as carnations, where the flowers are grown for show
plants, because the presence of the fungus cannot be foretold
before the opening of the flower, and after the latter event the
smut spares discolor the flowers s > that they arc worthless for
the market. It can readily be seen that this fungus has car-
ried to a remarkable degree of efficiency its selective power,
having learned not only t«> repress its sj> >re formation until a
most favorable moment but also to choose a most advanta-
geous special floral part for the spores.
5
Chapter V.
Fungi. Parasites on Animals.
An account of the parasitic fungi would be incomplete with-
out some mention of those fungi which attack animals and
cause disease in them. These fungi are becoming more and
more of economic importance, especially in their use m com-
bating insect invasions on agricultural crops. They are fur-
thermore of great interest in the diseases which they cause in
man and the lower animals. In general, these fungus parasites
belong to the lower or algal fungi, the water molds, bread-
mold-allies and insect molds; but not a few are found amongst
the higher fungi, e. g., the caterpillar fungus, the green mold,
and even yeast-like fungi.
Diseases of lower animals. Not even the most lowly
groups of animals are exempt from fungus parasites — on the
contrary, they seem to suffer to an unjust degree. Those
small unicellular animals which usually inhabit the water are
often attacked by the simplest of fungi, also unicellular and very
minute plants. The fungus finds its way through the wall of
the animal cell and draws its nourishment from the animal
protoplasm. Sometimes the fungus is exceedingly minute
and may confine itself to only a special port'on of the proto-
plasm, as do nuclear parasites.
Where (as in the Coelenterates) the host animal possesses
a protective coat of lime the invading parasite may bore
through the lime. The resting stage of these small animal-
cules furnishes an especially inviting host, since here the fun-
gus meets with less resistance. One parasitic fungus is known
to live only on the eggs of the little animals known as wheel ani-
malcules.
The pin worms are likewise subject to fungus diseases and
one often finds an epidemic raging amongst colonies of
these little creatures. As these worms are often greenhouse
Minnesota Plant Diseases. 67
pests such a fungus may become an efficient aid to the horti-
culturist. The method of attack of this fungus is a very un-
usual one. The mycelium is built on the principle of a net in
which the threads of the fungus form loops or meshes. In
these meshes the wiggling pin worm becomes entangled and
every effort to free itself usually results in a securer imprison-
ment. When the worm is held fast the fungus sends out
threads which penetrate the body of the prisoner and absorb
its substance.
Amongst the true worms, fungi have been reported on
the common earth worm. These fungi belong to the fish or
water molds. The little water flea (Daphne) is the host of a
very interesting fungus. This fungus is said to be a relative
of the yeast fungi which are not, as a rule, parasites, but true
saprophytes. The spores of this yeast or yeast-like plant are
long, pointed, almost needle-shaped, and when taken into the
alimentary canal of the water daphne they penetrate the wall
of the canal and get into the body cavity. Here a fight ensues
between the white corpuscles and the spores. If the latter con-
quer they soon commence to divide in yeast fashion and rapidly
use up the nutrition derived from the fluid of the body cavity.
The host animal soon becomes sluggish and dies. Later the
needle-shaped spores are again set free and may be swallowed
by other daphnes.
The crabs have also been reported as hosts for fungi, but
such occurrences have not been very frequently noted. The
parasites in these cases are water or fish molds. Amongst the
spiders a black fungus parasite is known. Even upon the clam
fungi have been reported, but their parasitic nature has not yet
been proven. Shell-boring fungi are often found on the shells
of such animals.
Diseases of insects. Of all the animals the insects are by
far the most popular hosts for parasitic fungi. Most of the
fungus parasites attack the insects in their larval stages, when
the latter, with worm-like habits, crawl through the soil or in
other moist places. Hence the fungi most frequent upon them
are forms of the algal fungi which are also typically aquatic in
habit, though of course many have learned to live in dry situ-
ations. The fungi of insects have certain advantages. In the
68
Minnesota Plant Diseases.
body of an insect there is considerable chance for aeration on
account of the large number of air-tubes which traverse the
insect body. This very probably accounts very largely for the
popularity of the insects as fungus hosts. Of these fungi
the insect molds are very abundant as is also the "burnt wood"
fungus known as the caterpillar fungus, and these two groups
of fungi are responsible for most of the disease epidemics of
insects.
Plant lice have been known to suffer from attacks of both
of these fungi. The common housefly and its relatives are de-
stroyed in enormous numbers every fall by an insect mold
causing a disease commonly known as fly cholera. Such flies
are seen clinging to window panes or the ceiling or walls of a
room, surrounded by a dim circular haze or halo of the fungus
spores which have been forcibly snapped off from fungus
threads and caught on the glass. Of course most of the spores
have been thrown off into the air where they may float about
until they come into contact with another fly. The fungus
continues to form spores as
long as there is available
food material in the insect
body. When spores alight
on an otherwise healthy fly
a fungus thread is pro-
duced which may make its
way through the skin to the
inside of the body and
there continue to grow.
The mycelium soon causes
the death of the insect and
later comes again to the
surface to produce its
spores. Other insect molds have been known to attack com-
mon house fly relatives. The mosquito may also prove a prey
to fungus diseases and attempts have been made to fight
it by aiding the spread and dissemination of those par-
ticular insect-molds which are parasitic upon it. One of the
most remarkable groups of insect parasites are the beetle
fungi, relatives, perhaps, of the black fungi. They are found
FIG. 30. — Beetle fungi attached to an insect.
The black spots at the base are the at-
taching organs. Highly magnified. After
Thaxter.
Minnesota Plant Diseases. 69
on the legs and wing' covers of flies and particularly of water
beetles. They are highly specialized as to their abode, often
occurring constantly on a certain joint of one leg. This defi-
niteness of position is explained in the spore distribution, as
the plant sexes are often separated, growing on different plants,
and the sexual cells of the fungus are brought together dur-
ing the breeding acts of the insects. These beetle fungi are
not, as far as is at present known, harmful to the insect
which they inhabit. In form they are very minute and visible
only by the aid of strong lenses. They usually have the shape
of little broom brushes and are attached by a blackened disk.
The butterflies, particularly in their caterpillar stages, arc
also common prey for the insect mold. Perhaps more com-
monly, however, they are attacked by the fungus known as the
caterpillar fungus, a member of the black fungus group. This
fungus has learned to produce a variety of spores, each special-
ized for a certain purpose. Cylindrical spores are produced
upon orange-colored fruiting bodies in the autumn. When a
spore falls on a caterpillar it sends out germ-threads which can
eat their way through the covering of the caterpillar and enter
the body cavity. Here the threads immediately form long nar-
row spores which are pinched off into the fluid of the body
cavity and can move around easily, thus rapidly spreading the
fungus. These spores germinate immediately and more spores
are formed. Meanwhile the threads produced by these spores
branch profusely and soon permeate all parts of the insect
body-cavity and invade the various organs, finally working
their way even into the muscle fibers. The caterpillar gradually
becomes sluggish and finally dies. After death, the fungus
continues to grow and to appropriate the insect substance for
food. At fist the threads are very thin and are thus able to
work their way with more ease through all parts of the bod\.
As s win. however, as the threads Inxonie very numerous they
grow thicker and lay up nutrition as storage material in the
form of oil and fungus starch. Finally the threads have com-
pletely absorbed all of the insect's soft parts, filling the chitin-
ous covering, and retain in their densely compacted form, the
exact shape of the larva — not < nly in the external form but in
the form of the internal oryans. In other words a inunimv
70 Minnesota Plant Diseases.
and model has been formed ; this mummy contains a great
abundance of food material, but no part of the insect can be
found in it. The mummy now acts as a storage and resting
organ and requires apparently considerable time — months,
perhaps — to ripen. Under favorable conditions this mummy
will send up an orange-colored club-shaped body, which will
again produce the kind of spore which was described at the be-
FIG. 31. — Various kinds of caterpillar fungi with fruiting bodies. (Cordyceps militaris, C.
stylophora and Isaria sp.) The forms of the caterpillars are preserved by the fungus
storage organs and the upright clubs bear the spores. 1 and 2 bear clusters of pinched-
off accessory s lores; 3 and 4 bear sac- spores in capsules. (See chapter 9.) About
natural size. Original.
ginning of this account. Under some conditions, however, the
mummy can be made to produce a dense growth of threads
from its entire surface, so that it looks like a small ball of cotton,
and from these threads another kind of spore is formed. These
spores are pinched off in great numbers. They have the power
of germination and infection of the larva in a way similar to
that of the sac spore already described. Caterpillar fungus
epidemics are not infrequent and thousands of larva may be
Minnesota Plant Diseases. 71
killed in a year. A caterpillar after infection can still crawl some
distance before death overtakes it and thus the scattering of
the fungus spores is materially aided. Attempts, made at vari-
ous times to utilize this fungus to combat grubs, have met
with varying success, but its use has not yet become general.
Silkworms frequently suffer from these fungi and the silk
growers of Europe have lost enormous sums of money
through such epidemics. The beetles are very frequently the
hosts of parasitic fungi, especially of the so-called "beetle fungi",
which have already been mentioned. The caterpillar fungus
and the insect molds are also to be found on the beetle as well
as upon the dragon flies and their allies. Ants, though not very
frequent hosts, have been known to harbor the caterpillar
fungus.
Diseases of fish and lower vertebrates. If we now consider
the vertebrate animals we find also abundant evidence of fun-
gus parasitism. One of the most important cases is that of the
fishes. Both the mature fish and its eggs may be attacked.
FIG. 32. — Dead minnow with fish mold (probably Saprolrgnia thurctii). Ordinal.
The fungi are the water or fish molds. Thousands of fish are
killed off annually by these parasites. They can be seen on
any minnow bait, which has died and been kept for several
days. A filmy mold gradually covers the whole surface of the
minnow. These fish molds are half saprophytes and live ordi-
narily upon dead debris in the water. When, however, they
come into contact with living fish, they may attack the latter
if conditions are favorable. They apparently are unable to
Minnesota Plant Diseases.
FIG. 33. — A spore-case of fish-
mold showing escaping swim-
ming spores; each of the
spores is provided with two
swimming lashes which whip
about in the water and propel
the spores. Highly magnified.
After Zopf.
attack healthy fish unless perhaps
through the respiratory system, but
succeed if the fish are in some way in-
jured, for instance at points where the
scales have been rubbed off. When
once the parasites are established they
gradually spread over the body of
the fish and ultimately cause its death.
The fungus produces an enormous
number of spores which are for the
most part furnished with whip-like
lashes for propelling purposes. Oc-
casionally these fish molds cause epi-
demics and vast numbers of fishes
may then succumb. The occurrence
of several such epidemics is known.
These fungi are very often the cause of
the death of fish in aquaria such as
common gold fish. The danger from
such fungi can be lessened by keeping
the aquaria scrupulously clean so as
to furnish little chance for the sapro-
phytic existence of the fungus. The
infected fish should be removed as
soon as possible to prevent the forma-
tion of more spores. The injuries of
these fungi are not confined to the
fish in lakes and streams but are
sometimes a cause of great loss in the
fish hatcheries where the eggs may be
attacked. Some of the bread mold
allies are also known as inhabitors of
fish eggs. On the Amphibia, the
frogs and their relatives, few fungi
have been found. In this state mud
puppies have been observed, which
have been killed by certain fish molds.
The fungus appeared on an apparent-
ly healthy mud puppy as a thin filmy
spot which rapidly grew larger, coa-
lescing with other spots until the ani-
Minnesota Plant Diseases. 73
mal was completely covered. Meanwhile the puppy gradually
grew sluggish and finally died. Soon after death the fungus
had formed around the mud puppy's body a dense mass of mold
almost an inch thick. All the mud puppies left in the same
aquarium were finally killed by this mold.
Diseases of birds. Birds are not without their fungus para-
sites. However, these parasites are members of a different
group of fungi from those inhabiting fishes and amphibians.
In the latter the parasites are adapted to aquatic habits while
on the birds one finds fungi which have become adapted to
aerial life. The birds offer somewhat analogous advantages
to fungi which one finds among insects; that is to say. abun-
dant aeration furnished by the bird habit of life. One fungus
disease of birds is caused by forms of the green molds which
affect particularly the respiratory organs causing inflammation
of the affected parts. Almost all classes of birds have been
reported as hosts of these parasites. Chickens sometimes suffer
from a comb scab which is also of fungus origin. This fungus,
when raised on gelatine plates, shows similar life habits to the
yeast fungi. In this disease scabs are formed on the comb and
the fungus inhabits the scab spots. The same form, or a close
relative of it, may attack the crop of the chicken and form a
pustule disease. Hens' eggs, as has already been mentioned,
are not infrequently attacked by fungi of the green or black
mold group and egg rot ensues. Such fungi may. however, be
mere saprophytes living on the albumen of the egg.
Diseases of lower mammals. There are several diseases of
considerable importance among the mammalians. The most
serious of these is the disease of cattle known as lumpy jaw.
The cause of this disease is apparently a fungus but its position
in the classification of fungi is not yet known because its spores
have never been observed. It occurs in little nodules which ap-
parently multiply very rapidly. It attacks most commonly the
jaws and mouth parts of cattle and the diseased animal's head
becomes much swollen and presents the lumpy appearance
which gives the disease its common name. The results are
usually fatal. Infection apparently takes place from the food,
particularly from the hay and grain foods, upon which the fun-
gus has been found to exist. The fungus is probably intro-
7| Minnesota Plant Diseases.
duced in cuts in the mouth made by grass blades when the
animal is feeding, and from these points spreads throughout
the mouth parts. Inoculation with the nodules results in the
typical disease. At times the disease becomes epidemic, prob-
ably on account of the prevalence of the fungus in certain food.
The same fungus, or one very closely related to it, attacks
swine. It is not always confined to the mouth parts. Horses
have also been known to suffer from the same disease. In the
lungs of rabbits, cats and dogs the spores of green molds may
lodge. Under favorable conditions of weak resistance, the
spores may germinate and induce inflammation in the sur-
rounding parts, causing the formation of tubercular growths in
the lung tissues. The disease is known as a mycosis. Such
fungus spores injected into the blood of animals may also give
rise to mycosis in various organs of the body. The intensity
of the disease seems to be proportionate to the number of
spores injected or inhaled. This is of course not the cause of
ordinary tuberculosis.
Bread mold allies are reported as responsible for diseases
in rabbits. They gain entrance to the intestine with the food
and produce diseases of the intestinal tract. When injected
into the blood the spores may produce diseased conditions in
the kidneys and other organs and even in the bone marrow.
Death sometimes results from the attack of these molds.
An ally of the yeast fungus, and apparently also of the comb
scab disease of chickens causes in the throat and mouth parts
of young cats and dogs pustules and scabs similar to those
produced in throats of children. The fungus is found in the
scabs and pustules thus formed. Several other external scab
diseases of the skin of animals are produced by these fungi,
as are also the bald spots, accompanied by scabs on the exter-
nal head and throat parts, often found on cattle and less often
on dogs, horses, cats, etc. The latter may be identical with
bald spot disease in man.
Diseases of man. Skin diseases of man. analogous to those
of the lower mammals, are caused by fungi. Ring worm and
some bald spots are prominent among these. They are caused
by fungi perhaps identical with those of lower mammals, at any
rate verv similar to these in all their characters.
Minnesota Plant Diseases. 75
Cases of lumpy jaw in man, though not very frequent, are
well known. The disease is similar in all respects to that pro-
duced in cattle. The fungus is similar and the results are usu-
ally fatal. Infection takes place in all probability from cuts
by splinters or wounds by grass blades, or when a grass blade
is drawn through the mouth or grains in the field are sampled
by biting. The fungus thus appears to lurk in places similar
to those of the fungus of lumpy jaw of cattle.
Green mold fungi also cause disease in man. Some dis-
eases of the outer and middle ear canal are of this nature.
Here the fungus grows as a saprophyte in the ear secretions
and by its presence sets up irritation and consequent inflamma-
tion. It is doubtful if the fungus in this case is a true
parasite. These molds, moreover, when inhaled into the
lungs in sufficiently large quantities, may produce lung and
bronchial troubles. The latter are often asthma-like in their
symptoms. Children are subject to the attack of one of the
yeast-like fungi, similar to the comb-scab of chickens and the
throat troubles of cats and dogs. As with the last two the in-
ternal throat-parts are attacked and scabs and pustules pro-
duced in which the fungus is found, giving rise to sore throats.
Somewhat similar throat troubles have been produced also in
adults by a similar fungus.
Contrast of parasitism in plants and animals. A great dif-
ference is noticeable between the known number of fungi para-
sitic on animals and plants. The former have been estimated
as less than two hundred while the latter must now exceed ten
or fifteen thousand. This difference can. in part, be accounted
for by certain general differences in surroundings. Fungi as a
rule require neutral or acid media, while animal tissues are
usually alkaline. Plants offer in their tissues more air space
and thus furnish more air. which is essential to the growth of
fungi. The body temperature is, in all higher animals, above
that at which most fungi develop under normal conditions, and
finally, the resistance of the white corpuscles of the blood is an
important factor. Fungus parasitism on animals is, with per-
haps the exception of lumpy jaw. an immediately destructive
one. and shows no effect of mutual partnership between fungus
and animal parts.
76 Minnesota Plant Diseases.
Just as with bacteria, so with fungi, — white blood corpuscles
seem to form the garrison guarding against attacks. As soon
as the fungus threads enter the tissues, the corpuscles gather
around them and the battle begins. Moreover, the corpuscles
are often produced in extraordinary numbers in the vicinity of
the fungus attack. They may thus exclude air from the fun-
gus and so materially hamper its growth. Plants have no such
protection and hence suffer more. The fungus may sometimes
encrust itself with lime, as in lumpy jaw, perhaps protecting
itself in this manner from unfavorable conditions.
Chapter VI.
Fungi. Parasites of Plants.
Jtf
Effect of parasite on host. We have already seen that para-
sitism, in the broader sense, of a fungus on leaf-green plants
is always one of two kinds of partnership, equal or unequal,
and of the latter either the host or parasite may dominate.
Now, equal partnerships are rare, and those unequal associa-
tions with dominant hosts are also comparatively few, though
science is rapidly adding many new examples to the list already
known. The greatest number of partnerships are those in
which the parasite is the profit-making partner and the host
Fie. 34.— Damping off of seedlings, caused by a fungus ( I'ythium dcbaryanum) which
immediately kill* the hust plant — a low, though effective, type of parasitism. After
Atkinson.
the loser. It has also been pointed nut that different fungi have
acquired different degrees of efficiency iy obtaining their prof-
its, and that highly specialixed parasites can influence the host
to over-production of food stuffs for the benefit of the former.
78 Minnesota Plant Diseases.
Immediate destruction. The immediate destruction of
plants or plant parts has been characterized as an amateur
method. It is admittedly not as clever a method as is the de-
layed destruction preceded by stimulation. But the perform-
ance of even such amateur methods can be carried to a high
degree of proficiency and that is what many fungi have done.
The green-mold fruit-rot effects its parasitism not only accord-
ing to amateurish ways, but is a beginner in this work. This
is not so with the potato blight, which is an adept at its meth-
ods of killing and feeding on the potato plant. There are
many special methods to be found among these parasites but
they may be brought under these heads : the destroyers of
small areas of plants, the destroyers of whole organs, and the
destroyers of whole plants.
The destroyers of small areas. Among the simplest of the
algal fungi one finds certain kinds which possess a very small
mycelium so that they occupy only a single cell of the host.
This cell the parasite may immediately destroy without effect-
ing any change in the surrounding cells. In some cases, how-
ever, it may affect neighboring cells and these may grow ab-
normally large. Such growth results in the formation of galls.
Galls vary in size from that of a pin head, or even smaller, to
walnut size, and some galls are known to be even very much
larger. Not all plant galls are of a fungus nature ; for by far
the great majority are caused by the sting of insects when the
latter deposit their eggs in the plant tissues. Such are the very
common galls formed so abundantly on leaves or branches of
oaks, as in the nut galls of commerce.
Most small-area-destroying fungi do not confine their at-
tacks to one cell but prey on a large group of cells. Typical
examples of these fungi are found among the leaf spots.
These fungi are exceedingly abundant parasites and are usually
characterized by the destruction of limited, often circular, spots
of the leaf which they inhabit. These spots usually turn brown
and are sometimes fringed with a red or white band. The
spots of strawberry leaves which are so destructive to certain
varieties in our state^ are excellent examples of leaf spots.
Many fungi of this class are very injurious if they occur in
abundance, while others do not perceptibly affect the general
Minnesota Plant Diseases. 79
health of the host. Certain smuts and powdery mildews may
also be confined to small and limited areas. In the former case
the area is converted into a smut heap while in the latter it be-
comes mildewed and later dotted with the very small spore
cases. Most smuts and mildews, however, are not restricted to
small areas. The mildews are seldom confined to small areas
Fie. 35. — Strawberry leaf-spot. The fungus (Sphacrclla fragariar) destroys small arras of
the leaf. Original.
of the leaf surface or even to the leaf itself, though usually this
is its favorite habitation. The smuts, although often occupy-
ing a sharply delimited area, more often occupy whole plant
organs, as fruits or stamens. Moreover, the smut mycelium
always dwells inside of the leaf while the mildew is external in
its habits, except in its sucker-threads. Rusts, though often
confined to certain organs of the host, are not usually restricted
to particular or limited areas.
Methods of killing tissues. There seems to be two ways by
which tissues of the host plant arc killed. The nutrient sub-
stance of the host tissues can be directly absorbed through the
membranes of the fungus thread wall and also, in some cases,
through the wall of the host cell. The substances are with-
8o Minnesota Plant Diseases,
drawn before the death of the host-plant part. In the second
case the fungus produces on the surface of its invading threads
a chemical substance which kills the host plant tissues and the
fungus absorbs its nourishment later from this killed area. It
is only fungi which know the first method that can stimulate
their host to extraordinary growth and over production of food
material, as in the witches'-brooms. The second method is
common among half saprophytes.
The destroyers of organs. Many leaf mildews attack so
vigorously that the whole leaf is unfit to perform its natural
function. In this case the leaf is impoverished and usually
turns yellow or brown and falls. In other cases the fungus,
while not withdrawing much nourishment, may cause leaves
to fall prematurely. Such are often known as leaf-casting dis-
eases. The blight of potatoes may extend over all of the foli-
age leaves, blighting them and causing death. The death or
fall of leaves before the normal period of fall is a serious injury
to the host, as every leaf lost is a fractional loss in the manufac-
ture of starchy material. The destructive attacks of smuts on
the fruit of grasses and upon the stamen of pinks have already
been mentioned. Rusts of grasses never, of course, cause the
fall of leaves but they may very seriously affect the starch-
making power of the plant, and so very materially injure, the
crop. Branches are sometimes killed off by fungus parasites.
Such may be the wound parasites which attack the trunks and
branches of trees. The tax which a witches'-broom levies on
a branch may kill off, by indirect action, the branch beyond its
insertion. Whatever the attacked organs may be, if invaded
in sufficient numbers their loss may cause the death of the
whole plant.
The destroyers of whole plants. There are many fungi
whose usual effect of parasitism is the death of the whole host
plant. Conspicuous among these is the damping-off fungus
which attacks seedlings. Wound-parasites of trees, when they
have successfully invaded the trunk of the tree, or root-wound
parasite may cause the death of the whole tree. Powdery mil-
dews, rusts, and especially the downy mildews, such as the po-
tato blight, very often kill the whole plants. Death is here the
accumulative effect of the attack on the various organs. Sev-
Minnesota Plant Diseases.
8r
eral fungi suffocate
plants, causing
death with or with-
out true parasitism.
A shelf fungus not
uncommon in Min-
nesota grows on the
ground and often
envelopes the bases
of shrubs or sap-
lings with its dark
b r o w n fruiting
body. \Y hen it
meets seedlings this
envelopment may
prevent the further
growth of the host
and suffocation re-
sults. One of the
black fungi attacks
several kinds of
grass plants and
prevents the unfold-
ing of the leaves
and finally causes
the death of its host
plant.
Stunting of
plants and plant
parts. Fungus par-
asites in many cases
do not produce
death but succeed
only in stunting the
host plant or its
Fir.. :>;.- -I .arch tree killi-il liy
the parchment pore-fungus
( I'.ilystictus perKaniemiM.
The entire tree was killeil
l>y tins half parasite. Orig-
inal.
82 Minnesota Plant Diseases.
parts. This stunting is shown in a few cases in the leaves of
plants. It may be accompanied by a stimulation of certain parts
of the leaf. For instance, a very simple little fungus may attack
dandelion leaves and produce tiny galls which appear as rough-
nesses on the surface of the leaf, while the leaf as a whole is con-
siderably smaller than an unattacked one.
More frequently one meets with the stunting or total sup-
pression of flowers. Some plants, for instance, which may sup-
port a parasitic fungus for many years, never produce flowers.
Again, curiously deformed flowers are produced in which one
or the other kind of floral leaves are missing. Sometimes the
floral parts are present but strangely unlike the normal struc-
ture ; petals may be green and like simple foliage leaves or like
sepals. Fruits may be stunted in their growth. In cherries or
plums when the fruit is attacked by certain sac fungi "pockets"
are produced. These fruits, though much enlarged over the
normal fruits, never produce natural seeds and the stone is also
undeveloped. Not only may stunting affect the form and size
of the host, but the life of parts may be shortened. The
witches'-broom often furnishes examples of such age shorten-
ing. Here the leaves may fall long before the normal time.
Stimulation of host. More conspicuous and more common
is the occurrence of stimulation of the host by the fungus para-
site. This stimulation may result in one or more of four effects,
viz. : (a) an increase in size ; (b) an age stimulation ; (c) the de-
velopment of normally undeveloped organs ; and (d) the forma-
tion of new organs.
(a) Many cases of increase in size of organs are met with
as a result of fungus parasitism. The fungus galls mentioned
above are the simplest cases of such enlargements. The
branches of witches'-brooms are usually enlarged not only in
size but in numbers. The plum and cherry "pockets" are like-
wise enlargements. On the leaves of Labrador tea and other
heath plants may be formed large solid galls which are covered
with the spores of the parasite. Rusts produce enlargements of
the stems of various pines, forming huge spherical, burl-like
swellings. Roots of the rushes are enlarged by the attack of
a smut fungus. Moreover, floral parts are often enlarged.
Petals, sepals, stamens or pistils may be stimulated by fungus
parasites to extraordinary growth.
Minnesota Plant Diseases.
(b) Many rusts have remarkable powers of stimulation, not
only in their influence on size but also in the age of parts. Al-
though a host plant may bear the load of such a parasite the
fungus may still stimulate it sufficiently to enable it to maintain
its normal age relationships so that the fungus and host may
live together for years. In the darnel grass lives a smut-like
fungus which is parasitic and which infects the embryo in the
seed before the latter is ripe, and thus this fungus lives on from
year to year in-
fecting its host
without the need
of spores. Such
a partnership has
become almost, if
not altogether, an
equal partnership,
and approaches
the degree of uni-
fication attained
a m o n g the
lichens.
( c ) A in o n g
the most remark-
able effects of
stimulation are
the changes in
:. "Ji. — 1-uriRUS gall on leaves nt l.ahrailor tea. I lie linmus . a -__l r«..*c ~f
(ExobMidium) it one of the gall-forming basidium U -a: Dial parts OI
host plants. It is
well known that
in some plants there are two kinds of flowers, one bearing
stamens and the other pistils. This is the case in certain mem-
bers of the pink family. In these plants, however, this so-called
(and incorrectly) "unisexual" condition has been brought
about by the failure of the beginnings of one of the floral parts
to develope. Thus, we find in such flowers either the stamens
alone fully developed, with the undeveloped beginnings of the
pistil, or vice versa. Very often such flowers arc attacked In-
certain smut fungi and the parasite often exerts a stimulating
effect upon the undeveloped beginnings of the floral parts and
ing fungi and cause* a stimulation in the leaf which
thereby furnishes additional nourishment for the
The latter is an accomplished parasite. Original.
84 Minnesota Plant Diseases.
excites them to growth, so that where normally only one
kind of floral leaf is developed, two may be produced in the
diseased flower. The stamens may be produced in pistillate
flowers or pistils produced in staminate flowers. In still an-
other case stamens may by the influence of a fungus parasite
be transformed into petal-like bodies, thus producing a doub-
ling of petals.
(d) All of the effects of parasitism mentioned thus far have
been either changes in normally developed organs or the
growth of undeveloped beginnings of parts. There are known
at present only a very few cases where a fungus excites the
formation of absolutely new organs. In these cases the organs
are produced by the host only when the fungus is present and
they have to do solely with aiding the parasite in the produc-
tion and dissemination of its spores. Such new organs are
known on a cone-bearing tree of Japan closely related to our
own white cedar and the fungus causing the formation of new
organs is a rust.
Effects of parasitic fungi on tissues and structure of hosts.
It has already been said that fungi may cause increase in size of
plant parts. This increase in size is effected in two ways: first,
by an abnormal multiplication of the cells of the tissues affected
which takes place under stimulus from the fungus, and second,
by the enlargement of each cell. Both processes may go on at
the same time.
Fungi act differently in their invasion of tissues and each
has its own method of attack. This is noticeable in the effect
upon the leaf-green of plants. Some fungi cause a decrease in
the amount of leaf-green found in the host plant, often effecting
its complete disappearance. Such plant-parts have a yellowish
color. Certain rusts have such an effect upon their hosts.
One may find other cases where only a partial decrease of leaf-
green occurs as in the balsam-fir needles on the witches' -broom,
also produced by a rust fungus. On the other hand the fungus
may excite the tissues to the production of an extraordinary
amount of leaf-green, or to the retention of leaf-green after sur-
rounding' parts have lost it. Such green spots on leaves have
been known as green islands and are striking examples of the
unification of fungus and host-parts into a virtual individual.
Minnesota Plant Diseases. 85
Fungi are even known to excite the formation of leaf-green in
plant parts usually devoid of it, e. g.. in petals of flowers, as is
the case in the white rust on mustard plants. In this case it is
very probable that we see simply the stimulation to the devel-
opment of latent beginnings of the leaf-green bodies, just as the
stamens and pistils are sometimes formed in flowers usually de-
void of them. As leaf-green furnishes the machinery for starch-
making, one sees that the amount of starch formed in a fungus-
inhabited part may vary with the fungus. However, leaf-green
is not the only agency of starch production. There are other
agencies for the transformation of starch from other com-
pounds. Aside from the effect of the fungus, upon leaf-green,
fungi react directly upon the starch, producing certain chemical
substances which dissolve the starch. Some fungi use all of
the available starch as soon as it can be reached, while others
cause a great accumulation of starch temporarily and dissolve
it in the important stages of their life history, during and just
preceding the formation of spores. A great many fungi are
able to dissolve starch and among them may be mentioned cer-
tain rusts, black fungi, white rusts and many wood-destroying
fungi.
When tissues of plants are examined under the microscope
a honeycomb-like structure of cells is seen. The walls of most
cells are whitish, soft and composed of a substance called cellu-
lose. The walls of the cells of woody tissue enclose in the
youngest stages the protoplasm, but soon lose the latter. The
"woody" character of wood tissues is imparted by the thickness,
size and form of their cell walls, and the chemical compounds
found in them. In young stages, the wall is whitish and not
particularly resistant nor hard, for it is a cellulose wall. Later
new substances are added, which collectively are known as lig-
nin. and the tissues then become woody. But woods differ
among themselves due to variation in the above-mentioned
characters. The cellulose membranes are sometimes pierced by
fungus threads in a mere mechanical fashion, just as one would
force a pin or needle through them. Wood membranes offer
considerable resistance to most fungi, but some of the latter
have solved the problem of penetration of these walls. Such
are the wood-destroying fungi already mentioned. The
86 Minnesota Plant Diseases.
threads of these parasites exude certain chemicals which are
able to attack the lignin of woody tissues and to dissolve out
the substances which make up this lignin. These cell walls
now have the same chemical constitution which they had before
they became lignified. But the fungus is also able to attack the
cellulose walls and the final result is a more or less complete
breakdown of the walls. The wood crumbles easily and is con-
verted into punk, which is characteristic of rotten wood. The
threads make their way from cell to cell, usually by boring
through the walls, whether they are wood walls or cellulose
walls, and in tissues attacked by these fungi one sees large
numbers of holes through the cell walls, where fungus threads
oooo
FIG. 38. — Two ways in which wood is destroyed by wood-rot fungi. On the right the wood
cells are destroyed from within outwards. On the left they are destroyed from the
middle of the wall toward the center of the cell. Highly magnified. After Hartig.
have passed. From these points the dissolving substance
spreads over the cell wall completing the rotting process in
that vicinity. Since woody tissues can be colored characteris-
tically by using certain chemicals, one can determine by the use
of these chemicals just how far the rotting has proceeded.
It is worthy of notice that fungi have different methods of
attacking and rotting woods, using different substances and ap-
plying them in various ways. The study of the rotting of
woods is still in its infancy, but it is now known that certain
wood rotting fungi can be determined by the kind of rot which
they produce. The wood-rot, therefore, often gives very def-
inite symptoms of determinable diseases. The study of wood-
rots is receiving considerable attention at the present time on
Minnesota Plant Diseases. 87
account of its vast importance economically. To realize this
importance one has but to think of the great losses sustained
yearly by the decay of mine timbers, house-foundation and
cellar timbers, of bridge-timbers, railroad ties, paving blocks,
fence posts and rails — in fact, timbers wherever air and moisture
can reach them. The creosoting of pavement blocks and the
tarring of cedar posts are attempts to aid the wood in resisting
fungus attacks. Tar and creosote are substances in which the
fungi cannot live and their presence protects the wood. But
as soon as the substances are washed off the fungi commence
their attack. At present a considerable amount of money is
being expended to find a process or substance which will pro-
tect railroad ties from fungus rot. What is wanted is some
substance which when deposited in the wood will prevent the
entrance of fungi and which will not readily leach out into the
soil during heavy rains.
Effects of parasites on anatomy of host. The effects of fun-
gus parasitism described above have to do with the destructive
attacks upon cells and tissues, particularly in those cases where
enlargement of parts is caused. One often finds other effects
in tissues, viz. : changes in quality and amount of certain kinds
of tissues. The covering layer is often affected by fungi which
live on the surface, and may also be ruptured by the spore-pro-
ducing hyphae of interior-dwelling fungi as in red rusts. Some
fungi excite in certain plants an abnormal growth of cork which
constitutes the cuter layers of the bark. In general, in the en-
larged parts of the hosts, the supporting or strengthening tis-
sues are not as well developed as in the normal host. Many tis-
sues, moreover, which are usually woody are not so in the dis-
eased and enlarged parts, although there are exceptions to this
generality. Sometimes the fungus attack stimulates the ex-
cessive production of resin in pines and their allies. ( Hher
products and tissues may undergo change, though no generali-
ties can be discovered in the action of fungi. It seems, how-
ever, that, in general, those changes take place which transform
the host part into a most suitable and profitable dwelling and
food store for the parasitic fungus without regard to the host's
needs, and often to the direct detriment of the host plant.
There is usuallv in this connection a trreat amount of tissue
88 Minnesota Plant Diseases.
produced which is especially fitted for storage of food materials.
The cells therefore are large, thin-walled, closely crowded and
contain much starch and other storage food.
Effects of hosts on parasites. In the unequal partnership of
host and parasite, where the fungus is the dominant partner, the
latter is often profoundly affected by the host plant. It be-
comes so accustomed to peculiarities in the life history of cer-
tain plants or groups of plants that it has learned to shape its
own course in harmony with these peculiarities. First of all,
then, one finds a parasite capable of living on but one particular
kind of host — it is found on no other, and an attempt to culti-
vate it on even the most closely-related plants fails. Such a
condition of parasitism, though by no means unknown, is not
very frequent. Far more common is that condition where the
parasite has learned to shape its general habits to comply with
the peculiarities of each of a group of plants very closely re-
lated and is capable of infecting any of them. It is found, how-
ever, that the previous habitation of a fungus has in some rusts
at least an important effect upon the spore of that rust in the
infection of other host plants. In general, infection succeeds
best upon the identical kind of host upon which the spores were
formed, while the nearest relatives of this host are more easily
infected than are distant relatives. One must infer from these
facts that the effect of nutrition, etc., received during habitation
on a host are far reaching and influence the fungus towards a
preference for this same host.
Certain fungi, again, are able to attack any of a number of
host plants which are but widely related. Such fungi show
general abilities and no special education in selection of host.
In other words, they are not so deeply affected as the previously
mentioned specialists.
It has already been noted that certain rusts, in order per-
haps to produce spores continuously throughout the season,
have learned to live on different hosts at different times of the
year. Such fungi may also exercise exact preference for their
hosts, though, of course, two hosts are necessary. The influ-
ence of the host-effect may here be carried over through the life
on the second host until the fungus again inhabits the first host
plant. Such an impression must indeed be a profound one.
Minnesota Plant Diseases. 89
Host-influence on parasite may be exerted even at the time
of spore germination. The spores of a great many parasitic
fungi will start to grow when placed in pure water. Some
fungi, however, as most of the smuts, require nutrient material
before they will germinate. Again, other fungi must bring
their spores into direct contact with the host plant in order to
bring about germination.
After the spore has germinated the germ-tube penetrates
the tissues of the host plant. In some cases, where the fungus
spore is not directly influenced in its germination by the pres-
ence of the host, a spore may germinate on an unfavorable
host and the germ-tube may even penetrate into the tissues,
but here its progress is prevented as the host does not permit
of further growth. Such a struggle may continue for some
time, but is usually short if the host is at all unlike the usual
host of the fungus. The preference shown by fungi for special
plant parts as dwelling places, as the grass-fruit-inhabiting
smuts, is but another expression of the influence of the host
plant parts upon the fungus.
Chapter VII.
Fungi. Plant Diseases.
Disease in plants. It is not always an easy matter to tell
whether or not a given plant is healthy or diseased. For in-
stance, a plant may be placed under very slightly unfavorable
conditions of moisture and sunlight. If it were to obtain
slightly more or less moisture or sunlight, as the case might be,
it would thrive or sicken. Still the unhealthiness of such a
plant would hardly be termed a disease. If, however, we were
to further change the unfavorable surroundings, we might bring
the plant to a condition where its life would be seriously threat-
ened and such a plant would unhesitatingly be called diseased.
We can therefore see that one may conceive of all sorts of
possible conditions between so-called good health and undoubt-
ed disease in plants, and that disease and health are only con-
ventional marks, as it were, on an artificial scale of the life con-
ditions of organisms. No plant ever enjoys all of the best con-
ditions possible for it can only approach such a condition. If
it could, it would touch the top mark of the life-scale ; the bot-
tom mark is the disease-death of the plant. We might say a
premature death instead of a disease-death because it must be
remembered that all plants as we know them today are destined
to die sooner or later. Some, as many of our common weeds,
live only a year, while, on the other hand, our great forest trees
live for centuries, but sooner or later their constructive powers
are no longer successful in repelling the attacks of unfavorable
conditions and they succumb. Such a "natural death" is not in
the nature of a disease, as we commonly understand that term.
Yet disease merely hastens this death, and again we might
trace all conceivable conditions between an imperceptible has-
tening of death to a violent death from a well-defined disease.
All of the efforts of agriculturists and horticulturists are
summed up in saying that the conditions of growth of selected
Minnesota Plant Diseases. 91
plants are artificially favored. The fertilizing of soils, the selec-
tion of various soils for certain plants, processes of cultivation,
and so on, are all directed toward this end. Men engaged in
these pursuits are fast learning to recognize the advantages and
profits of such processes and no improvement, however small it
may be, is too insignificant for notice and application. We
might term such processes improvements of health.
There is another aspect which often escapes the busy prac-
tical farmer or horticulturist of today. In the absence of an
analysis he recognizes in disease only those sharply marked or
violent disturbances which are very obviously threatening the
life of his plants. The small losses by inconspicuous diseases
are often overlooked. For instance, no farmer fails to calculate
his loss when a heavy rust epidemic attacks his wheat or an
epidemic of smut invades his oats. Few farmers, however,
realize that every year rust levies a tax of a fraction of his crop,
although that fraction may be small. \Vhy should he not be
alive to these facts and to the necessity for alleviating such
troubles as he is to the small improvements of cultivation and
introduction? And such conditions can only be improved by a
fair intelligence of the cause and spread of the diseases of plants.
It is only by such knowledge that intelligent remedies are
applicable and the greatest profits attainable from the products
of the soil. It is only then that our plant proteges will at all
approach the highest mark of good health.
It is a well known fact that the offspring of a plant may vary
considerably in their characters. If we take an extreme case
AVC can easily imagine two offspring of one plant to be so dif-
ferent in character that under the same conditions one would
thrive very well while the other would suffer very perceptibly.
The variation in the latter case would be indistinguishable from
disease for it tends under existing conditions to prematurely
end the life of that plant. Of course such a plant, if placed un-
der different conditions, might thrive exceptionally well, and
man's great interest in variation is the puzzle of fitting together
varieties and conditions to the best advantage.
As seen in one light the life of a plant is unlimited in time-
is, so far as we know, immortal through the germ cells which
contribute to the formation of new offspring. Individuals,
92 Minnesota Plant Diseases,
however, have a limited life. A plant evinces two processes
constantly at work, viz. : a constructive process which is build-
ing up the tissues, increasing or replacing them, and a repel-
lant process which organizes and otherwise provides for the
repulse of unfavorable conditions among which may be includ-
ed the attacks of injurious weather and soil conditions as well
as those of fungi and other organisms. Now in the normal
vigor of youth a plant is capable not only of successfully re-
pelling external attacks but puts much energy into the con-
structive work. Gradually less and less of an increase of tis-
sues is noticeable because of the necessary replacement of lost
tissues and finally we reach the mature vegetative condition of
a plant where the latter has attained its greatest possible size
and all of its constructive power is exerted to replace lost mem-
bers or parts. If conditions were ideal, one might imagine such
a mature or prime condition to last indefinitely, but now with
the increase in size and complexity we find also an increase in
the attacks of foreign organisms or the unfavorable conditions
due to accidents, as lightning strokes or storm damage. If the
repelling power of the plant does not increase, the disintegrat-
ing forces gain and the plant enters the period of old age and
decline which is terminated only by the complete success of
the disintegrating forces, i. e., the death of the plant. Among
the shortest-lived individuals are those plants which live but a
single season. Among the longest-lived are not only our giant
trees but also those herbaceous plants which have creeping
underground stems, that travel from year to year, carrying
their reserve material as a capital for starting work again in the
following spring. Such plants as iris, bloodroot and many of our
grasses are good examples of such long-lived plants. The at-
tack of some foreign organism has in general more chance of
success during the old age period than during the vigor of
youth and old age in a plant, therefore in general predisposes
that plant towards disease.
Factors of disease. Disease in plants has these three fac-
tors : first, the immediate cause of disturbance, as a fungus or
some insect or some unfavorable atmospheric agency; sec-
ond, the resultant change in the life of the host ; and third, the
previous condition of the host plant, i. e., its predisposition in
Minnesota Plant Diseases. 93
particular towards that disease. The first factor will be con-
sidered later. The second has been discussed in Chapter VI.
^Te will now examine more in detail the third factor, i. e., pecul-
iarities in internal and external conditions which make a plant
more or less susceptible to disease.
Predisposition. This susceptibility is in almost all cases a
specific one toward a certain disease and less often toward many
diseases. When a plant is subject to the attack of numerous
agencies we can easily imagine same change in conditions,
as. for instance, transplanting from a dry to a moist atmos-
phere, which would favor the attack of all of these diseases.
The conditions become such that fungus attacks in gen-
eral are facilitated. But most predispositions are in the nature
of special conditions which are favorable to only one spe-
cial disease or class of diseases. This distinction is expressed
in the terms general and special predisposition. An illus-
tration may make this clear. Wheat rusts are of different
kinds caused by several fungi. In general, moist warm weather
in the growing season predisposes all kinds of wheat plants in
many ways to the attack of rusts, and such condition-; furnish
general predisposition. Hut if a certain variety of wheat he
particularly susceptible to a given rust fungus, abundant in the
region into which the wheat is introduced, the new condition of
position in the wheat plant predisposes it very much to that
disease. Other varieties of wheat, less susceptible to that par-
ticular disease, might be unaffected so that we may have here a
special predisposition.
It is a fact which must not be lost sight of. that the predis-
position of the plant in itself may not be harmful to that plant,
but may be a condition which might be highly recommended
when considered alone. Hut it is the other factor, the fungus or
inject, which may be the disturbing influence and which is
especially favored by this condition of the host p'ant. Such a
distinction is of very great importance to practical agricultur-
ists and horticulturists because it is not only the immediate
condition of the plant or. on the other hand, the presence of
disease-causing conditions, but it is the relationship between
these two factors that is all important. There is another fact of
great importance that must be emphasi/ed. \o plant, as far as
94 Minnesota Plant Diseases.
is at present known, ever inherits a disease — no disease passes
directly from parent to the offspring plant in the germ cells.
Predispositional characters may be inherited but the first dis-
ease factor is never inherited. The infection of the host plant
may take place so early in life that at first sight there may ap-
pear to be an inheritance, but all such cases at present known
have been shown to be simply early infections of the host plant.
For instance, oat plants are infected in the seedling stage just
after the little plant arises from the grain, while in the darnel
grass the infection of the host plant takes place inside of the
seedling before the seed is ripe — for, as is well known, the little
plant is already well developed when the seed is ripe and has
been growing for some time previously. That is to say, in the
darnel, the plantlet (commonly called the "germ") inside of the
grain is already infected with the fungus. But in neither of
these cases is there an inheritance of the disease.
Kinds of predisposition. Predisposition may be therefore
of two kinds, the natural and inherited condition of structure
and habit due to internal causes, and the accidental or abnormal
conditions which are due, not to internal inherited traits, but to
the accident of external forces. Thick-skinned potatoes are
known to be more resistant towards certain rots than thin-
skinned potatoes, i. e., the thin-skinned forms are naturally
predisposed in their structure to that disease. Again, oat
grains germinate at about the same time when the oat smut
spores germinate and hence the young oat plants are predis-
posed to smut attacks by their inherited habit of germinating in
the spring. Such might be termed a natural predisposition of
habit. On the other hand, a wounded plant is predisposed to-
wards the attack of wound parasites by an external force as in
pruning, or by wounds caused by cattle or deer, or a wagon
wheel, and is more liable to such attacks after receiving a
wound.
Again, the transplanting of plants from a dry to a moist
climate may predispose such plants to disease. Here the pre-
disposition is induced by external factors. It is noticeable that
in both of these predispositions of external cause the pre-
disposition as in a wound or in transplanting may not in itself
bring about serious injury to the plant. Plants have an effect-
Minnesota Plant Diseases. 95
ive method of healing over wounds and a removal from a dry
to a moist atmosphere frequently stimulates the plant to ex-
traordinary growth. But it is in opening a new field of attack
for invading organisms and other disease-causing factors that
such externally caused conditions may prove dangerous to the
host-plant.
Many other plants besides oats are predisposed towards dis-
ease during their youth or during the youthful stages of certain
organs. The corn plant is attacked by the corn smut only in
young growing parts and the fungus cannot invade mature tis-
sues. Certain conditions of the youth of plants aid in the at-
tack of disease; for instance, the thinness of the tissue skins,
and the abundance of food material. It must not be assumed
that all plants in their infancy are predisposed towards disease,
but there are certain conditions which may in general tend
to increase susceptibility towards disease. Perhaps the prob-
lems of old age are still more productive of predispositions.
Young tissues have the advantage of vigorous protoplasm,
while aged plants have reached their limit of growth and are
losing ground. Again, seasons may bring predispositions, as
in the oat smut, for several causes may contribute to the same
predisposition. A rest period may also be productive of dis-
ease since the protoplasm is not as active in resistance when
resting as in the rapidly growing condition. Such is the case
of the ripe rot of fruit. Predispositions of form have already
been cited in the thin-skinned potato. Immunity from certain
diseases sometimes comes with wax-coated surfaces or thick
cork, etc. Physiological habits of plants, as in the oat smut,
are likewise productive of predisposition or immunity. Such
habits as in the germinating period of grains growing in differ-
ent regions may be important in assisting the plant to escape
disease. This is the partial explanation of the advantage of
selection of seeds growing in certain regions, e. g., northern
grown seeds for northern localities.
Plants kept under peculiar conditions of moisture or tem-
perature may acquire a predisposition towards disease. Hot-
house plants suddenly planted in very dry conditions are some-
times not able to adjust their water evaporating apparatus to
the dryer conditions and suffer wilting and accordingly in some
96 Minnesota Plant Diseases.
cases death. Likewise, when trees grown in the protection of
forest shade are suddenly transplanted to a prairie or isolated
by the cutting down of surrounding trees, they may fall a prey
to sun scorch.
External causes may be fertile in many other predisposi-
tions: Wounds by pruning, root injuries, insect boring, hail-
stone wounds and injuries by lightning strokes, frost cracks and
sun scalds, etc.
It has already been explained that disease is never inher-
ited. On the other hand, it is a fact that natural conditions,
e. g., of form or of habit, which are, in reference to certain dis-
eases, causes of predisposition or immunity, may be inherited.
Such accidental conditions as wounds are of course not capable
of transmission. In other words, only natural or so-called
normal predispositions are inheritable.
Variation and predisposition. The selection of varieties in
agriculture and horticulture is very greatly concerned with this
phase of the subject. Variation in structure, form and habit
give to plants different degrees of resistance toward certain dis-
eases, some greater and some less. Of course there is likewise
variation in respect of other conditions and one may select vari-
eties for those conditions. For instance, wheat varieties may
be selected for their fitness for milling, size of grains, crop
yield and other characters. Fruit tree varieties are selected
for size of fruit, keeping qualities, yield and so on. Now one
can also select varieties of agricultural plants for the resistance
which they exhibit towards a given disease. For instance, cer-
tain varieties of strawberries will resist the strawberry spot fun-
gus more successfully than others, and where this disease is
prevalent might be very desirable. Again, some apples or crabs
are more susceptible to apple scab than others, and the selec-
tion of these varieties may be a distinct advantage. Of course
such varieties might not be the most desirable in other respects.
In other words, the intelligent grower of plants has before him
a very complex problem. The object to be gained is the best
crop under the existing conditions. These conditions he must
know thoroughly before he can solve the problem, and the
varieties must be selected accordingly. It should be empha-
sized that the conditions must be thoroughly understood and
Minnesota Plant Diseases. 97
the difficulties appreciated. If they are not, the plant grower is
working in the dark. The wheat rusts furnish a good illustra-
tion of the complexity of the problem which is presented.
Wheat rust may be caused by one or more of several kinds of
fungi which are very closely related but are nevertheless dis-
tinct kinds. A wheat variety which might resist one of these
would be unable to resist others. Now an intelligent solution
of the problem must include a knowledge of the particular rust
fungus attacking wheat in certain localities and then varieties
must be selected which will resist this particular fungus. If
more than one fungus is prevalent in this locality the selection
of a rust-proof variety becomes more difficult. In other words,
rust-proof varieties may have to be selected for certain kinds of
ru^ts and not for rusts in general, although, on the other hand,
it is not conceivable that certain varieties may possibly be de-
veloped which will offer general resistances to the whole group
of rusts, e. g., where they are able to withstand the predisposing
effects of moisture, or in their early or late sprouting habits
might dodge, as it were, the time of year when rusts' spores are
most abundant. Early sowing of wheats was an attempt to
evade this period of the year but not as yet with very conspicu-
ous results. In a word, the greatest success in selection of vari-
eties is still to be obtained, but can only be won by more knowl-
edge of the habits and forms both of the hosts and of the fungus
causing the disease. More knowledge and the hearty coopera-
tion of the practical plant grower with the plant disease special-
ist are the requirements of the solution of these complex prob-
lems.
Infection of host. We have already seen that fungi use vari-
ous methods and agencies for the distribution of spores and
there are consequently various methods of inoculation of host
plants. In the first place it must be pointed out that inocula-
tion and infection are two different things, e. g., a plant may be
inoculated with fungus spores which may even start to grow,
but a successful continuance of growth does not always follow.
When the fungus does succeed in living with the host, infection
in the true sense is accomplished. Infection is successful inocu-
lation.
98 Minnesota Plant Diseases.
The wind transports many fungus spores from plant to plant
and some great plant epidemics are due in part to this agency.
It seems possible that red rust spores may be blown from warm-
er climates, where they pass the winter, many miles, inocu-
lating in the early summer or spring the plants of northern
countries where the summer spores cannot be formed through-
out the year. Inoculation of some fungi occurs chiefly through
swimming spores and in such, only wet seasons will enable the
disease to become serious. Such a parasite as potato blight will
spread with remarkable rapidity on plants in low, damp situa-
tions or during excessively moist weather. Some of the algal
fungi, as white rust, combine the two methods in distributing
by means of the wind, spores which in subsequent rainy weather
break up into swimming spores and thus act as new centers of
inoculation. Insects carry spores of fungi from plant to plant
and are allured by "honey dew" or by other sweet and odorous
liquids. In the case of ergot of rye the insects are attracted by
a honey-like fluid, which is exuded by the 'young grain, on
which the fungus has formed an abundance of summer spores.
These are then carried by the fly to other young flowers and the
disease thus spreads rapidly. It is known that many other ani-
mals effect the spread of plants by distributing spores under
favorable conditions. The furry coats of some rodents have
already been mentioned as depositories for spores. Man is re-
sponsible for many inoculations of fungus spores on plants.
All of the numerous methods of transportation and travel and
commercial intercourse furnish means by which man scatters
spores of fungi, often bringing them into most favorable condi-
tions. The introduction of mallow rust from South America
has already been cited. Careless pruning or wounding of trees,
untidiness in horticultural and agricultural pursuits and lack of
knowledge of the nature and various methods of infection of
certain diseases all conspire to make man an efficient aid in the
spread of fungus plant diseases. In manure heaps dangerous
fungi often multiply or pass the winter. The debris of trees or
other plants which have been diseased is also a menace. The
various farm implements, in passing from one place to another,
may carry spores and effectually scatter them. The sowing of
smut-infected oats without taking the precaution to kill off the
Minnesota Plant Diseases.
99
fungus is a good case in point. Finally, the fungi may actually
aid by special devices the spread of disease. Such devices are
seen in the sac fungi where spores are forcibly ejected and so,
caught by the wind, are easily scattered. Again, infection may
take place not only by spores but also by mycelium, and does
so in many cases. This is noticeably true in those fungi which
Fie. 39. — A good example of »n epidemic. Potato alight hat. within a week, entirely
destroyed the potato plant* in this field. After Clinton.
attack trees and particularly root parasites. Contact between
a diseased tree trunk or roots and a healthy one may offer the
mycelium a chance to pass over directly from the one to the
other and a successful infection may ensue. Some of these
fungi have a special shoe-string-like strand of threads which
are especially proficient in effecting mycelial infection.
ioo Minnesota Plant Diseases.
Epidemics. When a fungus disease becomes particularly
abundant and devastates great fields or forests of certain host
plants there arises an epidemic. There have been notable epi-
demics of continental extent in historical times just as there
have been famous plagues attacking man. Potatoes have many
times been decimated by the blight, forests have been threat-
ened by the honey mushroom; the mallow rust has swept over
Europe and America damaging many kinds of mallow; while
year after year one may read of epidemics of grain rusts and of
smuts. These epidemics are more widespread in some years
than in others. This last season (1904) has seen wheat-rust
epidemic almost throughout the northwestern United States
and Canada. In Ceylon the coffee disease has ruined hundreds
of coffee plantations. A remarkable fact in these epidemics is
that the fungi which produce them may have been present a
long time previous to the epidemic without exciting any great
amount of damage. It is well known, for instance, that potato
blight, wheat rusts, mildews and smuts are always with us, but
that not every year furnishes epidemics. It is therefore evident
that other factors besides the immediate cause or fungus fac-
tors must be present. Of these, weather conditions are usually
the most important factor. Potato blight never thrives in dry
weather or on plants in sandy soil, but is at its best when the
weather for days is misty and moist so that the fungus can form
its swimming spores and distribute them rapidly. It is just in
such weather as this, and particularly after a warm growing sea-
son, when the leaves are swollen with moisture and rich in food
material, that blight strikes. Several of such epidemics of enor-
mous extent have been known. It is also a well-known fact
that wheat rust often follows upon very moist springs and early
summers. In fact many people still think that the wet weather
causes rust. And they are not altogether wrong, but the effect
of the weather is not exactly as such people imagine. Warm,
moist weather is just the kind of weather which is favorable to
the development of the summer spores of the rust fungus and
the fungus grows luxuriantly, producing in two weeks or less
another crop of summer spores, thus multiplying an hundred or
a thousand-fold in this short time.
Minnesota Plant Diseases.
101
ftjj.
_ ,-*.
= =
5 V
s-
s
'£•£
s £
iO2 Minnesota Plant Diseases.
The success of smut infection depends largely upon the abil-
ity of the spores to germinate and the germination of the spores
at a suitable season for attacking the host-plant, e. g., in oats,
in the seedling stage. An epidemic of smut must, therefore, be
preceded by a season favorable to spore germination and also
coinciding with the seedling stage of the grain. Such epidemics,
moreover, are greatly favored by the clinging of smut spores to
the grains since they are thus sure to be near the latter when
these commence to grow.
Many other causes of epidemics might be mentioned. Un-
der so-called normal conditions the fungus may create no ex-
traordinary damage but under propitious conditions it becomes
epidemic. One can easily understand that any disease may be-
come epidemic if the conditions are right, and since the horti-
cultural and agricultural changes instituted by man are so great
in many cases it is to be expected that the danger of epidemic
diseases is always an important and ever-present source of
trouble. The older horticulturists and agriculturists took cog-
nizance of epidemics only after they occurred, when, of course,
remedial measures were impossible. Now the raiser of plants,
just as does the medical practitioner among men, keeps close
watch upon all kinds of diseases and attempts to prevent epidem-
ics rather than to cure them. Every introduction of a plant into
a new country and new surroundings, every appearance of anew
hybrid opens up new fields for numerous parasites who may find
in the newcomer just the right conditions for an epidemical
growth. Every introduction of a new plant to a certain com-
munity may also bring new fungus diseases which may be able
to attack plants of this community if the latter have not learned
to withstand their attacks. Thus may result an epidemic simi-
lar to that of mallow rust. It is useless to suppose that
we shall ever get rid of the plant disease question and be able
to lay it aside under the weight of a few rules for spraying or
other treatment. On the contrary, the more complex and ad-
vanced our agriculture and horticulture become even more so
becomes the question of immunity from fungus epidemics. As
the host plants vary so also may the fungi, and those parasites
which are apparently harmless today may in years to come be
very dangerous pests.
Chapter VIII.
Fungi. Kinds of Fungi. Algal Fungi.
M
The fungi are undoubtedly descended from algal stock and,
as commonly understood, more than one line of descent is prob-
able. That is to say, the ancestors of the present day fungi
were all algae, though of at least several kinds. The algae com-
prise a group of plants which have in general a water-habit. A
great many fungi still retain this water-habit but unlike the
algae, which possess leaf-green, they are unable to manufacture
their own food. On the other hand, a vast number of fungi
have learned to live in the open air or in the tissues of other
plants or on the ground ; in short, have abandoned the aquatic
for some terrestrial habit. With this change in habit have gone
on changes in form and methods of reproduction. Botanists
recognize three great groups of fungi. The lowest group is
that of the algal fungi, including those of which the majority
have retained the aquatic habit and in which the reproductive
methods have been less strongly altered than in the two remain-
ing higher groups. The latter groups are in general terrestrial,
and have adopted two very distinct methods of reproduction.
In all of the sac fungi spores are formed inside of sacs and these
sacs in most forms are elongated cylinders containing eight
spores each. In the stalked fungi the spores are produced ex-
ternally on fungus threads, and are borne on fine and delicate
stalk threads. The number of such stalked spores on each
thread is commonly definite for any given species and the usual
number is four. The production of spores by breeding is
known to occur throughout the algal fungi and has been ob-
served in many cases among the sac fungi and probably occurs
throughout the latter group. Up to within recent times no
undisputed evidence had been produced of the presence of a
breeding act among the stalked fungi : but it is now known that
104 Minnesota Plant Diseases.
a fusion process takes place and this has been interpreted as a
breeding act by some botanists.
The algal fungi (Phy corny cetes). It has already been stated
that these fungi are for the most part aquatic in habit but that
some forms, as the insect molds and black molds, have aban-
doned the water and taken to dryer situations. It is a noticea-
ble fact, however, that even insect molds and black molds re-
quire very moist conditions. It is in the algal fungi, therefore,
that swimming spores are commonly produced and especially,
though not exclusively, in the aquatic forms. White rust of
mustard produces swimming spores at certain stages, but this
only occurs when an abundance of water is present, so that the
fungus may be considered aquatic during a part of its life and
terrestrial during the remainder. Spores are produced by a
breeding act and often these are special spores for resting pur-
poses ; they are therefore provided with very thick walls. In
some families, as in the black molds, large numbers of spores
are produced in cases which to the naked eye look like tiny
black spheres about the size of a pin-point. These spores are
not provided with swimming lashes but depend upon the wind
for aerial distribution. The algal fungi are structurally pecul-
iar in that the threads have no crosswalls except when spores or
spore-cases are about to be formed. The following groups are
the most important among the algal fungi : Chytridines or
Lowly Algal Fungi, Water Molds, Fish Molds, Sewer and
Drainpipe Molds, Damping-off Fungi, Downy Mildews, White
Rusts, Black Molds and Black Mold Parasites.
Lowly algal fungi (Chytridinccc). In this group are found,
in general, very simple fungi. All of them are minute and it
requires strong powers of the microscope for the observation
of most of them. The simplest are tiny single-celled spheres
and resemble much the Flower Pot Algae, except that they
have no leaf-green. In fact, it is very probable that they have
descended from these algae. Some have become elongated
into simple threads and still others are even considerably
branched. Spore cases and breeding spores are produced and
each forms, by internal division, swimming spores. These
swimming spores are the chief agents of distribution and are
provided with one or two lashes which, by whipping about in
Minnesota Plant Diseases.
105
the water, drive the spore forward with a combination of a hop-
ping, whirling and swimming motion. These spores, when
they come to rest, draw in their whips and immediately grow
out into the mature plant. The function of the resting spores,
whether a breed-spore or not, is to tide the plant over unfavora-
ble seasons. When breeding occurs, the two breeding organs are
exactly alike and indistinguishable, as is the case in some pond
scum algae. These lowly fungi are
found in a great variety of habitats.
Most of them are parasitic, though
some are saprophytes. They are
found on algae as well as on lowly
water animals or on the eggs of the
latter. Some are found on fungi, par-
ticularly on water and fish molds,
while a large number inhabit the
leaves and stems of the flowering
plants. In their parasitic habitat they
often arouse the host to extraordi-
nary growth and swellings or galls are
thus produced. Hence they are some-
times known as gall fungi. Galls of
this nature are produced on the leaves
of dandelion, anemone and on garden
plants such as cabbage. Few. how-
ever, produce diseases of very great
importance. In that they damage
algae and water animals in the waters of fish hatcheries they
injure or diminish the food supply of the young fish. One spe-
cies attacks and gains entrance to pollen grains of the pine
when the latter lie on the surface of water or are submerged in
ponds, and lives inside of the spore until it forms its swimming
spores when the latter are thrown out into the water. Some
have even learned to penetrate and to live in the pill-box algae,
which are provided with walls of silica. ( Figs. 41. _> i i . )
Water molds and fish moldsuVd/vWr^/f////^ in />(//•/). These
fungi are more highly organized than the group of fungi just
discussed. In the first place they all possess a branched and
well developed system of thread mycelium. They are. how-
Fic. 41. — A lowly algal fungus.
Above, the resting condition
of a single-celled fungus in
the tissues of the host plant.
Below, young fungus plants
are seen in the cells of the
host. Highly magnifi -d.
After Schroctcr.
io6
Minnesota Plant Diseases.
ever, all aquatic in habit and thrive in stagnant pools where
decaying animal and plant materials are particularly abundant.
They are typically half-saprophytes, passing most of their life
feeding on dead material in the water, but living parasitically on
fish or other animals, as occasion presents itself. As wa-
ter plants they utilize the swimming spores and these are usual-
ly formed in enormous numbers in spore cases of various
shapes. The swimming spores are of the same general struc-
ture as those of the lower algal fungi, though in a few cases
they seem to be unable to get out of their spore cases and they
then grow out into
threads while still
inside of the case
and never develop
whips. All the fish
and water molds
develop breeding
organs of two kinds,
male and female.
The female organs
are usually spher-
ical cases, which
contain a small
number of eggs,
and the male organ
is an elongated
thread which is
sometimes branched
and usually arises
from the same
thread which pro-
duces the swollen
egg case. Now the
male thread pene-
trates the egg case
and can be seen
making its way between and around the eggs, but a remarkable
feature lies in the fact that they never as far as has yet been
observed breed with the egg cells. The latter nevertheless
FIG. 42. — Water and fish molds. 1. A fungus thread with
an unopened spore-case. 2. An opened spore-case
with the escaping swimming spores. 3. An egg-case
with the male threads penetrating it. The spherical
bodies in the egg-case become the resting egg-spores.
Highly magnified. 1 and 2, after Thuret; 3, after
DeBary.
Minnesota Plant Diseases. 107
seem to be stimulated for they now become the egg spores
whose special function is that of resting spores. They cannot
be made to develop further until they have rested for some
time. After this rest period they divide up internally into
swimming spores.
These water molds grow luxuriantly on almost any kind of
decaying organic matter in the water. When the bodies of
dead insects, such as flies or grasshoppers, fall into the water
they soon become surrounded by a halo of fungus threads from
the water mold which quickly forms swimming-spore cases in
countless numbers. When the nutrient material becomes
scarce egg spores are produced. Dead minnows or fish are
also quickly attacked by these fungi and the rapidity with which
the fungus spreads is well seen in the growths on a fisherman's
minnow bait. Not only are dead fish attacked. When living
fish have suffered the loss of a few scales or some other slight
injury, the fish mold may gain entrance through this spot and
may spread rapidly as a parasite and finally kill the fish. It
may even gain entrance through the gills or in the eyes of the
fishes, and it very frequently attacks their eggs. The fish
molds therefore may become dangerous pests in hatcheries.
Numerous epidemics of these molds are known to have de-
stroyed myriads of fishes in their native streams and lakes as
well as in hatcheries. Not only fishes but other aquatic animals
such as mud puppies and probably other amphibians are sub-
ject to attack, as are also many of the tiny microscopic water
animals so abundant in stagnant pools and lakes, and thus the
fungus preys on the food of fishes. A few forms are known
which attack the pond scums. As is to be expected in such
plants, the parasite is not of a high type. i. e.. no exact selection
of host seems probable though this simple method is highly
proficient in its own way. The proficiency is due largely, no
doubt, to the great number of swimming spores formed and the
rapidity of their formation. (Figs. 32, 33, 42.)
Sewer and drain pipe molds (Saprolcgniinccc in part). It is
to be expected that sewer- and drain-pipes would offer favorable
habitats for fungi of the general habits of the water molds and
there are fungi which are constantly found in these places. A
large amount of decaying organic material is always present to-
io8
Minnesota Plant Diseases.
gather with constant moisture. These fungi are close relatives
of the water-molds, differing from them in the long-beaded
shape of their threads and in the presence of but one egg in the
egg-case. Swarm-spores are again the chief means of distribu-
tion, though bits of the threads may be carried along in the
pipes and become lodged. By growth these again produce an-
other colony. In all kinds of drain-pipes,
in sewers or in the drains of refrigerators
these molds abound. They form dense,
compact masses of mycelium which may
ultimately stop up the pipe and thus
cause trouble. They may also abound in
streams, below factories or at the mouths
of sewers, and may form large woolly
masses of mycelium. (Fig. 43.)
Damping-off fungi (Saprolegniinecein
part]. These molds are also relatives of
the water-molds but have approached
more nearly to the terrestrial habit. In
fact many of them are able to live com-
fortably in a very moist atmosphere,
though typically they live in or at the
surface of the water. The damping-off
fungi have swimming spores and egg-
spores ; only one egg is produced in a
case and the breeding between egg and
male elements has been observed. The
egg-spore is again a resting spore. Like
the fish- and water-molds the damping-
off fungi may live as saprophytes upon
dead organic matter in the water,
(more highly magnified), i\[anv of them are, however, parasitic on
with characteristic gran-
ules near constrictions. 3. algae, such as pond scums and green
Swimming spores. High-
ly magnified. After felts, while a few attack pimvorms. By
Prinpsheim.
far the most common forms are, how-
ever, those which cause the disease known as damping-off.
When seedlings, particularly of the mustard family, are sown
very thick and are kept very moist, the damping-off fungi ap-
pear. They attack the seedlings just at the surface of the soil or
FIG. 43 — Sewer-pipe fungi. 1.
Fungus threads with pecu-
liar constrictions. 2. Same
Minnesota Plant Diseases.
109
below it, killing the tissues and the seedling tumbles over and is
further appropriated by the fungus. In this way the fungus gains
strength and large numbers of seedlings may fall. Not only
mustards but clover and beet and other plants are subject to at-
tack. In the slight preference of host, the damping-off fungus
shows a slight indication of advance in parasitic methods, but
the latter are still primitive and success only attends such favor-
able conditions as excessive moisture and crowded host plants.
(Fig. 34.)
FIG. 44. — Downy mildew*. 1. Ilowny mil. lew of seedlings ( I'hyto|>hthora omnivon) ;
formation of egg-spores by breeding act; a male cell and egg-cell case. 2. i'otato
blight ( I'hyt.'i'hthora infentans). tlirrad with >;•• n- like swimming spore-case* (•). 3.
(Pcronospora alsinearum.) Formation of epg-itpore by breeding act in another mil-
dew; letters as in 1. 4. Kgg s;»orc formation in still another mildew; letters as in 1.
5. Thread of a downy mildew ( f'eronos;»ora leitosperma) he.iriiiR spore-like swimming-
spore-cases (s). All highly magnified. After Deltary.
Downy mildews and their allies (Fcronosporinc<c in part).
Long ages ago, when the fungi had developed the saprophytic
and parasitic habits, as one sees in the damping-ofT fungi, it
became advisable to abandon the aquatic life because more op-
portunities are presented in aerial conditions. The damping-ofT
fungus shows some such tendency but the blights or downy
mildews show it still more clearlv. for most of these fungi are
iio Minnesota Plant Diseases.
parasites on common garden plants. It is a noteworthy fact,
however, that they still require very damp atmospheres in
which to develop well and only become epidemic in excessively
moist seasons. These fungi have a very well developed system
of threads which are much branched and spread through the
tissues of the host plant. They are provided with little sucker-
threads which penetrate the cells of the host plant and often
form here very densely branched systems of threads. These
sucker organs steal the nutrient material from the host plant.
It is moreover a robber method similar in some respects to that
of the damping-off fungus, for the host-plant parts attacked
are ruthlessly and almost immediately killed. Such is the com-
mon effect of potato blight or downy mildew of vines. On the
other hand, these fungi show more power of selection than do
the damping-off fungi. Some are capable of attacking differ-
ent and even distantly related plants but in general a given
fungus of this group is quite constantly found on the same
host or on closely related plants, e. g., members of the same
genus or family. Wherever the threads of the fungus become
abundant, the host plant is killed. The ancestral aquatic habit
of these plants is still retained in the method of distribution
by spores for these are swimming spores. Hence the fun-,
gus can spread rapidly only when there is a great abundance
of moisture, as during excessive rains and cloudy, misty days.
Under such conditions the swimming spores spread rapidly in
the water drops and may be carried in these drops from plant
to plant. An epidemic may thus result. On the other hand,
these fungi have learned terrestrial methods of spore distribu-
tion. We find upon a close examination of the area infected
by a potato blight, or false mildew, at first a thin grayish or
whitish haze or shimmer spreading over the leaf, and that this
fine mold-like growth is caused by an enormous number of
usually much branched threads which come out of the air pores
of the leaf. They pinch off of each branch end small, round,
pear- or lemon-shaped bodies which look very much like spores
and are commonly so-called. These bodies are light and easily
carried by the wind and thus alight on other plants. In the
potato blight and some of its allies this spore-like body does
not betray its real nature until the conditions of moisture are
Minnesota Plant Diseases.
1 1 1
favorable. Then it shows itself to be a spore-case and forms
internally numerous swimming spores, which escape and spread
the disease. Some of the downy mildews, however, have
learned still more thoroughly the terrestrial habit and have al-
most entirely forgotten the ways of aquatic fungi. In these
the spore-like body really acts as a spore, grows out directly
into a thread and does not develop swimming spores at all,
although in some forms it starts out as though it were going to
form them and then abandons the attempt. We have here an
excellent example of the persistence of a habit even after it is
FlC. 45. — A Downy mildew with the as|*ct of a white rust. Under surface of burweed
elder (Iva xanthiifolia) showing dense clusters of »|>ore-like si>ore-caM-«. Original.
ill adapted to the plant's new methods of life. Egg-spores
are also formed throughout this group, though in a few cases,
as in the common potato-blight, they have not yet been ob-
served. As in the dampir.g-off fungus, the breeding act of
many forms has actually been demonstrated. The egg spores
are typically resting spores and, as in the damping-off fungus,
serve to tide the plant over winter or other unfavorable sea-
sons. They are usually found in abnormally swollen parts of
the host. The plants of this group are all parasites and most
of the known forms attack cultivated garden plants. They live
1 1 2 Minnesota Plant Diseases.
chiefly in the leaves where, in the roomy air-spaces, which are
charged with moisture, they realize most nearly their prefer-
ence for moist conditions. Perhaps the most famous fungus
in this group is the potato blight, which causes rot of the plant
in the field arid a dry brown rot of the tubers in the cellar.
Epidemics of this disease follow excessively moist and warm
seasons and have been known to cause great damage. Toma-
toes and other plants of the potato family also suffer attack
from this fungus. Another very famous fungus of this group
is the downy mildew of vines, which attacks the vine foliage
and fruit, both of the old and new world, and causes great dam-
age. Others exhibit habits similar to damping-off and attack
seedlings. Some are found on bean plants, on grasses, and a
very conspicuous one inhabits members of the carrot family.
They are also found on sun-flowers and again a very impor-
tant one is known on melons and cucumbers and their allies.
Lettuce, beets, clovers, onions and tobacco plants, besides a
large number of wild plants, as violets and anemones, ar^
known as hosts to these parasites — in fact, almost every family
of plants has its downy mildews. (Figs. 2, 39, 40, 44, 45, 166
to 171, 196 to 198.)
White rusts (Peronosporinccc in part}. Very closely allied to
the downy mildews are the white rusts. In their egg-spores
and general habits they are quite similar. Just as in the potato
blight, spore-like bodies are produced which later show their
spore-case nature, but these spore-cases are not cut off singly
from the ends of threads. They are formed in chains and these
chains are arranged together in such dense clusters that they
form a white rust-like mass when the host-plant skin has been
broken and thrown back.
The most abundant of the white rusts is one common on
the weed plant known as shepherd's purse, and found also on
other mustards. Another is found on pig weed and on portu-
laccas, others on morning glories and on a great many other
plants. As in the downy mildew the egg-spores are often found
in swollen portions of the host where the fungus has excited
the host plant to unusual effort. The advantage to the para-
site is evident, since it is in the egg-case-producing part of the
plant that much nutrition is needed. (Fig. 45.)
Minnesota Plant Diseases.
1 1
Black molds (Mucorinccc in / art). These fungi are exceed-
ingly common plants found on starchy materials and hence
often called bread molds. Although they have descended from
water-inhabiting plants they have retained almost no trace of
an aquatic habit, with the exception of the requirement of a
moist atmosphere for growth. That is to say. there is no
formation of swimming spores; for all of the spores, except
the resting spores, are distributed by the wind, though aided in
some cases by a special explosive apparatus. The spores, as in
other algal fungi, are of two kinds, viz. : the egg spores and
those produced without breeding. The former are formed by
a different method from that of the false mildew where an egg
and a differently shaped male thread branch are found. In the
black molds both breeding organs are alike in size and shape
and are indistinguishable, just as is the case in the pond scums
among the algae. The egg spore is a resting spore and is
provided with a large, thick, resistant, usually black-colored
coat. However, the most common form is that of the non-
sex ually produced spore. These are
produced in tiny, black, spore-cases,
which appear like small, black points in
the mass of mold threads. Each case
contains a great number of spores which
escape by the breaking of the spore-case
wall and are blown about in the wind.
In some molds, which are particularly
abundant on horse dung, there is a swell-
ing in the thread just below the spore
case and this swelling acts as a syringe
bulb under pressure. \\ hen the spores
are ripe the whole spore case contents
arc blown off at once and thrown a half-
foot or more into the air.
The black molds are of very great im-
portance on account of the damage which they cai^e to food
stuffs, particularly the starchy foods. liread. cake and pastry,
when kept moist, will almost surely develop mold, because mold
spores are to be found in the air of almost any region and at
almost any time of the year. The black molds are all typically
. 4«.-A black in..l,l. The
black »porc-casc» art seen
on thr end* of the fmiyus
threads. Highly magnified.
After Z-.-.f
ii4 Minnesota Plant Diseases.
saprophytes. A few have, however, learned just the beginnings
of parasitism, e. g., those black molds which attack ripe fruits
through wounds or thin skins. Since the protoplasm in fruits
is in a dormant condition and contains an enormous amount of
food material, sugar, etc., the black mold is able to live here,
amateur though it may be, as a parasite. Some animal dis-
eases have already been mentioned as the result of black mold,
though in these cases it is "doubtful whether the fungus is actu-
ally parasitic, or merely saprophytic. It has in recent years
been found that some molds have the power of changing the
starchy material into sugars and adepts in this process have
been selected and are now used to convert potato starch into
sugar ; from these sugar solutions, by the action of yeast, alco-
hol is then produced. In this process the potato starch is ster-
ilized by heat and enclosed in perfectly clean casks, and the fun-
gus is then introduced under perfectly clean conditions. When
the starch is all converted, the yeast is introduced, also in the
pure state, so that the whole process is as carefully conducted
as in the culture of bacteria by an expert bacteriologist. By
this process the yield of alcohol has been enormously increased.
Moreover, some black molds when submerged in a sugar solu-
tion have the power of forming alcohol and carbonic acid gas
just as do the yeasts ; but they are not vigorous enough to be of
economic use.
Some of the peculiar intoxicating drinks of Asiatic tribes
are produced by the introduction of certain black molds and
yeasts into starch mixtures.
Many black molds are also to be found on decaying fungi,
as mushrooms, though it is not certain that they are actually
parasites, they undoubtedly hasten the decay. (Figs. 14, 16,
17, 46.)
Black-mold parasites (Mucorinecc in part). Closely related
to the true black molds are certain forms which live chiefly as
parasites on other black molds. They are also found on a few
other fungi. If a piece of bread with an abundance of black mold
on it be left in moist conditions for some time these parasitic
molds almost always appear. They are very minute plants and
require high powers of the microscope for their observation.
They form a delicate thread mycelium from which fine branches
Minnesota Plant Diseases.
FlC. 47. — An insect
mold. (Fly chol-
era fungus.) 1. A
cluster of threads
with spores clinp-
ing to hairs on
the insect's body.
2. Fungus threads
from the fat body
of an insect. 3.
Spore -bearing
threads, highly
m a g n i fi e d. 4.
Above, a single
spore; below
germinating spore
forming a sec
ondary spore
Highly magnified
After Brefeld.
are sent into the threads of the host plant
where they obtain nourishment for the para-
site. They are also found on certain of the
blue-mold group of fungi.
Insect molds (Entomophthorinece). Of all
the algal fungi these are most clearly non-
aquatic in their habits. Like the black molds
they form breeding spores, from similar sex
organs, though these spores are not of fre-
quent occurrence. On the other hand the
non-sexual spores are very abundant and
are pinched off from the ends of special
threads. Moreover, there is usually some de-
vice for throwing the spore to a distance.
The thread is swollen just below the spore
and when the latter separates from the thread
the release of pressure in the swollen portion
results in the forcible ejection of the spore.
This is the case in the common fly cholera
fungus. Most of the insect molds are para-
sites on insects either in the adult stage, as
in the fly cholera, or on the larva.
When the fungus has gained entrance to
the body of the insect it soon kills the
latter and then lives saprophytically, pro-
ducing a great abundance of s|x>res. House
flies are commonly attacked by fly cholera in
autumn and when they die cling tightly to
window panes and other objects. They are
soon surrounded by a halo of spores thrown
onto the pane from the fungus threads by
means of the spore-throwing device described
above. Many other insect diseases are
caused by these fungi. Caterpillars some-
times become covered with moldy growths
which completely envelop them. From the
surface of these growths are thrown the
fungus spores. These parasites of insects
prove of great benefit to plant growers
1 1 6 Minnesota Plant Diseases.
because they destroy so many insect pests of plants, as lice, lo-
custs, etc. They are also responsible for some destruction of
such common pests as mosquitos. Some insect molds are sap-
rophytes living on dung and are apparently of no economic im-
portance. A few attack plants and particularly the sexual
plants of ferns when cultivated in greenhouses. They cause a
disease similar to damping-off. The economic advantages of
this group, however, far outweigh the injuries. (Figs. 14, 47.)
Chapter IX.
Fungi. Kinds of Fungi. Sac Fungi.
Sac fungi (Ascotnycctcs). The second of the three great
groups of fungi is that of the sac fungi and this group is in
short easily distinguished because all of its members bear at
least some of their spores inside of sacs. These sacs may be
spherical or pear-shaped or long-cylindrical, according to the
plant, and they always contain a definite number of spores.
The sacs in the simplest of these fungi are borne irregularly
upon the loose weft of the mycelium but in the very great ma-
jority of sac-fungi they are borne in capsules of various shapes
and often of great complexity.
Sometimes these capsules are little, black spheres, as in the
powdery mildews, with or without an opening, while in others
they may be borne in the fruiting bodies known as truffles or in
the cups of cup-fungi. According to our present knowledge a
breeding act seems to precede the formation of the sacs and in
some cases one. in others, numerous, sacs may arise as the re-
sult of a single breeding. A vast number of sac fungi form
more than one kind of spore — in fact many produce two
or three so-called accessory spores, so that the study of
such forms becomes a very difficult matter. Indeed, one may
find many of these accessory forms without the main sac-form
and it is then often exceedingly difficult or altogether impossi-
ble to even determine the fungus. Thousands of such fungi
have been found — many causing important diseases of plants —
which are thus imperfectly known and are described un-
der provisional names until more facts are discovered about
their life-stories and their proper sac forms. Not until then can
they be accurately and permanently classified. Such fungi are
called imperfect fungi. It is even probable that many have for-
gotten how to form their sacs and now produce only the acces-
sory spore-forms and thus present an actually imperfect life-
n8
Minnesota Plant Diseases.
story. Again, the sac spores may be of such seldom occur-
rence that they have been entirely overlooked.
Conspicuous examples of accessory spore-forms are seen in
the green mold growths of cheese, in the powdery mildews or
summer spores of the mildew fungi and in the honey-dew spores
of the ergot. The groups of fungi discussed in this and the
following chapter are subgroups of the sac fungi. (Figs. 10, 14
and below.)
Yeasts and their allies (Saccharomycetes). Undoubtedly the
simplest of all of the sac fungi, at least as far as structure is
concerned, are the yeast fungi, though this simplicity is to be
explained by a reduction from a more complex form, due to
peculiar habits. The yeast plant consists of a single sphere-
like or somewhat elongated
cell, so small in size that high
powers of the microscope are
necessary for their examina-
tion. These cells multiply
rapidly by bulging out little
spherical "buds" which be-
come separated from the par-
ent cell and soon produce new
buds in their turn. A cell
may continue to bud off little
plants as long as nutrient ma-
terial is available. Sometimes
the daughter cells do not sep-
arate from the mother cells
completely but remain more
or less loosely attached and
thus false filaments or threads
are built up. Such are often
found in the scums on the sur-
face of yeast-containing fluids.
The simple method of propa-
gation by budding suffices the
yeast plant for multiplication during favorable conditions and
the ordinary yeast-plant-cell is often, moreover, capable of re-
sisting successfully very unfavorable conditions. But when
FIG. 48. — Yeast fun
cells.
Ordinary
bread yeast, showing sprouting vegeta-
tive cells. b. Spore formation in a
yeast; four spores in a sac. Below are
shown four free spores. Highly magni-
fied. After Rees.
Minnesota Plant Diseases. 119
their nutrition runs low, yeast plants may prepare for unfavora-
ble seasons by forming sac-spores. A breeding act has been
described for at least two kinds of yeasts, preceding the forma-
tion of the sac-spores. The two plant cells which unite are
both similar, and inside of the united cell four spores are
formed. In most yeasts, however, no breeding act precedes
the formation of sac-spores. The sac-spores have thick walls,
are resistant and are often capable of resting for a long time
before resuming growth.
Yeast plants are, in general, found growing most vigorous-
ly in liquid solutions of nutrient material for the budding habit
is of peculiar advantage in such an environment. The daughter
cells are easily separated from the mother cell and are carried
by convection currents to other parts of the liquid where they
get more nourishment. It is in sugar solutions or in closely
allied substances, as starch, that the yeasts thrive best. In
nature they are found in the juices exuding from ripe grapes or
other fruits.
Many yeasts possess the power of breaking down the sugars
into carbonic acid gas — which escapes in the form of bubbles —
and into alcohol ; i. e., they have the power of fermentation.
This process is made use of in bread-making and in beer and
wine making. In the former the carbonic acid gas is used
in the raising of the bread while in the latter the alcoholic
products are those sought for. Xot all yeasts have the power
of fermentation and many, although possessing this power, are
not vigorous enough to be of commercial use. The common
beer and bread yeasts have been chosen because they are vig-
orous fermenters. Moreover, many yeasts can ferment only
certain kinds of sugars, as milk, or cane or grape sugar. One
may also find several kinds of yeasts which, as far as structure
and appearance is concerned, might be considered identical
but which show that they are different in their powers of fer-
mentation. Yeasts also play an important part in the produc-
tion of many drinks of far eastern peoples, as of Japanese
"saki." of kefir and kumys. though in these crises certain bac-
teria and blue molds may aid in the process. In the produc-
tion of by-products, singly and in combination, yeasts may
differ in the quality or tastes of the liquors thus produced, and
I2O Minnesota Plant Diseases.
the custom now obtains in some breweries of using only pure
cultures of yeasts of a known kind, thus insuring uniform re-
sults. Certain wild yeasts and bacteria may find their way
into the brew and by the formation of peculiar compounds may
spoil the flavor. It has already been mentioned that certain
yeast-like fungi cause several diseases of lower animals as well
as thrush and sore throat in children. The systematic position
of these fungi, however, is uncertain at present since the sac-
spores have noc been found. The power of fermentation is not
confined exclusively to the yeasts since other fungi, though not
many, possess this power, and it is possible that the thrush fun-
gus is a member of some other group of fungi. As far as is
known at present no yeasts can be said to cause undoubted
parasitic disease in plants. It must be remembered, however,
that in the exuding sugary juices of fruit under natural condi-
tions, or from wounds, yeast cells are very commonly found,
and it is not inconceivable that they work their way into the
fruit and assist in fruit rot. (Fig. 48.)
Slime-flux fungi (Endomycctacccc). In the slimy exudations
which often flow from wounds in trees a great variety of such
organisms as bacteria and fungi abound, and among them a
close relative of the yeast fungi is not uncommon. This fun-
gus differs from the yeasts in always possessing a thread myce-
lium and forms its spores on branches of this mycelium. It is
not certain \vhether or not this fungus is the cause of the flux
or whether it simply finds in the flux congenial conditions and
appropriate food.
Leaf curls and plum pockets (Exoascacccc). These fungi
are of frequent occurrence on plants of the plum family such as
domestic plums and cherries and peach plants. The host plant
part is usually swollen. Leaves thus affected sometimes curl
much and become distorted. Plum and cherry fruits when at-
tacked by the fungus form the well-known "pockets" without
stones. Both pockets and curls bear the spores of the fungus
in a layer which covers the whole or a considerable part of the
affected organ. This region takes on a greyish white color
which is due to the presence of a great number of short cylin-
drical sacs, each containing eight spores. The spore-sacs stand
side by side, like posts in a palisade, upon the surface of the
Minnesota Plant Diseases.
121
leaf or pocket, and at right-angles to its surface. They arise
just under the cuticle which is pushed up and sloughed off as
the spore-sacs ripen. Xo breeding act has been seen tp pre-
cede the spore-sac formation. The sac-spores are often capa-
ble of budding in yeast fashion when placed in sugar solutions,
and in some of the fungi they bud in this fashion before they
are released from the sac so that the latter may then contain
a large number of spores. In addition to the effect upon fruit
and foliage of plums, these fungi often cause witches'-brooms
on cherries and plums as well as on birches and alders. Oaks,
FIG. 49. — 1'lum-pocket fungus ami loose-weft IHIIKH- 1. A loose wcfted collection of
spore sacs, which is surrounded by barbed threads. A !<•.•-« wi it fungus. 1*. A smill
group of threads from 1, bearing a number »f MCS. It. Same at -'. showing a single
sac with its sac-spores. 4. Plum pocket fungus. Shows the *|>ore-sacs of a |>lum
pocket fungus arranged in a palisade on the surface of the pocketed plum; c the cells
of the plum; m fungus threads and h the fungus spore sics. All highly mtgniried.
1, 2, 3 after Sachs; 4 after Hillary.
poplars and cottomvoods and sumacs are also attacked by
them. (Figs. 49. 193.)
Loose-weft fungi (Gyntnoascaccff) Very closely related to
the slime-tlux fungi are the loose-weft fungi. The spore sacs
are borne in dense clusters on a very loose weft of threads and
in no regular arrangement. In some, there is a loose system
of threads surrounding the cluster, forming a covering not un-
like a large-holed basket. These* threads are also usually
armed with tiny spines. Such a covering is merely an ama-
teurish, spore-sac capsule. The loose-weft fungi are peculiar
in their habits. Manv are found exclusively on feathers.
122 Minnesota Plant Diseases.
some on bones, some on bees' nests, while others seem to pre-
fer animal remains and meat extracts. They are not, however,
either conspicuous in number or in size. (Fig. 49.)
Green and blue molds (Aspergillacea). The blue and green
molds are amongst the best known and most conspicuous of
fungi. They are the great destroyers of food stuffs and as such
are well-known to every housewife. The common green or
blue mold is an accessory spore stage. In this form thousands
of threads stand upright side by side, each branches very pro-
fusely in broom fashion and each branch terminates in a long
row of pinched-off spores which are of the characteristic green
color. Millions upon millions of these spores may be produced
by a small patch of mold. Such mold spores are present in
great quantities in the air at almost any time of the year, so
that just as soon as any food-stuff is exposed to the air it may
be sown with green mold spores. These will quickly germi-
nate and will produce in a very short time — often in a few days
— another crop of mold spores. The green-mold spores,
though the most common, are not the only spores produced by
these fungi. There is also a sac-spore, though in most forms
it does not occur frequently — in fact it is usually rare. These
sacs are spherical as in the loose-wefted fungi, but are found on
threads tightly woven together, and the whole spore-sac
mass is surrounded by a membrane-like wall or covering, which
is formed by closely united threads. These sac-capsules are
often yellowish or black and are seldom larger or even as large
as a pin-point. They are usually tiny spheres and of a solid
structure. The spores, when ripe, are released by the de-
cay of the capsules. There is no definite arrangement of the
sacs in the capsule nor is there a special opening through the
capsular membrane to allow of the escape of the spores. In
some forms, at least, a breeding act precedes the formation of
the capsule. The green and blue molds are especially fond of
bread and other starchy materials, preserves, etc. They are
also found on cheese and some varieties of mold are used to
ripen the cheese, where the flavor is largely due to the green
mold present. They are frequently found in preserved fruits
and jells and also as simple parasites, causing mold-rots of
fruits. (Figs, i, 1 88, 189.)
Minnesota Plant Diseases. 123
Allies of green and blue molds. There are numerous allies
of these molds which have strange habits indeed. Some, as in
the loose-weft fungi, live on feathers and some live on the
horns and hoofs of cattle. These fungi are of comparatively
rare occurrence and have not yet been collected in Minnesota.
Others, however, which resemble the powdery mildews in many
respects, are found on the leaves and twigs of living plants,
though seldom assuming a destructive parasitic habit.
False truffles (Tcrfcziacea). As is well known, the truffles
are underground bodies resembling, to a small degree at least,
small potatoes in appearance. Now the false truffles are very
similar to the true truffles in appearance but they differ in some
characters. The spore-sacs are not arranged with the same
regularity which is common in the true truffles but are found
in a loose weft as those in the loose-weft or blue-mold fungi.
They may, in fact, be considered as huge underground spore-
sac capsules of blue-mold-like fungi. Some of these false truf-
fles are apparently the producers of fungus root-hairs in some
flowering plants. They have not yet been collected in Minne-
sota.
Black fungi (Pyrcnomycetinca'). These fungi constitute an
enormous group of plants. They all agree in having a spore-
sac capsule in which the spore-sacs are arranged in definite or-
der and arise from the bottom of the capsule. The latter are
usually, but not always, black in color and often resemble burnt
wood. The spore-capsule in all. except the powdery mildews,
has a definite method of opening by means of a pore which is
sometimes protected by spiny processes. The simplest forms,
the powdery mildews, are very similar in many respects to the
blue and green mold plants and are their nearest relatives.
Like these molds the black fungi possess accessory spore-forms
and those of the powdery mildews, constituting the summer
spores, are particularly like the green mold spores of the green
mold fungi. They are not. however, green in color. The
black fungi are conspicuous in the great number and variety
of accessory spore-forms. Some species alone possess three or
four kinds of such spores in addition to the sac-spores. The
common Minnesota forms of the vast number of plants in this
group can be arranged in the following ten groups.
124
Minnesota Plant Diseases.
Powdery mildews (Erysiphaceai). The mildews constitute
the simplest group of black fungi. The mycelium is usually
to be seen on the surface of leaves as a white, moldy covering.
The threads send branches into the skin cells of the host and
there absorb their food and live parasitically, but the main my-
celium of the fungus never lives inside of the host. In the
FIG. 50.— A powdery mildew on common plantain leaf. The powdery coat of the threads
and the small black fruiting bodies can be clearly seen. Original.
summer, spores are produced in enormous numbers and form a
dust-like covering over the leaf, whence the common name of
powdery mildew for this group of fungi. These spores are
pinched off in rows from upright threads, which thus become
converted into chains of spores. Towards fall there arise, on the
Minnesota Plant Diseases.
125
mycelium, minute spheres about the size of a pin point. They
are at first white, then become yellow and finally dark brown to
black. They are the sac capsules and bear one or more spher-
ical or pear-shaped sacs with two to eight spores in each, ac-
cording to the species. The capsular wall has no special meth-
od of opening but it may often possess elaborately-shaped
threads known as appendages, which are often much branched
and form a crown
or circle around the
case. Such may as-
sist in the distribu-
tion of the who'e
spore-sac capsule.
The powdery mil-
dews live entirely on
the outside of leaves
and young branches
of plants and are
often danger o u s
parasites. A great
number of our com-
mon garden plants
as well as wild flow-
ers are attacked by
some sort of pow-
dery mildew, though
the conditions are
not usually such as
to create epidemics. Roses and grapevines are conspicuous suf-
ferers as are also gooseberries and other garden plants. These
fungi are also found abundantly on lilac bushes, all kinds of wil-
lows, birches, poplars, elms. oaks, maples, and many others, but
on these do not often cause much damage. ( Figs. 10. 50 to 5-'.
134. 135. 1 5_>. HJJ. jo_> to -'04. Jio. )
Honcy-dcw fungi (Pyrciwinycctinctc in purl). Structurally
this group of fungi is a close relative of the mildews. The
spore-sac-capsule is built on the same general plan but does
not usually contain appendages while, on the other hand, it is
usually furnished with a pore for the exit of the sacs and
. 51. — The (ruiiuiK l>o<ly of the powdery mildew of
hlack haw. glimtniK (he ;i •;* n.i.mr-.. The sac -capoulc
has hern hruken and (he *ai-s. each with about ri^lit
•(Mire*, .in < inrtjjini; fnnii the -'!n. Highly magnified.
MuT<>|>li»t..Kra|>h >>y I W. I>. llolway.
126
Minnesota Plant Diseases.
spores. Accessory spores are also found in abundance in these
fungi, many being enclosed in special capsules similar in ap-
pearance to the sac-capsules. The mycelium is, moreover,
often black. Many of these fungi live on leaves but not in a
typically parasitic fashion. They thrive well on the excretion
of certain insects and since such excretions are found abun-
FIG. 52. — The fruiting body of the powdery mildew of willow, showing the appendages and
spore-sacs. The latter have been forced out of splits in the sac-capsule. Highly mag-
nified. Microphotograph by E. W. D. Holway.
dantly on the leaves of plants these fungi are also found on the
surface of the leaves. On account of the abundance of myce-
lium produced and on account of its dark color a vigorous
growth of mycelium may exclude sunlight from the leaves and
thus injure the leaf, although the fungus may not in itself be
harmful. These fungi are often known as the sooty molds on
account of the soot-like mycelium which is developed.
Minnesota Plant Diseases.
127
FlC. 53. — Ergots of grasses. On left is one on a reed-grass: on right one on quack grass;
s sclerotium or "ergot," the fungus storage organ. Original.
128
Minnesota Plant Diseases.
Ergot fungi (Hypocrcacccc in part}. The fungus which pro-
duces ergot is a member of the black fungus group, though not
a very close relative of the mildews. The life-story of such a
fungus is somewhat com-
plex and we may illus-
trate by that of the ergot
of rye. In the summer,
when the youngest
grains are commencing
to fill, or just before that
period when the grass
flower opens, the spores
of the ergot fungus may
lodge in the flower and
start to grow. The
young threads are capa-
ble of attacking the grow-
ing grain and in a short
time almost completely
absorb the latter, form-
ing a more or less soft,
spherical or elongated
mass of mycelium, at the
summit of which are
formed, in convolutions
of the surface, thousands
of summer spores. These
are accessory spore-
forms. The production
of these spores is accom-
panied by the formation
of sweet saccharine fluids
which are very attractive
to certain insects. Visit-
ing insects become at
least partially covered by
summer spores in the
sticky solution and in their visit to other flowers transfer
these spores, just as they do the pollen, from flower to flower.
54. — I-rgot iunstis on canary grass; s sclerotium
or storage organ of the fungus. Original.
Minnesota Plant Diseases. 129
Now it is only in the young stages of the flower that these
spores can attack the grain so that rapid spread of spores is
necessary and is, moreover, readily accomplished by this insect-
method of spore distribution. These spores are produced by
the fungus for some time. Toward the time of ripening of the
grain, the production of summer spores ceases and the fungus
commences to pack up reserve nutrition in its threads. These
are now compacted together in a very solid mass the exterior
of which turns violet black. The whole structure becomes a
storage organ or sclerotium, and often requires a rest period be-
fore it will develop further. In this sclerotium nutrient mate-
rial is found in the form of fungus starch and oils. Certain vio-
lent poisons are also found in them and are extensively used in
medicine, for this storage organ is known in pharmacy as the
drug "ergot." Of just what use to the fungus these poisonous
compounds are is not quite clear. Possibly they tend to pre-
vent the consumption of strongly ergotized grains, thus avoid-
ing destruction by feeding animals.
In the spring time, after their winter rest, the ergots are
capable of further growth. When placed in proper conditions
of moisture and temperature they send out small cylindrical
stalks which bear tiny spherical heads about the size of small
brown mustard seeds. These little heads become blackish
in color and bear the sac spores. They are not, however, single
sac-capsules but, if one examines the surface of this sphere, one
finds a large number of little openings and. upon further inves-
tigation, these openings are seen to connect with pear-shaped
cavities just beneath the surface. Each of these cavities is in
reality a spore-sac capsule. In other words, the spore-sac cap-
sules have been aggregated together onto a common surface
and produced in abundance on account of the great amount of
available storage material in the ergot. In each sac capsule
are numerous very long, cylindrical sacs, and each sac contains
eight long thread-like spores, which have already been divid-
ed by cross-walls into about sixty-four cells. These cells sepa-
rate very readily and each is capable of growing out into a my-
celium, so that each sac contains about five hundred spore cells.
In addition to the spore-sacs there may be long, swollen
threads in the sac-capsule, which aid especially in discharging
130
Minnesota Plant Diseases.
the spores and sacs from the capsule. The spore-cells or the
honey-dew spores may be carried to another flower and thus
the life-story is recommenced by the new infection of the grain.
The ergot fungus is common on a great many grasses and
particularly upon cultivated species as wheat, rye, barley, etc.
It is found very abundantly upon wild rice in many places and
is also abundant on grasses growing on railroad right-of-ways.
(Figs. 53 to 55, 154, 155.)
FIG. 55. — Fruiting bodies and spores of the ergot fungus. 1. Young ergot in honey-dew
spore stage. 2. Small section of the top of 1, showing summer or honey-dew spores.
3. A germinated ergot with sac-capsule-bearing clubs. 4. The end of one of the clubs
in 3. 5. Section of 4, showing capsules at surface of head. 6. An enlarged view of a
capsule, showing arrangement of sacs. 7. A single sac showing long, thread-like
spores. 1, 6 and 7 highly magnified; 4 and 5 of medium magnification. 1-6 after
Tulasne; 7 after Brefeld.
Caterpillar fungi (Hypocrcacccc in part}. A very close rela-
tive of the ergot fungus is the caterpillar fungus, the habits of
which have already been described in a previous chapter.
Spores of the fungus send out germ threads which penetrate
the hard coat of the caterpillar or grub and, feeding on the soft
Minnesota Plant Diseases.
parts of the insect-body, build up a mycelium which consumes
all of the interior of the host except the chitinous skin. It
thus stores up an enormous amount of nutrient material in the
form of a storage organ or sclerotium, which is an exact cast,
not only of the external form of the insect but also of the in-
ternal organs. When this storage organ has rested for some
time, and when conditions of moisture and temperature are
favorable, it sends up,
usually one or more,
rarely two, stalks,
which come above
ground. Here they
form a c!ub-s h a p e d,
bright-orange - colored
body which may easily
be mistaken for a club
fungus. Close exam-
ination shows this
body to contain nu-
merous small holes
just as in the head of
the stalk on the germi-
nating ergot, and these
holes again communi-
cate with pear-shaped
cavities, which are the
s p o r e-sac capsules.
The sacs also contain
eight long, thread-
shaped spores, divided
into numerous cells,
each of which is able to form a germ thread and thus infect
other grubs or caterpillars. Sometimes the storage organ
does not produce a sac-capsule-bearing stalk, but produces in
one of several ways a great abundance of accessory spore forms
which are pinched off from threads in enormous numbers.
This happens if one places a freshly developed storage organ
in a moist chamber, or it may happen in nature where one
finds fraved-out branches or strands from the storage oriran
FIG. &«.— A caterpillar lun^u-. The insect -h.i
bodies are fungus casts of threads wlurli f
storage organ; raising from these are cluli sha
bodies which are covered above with fine wa
These warts are the tops
i )riginal.
>f the sac-spot e-caj>su
132
Minnesota Plant Diseases.
giving rise to a
dust of white
spores at the sur-
face of the
ground. These
spore-forms have
all been described
as of separate and
independent
plants. They
seem to be able to
infect the insects
just as do the sac-
spore cells. These
fungi are thus
seen to be very
similar to the er-
got fungus in all
essentials but the
accessory spore
forms are more
numerous and are
found under dif-
ferent conditions
than are those of
the latter. (Figs.
!0, 15, 3i, 56.)
Strangling fungi
(Hypocreacea in
part). On a few
grasses in the
state occurs a fun-
FIG. 57. — A strangling
fungus on grass leaves
and stems. A few
leaves extend above the
fungus fruiting body,
but the growth of the
host is usually stopped.
The surface of the fun-
gus fruiting body is
covered with warts
which are the ends of
the spore-sac-capsules.
Original.
Minnesota Plant Diseases.
133
gus which is closely related to the last two groups of
fungi and particularly to the caterpillar fungus. This fun-
gus exerts a strangling action on the host plant. It appears as
a whitish or light-tan-colored ring around the young leaves at
the tip of the plant. The threads soon form a solid mass en-
closing the young leaves and pre-
venting them from unfolding.
The branch on which the fungus
is thus formed may ultimately die
off. \Yhen the fungus has in-
creased somewhat in thickness the
sac-spore capsules make their ap-
pearance as pear-shaped cavities on
the surface of the fungus, just as on
the clubbed stalks of the caterpillar
fungus. The sacs and spores are
also similar to those of this fungus
in appearance. The accessory spore-
forms appear on the fungus preced-
ing the sac-spore forms. The life
story in this fungus is thus seen to
be simpler than in either the ergot
fungus or the caterpillar fungus.
No storage organs are developed.
(Figs. 57, 58.)
Other allies of the caterpillar fun-
gus (Hypocreacecc in part). Very
commonly on the milk mushrooms
are found fungi which cause the
abortion of the gills of the host and
which spread themselves out all
over the latter, covering it with a
bright red-orange color. On the
surface reddish wart-like bodies
can be seen and these are the spore-
capsules which, as in the caterpillar
fungus, open by pores to the sur-
face. The sacs are also of a similar
shape but the sac-spores are not as long.
— A strangling fungus. 1. A
grass stem will a fungus fruit-
ing body, part <
removed, showi
capsules in |x>si
sac. showing 1<>
f which has been
ig the sac-sporc-
ion. 2. A single
ig thread spores.
3. A single spore. 2 ami 3 highly
magnified. 1 after Winter: ?
and 3 after l!rt feld.
1 34 Minnesota Plant Diseases.
Bright colored stick-fungi are also allies of these fungi and
are very common on dead poplar or cottonwood sticks. On
the latter, cushions an eighth to a quarter of an inch in height
and breadth, are formed by the fungus and on the surface of
the cushion arise the accessory spores in great abundance.
After a time these spores cease to form and there is now pro-
duced from the same surface, supplanting the accessory spores,
the sac-spore capsules of the fungus, which are again pear-
shaped cavities with pore-like opening to the exterior. The
sac-spores are short and rounded at the ends and two-celled.
Some of these fungi are wound-parasites attacking orchards
and timber trees through storm or hail-wounds, etc. They are
sometimes known as reel knot. In some of these fungi still
other kinds of spores and spore bearing organs are encountered.
Chapter X.
Fungi. Kinds of Fungi. Sac Fungi.
if
Black knot and allies (Dotlridcacccc in part). One of the
most conspicuous fungi of Minnesota is the so-called black-
knot fungus of cultivated and wild cherries and plums. In
the mature stage of the fungus, its host-plant branches carry
black knot-like swellings and distortions, which
are very conspicuous. These knots so interfere
with the nutrition of the branch beyond that
the latter usually dies off in a year or two. The
fungus then gradually works its way downward
to the intersection of another branch, when this
is in turn killed off. The mycelium, which lives
inside of the bark, causes an increase in the
thickness of the latter, followed by a splitting
lengthwise. There is also a swelling of the un-
derlying wood and the fungus feeds upon this
swollen, soft mass. It builds up a dense mass of
the mycelium on the outside of the branch.
This mass when it first appears is a light-yellow-
brown and forms on its surface numerous sum-
mer spores which rapidly spread the disease.
These spores are pinched off of the ends of short
upright threads and are produced during the
summer. In the fall the mycelial mass becomes
knot darker until it is jet black. It looks not unlike
charcoal. In this mass are formed numerous
|>ear-shape<l sac-capsules over the entire surface.
These capsules open by minute pores to the ex-
terior so that in the spring the surface of the
knot appears to be covered with tiny warts, each wart indicat-
ing a spore-sac capsule.
:,-.'. i
" "morbusaV.
136 Minnesota Plant Diseases.
The sacs are long cylinders and contain eight spores, each
of which is made up of one large and one small cell. The sac
spores are shed in the spring and can infect new branches or
other trees. Almost all of our plums and cherries are subject
to the attack of this very dangerous fungus and in the wild
plants it is often found in very great abundance. It has proved
a dangerous pest to cultivated plants, and in many places in the
United States has ruined whole orchards and rendered aid by
state laws necessary for protection.
Another very common disease which is a close relative of
the black-knot is the fungus producing black spots on a great
many grasses both wild and cultivated. These spots are formed
on the leaves and are often mistaken for black rusts, but they
can easily be distinguished from the latter diseases by the fact
that the skin of the host is not split open in long lines and the
spores are not produced in the way well known for rusts. The
spores are formed in sacs borne in small spherical cavities or
capsules. These appear in clusters at the surface of the black
spots just as they are found in black-knot. The fungus is often
very abundant on grasses. In such cases they undoubtedly
levy a considerable tax on the starch-making apparatus of the
host and thus impoverish the latter.
Similar spots are produced on the leaves of elm trees. The
leaves of the common white elm are often found almost com-
pletely covered with such spots. The capsules and sacs are
produced in a manner somewhat similar to that in the black
spots of grasses and, though never seriously threatening the
life of the elms, undoubtedly steal much nourishment from
them. These black spots must not be confused with the tar
spots of maple and willow which are different diseases. The
latter are also sac fungi but belong to the cup-fungus group.
Superficially these fungi resemble each other; in the black spots
of grasses and elms, however, the sacs are found in pored cap-
sules while in the tar spots they occur in cups. (Figs. 19, 59,
191.)
Dung fungi and their allies (Pyrcnoniycetinea: (in part)
including Sordariacccc and Clicetomiacea). If horse dung be
placed in a moist closed chamber and allowed to remain un-
disturbed for a week or two there will almost invariably arise
Minnesota Plant Diseases.
137
dense crops of very small, black, thickly-crowded, pear-shaped
bodies. These often bear crowns of dark tangled hairs surround-
ing an opening at the tip. They are sac-spore capsules and dense
masses of spores can be seen
collected near the opening
or scattered as a dense
brown or black dust around
the capsules. The latter
are formed singly and some-
times but not usually up-
on mycelial masses, as is
the case in black knot, cat-
erpillar fungus and ergot.
The spores occur usually
eight in a sac and often
have curiously-shaped tail-
like appendages. These
fungi (Sordariacea?) are
very abundant and at first
sight seem insignificant but
are of some importance
nevertheless. The dung of
horses is made up largely of
the indigestible woody
parts of plants, e. g., the
veins of the leaves of
grasses, and it is on these that the fungus feeds, disintegrating
them as wood-destroying fungi do timbers.
Another group of forms (Chaetomiaceie) closely allied to the
dung fungi is found chiefly on moldy paper. Here the sac cap-
sule is provided with great twisted and tangled masses of crown
hairs in which the spores are lodged after ejection from the
sacs and sac-capsules, and are later from this point shaken out
and distributed. Building paper is often rotted by these fungi.
(Fig. 60.)
Sphere-fungi and their allies (Pyrenomycetinccc (in part] in-
cluding Sf>hccriacc(C and other families}. This is one of the very
largest groups of fungi, rivalled in point of numbers only by
the mushroom allies and cup fungi. It is also of great impor-
I-'ic. 60. — Above i* seen a we capsule of a dunn
fungus (Sordariaccar) showing the escaped
s.ics, which arc cylindrical and contain
each eight spore*. Itroken sacs and free
sac-spores are also tern. Itelow are two
sac-capsule* of another fungus of this
group (Chaetomiaceae). At (he summit of
the fruiting body are teen great tangles of
twisted threads in which the spores arc
caught. Magnified. Micmplii-tograph by
F. K. Butters.
138 Minnesota Plant Diseases.
tance economically because of its numerous diseases. The
sphere fungi are close relatives of the dung fungi and build
similar sac-capsules which are usually tiny spheres. These are
generally formed singly or are sometimes grouped on a mycelial
cushion somewhat similar to black knot. The sac-capsules are
very often microscopically small. These fungi are remarkable
for the great numbers and variety of accessory spores produced.
Most of the so-called imperfect fungi are undoubtedly merely
accessory spore-forms of these fungi. Although the group is a
large one the sac-capsules agree to a remarkable extent in their
essential structures and vary only in such characters as
hairiness, wall structure, shape and structure of sacs and spores
and other minor details. The accessory spores are some-
times found on simple erect threads, from which they are
pinched off in regular succession. In other cases the spore-
producing threads may be bunched together into cushions, and
in still other cases they may be formed in cavities or cases,
quite similar to those of many sac-cases in appearance, though,
of course, they do not contain sacs. Moreover, such accessory
spores may vary in number and arrangement of cells. They
may consist of a single cell or of a definite or indefinite number,
which may be built up into a net-shaped complex or into long
strings. On the characters of the sac-capsule structure and
opening, on sac-spore shape, etc., and on the grouping, struc-
ture, etc., of the accessory spores, an elaborate artificial classi-
fication of the group has been built up. This system, though
artificial, is nevertheless useful as a framework for collecting
and describing information about this vast group of plants.
The sphere fungi inhabit almost all plant parts though they
may be said to be most numerous upon the leaves of their hosts.
They are also very abundant on herbaceous stems and may
even be found on woody stems, on timbers, roots and fruits.
Many needle-cast diseases of cone-bearing plants, as pines, are
caused by sphere fungi. Certain root diseases of vines and
other plants, the leaf spot disease of strawberry and many other
so-called leaf-spot diseases are due to sphere fungi. Apple
scabs on leaves and fruits and many other diseases of cultivated
plants might be cited as further examples. In fact the great
majority of plants harbor one or more of these parasites. They
Minnesota Plant Diseases. 139
are not in all cases dangerous diseases. Moreover, not all of
the sphere fungi are parasites : many are saprophytes as are the
dung fungi, and many are half saprophytes or wound parasites.
(Figs. 35.60. 153, 183 to 187.)
Dead-stick and burnt-wood fungi. These are sphere fungi
which are found in great abundance on dead sticks and branches
of trees. They are saprophytes or half-saprophytes and the
latter do not usually produce their sac-capsules until after the
death of the host branch. The sac capsules are very often col-
lected together with or without a black mycelial cushion, and
they usually break out from beneath the bark, pushing out the
latter before them. Often the mycelial cushion is of great si/e
and thus resembles the black-knot in appearance. Such fungi
occur in great abundance on oak limbs or oak fence posts and
sometimes produce cushions a foot in length. These cushions
become black and hard and resemble burnt or charred wood,
whence their common name. They are often mistaken for
such wood by those unacquainted with their true nature.
Birch branches and in fact limbs and stumps, dead or fallen
trunks of almost any tree may show such burnt wood fungi.
They are very effective agents of decay in wood, though not as
conspicuous in their action as the pore and gill fungi of the
mushroom group. The highest forms of these burnt wood
fungi produce cushions which are club-shaped in appearance
and look like charred club fungi. A number of such forms are
abundant in our state. In the spring one finds such clubs cov-
ered with a white dust of accessory spores, while in the fall the
sac-cases are formed and the club is black and warted just as in
black-knot.
In some of these dead-stick and burnt-wood fungi one finds
sac-capsules which open, not by a pore, but by long slits or by
star-shaped openings. It is in these forms that we see the
transition to the cup fungi ; for a cup of the cup-fungus group
is merely a sac-capsule with a great wide-open top. It has a
pore which has become very large so that the capsule when ma-
ture has a beaker shape, or may even become saucer-shaped or
plate-like in form.
Beetle fungi (Laboulbctiiinccc). These fungi are parasites on
insects and are found in abundance on water beetles. The
140
Minnesota Plant Diseases.
plants are very minute and can usually only be clearly seen un-
der a compound microscope. On the one hand these fungi
show relationships with the sphere fungi, which are undoubted-
ly their closest fungus relatives. They form sacs containing
spores and these are contained in sac-capsules. The structure
of the sac-capsule is not however very similar to those of the
sphere fungi. The cases are often long pear-shaped and the
sacs are produced over a considerable period of time and do not
all mature at once. Moreover, the sac-cases are preceded by a
breeding act which is altogether unlike that of any of the sphere
fungi but can be best compared with the breeding act in the
FIG. 61. — A common cup fungus (Urnula craterium) growing on sticks sunken in the soil
and appearing abundantly in the spring. Original.
group of algae known as the red sea-weeds. The structure of
the mycelial threads is, moreover, very similar to that of the
red sea-weeds and the beetle fungi are therefore considered by
some botanists to have a common origin with that group of
algae. The beetle fungus plants are usually broom-brush-
shaped and are found on the legs and wings and outer parts of
insects. They are often highly specialized in locality, occurring
only on certain joints of the legs and on certain legs of the
host. The plants are often of two sexes though some contain
both female and male organs. These fungi are undoubtedly
numerous in Minnesota though no attempts have as yet been
made to collect or determine them. They seldom, however,
are very destructive parasites, as is the caterpillar fungus or the
Minnesota Plant Diseases.
141
insect molds, and hence are not, as far as is at present known,
of great economic importance. (Fig. 30.)
Cup fungi (Discomycctcs). These comprise one of the larg-
est groups of fungi. The range of habit and structure is very
great within the group. The cup fungi are very
closely related to the sphere fungi, as has al-
ready been pointed out. They are all sac fungi
and the sacs are always borne in structures com-
monly called cups. These cups may be con-
sidered as wide-mouthed spore-sac-capsules
such as are common in the sphere fungi. In the
early stages of many cup-fungi the cup is in fact
a sphere entirely closed or with a small pore-like
opening. The cups vary greatly in shape and
size. In many forms it is very minute and
requires a hand lens for its examination. In
others it is large, reaching six inches in diame-
ter and even exceeding this. Some forms are
like long goblets, while others resemble beakers
of all shapes. Many, again, are saucer-shaped
and some perfectly flat or even more or less con-
vex. Some are gelatinous in texture, others
cartilaginous or waxy, still others are more or
less leathery or simulate burnt wood. Few, if
any. have woody cups. They may be furnished
with hairs, sometimes with dense masses, and
often they have eye-lash-like, hairy spines lining
the edge of the cup. The cup is often a very
complex organ structurally and in a great ma-
jority of cases contains between
• the sacs sterile threads of very
characteristic shapes. The sacs
are usually long cylinders and
line the inside of the cup with a
dense palisade, standing upright
in the cup — that is, at right angles to the inside surface. The
function of the sterile threads is probably that of assistance in
throwing out the spores. The sacs are often provided with
little lids at the apex and when the spores are ripe the lid comes
FIG. t>2. — A single sac and sterile threads
front the palisade of »acs of the
fuiiKus shown in Fig. Cl. The sacs
show eight spores. Highly magni-
fied. After Scavers.
142 Minnesota Plant Diseases.
off and the spores are thrown out in a tiny drop of liquid. Very
often comparatively large areas of sacs in a cup throw out their
spores simultaneously and then one sees small dust-like clouds
arising from the cup. If a little slip of glass be placed over
the cup at such times the spores will be found in groups of
eight in little drops of liquid on the glass. If cups be placed
in a moist chamber and allowed to remain undisturbed for sev-
eral hours they will often, upon the removal of the moist cham-
ber lid, begin to send up the dust cloud of spores. The change
of moisture conditions seems to initiate the expulsion of these
clouds. A few cup fungi have another device by which the en-
tire unopened sacs are thrown out. Accessory spore-forms are
known in a great many cup fungi though not nearly so numerous
nor in such great variety as those of the black fungi. The great
majority of cup fungi live on the ground or on dead wood and
are saprophytes, but not a few are parasitic and some cause
serious diseases of their host plants. As agents in the disinte-
gration of plant debris they are important economically, though
not nearly so conspicuous in this effect as are the black fungi
and the gill- and pore-fungus allies. The two following groups
contain most of the common forms of cup fungi.
Tar-spot fungi and their allies (Phacidiinecs and Hysteriinea>).
This group of fungi may be considered as a transitional group
between those black fungi whose sac-capsules have large oval or
slit-like mouths and the true cup fungi. They produce densely-
woven mycelial masses which form crusts with the substrata
and upon these burnt-wood-like masses arise the little cups
which are similar in texture. The cups are at first closed
and simulate the spore-sac-capsules of the black fungi, but
the sac-bearing area is soon exposed. The sterile threads
between the sacs are usually longer than the sacs and the ends
come together above the sacs forming a covering. Accessory
spore bodies are not uncommon. These fungi occur on leaves
and branches of trees and have the habit of leaf- and dead-stick-
inhabiting black fungi. They are, moreover, usually sapro-
phytic though tree tar-spots are parasites of economic impor-
tance. The tar spots of willow and maple leaves are very abun-
dant in Minnesota. The mycelial mass which forms on the
leaves in summer and in fall looks like a drop of tar and does
Minnesota Plant Diseases.
not show any mature cups. The latter are formed on the fallen
leaves in the spring. (Fig. 133.)
True cup fungi (Pczizinecc). The greatest number of cup
fungi belong in this group. The great variety of form and size
has already been mentioned. Many have long stalks, others are
sessile. While the cups vary considerably as to texture, they
are usually fleshy or soft and seldom or never woody. More-
over, they are very frequently brightly colored, especially in the
sac-bearing region. The color is usually contained in the ends
Fie. 63.— A cluster of cup fungi, showing cups appearing just above the ground. They are
attached to long stalk*, which arise underground from a Morage organ. (See Fig. 4.)
Original.
of the sterile threads between the sacs. The most common
colors are reds varying on the one hand from bright scarlet
through orange and yellowish reds to lemon-yellows or even
lighter shades, and, on the other hand, from scarlet to chestnut,
chocolate and violet browns. A few are lilac-tinted and many
are water-colored or very dilutely brown and tan. There is a
great diversity in the surface coverings. Many are perfectly
smooth while others are covered with verv dense hairs and mi-
144
Minnesota Plant Diseases,
merous intermediate conditions exist showing great differences
not only in the number of hairs but in the kinds produced.
The spores are usu-
ally oval in shape
and s i n g 1 e-celled,
though some are
somewhat elongat-
ed and many-celled.
The explosive appa-
ratus for spore or
sac ejection has al-
ready been noted.
Tt is in the true cup
fungi that these de-
vices reach the
greatest degree of
perfection. Acces-
sory spore-forms are
not at all common.
The smaller forms
of the true cup fungi
abound on dead
sticks or dead stems
of herbaceous plants
or on the ground,
especially among
mosses, and are
often no larger than
a pin head. Many
grow on dung. The
stick - inhabiting
forms are not usual-
ly brilliant in color,
though some are
lemon colored. Not
a few are parasitic.
FIG. 64. — A cup fungus (Plicaria repanda) on the bark of
a fallen and decaying tree. Original. IVIost of the lar°"est
forms are saprophytes upon the ground or upon decaying tree
trunks or on dung, and are often very brightly colored. Some
Minnesota Plant Diseases.
cup fungi, and in particular parasitic forms, build storage or-
gans, often as large as a small filbert nut, and the cups are
produced in clusters upon this
storage organ in the follow-
ing spring. Wild anemones,
cultivated clovers and plant
bulbs are often attacked by
such storage-organ-forming
cup fungi, as are also plants of
the blueberry family. In the
latter case the storage organ
replaces the fruit of the host
plant and cases are known
where the same fungus lives on
two different hosts in its life-
time just as do many of the
rust fungi; i. e., the fungus
produces accessory spores on
one host and sac spores on the
other. A common disease of
certain coniferous trees in the
northern part of the state is
due to one member of the cup
fungus group. Compared
with other disease-producing
groups, however, the tree cup-
fungi are not of very great
economic importance, and this
is especially noticeable since
the cup fungi constitute such
a very large group of plants.
(Figs. 4, 10. 14, 6 1 to 65.)
Lichen-forming fungi. It
has already been stated that
lichens are equal-partnership-
organisms consisting of an alga and a fungus. In a vast ma-
jority of cases, the fungi are members of the cup-fungus group,
as is seen by the production of cups. In some lichens, how-
ever, black fungi participate and in a very few stalked fungi
10
Fie. •£.— C"u|> fungus ( Hrtotium cilrinum)
tut decaying wood. Slightly magnified.
146 Minnesota Plant Diseases.
are the fungus constituents. The number of lichens in Min-
nesota is very great, but a mere passing notice of these
can be given here. The constituent fungi of lichens are in
reality parasites — in the broader sense — on the algae, but
the latter also derive benefit from the partnership. Obvi-
ously, therefore, this group of fungi does not produce any
diseases of higher plants. The lichens attach themselves to
tree-trunks or limbs where they are held in an advantageous
position or they grow on the soil or as crust on rocks. In the
latter case they act as the pioneers of vegetative life in the
invasion of rock surfaces and are usually the first to obtain a
foothold. Lichens have invented a peculiar partnership prop-
agative body, which is merely a packet of algal cells, wrapped
up in a net-work of fungus threads. When such packets come
into proper conditions, they commence growth and build up a
new lichen plant. In addition, the fungus produces its proper
sac-spores and in many cases accessory spores, but when these
germinate the resulting mycelium must soon come into contact
with the proper algae or the fungus perishes. This is therefore
an uncertain means of reproduction of the lichen and the packet
device can easily be seen to have advantages over it in the pro-
vision for the algal constituent as well as for the fungus. (Fig.
21.)
Morels, saddle fungi and their allies (Helvellinecs). The
saddle fungi are very common plants of our woods. They are
all fairly large forms and are fleshly. Their relationship with
the cup fungi is easily understood by comparison with the long
stalked cups whose sac surface is flattened or turned back.
Such are in reality the simplest of the saddle fungi. The stalk
in some forms, however, becomes channeled and is often hol-
low. The cups in many, moreover, are not only turned back as
one might imagine a rubber cup to be turned inside out, but
the sac surface often becomes convoluted and lobed or ridged
so that the sacs may thus be produced over a greater surface.
The saddle fungi are usually whitish in color, or may vary from
grey to greyish brown.
In the morels the cup, or as it is here termed, a cap, has
very greatly increased its spore surface by the formation of
ridges which join and form a network enclosing deep depres-
Minnesota Plant Diseases.
sions. All over the depressions are formed the spore sacs. In
some morels the cup does not extend outside of the usually
broad stalk, but in others it laps over slightly at the edge. In
all morels the cup is drawn out so that seen from the side it is
either conical or spherical in appearance. In some forms, the
cup is very much convoluted so that it gives a brain-like appear-
ance.
Closely related to these fungi are certain "earth-tongue"
fungi. Many of these are black and burnt-wood-like and look
much like club fungi or like the sac-capsule-bearing branch of
FlC. 06. — Morel fungi. The ridgtd caps air to In- rtgarded as t-v» rti-d cups, whist- sur-
face has become ridged and hollowed to afford large area for spore formation.
Original.
the caterpillar fungus. The upper part of the club, however, is
really a pulled-out cup and hence is like a morel which has lost
its ridges and become smooth. They grow commonly in the
148 Minnesota Plant Diseases.
ground among grasses and are not at all conspicuous or very
large. Another relative of the morels is the spathula fungus
which is so common on the mossy floors of our northern
woods. Here the cup is drawn out and flattened like a spathula
and is yellowish in color. Very common on the ground and
amongst moss in summer and fall, can be found a peculiar little
gelatinous fungus of a light to dark green color. The fungus
has a stalk and a bent back cup similar to the saddle fungi, to
which it is closely related, but its cup is neither wrinkled nor
ridged. (Figs. 10, 66, 67.)
FIG. 67. — Saddle fungi (Helvella lacunosa). The saddle is an everted cup with the edges
turned back. Original.
True truffles (Tuberinece). At first sight the truffles would
not be recognized as relatives of the cup fungi, but such they
are nevertheless. The cup remains closed, however, and the
plants are found underground, never coming to the surface as
do many puff balls to discharge their spores. The spores,
therefore, are only distributed after the decay of the cup by
being washed away in rainwater or are scattered by the scratch-
ing or burrowing of animals. They are sought after by animals
as food and they are also much prized for food by man. Euro-
pean truffles furnish the most highly prized mushrooms known.
The closed cup of the truffles has a sac-bearing area, which is
usually greatly convoluted, so that the interior of the truffle
Minnesota Plant Diseases.
149
consists of a great labyrinth of pockets and canals which are
lined with the spore sacs. The truffles which have been found
up to the present time in Minnesota are not large, the largest
reaching the size of
a small walnut.
They are brownish
or blackish in color
and regularly or ir-
regularly spherical
in shape. Two
forms have been
discovered and un-
doubtedly more ex-
ist. Many forms
mature their under-
ground cups late in
autumn so that
they can be found in
the ground in early
spring. Others ma-
ture in the summer.
(Figs. 10. 68. 69.)
Imperfect fungi
and leaf spots (Fungi
impcrfecti). As has
already been ex-
plained, the so-
called imperfect
fungi include an
enormous number
of plants which are
as yet incompletely
known. Most of
them are undoubt-
edly accessory spore-forms of the black fungi or of the cup fungi.
One can imagine that a fungus spore-form of this kind might be-
come separated from its connection in the life-story of a
black fungus, in that the mycelium arising from such a spore
would give rise only to the accessory spore-form. On ac-
Kic. 68.— Truffles (Tuber lyoni). The truffle may he re-
garded as an unopened cup fungus with its minn.il
spore bcantiK surface greatly convoluted, 'lli.it which
Correspond* to the opening of the cup fungus w. seen
as a furrow in 2 and in the sections 1 as a broad
whitish streak. 1 shows the trunk- cut open; the
chambers in which the spore-sacs are formed can be
clearly seen. I'hotogrcph by F. K. Huttcrs.
Minnesota Plant Diseases.
count of the infrequency of the occurrence of proper condi-
tions, it might forget how to form sac-spores and would thus
become independent of the sac-spore form. Both the produc-
tion of different kinds of spores by one fungus plant and the
production of spores on different hosts in one life-cycle would
tend to furnish fungi where such a separation might occur. In
addition to those forms where this actual separation and inde-
pendence occurs there is a considerable assembly of spores,
where the connection
of apparently inde-
pendent forms with
sac-spore stages is
known, and in such
cases the term "imper-
fect" is in a sense a
misnomer. In a vast
number of forms, the
connection is indicated
to a certain degree by
the connections of an-
alogous forms. For
instance, the accessory
spore forms of the
powdery mildew is of a
definite type known as
an Oidium, and when
one meets with such
isolated spore forms, if
they occur in the usual
habitats of mildews, one may refer them to the powdery mil-
dew group. Indeed it may be that all so-called imperfect
fungi are actually traceable in their connections with sac-spore
forms, but many have, as yet, frustrated all attempts to prove
such connections. We may sum up these forms in this re-
spect into three groups : first, those isolated forms whose con-
nection with sac-spore forms is known ; second, those isolated
forms whose sac-spore connection is not known, but suspected
from analogy with known forms ; third, those isolated forms
whose sac-spore connections are not even suspected or have
become actually independent.
Fie. 69. — Truffle. 1. Fruiting body cut open; surface
furrow which corresponds to the opening of a
cup fungus is seen below and the convoluted sur-
faces of the cup interior above. 2. A portion of
the interior showing the sacs, each with four
spores (highly magnified). 3. A single sac show-
ing four spiny spores. Very highly magnified.
After F. K. flutters.
Minnesota Plant Diseases.
As a matter of convenience and for the collection of statistics
and data, the imperfect fungi are classified in an artificial sys-
tem according to the aggregation of spore-bearing threads, and
each of these again into groups according to the number of
cells in a spore and the arrangement of these cells. The three
primary groups are: first, the loose-thread forms, i. e., those
in which the
spore - bearing
threads are borne
loosely in mold-
like fashion ; sec-
ond, the cushion-
forms, those in
which the spore-
bearing threads
are joined to-
gether to form
cushions; and
third, the capsu-
lar forms, those
in w h i c h the
spore - bearing
threads are borne
in cases, often
similar in appearance to the sac-capsules of the black fungi. Un-
der each of these are sub-groups based <>n the color and cell
structure of the spores.
The imperfect fungi arc of very great importance econom-
ically on account of the great number of serious diseases pro-
duced by them. These diseases often take the form of spots
on leaves of the host plants and are then known as "leaf spots."
Hence the fungi are often known as leaf-spot fungi. These
spots may be whitish or brownish and are sometimes ringed
with a whitened or reddened area. The spot is often character-
istic for certain fungi. In sonic cases they arc black, whence
the disease is known as coal-spot disease or anthracnose.
Sometimes the infected spot region falls out. leaving small
holes which give rise to the common "shot-hole" disease of cer-
tain cultivated plants. The spots are not. however, in all cases
Fie. 70.— Two types of imperfect fungi.
1. An elongated cushion ty;>e where
the spore-bearing threads arc crowd-
ed together to form a cushion. The
free, many-celled spores are seen
above. 2. A capsular type. The spore-
dust i* seen above escaping from an
opening in the top. Both highly
magnified. A third type might be
illustrated in Fig. 1. After Tulasnc.
152 Minnesota Plant Diseases.
well defined but may extend out indefinitely over the attacked
organ. Many fruit rots are caused by these fungi, as the brown
rot of plums and ripe rot of apples. Sometimes the influence
of the fungus causes the fall of the leaves with great injury to
the plants, as on currant bushes. Some imperfect fungi; more-
over, attack stem portions, particularly the young stems, and
then may do considerable damage. Many are, on the other
hand, saprophytes and as such, just as the majority of black
fungi, are important agents in the disintegration of plant debris.
(Figs. 35, 70, 156 to 159, 164, 165.)
Chapter XI.
Fungi, Kinds of Fungi. Basidium-bearing Fungi.
M
The stalked or basidium-bearing fungi (Basidiomycetes).
This is the third of the three great groups of fungi. The
members of this group do not, as the sac fungi, bear their
spores in sacs, but form them upon more or less definite stalks,
which occur with some degree of regularity upon special por-
tions, usually the ends, of the fungus threads. From these
stalks the spores are pinched off just as are many accessory
spores in sac fungi. They are not formed internally, as the
spores are in sacs, but are externally formed in the pinching-
off process. The stalks usually occur in fours at the end of
the thread though they may be fewer or greater in number
and may arise laterally on the stalk-bearing threads. The cell
or cells of the thread which bear the stalks are known as the
basidium. In the lower group of the stalked fungi, the basidi-
um is composed of a number of cells each of which bears a
stalk with its spore as in rusts and smuts, "Jews' ear," trem-
bling and weeping fungi. In the higher forms, comprising the
other groups, r.ll of the stalks arise from a single undivided
cell. The basidium may arise directly from a spore (winter
spore) as in the rusts and smuts. In these forms, of course,
they are often found singly, but when the winter spores are
formed in crust-forming clusters they are produced in a more
or less dense mass. In all other stalked fungi the basidia are
borne on or in some fruiting body or on the surface of mold-
like growths. The former is by far the more common form,
as in the gelatinous fungi, in the mushrooms and all of their
allies and the great alliance of puff balls, birds'-nest and car-
rion fungi. When borne at the surface of a fruiting body the
basidia usually stand closely together side by side and perpen-
dicular to the surface of the fruiting body, with occasional
sterile threads between them, thus constituting a palisade, cov-
1 54 Minnesota Plant Diseases.
ering the entire spore-bearing surface. Such palisades are
common in all of the mushroom allies, in most gelatinous
fungi, "Jews' ears," etc. In many of the closed fruiting bodies,
e. g., puff balls and birds'-nests, internal chambers, which are
formed in the early stages of growth, are lined with such pal-
isades. The fruiting body may assume many shapes, which
apparently tend toward the increase in spore-bearing area or
have to do with advantages of distribution.
The variety of forms is enormous — ranging from such sim-
ple types as the club fungi and smooth shelves to the tooth, pore
and gill fungi, and from puff balls to carrion fungi. The teeth,
pores and gills are the basidium-bearing regions. In the puff-ball
allies, the birds' nest and carrion fungi, the spore-bearing region
is in a closed fruiting body which either opens only by decay
or at maturity by a special pore or other device. Inside of
these closed bodies the basidia may occur in palisades lining
the surfaces of chambers, or they may occur on wefted threads
in no regular arrangement. The details of the fruiting bodies
will be given under the various groups. In a comparatively
few forms accessory spore-forms are found but they are not
nearly so common in this series of fungi as they are in the sac
fungi. The question of the occurrence of a breeding process
is still an open one. A fusion of elements in the young basid-
ium or in the winter spore of rusts is interpreted by many as
a breeding act, and recent investigation has shown that in the
rust winter-spore the fusion is the culmination of a breeding
act which begins in the cluster-cup stage. The stalked fungi
do not seem to show any striking similarities to either the
algal fungi or to the sac fungi, so that in the light of present
knowledge only an isolated position can be assigned to them.
Various theories have, however, been proposed uniting this
group with each of the other great fungus groups. The latest
investigations indicate a relationship with the red sea-weeds.
Perhaps the majority of the stalked fungi are earth-inhabiting
or wood-inhabiting saprophytes. Many, however, as the rusts
and smuts, are highly specialized and destructive parasites,
while not a few, as pore and other shelf-fungi, are half-sapro-
phytes. The timber and timber-tree diseases are largely mem-
bers of this group and the rusts and smuts are without doubt
Minnesota Plant Diseases.
155
the most destructive disease-causing alliances of the whole
group of the fungi. As food producing fungi, the stalked fun-
gus group is very important since all of the true mushrooms,
the edible pore fungi, club and tooth fungi, as well as the great
variety of puff balls are found in this group.
The basidium-bearing fungi comprise the following twelve
groups. Of these the last eleven possess true basidia. i. e..
with a definite number of stalks and spores which are usually
definitely arranged as at the summit or on the sides. In the
smuts, however, the basidium, if so it may be called, bears a
great number of spores which are budded off in yeast fashion
from the side of the basidium cells. In other words the basid-
ium of the smuts has not attained to the definiteness of the
other basidium-bearing fungi and the smuts are often classed as
a group outside of these. (For figures, see following groups.)
Smuts (Ustilcghtcce). Though not a very large group of
fungi the smuts are very important from the economic stand-
point because they contain many disease-producing forms.
The smuts possess the simplest form of
basidium found in the stalked fungi. They
are all parasitic and many of them are
half-parasitic in habit, since they are able
to live in certain stages for an indefinite
period in culture media. They can, how r
ever, complete their life-story only as para-
sites on certain plants. The basidium
arises directly from a resting-spore which
is commonly known as the smut spore,
producing the so-called smut of grain and
of other plants. This smut or resting
spore is usually black, dark-brown or dark-
green in color and has a thick outer coat,
which, under favorable conditions of moist-
ure, breaks open and allows the inner wall
to be shoved out in the form of a thread.
This thread grows out to six or more times
the length of the spore. It then becomes
divided by cross-walls into three or four
cells, each of which buds off an indefinite
Fir.. 71. — S in u t scores.
germinating ; cl t h e
smut spore, t tile threat!
growing from it, and c
the spore produced by
the t u b e. 1. Wheat
smut — the threat] is di-
vided ii'i by cross walls
into cells, each of
which buds off spores
fro m its side. 2.
Stinking smut of wheat
— the thread from the
s ><>re is undivided ant]
produces a crown of
thread-like spores :«t the
t»p. Highly magnified.
After Brefe'ld.
156 Minnesota Plant Diseases.
number of spores from its side or end. The thread thus con-
stitutes a basidium. In one of the smut groups the basidium is
not divided but consists of a single cell from the end of which
the spores are produced. These spores may be known as the
basidium-spores. They germinate immediately in warm, moist
conditions, by sending a fine thread, which seeks the host plant
and penetrates into the tissues, thus beginning the parasitic life.
If the basidium-spores are placed in a nourishing solution they
bud in yeast fashion and will so continue to do for an indefinite
period as long as the nutrient material is present. It is still
able to infect a host plant under proper conditions.
The parasitic life usually begins in some young undeveloped
part of the host, e. g., the corn smut infects only young leaves
or young kernels of the corn. Here the parasitic mycelium
grows and builds itself up at the expense of the host plant. In
the oat smut the parasite gains entrance to the oat plant only in
the seedling stage of the latter. Now this penetration is accom-
plished in a peculiar way. In an oat field with smut the sound
grains of the oat become dusted with the spores of the smut
and thus at the seeding time in the spring the seed grains may
have spores on their surface. Now the conditions favorable to
the germination of the oats are also favorable to the germina-
tion of the smut spores and when the seedling oat appears
above ground there are also near by germinating basidium-
spores of the smut. The threads of these spores therefore
easily reach the young seedling and rapidly penetrate to the
growing-point of the stem, although this growing-point is hid-
den by the first leaves of the seedling. When the seedling
continues to grow, the parasite also grows, always remaining
in the growing point and forming patches of mycelium in
the growing points of all of the branches. The oat plants
thus affected do not appear very different from uninfected
plants until the grains mature. When the grains are still
very young the parasite invades all of them and here builds
up a dense mass of mycelium at the expense of the rich food
materials which the oat plant furnishes to the grains. At
the time when the oat grains are ripe the fungus threads
divide up into numerous cells and from each cell is formed
a spore, whose wall is at first gelatinous but later is black,
Minnesota Plant Diseases.
thick and hard. These
spores are produced in
enormous numbers re-
placing all of the
grains and are then
seen as a smutty pow-
der which is familiar to
every farmer who
raises oats. These
smut-spores are now
in an advantageous
position and are scat-
tered by the wind and
carried to sound grains
and may, as described
above, again cause
infection of the oat
in the seedling stage
in the following
spring. This life-story
explains the success of
the hot water method
in preventing oat
smut, for if the smut
spores, clinging to the
grains are killed by
steeping in hot water,
which will not injure
the grain, then the
chances of infection of
the seedling plants
from these treated
grains are greatly re-
duced or entirely de-
stroyed.
157
Fie. 72. — Loose smut of wheat.
(Ustilago tritici. ) The loose
powder of spores has been par-
tially shaken out; the grains
of the wheat are all smutted.
Original.
158 Minnesota Plant Diseases.
Smuts very often possess the power of stimulating their host
plants to abnormal growth. Thus in the corn smut, the attacked
part of the corn plant swells up into a tubercle many times larger
than the original plant part. The advantage of this to the para-
site is obvious, for it increases many-fold the area of the feeding
ground as well as the spore-producing area. Such tubercles in
corn smut are found on leaves, young stems and on kernels and
even in the tassels.
In some smuts the stimulation is exerted on the rudiments
of organs which are not normally produced in certain flowers
causing the rudiments to develop into mature organs. Such is
the case in certain pistillate flowers of the Pink family where
the smut stimulates the rudiments of the stamens to mature de-
velopment.
The smuts are parasites, chiefly of the flowering plants and
particularly of the grass family. One smut, however, inhabits
the capsule of the peat moss plant. The choice of organs for
the establishment of the parasitic mycelium varies with different
smuts. A very large number live in the grains and seeds of
plants, where they get both advantage of position for spore dis-
tribution as well as an abundant supply of food material.
Sometimes a whole inflorescence is destroyed. The floral parts
are also attacked by smuts, e. g., certain smuts fruit only in the
anthers of species of the carnation family, forming their spores
in place of the pollen so that when the flower opens a violet
smut dust is discharged from the anthers instead of the pollen
dust. Leaves of the host plant are commonly attacked and are
often swollen on account of the stimulation of the parasite.
Stem parts may be attacked and one smut is known in Minne-
sota to produce its spores in the roots of certain rush-like plants.
Almost every cereal plant is subject to the attack of one or
more smuts and many of the wild grasses are likewise invaded.
The common corn, oat and wheat smuts are best known.
Many garden plants such as onion and violet are subject to
smut attacks and this is also true of many members of the Pink
family, where the smut often lives in the anthers of the flowers.
The dock family of flowering plants is also peculiarly subject
to smut attacks and this is also true of the pink family. Other
flowering plants are attacked but not so commonly as the above
mentioned groups. (Figs. 27, 71, 72, 146 to 151.)
Minnesota Plant Diseases.
159
Rusts (Uredinea). The rust fungi constitute a larger group
of plants than the smuts and exhibit more variety of structure
and habit. They may be considered as relatives of the smuts
in that the winter spores of the latter may be compared with
Fie. 73. — Spores of rust fungi. 1. A clus
graminis) on wheat plant. -. A wintr
(promycclium — basidium), each of win
The winter spore germinates in the sp
The sporidia arc blown by the wind
in 3 and -1. 4. Shows the Kerniin.it
infection will soon take place. 5. A ge
germ tubes which on a wheat plant ca
lii of winter SJXTCS of wheat rust il'-.uiim.i
i spore germinating to a thread of f»ur cells
h bears a small s|>ore (sporidiumj on a stalk,
ing while still in the straw or on the ground,
o another plant and there germinate as st-ni
on of a sporidium on a barberry leaf; here
mutating summer s;>ore of wheat rust, showing
i cause infection (as shown in Fig. I."'). C. A
rare grass rust s^ore (amphispore of 1'uccinia vcxans) germinating; it germinate*
as a summer spore, but has a thick coat and rests over winter as a winter spore. All
highly magnified. 1-5, after Ward; <J, after Carleton. (See also Fig. 74.)
the smut spores The rusts, however, exhibit a great number
of accessory spore forms. They are all parasites and are of great
economic importance on account of the large number of dis-
ease-causing forms. The life-story of a rust plant is often very
160 Minnesota Plant Diseases.
complex. We will start with the winter spores. These spores
are in a great majority of cases resting spores and, as in the case
of the smut spore, are provided with very thick outer coats.
These winter spores may be formed singly on stalks on the ends
of short threads, where they are usually produced in dense clus-
ters, just under the host plant epidermis and are liberated as a
brownish or blackish powder by the rupture of this epidermis.
This procedure is common in grass-inhabiting rusts, in the rusts
of sunflower and mints. In the rusts of willow and poplar the
winter spores occur in a crust-forming mass, just under the
host cuticle, and are never shed but germinate in place. This is
also the case with the common golden-rod rust. The winter
spores in the cedar apple disease of cedars are borne in various-
ly-shaped masses of gelatine which expand much on absorption
of water and in which the winter spores germinate producing
the basidium-spores at the surface of the gelatine. Some,
again, as in the milkweed rust, produce long, thread-like bodies
composed entirely of winter spores. In the rust of the cow-
berry the winter spores remain in the cells of the host epidermis
and germinate there. Whatever the location or method of dis-
tribution of the winter spore may be, it always germinates in
essentially the same way. There are usually thin places in the
outer walls and through one of these the inner spore wall is pro-
truded in the form of a thread. This thread increases in length
as does that of the smut spores and also becomes divided, usual-
ly by three walls. Each of the resulting four cells sends out a
stalk on the end of which is formed a spore. The thread bear-
ing the four stalks and spores is the basidium and is noticeably
more definite than the smut basidium in the production of but
four spores, which are formed on stalks. The basidium-spores
are scattered by the wind, and germinate as soon as placed un-
der favorable conditions ; they are capable of infecting host
plants just as is the basidium-spore of the smut. The winter-
spore is not the only spore-form produced by rusts. In the
spring the mycelium, which develops from the basidium-spore,
produces what is known as cluster cups. These are tiny
cups scarcely as large as a pin head, usually yellowish or whitish
in color and found in clusters. They are most commonly found
on conspicuous yellow spots in the host plants caused by the
Minnesota Plant Diseases.
161
mycelium of the fungus. The cups are at first closed and then
resemble small spheres ; the walls later open at the summit, roll
back and expose the spores as an orange-yellow dust. The
spores are formed in chains which arise in a pal'sade from the
floor of the cup and are formed continuously for some time,
FIG. 14. — More spores of ru»
capsular spore-brai ing f
•pure-bearing threads fn
spores are probably the r
They appear to be funot
been known to cause i
formed in chains: p, thr
I'UIIKI. 1. A pycnulium (from wheat rust on barberry), a
uiting body showing dust ol s;»oreg at r. 2. Spores and
i 1 greatly enlarged. 3. S. ni<- s|H>rrs germinating- These
lies of male reproductive cells which have fallen into disuse,
onless since they do not usually germinate and have never
fection. 4. A cluster cup of an Anemone rust; s spores,
ads forming the cup of thv cluster-cup. All highly magni-
fied. After Tavi-1.
those at the summit being the first to mature. These cluster-
cup spores are ball-shaped or have flattened sides and their
outer wall is frequently provided with small warty roughnesses.
The cluster-cup spores are blown about by the wind and are
capable of immediate germination. When germinating they
send out a germ thread which causes infection. Accompanying
ii
1 62 Minnesota Plant Diseases.
the cluster-cup stage or rather just preceding it one very often
finds another accessory spore-form in which small spore-cases
of pear-shaped structure are produced, sunken into the oppo-
site — usually upper — side of the leaf from that on which the
cluster cup occurs. Inside of these pear-shaped cases the spores
are produced on long threads from which they are pinched off
just as in very similar structures found in many of the acces-
sory spore-forms of the sac fungi. These spores are often ac-
companied by the production of sugary, sweet fluids which are
probably attractive to insects and thus aid in spore distribution.
The exact use of these spores is not yet known for they have
not been proven to be able to cause infection of a host plant
though they will germinate under certain conditions. They
have been supposed to be unused male sexual elements and re-
cent research points to a confirmation of such a supposition.
Sometimes this pycnidium spore accompanies other spore-
forms, e. g., the summer or even the winter spores. The cluster-
cups are produced almost universally in spring so they are the
first rust spores (excepting the pycnidia and basidium-spores)
which one finds after the resumption of growth by flower-
ing plants, after the winter has
passed. In early summer or
even late spring and from this
time throughout the summer
season and far into the au-
tumn are found what are
known as the summer spores
or red rust spores. These
are like the cluster-cup spores
FIG. 75. — Cluster-cups of ash-leaf rust fun- • cr»mp rpunprts • tliev nrp nr
gus, on ash twig. The cups are long
cylindrical Highly magnified. Micro- angg-red Or yellow ill Color
photograph by E. W. D. Holway. J
and are often provided with
external warts or spines. They are, however, not formed in
closed cup cases and are not formed in chains. They arise
singly on short stalks in dense clusters from which they are
shed as a red-rust powder. They may be formed continuously
for long periods from the same cluster, and are capable of im-
mediate germination under favorable conditions. They ger-
minate by sending out a fine thread in a similar manner to that
Minnesota Plant Diseases. 163
of the cluster-cup spore and this thread may cause infection.
They are scattered by the wind and are the chief cause for the
rapid spread of rusts through the fields of wheat and other
cereals. Towards the .end of the summer, often in the same
cluster with the summer spores, the winter spores commence to
develop and continue to form until late in autumn. In many
cases, however, the winter spores are formed in separate clus-
ters. The variety of habit of these winter spores has already
been described. They are in general resting-spores and germi-
nate in the following spring, thus again commencing the life-
story. It may be well to summarize at this point the order of
succession of these spore forms. First at the germination of
the winter spore on the ground or under moist conditions any-
where, the basidium spores are produced. Soon after on a suit-
able host the pycnidia appear, followed closely or accompanied
by the cluster-cup spore. Next in late spring commences the
formation of the summer
spores which may continue to
form until late in fall. From
mid-summer on the winter
spores may be produced until
snow flies in late autumn.
There are thus five kinds of
spores of which the winter
spore corresponds to the smut Fic 76._riuitfr.cup sporc. fr<)nl rust fun.
spore of the smuts. In addi- «"• of. ,Fi'- ?•. "iB^y ™™ifi'd-
Microphotograph by K. W. D. Holway.
tion to these five forms a sixth
is known but is of rare occurrence and seems to be very similar
to the summer spores in some respects.
Not in all rust fungus life-stories, however, do all of these
spore-forms occur. One or more may be missing so that nu-
merous combinations are conceivable and actually occur. For
instance, a rust fungus may possess no cluster-cup stage or no
summer-spore stage, or both may be missing. In fact, some
have apparently retained only the winter spore form, which, of
course, always bears the basidium spores later.
In addition to this variety of spore-forms, rusts have fur-
ther complicated their life-stories by selecting different hosts
upon which to form their various spores. For instance, one of
164 Minnesota Plant Diseases.
the common rusts of wheat forms its summer and winter spores
on the wheat plant, but the pycnidium and cluster-cup spores
are formed on the common buckthorn.
The fungus which forms its winter spores on the cedar ap-
ples of the red cedar produces its cluster-cups on apples and
pears, having no summer spores in its life-history, but it pro-
duces its cluster-cups throughout the summer. The life-story
of such a rust fungus which possesses five kinds of spores, four
of which are produced from a parasitic mycelium and two of the
latter on one host and the other two on another host, offers an
exceedingly complex history. It may be remarked in passing
that to combat such accomplished parasites requires an intimate
knowledge of their histories.
The question of a breeding-act in the rust life-history is
still, perhaps, an open one. A fusion of two elements in the
young winter spore has been interpreted as such an act by some
botanists. Recently, the beginning of the association of these
sexual elements has been discovered just preceding the forma-
tion of the cluster-cup.
The rusts are all parasites — true parasites, unable to live ex-
cept in the tissues of their hosts. The mycelium grows inside
of the tissues and the spores are in almost all cases borne at the
surface of the plant, whence they can best be shed; but some,
buried in the tissues, depend on the decay of the host plant for
their release.
The rusts vary greatly, also, in their location on the host
plants. Most commonly they are found upon the leaves but
in many forms the stem is also attacked and even the under-
ground portions may be invaded. Floral parts are seldom
directly attacked. The rusts also possess in some cases the
power of stimulation of the host to extraordinary effort, thus
increasing the available food supply for the fungus parasite.
The cedar apples of the red cedar are merely enlarged twigs
of the cedar tree in which a rust mycelium is at work. Some
rusts on pines produce great swellings on the stem and still
other cases might be cited of the deforming and stimulating
effect upon the host by rust parasites. Witches'-brooms are
very often of rust-fungus origin. Such is the common birds'-
Minnesota Plant Diseases.
nest broom of the red
cedar and the great bush-
like brooms of the bal-
sam fir. These have -al-
ready been described as
stimulated portions of
the host plant which,
with the fungus parasite,
live in partnership at the
expense of the neighbor-
ing parts of the host.
Besides this deforming
power of many rusts
these parasites are injuri-
ous in the stealing of
nourishment which they
accomplish at the ex-
pense of the host and in
the wounding of plant
parts. The host, as a re-
sult, becomes impover-
ished and may finally en-
tirely succumb. Thus
wheat rust annually robs
farmers of enormous
sums of money by im-
poverishing wheat plants.
Practically all classes
and groups of flowering
plants are attacked by
rusts as are also certain
fern plants. The lower
plants as mossworts and
algae seem to be free
from these parasites.
The favorite hosts of the
rust fungi seem to be the
grasses, for on these
plants are found an enor-
a vcxans
Ulle. sum
mi nu-r-s. in
vi r wit
I a «rass rust iu:ixus ( 1'uc-
above, winter s)i'>r<s; in the
r sjioris; b:-l»w. amphispores.
like in Ktrminalion, but rest-
trr. > lliiilily inaKiiilU-il. Micm-
K. W. D. Hulwav.
1 66
Minnesota Plant Diseases.
mous number of rust fungi, constituting- many of the most im-
portant diseases of cultivated crops. Wheat rusts have been
mentioned. The cluster-cups of the cedar apple fungus are
often destructive to pear and apple trees. Of great importance
are also the asparagus rust and mallow rust and the numerous
rusts of beans and clover. The great rust disease of the coffee
plant, though not, of course, directly affecting Minnesota plants,
has been of enormous importance in its devastation of the
coffee crops of India and Ceylon. In
addition to these might be mentioned a
host of parasitic rusts which yearly levy
a tax on field and garden crops, on wild
plants and greenhouse plants — -in fact,
they are almost universal in their distri-
bution. (Figs. 2, n, 23, 26, 29, 73 to
77, 136 to 145, 160 to 162, 181, 182, 199
to 201, 205 to 209.)
Jews' ear fungi (Auricular iinea:}.
This group of fungi derives its name
from the name of a common member of
the group — a very widely distributed
fungus. The nearest relatives of the
Jews' ear fungi are the rusts, though at
first sight this fact is not apparent.
These fungi are almost all saprophytic,
growing chiefly on wood, but one spe-
cies is apparently a parasite upon
mosses. Unlike the rusts, winter spores
are not produced, but a basidium very
similar to that of many rusts is formed
directly on threads of the fruiting body.
The basidia are long cylindrical bodies of
four cells, and they stand side by side in a dense palisade, form-
ing one surface of the fruiting body. The latter is variously
shaped : club-, spoon-, shelf-, or ear-like, and is found at the
surface of the log or whatever substratum may furnish the
nutrient material. The vegetative mycelium is found in the
log just as is the mycelium of the pore or shelf fungus in wood-
inhabiting saprophytes. The fruiting body of the Jews' ear
FIG. 78. — Various basidia and
spores of the lower basid-
ium-bearing fungi. 1.
Jew's-ear fungus; a, a
basidium; b stalk with
basidiospore. 2. Trembling
fungus; the basidium is
longitudinally divided. 3.
Weeping fungus; has an
undivided and forked basid-
ium. Highly magnified.
After Brefeld.
Minnesota Plant Diseases. 167
fungi is in almost all cases of a gelatinous consistency, especial-
ly in the interior, and this is due to the gelatinization of the
outer portion of the fungus threads, which compose it. The
threads, therefore, appear as a very loose network in a great
mass of gelatine. Near the surface of the fruiting body the
thread walls do not gelatinize but, by the dense network there
produced, form a tough covering. The basidia usually cover a
special area as they do in the common Jews' ear fungus. In
the young basidium a fusion of elements similar to that in the
young winter spore of rusts occurs, and has also been inter-
preted as a breeding act. When the fruiting body is dried, it
usually becomes hard and horn-like and shrinks very greatly in
size.
From each of the four cells of the basidium a stalk is sent
up to the surface of the palisade area and there pinches off a
single spore just as do the basidia of the rust fungi. The Jews'
FlC. 79. — JcwVcar fungus fruiting bodir* on a dead branch of balsam fir. Original.
ear fungi have also accessory spore-forms, but not in such
abundance nor with such variety as they are found in the rusts.
The common Jews' ear fungus, which is found almost all over
the world, has been collected only in the northern part of our
state, where it occurs in great abundance on dead logs of bal-
sam fir. white cedar and other trees. (Figs. 78. 79.)
Trembling fungi (Trcntcllinccr). These fungi include forms
which have a great superficial resemblance to the Jews' ear
fungi and derive their common name from the gelatinous con-
sistency which allows them to tremble, as it were, at the
slightest agitation. They are all saprophytic. usually on de-
caying wood and logs. The fruiting body assumes in different
i68
Minnesota Plant Diseases.
plants a great variety of forms — usually from club-shaped or
cylindrical to ear-shaped and shelf-like. Many of them are
very irregular in form and much convoluted, forming brain-like
masses, while still others have a surface furnished with teeth in
an exactly similar fashion to those of the true tooth-fungi.
They are all, however, gelatinous and this character is due to
the same structure of the threads as was described for the
FIG. 80. — A trembling fungus (Tremella so.), on the end of a log. The portion
of the fruiting body near the top has partially decayed and deliquesced. (In the center
of the cluster are two white caps of a gill fungus.) Original.
Jews' ear fungus. From the latter and from the true palisade
fungi the trembling fungi differ in their basidium. This is
formed directly from the ends of threads as in the Jews' ear,
but the walls, which divide up the basidium into cells are longi-
tudinal or oblique and the basidium itself is spherical or pear-
shaped, while in the former groups the basidium was cylindrical
Minnesota Plant Diseases. 169
and bore cross walls. Externally, therefore, the Jews' ear and
trembling fungi and also the following group may be very simi-
lar and indistinguishable to the naked eye, but the microscope
shows a difference in the structure of the basidium. Similar
accessory spore-forms are also produced in the trembling fungi
and a very considerable variety of such forms is found. The
trembling fungi are very common in our woods, growing on
dead sticks and logs, especially after heavy rains. After shed-
ding their spores they usually liquify under the action of bac-
teria and other organisms, for they furnish good media for
these plants. When dried the trembling fungi become hard
and horn-like, resuming their gelatinous nature when again
placed in water.
One of our common forms resembles a brownish, irregular
or shelf-like mass of gelatine and is commonly known as
witches'-butter. The brain-like forms are also very common,
often producing masses weighing five pounds. Toothed forms
have been found in several places in the state but are seldom
abundant. These toothed forms are not unlike the true
toothed fungi in appearance but are always more or less gelatin-
ous. Economically this group of fungi is not important,
though they may aid in timber rotting to a slight extent and a
few forms have been pronounced edible. ( )ne very common
form is tough and leathery and resembles greatly a much-
branched club fungus. (I*igs. 78. 80.)
Weeping fungi (Dacryomycctinca). These fungi include an-
other group of gelatinous fungi similar in apparent characters
to the two previous groups. There is again a variety of shapes
produced, but our commoner forms are irregularly club-shaped
or brain-like. The basidia are again arranged in palisade-like
areas at the surface of the fruiting bodies, but these basidia arc
single-celled, having no walls dividing them into several cells.
The basidia are fork-like in form and each of the two tines of
the fork bears at that end which comes to the surface of the
gelatine a single spore. Accessory spores are also produced.
The most common Minnesota form is one. which is abundant
on fallen logs and stumps of larch and other soft woods. It is
at first bright orange, but soon after the shedding of the spores
the fruiting body liquifies, whence its common name of weeping
fungus.
Chapter XII.
Fungi. Kinds of Fungi. Bastdium-bearing Fungi.
Jff
The palisade fungi (Hymenomyceies). All of the remaining
groups of the basidium-bearing fungi have one common charac-
ter, viz. : the structure of the basidium. Like that of the weep-
ing fungus the basidium is a single cell, not, however, fork-like.
It usually bears its spores at the summit. The spores are com-
monly four in number.
The palisade fungi possess such single-celled basidia. The
basidia are borne on fruiting bodies and are always arranged in
a palisade which at least at maturity is exposed to the open air.
This palisade of basidia lines special surfaces and only in a few
cases does it cover the entire fruiting
body. The fruiting body therefore
exhibits a great variety of forms each
of which is a special solution of the
problem of furnishing large spore-
bearing surfaces and exposing them
to the wind for advantageous distri-
bution. The simplest forms are pros-
trate and mold-like. From this to
the highly-organized pore and gill
fungi we find an enormous variety of
fruiting bodies. Comparatively few
accessory spore-forms are known
though some exist. The palisade
fungi constitute an enormous group
of fungi and since the basidia are sim-
ilar in all, the shape of the fruiting body is utilized in arranging
the forms into groups. The group may be divided into the fol-
lowing seven sub-groups :
Gall-producing fungi (Exobasidiinece). These fungi are all
parasites, chiefly of the blueberry and heath families. The my-
FiG. 81.— Basidia
spores of all
and basidio-
of the higher
basidium-bearing
stalked
fungi. 1. The usual type. 2.
The basidium of a stalked puff-
ball. Highly magnified. 1.
After Brefeld; 2. After Schroe-
ter.
Minnesota Plant Diseases. 171
celium stimulates the leaves or stem to excessive growth, and
gall-like swellings, often reddish in color, are thus produced.
On the surfaces of these galls the palisades of basidia are pro-
duced, and the basidium-spores appear to the naked eye as a
fine white powder. Four spores are produced on each basid-
ium. These spores germinate by forming a thread, which is
again capable of causing infection. The galls so produced are
fungus-galls and must be distinguished from the insect galls of
plants which are much more common in occurrence. The
most common Minnesota member of this group is one which
forms galls on Labrador tea in the northern part of the state.
The gall on blueberry and cranberry undoubtedly also occurs
but it is not very abundant and good specimens have not been
collected. (Figs. 37, 81.)
Mold palisade fungi (Hyfxtchnacetf). These comprise the
simplest of all palisade fungi since no true fruiting bpdy is
formed but merely a dense mold-like mass on rotting logs or
decaying wood. On the surface of this mold-like mass are the
basidia arranged irregularly and only suggesting the true pal-
isade of the higher groups of this alliance.
Smooth shelf fungi (Thclcphoraccic). In this group of fungi
the palisade is usually the under surface of a shelf-like fruiting
body. In some forms, however, the fruiting body is prostrate
and closely grown to the log or substratum on which it grows
and no part of it shelves out. In this case the whole upper sur-
face is covered with a palisade. Such prostrate forms often ap-
pear as thin, grey-brown or whitish crusts on the bark of dead
twigs and trunks of trees. Whatever the form of the fruiting
body the palisade surface is always smooth and in this respect it
differs from the pore and gill fungi. The palisade surface,
moreover, is not entirely composed of basidia but may contain
certain sterile cells of peculiar structure, known as cystidia.
They are usually long, sharply-pointed cells which project
from the surface very considerably and are frequently coat-
ed with certain salts which give to them additional rigidity.
Their function is probably protection. \\ hen occurring in
great numbers they give to the palisade surface a velvety ap-
pearance as seen by the naked eye or under a low-power hand
lens. The smooth shelves are very common Minnesota fungi
172
Minnesota Plant Diseases.
and not a few timber diseases can be traced to this group. Most
forms are, however, saprophytes. The common smothering-
fungus which is found at the base of young shrubs and trees is a
smooth-shelf fungus. (Figs. 81, 82, 117, 118.)
Club fungi (ClavariacecE]. As the common name implies,
these fungi have club-shaped fruiting bodies. The club in some
forms is single and thus simple. In other forms it may be
branched and the most common of our club fungi are very
abundantly branched thus forming dense tufts. The palisade
surface is usually confined to the upper part of the club
which is in general smooth, so that one may consider these club
FIG. 82.— A smothering fungus (Thelephora laciniata), growing on the ground. The
fruiting body has narrow shelf-like divisions. Original.
fungi as but modifications of a similar scheme of fruiting body
to that of the smooth shelves but of a special kind. The basidia
are of the usual type and the spores vary from white to yellow.
The clubs are sometimes hollow and very brittle, in other cases
they are solid and fleshy. All of our club fungi are saprophytes
inhabiting decaying wood or ground where wood has been scat-
tered. They vary in size from tiny thread-like cylindrical clubs,
on the one hand to large single clubs measuring six inches in
length and one inch in thickness and on the other hand to clus-
ters of branched clubs six to eight inches in diameter and even
larger. One little club, not commonly, but occasionally, found
in Minnesota, has a swollen and somewhat convoluted club top
Minnesota Plant Diseases.
173
174
Minnesota Plant Diseases.
which is internally more or less gelatinous and of which the en-
tire surface is covered with the palisade of basidia. A large
number of the club fungi are edible and furnish many common
and abundant forms. (Figs. 10, 81, 83.)
FIG. 84. — The coral fungus — a toothed fungus (Hydnum coralloides), on the under side of
a log. Original.
Tooth fungi (Hydnacc(c). The fruiting body of the tooth
fungus is in some respects more complex than that of the
smooth shelves or clubs. The palisade surface is here distrib-
uted over an area covered with teeth which thus increases the
spore-bearing surfaces considerably. These teeth may be com-
Minnesota Plant Diseases. 175
paratively short — one-half inch or less in some forms — or they
may attain a length of three inches in others. They are chiefly
wood-inhabiting saprophytes and comprise some serious timber
rots and diseases; some are found on the ground. The coral
fungus and the very similar bear's-head fungus are exceedingly
common tooth-fungi, found on logs in autumn or throughout
the summer. The fruiting bodies of most of these fungi are
edible. (Figs. 81, 84, 119.)
Pore fungi (Polyporacea). This is one of the largest of the
groups of the palisade fungi and contains many of our most
conspicuous forms. They are palisade fungi which have in com-
mon the formation of pockets or pores in the fruiting body and
on the surfaces lining these pockets or pores are found the pal-
isades. A safe position and a great increase of spore area is
thus effected. There is considerable variety in these fungi in
respect of the consistency and form of the fruiting body. One
alliance of forms has more or less gelatinous fruiting bodies in
which ridges which cross and recross each other form shallow
pores. Many of these gelatinous pore fungi have single, pros-
trate fruiting bodies, though some form true shelves. Such
gelatinous pores resemble many of the trembling fungi and
their allies. To this group belongs the well known dry rot fun-
gus which is probably the most dangerous timber-saprophyte
known. They are common on rotting logs and stumps. The
majority of pore fungi have tough, leathery or more or less
woody fruiting bodies of a true shelf-habit. Most of our com-
mon shelf fungi belong to this group and they comprise a
great many of our most common timber diseases. A variation
is noticeable in the form of the pores and upon this variation is
based in a large measure the classification of the numerous
forms. Some pores are cylindrical pockets, others are elon-
gated and often fuse with neighboring pores and thus form
complex labyrinths; others, again, are hexagonal in outline.
The pores, moreover, vary in depth, in their relationships to sur-
rounding parts, in methods of formation, etc. Again, some
shelves last but one year while others live from year to year,
adding new substance to the fruiting body every year. In one
alliance of forms the shelves may be branched, forming large
compound shelves. The birch shelf-fungus, the sulphur fungus,
176
Minnesota Plant Diseases.
Minnesota Plant Diseases.
177
and the tinder fungus, may be mentioned as a few of the numer-
ous common forms of these pore fungi. In addition to the gelat-
inous and tough and fleshy pores are the beefsteak fungi which
are very soft; in these the pores with their surrounding walls
are free from each other and look like small dependent tubes
!•" IG. &>. — A stick-dwelling gill fungus (Ix-n/it. s brtulina). on a tlcatl branch of a birch.
( Iriginal.
hanging from the fruiting body. Most of these forms are edi-
ble. Somewhat similar to these are the species of Boletus, all of
which are fleshy and grow on the ground, often in swampy
places. The pores are here also found in tubes which separate
from each other readily and the tubes are combined into a sep-
arate layer. The pores are usually large and the fruiting body
always possesses a central stalk and mushroom-like cap. On
the under surface of the cap are found the pores. The pore
surface is sometimes enclosed in young stages by a veil-like
178
Minnesota Plant Diseases.
covering below which attaches the edge of the cap to the
stem. At maturity this ruptures and a part of it remains at-
tached to the stem as a so-called ring. They are all earth-in-
habiting saprophytes and most forms are edible while a few
are poisonous. (Figs. 5, 10, 36, 81, 85, 120 to 127, 163.)
Gill fungi (Agaricaccce). In this group of fungi the palisade
layer is spread over structures known as gills. These gills are
plate- or leaf-like bodies arranged on the under side of an um-
brella-like cap and run from the stalk to the cap edge. When
the cap is young the
gills may be closely
pressed together but
are later spread apart
to allow the spores to
be shed. This group
contains an enormous
number of plants, be-
ing by far the largest
of the palisade fungi,
and it includes not a
few plants of economic
importance. The fruit-
ing bodies vary in size
from not larger than a
large pin to umbrella-
like forms more than a
foot in diameter. In
consistency the fruit-
ing bodies may be gel-
atinous, waxy, fleshy,
leathery or even
woody. Some forms
are stalked while oth-
ers are attached direct-
ly by their cap edges.
In the higher forms
the fruiting body possesses veil-like structures which enclose
the gills or the whole cap as long as the gills are still immature.
As soon as the spores are ripe the veil breaks, leaving a cup-like
FIG. 87. — Shaggy-mane fungus (Coprinus comatus).
This is an inky-gill fungus. The cap is seen to be
blackened at the base, where the whole substance
of the cap deliquesces and drops its black spores
in an inky mass. Original.
Minnesota Plant Diseases.
179
structure at the base of the stem or a ring-like fragment on the
upper part of the stem. The gills are then exposed to the
air and are ready to shed their spores. If the cap of such gill
fungi be cut off, placed on paper and kept thus in a closed
chamber, the spores will fall in
such numbers as to give a very
distinct map of the gills. The
spores are of various colors,
white, pinkish salmon, ochre-
brown, dark-purple or black,
and this color difference has
been used as a basis for a
classification of the gill fungi.
In some dung-inhabiting
forms the gills liquify when
the spores are ripe and the
latter drip from the plant in
an inky fluid mass. Some
caps when broken exude
milky fluids of different col-
ors : white, red or yellow.
Such are known as the milk
fungi. The great majority of
the gill fungi are true sapro-
phytes. Many are earth-in-
habiting or dung-inhabiting
and an enormous number are
wood-dwelling forms. These
contain many of the chief tim-
ber-rot fungi as well as many
wound-parasites. A few aie
The gill fungi find their chief
economic importance, outside of their timber-rotting effect,
and as agents in the decay of plant debris, in the food products
which they furnish to man. The commercial mushroom is a
member of this group and hundreds of wild forms are ed-
ible. The latter are being used more and more extensively as
food by those who take the pains to hunt them up and to know
them. There are likewise some fungi of this group which are
FIG. 88. — The sliaKKy-manc fungus. This
fruiting Ixxly is in a more advanced
stagr of deliquescence than that shown
in Fig. K7; almost the rntirr ca;> ha>
(1ripi>c<l oil. A ring (annuluo) i» seen
at tin- bast- of tin stalk. Ordinal.
parasitic on other gill fungi.
r8o
Minnesota Plant Diseases.
so
Minnesota Plant Diseases.
181
exceedingly poisonous and fungus eaters must take good care
that they are familiar with the poisonous varieties found in the
state. (Figs. Frontispiece. 6 to 8, 10, 18, 20, 81, 86 to 89, 116,
128 to 132.)
Puff-balls and their allies (Gasieromycefes). All of the re-
maining basidium-bearing fungi have closed fruiting bodies.
The basidia are borne inside of this structure either in palisades
lining the surface of chambers or in irregular fashion on loose
threads throughout the fruiting body. The latter arrangement
FlC. 90. — A group of the common crnimnl puff-ball* ( I.ycupcrtlon ftrmmalum) ju»l lirfure
iipc-ning; the |« sin. 'ii of ihc future opening » sctn at the ilarkrnnl t'-i'- <>f the
fruiting budiis. Original.
is prevalent in the wefted pufT-bnIls (including the first, second
and third of the following groups), while the remaining groups
possess the palisade arrangement of basidia. The fruiting body
always possesses one or more covering membranes. These
fruiting bodies may remain closed until the membranes de-
cay, when the spores are released, or they may open in charac-
teristic ways, by pores or by splitting, and thus allow of the es-
cape of the spores. In most forms the interior of the fruiting
body partially disintegrates, leaving only the spores in a line dust
held in a loose weft of long and strong thread> which give the in-
terior a sponge-like texture. The spores are then thrown out in
182
Minnesota Plant Diseases.
dust-like clouds or puffs and are caught by the wind and may
be transported considerable distances. The chambers with
their palisade lining are not seen in the mature fruiting body
and can only be observed when the latter is young. The inte-
rior is then fleshy, white and more or less solid, and with age
gradually gets yellowish-green and soft, and even semifluid,
finally producing the dust of spores in the thread weft. (Figs.
81 to 91, see also following seven groups.)
FIG. 91. — The same group as in Fig. SO, taken two weeks later; shows the opened puff- balls.
Original.
Long-stalked puff-balls (Tulostomacce). One frequently
meets in sandy places and in open fields groups of small puff-
balls about one-half to three-fourths of an inch in diameter,
mounted on long stalks which in some cases attain a length of
six inches. At maturity the spores form a powdery dark brown
mass and are thrown out through a pore in the puff-ball wall.
The puff-ball is formed just under the surface of the ground and
is raised up above the ground by the somewhat rapid growth
and elongation of the stalk, so that the puff-ball is elevated to
an advantageous position for the scattering of spores. The
mycelium forms strands and the fungus is an earth-dwelling
saprophyte. (Figs. 3, 81, 92.)
Minnesota Plant Diseases. 18^
\J
Hard skinned puff-balls (Sclerodcrmatacca'). Many of these
puff-balls form their fruiting bodies at least partially under-
ground. The coat is hard and leathery in texture and usually
opens by splitting in some irregular fashion. The spores also
form a powdery mass which in our common species is dark vio-
let in color. The fruiting bodies are usually large in size, at-
taining a diameter of five and six inches in many cases. In their
immature condition they are superficially not unlike potatoes
in appearance. These fungi are a'.so earth-dwelling sapro-
phytes.
FlC. 92. — Stalked puff-balls (Tiilostomi mamrtiosum). The puff -balls have been raised
from the sandy ground on stalks ju»t before the owning and shedding <>! -j,..|,x.
Original.
Sphere-throwing fungi (Sphacrobolacctc). These are very
minute fungi and not easily recognized as puff-balls. The fruit-
ing body is usually not more than three-sixteenths or one-
eighth of an inch in diameter and covered with a soft whitish
outer coat. Inside of this is an elastic covering which, at the
maturity of the spores and after the outer coats have been
split, inverts and forcibly ejects the whole mass of spores. The
latter remain attached together in a solid sphere and never form
ii powdery mass. The sphere may be thrown as far as six feet
184 Minnesota Plant Diseases.
into the air. The spores begin to germinate in the mass and
thus a new mycelium is started. These fungi are wood-inhabit-
ing saprophytes and are frequently found on pine wood, as on
decaying sidewalk planks. (Figs. 14, 81.)
Underground puff-balls (Hymcnogastracccc). These fungi
form their fruiting bodies under the ground, sometimes an inch
or more below the surface. They are often thick-skinned and
never open except by the decay of the walls. The interior does
not develop a spore-powder mass but remains chambered to
maturity, and the chambers are lined with palisades of basidia.
These fungi are saprophytic. They are not abundant in Minne-
sota though several forms are known. They resemble very
much the true and false truffles, but, of course, differ from these
in the method of forming spores, for the puff-ball spores are
never found in sacs but always on a basidium.
True puff-balls and earth-stars (Lycopcrdincce). This group
includes many exceedingly common fungi which can be found in
great abundance in early fall. The puff-balls are therefore very
familiar objects. The fruiting body is usually spherical and is
always at least at maturity found on and never below the surface
of the ground. It is usually provided with at least two coats,
the outer of which is shed in various ways and the inner coats
peel off, undergo splitting", or open by a definite pore-like aper-
ture. In one group of very common puff-balls, the outer coat
forms small bosses, or more or less elongated spines, which at
maturity fall off (Figs. 90 and 91) and leave characteristic scars
on the inner coat.
One of the most familiar of this group is the gemmed puff-
ball in which the short spine-bosses are grouped together in
clusters. Some true puff-balls have paper-like and very thin
coats and our common form of this group is almost perfectly
spherical. The outer coat peels off in shreds and the inner
opens by a pore. In still other forms the puff-ball's outer coat
splits along the equator and the upper half then becomes in-
verted and looks like a saucer containing a puff-ball. The puff-
ball fruiting body always contains its spores in a powdery mass
which lies loosely in a cotton-like tangle of sterile threads.
When jarred in any way the puff-ball emits clouds of spores
which look like dust, olive-green, brown or black-purple, as
Minnesota Plant Diseases. 185
the case may be. The distribution of the spores may thus con-
tinue for an unlimited period. Of course wind is the chief
agent of distribution. The earth-stars are puff-balls with usu-
ally three coats in the wall of their fruiting bodies. The outer
falls off and the median coat splits from the tip nearly to the
base in a number of places and each lobe, so formed, bends back
when it absorbs water, giving to the fruiting body the form of
a star. By this bending back of the lobes the puff-ball is broken
loose from its mycelium and raised up in the air. Thus the
IMC. 93.— Karth stars, (deaftter triplex.) The uiu-i-vcrrtl strain! mycelium <-f tins fun^u*
is seen to the rifjiit. below; in the crnter anil to the rijiht above are unowned fruiting
bodies; above in the center is a star, just o.icniiiK. ami below to the left I* a fully
•opened or vaulted star with o >eiitd puff-ball in the center. Original.
spores obtain a more advantageous position for distribution.
In most earth-stars this vaulted condition is permanent but in
one form (really, however, a welted puff-ball) the coat opens and
closes depending on the presence or absence of water. The
bending back of the lobes is affected by the greater swelling
which takes place in the inner threads of thi> coat while the
outer threads are tough, remain somewhat rigid and are not
greatly extensible. One Minnesota earth->tar which in the
younger stages is found just below the surface of the leaf mold
is able to lift itself out of the mold and becomes vaulted directly
1 86 Minnesota Plant Diseases.
over the hole from which it was torn loose. The puff-ball fruit-
ing body in the very young stages is internally fleshy, more or
less solid, and usually pure white, and in this condition is edi-
ble and frequently sought by mushroom eaters. Caution must
be exercised to prevent mistaking for them the young button-
like stages of the poisonous gill fungi, which are not at all un-
like certain puff-balls. Puff-ball fruiting bodies vary enormous-
ly in size. The smallest are little larger than good-sized peas
while the giant puff-ball, a form much sought for by mycopha-
gists, has been frequently collected in Minnesota a foot or more
in diameter. In the youngest stages the interior of the puff-
ball is chambered and the chambers are lined with a palisade
of basidia. The mycelium of certain puff-balls has been de-
scribed as furnishing the mycorrhizal threads which live in part-
nership with roots of certain trees. These fungi are otherwise
saprophytic in habit. (Figs. 10, 81, 90, 91, 93.)
Birds' -nest fungi (Nidulariinece). This group of basidium-
bearing fungi would at first sight be scarcely recognized as a
close relative of the puff-balls. Such it is, however, with pecul-
iar variations from the typical puff-ball structure. The cham-
bering here becomes permanent and the chambers are lined as
usual on the inside with a palisade; they become separated by
the breaking down of the threads between. The chambers thus
come to look like small hard-coated egg-like bodies, which lie
loosely within the walls of the puff-ball. These walls open at
the apex by a broad-mouthed opening, which in the earliest
stages is closed by a parchment-like membrane, so that at ma-
turity the fruiting body has an open beaker-like form. In the
beaker or cup lie the egg-like chambers. The latter are in o'ur
commoner forms attached to the wall by thin stalks of exceed-
ingly elastic fungus threads which are so extensible that in wa-
ter they, can be drawn out to a length of six inches or more
from one-fourth inch or less in the dry state. This stalk may
serve to attach the fungus to the legs of insects and again from
here to the twigs or trunks of trees. The stalk is somewhat gel-
atinous which aids in the fastening of the stalk. The spores are
thus distributed in packets, which are the separated chambers,
and they germinate directly from the interior of the chambers.
The birds'-nest fungi are saprophytes with chiefly wood- or
Minnesota Plant Diseases.
i87
dung-dwelling habits. They may exist as timber rots but are
seldom if ever abundant enough to cause serious damage.
(Figs. 13,81.)
Carrion fungi (Phallinea).
More unrecognizable still as
puff-ball relatives are the car-
rion fungi. In the very early
stages of the fruiting body,
however, this relationship be-
comes somewhat clear. The
mycelium usually forms whit-
ish strands and upon these
strands arise the fruiting bod-
ies as small spheres or pear-
shaped objects and as they in-
crease in size look superficial-
ly very much like puff-balls.
These "eggs" attain a size of
three or four inches in some
forms, while in others seldom
exceed a filbert nut. The tip
of the "egg" is usually just at
the surface of the ground.
The outer coats of the "egg"
enclose a great gelatinous
mass and at maturity this
swells up and the outer walls
break. There then emerges
from the "egg" a stalked body
with a terminal cap. The
stalk elongates rapidly from a
compressed condition in the
"egg:" the elongation is not
growth but a straightening
out of folds, much as a sponge
enlarges when it absorbs wa-
ter. The carrion fungus cap
is thus raised several inches into the air in a few hours or less,
so that the elongation is delayed until the spore> arc ready for
r.. «M.-A
carrion
fungus I 1 >ictyo;ihora
lavenellii I. I'.el
>w are seen the rein-
nai.ts ol
the "( -njs «
ich have
U. n hi.
ken an.)
remain as a ci
> arounil
the has.-
of the -,1-ilk. The latt
is si-en
to he sp
niK> : >>>
straightening
ut from
a coinpi
cssetl coi
.litioii it has
fle<l the
cap s»m
• inches
ilxive tile Kro
i.l. The
cap lias
still a i
insi.lerahlc s;
re mass
U ft; limits hav
-, however. C
rie.l oil
the loss
ei porti.
n of the sp
re mass.
The o,l,
,r of the
latter is that of ha.lly
.lecaye.l
can ion.
( )rigii<:il.
i88
Minnesota Plant Diseases.
distribution. The spores are found on the upper surface of the
cap and at maturity are contained in a sticky, semi-fluid olive-
green mass which has a strong odor of carrion. Flies and other
insects are attracted by the odor, carry off the sticky mass, and
thus disseminate the spores. The attraction for insects is still
further increased by the presence in some forms of a lace-cur-
tain-1 ike veil which
hangs down from be-
neath the cap. In the
very early stages the
spore-bearing region
shows a series of cham-
bers lined with pali-
sades and very similar
to that of the puff-
balls, but at maturity
the chambers disap-
pear in the disintegra-
tion of portions and
only the sticky remains
with the spores are left.
The carrion fungi
show an extraordinary
amount of differentia-
tion and complexity in
the development of
their fruiting bodies
and the insect-distri-
bution of spores is car-
ried to a high degree
of efficiency. In these
respects the carrion fungi are undoubtedly the most highly de-
veloped of all of the basidium-bearing fungi, and it is doubtful if
any other forms in the whole realm of the fungi are their equal.
The carrion fungi are saprophytes and are all earth-dwelling
forms. (Figs. 3, 10, 12, 81, 94, 95.)
FIG. 95.— A carrion fungus (Dictyophora duplicata),
photographed just after the breaking of the "egg"
and while the cap was being lifted. The "egg"-
membrane remnant at the base is in sharp focus
since it did not move during the exposure; but
the whole top which has been lifted during the
15-minute exposure has been blurred. Below the
cap is a large lace-curtain structure which serves
as an additional attraction for insects. Original.
Chapter XIII.
Other Disease-causing Organisms.
Jff
Bacteria. One does not usually associate bacteria with dis-
eases in plants, but they are nevertheless frequently agents of
such disease. In recent years many diseases of bacterial
origin have been discovered and described. Man's chief inter-
est in bacteria is usually centered in the diseases of man which
are so largely caused by bacterial action. The bacteria were
formerly considered to be fungi but in recent years it has been
recognized that they are most closely related to the blue-green
algae, though they differ from the latter in important points.
They resemble the fungi in their mode of nutrition — for they ob-
tain their food in a partially elaborated condition and. with a
few exceptions, are unable to manufacture starch from air.
gases and water as do green plants. They are therefore devoid
of leaf green just as are the fungi, and thus differ
from the blue-green algae. They may possess
coloring matters of various kinds but are not as
a rule able to utilize these in the conversion of
the sun's light to energy in starch manufacture.
/\> \j They differ from the fungi, however, in their
method of growth and division, and in these re-
JMG. V: — liar- . . . . .
tcria of Mack spects and in general appearances resemble most
rot of cabl>.iK? ,,•>, , • ,
( p • e udomonas closelv the blue-green algae. I he bacteria, then,
c a m |>c s t ris). i .
They are Ken to mav be considered as c.ose relatives o! the blue-
be linv cylin-
der*. Highly green algae which have adopted fungus habits
magnified. After
of nutrition.
The forms and sizes of bacteria. The bacteria are all ex-
ceedingly minute plants consisting of single cells. They may
be less than one thousandth of a millimeter in length and the
largest are seldom more than about ten-thousandths of a milli-
meter. It requires, therefore, microscopes with powers of high
190 Minnesota Plant Diseases.
magnifications in order to observe and study them. The bac-
terial plants may differ somewhat in form and to these various
forms names have been applied, and upon them the classi-
fication of the bacteria was formerly based. It is now rec-
ognized, however, that several forms may appear in the same
life-story under differences of conditions, thus rendering the
former classification unsatisfactory. An approximately spheri-
cal bacterium is known as a coccus, a short, rod-like form is
known as a bacterium, in the narrower sense, and the long rod
form is a bacillus. Some forms are, moreover, comma-shaped ;
others are undulate or wavy in appearance, while still others ap-
pear much like corkscrew or long-drawn spiral coils. These
plants may differ, moreover, in the manner in which colonies
are formed. All bacteria in the broader sense multiply chiefly
by simple division of the cell into two, the resulting parts split-
ting away from each other — hence the name fission plants. By
such divisions filaments of cells may be built up, or by division
in two planes, plates of cells, or when division in three planes
takes place masses of cells are produced. As the external walls
of bacteria are frequently gelatinous, sheaths are formed which
serve to bind the plants together in such filaments, plates or
masses. A larger gelatinous colony may thus be built up and
is then known as a zoogloea. One sees among the bacteria a
great variety of habits ; a large number inhabit fluid media.
As a special means for dissemination many of such forms have
lash-like projections of the protoplasm which whip around in
the water and propel the plant cell about.
Multiplication and reproduction. The fission method of
multiplication which is common in the bacteria is a very effi-
cient one. It is also common to certain groups of blue-green
algae. In bacteria the successive splittings into cells may fol-
low with some rapidity, e. g., under the most favorable condi-
tions the hay bacillus completes a division in twenty minutes.
It has been calculated that if a bacillus two-thousandths of a
millimeter in length were to divide uninterruptedly at the rate
of once every thirty minutes, at the end of five days the volume
of the resulting bacteria would fill all of the ocean beds of the
globe. Competition and unfavorable conditions, of course,
prevent such disastrous results, but the possible rapidity of
Minnesota Plant Diseases. 191
multiplication is thus well illustrated. When unfavorable con-
ditions confront a rapidly dividing bacterium, spore formation
may take place. The spore, just as most fungus spores, pro-
vides itself with thick walls and is thus protected during the
continuance of the unfavorable surroundings. These spores
may be formed inside of the cells, or by the mere transforma-
tion of the ordinary cells by wall thickening and condensation
of protoplasmic contents. When placed again under favorable
conditions the spore may grow out in various ways into the
ordinary bacterial cells. No breeding act is known among the
bacteria.
Physiology of bacteria. The physiological activities of the
bacteria are most varied and interesting. They are of immense
economic importance for upon them are built a host of indus-
trial processes as well as many diseases in man and in plants.
Many geologic deposits, as iron ores, may possibly owe their
existence to bacterial activities.
Air-loi'ing ami air-slintniing bacteria. Most bacteria resem-
ble other plants in their requirements for air gases during their
life processes. Oxygen, one of these gases, is utilized in burn-
ing up certain compounds and in this combustion energy is
liberated to run the protoplasmic machinery. This use of oxy-
gen is common to animals as well as plants and the ultimate
products of the burning are carbonic acid gas and water. Such
bacteria may be known as air-loving bacteria or perhaps, more
strictly speaking, oxygen-loving. There is another class of
bacteria which is capable of obtaining such energy as the air-
loving bacteria derive from combustion of compounds in a dif-
ferent way. viz. : by the breaking down of complex orgairc
compounds into simpler, during which process the necessary
energy is liberated. This process may take place, moreover,
when no air is present, and in certain cases the exclusion of air,
and particularly of oxygen gas. is necessary. Such bacteria are
known as air-shunning bacteria. They have a method of break-
ing down complex substances different from that of the com-
bustion method and may carry on such a process even when the
air is entirely excluded.
Among the many air-loving forms the vinegar bacteria may-
be mentioned while the rancid-butter bacteria are examples of
air-shunning kinds.
192 Minnesota Plant Diseases.
Influence of external forces as ligJit, temperature, etc. It is a
well-known fact that most bacteria do not thrive in sunlight
but that the direct rays of the sun are fatal to them. Too much
stress cannot, therefore, be placed upon the necessity for sun-
shine in thorough processes of sanitation. Waters of lakes and
rivers are largely purified by direct sunshine which can fatally
affect bacteria to a depth of several feet below the surface. Of
course this is not the only agent of purification but is one of
the most important. It is to be expected, therefore, that when
bacteria cause disease in plants it is in the underground por-
tions, as bulbs or roots or stems, or in situations where the illu-
mination by the sun's rays is always poor. Excessive moisture
may, moreover, aid in bacterial dissemination. The bacteria
are easily carried about in the water currents especially if they
have the whip-like swimming apparatus which is common
among so many forms.
Some bacteria can live and even reproduce in temperatures
near the freezing point, while the resting, inactive cells are often
capable of resisting very much lower temperatures. On the
other hand, heat-loving bacteria are known which thrive in
comparatively high temperatures — even fifty degrees Fahr.
above blood heat. The bacteria are thus seen to enjoy wide
extremes of temperatures. A given species, of course, has
usually a much more limited range and always possesses a
favorite temperature at which it grows best. In general, bac-
terial cells in the dry state are capable of enduring higher
temperatures than those in the moist condition, — facts which
are used to advantage in combating bacterial disease germs.
In the canning of fruits, for instance, boiling for a short time
will destroy most germ cells though spores will often re-
sist even such harsh treatment. The power of resistance in the
dry state is an important feature, for bacterial germs may live
for months and even years in such conditions, germinating
again as soon as favorable conditions of moisture and nutrition
present themselves. Thus germs of various diseases of man
may lurk in the air or soil, becoming evident only upon the ad-
vent of suitable conditions. Strong electric currents usually
destroy bacteria and this fact has led some to believe that elec-
tricity may be utilized in the purification of municipal water
supplies.
Minnesota Plant Diseases. 193
Bacterial partnerships and antagonisms. Bacteria often
form dense colonies of individuals developing in gelatinous
masses. These bacteria may all be of one kind, but frequently
are different, and may then live in a partnership apparently ben-
eficial to each other. It is evident that such forms do not com-
pete with each other for food stuffs. Bacteria may also form
partnerships with other organisms as with yeast plants. In such
cases the waste products in the nutritive processes of one may
be food for the other plant and thus a beneficial partnership is
established. Such is the association of bacteria and yeast in
the English ginger beer "plant" and in the production of other
drinks as the Asiatic kephir. Such a partnership is also ex-
plained in the fact that organisms of this kind often form waste
products which, if allowed to accumulate, may prove detri-
mental to the organism producing them. This is a common
method by which bacterial growth is limited. These com-
pounds are in the case of bacteria often poisonous and form the
toxins which in disease germs are the poisoning agents of the
disease. The accompanying organism of a partnership may
use up and remove these detrimental substances and thus allow
the first partner unhindered development. Antagonism of bac-
teria in colonies may result from competition for food materials
or from the production of substances by one, which are poison-
ous to the other organism.
Disease-causing bacteria. One of
the most useful classifications of bac-
teria is the arrangement of forms ac-
cording to their prominent physio-
logical effects. In such an arrange-
ment the disease-causing or patho-
logic forms are of great economic im-
portance. These are the forms which
give rise to most of the well-known
diseases of man and lower animals.
IMC. j»:.-r,actcria of tire bi^ht ,,f Cholera, tuberculosis, diphtheria and
apples (Bacillus amylovorus). t • i i e i \ \
Highly magnified, '.-\fter ii. typhoid are but a few of the destruc-
tive diseases of bacterial origin. By
nn accurate knowledge of the life-story, physiology, etc., of
these organisms preventive measures of sanitation and quaran-
:
194 Minnesota Plant Diseases.
tine have been made possible and an enormous saving of life
effected. Modern methods of medical and surgical practice
have been built upon such knowledge. Great as have been the
results in the past, still greater may yet be achieved in the future
by a more complete knowledge of these disease-causing bacteria.
This applies as well to those bacteria-causing diseases of
plants as to the diseases of man, though the former are not
so numerous nor so vital to man's interests.
Dye-forming bacteria. Another great group of bacteria
have the peculiar property of producing coloring matters dur-
ing their nutritive processes. This coloring matter is in some
cases found in the cells of the bacteria and in others is a by-
product of nutrition. Red and yellow spots on bread are fre-
quently of this nature and milk is sometimes colored red from
a similar cause. The blue coloration of milk is also of bacterial
origin. Certain bacteria form a beautiful ''bacterial purple"
and are furthermore peculiar in that, by means of this color-
ing matter, they seem to be able to utilize the sun's rays in a
manner analogous to the leaf-green plants which convert sun-
light energy by the use of leaf-green. The production of in-
digo dyes from indigo plants is also dependent upon the activ-
ity of bacteria; other blue colorations, as in certain kinds of
cheese diseases, and again, green colorations may have bacterial
origins.
Light- and heat-forming bacteria. In the conversion of
energy in which bacteria are engaged, many forms exhibit
still other peculiarities. Some utilize surplus energies in the
generation of light and such produce phosphorescence or
other illuminations. Sea phosphorescence is in part due to
these bacteria. Others again dissipate energy in the produc-
tion of heat and examples of these may be seen in heated
manure piles, in silos, in certain methods of curing hay, and
in tobacco curing. The generation of heat in all of these cases
is due to the activity of heat-producing bacteria. The tem-
perature may even be raised to such a degree that rapid com-
bustion of the materials may take place and such occurrences
are usually described as spontaneous combustion.
Fermentation bacteria. Still another great group of bac-
teria are capable of causing fermentation in fluids — a splitting
Minnesota Plant Diseases.
195
up of compounds accompanied by the production of gases
just as is effected by yeast plants in bread- and beer-making
processes. These fermentation processes are of many kinds.
Butter becomes rancid ' and milk may be broken up and
soured by the action of these bacteria. Upon the action of
milk-fermenting bacteria depend other processes in certain
methods of curing hay and ensilage. Again, fermenting bac-
teria are the agents of fermentation in the production of vin-
egar.
Nitrifying bacteria. Of great importance in agriculture
are those bacteria which live in the soil and by their action
prepare crude materials for leaf-green plants. The latter re-
quire a certain gas known as nitrogen which must be fur-
nished, however, in a particu-
lar kind of compound known
as a nitrate. Leaf-green
plants are unable to utilize
nitrogen gas in the free state
and this is the condition in
which it exists in the atmos-
phere. Now the nitrifying
bacteria are capable of using
compounds unavailable to the
leaf-green plants and by the
united action of several bac-
teria finally build up the ni-
trates desired by the leaf-green
plants.
Nodule bacteria. Certain
plants such as clover and
many other plants of the pea
family form small nodules on
their roots. In these nodules
dwell bacteria, which are capa-
ble of using free nitrogen
from the air. They then pass
the manufactured nitrates on to the clover plant. These nod-
ules are therefore special habitations for nitrogen-fixing bacte-
ria, which are thus protected and fostered by the clover plant.
Fie. 9S.— Itacterial nodules on root of com-
mon bean. .In these swollen portions of
the riK'ts arc found bacteria which as-
sist the plant in obtaining nitrogenous
food material. Original.
196
Minnesota Plant Diseases.
The latter derives its benefit in the nitrate product. A true part-
nership is thus effected. Clover and alfalfas and all such nodule-
possessing plants are therefore valuable rotation crops because
they accumulate by the aid of their bacterial partners nitrates,
where wheat or other crops have depleted the soil of these com-
pounds. These bacteria are now distributed by the Depart-
ment of Agriculture in quantity for sowing on poor soils where
leguminous plants as clovers, etc., are then grown. Such soils
can thus be greatly enriched so that other crops which do not
possess bacterial nodules can subsequently be raised.
Other economic phases
„,,»•—,• *— - .
of bacteria. A great many
other phases of bacterial life
are of importance in the
arts and industries and only
a few may be mentioned in
this short review. In tan-
ning, in diseases of wine and
beer, rennet curdling, in the
manifold processes of putri-
faction of organic matter, in
cheese industries, in the deposition of bog iron ore, the bacteria
appear in important roles. More particularly are we here con-
cerned with those forms which attack living plants and cause
disease. Such plant diseases are not numerous but investiga-
tion is steadily adding new examples and they promise to be-
come of sufficient importance to make this brief general dis-
cussion of this group of plants justifiable. The various bacte-
rial diseases will be considered individually in subsequent chap-
ters. (Figs. 96 to 99, 172 to 178, 195).
Slime molds (Mycctozod). This group of organisms is
now commonly classified with the simplest animals, though
they are very fungus-like in many of their characters. Most
slime molds are true saprophytes but a few have adopted para-
sitic habits. Some of the latter live in plants and others in ani-
mal tissues. The slime molds produce spores in structures very
similar to the fruiting bodies of many saprophytic fungi. These
fruiting bodies are usually very small — many are of pin-head
size but a few attain a diameter of six inches. The spores are
FIG. 99. — The bacteria of such root nodules of
the pea family as are shown in Fig. 98.
On the left of Vicia sativa (the spring
vetch), on the right of Medicago denti-
culata. Very highly magnified. After At-
kinson.
Minnesota Plant Diseases.
197
1
usually enclosed in cases which have definite methods of open-
ing. The spore mass is dusty or smut-like and the spores are
tiny spheres of microscopic size. If the spores be placed under
favorable conditions of moisture
and temperature they do not
send out a fungus thread as do
true fungus spores, but the wall
breaks and the protoplasmic con-
tents emerge in a naked mass,
not unlike a very tiny drop of al-
bumen in appearance. This
small mass creeps about by
changing form, engulfs food, and
lives in all essentials as do other
very simple animals. After a
time a large number of these ani-
mals of the same kind meet and
soon fuse together forming a
larger mass of jelly-like material
which is known as a plasmodium.
The plasmodium is often met
with on the forest floor or in
other moist places and is often
highly colored. Pink and yellow
are common colors though many
are yellowish white. The plas-
modium may be cake-like or may
be drawn out in various ways, as
into strands. It is in reality a
colony of slime-mold animals,
and this colony may move and
feed and otherwise behave as a
simple animal. After a time and
particularly as the atmosphere
becomes dryer the plasmodium
draws itself up into some kind of
a fruiting body which is often
composed of stalk and capsule. In the latter are found the spores
and also sterile threads, in appearance not unlike those found in
Fie. 100. — A slime mold. 1. An opened
(on right), and an unopened fruiting
body. From the opened fruiting body
is seen a protruding fluffy mass of
threads (capillitium), which encloses
the spores as in a mass of cotton. 2.
An isolated thread of the capillitium
and a siorc (highly magnified), (Ar-
cyria serpata). 3. a. young siwire
(Chondrioderma diffurme); b the
same, germinating; contents are
emerging as a naked bit of pro-
toplasm; c same in the free swim-
ming stage; has a single swimming
lash; d same in amoeba Mage; e sev-
eral amoeba-like masses fusing to
form a small plasmodium: f a young
plasmodium. 2 and 3 highly magni-
fied. 1 and 2 after Dcllary; 3 after
Cienkowski.
198 Minnesota Plant Diseases.
the fruiting bodies of puff-balls. In fact many of the fruiting
bodies resemble so closely the true puff-balls that botanists for-
merly classified them as such and the amateur is constantly de-
ceived by the resemblance when he first meets with these forms
in the field. When the fruiting body is formed the entire plas-
modium is used up in its construction and the spores are blown
about by the wind and thus disseminated. The slime molds
exhibit, therefore, a lowly method of animal life and a fungus-
like reproduction. The slime molds, living as plant-parasites,
live in the cells of the host plant and do not form fruiting bodies
like those of the true wood-dwelling saprophytes. One slime
mold parasite causes the club root of beets living in the cells of
the swollen portions. The slime-mold parasites of animals
cause various diseases. Malaria is due to a slime mold which
lives a part of its life in the body of the mosquito and is trans-
ferred to man in the bite of the insect. Texas fever of cattle
and several diseases of man are traceable to the action of organ-
isms of this slime-mold group. (Figs. 100, 179,180.)
Other kinds of plants as disease-causing organisms. As has
already been stated, fungi constitute an overwhelming majority
of those plant diseases which are of plant origin. Besides these
and the bacterial diseases, a few are known which are caused
by other kinds of plants though they are with few exceptions of
slight economic importance. Only a short account of them will
be permissible in this work.
Algae. A number of blue-green algae live as place parasites
in cavities and tissues of higher plants. Such are doubtless not
true parasites in their nutrition but their position in the tissues
of the host offers them protection of place and a safe harbor.
Such are found in floating water-ferns, and in the roots of
the greenhouse sago palms.
Some flower-pot algae are also place parasites. The posses-
sion of leaf-green enables them to manufacture their own food.
A few such green algae are known on water-inhabiting seed
plants, e. g., several species of the tiny duck weed. No diseases
of economic importance are known in these groups.
Mosses and fernworts and lower seed plants. No Minne-
sota members of these groups of plants or of their alliances are
known as parasites of other plants. Some of the latter groups
Minnesota Plant Diseases.
199
have already been mentioned as living in an unequal partner-
ship with root fungi in which the green plants are the dominant
partners. They are not however found as parasites on other
green plants.
Higher seed plants. A number of Minnesota species of the
higher seed plants are known as true parasites on other leaf-
green plants and a few of these are of economic importance.
When a race of plants which was originally self supporting by
FIG. 101— Twig of a witches' broom of spruce, showing the parasitic plants of the mistle-
toe which cause the "brooming" of the branches. The mistletoes are seen as very
small plants, scarcely larger than the spruce leaves; they are tipped with an ew
shaped body which is the fruit of the mistleti-e and contains a single seed. (See also
Figs. -4 and 25.) Photograph by the author.
means of a leaf-green apparatus, enters upon a parasitic life, the
leaf-green mechanism falls into disuse and may suffer reduction
or may even entirely disappear. Hence \ve find in confirmed
parasites of this group more or less of a bleaching of the para-
site. They are often, therefore, yellowish in color and the leaves
are reduced to mere scales or are wanting entirely.
2OO Minnesota Plant Diseases.
Special kinds of sucker roots are frequently produced which
penetrate the host plant tissues and absorb the manufactured
food stuff. Some of these parasites have only half learned the
parasitic habit and still retain some of their leaf-green apparatus.
A typical parasite of this group of plants is the little mistletoe
which occurs in great abundance on spruce trees in the north-
ern part of the state. This little plant lives in the twigs and
larger branches of the spruce and induces the formation of
witches'-brooms. Badly diseased spruces therefore show a very
irregular contour and may eventually be killed. The common
dodder is another confirmed parasite. It starts life from the
seed as a little leaf-green-possessing seedling but as soon as it
comes into contact with a suitable host plant it abandons its
leaf-green apparatus and coils itself closely around the support,
sending in its sucker roots which also serve to fasten it to its
support. The twining stem grows rapidly, bears very small and
reduced leaves, and the whole plant is yellowish in color. The
dodder is common on many wild swamp plants and is also occa-
sionally abundant on clover where considerable damage may be
caused. Of some interest are also those few forms which are
root parasites. The toad flax, which is a common Minnesota
plant, has partially learned this habit of parasitism. Here the
plant is apparently a typical leaf-green herb, but its roots may
be found penetrating the roots of other plants and there obtain-
ing nourishment. Parasitism is here an auxiliary process.
Other Minnesota plants, members of the broom-rape family,
have completely learned the root parasite habit and have con-
sequently lost all of their leaf-green. The stems are usually
small, reaching but a short distance above the ground, and bear
a few colorless reduced leaves and spikes of flowers. Several
species of cancer roots and broom rapes occur in this state.
They are not abundant, however, and produce no far-reaching
or destructive disease in plants. (Figs. 24, 25, 101.)
Chapter XIV.
Economics. Prevention and Cure.
The economic importance of plant diseases. A few well-
known figures will illustrate the great economic importance of
the fungus diseases of plants. These include only estimates of
epidemics. From the nature of the case it is impossible to esti-
mate the smaller losses due to sporadic diseases which have
probably caused more total loss than the great epidemics. In
the kingdom of Prussia the year 1891 was particularly favorable
for the rust disease of cereals. In that year the loss of wheat,
rye, oats and barley from rust has been estimated at over one
hundred millions of dollars. In Australia in 1890-1891 the loss
by wheat rust was estimated at twelve millions. In California
the grape disease from 1884-1886 caused an estimated loss of
twenty million dollars. A single English tomato house has in
one season suffered a loss of a thousand dollars by fungus dis-
ease. An agricultural expert has estimated the yearly loss in
the United States due to loose smut of oats, before successful
treatment was discovered and introduced, at eighteen million
dollars. One of the most striking illustrations of the enormous
losses due to fungus diseases is found in the history of the
coffee leaf-rust disease which has played such havoc in the east-
ern hemisphere. It has practically exterminated the coffee
plantations of Ceylon where the loss from about 1870 to 1886
was about five million dollars yearly and the total loss in those
years from sixty to seventy-five million. India's annual loss
from wheat rust has been estimated at from two to ten million.
In the United States loss by wheat rust for 1891 has been placed
at sixty-seven millions of dollars. In our own state Dr. Lugger,
the late state entomologist, estimated the loss from wheat rust
in Minnesota in 1888 as far in excess of the total loss by ravages
of all insects including even the dreaded grasshopper. One can
realize the enormous loss from this source in an estimate by
202 Minnesota Plant Diseases.
officials of the United States department of agriculture, which
placed the loss in the whole United States in 1882 on all agri-
cultural products due to insects' ravages at 200 to 300 millions
of dollars.
No estimates are readily available for losses on smaller epi-
demics nor on local ravages of fungus pests where conditions
have favored a restricted epidemic. It is well known, how-
ever, that the potato disease in certain wet seasons causes enor-
mous losses, particularly in eastern states and in Europe. In
the few years following its introduction in about 1845 the losses
amounted in many places to a complete destruction of the po-
tato crop. Garden truck and orchards yearly suffer in almost
all sections of the country. In many cases the losses are not
deemed important, but though slight, amount to great sums in
the aggregate. We hear of rust-free seasons for grains but no
year is absolutely free and such small unnoticed loss has come
to be accepted as an inevitable tax upon grain. It is against
such losses as well as against the great loss by epidemics that
attention will have to be directed. It must be clear from the
above figures that the fight against fungus diseases is not a
mere illusion entertained by a few enthusiastic specialists but is
a most important and vital economic feature of all future
branches of plant industries.
Prevention and cure. If there is one thing which will con-
tribute more than any other to the relief of agriculturalists and
horticulturalists from the losses incurred by the disease of
plants it is knowledge. No one would hesitate to affirm that
more extensive knowledge of the real nature of the diseases of
man has lessened enormously the destructive attacks of those
diseases. The force of this analogy is comprehended by few in
its application to plant diseases. The practical plant grower
wants to know only the cures, — sprays or whatever they may
be, — he often does not care to study or learn the details of the
disease-cause and its mode of action. But it is only with this
knowledge that an intelligent application of remedial measures
is possible. Probably no two occurrences of a plant disease
have exactly similar conditions. The generalities which under-
lie them are to be found only in a knowledge of the action of
the disease-causing organism. The details of treatment must
Minnesota Plant Diseases. 203
necessarily differ and the judgment of the operator is always im-
portant. The value of that judgment is measured only by his
knowledge. The more he knows of the causes and action of
the disease the more intelligently and the more successfully will
he be able to combat it. The various remedial measures — solu-
tions, formulas, sprays and spray machinery — are all important,
indispensable in fact — but they are not the ultimate object;
they are the means by which relief is secured and the observant
operator who knows what he is doing and why he is doing it
has many more chances of success than he who is following
book rule. I shall deem myself eminently successful in this
work if I shall be able to contribute to such a spread of useful
knowledge as shall fortify the efforts of all plant growers in the
state. The solutions of these problems lie largely — I might al-
most say entirely — with the men who are the operators. The ob-
ject of this work is to help him to an understanding which will
give reason and intelligence to his efforts. It is obvious, of
course, that an objection will immediately be raised, viz. : the
farmer cannot hope to master all of the details of the life-stories
of disease-causing organisms — his time is occupied with the
practical problems and operations of plant growing. And this
objection has much of truth in it. Nevertheless, success in all
lines is becoming more a matter of knowledge. What the farm-
er can do and must do is to know more about the plants with
which he has to deal — and these include not only his wheat and
apples but the enemies of these plants as well. He must pick
out from the results of those who have worked out and de-
scribed the details of disease such facts as are of use to him and
apply those results.
Successful agriculture is no longer the simple method it was
of old, i. e.. the planting of the seeds and the trusting to provi-
dence for favorable conditions of growth and produce. It is the
scientific control of those conditions. The farmer alone stands
helpless. The plant pathologist is an absolute necessity in the
agriculture of today. His results must increase the efficiency
of the farmers' efforts and they will if they are intelligently ap-
plied. In this specialization the plant pathologist is by no
means independent. He is just as dependent upon the coopera-
tion of the farmer as the latter is upon him. In other words,
204 Minnesota Plant Diseases.
both branches of this new agricultural machinery must work to-
gether in order to achieve successful results. The facts of ac-
tion and nature of diseases are useless unless applied and the
application of such knowledge is in the province of the plant
growers. In a word, the field of the plant pathologist is the
enlargement and spread of knowledge of diseases and their
causes and the field of the farmer is the application of such
knowledge to the raising of plants. Both parts of the machin-
ery of this new agriculture must work in harmony or both be-
come useless. The successful plant grower must not only know
what to do for certain diseases but why he does it, and the
pathologist only can tell him why. On the other hand, the
pathologist must look to the farmer for the solution of the
countless problems of practical detail in the application of that
knowledge.
Every one knows that the best way of fighting off disease
in man — as in typhoid, tuberculosis, etc. — is to prevent infec-
tion, and just so with plant diseases. Prevention is the most
successful treatment of disease. But how can a disease be pre-
vented unless one knows the nature of the disease? It must
not be supposed that no relief is possible from actual disease in
plants for much can be done to furnish such relief but it needs
no argument to convince a fair-minded grower of plants that
prevention is more to be desired than methods of cure. It will
therefore be convenient to consider the methods for combating
disease under the two heads of prevention and cure.
Prevention. Since prevention is of such great importance
it is obvious that a disease must be anticipated — headed off —
before it can get a start. Now the first stage of a fungus dis-
ease lies in the infection. Infection, as has already been point-
ed out, may be effected by fungus spores, as in rusts and smuts,
or by the established mycelium, as in timber and wood rots.
The prevention of infection is therefore first to be considered.
Wound infection. A very common method of infection is
through wounds in plants. Wounds open up passages through
the outer layers of plant tissues which ordinarily resist the at-
tack of fungus threads and through these passages the threads
gain entrance. Plants have methods of covering such wounds
with cork or callous tissues but these methods are slow and be-
Minnesota Plant Diseases. 205
fore they are completed the fungus has often established itself
within. It is therefore obvious that wounds in shade trees and
orchard trees must be covered with tar, creosote, or some other
substance which will prevent infection. Many wounds are
caused unnecessarily and special care should be exercised in
preventing as far as possible wounding of plants. Frost, light-
ning and storms cause many unavoidable wounds and such
should as far as possible be protected. Pruning is also a neces-
sity and need not be injurious if the wounds are likewise pro-
tected. It has been recommended that the pruning of trees be
done in winter or autumn. The tar coating is only efficient if
partially absorbed by the wounded surface and this soaking-in
occurs only when the tar is applied in autumn or winter. In
spring or summer the tar does not enter so freely and may leave
air spaces through which the fungus may enter. It should be
realized, however, that the bark of trees is a necessary protec-
tion and cannot be carelessly injured without serious results.
Insects cause wounds in plants and preventive methods may be
employed to avoid these injuries, such as tar-ringing.
The importance of localities. Certain plants are known to suf-
fer more from disease in one locality than they do in others.
This may be due to various causes. The dampness may favor
fungus growths, in which case dryer situations would be favora-
ble. Potato-blight frequently prospers in such moist localities.
Again, plants should not be placed in a region in which a dan-
gerous disease is known to be prevalent, or at least until the dis-
ease has been eradicated. Such has been demonstrated in flax
wilt. The disease germs often lurk in the soil for several years.
In such plants as are subject to rusts, e. g., cereals, care must
be exercised in the surroundings for such diseases may pass a
part of their life on other plants and from these may infect the
cereal. This is also true of apples and pears where the fungus
also dwells on species of juniper. Other fungi may live on wild
plants related to the crop plant. Of course it is not always
practicable to select localities, but the importance of this feature
should be kept in mind.
Rotation of crops and "pure cultures." The rotation of crops
has several advantageous features. When wheat is rotated
with clovers it is well known that the latter replenish the worn
2°6 Minnesota Plant Diseases.
out soil by the action of the clover root tubercles. In other in-
stances the rotation is effective in preventing disease ; the latter
can usually not infect the alternate crop and thus may be eradi-
cated before a new crop is planted. This is often a very effect-
ual method of preventing disease. By "pure cultures" are meant
the great fields of one kind of plant, such as the common wheat
fields of our own four neighboring states. The plants in such
fields are all at about the same stage of development. When
such a disease as a rust obtains a start in these fields the winds
rapidly spread the spores and no obstructions are raised to the
wholesale scattering. The result is a veritable epidemic. As
long as large, unprotected fields of this sort are planted just so
long will there be a tendency toward epidemics of rusts. The
planting of such pure cultures therefore carries with it undoubt-
ed risks. This is also true in forest culture where mixed for-
ests have in this respect advantages over pure unmixed ones.
Fertilizers. The manuring of soils may under some condi-
tions bring dangerous diseases. In some smuts the spores may
continue to live and grow for a long time in the nutrition fur-
nished by the manure and may be introduced into the field by
this means. Old manure is preferable to fresh manure, since in
the former fungi may have died out or become enfeebled. The
fresh manure may contain the more vigorous fungi. Of course
it must not be assumed that manuring of fields is therefore al-
ways injurious, but two points must be noted : first, the kind of
manure used and its source ; and second, the prevalence of such
diseases as thrive in manure, e. g., certain smuts of grains. In
other words, manuring may furnish favorable disease condi-
tions. That it does so always or even commonly is not implied.
Selection of varieties. The selection of varieties is becoming
more and more important for success in plant growing. The
immediate objects of such selection may be various, e. g., in-
crease in yield, quality of yield, hardiness, etc. It has already
been pointed out that plants of a given species may vary in their
susceptibility toward certain diseases. The cause of such im-
munity or predispositoin is not understood in many cases, but
certain facts of immunity are undoubted. It is possible, there-
fore, to select varieties of plants which may show successful re-
sistance toward prevalent diseases — in other words, disease-
Minnesota Plant Diseases. 207
proof varieties. It must, of course, be understood that a variety
may be immune from one disease and not from another totally
different disease. In the selection of varieties this feature must
be constantly kept in mind. Moreover, there are usually other
features of importance in plant growing such as annual yield,
quality, and so on. which are of great importance in the selec-
tion of varieties. The best variety is, of course, that which, un-
der given conditions, will yield the best sum total results. It
is sufficient here, however, to point out the fact that plant dis-
eases are very imporant factors in the selection of plant varieties,
and that such selection can assist the plant grower in the pre-
vention of diseases.
Prci'ention of spread. The methods of prevention discussed
above all deal with a prevention of infection. They are at-
tempts to prohibit the beginnings of a disease. But diseases
may sometimes obtain a start and the plant grower may still be
able to use preventive methods. The latter now. however, are
directed towards a prevention of the spreading of a certain dis-
ease— in other words — to prevent epidemics. Such preventive
methods usually consist in the burning up of infected plant
parts so that the fungus spores or mycelium will be destroyed.
The spread of wood rots may be prevented in this way and the
infected branches of the black knot of plums and cherries should
always be removed and burned. It is well known that a large
number of diseases live over winter in the fallen leaves or dead
branches of trees or in the stubble of wheat or straw or refuse
piles. It becomes apparent that cleanliness must be an impor-
tant weapon in fighting plant diseases. The only successful
method of removing such refuse, fallen leaves, etc.. is by burn-
ing. In the case of field crops fall plowing may also be useful
in addition to the burning process. It is not recommended that
all straw stacks be immediately burned. It is necessary, how-
ever, for the grower of plants to know the disease he is com-
bating, and if it is found to winter over on straw or refuse of
any kind, measures should be taken to prevent the spread of the
disease by destroying its winter abode or by rendering the spread
of the fungus from these places impossible. A preventive
method already mentioned may be recalled here. It relates to
those diseases, as rusts, which live at different times on different
208 Minnesota Plant Diseases.
host plants. The careful plant grower will see to it that those
plants which harbor diseases dangerous to his crops are alien-
ated. It is known, for instance, that rusts of apples live also on
red cedars. If, therefore, an apple orchard is attacked by rust,
the owner should see to it that the alternate hosts, i. e., some
juniper trees, in the neighborhood are closely watched and re-
moved if necessary. Here intelligent action and knowledge of
the habits of the disease are indispensable.
State aid and cooperation. Most agriculturists are acquaint-
ed with the fact that combating methods against many diseases
are often of no avail unless the cooperation of all farmers in the
community is obtained. If a farmer refuses to kill off the grass-
hoppers on his land not only does the guilty one suffer, but
his neighbors suffer as well. Or if one farmer suffers injurious
weeds, such as mustards, to grow on his field all of his neigh-
bors suffer. It is just so in the fight against fungus diseases.
We have in our state a state entomologist, whose duty is to
aid in the combating of insect diseases of plants and it will not
be many years before the farmers of our state will demand a
specialist in the fungus diseases whose duty shall be to assist
farmers in combating those diseases and to direct movements
against the epidemics of these pests. State aid is absolutely
necessary in many cases and state laws are likewise a necessity
to protect the intelligent farmer from the ignorance or lazi-
ness of his neighbors and to carry on experiments on the larger
scales which individual agriculturists cannot attempt. Not
only does our state support the fight against insects but our
forests are under the protection of a forest warden, and very
rightly so, and no one questions the advisability of such pro-
tection. In combating animal disease and the diseases of man,
our state board of health is an absolute necessity. Now plant
diseases require quarantine and sanitation methods just as do
animal diseases, and the highest success of the agricultural in-
terests of the state will not be attainable until combative meth-
ods are supported by state aid. There should be established,
therefore, a corps of specialists whose duty it should be to be-
come familiar with the diseases of plants in this state, to in-
vestigate those not yet understood, to disseminate the knowl-
edge of the habits and treatment of such diseases and direct the
Minnesota Plant Diseases. 269
operations against disease epidemics. In connection with such
a department a museum of plant disease would be found to be
an excellent aid, where exhibitions of plant products, with the
important diseases and graphic descriptions and illustrations of
them, would assist visiting agriculturists in recognizing and un-
derstanding the diseases of his crops. Such a museum would
be of great value to the farmers of the state above all in the dis-
semination of knowledge.
Other preventive aids. Many of the treatments described
below as curative are also used as preventives and are found
in very many cases to be of great service. \Yhere the begin-
nings of disease are not yet demonstrated but may be strongly
suspected, or where the likelihood for the occurrence of certain
diseases is strong, spraying is sometimes of use in prevention.
Methods of cure. Methods of cure cannot always be sharply
distinguished from preventive methods. Indeed the same
method may sometimes be used with both objects in view.
Curative methods in general, however, are directed toward the
destruction of the parasite which has already established itself
upon its host plant or which threatens such an attack, by the
presence of the spores. Two courses are open in such cases.
The fungus, together with the infected plant parts, may often
be removed by mechanical means, or chemical poisons may
be used, as sprays, dusts, etc., to kill the parasite without
injuring the host plant. The first of these methods has al-
ready been considered in its important aspect of prevention,
for it is properly a method of prevention against the spread
of disease. The accumulation of refuse should be prevented,
diseased parts of trees and shrubs and perennial herbs cut off,
and burned, and the spore-producing organs of disease-forming
fungi cut off and destroyed. Particular care should be taken
to destroy the plant parts in which certain diseases pass the
winter. Prompt action, so necessary on the first appearance
of a disease which is to be treated by these methods of cutting
and burning, and cleanliness in farm management are two im-
portant essentials of success. The second method of cure, vix. :
the poisoning of the fungus and its destruction by means of
chemicals which do not, when used in the proper proportions,
injure the host plant, is one to which much study has been
14
2io Minnesota Plant Diseases.
given. A great many formulas and processes for various dis-
eases have been described and many of these have proven suc-
cessful. In general, there are three ways of application of these
substances, spraying of solutions in water, dusting in powder
forms, or immersion in solutions. A number of these formulas
will be considered though special references will later be made
in dealing with the specific diseases of plants.
Chapter XV.
Fungicides and Spraying Apparatus.
JC
Fungicides. By fungicides are understood those substances
which are capable of destroying or prohibiting the growth of
the spores or mycelium of fungi. Chemical solutions have
proved of great value when sprayed upon diseased plants.
Such a spray must not only not injure the plant, but must at
the same time destroy or hold in check the parasite. It becomes
evident, therefore, that such
sprays are of greatest benefit in
combating fungus parasites
which live on the surface of
the host plant, i. e., the epi-
phytic fungi, such as the pow-
dery mildews. These para-
sites can be reached directly
by the spray without the ne-
cessity of penetrating the leaf.
But the spray may be benefi-
cial in still other ways. For
instance, where the fungusl
lives inside of the host plant,
and comes to the surface to
form its spores. Potato-
blight is such a form. The
use of the spray consists in the destruction of the spores and
the prevention of the spread in such cases. ( )n the other hand,
a very large number of parasitic fungi produce their spores at
the surface of the host, but are not affected by sprays, e. g.,
rusts of grains. In some cases, however, the spray is benefi-
cial against endophytic fungi and in these cases it is because of
the destruction of the spores and the prevention of the latter
from germination. The internal mvcelium cannot be reached
Tic. 102. — A bucket pump
Co.)
(The Denting
212
Minnesota Plant Diseases.
without injury to the host plant. Only the best-known and
well-established formulae will be considered here. For de-
tailed accounts of the action on specific diseases, the special
portion of this work should be consulted, as also the experi-
ment station bulletins of the Department of Agriculture. A
great many of the bulletins of the Department of Agriculture
and of the various Experiment Stations have been consulted in
compiling these formulae. These may be referred to for fur-
ther detail.
The value of spraying in agricultural and horticultural work
has been proven to be considerable. It is no longer a chance
but a certainty. The kind of spray and number of applications
FIG. 103. — A knapsack pump. (The Goulds Mnfg. Co.)
must be left to the judgment of the operator. In general, bor-
deaux is of greatest use. Knowledge and intelligent judgment
on the part of the agriculturalist are indispensable. He must
be prompt in his action and, if possible, must extend his knowl-
edge so as to forestall any disease and thus save time, labor
and expense. It is usually best to spray too often than too
seldom. Timely application may kill thousands of spores and
prevent infection when a late application may be of no avail.
Prevention is always to be desired. Applications must be thor-
ough. Such a treatment usually requires but a little more at-
Minnesota Plant Diseases.
213
tendon than a careless one and must prove of much greater
benefit. The matter of apparatus, as pumps, nozzles, etc., must
also be left to the judgment and to the financial possibilities of
the operator. Good -apparatus is, however, indispensable.
Whether or not this shall be expensive depends on his ingenui-
ty and knowledge.
Effect of fungicides. The object of the application of fungi-
cides is the destruction of the fungus pest. The substances
are necessarily of a poisonous nature and the fear is often en-
tertained by growers of plants that such applications may be in-
jurious to the host plant or to the consumers of the crops or to
domestic animals to which the crops or foliage may be fed. It
has been found that the fungicides listed below, if sprayed on
plants even with considerable frequency, can be made very
effective and yet never injure in the least the plant foliage.
It has even been claimed that copper solutions such as bor-
deaux are beneficial, but such an action is doubtful, or, at best,
but very slight. The arsenic mixtures, such as Paris green,
which are used to combat insects, likewise exercise no injurious
effects upon the host plant when
sprayed on in proper amounts.
Copper salts in strong solutions
are able to injure the roots of
plants very seriously but it has
been shown that by ordinary
spraying absolutely no danger
arises from this source, since but
a very minute quantity of the
salts penetrate to the roots.
Sprays sometimes fall from trees
onto grass beneath but experi-
ments have proven that the
quantity is not sufficient to be
injurious to cattle, horses or
sheep. This was demonstrated
for arsenical insecticides. Still
another question arises, viz., the
effect of sprays on such crops as
F.C. 10I.-A barrel pump. (The Dcming orc|ianl CrOt)S where tllC
Co.)
214
Minnesota Plant Diseases.
are eaten by man or used in the manufacture of wine. In the
first place spraying at the time of maturity of the fruit is seldom
if ever necessary. In the case of earlier sprays it has been shown
that no danger exists to man from the eating of such fruits.
It has been estimated that of grapes sprayed with bordeaux in
the usual way an adult may eat "three hundred to five hundred
pounds per day without ill effects of copper." Even in the case
FIG. 105. — A simple type of barrel pump used in the horticultural department of the
Minnesota Agricultural Experiment Station. A return pipe keeps the liquid in the
barrel stirred up. The fluids are strained through the .brass strainer shown above
when poured into the barrel. Photograph by R. S. Macintosh.
of arsenic treatment of apples for insects it has been shown that
"even though all of the poison sprayed upon the apples in
making necessary treatments should remain there undisturbed a
person would be obliged to eat at one meal eight to ten bar-
rels of the fruit in order to consume enough arsenic to cause
any injury." Fruits should not, however, be sprayed with ar-
senic within two weeks of picking. In the case of the use of
corrosive sublimate for seed potatoes, however, the potatoes so
Minnesota Plant Diseases. 215
treated contain sufficient poison to injure cattle, if fed to them,
but in this case the potatoes are steeped in the solution. In
general, therefore, the sprays, when properly applied, do not
deposit upon the plants' sufficient poison to injuriously affect
man or his domestic animals.
SPRAYS.
Bordeaux mixture. "All things considered, it is believed
that the best results will be obtained from the use of what is
known as the fifty-gallon formula of this preparation. This
contains: Water, fifty gallons; copper sulphate, six pounds;
unslacked lime, four pounds. In a barrel or other suitable ves-
sel place twenty-five gallons of water. Weigh out six pounds
of copper sulphate, then tie the same in a piece of coarse
gunny sack, and suspend it just beneath the surface of the
water. By tying the bag to a stick laid across the top of the
barrel no further attention will be required. In another vessel
slack four pounds of lime, using care in order to obtain a
smooth paste, free from grit and small lumps. To accomplish
this it is best to place the lime in an ordinary water-pail and
add only a small quantity of water at first, say a quart, or a
quart and a half. When the lime begins to crack and crumble,
and the water to disappear, add another quart or more, exercis-
ing care that the lime at no time gets too dry. Towards the
last, considerable water will be required, but if added carefully
and slowly, a perfectly smooth paste will be obtained, provided,
of course, the lime is of good quality. When the lime is
slacked, add sufficient water to the paste to bring the whole up
to twenty-five gallons. When the copper sulphate is entirely
dissolved and the lime is cool, pour the lime milk and the cop-
per sulphate solution slowly together into a barrel holding fifty
gallons. The milk of lime should be thoroughly stirred before
pouring. The method described insures good mixing, but to
complete this work the barrel of liquid should receive a final
stirring, for at least three minutes, with a broad wooden paddle."
"It is now necessary to determine whether the mixture is
perfect — that is. if it will be safe to apply to tender foliage. To
accomplish this, two simple tests may be used. First insert
2l6
Minnesota Plant Diseases.
the blade of a penknife in the mixture, allowing it to remain
for at least one minute. If metallic copper forms on the blade,
or, in other words, if the polished surface of the steel assumes
the color of copperplate, the mixture is unsafe and more lime
must be added. If, on the other hand, the blade of the knife
remains unchanged, it is safe to conclude that the mixture is
as perfect as it can be made. As an additional test, however,
some of the mixture may be poured into an old plate or saucer,
and while held between the eyes and the light, the breath should
be gently blown upon the liquid for at least half a minute. If
FIG. 106. — A gear-power f
(Victor Spraying Machine.)
the mixture is properly made, a thin pellicle, looking like oil on
water, will begin to form on the surface of the liquid. If no
pellicle forms more lime should be added." (B. T. Galloway.)
It is very important that good lime be used. Stock solu-
tions of the lime and copper sulphate may be prepared, and may
be kept several weeks without deteriorating. "To make stock
solutions, dissolve fifty pounds of copper sulphate in fifty gal-
lons of water. In another barrel slake fifty pounds of good
stone lime and add enough water to make fifty gallons. These
barrels should be tightly covered to prevent evaporation.
Minnesota Plant Diseases. 217
When it is desired to make a barrel of bordeaux mixture, stir
the stock solution thoroughly, dip six gallons from each barrel
and place in separate tubs. Now dilute each to twenty-five
gallons and pour together as already described. The use of
the lime is to combine with the copper and form a compound
that will not burn the foliage. It also tends to make the fungi-
cide adhere to the plant upon which it is sprayed and later dis-
solves slowly in rain and dew water to form solutions pojsonous
to the fungus. To test the mixture to see if all of the copper
is combined with the lime, add a drop of potassium ferrocyanide
solution. If it changes color upon coming into contact with
the bordeaux mixture more lime should be added ; if it does not
Fie. 107. — A barrel pump in action on farm of I!. Hoyt. Si. Anthony I'ark. Minn.
change color the combination is complete. In using bordeaux
mixture upon peach or plum foliage it is better to use only four
pounds of copper sulphate per barrel instead of six. This is
the most common fungicide in use at the present time, but it
must be remembered that it stains the foliage and the fruit and
should therefore not be used when the fruit is approaching
ripening season." Maryland Kx. Sta. Rep. 13: 67-68. HJOO.
The proportion of lime and copper sulphate varies in differ-
ent formulae of the bordeaux mixture: six pounds of each is
frequently recommended and in weaker solutions six pounds of
2I8 Minnesota Plant Diseases.
lime to four or three pounds of copper sulphate. The tests
• given above should be applied and the need of strong or weak
solutions constantly kept in mind. Bordeaux can be very ad-
vantageously combined with insecticides so that the two appli-
cations can be made by one spraying. (For such combinations
the reader is referred to the Eighth Annual Report of the State
Entomologist of Minnesota, 1903.)
Dry bordeaux. (See under Powders.)
The following formulae are, in general, used only under spe-
cial conditions, for instance, where the spotting of the foliage
or other features of bordeaux are undesirable.
Bordeaux resin mixture.
"Resin 5 pounds.
Potash lime . I pound.
Fish oil i pint.
Water 5 gallons."
[N. Y. (Geneva) Bull. No. 188, 1900.]
Add to bordeaux as directed below.
To prepare a stock resin solution proceed as follows :
"Place the oil and resin in the kettle, heating them until
the resin is dissolved, then remove the kettle from the fire and
allow the mass to cool slightly, after which the solution of lye
is added slowly, the whole being stirred while adding the lye.
After adding the lye the kettle should be again placed over
the fire and the required amount of water added. The whole
should be boiled until the solution will mix with cold water
forming an amber-colored solution. Care should always be
taken to have the resin and oil cool enough so that when the
solution of lye or the water is added the whole mass will not
boil over and catch fire.
"Dilute this stock resin solution with eight parts of water
before adding to the bordeaux mixture, that is, in preparing a
fifty-gallon barrel of the mixture, the copper sulphate and lime
are diluted enough to make forty gallons after which two gal-
lons of stock resin solution are diluted to ten gallons, then
added to the bordeaux." [N. Y. Ex. Sta. (Geneva) Bull. No.
1 88 — 1900.]
This solution exceeds ordinary bordeaux in adhesive prop-
erties and has been highly recommended for asparagus rust.
Minnesota Plant Diseases. 219
Copper sulphate solutions. Copper sulphate is sometimes
used without lime. The following formulae have been recom-
mended :
"(A) Copper sulph'ate I pound.
Water 25 gallons.
For use before the buds open, the above solution is easy to
prepare and to apply. // should not be applied to any plant after
the leaves burst, as it will burn the foliage. Its action is equal
to bordeaux mixture, but it does not seem as lasting.
Weak copper sulphate solutions.
(B) Copper sulphate i pound.
Water 250 gallons.
(C) Copper sulphate i pound.
Water 500 gallons."
"We have been much pleased with the results obtained from
the above weak solutions. Formula ( B) can be used without
danger of injuring the foliage upon all except the most tender
plants, but for use upon peach and other tender plants we pre-
fer to rely upon still weaker solutions as given in formula (C)."
[Mich. Bull. Xo. i_>i : 7—1895.]
The strong solution has also been used as a seed steep (10
to 12 hours) to prevent smut in oats and wheat. It is then
followed by steeping the seed in a solution of lime (one pound
in four to ten gallons of water) for about five minutes, which
protects the grains from any injurious effects by the sulphate.
[Oregon Bull. Xo. 75 — 1903].
Eau celeste (blue water.)
Copper sulphate 2 pounds.
Ammonia i quart.
Water 50 gallons.
Dissolve the copper sulphate in six or eight gallons of wa-
ter, then add the ammonia and dilute to fifty or sixty gallons.
Ammoniacal copper carbonate.
"Copper carbonate 5 w..
Ammonia (26° Beaume) ^ pints.
Water 45 gallons.
Dissolve the copper carbonate in ammonia. This may be
kept any length of time in a glass-stoppered bottle and can be
diluted to the required strength. The solution loses strength
22O
Minnesota Plant Diseases.
on standing." [Mass. Bull. No. 80 — 1902.] Only the clear
blue fluid should be used. This solution is recommended
only when the staining of the foliage and fruits by bordeaux
is objectionable, e. g., in fruits Hearing maturity and on green-
house plants. It has been recom-
mended for fungus parasites as the
powdery mildews which possess a
conspicuous and superficial mycelium.
A solution of copper carbonate (one
pound to forty gallons of water) with-
out ammonia has also been recom-
mended for fruit rots.
Copper acetate.
Copper acetate (diba-
sic acetate) 6 oz.
Water 50 gals.
First make a paste of the copper
acetate, by adding water to it, then
dilute to the required strengh. Use
finely powdered acetate of copper, not
, the crystalline form. [Mass. Bull.
FIG. 108. — A powerful horizontal
type of spray pump for or- No. 8(3 K)O2]. May be USed aS 3.
chard spraying. (Goulds i ,-, r .1 i
Mnfg Co.) substitute for the copper carbonate
mixtures.
Saccharate of copper.
"Copper sulphate 4 pounds.
Lime 4 pounds.
Molasses 4 pints.
Water 25 gallons.
Slake four pounds of lime and dilute the same with water.
Dissolve four pints of molasses in a gallon of water and mix
with the lime. Stir thoroughly and let it stand a few hours.
Dissolve four pounds copper sulphate in ten gallons of water
and pour into it the lime-molasses solution while stirring brisk-
ly. Allow the mixture to settle. Draw off the clear greenish
solution for use." [Mass. Bull. No. 80 — 1902.}
Potassium sulphide.
"Water 10 gallons.
Potassium sulphide 3 oz."
[Mass. Bull. No. 80—1902.]
Minnesota Plant Diseases. 221
Dissolve the potassium sulphide in a few quarts of hot water
and add enough cold water to complete the solution. This has
been recommended for checking powdery mildews and rust of
chrysanthemums and in general for greenhouse use.
Potassium permanganate.
Potassium permanganate i part.
Soap 2 parts.
Water 100 parts.
Recommended in France for black rot and mildew of grape,
etc. [Mass. Bull. No. 80 — 1902.] On account of expense can
be profitably used only on greenhouse or garden plants. It
has been recommended for rust diseases of hollyhocks and car-
nations.
Iron sulphate and sulphuric acid.
Water (hot) 100 parts.
Iron sulphate As much as will dis-
solve.
Sulphuric acid I pint.
Prepare the solution just before using. Add the acid to the
crystals and then pour on the water. Valuable for treatment
of dormant grapevines affected with anthracnose, applications
being made with sponge or brush. [Mass. Bull. No. 80 — 1902.]
This solution should be made in wooden vessels. It has been
recommended for disinfection of bark, ground, etc.. where dis-
ease has previously existed. The solution will destroy the foliage
so it must be used in late fall or early spring, or applied only
to tree trunks.
STEEPS.
Formalin. (A) Kor oat smut and stinking smut of wheat.
Add one-half pound of formalin to thirty gallons of water
and immerse the seed grain for two hours, then spread out and
dry.
Or, sprinkle the grain with the formalin solution until thor-
oughly wet, shoveling over rapidly to distribute the moisture
evenly, then place in a pile (covered with sacking) for two hours
and finally spread out and dry as in the first method.
222
Minnesota Plant Diseases.
Minnesota Plant Diseases. 223
Grain swollen in this manner requires the drill to be set
somewhat wider to permit the usual amount of seed to be sown
per acre. [Indiana Ex. Sta. Bull. 77 — 1899.]
This has been found a very successful, safe a.nd cheap
process for combating smut. Xot all smuts are, however, pre-
vented by this treatment. Corn smut and loose smut of wheat
are not affected by it. It is undoubtedly, however, effective
against the smuts mentioned above. This method has advan-
tages over the hot-water method in the smaller degree of skill
required in handling. The seed can be left in the solution an
hour or more over the specified time without much injury, but
the prescribed two hours are usually sufficient to kill the spores
of the fungus. Oats require more of the solution than wheat
since they do not give access through the hulls so readily. "If
seed is kept long after treatment care must be taken that it
does not heat, otherwise no harm or disadvantage will result.
Professor Bolley, from some preliminary trials, estimates that
when sown soon after treatment it will be necessary to set the
drill for three and a half bushels of oats per acre if the equivalent
of two and one-haW bushels of the dry seed is desired, and with
wheat must be set for one bushel and eighteen quarts per acre,
if desired to sow one bushel and four quarts." [Indiana Ex.
Sta. Bull. 77—1899.]
The same formalin solution can be used three or four times
but the seed must be left longer in each successive treatment
since the solution weakens. Formalin is not a violent poison,
so that the handling of this solution or that for the potato scab
is not at all dangerous for the operator. Special machines for
thorough immersion and rapid handling with the formalin solu-
tion have recently been placed upon the market.
(B) For potato scab.
''The formalin treatment of seed potatoes practically frees
the crop from scab, with slight expense and trouble.
"Add one-half pound of formalin to 1 5 gallons of water and
immerse the seed tubers for not less than two hours. If the
potatoes are not much sprouted a longer wetting is advanta-
geous. After removing from the solution, cut and plant as
usual." [Ind. Ex. Sta. Bull. 77—1899.]
224
Minnesota Plant Diseases.
Minnesota Plant Diseases.
225
Hot water method for smuts (Jensens.)
"Provide two large vessels, preferably holding at least twen-
ty gallons. Two wash kettles, soap kettles, wash boilers, tubs,
or even barrels, will do. One of the vessels should contain
warm water, say at 110° to 120° F., and the other scalding
water, at 132° to 133° F. The first is for the purpose of warm-
ing the seed preparatory to dipping it into the second. Unless
this precaution is taken it will be difficult to keep the water in
the second vessel at the proper temperature. A pail of cold
water should be at hand, and it is also necessary to have a
kettle filled with boiling water from which to add from time to
time to keep the temperature right. Where kettles are used, a
very small fire should be kept under the kettle of scalding
water. The seed which is to be treated must be placed, half
a bushel or more at a time, in a closed vessel that will allow
free entrance and exit of water on all sides. For this purpose
there can be used a bushel basket made of heavy wire inside
of which is spread wire netting, say twelve meshes to the inch ;
or an iron frame can be made at a trifling cost, over which the
•wire netting can be stretched. This will allow the water to
pass freely and yet prevent the passage of the seed. A sack
made of loosely woven material, as gunny sack, can be used
instead of the wire basket. A perforated tin vessel is in some
respects preferable to any of the above. In treating stinking
smut of wheat, the grain should first be thrown into a vessel
filled with cold water; then, after stirring well, skim off the
smutted grains that float on the top, and put the grain into the
basket or other vessel for treatment with hot water. This skim-
ming is entirely unnecessary with other grains and even with
wheat, when only affected by the loose smut. \o\v dip the
basket of seed in the first vessel containing water at 110° to
120° F. ; after a moment lift it. and when the water has for the
most part escaped, plunge it into the water again, repeating
the operation several times. The object of the lifting and
plunging, to which should be added a rotary motion, is to bring
every grain in contact with the hot water. Less than a minute
is required for this preparatory treatment, after which plunge
the basket of seed into the second vessel, containing water at
I3_>c to 133° F. If the thermometer indicates that the teni-
:
226 Minnesota Plant Diseases.
perature of the water is falling, pour in hot water from kettle
of boiling water until the right degree is maintained. If
the temperature should rise higher than 133°, add a little cold
water. In all cases the water should be well stirred whenever
any of a different temperature is added. The basket of seed
should very shortly after its immersion be lifted and drained,
and then plunged and agitated in the manner described above.
This operation should be repeated six or eight times during the
immersion, which should be continued ten minutes. In this
way every portion of the seed will be subjected to the action of
the scalding water.
"After removing the grain from the scalding water, spread
on a clean floor or piece of canvas to dry. The layer of grain
should not be over three inches thick.
"The important precautions to be taken are as follows: (i)
Maintain the proper temperature of the water (132° to 133° F.),
in no case allowing it to rise higher than 135° F. ; (2) see that
the volume of scalding water is much greater (at least six or
eight times) than that of the seed treated at any one time; (3)
never fill the basket or sack containing the seed entirely full,
but always leave room for the grain to move about freely; (4)
leave the seed in the second vessel of water ten minutes."
[Yearbook U. S. Dept. Ag., 1894.]
This method is known to be very effective if carefully fol-
lowed in all details. If due care and precaution are not taken,
not only will no good result but the effect of the treatment may
even be harmful. In respect to the care necessary in handling,
the formalin method is of greater advantage since less skill in
the operation is required.
Corrosive sublimate.
Corrosive sublimate 2 oz.
Water 15 gallons.
Dissolve the corrosive sublimate in two gallons of hot water,
then dilute to fifteen gallons, allowing the same to stand five or
six hours, during which time thoroughly agitate the solution
several times. Place the seed potatoes in a sack and immerse
in the solution for one and a half hours. Corrosive sublimate is
very poisonous, consequently care should be taken in handling it,
and the treated potatoes should not be fed to stock. The
Minnesota Plant Diseases. 227
solution should not be made in metallic vessels. [Mass. Bull.
No. 80 — 1902.] This steep is very effectively used against
potato scab.
POWDERS.
Sulphur. "In the dry powdered state this is known as flow-
ers of sulphur. It may be sprinkled over plants in the dry
state or it may be converted into fumes by heating. Care
should be taken not to heat it to the burning point as it would
thereby form a compound that would destroy green plants as
well as fungi. It is usually sufficient to place it upon the hot
pipes of the greenhouse." This has been recommended for
powdery mildews and similar superficial parasites.
Sulphur and lime. Mix the flowers of sulphur with equal
parts of powdered lime. This may be used in the same manner
as the pure sulphur.
Dry bordeaux. "The new bordeaux powder can be made
by any fruit grower or gardener with very little trouble, and at
a very nominal expense. It can be made during the winter and
stored in a dry place, where it will keep indefinitely.
"In order to make this new bordeaux powder one should
first make a large quantity of air-slacked lime. This can be
readily done by taking about seventy-five pounds of good
quicklime, pounding up the lumps and spreading it over a large
area, thus allowing it to air-slack readily. When completely
air-slacked, this should then be sifted through a fine sieve; a
loo-mesh sieve is the proper one to use. One can break up the
lumps in this sieve so as to utilize the bulk of the air-slacked
lime by rubbing it through the sieve by means of a block of
wood. As this is a stock dust, to be used as a carrier in the
place of water, it would be just as well to make up a much
larger quantity, so as to have it on hand at a minute's notice.
After it is thoroughly air-slacked and sifted, the powder should
be kept in a dry place, such as the hay loft or the garret of the
house.
"Dissolve four pounds of copper sulphate in two and one-
half gallons of water by placing the copper sulphate in a coarse
228
Minnesota Plant Diseases.
FIG. 111. — Various fixings, tools and appliances for spraying anparatus. 1. Double Ver-
morel nozzle (showing side). 2. Double Vermorel nozzle (showing end). 3. Double
Vermorel nozzle, on bamboo extension. 4. Shut-off on bamboo. 5. Inner and outer
views of reducing caps for Vermorels. 6. Vermorel nozzle attached to a brass ex-
tension rod. 7. A McGowen nozzle. S. Gem nozzle. 9 and 10. Calla nozzle. 11.
Fuller nozzle. 12. Pliers used for putting in place brass hose coupler No. 13. 14.
Iron couplers to which the hose is attached when a coupling is desired. 15. A pair of
pipe tongs, which are very serviceable for tightening hose couplings. 16. Two
reducers, used for attaching either % or % inch nozzle to hose or rod. 17. Two
views of hose clamp. 18. Plug used when one attachment only of hose to pump is
desired. After J. C. Blair.
Minnesota Plant Diseases. 229
bag and suspending it just below the surface of the water until
dissolved. This is to be kept in a vessel by itself.
"Slack four pounds of good quicklime by sprinkling over it
slowly two and one-half gallons of water in such a manner as
to slack the lime to a fine powder and give as a result a milk of
lime solution. This must now stand until cooled before
using it.
"In a large shallow box one should then place sixty pounds
of the sifted, air-slacked lime which has already been made as a
stock carrier. In another vessel pour the milk of lime and the
copper sulphate solution, both at the same time, and stir thor-
oughly until the whole is well mixed. Then turn this into a
double flour sack and squeeze out most of the water.
"Empty this blue material just made into the sixty pounds of
air-slacked lime, and at once work it up thoroughly with a hoe.
If after this has been thoroughly mixed the material is too wet
more of the lime dust should be added. This material must
then immediately be rubbed through a comparatively coarse
sieve while it is still somewhat damp. It should then be thor-
oughly mixed again by means of a stick and spread out in a dry
place and allowed to dry. \Yhen this is perfectly dry it must be
sifted through a fine sieve of a hundred meshes, in which case all
lumps can be ground by means of a stick rubbed over the sieve.
The resultant powder should have a uniformly blue color. In
case it looks streaked or mottled, it should be stirred until all of
the mixture is of a uniformly blue color. This powder, now
completed, will keep indefinitely in a dry place, and contains
copper sulphate in the same chemical combination as is found
in the liquid bordeaux mixture. There is a large excess of
powdered lime in this which is not in chemical combination
with copper, but which is there simply as a carrying agent."
[Country Gentleman. Aug. 13. 1903.]
SPRAYING APPARATUS.
The selection of spraying apparatus is a subject upon which
no extensive advice can be offered here but which is best left
entirely to the ingenuity of the plant grower. A few general
principles as laid down by those who have paid considerable at-
230 Minnesota Plant Diseases.
tention to this subject together with a few illustra-
tions of common types of apparatus now in use will
suffice. They are intended merely for suggestions
which will lead to more careful study of the subject
by those seriously interested in this matter and as a
general description of modern methods of applying
fungicides.
There are in general three kinds of pumps in com-
mon use. Bucket pumps are made for use with small
amounts of the fluid in ordinary buckets. They are
intended for small garden use and around the house
but are not convenient for extensive sprayings.
Knapsack pumps are suited for more extensive work
FIG. 112. A and are used for low shrubs or potatoes or such crops
convenient
nozzle for not easily accessible to barrel-pump apparatus. The
spr a y i n g r
the under knapsack apparatus usually carries about three to
(Demfn'gCo)five gallons of fluid and is strapped on the back of
>the operator in knapsack fashion. Each is furnished .
with a small pump and the operator works both the
pump and the spray.
The barrel pumps are larger pumps intended for
attachment to barrels and should be strong enough
for spraying even fair-sized trees. They possess more
general usefulness than either the knapsack or bucket
pumps on account of the greater amount of fluid
carried and the capacity for work. The barrel is
best mounted on a farm wagon or truck and for or-
chards a platform for the operator is of great as-
sistance. The following have been given by Mr. H.
O. Gould of the Maryland Experiment Station as
the points of greatest importance in a good pump.
"(i) The air-chamber should be sufficiently large
to ensure a steady spray and be so placed on the
pump that the latter will not be rendered top heavy
'thereby, or unduly cumbersome.
F Nozzle .for (2) Some means of keeping spraying mixture
plants in thoroughly stirred is essential, but it is not necessary
rows. J
(Goulds Mfg. that this be attached to the pump.
Co.)
Minnesota Plant Diseases.
231
FIG. 114.— An effective nozzle
sprays. (Gouid« Mnfg. Co.)
mist-like
(3) The working parts should all be of brass and be so ar-
ranged that they can be examined without undue difficulty.
(4) The pump when mounted should not extend above the
barrel more than is necessary.
(5) It is desirable to have the device for attaching to the
barrel so arranged that the pump can readily be mounted or re-
moved from the barrel.
(6) The different portions of the pump should be so con-
structed that they can be
readily taken apart, espe-
cially those portions which
enclose the valves. tmamffl •
(7) All points for attach-
ment of the hose should be
. , , .
cut with threads of stand-
ard size." (Maryland Ann. Rep. 13. 1899-1900.)
Horizontal pumps are also used for very extensive work in
spraying. These pumps are in general more powerful than
the ordinary barrel pump and can accomplish more work. They
are usually of sufficient strength
to operate several lines of hose.
Various accessories are not
only desirable but almost neces-
sary to the successful use of
spraying apparatus. A number
of such accessories together with
different kinds of nozzles are
given in the accompanying fig-
«=r T)X^
^^COM.^^ Special spraying apparatus
has been devised for various pur-
poses. Asparagus spraying has
been carried out successfully
against rust by a very complicated machine which will spray
several rows of asparagus at one time. (See X. \ . Ag. Ex. Sta.
Bulletin 188.)
In barrel and all smaller pumps the power is hand power,
in the larger machines wheel gears and chains transform the
power from the wagon motion, while in still other cases, espe-
M. CAT
I'ic. 115. — I'owdcr gun with attachments.
(Lessen.)
232 Minnesota Plant Diseases.
cially for spraying high shade trees, stationary engines have
been used.
In the application of powders, apparatus is also necessary.
Blow guns, pepper shakers and powder guns of various kinds
are in use. Figure 115 shows a powder gun in very common
use, together with various accessories and attachments.
Machines have recently been devised for the treatment of
oats and other grains against smuts. Such machines aim to
completely immerse the grains in the solution and to keep them
agitated so that all parts of the grain surface are reached by
the fungicide.
The above pretends to be only a general and elementary
exposition of the general types of machinery in use at the
present time. For further information and detail the reader is
referred to the Minnesota State Entomologist's Report for
1904 and to other Agricultural Experiment Station literature.
PART II.— SPECIAL.
Chapter XVI.
Diseases of Timber and Shade Trees — Timber Rots.
Jff
Wound parasites and timber rots. Features of these sub-
jects have been treated of in former chapters and little remains
to be said here. These fungi include chiefly members of the
palisade basidium-bearing groups, as pore and gill fungi. They
are capable of attacking woody tissues, feeding upon them,
and converting them into the crumbling, friable mass, known as
punk. Many of these forms are entirely saprophytic and occur
only on fallen logs, cut timbers or standing stumps and are sim-
ply timber rots. Others, however, are half saprophytes and
are capable of attacking the living tissues of the stem or root.
Such usually gain entrance through the bark, by means of
wounds in the latter and. after a more or less short saprophytic
life, penetrate outward to the living parts of the stem or roots
and there attack the growing zone and inner bark. The ulti-
mate result of this parasitic life is usually the death of the tree,
after which the fungus continues to live on in a truly sapro-
phytic manner. To the living forest trees, therefore, this
class of fungi is a constant menace, and to the fallen trunks
and broken trees almost a certain evil. The danger does not
even stop here, for many of these forms attack stored timbers,
and lumber, especially, if the latter is improperly kept. They
even invade the standing and foundation timbers of houses.
Some of the most serious problems in the construction of
wooden houses lie in the prevention of subsequent rotting.
The so-called dry rots are particularly harmful in this respect
and are frequently found in their fruiting stages in damp cellars.
Thorough seasoning is the only efficient remedy against such
diseases. Application of creosote to the ends of joists and other
timbers has also been recommended. Large timbers are often
bored through lengthwise and ventilating holes bored at both
ends at right angles to the long holes to allow of circulation of
2^6
Minnesota Plant Diseases.
Minnesota Plant Diseases. 237
air to prevent dry rot. Other accessory cautions are also ad-
visable and will be mentioned in the discussion of the true dry
rot of timbers. Timbers in mines, tunnels and railroad ties suf-
fer especially severe depreciations from fungi of this class.
Prevention. As to the prevention of the ravages of wound
parasites of this group, an avoidance of wounds is first of all
advisable. Of course this is impossible in forest culture but in
shade trees it is practicable. \Yhere trees are pruned the cut
surfaces should be carefully covered with creosote or some simi-
lar substance to prevent the entrance of spores and their germi-
nation. Fall and winter are preferable for this pruning since
the absorption of the creosote is more complete at that time
than in the spring or summer and the exclusion of the fungus
threads is therefore more complete. In the second place the
fruiting bodies of all disease-causing fungi should be removed
as soon as discovered and burned immediately to destroy all of
the spores. This is a prevention against the further spread of
the disease. Badly infected trees should in most cases also be
removed and thoroughly seasoned or used for firewood.
Where the fungus is a root parasite traveling from root to root,
as is known to be the case in a few forms, a trench is dug
around the infected trees and all roots severed so as to prevent
the spread to other trees. The isolated trees are carefully
watched and the fruiting bodies destroyed as soon as they ap-
pear. Many valuable shade trees are annually lost as a direct
or indirect result of timber diseases and such a loss can be almost
entirely averted by careful attention as indicated above.
In forest culture dead trees should be immediatly cut and
harvested. This saves the available timber and gives it no chance
for deterioration which is sure to set in if the timber is left
standing. Such treatment also prevents the formation of fun-
gus fruiting bodies, which would spread disease to standing
trees. There is an age at which trees may be said to become
mature and at this age the natural forces of recuperation just
balance the external destructive influences. This age varies in
different trees. At this time the tree should be harvested, for
in every succeeding year the chances of destruction by fungus
pests increase and the tree loses in value.
238 Minnesota Plant Diseases.
The subject of timber rots has in recent years been made the
object of special study by agents of the U. S. Department of
Agriculture. The following abbreviated account is base'd
largely on these reports. The importance of timber rots can be
realized in the consideration of the ties, fence posts, telegraph
and telephone poles, mine and ship timbers, paving blocks and
bridge timber which are all subject to conditions extremely fa-
vorable for decay, in addition to all other building timbers
which, though not under such unfavorable conditions, may still
undergo serious rotting. Efforts have been made at different
times for more than a hundred years to lengthen the "life" of
such timbers by various kinds of treatments. From the nature
of the case, long periods of time are necessary for carrying on
experiments in this line and a great deal of progress has not
yet been made. A number of satisfactory methods, however,
are known at present, but on account of the cheapness of timber
in this country have not until recently been introduced and are
not even yet extensively employed.
In the first place seasoning of timber is an important factor.
Green timber contains more moisture, which is directly favora-
ble to the fungus growth and subsequent decay of the wood.
It must also be noted that different kinds of timber require
different lengths of time for seasoning. Beyond a certain point
seasoning does no good but may work harm. Even wood of
the same kind from different localities may require different
treatments. Seasoning, therefore, is not only an important fea-
ture but is also one which is not altogether simple. Its value is
beyond doubt, as has been shown by numerous experimental
results. Another feature which needs mention at this point is
the storage of the timbers. Close piling often results in closed
moisture-laden chambers, which easily encourage the growth
of fungi and the close contact of the wood admits of the rapid
spread of the decay from piece to piece. The drainage of
water is also seriously interfered with. Timbers, therefore,
should be piled so as to admit of as complete aeration as possi-
ble, so that each piece shall have the opportunity of thorough
drying out in proper season. The clangers of the storage of
contaminated timbers with sound timber have already been
mentioned.
Minnesota Plant Diseases. 239
• The various methods of treatment of timber to prolong its
usefulness consist entirely of impregnation processes. By
these, chemical compounds in solution or emulsion are forced
into the timbers or boiled in, so that they permeate the whole
timber or at least the surface portions. These substances must
be fungicides and antiseptic as well. They must prevent the
germination or growth of the fungi or bacteria and thus pre-
vent rotting. It is not always necessary that they penetrate to
the center of the timber, since the surface portions, if properly
impregnated, will keep out all decay-forming organisms. Of
course such a substance which would penetrate to the very cen-
ter would be of great advantage in the resistance towards the
leaching-out process. It must be kept in mind that many com-
mon fungicides are soluble in water and hence would leach out
under heavy rains. This is an important factor in the impreg-
nation of timber. A substance must also be selected which can
be injected with ease into woods. In the case of soluble salts,
the easier the injection the easier the leaching out. However,
in view of the cost this is an important factor. It will not be
many years when the price of timber will be such as to compel
the adoption of some methods of treatment for many timbers
and such is already the condition in European countries. It is
rapidly becoming imperative in certain classes of timber at
present and particularly those mentioned above as most liable
to decay, e. g.. ties, poles, etc. At present, however, the cost
of impregnation is one of the first factors for consideration and
often of paramount interest.
The following substances have been used with considera-
ble success. Creosote is sometimes forced hot into timbers
placed in tanks from which the air has largely been re-
moved. Hy this method a j>enetration of several inches may
be effected. This process has been described as the most
effective known, though on account of the considerable ex-
pense of the creosote is not generally applicable. A cheaper
but less effective method is that of the use of xinc chloride.
This has been more extensively used. Another process is
known as the Hasselman treatment. In this the timbers are
boiled in a solution of the sulphates of copper, iron and alu-
minum and a small amount of kainit for several hours. By this
240 Minnesota Plant Diseases.
means the wood is thoroughly impregnated and the salts de-
posited, not only in the cavities, as with most other substances,
but also in the walls of the cells. This process has not yet been
thoroughly tested but has apparently many excellent features
which may perhaps, in the future, make it a valuable treatment.
Other processes, either new or imperfectly known, may merely
be mentioned here. In one electricity is utilized and is passed
through the timber in a solution of magnesium sulphate. Two
things are claimed for this treatment: cheapness and a com-
plete distribution of the impregnating salt. Another method is
directed toward a saving of expense in the pure creosote meth-
od by using an emulsion of the oil in resin and a strong solution
of soda lye. This has again been modified by the substitution
of formalin in the place of the lye.
The following list of timber rots and timber-tree diseases is
by no means complete for the wound parasites and timber rots
of Minnesota ; but it includes many common forms and above
all is intended to give the reader an idea of the kind of organ-
isms responsible for the rots of timbers and the deaths of timber
trees. Other related forms will be readily recognized by their
general similarities with these forms. The general preventive
methods have been mentioned above. Only in special cases
are additional measures given.
Stereum wood rot (Stereum species). On the dead trunks of
many of our broad-leaved trees, can often be found numerous
shelf-like fungi projecting in the manner of the pored shelves.
In some species the upper surface is rough, hairy or silky, and
the under surface is smooth. The latter does not contain pores
as in the true pore-fungi. The shelves are usually of a leathery
consistency and in dry weather often curl up, expanding again
in wet weather. The spores are borne on typical basidia in pal-
isades which cover the under surface. In some cases, instead
of shelf-like bodies, prostrate, crust-like objects are formed
which are sometimes turned back at the margins. In these
cases the spores are found on the upper surface of the prostrate
body. There are several species of this genus which are de-
structive parasites of our forest trees. Oaks are very often at-
tacked. The fungus usually gains entrance through wounds
and grows outward from that point. Fig. 117 shows an oak
Minnesota Plant Diseases.
241
tree attacked by a Stereum. The progress of the mycelium up-
ward in the stem is indicated by the size of the fruiting bodies,
which are largest
I'ic. 117. — A Stereum wound parasite (a species of Stereum).
The fungus obtained entrance in the wound at the base
of the tree (an oak), and. as shown by the fungus fruit-
ing bodies, is gradually progressing unward. This tree
died about a year after the photograph was taken.
Original.
HI
hood of the
wound and dinr'n-
ish gradually
away from the
wound.
Oak attacked
by Stereum hir-
sutum Fr. is
known as white-
piped or yellow-
piped oak. The
\v o o d becomes
brownish at first.
Longitudinal
white or yellow
streaks then arise
where, under the
influence of the
fungus mycelium,
the wood loses
its woody charac-
ter. The whole
block then grad-
ually undergoes
further decompo-
sition. In a cross
section of the
w o o d these
.streaks are seen
as whitish specks
which have given
the name of "fly
\V O O (1" tO tllC
\y O O d SO a t-
242
Minnesota Plant Diseases.
Partridge wood rot (Stereum frustulosum Fr.). This is a
very characteristic rot of woods and is not uncommon in Min-
nesota. It attacks chiefly oak and may live either as a wound
parasite or in a saprophytic manner on felled timber. The
fruiting bodies are hard and crust-like, light-brown to greyish
FIG. 118.— Partridge wood rot. 1.
The fungus (Stereum frus-
tulosum), fruiting bodies on
decaying wood. 2. The cut
surface of the decaying wood
showing the characteristic
holes caused by the action
of the fungus mycelium. At
the edge are seen a few fruit-
ing bodies in section. 3. A
thin strip of decayed wood
showing holes as in 2. 4. Decayed wood seen from the end of the block. Original.
masses, and are found in dense clusters. They are usually
polygonal, often five-sided, and grow from year to year, so that
a section through the fruiting body exhibits a layered structure.
On the upper side of the fruiting body, the spores are borne on
Minnesota Plant Diseases. 243
basidia in a palisade layer similar to that of the Stereum wood
rot. The fruiting bodies are very easily recognized, but the rot-
ting wood is even more characteristic. In the early stages of
rot there are seen whitish, circular or oval patches in the wood,
which are more or less permeated with the mycelium of the fun-
gus. In these patches the wood is quickly disintegrated while
the wood dividing the patches remains very hard. In later
stages the whitish patches become hollow by the complete de-
struction of the wood and a longitudinal section of such a timber
would show a net-like arrangement of wood enclosing the de-
cayed patches. Around these holes can be seen a lining of
the whitish mycelium. Finally the walls between the holes also
disintegrate and the entire timber crumbles.
The smothering fungus of seedlings (Thclcphora tcrrestris
Elirh. and T. laciniatuiii Pcrs.). One often finds, particularly in
damp situations at the bases of young saplings of hard maples
and other trees, blackish, soft, leathery masses forming an
irregular ring around the base of the stem just above the
ground. At first sight they may seem shapeless and they are
not at all conspicuous objects. A close examination shows
them to be composed of numerous shelves, like the shelf fungi,
and usually hemispherical in shape, jutting out from the main
mass of the fungus. (T. terrestris.) Another species, Thele-
phora laciniatum. forms masses with irregular projections
which vary from club- or tooth-shaped to fan-like in form and
are usually combined into a rosette. If one examines the under
surface of these shelves or clubs with a microscope one finds
there numerous dark-colored spores with very rough outer
walls. These spores are produced in fours on basidia which
occur in palisades in the way usual for the palisade fungi.
These fungi are not truly parasitic but derive their nourish-
ment from matter in the soil. They have nevertheless been
reported as dangerous to forest culture on account of their be-
havior toward seedlings. The fruiting body starts as a shape-
less mass lying on the ground and when it conies in contact
with any upright support it grows upward a short distance and
then produces the projections of the mature form described
above. If this support happens to be a seedling the latter may
become completely engulfed and destroyed. As this fungus is
2 44 Minnesota Plant Diseases.
not very abundant in Minnesota it seems doubtful that any con-
siderable damage results from it. The fungus fruiting bodies
should be removed and destroyed. (Fig. 82.)
Club fungus rots (Species of Clavaria). There are many
species of club fungi which occur on woods of various kinds in
Minnesota. These fungi, however, seem to prefer those logs
already in advanced stages of decay, or they may be found on
the ground where wood debris is abundant. They less fre-
quently occur on solid logs or timbers. They are not, there-
fore, usually counted in with the dangerous timber rots of our
state. (Figs. 10, 81, 83.)
The coral fungus rot (Hydnmn coralloides Scop.). This fun-
gus is very abundant in the hard woods of our state. The fruit-
ing bodies occur on the under sides of fallen logs, in hollow
logs or less frequently on standing trees. They vary greatly in
size. The smallest are seldom smaller than a man's hand, while
the largest would fill an ordinary water pail. The fruiting body
is pure white or very slightly tinged with yellow and is very
much branched. From the branches arise small teeth about
one-half inch in length, which are found chiefly on the under
side of the branches and hang down. The whole mass is not
unlike a delicate cluster of coral growths. These fruiting
bodies are higly prized by mushroom eaters as choice delicacies.
The mycelium, of course, lives in the wood where it causes de-
cay of the wood tissues. The spore-bearing basidia line the
whole surface of the teeth and the spores are white. The fun-
gus is not important as a timber rot.
Closely related to the coral fungus are t\vo other toothed
fungi which are also found on wood under conditions similar to
those of the coral fungus.
The bear's-head fungus differs chiefly in the possession of
larger teeth and coarser texture.
The medusa-head fungus produces fruiting bodies more yel-
lowish in color and the teeth are very much longer, often attain-
ing a length of several inches. The teeth are usually densely
packed together and the whole fruiting body presents a more
nearly solid mass than either of the preceding forms. It is
found on forest logs and stumps and specimens have been re-
ported on building timbers in cellars. (Figs. 81, 84, 119.)
Minnesota Plant Diseases.
245
Dry rot or house fungus rot [Merulius lacrymans (Wulf.}
S churn.']. This fungus is one of the most destructive of timber
rots both on ac-
.^0^. ^^^M^A
count of its action
and its frequent oc-
currence. It is one
of the simplest of
the pore fungi, hav-
ing only shallow
pores on a flat pros-
trate fruiting body.
It may almost be
termed a domesti-
cated fungus for it
appears almost ex-
clusively in the
neighborhood
of dwellings and is
very seldom seen
native in the woods.
It has therefore been
called by the Ger-
m a n s "h a u s-
schwamm" or house
fungus. It is also
popularly known as
the weeping fungus.
It attacks chiefly the
soft woods of needle
trees but may also
destroy oak and
other hard woods. This fungus is a typical saprophyte and de-
rives its nourishment from the wood which it destroys. When
the mycelium has permeated a wood tissue it leaves the latter
as a spongy mass of brownish material, a common condition in
timbers which are kept in moist places. Such decayed wood
absorbs water readily and retains it so that the wood holds its
original size and shape, but when dry the decayed portions
shrink, causing cracks which form at right angles to each other,
Fie. 120.— The fruiting body of the dry rot fungus
( Merulius lacrymans). The under surface covered
with shallow |>ores is shown in the photograph. Much
reduced. Original.
246
Minnesota Plant Diseases.
Minnesota Plant Diseases. 247
commonly forming squares. Wood so affected is very friable
and can be easily rubbed to a powder. Water passes easily
through such decayed parts and further aids in the invasion of
new portions and of other timbers in contact with it. In moist,
dingy cellars, where the atmosphere is always more or less
damp, and the timbers never have a chance to thoroughly dry
out, the fungus develops a vigorous, superficial mycelium,
which appears at first as a fine, thin, woolly coat of pure white
threads. This soon grows into a dense sheet of white felt
which can easily be peeled from the wood. In this sheet there
develop later thick strands composed of threads which are
packed with nutrient material. These strands are of great im-
portance as they often grow to great lengths and may carry in-
fection to timbers distantly located. Walls of stone or earth
offer no obstacles to such progress, since the fungus strands
are provided with a great amount of nutrient material. When
they finally again enter the wood they establish a mycelium
which supports itself upon the wood tissues.
The fungus is also remarkable on account of its ability to
attack almost perfectly dry wood: It can absorb sufficient
moisture from the air to keep it from drying up and may thus
slowly destroy the wood. The excess of moisture absorbed by
wood attacked by this mycelium often condenses out into drops
on the infected parts and has given rise to the common name of
"weeping pore fungus."
The fruiting bodies are flat and prostrate and never form
shelves. At first they are white, then reddish and later turn
dark yellow brown on account of the numerous spores pro-
duced on the surface. Wrinkles and folds form on the surface
of the fruiting body and shallow pores are thus produced. The
spores are dark yellow-brown and very small. It has been esti-
mated that 65.000 millions could be crowded into a space of
one cubic inch. The fruiting bodies are often five or six inches
in diameter. In one end of the spore wall is a thin place
through which the germ tube emerges when germination takes
place. This pore is closed with a small plug and it has been
claimed that this plug is removed only in the presence of alka-
line material, as wood ashes, coal dust and humus materials.
Afternic removal of the plug the germination can proceed as
248
Minnesota Plant Diseases.
FIG. 121. — The dry-rot fungus (Mcrulius lacrymans). Shows the surface of a pine
board which has been attacked by the dry-rot mycelium; it is not yet, however, com-
pletely converted to punk. The felted mycelium has been partially removed, show-
ing the accentuated grain of the attacked portions. The mycelium has penetrated!
some distance beyond the white mycelial felt. Original.
Minnesota Plant Diseases.
249
under conditions normal to other spores. It has therefore been
recommended that such substances as furnish alkaline materials
be not brought unnecessarily into contact with structural tim-
bers. The fruiting body has an agreeable odor when young
but when old and in the stages of decay emits foul odors and in-
jurious gases and an excessive amount of water may be exuded
by the diseased timbers.
Fie. 122. — The dry-rot fungus (Mcrulms lacrymans). l.uu i decay stages than that shown
in Fig. 121. From the board (hown on the left, the mycrlial frit has been removed
and the checked portion of the board i* seen. This appearance is caused by the
drawing of the tissues in drying after the decay has been well started. The removed
mycrlial felt is shown in Fig. 6. The board shown on the right is in a still further
stage of decay and the wood under the mycelium is reduced to friable punk. Original.
As has already been stated, infection of timbers does not
usually take place in the forest. It may occur where old timber
is stored with fresh lumber or where old timber is used in the
building of a new house. \Yorkmen may carry spores on their
clothing or tools and thus cause an infection of timbers. The
250 Minnesota Plant Diseases,
eyils of green lumber are here apparent, for infection takes
place more readily than in well-seasoned material.
The preventive measures are indicated in the above ac-
count. The fruiting bodies should be destroyed as soon as they
appear. Well-seasoned wood is preferable to green wood.
The use of partially diseased wood is dangerous on account of
the probable spread of the disease to other timbers as well as
to the healthy parts of the diseased timber. Moist deadening
material of all kinds should be avoided as also such substances
which could create alkaline solutions in the presence of mois-
ture. Ventilation of large timbers is sometimes effected by
boring longitudinal holes through the center and transverse
connecting holes near the ends. In general, the formation of
stagnant, moisture-holding cavities should be avoided wherever
possible. (See also Fig. 5.)
The false tinder-fungus rot[Foines igniarius (L.) Fr.~\. This
is one of the true pore fungi and is a dangerous and common
timber parasite. The plant gains entrance to the living stem
through the bark, usually at a wound or other opening which
may have been caused by such agencies as wind, hail, squirrels,
birds or boring insects. When the fungus has gained entrance
it attacks the growing portion of the stem, which is situated
just beneath the bark and it may establish here an extensive
mycelium. From this mycelium are later produced the shelf-
like fruiting bodies. The latter are usually half globular when
young, becoming hoof-shaped when older. The lower surface
is lined with a layer of pores which are white when young, be-
coming dark yellow-brown with age. New layers are added in
successive seasons. The upper surface of the fruiting body has
usually a very hard coat. Internally it consists of a softer
brownish felt-like material and numerous long tubes, which end
at the lower surface. The hard skin of the upper surface of the
fruiting body is usually cracked in older specimens. The wood
attacked by this mycelium undergoes a white rot. It first be-
comes dark in color, then as the process of disintegration con-
tinues it becomes yellowish to white. The fungus threads at-
tack the walls of the wood elements destroying their woody
characters and leaving them softer and lighter in color. The
chief danger of this fungus lies in the destructive parasitic habit
Minnesota Plant Diseases. 251
for whole forests have been reported killed by it. It is not
uncommon in this state, particularly on oaks.
Tinder-fungus rot [Ponies fomcntarius (L.) Fr.]. This fun-
gus is similar in its habits and characters to Fomes igniarius.
Like the latter it is a true pore fungus. The pores on the lower
surface are at first whitish, becoming grey-brown with age.
New layers of pores are laid on each year as can be seen by the
zoned character of the shelf. The upper surface of the fruiting
body becomes covered with a very hard coat of greyish color.
Internally the fruiting body consists of a felted, softer material
above and a tinder mass, through which the long pores, built
up in zones, extend to the openings on the lower surface. The
age of the fungus can be approximately figured from the num-
ber of zones in the fruiting body. It may be of considerable
age and of such a size as to be useful for tinder. Specimens
havje been observed which were almost a century old.
The tinder fungus is, like the false tinder-fungus, a danger-
ous parasite and gains entrance through the stem in a similar
manner. The growing zone beneath the bark, chiefly upward
and downward from the point of entrance, is killed and the
wood beneath undergoes rotting. \Yood attacked by the tinder
fungus becomes yellowish. Radial patches of the white felted
mycelium may often occur in such wood.
The fruiting bodies of the tinder fungus were formerly ex-
tensively used in Europe for tinder and also in the manufacture
of caps, gloves, etc. The tinder has also the property of
staunching blood-Mow from cuts and has been used for that
purpose.
The flattened pore-fungus rot [I:<>mcs a^hinatus (P.}
ll'iiHr.]. This is a very common pore fungus on old stumps
and fallen logs, less commonly found growing from wounds on
living trees. The hard-crusted shelves vary greatly in size,
some of the largest attaining a width of several feet. The shelf
is woody and the upper surface greyish to brown. The latter
is often covered with a fine dust of accessory spores of a dark
reddish brown color. The upper surface is covered with a hard
crust and the interior of the shelf is of a softer fibrous texture
and dark brown in color. The pores are very small and cover
the under surface, which is pure white, when newly formed.
252
Minnesota Plant Diseases.
The fruiting body lives from year to year, adding new growths
of pores annually.
The sulphur-fungus rot [Polyporus sulphur eus (Bull.} Fr.].
After a prolonged rainy season in spring or summer one often
FIG. 123. — The fruiting body of the flattened pore-fungus (Femes applanatus) ; on a
standing dead tree trunk. Original.
finds, particularly on oak trees, large masses of a tough, fleshy
fungus, consisting of numerous shelves overlapping each other.
The shelves are yellow to bright red above, becoming yellowish-
white with age ; the lower surface of each shelf, where the pores
occur, is of a pure sulphur-yellow color from which the common
Minnesota Plant Diseases.
253
name of the fungus is derived. In the young stages the fruiting
bodies are somewhat soft, fleshy or cheesy and are often eaten
by mushroom hunters. When older and especially under dryer
conditions, they become tougher in consistency and paler in
color. Very old masses are often found to be badly worm-
eaten and much of the fruiting body is reduced to a powder.
The fruiting bodies do not persist from one season to another
but go to pieces each year. New crops are produced yearly.
IMC. 124. — Fruiting bodies of the- sulphur pore fungus < I'oly «>ius sjli>hurtu») ; on a drail
oak stum;>. Original.
The fungus is a common wound parasite. The wood, when
attacked, becomes brownish red and dries out rapidly. Slits
and cracks soon arise in the wood and these become filled with
dense masses of the thickly felted mycelium. The wood in the
last stages becomes brittle and the entire tree usually succumbs
to the attack of the fungus.
Oaks in our state appear to suffer considerably from the
sulphur fungus but other deciduous trees and some of the
conifers mav also be attacked.
254
Minnesota Plant Diseases.
The scaly pore-fungus rot [Polyporus squamosus (Huds.}
Fr.]. This is a very common pore fungus which causes a white
rot of timbers. It occurs abundantly in spring, forming large
shelves, usually in groups. The fruiting bodies are soft and fleshy
at first and their upper surface is conspicuously marked with dark
brown or blackish scaly patches (squamae). It is attached, usu-
ally by a short stalk, which is almost always found on the edge
of the fruiting body. As the latter gets older it loses its fleshi-
ness and becomes harder, dying the same season, so that a new
FIG. 125. — Fruiting body of the scaly pore fungus (Polyporus squamosus), seen from
both surfaces. After Loyd.
crop of fruiting bodies must be formed again the following year.
The pores are very large, somewhat shallow and angular and
often run down some distance along the stalk. This fungus is
usually found on dead logs or stumps but may also grow on
dead parts of living trees.
The birch-fungus rot (Polyporns bctulimis Fr.) This birch
fungus is perhaps the most common of our pore fungi. In al-
most every clump of birches its fruiting bodies may be found.
Minnesota Plant Diseases.
255
The latter are annual and have a very characteristic and beau-
tiful appearance. They are hemispherical in shape and the
short stalk is always attached to the side. The upper surface is
grey to light brown in color, is very smooth and covered by a
thin skin. The pores on the under surface are small and rather
deep and the layer in which they are found is easily separable
from the rest of the fruiting bodies. The flesh of the fruiting
body is pure white and somewhat spongy in texture. In old
dried fruiting bodies the flesh is very commonly found to be
honey-combed by the larvae of insects.
FIG. 126.— Fruiting body of the birch pore fungu* (I*oly|Miru» bctulinu*). on a branch of
a white birch. Original.
The parasitic relationships of this fungus with the birch trees
have been established by several investigators and there is little
doubt that the fungus causes the death of many birches in this
state. The fruiting bodies are usually found on dead birches,
often accompanied by other pore fungi. The mycelium in the
living tree grows not only through the growing region of the
stem and the inner bark but also attacks the wood. \Yhen the
mycelium which may be growing for years has accumulated
sufficient food material a fruiting body is formed. A new crop
is produced every year, if conditions are favorable.
256 Minnesota Plant Diseases.
Trametes root-rot (Tramctes radiciperda Hartig.). This
root-inhabiting pore fungus has been very thoroughly investi-
gated in Europe where it has done an enormous amount of
damage to coniferous and broad-leaved forest trees. The myce-
lium of the fungus travels from root to root in the living trees
and the disease is thereby rapidly spread. It later passes from
the root into the stem, chiefly through the inner bark, and here
attacks the wood. The affected trees soon die and the wood
undergoes a red rot. The fruiting bodies are formed where
they may distribute their spores into the air and are therefore
usually above ground. They are irregular in shape varying ac-
cording to their position ; they are brown above, have white
flesh, and the lower surface, upon which the pores are formed,
is also white. The fungus is not infrequently found on timber
in mines.
European botanists recommend for the prevention of the
spread of this disease the isolation of the infected region by dig-
ging ditches deep enough to cut through all of the roots, there-
by preventing the spread of the mycelium by way of the roots.
In the isolated areas, fruiting bodies may develop either from
the exposed roots or from the standing trunks. To prevent the
spread of the disease by means of the spores so formed, the
roots should again be covered with soil and the trunks and
stumps burned. The formation of mature fruiting bodies
should be prevented. The extent of the distribution of the fun-
gus in Minnesota is as yet unknown.
Ring scale of pine [Trametes pini (Brot.} Fr.]. Ring scale
is a very common parasite on pines both in Europe and in this
country ; it is also known on Douglass fir. The fungus gains en-
trance to the tree usually through wounds or broken limbs, par-
ticularly the older branches, in the heart-wood of which no pro-
tection-coat of resin has been formed. After it has gained en-
trance to the stem, the mycelium grows in longitudinal stripes
above and below the points of entrance; in' the same year's
growth and in successive years it works from the interior to the
exterior. In this way zones of the diseased regions are formed
exteriorly (ring scale). The wood attacked by the ring scale un-
dergoes a peculiar disintegration. There are formed in the de-
caying wood numerous small, isolated patches of the white my-
Minnesota Plant Diseases.
257
celium of the fungus. These differ from the similar patches in
the Trametes root-rot in the usual absence of black centers.
The fruiting body is brown and either forms a shelf or is
diffused into a coating over
the bark. It is woody and
perennial, producing new
pore areas successively for
many years. The pore area
is on the lower surface of the
shelf forms and on the outer
surface of the prostrate
fruiting bodies.
The oak Daedalea [Dcr-
dalca qnercina (L.) Pcrs.~\.
The cause of this disease is
a pore fungus and is not un-
common on the dead trunks
of oaks ; it is one of the most
common rots of oak railroad
ties. The fruiting body is a
thick shelf, woody in ap-
j>earance but in consistency
tough-corky. It is pale buff
in color and the upper sur-
face is smooth, though usu-
ally more or less zoned and
sometimes ridged. The
pore surface is often half-
cone-shaped and the p >res
are elongated from the cen-
ter toward the edge. The
|x>res are more or less sinu-
ous or wavy in outline and
are especially elongated to-
ward the point of attach-
ment. The jx>re surface is
of the same color as the top
of the shelf.
258 Minnesota Plant Diseases.
The parchment pore-fungus rot (Polystictus pergamenus Fr.~).
This is an exceedingly abundant pore fungus found on various
kinds of soft wood trees. It is very common on birch, where
one frequently finds whole logs covered with the densely
crowded fungus shelves. Occasionally one finds the fungus on
the living trees. It has also been observed on living larch trees
where it occurs in great abundance. The fruiting body is a
thin, reflexed shelf which is very light tan colored above and
covered with dense hairs. The pores are found on the lower
surface and are shallow at the edge, increasing in depth toward
the center. They are often of a purplish or violet tinge and
the pore walls become, with age, so badly torn that the under
surface of the shelf has the appearance of a toothed or hedge-
hog fungus. There is strong evidence that it has caused the
death of numerous larch trees in Minnesota. (Fig. 36.)
Wood-rot of the creeping pore-fungus [Polyporus vapora-
rius (P.} Fr.]. This fungus is reported as very abundant in Eu-
rope and forms very similar to it are known in Minnesota. A
description of this fungus will therefore not be out of place
since it is not improbable that it exists in the state. The fun-
gus attacks chiefly soft coniferous woods and is a wound para-
site. It is found in the roots and on the stem and is a danger-
ous enemy to trees. The mycelium develops in cracks and un-
der the bark, forming a dense, white felt and causing rapid de-
cay of the wood. The fruiting bodies are white, flat, prostrate
forms and do not produce shelves. The pores are small and cover
the upper surface of the fruiting body and are very numerous.
The mycelial felts and strands are not unlike those of dry rot
and the disease is often confused with that of true dry rot. It
is frequently found in the timbers of dwellings where it is a
dangerous agent of decay very similar in its action to that of
the dry rot fungus.
The zoned Polyporus rot [Polystictus verslcolor (L.) Fr.].
This is one of our commonest of pore fungi, found chiefly on
old stumps and decayed timbers. The shelves are thin and
leathery and conspicuously zoned above. The zones are of dif-
ferent colors varying from light tans to very dark brown or
black and are frequently velvety in appearance. The pores are
on the under surface and are very small. They are white at the
Minnesota Plant Diseases. 259
surface when fresh. The pore walls often become torn with
age. The shelves vary somewhat in size; they are generally
from two to three inches across and are aggregated together
into very dense clusters in shingle fashion. They appear usual-
ly when the logs or branches upon which they form are in ad-
vanced stages of decay. The zoned pore fungus is perhaps not
of great importance as a timber rot, though it is very frequent
on railroad ties.
The pitch-stemmed pore-fungus rot (Polyporus picipes Fr.\
This form of pore fungus is conspicuous in our woods on account
of its large, thin fruiting todies which are attached by a short
black stem. It occurs on broad-leaved trees and is usually found
on decaying logs or stumps. It has been reported as occurring on
living trees but little is known of its relationship with the latter.
Though not uncommon, especially in hard maple and basswood
forests, it is not usually very abundant. The fruiting bodies
are thin and tough, leathery when moist, becoming brittle when
dry. They are usually broad-beaker-shaped to flattened when
mature, are dark red-brown above and have a short central
'black stem. The fruiting bodies are not at all fleshy. The
lower surface, which contains the very minute pores, is dirty
yellow in color.
The hairy pore-fungus rot (/ 'olystictus hirsntus /•>.). This is
a very common shelf-pore form which occurs abundantly on
dead sticks and limbs of trees. It has been reported also on
living trees of hornbeam, alder, birch and oak but exact details
of its relationships with these plants are wanting.
Chapter XVII.
Diseases of Timber and Shade Trees, Timber Rots
(Continued}.
The shoe-string fungus rot [Agaricus (Armillaria) melleiis
Bahl.]. This fungus is also known as the honey-colored mush-
room. It is undoubtedly the most common of all of our fall
mushrooms. Its edible fruiting bodies may be found at the
base of almost any of our indigenous trees. They are very
frequent at the base of dead stumps, but may also occur on
the ground. They are usually found in dense clusters the lower
of which are covered with the fallen spore-powder from the up-
per fruiting bodies. The whole fruiting body, except the gills,
is more or less honey-colored — hence its common name. The
stalk is usually swollen toward the base and carries near its sum-
mit a membranous remnant, the so-called annulus. The annu-
lus is usually conspicuous especially in the younger stage, but is
sometimes only slightly developed and occasionally entirely
wanting. The mushroom cap is lined on the under surface with
plates or gills which radiate out from the stem and bear the
spores. These are white and may often be found as a fine white
powder covering sticks and leaves under the fruiting bodies.
The honey-colored upper surface of the latter is covered with
fine, fibrillar scales of a darker color. These scales may also be
found on the young stem. When old the whole fruiting body
may become entirely smooth.
At the base of the stipe may usually be found a shoe-string-
like strand of the mycelium from which the fruiting body orig-
inates. These strands which resemble small, leather shoe-
strings in appearance run long distances through the earth and
also occur just underneath the bark of trees where they
are usually somewhat flattened. The mycelium of the honey
mushroom may be parasitic on trees and is one of the most de-
structive of timber diseases. When the strand of a mycelium
Minnesota Plant Diseases.
261
5-3
s-
Si
3 ?
r-
„ cr
3 £,
o »
3 -
ft 3
262 Minnesota Plant Diseases.
comes into contact with the living root of a tree it bores its way
through the outer bark into the soft bark and the growing re-
gion ; here it frays out into a fine felt-like expansion and attacks
the living cells. The latter are killed and the fungus proceeds
between bark and wood up to the stem and often for some dis-
tance up the latter. From the stem the mycelium may make
its way down into healthy roots. The attack on the root sys-
tem results in the death of the tree by cutting off the supply of
crude materials. At the base of such a trunk one may later in
the autumn find the fruiting bodies. The mycelium in the
trunk and roots assumes the form of shoe-string strands and
these may grow into a very well developed net-work just under
the bark. The mycelium may continue to live on the timber
saprophytically after the death of the tree. This fungus has
often been reported as a timber-destroying fungus in mines. The
honey-colored mushroom attacks the oaks and probably other
broad-leaved trees in our state. In Europe it has been reported
as particularly destructive to coniferous woods, as well as to
broad-leaved trees.
When the disease becomes epidemic, no successful combat-
ive measures are known. All diseased trees and fruiting bodies
should be burned and young trees should not be planted on in-
fected areas. (See also Figs. 6, 7.)
The fatty Pholiota rot (Pholiota adiposa Fr.). On standing
trees and particularly on felled timber of oaks and other broad-
leaved trees, one often finds in fall clusters of a conspicuous,
bright-yellow mushroom, which is responsible for a white rot
of timbers. The fruiting bodies may be six inches or more in
length ; the cap is bright yellow with concentric, blackish spots.
The latter are also found on the stem, which is about of equal
diameter throughout its length and is tough-fleshy. The cap
in moist weather is covered with a slimy gelatinous coat. On
the under surface of the fruiting body are gills radiating from the
stem as in the honey-colored mushroom. These gills are in this
case, however, yellowish to grey in color and throw off ochre-
brown spores, which often discolor the stem or other objects
upon which they fall. The mycelium attacks the wood and
forms bands of white felt which separate the wood up along
the lines of the annual rings. Although not infrequently met
Minnesota Plant Diseases.
263
with, this parasite is probably not very destructive to timbers
in this state. It has been observed on living shade trees.
Fie. 129.— Fruiting bodies of the fatty I'holiota (Pholiota adiposa), in a wound of an oak
tree trunk. Original.
The scurfy Pholiota rot (Plwliota squarrosa Miill.}. This is
a close relative of the fatty Pholiota and forms fruiting bodies
which resemble those of the latter. They are not so viscid in
rainy weather and are persistently scurfy. It occurs on logs,
264
Minnesota Plant Diseases.
Minnesota Plant Diseases. 265
stumps and cut timber in a manner similar to the preceding
species.
The velvet-stemmed Collybia rot (Collybia vclutipcs Curt.}.
This is an exceedingly abundant fungus especially on cut tim-
ber and standing stumps or fallen logs. The fruiting bodies are
of the gill-fungus type and usually occur in clusters. The upper
surface of the cap is yellowish to tawny and in wet weather is
viscid. The gills are light yellow to tawny and produce white
spores. The stem is covered with a velvet-like coat of a dark
brown to blackish color, especially toward the base of the stem.
The fruiting bodies are about one to three inches in length and
FIG. 131. — Fruiting bodies of the tapid I'lcurotus (IMturott:* sapidrs). on a standing yellow
birch trunk. Original.
the cap about one to two inches across. They may be found
at almost all seasons from early spring to late fall. This fungus
causes one of the rots of timbers and is usually a saprophyte.
It has been observed on living elm trees, however, and is possi-
bly a wound-parasite.
The elm Pleurotus rot (Tlcnrotus nlmarius Bull.). This very
common gill-fungus is usually found on elms and maple trees,
growing from dead trunks or from wounds in the living trees.
266
Minnesota Plant Diseases.
jn rt
''
A parasitic life has not been demonstrated for it, but its pres-
ence in the wood of living trees is known. It is frequently
found on shade trees,
especially on trunks,
which have been pruned
and not subsequently
protected. The fruiting
body is pure white and
usually large, often at-
taining a length of six
or seven inches and an
equal cap width. It is
usually fleshy and the
stem is slightly removed
from the center of the
cap (eccentric). The
spores are pure white.
The fruiting bodies are
frequently clustered.
This is a popular edi-
ble fungus.
Several other close-
ly related forms are
likewise saprophytes on
timbers. Of these the
oyster fungus (Pleuro-
tus ostreatus) and the
sapid fungus (Pleuro-
tus sapidus) are best
known and very com-
mon forms. They are
all three prized as edi-
ble mushrooms. (See
also frontispiece and
Fig. 20.)
The pine Lenzites
[L en zit e s abietina
(Bull.) Fr.]. This is an exceedingly common timber rot on soft
Avoocls. It occurs on railroad ties, fence rails and posts and on
Minnesota Plant Diseases. 267
soft wood timbers wherever they are placed in conditions favor-
able to the fungus. The fruiting body is either a flat prostrate
one or may become a low shelf. It is seldom large and does
not usually exceed a few inches in diameter. The exposed sur-
face is covered with gills which often radiate from the center in
the prostrate forms. The fruiting bodies are tough-leathery to
woody and dark-yellow- to red-brown in color. The top of the
cap is somewhat hairy when young, becoming more or less
smooth when old. The gills are rather thick.
The scaly Lentinus rot (Lcutimis lepideus Fr.). This is a
very familiar gill fungus which inhabits almost all kinds of soft
needle-leaved tree timbers. It is, as far as is known at present,
a saprophyte. It is very frequently met with on fence rails and
posts, dead and down tamarack and other kinds of coniferous
wood, as well as on wood partially submerged in the soil or
water. The fruiting body is a stalked form with a central stem
and is very tough-fleshy. The cap is two to three inches or
more across and is at first pale yellow. Later, black scales de-
velop on the upper surface. The flesh of the cap is white.
The gills are slightly wavy, running down the stem for a short
distance and the margins are irregularly toothed. — a character by
which this fungus and its close relatives can readily be distin-
guished from other gill fungi. The gills are white, tinged with
yellow. The stem is one inch or more in length and usually ta-
pers toward the base, is hard, pale in color and has scales similar
to those of the cap. The fruiting bodies sometimes grow in
clusters.
The green cup-fungus rot [CMoros/>lcmum acrughwsum
(Ocdcr.) /V.V.J. On various kinds of woods, including bal-
sam fir and birch, grows a fungus with a remarkable habit.
The mycelium penetrates deeply, being especially prominent
in the spring wood. It colors the wood a very beautiful, deep
verdigris green, varying in shade in the different parts. It is
more abundant in the summer wood, thus accentuating the
grain. The rot works very slowly. Wood, so colored by artificial
infection, is used in the arts in the manufacture of Tunbridge
ware. It is also used for the extraction of the pigment which
resides both in the mycelium and the adjacent walls. The fruit-
ing body is a small stalked cup which at first sight looks much
268 Minnesota Plant Diseases,
like a smooth-surfaced palisade fungus. The whole fruiting body
seldom attains a length of more than three-eighths of an inch
and a width of one-fourth inch. The sacs, with eight spores
each, line its upper surface. The whole cup is colored similar-
ly to the mycelium. This rot is particularly abundant in the
northern part of the state, though on account of its slow
growth and its preference for the smaller branches it does com-
paratively little damage.
Stem canker of balsam fir [Dasyscypha resinaria (Cook
and Phil.) Rchm.]. The cause of this disease on the common
balsam-fir is a very small cup fungus. It causes canker swell-
ings on the stems and branches. These cankers usually par-
tially and sometimes entirely encircle the stem. In the latter
case the tree trunk is killed and the balsam dies. In the canker
an abundance of resin is formed. The disease is very similar
to the European larch canker, which forms on the common
larch of Europe a similar resinous canker. The fungus fruiting
cups are produced only on the cankers and are formed within
a year of the death of the infected branch or tree. The fruiting
bodies are thus produced during the saprophytic life of the fun-
gus. The earlier life of the fungus is probably parasitic, though
no infection experiments have been carried out to prove this
point.
The fungus cups are very small — about one-fifth of an inch
in length and of about the same width. They are provided
with a very short stalk and are covered with very fine hairs.
The disc or inside of the cup where the spore sacs are formed is
orange-colored. The attacked portion of a branch shows a
thickened inner bark and the wood rings are also increased in
thickness. No remedial measures have been worked out.
Tar spot of maple [Rliytisma accrinum (P.) Fr.]. One fre-
quently meets with b'ack. tar-like spots on leaves of maples in
late summer or early fall. These tar spots are caused by a fun-
gus of the cup-fungus group and the spots are in the nature of
a storage mass of threads which persist through the winter.
In the early summer the spots are yellowish ; they then produce
small pear-shaped depressions, containing very small spores,
which flow out of the depressions onto the surface of the spot.
In the fall the spot turns black and then resembles a drop of
Minnesota Plant Diseases.
269
tar. In this condition it rests over until spring, when the cup
fruiting-bodies are produced. Several cups spring from each
spot and each cup is lined, on its inner surface, with a pal-
isade of sacs containing eight spores each. Between the sacs
c =
II
are numerous sterile fungus threads. Spotted leaves should he
collected in the fall and burned to prevent a spread of the dis-
ease in the following spring. The formation of the sac spores
is thereby effectively prevented.
270 Minnesota Plant Diseases.
Tar spot of willow [Rhytisma salicinum (P.) Fr.]. This dis-
ease is very similar to that of the tar spot of maples. (See the
latter.) The tar spots become black in August and September
and may be formed in great numbers. Sometimes leaves are
completely covered by the spots and are consequently seriously
injured. When the disease threatens to become serious the
spotted leaves should be collected and burned in fall.
Ring fungus or ring disease of cone-bearing trees (Rhizina
inflata Quel.\ This fungus is a member of the morel group of
sac fungi, but might almost as well be included in the cup fun-
gus group. The fruiting-body is a flattened, crust-like object
of very dark brown or blackish color, fleshy in consistency and
sticky in moist weather. It may attain a width of several inches
and is usually irregular in shape. It is found at the base of
trees or on old stumps and is commonly a saprophyte. It is
attached to the soil or tree stump by numerous strands of the
mycelium which run into the substratum for some distance.
The sacs of the fruiting body are long cylinders and contain
eight spores each. The mycelium may under favorable conditions
become parasitic on the roots of trees. It grows around the
root, killing the tissues, and may thus ultimately effect the death
of the entire tree. It has not yet been reported from Minnesota
but is known in Wisconsin and very probably exists in our
state. The fruiting bodies should be destroyed.
The green mold rot of timber (Species of Penicillium}.
There seems to be some evidence that the common green
molds, which are so conspicuous as saprophytes on starchy food
materials and on cheese, are capable in themselves of causing
rot of timbers. Such a mold thrives on the starchy material
which is stored up in the medullary rays of woody tissues and
from this point invades the woody fibres. The green mold very
frequently accompanies other rots and may assist in the disin-
tegration of the wood. It is doubtful, however, that it is ever
in itself alone a very serious cause of the decay of timbers. The
ordinary mass of green mold is composed of thousands of
minute, brush-like clusters of strings of green spores which are
exceedingly resistant and can retain their power of germina-
tion for a long time. The winter spores are formed in sacs,
produced in closed capsules, which open only by irregular split-
Minnesota Plant Diseases. 271
ting or by the decay of the walls. These capsules are not con-
spicuous and are not met with frequently. For a more com-
plete account of the life history of these fungi the reader is
referred to Chapter IX. The growth of this mold is favored by
close, moist conditions.
Slime flux of trees. Slimy, mucilaginous material can some-
times be found flowing from wounds in oak, apple, birch, elm,
maple and other trees. The wound in itself may not be due
to any fungus disease but may be caused by pruning, frost or
sunscald, etc. In the slime which proceeds from the wound,
however, one usually finds a simple form of the sac fungi (an
Endomyces) closely related to the mold of the honey mush-
room, and to the yeast fungi. The fungus mycelium is com-
posed of branched threads, on which the simple four-spored
sacs are found. There is considerable doubt that the Kndo-
myces is the cause of the slime flux. In the flux one may also
find one or more yeasts and other fungi, bacteria and plants be-
longing to the blue-green algae. Through the agency of the
yeasts fermentation often sets in and the flux may then have
an odor of beer. Slime-flux wounds often increase in size until
large areas of bark die off and the whole tree may subsequently
die. Shade and park trees arc sometimes killed off in this
manner. As the cause of the flux is not definitely known,
methods of prevention are not understood. The usual precau-
tions which are recommended for treatment when trees are
pruned should be followed.
Witches'-broom of birch (Species of E.voascns}. Cultivated
birches are sometimes attacked by this fungus. The results are
seen in the production of witches'-brooms, somewhat similar to
those produced in cherries. The fungus is a similar one and
produces its sacs on the twigs and leaves. The infected por-
tions should be cut back and burned.
The Nectria of red-knot rot [AVr/r/d cinnabarimi (Todc) Fr.].
This fungus is not uncommon in the state. It is a wound par-
asite, gaining entrance to the inner bark of the tree by such
wounds as are produced by hail, birds, squirrels, storms or
pruning. Infection takes place from the mycelium which
grows into the bark from the wound and establishes itself in
the water-conducting tissues of the wood. ]\\ continued
272 Minnesota Plant Diseases.
growth the mycelium permeates the wood and then the grow-
ing zone of the tree and the bark are destroyed. The fungus
continues to live in the dead wood as a saprophyte and under
such conditions produces its fruiting bodies. At first, small
clusters of soft, bright red, button-like cushions arise. From
the surface of these cushions are produced tiny summer spores,
which are successively pinched off from upright threads on the
surface of the cushion. These spores are capable of immediate
germination and may spread the disease very rapidly. After
the formation of these spores has gone on for some time, they
decrease in number and finally cease to form. There then
appear upon the same cushion small, red, pear-shaped to spher-
ical protuberances, which contain a central cavity and a pore-
like opening to the exterior. These are the sac-spore capsules.
At the base of the cavity are found long, cylindrical sacs, each
of which contains eight spores. The opening of the capsule is
lined internally with hairs which clothe the whole canal, leading
from the cavity to the exterior. The sac-spores and the sacs
are extruded through this opening. The spores will germinate
tinder favorable conditions and will again produce a mycelium
in the wood.
The treatment of this disease is similar to that of wound par-
asites in general, i. e., burning of the infected twigs and wood
and clearing up of felled wood to prevent the growth of wild
spores.
Leaf blister of oak (Species of Taphrina). This fungus is
a relative of the fungi of plum pockets and leaf curls and of the.
witches'-broom fungus of cherry and birch. The spores are
produced in sacs which are arranged in a dense palisade on the
under surface of the leaf. The leaf is usually distorted in a blis-
ter-like fashion, whence the common name of the disease. The
red oak has been found in this state attacked by this fungus,
though not to any serious extent. The removal and burning
of the affected parts would be advisable to prevent a severe re-
currence of the disease.
Willow blight or powdery mildew [Uncinula salicis (D. C.)
Wint.]. The blight of willows is an exceedingly common dis-
ease not only of the willows, but also of the poplars, cotton-
woods and birches. The mycelium is usually very abundant and
Minnesota Plant Diseases.
2/3
conspicuous in late summer and forms a thick, whitish covering
over the leaf. On this arise the spore-sac capsules as tiny,
black, pinhead-like bodies, which often occur in great numbers.
The mycelium may cover both sides of the leaf and may some-
times be found on almost every leaf of the affected tree, though
it is usually most abundant or entirely confined to the leaves
of the lower branches. All species of willow are attacked.
l-'ic. 13-4.— 1'owdery mildew of willow leaf (I'ncinula salicis). The minute black s|>ots are
the spore-sac capsules and under tluse can be seen the whitish myceliul coat of threads.
Original.
The sac-capsules are large conipared with most other Min-
nesota powdery mildews. They are black in color and have a
ring of numerous, colorless, thread-appendages, each of which
terminates in a single-pointed hook, in a manner similar to
that of the vine powdery mildew. Each capsule contains at
least several sacs, in each of which are found eight spores. The
summer spores occur in the manner usual for the powdery mil-
dews, producing a powdery, starchy, dust-like coating.
274
Minnesota Plant Diseases.
Though a very common fungus, it does not very often occur
in sufficient amount or at the proper season to cause very ex-
tensive damage and usually no preventive methods are deemed
necessary. The ordinary sprays for the fungi with superficial
mycelia would probably prove effective against this disease.
(See also Fig. 52.)
Powdery mildew of e>\ms(Undnula macrospora Peck}. This
mildew is not uncommon, though it cannot be said to be abun-
dant throughout the state. It attacks only the young trees or
saplings of elms.
On an affected
tree the fungus is
usually exceed-
ingly abundant,
covering many or
most of the leaves
with a very con-
spicuous mildew.
The latter attacks
the leaves and oc-
curs on the upper
surface. White,
circular patches
of the superficial
mycelium are
formed and these
may combine
with neighboring
ones to cover the
entire leaf. These
patches are con-
spicuously white
and dense and
have a somewhat
starchy appear-
ance. The win-
ter-spore fruiting
FIG. 135. — Powdery mildew of elms (Uncinula macrospora),
on an elm leaf. The exceedingly minute black spots are
sac-capsules of the fungus. The fungus mycelial threads
form in spots which are very conspicuous. Original.
bodies are
saC-CapStlleS and
Minnesota Plant Diseases. 275
appear on the mycelium as very minute dots which are at first
yellowish and finally become black. Each capsule, when seen
under the microscope, is surrounded by a dense circle of thread
appendages which are hooked at the end in a manner similar
to those of the powdery mildew of willows. Each capsule con-
tains numerous sacs and each sac contains two very large
spores. It is very possible that this fungus causes a considera-
ble amount of damage to young elms in forests. The summer
spores are formed earlier and cause the starchy appearance of
the young mycelium. The fungus does not seem to be widely
enough distributed to be a serious menace at present though
the vigor with which it attacks is an indication that it may at
some future time become a dangerous pest.
Pine stem rust (Species of Pcridermium}. The branches and
stems of pine trees are attacked by this fungus. The result-
ing disease is commonly known as pine knot. The infections
are more or less localized and do not extend through the whole
plant. The infected portion is stimulated to the production of
boil-like swellings which may continue to grow for years. The
swelling is often accompanied by an abundant formation of
resin and turpentine which sometimes exudes from the canker.
The fungus attacks the growing zone in the stem and may
finally completely encircle the latter, but this usually happens
only after a struggle lasting through several years. The con-
duction of the water through the stem is seriously interfered
with and a drying up of the upper part of the tree may result.
The fungus causing this disease is a rust fungus and is a
true parasite. The complete life histories of the American
pine-stem rusts have not yet been unraveled ; but from a com-
parison with better known European forms it seems very prob-
able that our species pass a part of their life on another host, be-
side the pine. On these so-called alternate hosts the winter
spores are to be looked for; these spores are therefore at pres-
ent unknown. The swellings of the pine stem described above
always bear the cluster cup spores. The latter are found in
cluster cups or over flat areas on the surface of the canker.
They are light yellow or yellowish-orange in color. When the
cluster cups open in the spring, large areas on the surface of the
canker are covered with a bright yellow coat of spores which
276
Minnesota Plant Diseases.
are later uncovered by the splitting off of scales of the bark.
Jack pine in Minnesota is very commonly affected and the
white and red pines are also though not so frequently attacked.
Scotch pines in nurseries and experimental forests are some-
times very seriously affected.
FIG. 136. — Pine knot (a species of Peridermium), on Scotch pine. ]. The branch on the left
is seen with a good-sized knot which is covered with the conspicuous clusted-cup spores.
The branchlets of this branch are seen to be thicker than the normal branches; the
leaves are shorter and not as green and die early. 2. Section through a knot. 3.
Section through the same branch as shown in 2, but below the knot, showing that a
very great growth has been caused by the parasitic fungus in 2. Original.
In view of our lack of knowledge of the life history of these
forms no preventive methods of combating this disease are
known. All diseased branches should be cut off and burned
as soon as they are discovered.
Leaf rust of pines (Species of Peridermium). This is a close
relative of the stem rust of pines. It is likewise a rust fungus;
Minnesota Plant Diseases. 277
but attacks the leaves instead of the stem. The attacked leaves
are often normal in appearance and not at all distorted. The
cluster cups are formed on the surface of the leaves in the
spring. They are large, swollen, sac-like affairs and contain
a powder of light-yellow spores. It is possible that this is the
same fungus which forms its summer and winter spores on
asters and goklenrods and which is there known as the aster
and goldenrod rust.
The leaf rust of pines is seldom present in sufficient quan-
tities to injure the trees seriously.
Ash leaf rust [Puccinia fra.rinata (Lk.) Arthur.]. Ash leaves
are attacked by a cluster-cup rust which is not at all uncommon
in the state, though it does not seem to be abundant. Several
species, including the green ash. are the hosts. The cups are
formed on large yellow spots on the leaf blade or petiole and
the infected portion is often considerably distorted. The dust
of spores is a bright orange red. Within recent years this clus-
ter-cup stage has been shown to be connected with winter
spores on the common grass plant, Spartina cynosuroides.
(See also Fig. 75.)
Witches'-broom of balsam fir (Acciiiinm chitinum Alb. cl.
Schw.). There are formed on the balsam firs throughout the
northern part of Minnesota peculiar bush-like branch-growths
known as witches'-brooms. The production of this bush is due
to the action of a rust fungus, which lives in the tissues of the
branches. The first result of the attack of the parasite is the
formation of a spherical swelling on the side branch of the
balsam fir tree. From this swelling arise a very large number
of branches, which grow very fast and become much longer
than the unaffected branches. They often have a somewhat
climbing, tw'ning habit and grow upward instead of in a hori-
zontal direction as do the ordinary lateral branches. The dis-
eased branches do not hold their leaves through the whole
year but shed them every fall. The fungus forms cluster-cups
on the leaves of the broom shoots in great abundance in early
summer and when the spores are ripe, a cloud of yellow dust of
cluster-cup spores can be shaken from the broom. The broom
increases in size from year to year and often several brooms are
developed on the same tree. In some cases, almost the entire
tree mav be broomed. Not onlv is the svmmetrv of the growth
278
Minnesota Plant Diseases.
of the tree interfered with but the tree is usually stunted
and may eventually die. The leaves of the diseased shoots
contain less leaf-green and are paler in color than the ordi-
nary leaves. The exact method of the infection by spores in
this country is not yet known. A similar disease on the silver
fir in Europe has recently been thoroughly investigated. It is
found that the cluster-cup spores of the silver fir brooms can-
not infect the silver
fir leaves but can
cause infection on
certain plants be-
longing to the pink
family, e. g., the
common chick-
weeds. Here the
fungus gives rise to
the summer- and
winter-spore stages.
From the winter-
spore forms infec-
tion of the silver fir
takes place. The
commencement of
the characteristic
broom-like growth
of the branches
takes place in the
FIG. 137.— Poplar leaf rust (Melampsora populina). A lOllOWing year. No
poplar leaf showing the fine, black spots of the crust- experiments h a V 6
like clusters of winter spores on the under surface.
Original. yet been carried on
to determine wheth-
er or not the American fungus on the balsam fir is or is not
identical with the European form on the silver fir.
All brooms should be removed and burned especially before
the formation of the cluster-cup spores in the spring. (See
Fig. 23.)
The poplar rust [Melampsora populina (Jacq.} Wint.]. The
poplar rust is exceedingly abundant in Minnesota and in some
cases probably effects considerable damage of young poplars
Minnesota Plant Diseases. 279
and cottonwoods. Older trees are seldom if ever seriouslv
affected. Only the summer and winter spores occur on the
poplar and cottonwood while the cluster cup stage is found on
some other plant.
The summer spore groups are small, bright-yellow, resin-
like cakes before maturity and when ripe produce a bright-
yellow powdery mass of spores. Abundant, sterile, club-
shaped cells are found intermixed with the summer spores.
The summer spores are very abundant on poplar leaves in
August. In early autumn the winter spores commence to
form and soon, small, dark-brown, crust-like spore groups
are produced, which later become black in color. Fallen pop-
lar and cottonwood leaves, particularly those from the lower
parts of the trees, are often entirely blackened and the under
surface is almost completely covered with the black crust of
winter spores. The winter spores pass the winter on the fallen
leaves and in the following spring germinate without separating
from the spore group.
In case of a serious epidemic the leaves should be collected
and burned in the fall.
The birch leaf rust [Mchimpsora bctulina (Pcrs.) II' int.].
This rust is closely related to that of poplars and the rotation
of spore forms is similar. The appearance of summer- and win-
ter-spore forms also resembles the rust of poplars.
The willow leaf rust [M clam psora salicis-caprac (Pcrs.)
ll'int.]. The willow leaf rust is exceedingly abundant on all the
species of willow in Minnesota. This rust is also similar in
general to that on the poplar leaf and is a closely related form.
The leaves of younger shoots are not uncommonly so badly af-
fected that they shrivel up and die. The winter spore groups
form similar black crusts to those of poplar rusts and rest over
winter; the spores germinate the following spring. This dis-
ease occasionally occurs in sufficient amount to threaten seri-
ously the cultivated willows. When occurring in such trouble-
some quantities the fallen leaves with their winter-spore groups
should be burned in late fall.
The cedar apples of red cedar (Gymnosporangium macropus
Link and G. globosnm Fat 1.). (See Leaf Rust of Apples — Dis-
eases of Orchards.)
280
Minnesota Plant Diseases.
Rust of pyrola \Chrysomy.\~a pirolac (DC.) Rostr.]. The
cluster cup stage probably occurs on some conifer. See Dis-
eases of Wild Plants.
Rust of milkweeds
\Cronartiwn asclepia-
deum (Willd.) Fr.].
Sometimes found on
oak leaves. See Dis-
eases of Wild Flowers.
The cluster-cups are
probably produced on
pine leaves. See Leaf
Rust of Pines. Dis-
eases of Timber and
Shade Trees.
The mistletoe dis-
ease of spruce [Ra-
zoumofskya pus ill a
(Peck) Kuntse]. This
parasite is a flowering-
plant of the mistletoe
family, and is the only
plant of this family
which is native to our
state. It produces a
verv serious disease of
the spruce and both
white and black spruce
are a ff e c t e d. The
presence of the para-
site in the tree can
usually be discovered
from a distance by the
presence of large
"w i t c h e s'-brooms."
The part of the spruce
which is attacked mul-
tiplies itS branches and pIG. 13S.— Willow leaf rust (Melampsora salicina). A
these ire SO deiiselv willow leaf almost covered with the crust-like clus-
ters of winter spores. Original.
Minnesota Plant Diseases. 281
clustered that the so-called broom looks like a foreign bush
growing on the spruce tree. In badly infected trees the
whole plant may consist of bunches of these brooms. By
the death of the lower broom-branches, the tree may be left
with only a few brooms remaining at the top. The symmetry
of the tree is therefore entirely destroyed and the natural
growth is very seriously interfered with. \Yhole forests in Ot-
tertail and Becker counties are badly infested so that in many
cases a majority of the trees are diseased. It has also been re-
ported from Itasca county. In view of the decline of the pine
forests and the growing importance of the spruce, this disease
will later prove of very serious consequence. It is not appar-
ently common on the north shore of Lake Superior but will
probably reach all of the spruce-growing regions of the state in
the course of time unless measures are taken to prevent it.
The parasitic plant is very small, seldom an inch in length,
and its parasitic habit has greatly affected its structure. The
leaves are reduced to mere scales and the very short stem is
reddish or only slightly greenish. It is rooted in the branches
of the spruce tree from which it derives its nutrition. Many
plants often arise from the terminal region of a single spruce
branch. The flowers are very much reduced in structure and
are of two kinds, staminate and pistillate, growing on separate
plants. The seeds are produced in berry-like fruits and are
provided with sticky envelopes by means of which they cling to
the branches of the trees. They are probably distributed by
birds.
The only known remedy is the destruction of the infected
trees, which will prevent the spread of the disease. This can
easily be effected when the trees are bad1)' diseased for tlu* lat-
ter can be readily recognized by the brooms and the general
irregularity of growth. Care should be taken to find those in
the early stages of infection for such trees have not yet devel-
oped conspicuous brooms and may still harbor the parasite and
thus become the center for new infections to the neighboring
trees. (See- Figs. 24, 25. 101.)
Downy mildew of seedling treesi rhytophthoni <nnnh'ora DC
Rar\). See Diseases of ("ireenhoiise and Ornamental Plants.
Chapter XVIII.
Diseases of Field and Forage Crops.
Jff
The rusts of wheat and other cereals [Puccinia graminis
Pers., P. rubigo-vcra (DC.} Wint., and P. coronata Cda.]. What
is commonly known as wheat rust may be due to one or more of
a considerable number of rust fungi. These fungi, moreover,
may be found on a large number of grasses. The three most
important forms of cereal rusts are : the Black or Stem Rust (P.
graminis), the Orange Leaf Rust (P. rubigo-vera) and the
Crown Rust (P. coronata). In all of these forms, the sum-
mer and winter spores are formed on the plants of cultivated
cereals or of wild grasses and in the former case (i. e. sum-
mer- and winter-spore stages), cause annually an enormous
amount of damage. The summer spores first appear in early
summer and are formed with great rapidity so that as the
grain is growing the disease is also rapidly gaining ground.
These spores occur in red lines, crowded between the parallel
veins of the leaf. This form is commonly known as red
rust and is particularly in evidence after very moist weather con-
ditions, for these are very favorable to the rapid development of
the fungus parasite. Toward autumn the production of the
summer spores decreases and the formation of winter spores be-
gins. These are produced in long black lines, chiefly on the
stalks and form what is commonly known as black rust.
The orange leaf rust makes, as one might say, a specialty of
the red rust, or summer spore stage, so that this is the prominent
feature of this particular rust. On the other hand the most
abundant spore of the black rust is the winter spore, hence its
common name. But it must be understood that the orange leaf
rust also produces winter spores, and that the stem rust
produces summer spores and that both have cluster cups.
The crown rust also produces three kinds of spores on its para-
sitic mycelium. The three rust species can be distinguished first
Minnesota Plant Diseases.
28'
by their life-histories and
second under the micro-
scope, chiefly by the shapes
of the winter spores and the
forms of the spore clusters.
The summer and winter
spores may arise from the
same mycelium. The winter
spores remain unchanged
throughout the winter and
in the spring under favor-
able conditions of moisture
and heat produce from each
cell a short thread or promy-
celium, which gives rise to
four little spores known as
sporidia. These sporidia are
borne by the wind to other
plants, where they germinate
and produce a parasitic my-
celium, from which arise the
cluster cups and pycnidia.
In the stem rust this clus-
ter-cup stage is formed on
barberry leaves, in the or-
ange leaf rust on certain
borages, as hounds-tongue
(in Europe), and in the
crown rust on the buck-
thorn (species of Rhamnus).
The last is very abund-
antly found in Minnesota
on the alder-leaved buck-
thorn (Rhamnus alnifolia).
These cluster cups are usual-
1v formed On the Under leaf- F|C- 13?.-\Vluat rust (I'uccinia graminist.
0 l Stem* ..f wheat showing opened and un-
surface of their host and are ^ SLS^iwS' **&£%&
formed on yellowish spots.
I
284
Minnesota Plant Diseases.
The leaf underneath the spots is abnormally increased in size
and distorted in shape. The pycnidia usually accompany
the cluster cups and come from the same mycelium1, but are gen-
erally to be found on the upper surface of the leaf. They are
probably male-cell receptacles which have lost their fertilizing-
power and are now functionless. They illustrate a persistence of
a habit after its usefulness has passed, a by no means uncommon
phenomenon in nature.
FIG. 140. — Stem rust of wheat (Puccinia graminis). A section of such a stem as is shown in
Fig. 139, highly magnified. Clusters of winter spores have broken through the skin
cells of the wheat stem. The skin cells of the wheat are seen as erect chains of cells,
which have been thrown back by the growing out of the winter spores. Such wounds
allow the water in the stems to escape since the skin cells of the wheat, which normally
prevent the escape of water, are broken. Thus the wheat plants are dried up as well
as starved by the drain of the parasite. Each winter spore of the fungus is seen to be
two-celled. Highly magnified. Microphotograph by E. W. D. Holway.
The cluster-cup is composed of a thin wall, enclosing an in-
ternal mass of orange red spores. The wall splits at the summit
and opens out often in star-shaped fashion. The spores are
formed in chains from the floor of the cup. The cluster-cup
spores are scattered, when mature, by the wind and alight on
some grass plant, where they germinate into a tube, which pene-
trates into the interior of the host through an air-pore, and forms
Minnesota Plant Diseases.
285
internally a mycelium. The latter, under the most favorable con-
ditions in about eight days, and under less favorable conditions
usually within two weeks, again produces the summer spores.
The life-history of a wheat
rust can therefore be divided into
three parts; first, the stage on the
grass or wheat plant, producing the
red (summer) and black (winter)
spores in succession; second, the
germination of the winter spores
and the production of sporidia on
the ground or in the straw in the
springtime: third, the germination
of the sporidia on barberry (or bor-
age, buckthorn, according to the
particular form of wheat rust), and
the subsequent formation from the
mycelium so produced, of cluster-
cups and pycnidial stages.
In seasons that are favorable
for the development of the rusts
whole crops may be completely
ruined ; but the danger does not end
here. Crops are often not so con-
siderably affected and may appear
but slightly rusted. The latter cases
are often lightly passed over as of
no account but such is not the case.
If the rust is present in any notice-
able amount it is safe to say that
the parasitic fungus is levying a tax
of nutrition and energy upon the
host or crop plant which results in
crops correspondingly lighter than
should Ije the case if no rust were present. Thai is t > say. the
nutrition which could normally be. expended in the formation of
more and heavier grains is required to nourish the parasitic rust.
The almost fabulous figures recorded each year as the loss to
farmers by rust is more often probably underestimated than ex-
. HI.— Oat Mem- and leaf l.ases
with clusters <>f summer spores
of the oat rust. The spots are
large and not sharply defined.
286
Minnesota Plant Diseases.
FIG. 142. — Spores of the common "black rust" (Puccinia
graminis) of wheat. 1. Cluster-cup spores from the
barberry plant. 2. Summer spores from the wheat
plant. 3. Winter spores from the wheat plant. Highly
magnified. After Arthur and Holway.
aggerated because the smaller losses due to the presence of the
rust in very slight and therefore unheeded quantities may never
be computed. These
are, nevertheless, a
certain loss. There
is only a difference
in degree. The en-
tire elimination of
rust would therefore
increase the value
of crops throughout
the country by an
enormous per cent.
At present there
is no known method
for successfully com-
bating wheat rust.
Numerous attempts
to fight the disease
by spraying with
bordeaux and other mixtures have always proved unsuccessful.
Where stem rust is the principal form and barberry bushes are
common, it has been found that the removal of barberry bushes
will diminish the rust considerably. In Minnesota, however,
very few barberry bushes are grown, and of these many are often
not infected with grass-rust cluster-cups, while the host plants
upon which the crown rust and orange leaf rust grow are very
common wild plants. The cluster cup of the orange leaf rust
forms on plants of the borage family, but no cluster cups have
yet been found on these plants in this state, so that either our
orange leaf rust differs from the European form or else it can
here dispense with the cluster-cup stage altogether. Little can
therefore be hoped from the removal of the cluster-cup host
plants. There is still another factor which would help to de-
feat such a method. In at least one of these rusts, the my-
celium which produces the summer spores may live through
the winter and produce summer spores again in the following
summer, thus dispensing with the necessity of the cluster-cup
stage. It is also possible that even in some forms, where the
Minnesota Plant Diseases.
287
mycelium does not hibernate, that the cluster-cups can also be
omitted without injury to the rust.
It is an important fact that some of the injurious rusts are
found upon wild grass plants and infection from cereals from
such sources must not be overlooked. The stem rust in par-
ticular is dangerous on this account. It has been shown that the
stem rust of wheat is able to infect a half dozen or more com-
Fie. H3. — Spore* of crown rust of
wheat ( 1'uccinia coronata'). w. Win-
ter spores, with a crown of finger-
like protuberances at the top of each
spore; from the wheat plant, s.
Summer «pores from the wheat
plant. c. Cluster-cup spores from
the alder-leaved buckthorn.' Highly
magnified. After Arthur and Hoi-
way.
mon wild grasses, including squirrel tail grass (Honleum
jubatum), and also that the rust from these can infect
wheat plants. This is a very discouraging feature, for it seems
almost impossible to eliminate all of these weeds. t'nless
this is done, however, the spread of stem rust cannot be pre-
vented. The stem rust moreover is the most virulent rust for
the spore specialty is the winter spore and this is found chiefly
on the stems, hence the common name of stem rust. In this posi-
288
Minnesota Plant Diseases.
lion the mycelium rapidly drains away the nourishment which
should go to the heads and allows of an uncontrollable evapora-
tion of water through the broken skins; as a result the berries
do not fill but remain shriveled. Such wheat therefore, even if
not entirely ruined, suffers a loss of grade.
FIG. 144. — Cluster-cups of the crown rust of wheat (Puccinia coronata), on swollen cushions
of the stem of the alder-leaved buckthorn. Photograph by Arthur and Holway.
It is also known that in states south of Minnesota the sum-
mer spores of grass rusts live through the winter and cause direct
infection of the grass plants in the spring. It is not impossible
that these spores from southern states can rapidly work their
way north in the early spring and commence the infection each
Minnesota Plant Diseases. 289
year. The rapidity of formation of successive crops of summer
spores would make this manner of spreading easily possible.
Eriksson, an eminent European specialist on rusts, has pro-
posed a theory known as the mycoplasm theory, which supposes
that the fungus threads live over in the grain of the wheat as
an amorphous substance, totally unlike the ordinary fungus
threads. This mycoplasm he supposes to be diffused amongst
the protoplasm of the cells of the grain, until the latter com-
mences to germinate, when it again assumes the form of threads
and causes an infection of the seedling wheat plant. We can-
not here go into the details of the evidence, but in the opinion
of a great majority of rust specialists this theory has not suffi-
cient foundation. Infection by the spore methods, described
above, is at present the only known method.
Recent work points to more probable success in combating
rusts along another line. It has been found that many of the
rusts are so closely adapted to the conditions found in the plants,
on which they occur, that they have great difficulty or fail en-
tirely in growing upon other varieties. At present there are
recognized, by the best authorities on the rusts of cereals, more
than a dozen distinct varieties and species. Many of these are
indistinguishable from other forms, as far as external characters
are concerned, even with the aid of powerful microscopes, but a
great difference is soon found when the spores are germinated
and infections attempted. It is then seen that some forms are
so especially adapted to the species or variety of the host plant,
upon which they occur, that they refuse to develop on other
varieties or s|>ecies of the same genus of host. Such rust forms
are called "biologic" species. On the other hand it will be seen
that some species and varieties of grasses and cereals may thus
be immune from some forms of rusts. A "rust-proof" variety
would not of course be proof against all forms of rust but might
be immune from certain forms. Consequently something bene-
ficial may be expected from the efforts of plant breeders in the
production of rust-proof cereals. With intelligent care in the
selection of cereal varieties and with a broader and letter knowl-
edge of the habits and life-history of the parasitic plants causing
rusts, it is very probable that the ravages of this disease can be
at least considerablv checked.
290
Minnesota Plant Diseases.
In the production of rust-proof varieties the selection of seed
becomes of great importance. Many farmers instinctively believe
that seed from rilsted fields will necessarily produce a rusted
crop. Such is not the case as can easily be seen by a perusal of
the above life-history of the rust. The rust does not live over
in the seed and seed from rusted fields have no more chance of
becoming rusted than that from fields that have had no rust,
provided, of course, that it is not shriveled or in other way dam-
FlG. 145. — Cluster-cups of the black or stem rust of wheat (Puccinia graminis). on stems
and leaves of Barberry. Photograph by Arthur and Ilohvay.
aged. In fact good seeds from rusted fields should be highly
prized for seeding purposes since they indicate that the plants
which bore them were probably rust-resistant. It would there-
fore be advisable to select seed from rusted fields, but such seed
must be carefully cleaned and graded so that only strong and
healthy berries are used. Of seed from regions free from rust
nothing definite can be predicted. The absence may be due to
rust-resistance or it mav be due to an absence of the fungus in
Minnesota Plant Diseases. 291
that locality. In the former case the seed would of course be
valuable, in the latter it might easily fall a prey to the first attack
of rust.
It must further be pointed out that the conditions in a given
community must be thoroughly known, i. e. the chief kind of
rust and the conditions favoring its spread, as alternate host-
plant, etc. The problem, therefore, may divide itself into special
sectional problems. Again any new rust-proof varieties may not
always remain so, for the rusts can vary and adapt themselves
to new hosts and may at some future time find a way to invade
the new rust-proof variety. It seems therefore that the problem
before us is not one to be dispensed with by one discovery, but
that it may involve a long series of breeding experiments — in
other words, a continuous fight. It seems furthermore reason-
able, when all evidence is weighed, to hope that in such a com-
bat the plant breeder will ultimately emerge victorious. (See
also Fig. 1 1 and Chapter XI.)
In view of the importance of wheat rusts, detailed accounts
may be of value, and are given below for the benefit of those
who may be especially interested in this subject and who may
wish to be able to determine the chief rusts in the field or
laboratory. The italicized portions point io distinguishing
differences. The crown rust occurs chiefly on oats, more rare-
ly on wheat. In can be recognized microscopically by the
crown of prejections at the end of the winter spores. (See
Fig. 143.) The two remaining are the important wheat rusts.
The orange leaf rust (commonly called "red rust"). The clus-
ter-cups are unknown in this country (except for a form on
Klynius with cluster-cup on Impatiens). The summer-spore-
clusters (so-called "red rust"): chiefly on the lower surface of
///c leaf blade, often abundant: occasionally on the leaf sheath;
small, oblong, up to i m. m. long, usually arranged in rows and
often running together forming long lines, orange-colored when
fresh. The summer spores (under the microscope): globose or
somewhat globose or broadly elliptical, finely spiny, orange-
colored. The winter-spore-clusters: accompany and follow
summer spores; on the leaf blade (seldom on (lie stem); arranged
in lines or scattered; oblong, dark brown or black; remain cohered
by the host epidermis for a long time. The winter spores: club-
shaped, rounded or truncate or conic at the apex, slightly con-
292 Minnesota Plant Diseases.
stricted near the middle, two-celled, brown, smooth, have a
short stalk or none; accompanied by sterile threads (paraphyses).
The stem rust (commonly called "black rust"). The cluster-
cup grows on barberry. The summer spore clusters : chiefly on
the leaf sheath, occasionally on the stem, seldom on the leaf blade,
scattered or in rows, elongated or linear, (2-3 m. m. long), often
running together to long lines ; bounded by the fissured epider-
mis of host, becoming powdery, brown when fresh, yellow when
dry. The summer spores : usually ellipsoidal or ovate oblong,
finely spiny, yellow brown (when fresh). The winter spore clus-
ters (so-called "black rust") : chiefly on the stem or on the leaf
sheath (less common on the leaf blade) ; scattered or in
rows, elongated, often running together into long lines, i. c. m.
or longer; soon exposed (naked) by the breaking of the host epi-
dermis, black and powdery. The winter spores : oblong or club-
shaped, two-celled, smooth, chestnut brown ; apex rounded or
long-conical and much thickened; base attenuate; have brown
stalks, often as long as the spore; no sterile threads.
Rust of corn (Puccinia sorghi ScJiw.). This very common
rust occurs on species of sorghum and on corn. The cluster-cup
stage has recently been discovered; summer and winter spores
are well known. The two latter spores occur in usually small,
sometimes considerably elongated, groups or sori of red- or red-
dish-brown color. The winter spores are two-celled. The clus-
ter-cup is found on a species of Oxalis. This rust is usually not
in sufficient abundance to cause any serious loss.
Clover leaf rust [Uromyces trifolii (Hedzv.) Lev.~\. The
clover rust occurs on several kinds of clover, notably on red and
white. Cluster-cups are formed, but not commonly, in the
spring, on the petioles and blades of the leaves, and summer and
winter spores are found later appearing as red and brownish
powdery spots, usually on the under surface of the leaf. The win-
ter spores are single-celled. The fungus thrives in damp cold sum-
mers and is usually not abundant or dangerous in the spring:
but it may increase during the summer, especially if conditions are
favorable. The early red clover crop is therefore usually unaf-
fected, but later crops may be damaged.
The plowing under of later crops when badly infected has
been recommended, as has also the burning over of the fields
to prevent a recurrence of the disease in the following season.
Minnesota Plant Diseases.
293
Loose smut of oats [Ustilago avcnae (Pers.) fens.]. This
exceedingly common and destructive disease is very well
known on account of the enormous damage which it yearly
causes to oat crops. In the
United States alone, losses of
many millions of dollars year-
ly, by oat smut, have been re-
corded. The application of Jen-
sen's Hot Water Method and
the formalin treatments have
in recent years greatly de-
creased the loss by this disease.
When an oat plant is at-
tacked, usually all of the heads,
and all of the grains in each
head, become smutted. Very
few if any grains escape in a
smutted plant and those that
do are always stunted. The
stamens of the flowers as well
as the ovaries arc attacked by
the fungus. The grain is con-
verted into a large sac with a
very thin membrane complete-
ly filled with the black spores
of the fungus. The smut
spores are blown about by the
wind before harvest time and
become attached to healthy
grains or fall on the ground.
In the following year when
the oat grain has commenced
to sprout, the fungus spores
a'so germinate. A spore in
germination first forms a very short chain of cells, which bud
off from their sides little secondary spores. These spores
sometimes fuse in twos, thus probably gaining in strength
by uniting forces. The spores either with or without fusion
may continue to bud off other spores when placed in favora-
ble nutritive conditions such as a culture medium. Thev
l-i «:. 14-..- I.,
294 Minnesota Plant Diseases.
are produced in yeast fashion. This is an important fea-
ture, for the fungus may thus continue vigorous in such
places as manures for an indefinite length of time. Any
of these spores, when placed under favorable conditions, can
send out a small germ tube which, when it comes into contact
with the seedling of an oat plant, will pierce the sheath of the
seedling and make its way to the little mound of growing tissue
at the tip of the stem. The fungus branches here freely and es-
tablishes itself, as a well developed mycelium, between the cells
of the host plant. There is no external mark by which such a
plant can be distinguished from a healthy one until the forma-
tion of the grain. The attacked plant appears perfectly normal.
The fungus in the growing point keeps pace with the latter in
its growth. The fungus threads disappear in the older tissues
so that the mycelium can usually only be found in the region of
the growing point. When the oat stem branches the fungus es-
tablishes itself in the growing point of the branch as well as in
the growing point of the main stem and this accounts for the
fact that usually all heads of an attacked plant are smutted.
When the head commences to form, the fungus invades every
flower and in the organs of the latter it forms its smut spores in
great abundance. It is not until this period that the fungus
comes into evidence. Every grain is thus attacked and filled
with the smut spore powder.
One well known method of prevention of oat smut is the hot
water treatment. This has in general been replaced in recent
years by the formalin method. Both of these treatments are de-
scribed under Steeps in Chapter XV. By both of them the
smut spores which cling to the grains are killed off, while the
grains themselves are not injured. Infection in oats is dependent
on the bringing together of germinating smut spores and seed-
ling oat plants, and the destruction of the smut spores attached
to the grain very considerably lessens the danger of infection,
as it is from these spores that infection generally takes place.
The smut spores also germinate most readily at about 50 degrees
Fahrenheit or about the out-of-doors spring temperature, and
their ability to germinate decreases with the rising temperature.
For this reason late sowing is sometimes recommended. This is
however entirely unnecessary when the above methods of pre-
vention are used.
Minnesota Plant Diseases. 295
Stinking smut of wheat [Tilletia tritici (Bjerk.) Wint.}. This
is a common smut-fungus of wheats and is well known to be
very destructive. The fungus gains entrance to the plant, when
the latter is still a seedling, and keeps pace with the growth of
its host, until flowering time. The mycelium then invades the
ovaries and replaces the contents of the latter with fungus
threads. These threads form an oily or greasy mass which is
later transformed into the smut powder. The smut spores are
blackish in color and have, in bulk, a very disagreeable odor,
which gives rise to the common name of the disease. The smut-
ted ovaries do not open until harvested. Smutted heads are
usually erect and can be detected in the field at harvest time.
The presence on smutted grains in quantity amongst the healthy
is a very serious damage as it unfits the crop for use as flour,
unless the smut is cleaned out by a special process. When
smutted grains are fed to animals the results are sometimes seri-
ous. Corn smut and other smuts of grasses are known to have
injurious effects upon animals. Horses, cattle, sheep and swine
may be affected. Xot much is known about the specific results
of poisoning from each kind of smut, so that confusion as to
symptoms exists. "As a result one generally finds a continuous
movement of the jaws, and a flow of saliva, also lameness, stag-
gering and falling." (Tubeuf and Smith, p. 306.)
The stinking smut of wheat difl'ers in its development very
radically from the smuts of the group to which the loose smut
of oats belongs. When the spore of the latter germinates a fine
tul)c is produced which is divided into a row of cells, each of
which buds off tiny, oval or spherical sjx>res from the side of
tube. In the stinking smut of wheat, the tu1>e of the germinating
smut spore is not divided into cells but forms its sjxires from the
end of the undivided tube. These secondary spores may fuse to-
gether in twos and from the fused cell, a third crop <>f spores may
be formed. Any of these secondary or tertiary spores are capable
of growing out into a fine tube; when it comes into contact with
a wheat seedling this tube penetrate;- into the tissues of the stem
and so begins its parasitic life. The life of such a smut can
therefore be divided into t\\\) stages: tir>t. the parasitic stage,
beginning with penetration of the infection tube and ending
with the formation of the smut spore powder: and second, the
296
Minnesota Plant Diseases.
saprophytic stage, beginning with the germination of the spore
and ending with the formation of an infection tube by the sec-
ondary and tertiary spores.
The secondary and tertiary spores, produced by the smut
spore, are capable of living in a nutrient solution or in fresh
manure, where they may form a saprophytic mycelium or may
continue to bud off more spores in a yeast-like fashion. They
may live thus for years, and when finally brought into contact
with the seedling plant, they may still cause infection.
FIG. 147. — Stinking smut of wheat. 1. A head of wheat with smutted grains (smutted
grains are colored black). 2. Small portion of a head showing smutted grains which
are fissured, and show the black spore mass within. 3. Isolated grains which are
smutted and have fissured walls. One grain is sectioned. 4. Smut spores germinated
and producing at the end of the germ tube long, needle-like spores, which sometimes
fuse together in pairs by cross-threads as shown on the left. 5. The thread spores,
shown in 4, in germination sometimes again producing secondary scores. 6. Smut
spores germinating to long infection threads without first forming spores. 4-6 highly
magnified. After Tubeuf.
The treatments used for loose smut of oats are also effective
against this disease. The Jensen hot water method (see chap-
ter on Prevention), has been found useful, but the most effective
and easiest method is the formalin treatment, which has practi-
cally supplanted the former. This smut can in practice be en-
tirely prevented by this method.
Minnesota Plant Diseases. 297
Loose smut of wheat [Ustilago tritici (Pers.) Jens.']. This
smut is also known as wheat brand. It is a destructive smut of
wheat and differs in many ways from the stinking smut. It can
be distinguished, botanically, by the behavior of its spores since
they develop at germination a chain of cells similar to the loose
smut of oats, instead of an undivided tube, as in stinking smut
of wheat. From this chain of cells are budded off the secondary
spores, which behave as do those of loose smut of oats. In other
characters, which are visible to the naked eye, this smut is well
marked off, from the stinking smut of wheat. The smut masses
are formed in the place of the grains, and may even supplant the
chaffy scales. This smut mass does not remain closed until har-
vest time, but opens at flowering and the spores are scattered by
the wind. At harvest time, therefore, only the bare stalks of the
wheat heads, with remnants of scales, remain on the plants. This
method of distribution gives rise to the common name of loose
smut. The spore mass is a dark, olive-green, dirty mass which
differs from the stinking smut in the absence of any fetid odor
such as the latter possesses.
No sure method of prevention is known. A modification of
the Jensen hot water process for loose smut of oats has given
some relief, but seems to injure the seed. The formalin method
is also uneffective. The only relief known at present is the selec-
tion of clean seed, which can only be done by obtaining the seed
fr< 'in a smut-free district. (See Fig. 72.)
Corn smut [Ustilago niaydis (DC.) Cda.]. The smut of corn
is a disease familiar to every farmer. It may attack almost any
part of the plant, but is particularly abundant upon the cobs,
staminate tassels and the leaves. When a cob of corn is attacked
a number of the grains become enormously enlarged and are
covered with a thin, whitish-grey membrane. The whole cob
may thus be enlarged to twice its natural size. The interior of
the affected grains is filled with a blackish to dark green pow-
der of smut spores. When a leaf is attacked, tumor-like swell-
ings are produced, which often become as large as an apple and
this tumor contains the blackish spore-powder. Upon the
staminate tassels, smaller tumors are formed which are of a
similar structure to those of the leaf. The smut spores rest
through the winter. In the spring they germinate, producing
298
Minnesota Plant Diseases.
small tubes which bear secondary spores in great abundance;
these spores are capable of yeast-like budding when brought
under favorable conditions, e. g., in piles of manure ; in this
manner the infecting ability of the disease is greatly increased.
These secondary spores are conveyed by the wind or other
agency to other plants and infection follows. Only young
parts of the plants can be successfully attacked. The disease is
only local in its effects, and in
this character it differs very de-
cidedly from such smuts as loose
smut of oats and stinking smut
of wheat. The part most fre-
quently attacked is the cob and
the harvest is often seriously
diminished by this disease. Cer-
tain varieties of sweet corn are
peculiarly susceptible to attack,
so that a selection of varieties is
often advisable.
Treatment of seed corn with
copper sulphate or formalin has
absolutely no effect on this smut.
If the disease has been bad in
the preceding year, fresh manure
should be avoided, as the multi-
plication of the spores is in-
creased by its use. All smut tu-
mors and spore masses must be
burned as soon as discovered.
Bordeaux spray has been found
successful to a certain extent,
but usually is unnecessary if the
spore masses are carefully removed.
Head smut of sorghum \Sphacelotheca rciliana (KuJui.) Clin-
ton]. This smut attacks the whole head of the sorghum plant
and often all of the heads of a plant. The smut mass therefore
replaces the entire head and is at first surrounded by a fine
white membrane, which later ruptures and exposes the smut
powder. Grains, glumes and all parts of the head are de-
FIG. 148.— Smut of corn (Ustilago may-
dis), on left, on the leaf of the corn;
on the right, in the tassels (stami-
nate inflorescence). After Clinton.
Minnesota Plant Diseases.
299
stroyed and only the loose strings of the woody tissues of the
head branches remain. The head smut can be distinguished
from the grain-smut by this habit. The smut mass forms a
blackish powder.
No preventives are known for this smut. It is possible that
the treatment for grain
smut will be effective.
Grain smut of sorghum
[Sphacelothcca sorglri (Lk.)
C lint o ;»]. This sorghum
smut attacks the young
grains and forms smut
masses in them, but does
not destroy the glumes.
The smutted grains increase
in size, chiefly in length,
and have a whitish wall
which encloses a mass com-
posed entirely of spores.
The spores rest over winter
and under proper condi-
tions, in the spring time,
form more spores, which
can in turn multiply in
yeast-like fashion; the re-
sulting spores are capable
of causing infection.
Sorghum is also fre-
quently attacked by other
smuts and certain varieties
of the sorghum are known
to be peculiarly susceptible
to smut. (See also Head
Smut of Sorghum.)
A few experiments on
this sinut have indicated
that lit it water treatment
may be beneficial. It ha> proved successful in the treatment of
the same smut on broom corn. It is also possible that the for-
malin method would be effective and useful.
'•
14!*.-- C'orn smut < 1'stil.iK" mnydis). on an
tar of corn. A few of the kernels near the
luitt have not b-.-en smutted. All of the
others have been attacked and have in-
creased enormously in size. The enl irged
kernels are fillid with the smut powder.
< Irini'ial.
300 Minnesota Plant Diseases.
Broom corn smut [S phacelotheca sorghi (Lk.) Clinton}.
This is the same fungus that causes 'the grain smut of sorghum.
When it attacks the broom corn, it seriously affects the forma-
tion of the brushes and the smut often discolors them. The
young grains and stamens may become smutted and usually all
of the grains of a cluster are destroyed. The spore mass is very
dark and the spores have an olive-colored tint. The host plant
is apparently infected only in the seedling stages and hence care
must be taken to avoid the presence of spores in a seed mixture.
Seed broom-corn should be treated in hot water in the usual
way at a temperature of 135 degrees Fahrenheit for ten to fifteen
minutes. Such treatment of seed will largely if not entirely pre-
vent the smut. It is probable that the formalin method would
also be effective.
Naked barley smut [Uslilago nuda (Jens.) Kcll. and Sw.].
The naked smut is more common than the covered smut of bar-
ley and also more difficult to combat. This smut attacks the
grains and forms smutted heads, which do not, however, remain
closed as long as do those of the covered smut. The smut
masses are at first enclosed in a membrane, but the spores do
not adhere so closely and when the membrane of the head breaks
the smut spores are quickly dispersed by the wind. The heads
of barley have then the appearance o-f wheat affected by loose
smut. The awns of the barley head are either only stunted or
may remain intact. The powdery spore mass is dark and black,
with a greenish tinge, differing in this respect from the covered
smut of barley. The exact method of infection of the host plant
is unknown but there seems to be some evidence that it is not
in the seedling stage.
"Soak the barley seed four hours in cold water and then let
it stand four hours longer in a wet sack. Finally dip and drain
as directed in the treatment for oat smut for five minutes in wa-
ter at a temperature of 126 to 128 degrees Fahrenheit, after
which dry and plant as in case of smut of oats." (Kansas Ex.
Sta. Rep. for 1889, p. 284.) This treatment is also ample for
the covered smut.
Covered smut of barley [Ustilago hordci (Pers.) Kell. and
Sit'.]. This is one of the two common smuts which attack the
barley plant. The smut spores are formed in the very young
Minnesora Plant Diseases.
301
302
Minnesota Plant Diseases.
Minnesota Plant Diseases. 303
grains, but are not scattered immediately after ripening. They
are enclosed in a membrane which includes the scales around
the grains. Not all of the interior of the spikelet is converted
into spores, but plates arid shreds of material remain, which are
not smutted. The spores are therefore held firmly together and
the smut is thus known as the covered barley smut. The spores
are black when seen in mass and have no greenish tinge. On ac-
count of the compactness of the smut heads, the disease does
not spread with very great rapidity. It is not known whether
the spores infect the seedling barley as in oat smut or cause in-
fection later, as in the corn smut.
The hot water method and the copper sulphate steep have
both been recommended. The treatment used for the naked bar-
ley smut is said to be effective against the covered smut. The
formalin method would probably be of use.
Brome smut (Ustilago bromivora Fisch.). Brome plants are
subject to smut attacks and the spore masses are formed in the
young grain. The heads of grains do not show any abnormal
growth. The spore mass is usually black.
Millet smut (Ustilugo craincri Korn.). A smut attacks millet
plants and is sometimes abundant. At flowering time, the fun-
gus replaces the ovaries with black masses of the smut spores.
All of the heads of the attacked plants are smutted. The spores
germinate in the usual way, forming a small tube from which,
however, secondary spores are not usually, if ever, produced.
Care should be taken to use clean seed free from smut. The
hot water method has been found to be an effective preventive.
Leaf smut of rye [L'rocystis occnlta. (ll'allr.) Rub.]. This
fungus attacks several cereals but is most frequent on rye. It
has not been rejx)rted as very frequent in this country and it is
probably not at all abundant in this state. It is unlike most of
our common smuts in many of its characters. The spores are
formed in elongated lines on the leaves and stem, which are at
first greyish but later, after the bursting of the epidermis, exhibit
a black powdery smut-mass underneath. The whole plant is de-
formed and injured. The spores are aggregated together into
true spore-balls. About a half-do/en sjxires cling together into
a solid mass, in which a differentiation of lnlx>r is evident. The
outer sjxires have lost their power of germinating and act as a
304
Minnesota Plant Diseases,
protective covering to the central spores, which have retained
their germinating power. Thus the functional spores obtain an
additional protection by means of the surrounding layer of sterile
spores. There are usually two or three functional spores in
each spore mass. Upon ger-
mination the spores produce
a tube from which secondary
spores are formed in the man-
ner usual for smuts. Jensen's
hot water method has been
recommended when the fun-
gus appears in abundance.
Formalin would probably
prove useful.
Powdery mildew of grasses
(ErysipJie graminis DC.). The
cereal grasses are sometimes
seriously damaged by the at-
tacks of this disease. A fine
whitish mycelium is formed
on the leaves in the summer
time. The myce'ium threads
derive their nourishment from
the skin cells of the host by
short sucker branches sent in-
to these cells. These sucker
branches are known as haus-
toria. Summer spores are
produced in large numbers
and rapidly carry the disease
from leaf to leaf and plant to
^
plant. I llCSC SpOTCS are
spherical OF egg-Shaped Cells
microscopically small ; they
are formed in chains which stand upright, often over the
whole upper surface of the leaf. Toward fall the sacs with their
spores are formed in sac-capsules. As is usual in powdery mil-
dews, the capsules appear as small black spheres about the size
of a pin point. In the earlier stages these capsules are whitish
FIG. 152. — Powdery mildew of grasses (Ery-
siphe graminis), on wild Rrnssolant
leaves. The white coat of the fungus
mycelium is very conspicuous. Original.
Minnesota Plant Diseases.
305
and as they mature, change to yellowish, then brown, and finally
to a dark brown or black. The capsule is provided with thread-
like appendages, which are dark brown in co'or and un-
branched, and are interwoven with the threads of the mycelium.
The mycelium sometimes forms brown spots on the leaves,
and if present in quantity, may very seriously interfere with the
nutrition of the leaf of the host plant and thereby occasion con-
siderable damage. Each capsule contains a number of egg-
shaped sacs, each of which contains about eight spores. The
spores are capable of growth, after a rest period, when placed
under proper conditions, e. g., out of doors in spring. \Yhen
germinating, a tube is sent out. which penetrates the epidermis
of the host. By a further growth and branching of this tube
the mvcelium is established.
Fie. 153. — "Itlack mold" of clover (Pbyllachora trifolii), on leaves of white clover. Original.
By the use of flowers of sulphur the spread and growth
of the disease can be prevented to some extent. Infected
plants should, however, be destroyed every year to get rid of the
sac-capsules. The disease is not often abundant enough to be
very troublesome.
"Black mold" of clover [I'liyHudiora trifolii (/'.) I'ckl.].
This is a very common fungus in Minnesota growing abundantly
on white and also on red clover. The summer stage is conspic-
uous, forming blackish spots on the leaves. The summer spores
306 Minnesota Plant Diseases.
are borne on the ends of "beaded threads and are two-celled. The
spore-sac capsules are borne in a blackish cake of mycelium,
somewhat similar in appearance to the tar-spot of willows. The
fungus is also known on the scarlet clover (Trifolium incarna-
tum). It is sometimes known as the black mold of clover.
Smothering fungus of grasses [Epichloc typhina (P.) Tul.].
This disease is also known as the Reed Mace Fungus. It is found
on grasses and is apparently confined to a few genera. It some-
times causes injury to fodder grasses. The fungus attacks the
above-ground portion of the grass and forms white or light tan-
colored cushions of mycelium around the leaves and stem of the
host. These cushions are so dense that they prevent further
growth of the leaves and stem, causing, as it were, strangulation.
From this cushion -arise first, small colorless spores on short
stalks. These are the summer spores, comparable to those of
the powdery mildews. Toward fall the sac-spore-capsules are
developed. They arise in great numbers, embedded in the outer
part of the cushion and are of the same color as the cushion.
They are long and pear-shaped, and open to the surface by
means of a pore at the end of a slightly protruding neck. In
each capsule a large number of sacs are produced in a group,
on the floor of the capsule cavity, and each sac contains eight
spores. The spores are very long and thread-like and are di-
vided into many cells, arranged in a chain. When ripe, the
spores may break up into segments, each of which is capable
of germination, producing a mycelium and causing infection.
The fungus, when occurring in great abundance on fodder
grasses, is said to be injurious to the feeding horses. It sel-
dom becomes a serious pest. (See Figs. 57 and 58.)
The ergot disease of grasses [Clcii'iccps purpurca (Fr.) Tul.
and other spccics\ The ergots of grasses are very closely related
to the smothering fungus of the same plants. The ergot fun-
gus attacks the very young and immature grains and the my-
celium soon permeates the tissues of the grain. It replaces the
latter entirely and forms in its stead a dense mycelium which
soon becomes so densely interwoven that it forms a solid body
of characteristic form and of doughy consistency. The outer
surface of this body is at first thrown into folds and ridges and
along these folds one finds the summer spores produced in
Minnesota Plant Diseases.
great numbers. These spores are small, oval, or cylindrical,
colorless cells. Their production is accompanied by the secre-
tion of a sugary fluid' known as "honey dew." which is at-
tractive to insects. The latter in their search for the "honey
dew" distribute the summer spores from plant to plant and
rapidly spread the disease. Toward the end of the summer,
the formation of summer spores ceases and the underlying fun-
gus mass becomes more compact and hard, and the external
threads form several layers of
cells which contain a very
dark purple coloring matter.
This fungus mass is now
known as the sclerotium and
is the ergot of commerce.
The form of the ergot varies
in the different grasses. The
ergot of rye (commercial er
got) is long and cylindrical
and slightly curved. The er-
got of wheat is much shorter
and thicker, while the ergot
of wild rice is still shorter and
roughly egg-shaped The er-
got is a storage organ and
usually rests through the win-
ter. The storage material is
a kind of starch, known as
fungus starch, which is stored
up in the eel's. The fungus
threads are so compacted to-
gether that they form a mass
of cells very similar in appear
ance to that of the pith of some flowering plants. The ergot
rests in or on the ground, where it is often sown with the grain,
until early summer. I'nder the proper conditions of moisture
it then deve'ops further. From the surface of the ergot arise
several short, violet-colored stalks, which bear at their tips yel-
lowish spherical heads. The latter are the spore-sac-capsule
cushions, as may be seen by the small protruding necks of the
I' ic. 154. — The «rt!»t f minus (Claviccps pur-
I'linii). on rye. Tlir lar^c IUIIKII* (tor-
HKC organ < sclcrntium or er^ot • is seen
near the toil of the h.-ail. After Clinton.
io8
Minnesota Plant Diseases.
ric. 15o. — Storage organs or ergots of ergot fungi on various grasses. 1. Commercial ergot
from rye. 2. On canary grass. 3. On wild rice. 4. On quack grass. 5. On a reed
grass (Calamagrostis). The size and shape of the grass grains can be seen in each
case, except in the rye. Original.
Minnesota Plant Diseases. 309
capsules with their pore-like openings. The arrangement of
the capsules is similar to that in the smothering fungus, except
that the cushion is spherical in shape. In the capsules are nu-
merous sacs, each containing eight spores. The latter are very
long and thread-like and are many times divided by cross walls
and each division is capable of the formation of a mycelium.
The flowers of the grass plant are again infected by these spore-
segments from the sacs.
The storage-body or sclerotium is widely used medicinally
and is known as the ergot of rye. In the grains of the latter it
is very commonly found. These ergots sometimes attain a
length of one and 'one-half inches. The presence of ergot
amongst grains from which flour is made may give rise, among
the consumers of the bread, to a disease known as ergotism.
Cattle fed with grains containing ergots in considerable amounts
may also be severely poisoned. Numerous cases of such poi-
sonings in our northwestern states have been reported.
Chronic effects, from long-continued small doses, can be distin-
guished from acute attacks. The shape of the sclerotium varies
with the grain, upon which it is formed. Ergots grow on many
of our very common wild grasses and are sometimes here even
more conspicuous than on the cereal grasses.
The only preventive means for ergot lie in the destruction of
all sclerotia and in the planting of clean seeds, i. e., seeds free
from an admixture of ergots.
Leaf spot of alfalfa [Pscmiopczizu mcdicaginis (Lib.) Sacc.].
This small cup fungus causes yellowish spots upon the leaves.
In the center of each spot are seen the tiny black fruiting bod-
ies. These are cups of such minute size that they can be clearly
seen only with the aid of the hand lens. The disease is some-
times serious, and in Iowa has at times caused a loss of one-
half of the crop. Frequent cutting keeps down the disease by
preventing the maturing of the fruiting bodies and thus pre-
venting infection. The spores mature in early summer, proba-
bly in June. Diseased plants may be cut when the disease first
appears.
Cup-fungus leaf-spot of clover (IJsemiof>csica trifolii l-ckl.}.
This fungus occasions local epidemics among clover and lu-
cerne crops. It is one of the cup fungi but the cup is so minute
310 Minnesota Plant Diseases.
that, like the cup of the leaf-spot fungus of alfalfa, it can only
be seen clearly with the aid of a hand lens. It appears on
a leaf in small spots where the mycelium establishes itself.
These spots become thickened and from the center of each
the cup uncovers by the splitting out of the upper part so that
a star-shaped opening is produced and the layer of sacs is ex-
posed. Each sac contains eight spores. The spots may be-
come so numerous that the whole leaf or even the whole
plant is destroyed. The fungus may spread with great rapid-
ity. Burning of the fields in fall has been recommended to
prevent the reappearance of the fungus in the following year.
Frequent cuttings also tend to prevent the spread of the dis-
ease.
Wheat scab (Fnsarium culmorum W . G. Sin ). The fungus
of wheat scab is an imperfect fungus. It attacks the grains of
the wheat just before ripening and causes the heads to ripen
prematurely. The heads may be entirely or only partially de-
stroyed. Affected parts turn whitish or are bleached. The
effects often travel from above downward in the head. The
mycelium runs over and through the spikelets and glues them
together. A gelatinous material is formed by the fungus
threads and this causes the glueing together of the spikelets.
The heads turn pinkish in color and the grains shrink. The
losses from this disease have at times been very serious.
Poor drainage is said to increase the amount of scab. It
has also been reported that strong plants will resist the scab
more successfully than weak ones. No remedy for scab is at
present known.
Flax wilt (Fnsarium lini Bollcy). Flax all over the world
is subject to a disease known as wilt. Whenever flax is raised
continuously on the same ground for a number of years it sick-
ens, and it soon becomes impossible to raise the plant success-
fully. This fact has been known for a long time in Europe and
rotation of crops has long been practiced there to prevent the
disease. The wilting is due to a fungus parasite which attacks
the roots and stems of the flax plants in all stages. So virulent
does the disease become that after six years of continuous cul-
ture of flax on one plat of ground it has been found impossible
to raise one plant longer than three weeks. The following ac-
Minnesota Plant Diseases. 311
count is taken from a bulletin of the North Dakota Ag. Ex. Sta.
by H. L. Bolley, who first discovered the true cause of the dis-
ease.
"The plants are attacked at all ages and die early or late in
the stage of growth according to the time and intensity of the
attack. If the soil is much affected, that is to say "flax sick,"
most of the plants are killed before they get through the surface
of the ground. Such areas appear in a field of fiax as centers
of disease, which enlarge throughout the summer as new plants
sicken, wilt, and die down around the margins of the spots,
finally giving the whole field a spotted appearance. Young
plants two to five inches in height wilt suddenly, dry up, and
soon decay if the weather becomes moist. Older plants which
are quite woody take on a sickly, weak, yellowish appearance,
wilt at the top, slowly die. turn brown, and dry up. Nearly
mature plants which are attacked, but not yet dead, are easily
pulled up, the roots breaking off easily at about the level of
the furrow s'ice."
_;.. '
lie. 156.— Flax wilt. Wilted sccdlinus. Alter Rollcy.
"Upon examination, most of the smaller branch roots are
found to be dead, as well as the tap root below the point at
which it breaks off. These dead roots and the parts of the tap
root already diseased have a very characteristic ashen gray
color. Many nearly mature plants, which are attacked late in
life, show this dead gray down one side of tin- tap root only.
The leaves, side branches, and a strip of the main stem above
this portion are dead, giving a peculiar one-sided blighting,
similar to the appearance of a tree struck by lightning."
"If the disease is sowed with the seed upon breaking, but a
few of the plants are attacked the first year: and. at flowering
time, dead plants will be seen to be quite evenly distributed in
312
Minnesota Plant Diseases.
the drills. If weather conditions are quite favorable, each new
infection increases sufficiently in area to reach over and attack
plants in two or three adjacent drills. These infection areas are
nearly always circu1ar in outline, and become much enlarged if
flax is seeded there the following year. The first year these
spots may reach a diameter
of one to three or four feet.
The second year these same
areas are usually . much
more than doubled, so that
it takes but three to five
flax crops upon such lands
to make the infection gen-
eral."
Diseased fields have not
lost their fertility, as was
formerly supposed, but can
produce good crops of
other plants, as corn, wheat, potatoes, etc. The d'sease seems
to thrive on strongly alkaline lands and often under conditions
of drouth.
FIG. 157.— Spoi PK of the flax wilt fungus high-
ly magnified.. After Bolley.
FIG. 158. — Flax wilt. The wilt fungus threads around the root of an at-
tacked flax plant. Highly magnified. After Bolley.
The fungus is an imperfect fungus and lives normally as a
saprophyte but becomes on occasion a destructive parasite. The
fungus threads live in the tissues of the flax plant root, coming
to the surface of the root to produce its spores. The latter are
formed in a loose weft arrangement. The ordinary spore is
Minnesota Plant Diseases.
313
long spindle-shaped, consisting of a string of cells. Thick-
walled spores are also produced, consisting of several cells, and
are capable of resting over in the soil for some time before ger-
minating. The chief method of distribution of the fungus is by
means of the spores which cling to the seeds of the flax.
Flax seed should therefore be treated before seeding to de-
stroy the fungus spores clinging to the coats.
Professor Bolley has recommended the following treatment
and preventive measures:
"Use formaldehyde at the rate of one pound of the standard
strength to forty or forty-five gallons of water (the same
strength used for wheat and oats). Spread the seed upon a
tight floor or upon a canvas and sprinkle or spray on a small
amount of liquid (a fine spray is best). Shovel, hoe, or rake the
grain over rapidly. Repeat this spraying, shoveling, hoeing or
raking until the surfaces of all of the seeds are just evenly moist,
not wet enough to mat or gum,
but evenly damp. (This can be
done without matting if the grain
is well hoed or shoveled over
while the solution is slowly and
evenly sprayed upon it.) When
the seeds are just evenly moist,
cease applying the solution, but
continue to shovel the grain over
so as to get it dry as soon as
possible. Avoid any excess of
moisture. If flax seeds are dip-
ped in the solution or are al-
lowed to get enough to soften
the seed coats so that they will stick together, they will be con-
siderably injured or even killed.
"It takes less than one-half gallon of the solution to properly
moisten one bushel of flax seed.
"Caution: One must treat flax with much more care than
that usually taken in treating wheat or oats for smut. The
solution recommended is strong enough to kill all seeds, if they
arc made thoroughly wet. or if they are allowed to stay quite
damp for some hours.
Fir.. 159.— Flax wilt. A »ection of a flax
root with fungus thread* and spores
at the surface. Magnified. After
Bolley.
3 14 Minnesota Plant Diseases.
"The grain must be handled over immediately after treat-
ment until it is found to be dry.
"Note : The seed should be thoroughly cleaned by running
through a fanning mill before it is treated because the solution
is not strong enough to kill the disease (fungus) which is inside
of bits of straw and chaff.
"After treating, it may be well to sow two or three quarts
more per acre, as some of the weaker seeds are apt
to be killed. Scaly flax seed and seed which has been
wet is always very poor for seed. Such seeds harbor the
spores of fungi which kill the young plants as soon as the
seeds germinate. Cease sowing flax year after year upon the
same land. Put at least one cultivated crop and two or more
other crops between flax crops. Burn as much of the old
straw and stubble which remains upon the ground as pos-
sible. Raise your own flax seed, grade it up to the best.
Watch for disease areas and notify the station. Thresh your
seed, when you can, in your own machine from a patch of
strong healthy flax and store it in a clean bin. Keep all the
flax straw out of the barnyard, unless it is intended to put all
manures through a several years' composting process. I can-
not say that this process will be successful in destroying the
fungus. It is destructive to most weed seeds and to the spores
of many fungi. Avoid the evil effects of deep planting. Much
damage is done to the flax crop of the state by too deep plant-
ing. The flax wilt disease does more injury to the seedlings
when the seed is placed deep in loose soil than when planted
shallow. One-half inch to three-fourths inch is the best depth.
The seed bed should be of even texture and quite compact."
Downy mildew of clovers (Peronospora trifoliontin DC
Bary). This parasite attacks clovers and its relatives, such as
lucerne, etc. The summer spores form on thread branches,
similar to those of the downy mildew of mustards and the win-
ter spores are also similar to the latter. Summer spore patches
are pinkish grey and are found on the stems, leaves and peti-
oles. Diseased plants should be destroyed to prevent the oc-
currence of the disease in the following year.
Sorghum blight (Bacillus sorghi Burr}. This is a bacterial
disease of sorghum plants. It appears on the leaves as reddish
Minnesota Plant Diseases. 315
spots which are usually elongated to narrow lines. Later they
increase to large irregular spots and may then entirely destroy
the leaves. Both the .sheaths and blades of the leaves are af-
fected. The roots are also attacked and it is possible that the
bacterium lives over unfavorable seasons in the soil. The bac-
terium is usually not found in the stems except in the wounded
portions. It is probably found in Minnesota though not yet
reported.
Land upon which diseased plants have been grown should
not be sown to sorghum for a year or two. All diseased plants
should be burned.
Chapter XIX.
Diseases of Garden Crops.
Orange- or red-rust of raspberries and blackberries [Gym-
noconia interstitialis (Scilicet.) Leigh.]. This rust is chiefly known
on account of the destruction occasioned by the cluster-cup
stages, on the
raspberries,
blackberries and
their allies. The
cluster-cup stage
differs from that
of most of our
common rusts by
the absence of a
cluster-cup wall,
so that the chains
of spores are
spread out on the
surface of the
leaves. These
spores are pro-
duced in great
numbers in early
summer and iate
spring and form
what is common-
ly known as the
orange rust. The
FIG. li!0.— Orange rust of raspberry and blackberry; to the . , • r»rr»r1iir»p>rl
right on a leaf of wild blackberry; to the left a normal
unattackcd leaflet. Original. on tne lmder Slir-
face of the leaf, and wild and cultivated raspberries, dew-
berries and blackberries suffer. The spores fall in a dense
orange powder. From golden orange, the lower surface of
Minnesota Plant Diseases. 317
the leaf gradually becomes lighter yellow. The sum-
mer and winter spores are not so conspicuous and occur on the
same host. The fungus threads live permanently in the rasp-
berry tissues, so that the destruction of the whole infected
plants is necessary.
All diseased plants should be dug out and burned. Spray-
ing with bordeaux has been suggested to hold the spread of the
disease in check.
The cluster-cup rust of gooseberry and currant (Accidium
grossitlariac Schum.). The fungus causing this disease is exceed-
ingly abundant on wild gooseberries and currants throughout
the state and is also known on cultivated forms. Serious dam-
age, however, is seldom reported. The fungus is a rust fungus
and is known at present only in its cluster-cup stage. This is
found on the leaves of the host plant and the cups are always
found on bright, orange-yellow, swollen spots of the leaf. The
cups stand on the lower surface and when they open, release
the golden-orange powder of spores, which may earn- the infec-
tion to other plants. The cups are accompanied by very
minute pear-shaped capsules, containing spores on the upper
surface of the yellow leaf-spots. The openings of these can be
seen with the naked eye as small black dots on the upper sur-
face of the leaf. These spores do not assist in spreading the
disease. It is not known where the summer and winter spores
are formed. They probably occur on some species of sedge.
In our lack of knowledge of the complete life history of the
disease, the only suggested remedy has been the destruction of
diseased parts of the plant.
Mint rust (Pnccinia mcntluic Pcrs.). Mint rust is very
abundant on a great many of our wild and cultivated mints. It
is said to be very destructive to the latter, where these are cul-
tivated on a large scale. The summer and winter spores are
most abundant and form small, dark-brown, powdery patches,
chiefly on the leaves. These patches, or sori. often occur in such
profusion that they completely cover the under surface of the
leaves. The cluster-cups are formed, as usual, in the spring or
early summer and are of less frequent occurrence. They occur
on the same plants. The mycelium passes the winter in the
underground stems of the host. The cluster-cup stage has
Minnesota Plant Diseases.
been reported from a greenhouse in this state where it de-
stroyed almost an entire winter crop of mint.
The complete destruction of all diseased plants and espe-
cially all subterranean portions is necessary. (Fig. 209.)
Asparagus rust (Puccinia asparagi DC.). Of recent years
this rust of asparagus has become of great importance in the
eastern states and in California and will undoubtedly soon be of
equal importance in this state. In parts of eastern states aspar-
agus culture in whole districts has been ruined by this parasite.
The cluster-cup stage is produced on the asparagus plants in the
spring but is usually
not conspicuously
abundant. After
the crops have been
harvested, the sum-
mer spores appear as
brown;sh spots on
the stems of the
host plant. The
winter s pore s are
produced later in
long, black streaks
upon the stem. The
rapid spread of the
fungus and the tax
Of the mycelium On FlG i(n,_\Yjntcr Slrrcs of the asiaragus rust. Highly
the nutrition Of the magnified. Alicropholograph by E. W. D. Holway.
host, greatly enfeeb'es the plant and the crop of the following
season is seriously affected. If no combative measures are
used, the fungus gains strength year by year and soon enforces
the abandonment of asparagus culture. The winter spores are
two-celled and gernr'nate in the usual way in the following
spring. Several fungus parasites on the rust plant are known
but they do not apparently exercise sufficient destructive in-
fluence to be of assistance to the agriculturalist.
This is a very serious disease and difficult to combat. It is
first of all necessary to remove all badly diseased plants and
to burn all infected plant remains in the fall. In badly diseased
districts this method will not alone suffice. Moreover, early
Minnesota Plant Diseases.
cutting and burning, injures the asparagus. Ordinary bor-
deaux mixtures have been tried but with little success. Resin
bordeaux is recommended by the New York Agricultural Ex-
periment Station where the rust has been successfully treated
with this mixture. The application with ordinary barrel pumps
is too laborious and slow, so that it was found necessary to de-
vise a special sprayer, the plans and description of which are
published in the bulletins of that station. (See N. Y. Ex. Sta.
Bull. No. 1 88.) Sulphur has very recently been shown to be
quite successful in keeping down the disease in California.
Bean rust [Uromyccs a^cndiculahis (P.) Link.]. This is not
usually one of the most serious of bean diseases, but may in
some localities become a dan-
gerous pest. It attacks chief-
ly the common garden bean,
but has also been reported on
other beans. All three spore
forms occur on the same host
plant. The cluster-cups are
yellowish and appear in the
late spring. The summer and
winter spores appear later in
small pustules, about the si/e
of a pinhead. These pustules
are light- to dark-red-brown
and appear chiefly on the leaf-
blades but can also be found
on the petioles, stems and
FlC. 162. — Rust of bran. Winter »;>ore clus , , >.•>.
icrs on the lower surface of a bean leaf. eVCIl Oil tllC pods 1 IlC pUS-
After Clinton. . , • , . t •
lines are circular in outline
and the spore masses of summer and winter spores are powdery.
The winter-spore pustules are dark-brown and may finally be-
come blackish in color. The winter spores are single celled
and germinate in the usual method for rust winter spores.
Certain varieties of bean resist the rust and such shou'd be
planted. Infected plants should be destroyed by burning.
Bordeaux mixture has also been suggested as a means of ho'd-
ing the disease in check, but is not in general use
^2O Minnesota Plant Diseases.
O
Onion smut (Urocystis cepulae Frost.}. This is a leaf -smut
and is due to a fungus somewhat similar to that of the rye
smut. The smut masses appear in lines on the foliage leaves
and may later appear on the scale leaves of the bulb. The spores
are aggregated into true spore-balls, of which the outer spores
are sterile and incapable of germination, while the inner are fer-
tile and well protected by the outer ones. The infection of the
host plant takes place in- the seedling stage.
Diseased plants should be destroyed. Care should be taken
not to plant seed in smut-infected soil, since the smut spores re-
tain their power of germination for many years. Care should
also be taken to prevent the transference of smutted plants or
smut-infected soil from one bed to another. When seeding in
infected soil, "apply in the drills per acre one hundred pounds
of sulphur thoroughly mixecl with fifty pounds of air-slacked
lime. Formalin (one pound to thirty gallons water) thorough-
ly sprinkled over the seed before covered with the soil, or ap-
plied by drip attachment to the seeder, is an efficient remedy.
Ground lime, drilled in the land with a fertilizer drill, at the rate
of 75 to 125 bushels per acre, is helpful in keeping the trouble in
check." (Conn. Ag. Ex. Sta. Bull. No. 142 — 1903.)
The currant pore-fungus rot [Fames ribis (Schum.) Fr.].
This disease of currant bushes is probably not common but has
been observed in this state. The fungus mycelium is parasitic
in the root of the currant, producing its fruiting bodies at the
surface of the ground, particularly around the base of the stem.
The affected portions of the root-tissue turn black and the
roots, and subsequently the remainder of the currant bushes,
are finally killed. The fruiting bodies are dark-yellow-brown,
woody, thin, saucer-shaped shelves and live from year to year.
The pores are small and line the under surface of the fruiting
body. The latter are sometimes six inches in diameter. It is
said also to attack gooseberry bushes.
All fruiting bodies and infected plant-parts should be re-
moved and burned as soon as discovered.
The sclerotium disease of cucumbers and other garden plants
(Sclerotinia libertiana Fckl.}. The fungus cause of this disease
is a sac fungus with a peculiar life history. When the sac
spores germinate at the surface of the soil they produce a my-
Minnesota Plant Diseases.
FIG. KI.-1'ori- -fuiijms r.-.t r,.t ..f curr:i!il ( lu.ms rit>i-). show ing shelf
at the base of the cam-s of an attacked currant plant. <>MKinaI.
322 Minnesota Plant Diseases,
celium, which feeds in a saprophytic manner upon vegetable
debris in the soil. After the mycelium has been strengthened
by this saprophytic life it is able to infect living plants. The
cucumber seems to suffer considerably but a large assembly of
other plants are also subject to the attack of either this or closely
allied species of fungi. The mycelium attacks the stem just
above the ground and the stem at this point is covered with a
fine white mold. The fungus proceeds rapidly up the stem and
the latter soon falls and dies. The mycelium now continues to
live in the dead tissues and builds up storage organs known as
sclerotia. These are small, dark, compact masses of fungus
threads in which a great amount of storage material such as
fungus starch is deposited. This sclerotium lives through the
winter in the dead stem and, in the spring time, produces a
cluster of cup-fungus fruiting bodies with long stalks. The in-
ner surface of the cup is lined with a palisade of sacs, each con-
taining eight spores.
The fungus may also attack stored roots and bulbs such as
dahlias, turnips and beets and has been known to cause consid-
erable damage. Growing lettuce is also subject to attack and
the resulting disease is commonly known as drop from the rapid
collapse of the host plant. In this common disease the sum-
mer spores of the fungus are produced. All diseased plant
parts should be collected and burned. It has been recommend-
ed that lime be sprinkled on the soil to kill off the saprophytic
mycelium from which the infection takes place. The use of
fresh manure should be avoided where the disease has once
been found. Sterilizing of the soil has also proven successful in
controlling the sclerotium disease of lettuce.
Drop of lettuce (Sclerotinia libertiana Fckl.}. See Diseases of
Greenhouse and Ornamental Plants.
Red knot of currants [Ncclria cinnabarina (Todc.} Fr.]. This
is not an uncommon disease in Minnesota. It attacks chiefly
the currant and often causes the death of the canes. The fruit-
ing bodies appear on the dead canes as small red buttons or
cushions which break through the bark of the cane. In an at-
tacked plant the foliage wilts and the fruit colors prematurely.
The fruit clusters of the currant are smaller than normal and
the berries fall off early. Sometimes only the central canes of
Minnesota Plant Diseases. 323
the bush are killed off. The fungus fruiting cushions at first
bear colorless spores, which are pinched off of threads on the
top of the cushion in great numbers. The spore sacs are
formed in the fall and arise in pear-shaped capsules. The latter
are formed as protuberances from the summit of the button and
have an apical opening, through which the spores are forced
out. The mycelium is perennial in the cane and can be trans-
ferred by cuttings. An infected bush may thus be a constant
source of infection. Cuttings from plants should therefore be
selected from bushes free from the disease. Infection from
spores probably takes place only through wounded canes.
Wounding of canes should therefore be avoided as far as possi-
ble. Diseased plants should be immediately and completely
rooted out and destroyed.
Strawberry leaf-blight [Sphacrclla fragariac (Tnl.) Suic.].
This disease is a very common one in the state and attacks cer-
tain varieties more vigorously than others. It appears on the
leaves and the first indication is a spotting of the leaf. The
spots are circular and purple in color. As they increase in size
the center of each spot becomes whitish and the edge remains
purple. On the whitish area appear in early summer minute
tufts of fungus threads, which constrict oil countless summer
spores of exceedingly small size. By means of these the fungus
disease may be carried to other plants. The spots are often so
numerous that they run together and cover such a considerable
portion of the leaf that the latter is rendered useless for starch-
making purposes. On the same white spot, later in the season
or in the fall after the leaf has fallen, the winter or sac spore is
formed. The sacs arc produced in very minute, spherical cap-
sules which protrude from the spot as tiny black points. They
open to the exterior by means of small apertures through which
the spores escape. The release of the spores is delayed until
the following spring, so that infection by the sac-spore myce-
lium does not take place until that time.
To check the spread of the fungus spraying with bordeaux
has proved beneficial and several applications should be made.
The plants should be sprayed just as the leaves unfold, again
after the petals fall, and once or twice after the fruit has been
picked. Where the disease is serious, a removal of the plants
324 Minnesota Plant Diseases
has been recommended, or the plants may be mowed in the fall,
removed and burned. Good results have also been obtained
by burning over the bed with the aid of a layer of straw. The
selection of varieties will also assist in the combating- of the dis-
ease, as certain varieties are much more susceptible than others.
(Fig- 35-)
Powdery mildew of strawberry (Sphaerotheca castagnei
Lev.}. This disease has not been reported from many localities
in the United States but seems to give promise of becoming a
destructive disease under favorable conditions. The leaves and
fruit are attacked though the former usually suffers most. On
the under surface of the leaf the fungus forms the characteristic
superficial mildew of this group of fungi and when the summer
spores are formed the powdery appearance is noticeable.
The leaves curl up and may finally dry up. The winter
spores appear in sacs borne in the receptacles (sac capsules)
usual for this group of fungi. The exact identity of the form is
not known but it is probably a close relative of the powdery
mildew of hops.
Powdered sulphur is usually recommended, or spraying with
ammoniacal copper carbonate.
Powdery mildew of cucumbers (ErysiphecichoracearumDC.*).
This disease has been reported as destructive to cucumbers,
especially those grown in greenhouses. It is a typical powdery
mildew and appears to be identical with the exceedingly com-
mon powdery mildew of composites, which appears so abun-
dantly on a great variety of our wild plants. The mycelium ap-
pears on the leaves or stems of the cucumber as small white
spots, which soon produce the mealy powder of summer spores.
The spread of the infection may be rapid and the infected spots
increase in size, becoming yellow and then brown, and may final-
ly destroy the whole leaf or even the entire plant. The winter
spores are formed in sacs, found in small black capsules, com-
mon in the powdery mildews. A large number of sacs is
formed in the capsule and the appendages of the latter are sim-
ple and interwoven with the mycelium. When the capsules are
formed, the mycelium has become a greyish or dirty white coat
on the leaf surface.
Minnesota Plant Diseases. 325
Sulphur dusting, spraying with ammoniacal copper carbon-
ate, have all given good results. The ground should not be
allowed to become infested with the resting spores (winter
spores), hence the diseased plant parts should be burned.
Powdery mildew of gooseberry [S pliacrothcca mors-uvae
(Schu'cin.} B. & C.]. Gooseberries are not infrequently attacked
by this destructive disease. The leaves, fruits and shoots are
coated with a fine whitish mycelium. Summer and sac spores
are produced as is usual in the true powdery mildews, and the
sac capsule is in general like that of the rose mildew, though dif-
fering, of course, in minor details.
There is another powdery mildew (Microsphaera grossu-
lariae) which is known to occur on the gooseberry though not
as commonly as that described above. It can be distinguished
by the many-times forked appendages on the sac-capsule and
by the large number of sacs in each capsule.
"Spray with potassium sulphide as soon as buds break mid
repeat about every ten days until end of June." (Conn. Ag.
Ex. Sta. Bull. 142 — 1903.)
Powdery mildew of \\ops(Sphacrotlh\-u castagnci /.<v.). This
is perhaps identical with the strawberry-leaf powdery mildew,
or a biologic form of this species. The mycelium of hop mil-
dew, like that of rose mildew, is superficial and forms a whit'sh
coat on the surface of leaves of hops. It also inhabits mem-
bers of the rose, composite and other families. The fungus
threads send sucker branches into the epidermal cells withdraw-
ing from the latter their nourishment. The sac-capsules are
similar also to those of rose mildew. Summer spores are also
similarly produced in chains. Where hops is raised in abund-
ance the mildew may cause very serious damage.
Bordeaux or ammoniacal copper carbonate can be used as
a spray.
Powdery mildew or blight of roses [Spluicrothccu punnosa
(ll'allr.) Lev.]. See Diseases of Greenhouse and Ornamental
Plants. (See Figs. 203 and 204.)
Powdery mildew of vetch and crowfoot [Iirysipltc com-
tinoiis iU'iillr.) /•>.]. This is sometimes found on cultivated
plants of the pea family. See Diseases of Wild Plants.
(26
Minnesota Plant Diseases.
Potato scab (Oospora scabies Thaxt.). Potato scab is an ex-
ceedingly common disease of potatoes. The cause has been
the subject of some dispute among botanists but it is now gen-
erally accepted that the common form of potato scab in Amer-
ica is due to a parasitic fungus while the European scab has a
very different cause. The American potato-scab fungus be-
longs to the group of "imperfect" fungi and is found amongst
the white, loose-spored forms. Scabby potatoes when freshly
removed from the soil show a very delicate moldy coating, in
which the loose spore-bearing threads are found. The surface
of an attacked potato becomes roughened and scabby, hence
the common name of the
disease. The fungus can
remain in the soil for sev-
eral years and badly in-
fested fields should not
be sown to potatoes.
Since the fungus is a
lurking parasite and
gains entrance through
the potato skin, it has
been found that a treat-
ment of the "seed" pota-
toes will kill off the scab
fungus. Immersion in a
solution of one pound of
corrosive sublimate to
fifty gallons of water for
one and one-half hours
will free the potatoes from scab providing other precautionary
measures are taken. After treatment, the potatoes must be
kept free from the disease. They must not, for example, be
brought into contact with other diseased potatoes or must not
be planted in soil which is badly infested with the scab. A
formalin solution may also be used as a steep. This solution is
made up of one pound of formalin to thirty gallons of water,
and the "seed" potatoes are immersed for about two hours.
The corrosive sublimate solution is very poisonous ; potatoes
treated by the first method must therefore never be fed to stock.
FIG. 164. Potato scab. After Clinton.
Minnesota Plant Diseases. 327
Scab of beet. See Potato Scab.
Anthracnose of currant and gooseberry [Gloeosporium ribis
(Lib.) Mont, ct Dcsm.]. This disease is well known in Minne-
sota. The fungus appears on the upper surface of the leaf in
very minute black spots which are cushions of fungus threads.
These are formed under the epidermis and then burst through,
finally producing spores on the surface of the cushion. The
fungus is therefore one of the cushion-forming "imperfect"
fungi. The spores cling together in gelatinous masses. When
the spots are very abundant the leaf turns pale and falls. The
whole bush may thus be deprived of its foliage and in conse-
quence may be seriously injured. The fruit on such bushes is
usually inferior and the crop for the following year may also be
damaged. Treatment with bordeaux has been recommended,
as follows: "First spraying with bordeaux before leaves ap-
pear, the second as the leaves are unfolding, and repeat at in-
tervals of ten to fourteen days until the fruit begins to turn."
(Conn. Ex. Sta. Bull. 142 — 1903.)
Bean anthracnose [Collctotrichitm lindcmuthiannm (Sacc. ct
Magn.} Bri. ct Car.']. Beans are very frequently attacked by an-
thracnose. The fungus causing this disease is an imperfect
fungus belonging to the cushion-forming group. It attacks
the pods and also the leaves but is more commonly found on
the former. Blackish spots are formed with purplish edges
and these spots enlarge, and when abundant may cover a large
part of the pod. The tissue under the spot is sunken so that
the fungus-thread cushions, which are formed in the center of
the spot, are at the bottom of small sunken areas. These cush-
ions bear numerous upright threads, from which spores are
pinched off. and between these threads arise sterile, sharp-
pointed, dark, spine-like threads, which bristle from the top of
the cushion in a formidable manner.
Spraying with bordeaux has been recommended and should
commence when the plants are small. They should be made
at intervals of a few weeks until the pods are ripening. Damp
situations should be avoided and all badly diseased plants
should be destroyed. The disease can be carried along
with the seed so that it is necessary to avoid seed from infected
pods. Care must also be taken to avoid planting beans in badly
infected fields.
328
Minnesota Plant Diseases.
The leaf blight of celery (Ccrcospora apii Fr.). The fungus
causing this disease is a loose
spored, imperfect fungus. It
causes the formation of red-
dish to brownish spots on the
leaves, which may spread and
increase in size until the leaf is
seriously injured. The fungus
thrives well on plants in dry
situations and is particularly
effective against young plants.
When badly affected the leaf
turns yellow and finally brown.
Spots may also appear on the
stem. The spores arise from
upright fungus-threads in the
center of the spot and are ar-
ranged in a fine, loose, mold-
like growth. Shade and moist
situations have been recom-
mended, but are only partially
successful. Spraying will also
keep the fungus in check.
The spraying should com-
mence early and bordeaux may be used at first but the arnmo-
niacal copper carbonate is used in the later sprayings.
The leaf spot of beets (Ccrcospora bcticola Sacc.). This is a
common spot disease on the leaves of the beet. The cause of
the disease is a loose-spored imperfect fungus. It forms small
circular spots on the leaves, often in great abundance. The
spots have a purple border and whitish centers, where the
loosely arranged threads bearing the spores are found.
Spraying with bordeaux mixture has been recommended.
Frequent applications should be made throughout the growing
season.
Black rot of tomato (Macrosporinm tomato Cooke). Tlrs
fungus attacks chiefly the fruits but is also found on the leaves
and stems. It is probably identical with the fungus of early
potato blight. It forms on the fruit circular spots, under which
FIG. 165. — Anthracnose of bean. After Hal-
sted.
Minnesota Plant Diseases. 329
the tissues soften and become discolored. The fungus threads
form black, velvety masses in the center of the spot and these
masses increase rapidly in size until large mold-like patches are
produced. The dark spores are pinched off of the threads
which are formed in a loose arrangement on the surface of the
fruit. This parasite is a sac fungus of the black fungus group
but the sac spores are very uncommon.
Bordeaux mixture has proved successful in combating this
disease. The first treatment should be given when the flower
buds open and should be repeated at intervals of two weeks.
Early blight of potatoes (Macrosporhtm solani Ell. ct Mart.}.
This disease is easily mistaken for the ordinary or "late blight,"
but has an entirely different cause. It affects early crops and
is in general found early in the season. The general symptoms
are those of premature ripening of the plants. The leaves turn
yellow toward the edge, curl up and finally become dark
brown. The entire plant is weakened and may die early, giving
the appearance of early ripening. The fungus is similar if not
identical with black rot of tomatoes.
Vigorous plants are said to withstand the attack, so that
careful cultivation has been recommended. Bordeaux mixture
applied early in the season is also an effective preventive.
The sterile-fungus rot of garden plants (Species of Rhicoc-
toniu). All kinds of garden plants are affected by a rot which
attacks the roots or lower stem and which frequently causes the
death of a great many plants. The classification of this fungus
cannot at present be determined, since it has never been found
to produce spores. It is therefore called a sterile fungus, though
it is of course possible that spores are formed under unusual and
rare conditions. The fungus produces tufts of threads on the
infected parts of the host plant. These thread tufts are usually
brown or blackish. The threads are brown and branch irreg-
ularly in forking fashion and often break up into lengths
which may germinate in the fashion of spores, but these lengths
are not considered real spores. The following list will show
some though not all of the plants attacked by this fungus
in the United States: bean. beet, carrot, celery, cabbage, cauli-
flower, lettuce, potato, radish, rhubarb, ornamental asparagus,
china aster, sweet william. coreopsis, and violet. In many cases
330 Minnesota Plant Diseases.
this fungus can be shown to be truly parasitic but in others is
doubtfully so. It is usually capable of unlimited growth in a
saprophytic manner.
The elimination of unfavorable conditions of temperature
and moisture are recommended. Freshly decaying vegetable
matter should be removed. The soil may be limed as an aid
but is not an absolute preventive. A complete sterilization of
the soil should entirely prevent the disease.
Grey mold of lettuce. See Diseases of Greenhouse and Or-
namental Plants.
White rust of mustards, cabbage, etc. [Albugo candidus (P.)
Ktzc.]. This is one of the most widely distributed fungi known.
It occurs on all kinds of plants belonging to the mustard family
on both wild and cultivated forms. It is most commonly found
on the wayside weed known as shepherd's purse, but is also
found on many other wild mustards. Amongst cultivated
plants the following are frequently infected : radishes, horse-
radish, cress, cabbage, turnip, water-cress and wall flower.
Plants closely related to the mustard, e. g., caper plants, are
also known to become infected.
The fungus attacks the plants in the seedling stage through
the seed leaves. The mycelium very frequently causes abnormal
and distorted growths in the host plant and in these regions the
summer spores are formed. These are produced in extensive
patches which at first have a porcelain-like appearance. Later,
by the bursting of the superficial tissue of the host plant, the
spores are set free as a white powder, hence the name white rust.
The spores are formed in chains and the spore powder is blown
by the wind to other plants. The spores require moist con-
ditions for germination, and under these conditions break up
into tiny swimming spores which scatter the infection by mov-
ing about in the drops of water on the leaf. When they come
to rest they germinate into a tube which infects the leaf. The
winter spores are formed as a result of a breeding act between
two swollen organs formed on the fungus threads and are pro-
vided with a thick coat. They are produced within, the tissues
of the host and are set free in the following spring by the de-
cay of the tissues. These winter spores produce swimming
spores in a similar manner to the summer spores.
Minnesota Plant Diseases. 331
This is not usually of serious importance to crops in this
state. Diseased plants should be destroyed.
Downy mildew of mustards, cabbage, etc. [Peronospora para-
sitica (P.) DcB\J\. This 'disease usually accompanies the white
rust of the same plants. It is found in general upon the same
plants as white rust and often causes deformations of the host.
The summer spores are produced on filmy patches of a downy
nature and can thus be distinguished from the white rust.
They are not produced in chains but in clusters on much-
branched threads, which protrude from the leaf of the host
and give the downy appearance to the infected regions. The
winter spores, which are similar in appearance to those of white
rust, do not, however, produce swimming spores, but germinate
into an infection tube.
For preventives see \Yhite Rust of Mustards, etc.
The downy mildew of potato. Potato blight [Phytophthora
infesttins (Mont.) DcR\.]. This disease has proved an exceed-
ingly destructive one both in the United States and in Europe.
It was first known in the United States between 1840 and 1845
and was introduced into Europe about 1845. It probably
came originally from South America, where it grows on many
wild p'ants of the potato family. Shortly after its introduction
into Europe, it caused complete failure of the potato crop in
many districts. In America it causes most damage in the
eastern states and is apparently not so destructive in Minne-
sota, though by no means unknown in this state. It may
sometimes be found growing on close relatives such as tomato
and other members of this family. The parasite has the typical
habit of the downy mildews and hence grows best in moist
seasons or in low-lying, damp situations. The mycelium is de-
structively parasitic and as soon as it is established in the
leaves of the host plant causes a diseased condition. The first
indication is the appearance of brownish spots, which rapidly
grow darker and finally become blackish. The discoloration is
often accompanied by a crumpling of the leaves. The diseased
leaves finally suffer complete decay and produce an offensive
odor.
The lower surface of the leaf-spots is seen to have a very
delicate downv coat, which increases to a white band around
332
Minnesota Plant Diseases.
the border of the spot. Here are produced the spores, which
are formed in a manner peculiar to the potato blight and its
close relatives. The method of spore formation serves to dis-
tinguish these forms from the downy mildew of vines and
other downy mildews. The spore-producing threads pinch off
spores from their apices and then the thread grows past the
spore, shoving the latter to one side. It grows on for a short
distance and then produces another spore apically. The
threads show somewhat pointed ends. They are, moreover,
K:c. 166. — Potato blight. Early stages of the blight on the leaves. After Clinton.
usually much branched, so that a miniature bush-like structure
is produced and each branch terminates in a spore. These
spores, as is true for most of the downy mildews, are in reality
spore cases, for when placed in water they later give rise to a
large number of swimming spores. When the latter come to
rest they germinate into a tube which causes infection of the
host plant. As far as is known at present, no winter spores
are produced. The mycelium, however, is capable of living in
the above ground stems and in the tubers of the potato, and
may live in the latter over winter, producing a brown rot of
the tubers. In the following spring they can again cause in-
fection by growing up into the stem and leaves. It is there-
Minnesota Plant Diseases.
Fie. 167. — Potato blight. Later stages on the
leaves. After Clinton.
fore unsafe to use for seed
potatoes tubers harvested
from an infected crop.
"Spray with bordeaux
before the trouble appears,
about July /th to loth, and
keep vines well covered, es-
pecially from the middle of
July to the middle of Au-
gust. Unless season is
very moist three sprayings
should suffice. If this
treatment is impossible
plant early varieties only."
(Conn. Ex. Sta. Bull. 142—
I903-)
It has been claimed by
various authors that the bordeaux spray not only destroys the
parasite but improves the foliage of the potato as well. Dis-
eased plants and tubers should be burned. \Vet soil should be
avoided, if possible, for infection can take place in the tubers in
spring as well as in the leaf. Thick-skinned potatoes have
been recommended as more resistant to the fungus than thin-
skinned ones so that, for storage in particular, these varieties
should be selected. (See also Fig. 39.)
Downy mildew of onion ( P cronospora schlcidcni Ung.). The
mildew of onions has long been known in Europe where it is
much feared. It has now become established in many places
in the L'nited States and has appeared in abundance in Wiscon-
sin. The fungus, like the other downy mildews, produces sum-
mer and winter spores. The former arc produced on the leaves
upon threads in a manner similar to that in the grape mildew.
They give to the leaf a grey to green, moldy appearance and
the leaf-gloss appears to be lost. The spores in moist condi-
tions produce swimming spores, but are very sensitive to. and
easily destroyed by, drying. The winter spores are provided
with a thick protective coat. They are very resistant and in
the spring following their formation produce swimming spores
in a manner common to the downy mildews. The fungus is
334 Minnesota Plant Diseases.
very common upon plants raised on previously infected land
and in such cases infection is almost certain. The disease
spreads rapidly and may cause great damage in a single season.
Infected plants should be destroyed to prevent future infec-
tions. When a field is badly infected, as when infected plants
are left on the field, the rotation of crops becomes necessary.
Spraying with bordeaux has given satisfactory results in com-
bating this disease. In some cases this has proved injurious to
the foliage when used in standard strength. There is also diffi-
culty in making the bordeaux adhere to the very glossy surface
of the onion leaf. Powdered quicklime (two parts) and sul-
phur (one part) has been recommended for checking the dis-
ease in the early stages. Spraying with potassium sulphide is
also effective. Of chief importance are the avoidance of too
damp conditions and too much shade, the removal of infected
plant parts and the rotation of crops, if necessary.
Downy mildew of cucumber, melon and other gourds [Plas-
mopara cubensis (B. & C.) Humpf.]. This has proven in certain
parts of the United States to be an exceedingly virulent disease
and has threatened to completely destroy the pickle crops in
those districts. It is not as yet known to be common in Min-
nesota, but it will probably appear here in time and the farmer
who is employed in the growing of cucumbers of other gourd
fruits will do well to know the disease and to keep a sharp look-
out for it. It is known to attack cucumbers, muskmelons,
pumpkins, warty and winter squash, watermelons and various
other gourd fruits. Unlike the powdery mildew of the cu-
cumber, it is more common in fields and gardens than in green-
houses, but it is not unknown under the latter conditions. It
is in many places the chief enemy of cucumber culture. An
important feature lies in the fact that it can spread from one
host to another.
The disease is best recognized by the action upon the
foliage, though it is by no means confined to the leaves,
but may occur on the stem as well. Infected leaves turn
yellow in spots and these yellow spots are bounded by the veins
of the leaves and are therefore usually four-sided and angular.
They are up to a quarter of an inch across, but by joining with
neighboring spots may become much larger. The spots in-
Minnesota Plant Diseases.
335
crease in size and number with great rapidity until the whole
leaf finally becomes yellow, then dries up and shrivels. The
oldest leaves, i. e., those nearest the hill, are usually first affect-
ed and then the disease travels toward the tip of the host plant
with great speed. The spread of the disease is particularly fa-
vored by hot weather and by a damp atmosphere. The yield of
cucumbers is quickly affected, because the whole plant is rapidly
weakened or may be entirely destroyed. On the older plants
IK.. 168. — Downy miKlcw uf tmigkntrlon. Illightrd vine in ih
After Clinton.
one finds on close examination a fine down, sometimes of a pur-
plish tinge, covering the under side of the leaf. This is caused
by the fungus threads, which bear the summer spores. The
latter are produced in a similar manner to those of the downy
mildew of grapes and are carried by the wind to other leaves
and plants. Here they form a large number of swimming
spores, which further scatter the infection under proper comli-
toins of moisture. The swimming spores germinate into infec-
tion tubes, and thus establish a mycelium within the leaf. This
fungus has not been known to produce winter spores. — prob-
ably does, however, under rare conditions. The method of
wintering over is therefore at present unknown. It undoubt-
edly does, nevertheless, pass the winter safely, as has been
shown by the experience of cucumber growers in many places.
336 Minnesota Plant Diseases.
"Repeated sprayings with bordeaux about every ten days
during a season, beginning at least by the middle of July, is
useful in keeping this disease in check." The number of spray-
ings is dependent on the season. In very wet seasons more
may be necessary. If the under surfaces of the leaf can be
sprayed, the results will be most successful, but great gain is
possible by the ordinary method of spraying.
Downy mildew of beans, peas, etc. (Phytophthora phaseoli
Thaxt.}. A downy mildew frequently attacks cultivated beans
and closely related plants and may create a very serious amount
FIG. 1G9. — Downy mildew of muskmelon, showing the under surface of an attacked leaf.
After Clinton.
of damage. The summer spores are produced in a similar man-
ner to the blight of potatoes. The young stems, leaves and
pods are attacked. The downy patches on the pods are usually
dense, woolly growths, whitish in color, while those on the
stems and leaves are less dense. As with most downy mildews,
moist seasons or moist situations favor the growth of the dis-
ease.
Diseased plants should be burned to prevent the recurrence
in following seasons. "As the fungus usually appears first and
most vigorously in low. moist places, the land used should be
high or well-drained. Spraying, beginning with bordeaux and
Minnesota Plant Diseases.
337
ending with ammoniacal solution of copper carbonate and re-
peated every ten to fourteen days from the last of June until the
first part of September, is helpful in keeping this trouble in
check." (Conn. Ex. Sta. Bull. 142—1903.)
This disease is known in eastern states but has not been re-
ported from Minnesota.
He. 17l>. — Uowny mildew of muskmrlor. I'ndcr surfscr i>f an attacked leaf. After 1". C".
Stewart.
Downy mildew of lettuce (#rrj///<; luctncac Kcgcl.). Ix'ttuce
in gardens and particularly in greenhouses is attacked by a
downy mildew. The spore patches form filmy, grey, mold-like
growths on the lower surfaces of the leaves. The spores are
borne on much branched thread < which terminate in four or
five short stalks arising from the rim of a saucer-like expansion.
At the ends of these stalks the spores are produced. The fungus
Minnesota Plant Diseases.
FlG. 171. — Downy mildew of melons and cucumbers. 1. A spore-bearing thread; sp. young
spores; 2, 2' and 2", mature spores of the ordinary form. 3. Spore-bearing thread
emerging from an air-pore on a leaf. 4. A cluster of spore-bearing threads taken from
a cucumber leaf in dry weather, t, unusual types of spore-bearing threads and spores.
6. A short stalked spore from a muskmelon leaf. 7. Cells of a cucumber leaf with the
fungus mycelium between them; sucker threads h, h' and h". 8. An unusual type of
spore from the cucumber. 9. A very large pear-shaped spore of unusual occurrence.
Highly magnified. 7. After Humphrey; all of the others after F. C. Stewart.
Minnesota Plant Diseases. 339
thrives best in a moist atmosphere and damp situations, hence
is often luxuriant in greenhouses. Infected plants are stunted
and turn pale yellowish in color.
"This disease is kept in check by subirrigation or care in
watering and ventilating to keep plants and atmosphere as free
from moisture as is consistent with good growth." (Conn. Ex.
Sta. Bull. 142 — 1903.) It has been recommended that infected
frames and houses be abandoned for lettuce culture at least for a
time.
The downy mildew of beets (Pcronospora schachtii Fckl.).
This disease may prove a serious pest in the raising of beets.
The fungus attacks chiefly the inner leaves and in seedling
plants may cause the death of the plant. The spore patches
are on the under sides of the inner leaves and are greyish, mold-
like patches. The fungus threads are said to be able to live
through the winter in the roots.
The infected plants should be burned. Rotation of crops
has been recommended in order to give the mycelium in the
roots a chance to die out.
The downy mildew of spinach |"P<*r<ww/»oni cffnsa ((7r«v.)
Rabh.]. Spinach and the other plants of the goosefoot family
are frequently attacked by a downy mildew which may cause
serious damage. It is also found on wild plants of the same
family. The mold patches of summer spores are found on the
lower surface of the leaf and are greyish lilac in color. The
winter spores are similar to those of downy mildew of clover.
The diseased plant should be burned to prevent the spread
of the disease and its recurrence in the following year.
Downy mildew of clovers. See Diseases of Field and Forage
Crops.
Downy mildew of violet (Peronospora z'iolac 7V#y. ). See
Diseases of Greenhouse and Ornamental Plains.
Damping-off of seedlings (Pytliinin dt'lniryiinuin IIcssc.).
See Diseases of Greenhouse and Ornamental Plants.
The seedling disease of cabbages [Olpiiiiitin brassicacdl'or.)
Hang.']. This disease is probably m>t serious in Minnesota. It
attacks seedling cabbages and causes a dropping of the plant
by the death of the stem. The fungus belongs to a very low or-
der of algal fungi and consists of a single cell which invades the
340
Minnesota Plant Diseases.
host plant, living in one cell of the host. When it forms spores
it develops a long tube, which reaches to the surface of the host
plant and throws out spores, which are provided with swimming
lashes and by means of these swim in raindrops or in the dew.
The swimming spores come to rest and invade the same or
other plants. A thick-coated, resting winter-spore is produced
inside of the host and this may carry the plant over to the fol-
lowing year. Diseased plants should therefore be burned and
cabbages should not be planted in beds in which the disease
has been serious. As the fungus is a water-loving plant, the
seed beds should be well ventilated and kept as dry as possible.
Too moist atmospheres should be avoided.
Wet rot of potato
(Species of Bacillus).
Wet rot is a well known
bacterial disease. The
bacteria enter the potato
throng h wounds or
through the ventilating
holes in the skin (cork),
and when once inside,
they commence the de-
struction of the contents
of the tuber. Large cav-
ities appear in the tuber
containing a fluid mass,
with the potato starch
grains still intact. The
tuber soon becomes soft
and the entire center is
filled with a putrescent
mass, from which the
common name of wet rot
is derived. This- fluid mass is at first acid, on account of the
formation of carbonic acid gas, and the acid of rancid butter.
When, later, the decomposition has proceeded still further, am-
monia gas and other complex organic compounds are formed
which eive to it an alkaline reaction.
Fie. 172. — Bacterial rot of potato. After Clinton.
Minnesota Plant Diseases. 34 1
Rotation of crops has been suggested to prevent a recur-
rence of the disease.
Wilt of cucurbits (Bacillus trachciphilus Sm.). Squash,
muskmelons, cucumbers and their relatives are attacked. The
existence of this disease has not yet been reported from Min-
nesota but is well known in eastern states. The disease is
caused by bacteria which gain entrance chiefly through wounds
in the stem or leaf. These wounds are often caused by insects.
The bacteria immediately seek out the water-conducting tis-
sues and settle there in such great numbers that the flow of
I'ic. 173. — llacirriil wilt <>f •> |ua»lt. Af:i r Clintin.
water is impeded. The result is a wilting of the plants and
death usually follows. This disease is of interest, in that it
shows an unhealthy condition in the host plant, induced not
by a directly destructive action of the disease-causing organ-
ism, but by the interference with the normal life processes of
the plant, i. e.. the obstruction of the water-conduction current.
The sprays which are used for downy mildew and nnthrac-
nose of cucurbits will prevent this disease. Rotation of crops
342 Minnesota Plant Diseases.
has also been recommended but is an uncertain aid and is
doubtfully of use.
Bean leaf b\ight(Pseudomonas phaseoli Smith). This disease
is of bacterial origin. It has not been reported from Minne-
sota but is well known in the eastern United States. It causes
a brown tipping of the leaves or dead spots in the leaf. The
entire leaf may die. Bean insects, irrigation and mulching are
said to have a tendency to increase the disease and certain vari-
eties are more susceptible than others.
Black rot of cabbage (Pseudomonas campestris Smith). This
is a bacterial disease and causes a rotting of the plant. Cab-
bage and a large number of related plants are affected. The
FIG. 174.— P>lack rot of cabbage. A badly infested field. After H. L. Russell.
following list of plants has been reported as sufferers from this
rot : cauliflower, kohl rabi, kale, brnssel sprouts, broccoli, col-
lards, turnips, rutabagas, winter radish and still others. Ruta-
bagas and their allies are not so commonly nor so severely at-
tacked as the cabbage group.
The effect of the disease is first seen at the edge of the
leaf. The lower leaves are most commonly invaded but all of
the leaves of a head may be attacked at once. The bacteria
work downward along the veins of the leaf to the stem of the
plant. The invaded veins turn black. From the stem the bac-
teria spread outward again with great rapidity. The attacked
Minnesota Plant Diseases.
343
Fie. 175. Black rot of cabbage. Artificial infection of cabbage plants. The plants in the
center (2), and on the right (1), were inoculated six weeks previously with bacteria.
The plant on the left (3) was not inoculated and is therefore unaffected. After H. L.
Russell.
leaves wilt, turn yellow and finally dry up, when
they become somewhat papery in appearance.
The disease may appear in stored cabbage in
which the heads may be entirely destroyed.
Other rots assist in transfornrng the diseased
heads into a rotting, bad smelling mass. Cab-
bage for storage should therefore be carefully
inspected and where any blackened veins in the
leaves show should be rejected. The bacterium
gains entrance either through wounds or
through the water-pores at the edge of the leaf,
weather assists in the spread of the disease.
Refuse matter should be removed from the field. Rotation
of crops will assist in ridding, in part at least, the soil of the
disease. I.ow. damp soils should be avoided and if irrigation :s
practiced reduction of moisture will prevent the formation of
water drops at the water-pores on the leaves, and thus reduce
the number of chances of infection. Diseased plants can read-
ily be detected by breaking off the lower leaves and examining
the stalk. If the fibres of the leaf-stalk are blackened, the plant
is diseased and should be rooted out and entire! v destroved.
FIG. 17«.-lt I a ck
rut <)f l.lhli.lLT.
Bacteria highly
magnified. After
H. L. KMXS.-II.
Rainv. moist
344
Minnesota Plant Diseases.
Allowing these plants to remain on the field only increases the
danger. It has been found possible and profitable to attempt
FIG. 177. — Black rot of cabbage. Cabbage heads, apparently sound, are attacked by the rot.
The progress of the disease is seen in the blackened parts of the stems and leaves.
After H. L. Russell.
a control of the disease in its early stages by a close inspect:on
of the young plants and by picking off the infected leaves.
FIG. 178. — Black rot of cabbage. A cabbage leaf showing the manner of infection. Dis-
eased area (15) unshaded except the blackened meshes of veinlets. A. A hole eaten by
insects. The disease was introducd at this point and spread backward to the main rib.
C. Blackened veinlets affected by the disease. 1). Water pores of the cabbage leaf
through which the disease germs gain a foothold, producing marginal infection. After
H. L. Russell.
Minnesota Plant Diseases.
345
Club-root of cabbage, radish, turnip and other cruciferous
plants (Plasmod'wphora- brassicoc ll'or.Y This disease is not un-
common in Minnesota but the exact extent of its distribution
is not known. The cause of the disease is not a true fungus
but is a slime mold or fungus animal. It forms no fungus
threads but produces spores somewhat similar to those of the
true fungi. The spores gain entrance to the host plant, usually
in the root region though the parasite may also exist in the leaf.
l-'lC. ITS. — C'lub-riHit i>f Miriiios. 1. Stra|>-lrai'. -. Al»cr«lccii. .'5. KulahaKa. 4. Simutiall.
5. Ciolilrn Hall. 6. Cowhnrn. 7. Ka»hmyr. After llaUtcd.
It lives within the host in a truly parasitic manner, destroying
the cells in which it dwells. It causes, however, great stimula-
tion of the tissues of the host, so that the latter produces wart-
like growths on its roots. The roots, moreover, become much
distorted, hence the common name of club root. The host
plant is much weakened by the attack and usually fails to head
out. The roots soon decay and thus the animal organisms,
which have already formed great numbers of spores, return to
346
Minnesota Plant Diseases.
the soil. Cabbages, radishes, turnips and even common weeds
of the mustard family, such as shepherd's purse, when planted
in such infected soil, will almost certainly become infected.
Even the transference of soil from such an infected field to an
uninfected one, as by clinging to wagon wheels or farm imple-
ments may carry infection with it. Manure from cows fed with
clubbed roots will easily infect crops.
No entirely successful treatment of club root is known. A
number of varieties of turnips have been tested and the ruta-
baga was found most susceptible. In general, it seems that those
turnips with branching and
deeply seated roots are most
susceptible, while those that
do not penetrate deeply and
which are not much branched
are least affected. Experi-
ments also seem to indicate
that buckwheat grown in tur-
nip land has a favorable effect
on the resistance to club root.
In general, infected fields
should not be used for the
same crop — or for any plants
of the mustard family — for
several years, as the slime
mold seems to be able to re-
tain its vitality at least for two
or three years. The infection
of new fields must be carefully
FIG. iso.-ciub root of cabbage. After ciin- ayoided bv preventing the
ton.
transference of soil or refuse
from the infected fields to other plots. The application of a
coating of lime to the soil in the proportion of seventy-five
bushels to the acre has been tested and has given very satisfac-
tory results. Weeds of the mustard family must be carefully
held in check.
Chapter XX.
Diseases of Orchards and Vineyards.
Jff
Orchards.
General treatment of apple orchards. The following has
been recommended as a general treatment for apple orchards
to keep out common fungus and insect pests. (Connecticut
Agricultural Experiment Station Bulletin No. 142.)
"i. Spray with copper sulphate solution just before buds
start, for Bitter Rot, Black Rot and Scab. This treatment is
often omitted.
2. Spray unfolding leaves with Paris Green or Lead Ar-
senate in Bordeaux for Bud Moth and Apple Scab.
3. Spray with same as soon as blossoms fall for Codling
Moth, Curculio, Canker Worm, Tent Caterpillar, Scab and
Sooty Blotch.
If badly infected with Sooty Blotch or Scab, spray with
Bordeaux mixture ten days later and for Sooty Blotch follow
with further spraying.
San Jose Scale, Bark Lice and Borers need other treat-
ment."
Leaf rust of apples and pears. Cedar apples of red cedar
(Gytnnosporangium macropns Link and Gytnnosf>oranginm
glohcsiun I:ur!.). One very commonly finds on the under sur-
face of the leaves of our apple trees large yellow spots. up<m
which are produced, in spring and early summer, long cluster-
cups with beak- or horn-like tops. The leaves are often swol-
len in the region of these spots and almost no leaf-green is
present. The spots frequently occur in sufficient numbers to
completely cover many of the leaves and in this case very seri-
ously injure the foliage, and consequently considerably impair
the strength of the tree. In the cluster-cups are produced the
cluster-cup spores. These spores infect young twigs of the
red cedar, which soon swell up. forming a ball-like growth
which is known as a "cedar apple."
348 Minnesota Plant Diseases.
The fungus passes the winter in this diseased portion of the
cedar and in the following year the winter spores are produced
in early spring. They are formed in a large number of cone-
shaped groups arising from little saucer-like depressions, scat-
tered all over the surface of the cedar apple. Each spore is
provided with a long stalk which swells up in rainy weather.
Since the winter spores are produced in large numbers there
are formed long (G. macropus) or short (G. globosum) beak-
like, gelatinous masses with a bright, orange-brown coating of
F(G. 181.— Cedar apples of red cedar. 1. Showing the swollen branches of the cedar with
the winter s >ore gelatine masses removed (Gymnosporangium globosum). 2. Cedar
apple of the same fungus with the gelatinous masses of winter spores. 3. Cedar apples
caused by another rust fungus (Gymnosporangium macropus), showing masses of winter
spores. 4. Same as 3, but larger specimen. Original.
spores. The cedar apples are therefore very conspicuous in
wet weather. Some cedar apples (G. globosum) produce win-
ter spores for several seasons in succession while the others
(G. macropus) produce spores only one season and then die.
The winter spores grow out immediately, while still in the
gelatinous mass, and produce a number of tiny spores (spo-
Minnesota Plant Diseases.
349
ridia), which are caught up by the wind and carried to an apple
tree or thorn tree. Here infection takes place on the leaves
of the host, where the cluster-cups are soon again produced.
Fruit tree culture is often seriously damaged by this apple
rust, and the disease may become epidemic over considerable
areas.
Since cedar trees are a harbor for the fungus, these trees
should be carefully watched and removed if necessary. At any
rate, branches bear-
ing cedar apples
should be prompt-
ly remove d and
burned. It has also
been recommended
that diseased leaves
and badly infected
branches of the ap-
ple tree be burned,
and that the entire
tree be destroyed if
badly rusted. Spray-
ing has been recommended, but is considered by many to be
of doubtful value. Bordeaux is used, and the first spray is
given just as the leaves expand and the second a few weeks
later. A third is recommended in very rainy seasons. As dif-
ferent apple varieties vary in their power of resistance to this
rust, resistant varieties may be selected where damage from
this rust is very great.
The two following diseases produce leaf rusts of apple very
similar to the above.
Club rust of juniper [Gymnosporangium clavariac forme
(JaiJ AuY.v.]. Another disease, similar in its effects to those
of the cedar apple and birds'-nest rust of red cedar, is a rust
which attacks our common juniper bushes. An attacked
branch swells up into a club-shaped body, often of considerable
length. From the surfaces arise, in early spring, small, yellow-
ish, club-shaped or cone-shaped groups of winter spores, which
swell up in moist weather. Very small spores (sporidia) are
produced in a similar manner to the cedar apple and these
FlC. IKi. — Rust of ap;>lc leaves. <."lustcr-cui> stage of a
cedar apple fungus. After Clinton.
35° Minnesota Plant Diseases.
infect the leaves of thorns or apples, where the cluster-cups are
formed, also in a similar manner to the above-mentioned rusts.
The disease may be dangerous to both ornamental junipers and
to orchard apple trees.
The preventive measures are similar to those of the leaf-
rust of apples produced by the cedar-apples of red cedar.
The birds'-nest rust of red cedar (Gymno sporangium nidus-
avis Thaxt.}. This is a rust disease similar to that of the cedar-
apple of red cedar. When this fungus attacks the red cedar
an enormous number of short branches are formed. They are
densely bunched together and look like a miniature tree
perched on the limb of the cedar tree. This bush-like growth
is known as a witches'-broom. At a distance it is not unlike a
very large birds'-nest in appearance. On examining the
branches of the broom, one sees that the leaves are larger and
stand out at a greater angle from the branch than do the leaves
on the normal branches ; they are also very sharp-pointed and
the general habit of the branch is more similar to that of the
common juniper tree. Near the base of the leaves in the dis-
eased portions of the cedar are found small, brownish, gelatin-
ous cushions of the winter spores. These appear at the end
of April. The cushions, just as do the beak-like processes of
the cedar apples, swell up in wet weather and shrivel up again
when dry. Under moist conditions the winter spores germi-
nate and produce tiny spores (sporidia), which are carried by
the wind to june-berry bushes or apple trees. Here the fungus
again develops a mycelium and causes a rust disease which is
very difficult to distinguish from that caused on the same plant
by the cedar-apple rust.
The preventive measures are similar to those recommended
for cedar-apples of red cedar and their leaf-rust of apples.
(Fig. 26.)
Plum leaf rust (Puccinia pnnii Pcrs.\ On the leaves of
many of our wild cherries and also on those of cultivated plums,
cherries, etc., is often produced a rust known as plum-leaf rust.
Only summer and winter spores are produced and they occur
in groups or sori on the under surface of the leaf. The sum-
mer spores are light brown or reddish and the winter spores
are darker. The spores arise in small, yellowish spots on the
Minnesota Plant Diseases.
leaf and these spots often occur in sufficient numbers to con-
siderably damage the plant. The winter spores are two-celled.
Spraying with dilute
bordeaux has been recom-
mended just as the buds
are opening and the leaves
are expanding, and at in-
tervals later. The fallen
leaves should be burned.
Apple scab [Vcntnria
ponri (Fr.) II7 int.]. Ap-
ple scab is by far the most ^^K
serious disease of apples.
The fungus first appears
in early summer on the
leaves of the apple tree as
light, greyish, circular i-'m. isa.— AI
spots which spread rapidly, often combining with neighbor-
ing spots to cover large areas of the lent. The spots later
turn olive green
and finally black.
The surface is
covered with up-
right threads
from which the
s u m m e r spores
arc thrown off.
These1 spores rap-
ilv increase the
spread of the fun
gus from leaf to
leaf ami tree to
tree. The spots
are frequently sn
1 a r g e and nu-
merous that the
leaves b e c o m e
considerably distorted and are often shed. Whole trees may in
this way he stripped of their leaves. This sometimes happens un-
n tin- fruit. Al'ti-r
352
Minnesota Plant Diseases.
der conditions favorable to the fungus and such conditions are
realized in cold damp summers. The shedding of the leaves, of
course, impoverishes the tree not only for one sum-
mer, but may weaken it for several successive years.
The fungus also attacks the fruit and forms here
even more characteristic spots than on the leaf. The
fruit spots are dark brown to black, lined with a
whitish rim, and are scab-like in appearance. They
are usually not over one-half inch in diameter and
are more abundant toward the further end of the
fruit, though they may occur anywhere on the latter.
When abundant the scabs may deform and dwarf
the fruit and they always disfigure it, so that its
market value is lowered. When the young fruit is
seriously attacked the whole fruit may fall. In ad-
dition to these injuries, the attacked portions of the
fruit become hard and often crack open, allowing
the apple to dry out. The cracks also open the way
to the soft rots, which soon destroy the apple. The
fungus lives through the winter in the sac-spore cap-
sule stage. The sacs each enclose eight spores, and
are contained in a pored capsule which is formed in
the tissues of the apple plant and bursts out at the
surface at maturity, ejecting' its spores through a
pore opening to the exterior. These sac spores are
thrown out in the spring, are carried to the lower
branches of adjacent trees and here cause the first
infection in the spring.
In combating this disease a number of recommendations have
been made. The disease can be very successfully fought by
means of spraying with bordeaux. Several sprayings are usu-
ally necessary. A winter spray, with strong copper sulphate, be-
fore the buds open should be applied. This should be followed
by bordeaux just before blossoming and again just after blos-
soming, and two or three other sprayings at intervals of two or
three weeks. The number of sprayings must be governed by
the amount of rainfall and coolness of the season. Good ventila-
tion and spacing of trees and proper pruning" will aid in avoid-
ing conditions favorable to the fungus growth. The fallen
FIG. 185.— Ap-
ple scab on a
twig. After
Clinton.
Minnesota Plant Diseases.
656
leaves, where the disease has been prevalent, should be collected
and burned, or plowed under, to prevent the formation of spores
in the following season. Certain varieties of apples are also
known to be more resistant than others toward this disease and
a proper selection may aid in combating the fungus.
Soft rots of fruits (Pcnccillhun, Mncor, etc.}. These rots
include some so-called ripe rots and storage rots. The soft rots
are due to various fungus growths. They are. in general, molds
e:ther of the black or blue mold groups. The habits of these
.,-*
l-'ic. JVi. -.\;-|i!c -cab i'ii (lie- leal. . \t"ur l.-m^vt ai.
fungi have already been pointed out in previous chapters. Thev
are amateurs in the ways of parasitism, for they need not only
assistance in gaining entrance to the IMSI. but they arc capable
also of successfully attacking only tln»e parts which arc in a
resting or dormant condition. The protoplasm of such plant
parts, as has already been pointed out. approaches the proteid
condition of dead plant debris. Kipe fruits of almost all kinds
suffer from these rots. The rots are most destructive in moist
warm conditions.
354
Minnesota Plant Diseases.
D
FIG. 187. — Spores of the apple scab fungus. A. Portion of a section through a scab spot
on an apple; b, fungus threads spreading under and lifting the cuticle; a and c, partly
disorganized cells of the apple; e, healthy cells of the apple. B. Two spore-bearing
stalks giving rise to summer spores. C. Spores germinating. D. Portion of a section
through an affected leaf of an apple which has lain on the ground over winter and
has given rise to the winter spore stage of the disease; g, spore-case containing a bundle
of spore-sacs. E. Two spore-sacs, more highly magnified, each containing eight two-
celled winter spores, three of which are shown at F. All highly magnified. After
Longyear.
Minnesota Plant Diseases.
355
Among these molds the blue (or green) mold is perhaps the
most common. (See Chapter IX.) So common are the spores
of these fungi in the atmosphere that one can find them at all
times of the year, often in great abundance, everywhere. An-
other common soft-rot of fruits is found in certain kinds of
black mold. (See Chapter VIII.) The effect of these rots is
a rapid softening of the affected parts of the fruit and, as the
fungus spreads, the fruit is finally entirely softened and rendered
worthless. The fungi gain entrance to the fruit chiefly through
wounds in the skin. Cracks in the skin, such as those caused
FIG. 188. — Blue mold soft rot of
After L. F. Kmiicy.
by apple scab, or holes formed by insects, or bruises and cuts
obtained in picking, packing and storing, all contribute to the
ease of entrance of the fungus.
The prevention of ripe-rots is possible to a certain extent by
avoiding those conditions favorable to the entrance and growth
of the fungi. Warm moist atmospheres should be avoided,
hence cold storage of fruits is desirable. Spraying may reduce
other diseases, such as scab, and in this way prevent the ripe rots
which usually follow such diseases. The spraying on the tree
is not. of course, directly beneficial against the ripe-rot, since the
356 Minnesota Plant Diseases.
latter are largely store-house diseases. Experiments in formalin
treatment and with other chemicals have been unsuccessful. Good
ventilation of the stored fruit and a frequent sorting to remove
the rotted fruits, thereby diminishing the chances for infection
from the spores which are formed on these fruits, are also recom-
mended. Any damage, such as bruising or cracking the fruit
skin, is to be avoided in all processes of handling the fruit. (See
Fig. i.)
Bitter rot or ripe rot of apples \_Gloinerclla nifomaculans
(Berk.) Sp. von ScJir.]. This is also known simply as apple rot.
It attacks apples before they are ripe, and also apples in storage ;
FIG. 189. — Blue mold soft rot of apple. Accessory spores of the fungus. Highly mag-
nifi^'i. After L. 1". Kinney.
it is a very destructive parasite. The parasite is one of the burnt-
wood fungi, and it is the summer-spore stage that is the most
conspicuous and the form which causes most damage. \Yhere
the fungus attacks the fruit, a small brownish red spot appears
and increases in size until a considerable area of the apple is in-
volved. The spot becomes somewhat sunken, is soft, and the
apple underneath has a bitter taste. On the surface of the spot
arise usually in well-defined circles the summer-spore masses
Minnesota Plant Diseases.
357
which are small, black cushions formed under the skin of the
apple. When the spores are ripe the skin is ruptured, and the
spores issue in a long cylindrical gelatinous mass which is some-
what spirally twisted. Rainwater dissolves the spores apart,
and the latter are washed to other fruits, again causing infec-
tion. The winter or sac spores are formed in small black cap-
sules which are produced in the
cankers on the twigs. These
cankers are usually found at
the bases of infected fruits.
The m y c e 1 i u m and winter
spores preserve the fungus
through the winter. The my-
celium, which produces the
winter spores, can apparently
live sapn »phyticallv.
Decayed fruit, whether in
storage or in the orchard,
should IK? destroyed. Diseased
twigs should als:> be pruned
FiC.lW.-«itterrotof,pple. After Clinton. 1)ack a»(I ^royed. Spraying
with Ixirdeatix mixture begin-
ning with a winter spraying, and continued frequently MI the
growing season, wili hold the disease in check. . \mmoniacal
copper carbonate should be substituted for the bordeaux as the
fruit approaches maturity. 1'otassium sulphide has also been
used to advantage.
Brown rot of apples. See Urown R«>t of I'luius (this
chapter).
Brown rot of plum|.SV/«v«'/////'</ frnstigi'n<j </'. ) Sclirt.]. This
is a very common dis'.'as.' of plums and may als > attack cherries
and apples, though the latter rather rarely. In state> where the
peach is grown, this fruit suffers most of all fron. the brown r<>'..
The fungus attacks the fruit at about tin- beginning of the ripen-
ing period, but may also extend to the twigs, haves and flowers.
The attacked portions of the fruit turn brownish, forming brown
spots which arc soft and rapidly gmw in she. On these spots
arise the summer spores in small clusters which are arranged in
circles in the spot. The spores are formed in chains. Hke strings
358 Minnesota Plant Diseases.
of beads. This summer-spore was formerly known as a loose-
spored "imperfect" fungus. The winter spores, however, are
now known. Sclerotia or storage organs, formed from densely
woven fungus threads, are sometimes produced in the fruit. In
the following spring, these sclerotia send up a cup fungus fruit-
ing body with a long stalk, and on the inner surface of the cup
is formed the layer of spore-sacs. The latter each contain eight
spores. These spores probably cause infection in the spring.
Attacked fruit falls to the ground or may remain attached to the
tree and becomes mummified, producing then an enormous num-
ber of spores. These fruit mummies, moreover, may persist
through the winter and continue to produce spores in the follow-
ing spring. It is therefore important that all decaying and rot-
ting fruit, whether on the tree or ground, be gathered and burned.
Affected twigs should also be pruned and burned. A winter
spray has been suggested and spring and summer sprays with
bordeaux have proved beneficial. In addition to the winter
spray the following applications have been recommended : with
bordeaux (i), just as the leaves begin to unfold; (2), just after
the petals fall ; (3), after the fruit sets, and with potassium sul-
phide as the fruit begins to ripen.
Black knot of plum and cherry \_Plowrightia morbosa. (Schw.}
Sacc.~\. This is a very common disease of our wild cherries and
is also common on wild and cultivated plums. The disease de-
rives its name from the black charcoal-like knots in the branches
of the tree. These knots are caused by the threads of the fungus
which inhabit the branches at the knotted points. The fungus
gains entrance, perhaps, through a crack or wound and imme-
diately causes a stimulation of the tissues, so that a large, soft
mass arises, which contains but a small amount of hard woody
tissue. This enlarged portion of the branch splits off its outer
cork layer and exposes a cushion of densely wefted fungus
threads. The cushion is at first yellowish-brown to yellowish-
green and turns finally to an olive or dark yellow-brown color.
This surface is at first covered with the summer spores which are
borne on short upright threads and are capable of causing infec-
tion during the same season in which they are formed. Later in
the year the knotted portion of the branch turns black and char-
coal-like and the surface is then covered with very fine, pimply
Minnesota Plant Diseases.
359
protuberances, each of which has an opening at its apex. These
openings communicate with the pear-shaped cavities of the cap-
sules, which contain the numerous spore-sacs, each bearing eight
spores. These are the winter spores and are capable of causing
infection during the year following their formation. The fungus
FlC. 191. — Black knot of wild cherry, shotting various
knots. Original.
in the development of the
mycelium may also live over the winter in the tissues of the host
and grows from year to year. The ultimate effect of the black
knot on a branch is to kill off the entire branch above the knot.
When a knot works downward to another branch the latter will
also soon be killed.
360
Minnesota Plant Diseases.
The fungus can be held in check by a persistent pruning off
of the knots. Such a pruning prevents the spread of the myce-
lium in the tissues of the host. The knots should be immediately
FIG. 192. — Powdery mildew of plums and cherries. 1. Cherry leaf. '2. S.>ore-sac capsule
showing the thread appendages with peculiar forking ends. 3. Spore-sacs, each with
eight spores. 4. Very highly magnified s Hires. 5. A chain of summer spores. (5. Two
summer spores germinating. All except 1, highly magnified. After Kllis.
burned. Care should be taken to prevent a prevalence of the
knots amongst wild cherries and plums in the neighborhood of
the orchard. Spraying with bordeaux would probably assist in
preventing a spread of the disease.
Minnesota Plant Diseases. 361
Powdery mildew of .apple [Podosphacra Icncotricha (E. ami
E.) Salmon]. This mildew attacks apples, pears, thorns and
juneberries. It affects chiefly the seedling plants by injuring the
leaves. It forms a fine, whitish, powdery mycelium on the sur-
face of the leaves. The small black capsules appear in late sum-
mer. Summer spores are produced in the manner usual for the
powdery mildews. The small, black sac-capsules are produced
in late summer. They are provided with appendages, which
form a crown on the summit. The appendages are branched
several times in a forking manner. The capsules, when broken
open, are seen to contain each a single spherical sac. enclosing
about eight spores.
Spray seedlings with bordeaux or ammrmiacal solution of
copper carbonate shortly after the buds have opened md at inter-
vals of ten to twelve days for two months.
Powdery mildew of plums and cherries [Podosphacra tridac-
tyla (ll'ulf.) DcR y.]. This mildew attacks leaves of plums and
cherries. It is f< und chiefly on young plants. It forms a fine
mycelium on the surface of the leaves. The small, black fruit-
ing-bodies appear in the fall. These sac-spore capsules are nro-
vided with appendages which resemble those of the p »wdery
mildew of apples K:ich capsuk* contains a single sa? with eight
sjx>res.
For preventives see Powdery Mildew of Apple.
Plum pockets (l^vonscns prnni l-'ckl.). Plum pockets are
very familiar objects to all raisers of plum trees. Cherries are
also affected by a similar disease. In this disease the fruit is
peculiarly enlarged to considerably more than its natural si/e and
is at first yellowish, becoming grey as a coat of spores form on
the surface. The diseased fruit has no st<'iie. the entire fruit
wall being soft. The mycelium j>enneates the tissue "f the
pocket and forms spores in sacs on the surface. The mycelium
may live over the winter in the twig" <>f the plants, s • tint a plant
part once infected may produce p >ckets yearly. This yearly pro-
duction of pockets does not always take place, but they may a|>-
pear only every other year. The disease does not seem to spread
with great ease, for it has l>ecn observed that trees neighboring
on a diseased one may remain free from pocket*- for a long time.
The spore> are borne In elongated sacs which are arranged in
(62
Minnesota Plant Diseases.
palisade fashion on the surface of the pocket. Each sac contains
about eight spores, which on germination may directly cause in-
fection of a host plant. The fungus of this disease is very closely
related to the peach leaf-curl fungus and to others forming
witches'-broom on birch, alder and cherry trees. It is a sac-
fungus with an arrangement of sacs similar to that in the true
cup fungi, but has no true cup, since the sacs occur directly on
the tissues of the host.
FIG. 193. — Plum pockets. These plums are devoid of stones and bear the fungus spores on
their surfaces. Photograph by H. Cuzner.
The only known effective remedy for plum pockets is the
pruning back of the affected parts, so as to remove the fungus
mycelium. The pruning must in some cases be quite severe. Of
course all pockets must be removed and destroyed, as should all
affected parts. It is also advisable not to use the parts of any in-
fected tree for grafting purposes, since the fungus mycelium may
be transferred with the graft. It has been suggested that the
treatment which is successful in combating the leaf-curl of peach
may also prove successful here. This consists in spraying with
bordeaux when the buds are swelling and again with bordeaux,
just before the petals fall. (See also Fig. 49.)
Minnesota Plant Diseases. 363
Witches'-broom of cherries [E.roascus cerasi (Fckl.) Sad.].
One not infrequently meets with wild cherry trees which have
the peculiar disease known as witches'-broom. On account of
the abnormally large number of branches developed in the af-
fected part of the tree, a bush-like object is produced which looks
not unlike some foreign shrub, parasitic on the cherry tree. In
this broomed portion the mycelium of the fungus, which is a
close relative of the fungi of plum pockets and peach leaf-curl,
may be found. This mycelium is perennial. The leaves mav
be considerably distorted, resembling curl, and over the surface
of these leaves the spores are formed in sacs. These sacs are
arranged in a palisade on the surface and give to the latter a
greyish-white appearance. There are about eight spores in each
sac. They germinate directly to an infection tube. The
broomed portions should be removed and burned.
Plum scab (Cladosporiutn carfophilum 7/i/wi.). This is an
imperfect fungus. Many of the species of the same genus are
exceedingly common mold-like saprophytes forming black, moldy
growths on dead sticks, stems, seeds, etc. The plum scab is
found on plums and cherries. Spots arise on the fruits shortly
before ripening. These spots are covered with brown or olive
growths of fungus threads from which dark spores are pinched
off. The spots may increase in size and number until the whole
fruit is covered. The latter then shrivels and is rendered unfit
for the market. Many varieties of plums are attacked and the
wild American plum seems to suffer as much if not more than
any other variety. The fungus is probably one of the black fun-
gus group of the sac fungi but its winter-spore stage has not yet
been discovered. It is possible that the fungus lives over the
winter in a sterile thread condition on the branches and bark of
trees. The fungus has been observed in Minnesota but the ex-
tent of its damage is not yet known.
Spraying with bordeaux has been recommended. Several
treatments should be given, l>eginning when the flowers are well
set. Diseased plums should be destroyed.
Black rot of apple (Sphncrnpsis nmlorum Peck.). The black-
rot attacks apples usually in the ripening stages or when the fruit
is in storage. It also attacks the leaves, forming reddish brown
spots, or the twigs, where blackish spots are produced. The
Minnesota Plant Diseases.
FIG. 194. — t!lack rot of aople. After Clinton.
fruit, when attacked, turns at first a reddish brown but later be-
comes black. On attacked portions of the tree the fungus pro-
duces its spores. It is an "imperfect" fungus and produces spores
in small capsules, which appear on the leaf, twig or fruit spots
as tiny black warts. These
open to the exterior by minute
pores through which the spores,
which are cut off of threads lin-
ing the interior of the capsule,
are thrown out.
The treatment which is
fcused against the apple scab is
[usually recommended in treat-
ing black rot. In addition. th<?
dead twigs and limbs should
be pruned to prevent the win-
tering of the fungus in the twig
spots. Rotted fruit should be
removed and destroyed. Win-
ter spraying has also been recommended.
Apple and pear blight [Bacillus amylovonis (Burr.} DeToni.].
This disease is also known as fire blight. Its cause is a bacte-
rium. The bacteria gain entrance to the twigs of the apple
through wounds or through the flowers. They are carried by
insects to the stigma of the flower and from this point work their
w ay into the branches. On the
branches they form first small, dead
spots, which later enlarge to canker-
like sores, from which a dark mucil-
aginous fluid oozes. In this fluid one
finds millions of bacteria. In the I
canker growth b'utyric acid, carbonic
acid gas, and alcohol are formed.
The branch above the canker is killed,
often suddenly, and the leaves turn
brown as though scorched by fire.
hence the common name of fire blight.
Xo successful remedy for diseased
branches is known. Pruning back is the only successful method
of combatingf the disease.
FIG. 195. — Fire blight of apples.
liacteria which cause the dis-
ease. Highly magnified. Aft-
er P>. M. Dupgar.
Minnesota Plant Diseases. 365
The branch should be cut six inches below the canker and
care should be taken to keep the knife clean, since it is an easv
matter to transfer the bacteria on the knife blade to heaUhy
trees. The blade should therefore be dipped in a corrosive sub-
limate solution. All diseased twigs should be promptly burned.
Since an abundance of moisture in the plant favors the develop-
ment of the bacteria, an avoidance of a too succulent condition
has been recommended, e. g.. draining the moisture from around
the base of the tree. This procedure has aided in keeping the
disease in check.
Downy mildew of seedlings (Phytophthora ommvora DcBy.).
See Diseases of Greenhouse and Ornamental Plants.
Vineyards.
Black rot of the vine [Guignardia bi-Jwcllii (Ell.) I'iala ct
/?</?-.]. This fungus has often proved a very destructive disease
and vine growers in the United States have suffered great losses
from it. The extent of damage in Minnesota is as yet unknown,
though the fungus is probably not uncommon. It has caused
considerable trouble in Iowa. The first indication is the produc-
tion of small reddish or brownish spots on the leaves On these
spots arise minute, black, capsular fruiting-bodies. These cap-
sules do not contain sac-spores, but produce one kind of summer-
spore. These spores are formed on threads in the capsule and
escape in a sticky mass from the apical opening. They are
washed apart by the rain and distributed to other parts of the
plant. The berries are also attacked and brownish spots appear
on them. Capsular summer sjx>res are formed here similar to
those on the leaves and in addition to these two other spore-forms
may appear. The berry shrivels and dries up and becomes black,
but still clings to the vine. Late in the fall the sac-spore cap-
sules appear on the shriveled grapes. They are small black
bodies with an opening, through which the sac spores escape in
the following spring. These sac spores probably recommence
the infection. All diseased portions should be promptly removed
and burned. All infected grapes should be destroyed and in no
case should the shriveled grapes be left on the vine until spring.
The disease needs prompt and persistent attention and a fight of
366 Minnesota Plant Diseases.
several years is necessary to hold it down to a minimum of dam-
age. Spraying with bordeaux has been found very beneficial.
Spraying should commence early and continue at intervals of
about two weeks until a few weeks before the ripening of the
fruit. In these later sprayings, ammoniacal copper carbonate
should be substituted for the bordeaux.
Powdery mildew of vines [Uncinula necator (Schzv.} Burr.].
This is one of the most destructive o<f the powdery mildews or
blights. It attacks grape vines and causes much damage, not
only to the leaves but also directly to the fruit. The summer
spores are formed in the usual manner for powdery mildews and
appear in great numbers spreading the disease very rapidly. The
spread is particularly rapid in moist weather. The mycelium
first appears in whitish areas, under which the cells of the leaf
are killed, leaving brown spots. The leaves usually wither. The
grapes dry up in the attacked region and often become split open
and subsequently wither or decay. The summer spores are
formed throughout the summer; and in the fall the sac spore
capsules appear as dark-brown bodies of minute size. The cap-
sule is provided with a crown of numerous thread-like append-
ages, the tip of each of which is bent back in the form of a stout
terminal hook. When broken open each capsule is found to con-
tain four to ten sacs, each of which contains four to eight spores.
The disease winters over in the capsular stage and infection is
accomplished in the spring from the sac spores, which alight on
the leaves. Here they send out a small tube with a flattened
disc, which serves to attach the parasitic plant to' the leaf. A
short sucker branch is then sent out into a cell of the host and
the growth of the mycelium proceeds. From this mycelium the
summer spores arise.
"Treat as for downy mildew with perhaps a late spraying in
the fall after gathering the berries, to destroy the winter spores.
Potassium sulphide is also used effectively against this fungus."
(Conn. Ag. Ex. Sta. Bull. No. 142 — 1903.)
"The sprayings with bordeaux mixture, that are generally
applied for other diseases, will do much to hold it in check, during
the early part of the season ; but later on, as the fruit approaches
maturity, the weak copper sulphate or the ammoniacal carbonate
of copper will be preferable. The application of flowers of sul-
Minnesota Plant Diseases. 367
phur to such varieties as are subject to this disease, at intervals
during the season, will also be of value, especially on grapes
grown under glass. In dry seasons the frequent stirring of the
soil will aid in keeping the vines healthy, but upon the first ap-
pearance recourse should be had to one of the above fungicides.'
(Mich. Ex. Sta. Bull. No. 121.)
The burning of the fallen leaves of infected plants is also to
be recommended.
Anthracnose of vines (Sphaccloma ampclinum DcBary).
This is also known as birds'-eye rot. The cause of the disease
is an imperfect fungus and causes great damage in many states
of the Union. The extent of its work in Minnesota is not yet
known. All parts of the plant are attacked and the disease is a
difficult one to combat. The fungus causes small black spots,
which later become whitish, though the edge is margined with
purple. The spots in the stem sink, leaving depressed regions,
while in the leaves dark-brown spots are produced, from which
the tissue sometimes falls as in the shot-hole fungus of plums.
On the fruit circular spots are produced with a black margin,
outside of a red ring, from which the fungus derives its name
of birds'-eye rot. The spots may be numerous on a berry and
eventually become scabby. An infected cluster of berries bears
usually few or no sound ones. The berries die and shrivel but
remain attached to the vine. The spores of the fungus are borne
in small, black spots, which appear on the leaf and fruit spots.
The spore-bearing threads are packed into a cushion which is
dark -colored. From the surface of this cushion arise the upright
thread branches, bearing colorless spores.
The treatment for black rot of grape is usually recommended
for the anthracnose. All diseased portions should l>e removed.
In addition to this, a winter treatment is given in Europe, where
the disease was first known and where it has caused a great dam-
age. In the old world this disease has been brought under con-
trol by winter and summer spraying and the destruction of in-
fected parts. "In Europe it is the custom to wash the vines and
stakes during winter or early spring witli sulphuric acid and sul-
phate of iron solution. The liquid is applied by means of swabs
or brushes. It blackens the canes and this is a test of the thor-
oughness of the work." (See chapter on fungicides. Iron sul-
phate solution.)
368
Minnesota Plant Diseases.
"If after two or three days there remain portions which are
unchanged in color the vineyard is treated a second time, partic-
ular attention being paid to the parts omitted at the first treat-
ment." Lodeman (The Spraying of Plants, p. 295.)
Downy mildew of vines [Plasmopara viticola (B. &C.) Berl.].
This is a very destructive disease of vines originating in the
United States, but since about 1878 causing enormous destruc-
KIG. 19(i. — Downy mildew of grape. Under surface of a leaf, showing down of mildew
threads spread over the entire leaf. Original.
tion of vines in Europe. The fungus is a downy mildew and is a
destructive parasite. It appears on all above-ground parts of
the vines, but most abundantly on the leaves. \Yhen the latter
are attacked they show, from above, pale green spots which later
become light yellow in color. This is the region where the my-
Minnesota Plant Diseases. 369
celium is at work within the leaf. On the under surface these
patches show at first a faint light grey shimmer, which later de-
velops into the grey mold-like growth of the fully developed
patches of the summer spores. These patches spread rapidly and
the whole leaf, in the course of a few weeks, dies, becomes brittle
and useless as a starch-making organ and dangerous as a pro-
1'ir.. 197. — Downy mildew of (jra;>c. On thr riyhl i* a lu.ililn hunch of urnpo
a hunch hrully disrasril. Original.
ihiccr of the fungus spores. The so-called spores behave as do
those of the downy mildews generally, i. e.. when they fall in very
moist surroundings they produce six or more swimming spores,
which swim alxwt in the water drops and spread the infection on
the leaf. When they come to rest they germinate by sending out
infection tubes and the latter establish new regions of the myce-
lium. The leaf patches commence to appear in early summer.
Minnesota Plant Diseases.
Later in the year the winter spores are formed in the usual way
for the downy mildews, i. e., from breeding organs. The winter
spore has a thick coat and remains in the leaf after the latter falls.
In the spring the decay of the leaf sets the spore free, and in moist
conditions it produces numerous swimming spores ; the infection
of the vines follows in the usual way. The destruction of fallen
leaves, to avoid future infection, is therefore seen to be of in>
portance.
FIG. 198. Downy mildew of grape. A. Section of a leaf with spore-bearing threads emerg-
ing from an air-pore. B. Greatly enlarged sucker threads, h. C. Formation of swarm
snores in the so-called summer spores; 1, summer spore (is really a spore-case) ; 2, same
with protoplasm divided into regular areas; 3, areas of 2 are seen separated, and the
whole mass escaping from the spore-case; 4, an escaped and free area of the protoplasm
which becomes the swarm spore, 5. D. Formation of egg-spores by the breeding act.
Highly magnified. After Millardet.
The treatment for black rot is usually recommended for this
disease. The sprayings may be at longer intervals. (See Black
Rot of Grapes.)
Disease-resisting varieties may also be used. It has been rec-
ommended that the vine be treated in the fall or early spring, be-
fore the buds commence to open, with an iron sulphate solution.
Chapter XXI.
Diseases of Greenhouse and Ornamental Plants.
Carnation smut [Ustilago violacea (P.) Fckl.]. This smut at-
tacks a large number of species of the plants belonging to the
pink family, such as common garden-pinks and carnations, and
such wild flowers as catch-flies, star-worts, soap-worts and corn
cockles. This is a very different disease from the rust of carna-
tions and cannot easily be confused with it. The carnation smut
attacks the stamens of the flower and converts the anthers into
smut-spore sacs. The smut spores form a violet-colored powder
and one can easily mistake this for abnormally colored pollen.
When the smut spores escape, many fall upm the petals and
sepals discoloring them and rendering them unfit for decorative
use. This fungus often exerts a remarkable influence upon those
members of the pink family which have pistillate and staminate
flowers, e. g., the corn cockles. The pistillate flowers, when at-
tacked, develop stamens which, in an unaffected flower, remain
undeveloped. These stamens, as well as those of the staminate
flowers, become a prey to the smut fungus. As a general rule no
other parts of the flower or plant are enlarged, or in any way dis-
torted. There is no indication of the presence of the fungus, and
the latter can only be detected at the ripening of the spores, or by
a previous examination of the anthers.
The diseased plants should be promptly destroyed to prevent
a spread of the disease.
The violet smut [L'rocystis riolac (Soic.) Fisch.]. Occasion-
ally on pansies and violets. (See Diseases of Wild Plants.)
The chrysanthemum rust (/'/uv/wc; clirysunthcnri Rose.).
This disease has appeared in recent years as an abundant parasite
on greenhouse chrysanthemums. It is not, as was formerly sup-
posed, identical with the common wild rust of sunflowers and
their allies but it is a distinct importation, probably, from Japan.
The summer spores are found in the fall and are produced in
372 Minnesota Plant Diseases.
very small clusters, which arise in great numbers, chiefly on the
under surface, but also on the upper surface of the leaf. These
sometimes coalesce to form larger spots. The clusters are at
first closed by the epidermis of the leaf but later break out and
expose a dark-brown powder of summer spores. The winter
spores are two-celled and are produced in black clusters. They
are not, however, common in this country. On account of this
latter feature the disease should not be very difficult to combat.
It is said to tend to disappear of itself after a regular run of a
given greenhouse. Great care should be exercised in preventing
the introduction of the disease into a greenhouse. This can be
done by close examination of all purchased cuttings and plants
and by carefully watching them for some time after their intro-
duction. The diseased plant parts should be promptly removed
and burned. In case of a persistent attack, "every leaf and stem
above ground should be destroyed at the end of the flowering
period and the young plants or cuttings, for the next season's
supply, be grown in an uncontaminated house, and, if possible,
fromuncontaminated material." (Ind. Ex. Sta. Bull. 85 — 1900.) It
has been reported that inside cultivation in summer and selection
of rust-free stock will be sufficient to keep the disease in check.
Rust of hollyhocks and mallows (Puccinia malvaccarum
Mont.). The mallow rust attacks members of the mallow fam-
ily, e. g., hollyhocks, marsh-mallows and the small, wild, creeping
mallow. It produces only winter-spores which can germinate
without a resting period. The spore groups occur in great
abundance on the leaf-stalks and leaf-blades and even on the floral
parts, causing deformation of these parts. In some cases the
plants are killed by the parasite.
The mallow rust has an interesting history. It was intro-
duced from South America into Europe by the Spair'sh about
thirty-two years ago. Before this time it was unknown in Eu-
rope or North America. It spread in Europe with remarkable
rapidity, growing on cultivated and wild mallows, and is at pres-
ent an exceedingly abundant and dangerous enemy to mallow
growers. It is said to have completely exterminated mallows
in many regions. This disease has been introduced from Europe
into the United States and is fast gaining ground. It has not yet
been reported from Minnesota but will probably reach this state
in due time, if not already here.
Minnesota Plant Diseases. 373
Spraying- with bordeaux mixture or a solution of permangan-
ate of potash has been recommended. Diseased parts should be
immediately destroyed.
The violet rust [Pnccinia violcc (Schiun.) DC.]. On all spe-
cies of our native violet can be found, often in considerable abund-
ance, this rust of violets. It also occurs on the cultivated violets
of greenhouses and may cause considerable damage. Cluster-
cups are formed on our wild violets, often in great abundance, in
the spring. Slight swellings of the leaf and distortion of af-
fected parts are usually caused, and the cluster cups occur on the
surface of the malformations. Later, summer and winter-spores
are formed, in small round patches, also, usually on the under
surface of the leaves. These do not usually show malformations
as in the case of the cluster cups.
Infected plants or plant parts should be destroyed.
The carnation rust [L'roinyccs caryophyllinns (Schrk.)
Schroet.]. On the leaves or stems of the carnation often appear
elongated, brownish patches, breaking through the epidermis and
exposing a more or less powdery mass of spores underneath.
These proceed from the mycelium, which lives in the stem and
leaves. The first spores produced are the summer spores and
these are light brown in color. They germinate immediately
after formation, and aid in spreading the disease. Later in the
season, darker, winter-spores are pnxluced and these pass the
winter before germinating. The mycelium, when once estab-
lished in a plant, remains there and forms pustules of spores in
succession. Diseased plants should not, therefore, be used for
cuttings, since the latter are sure to l>e infected. This disease has
proved very serious at times to carnation culture.
Diseased plant parts should be cut out and destroyed to pre-
vent the spread. Bordeaux in fine spray at intervals of one to
three weeks has proven effective in checking the d 'souse. Potas-
sium sulphidf has also been recommended. The cultivation of
hardy varieties has l>een suggested and particular attention should
be paid to proper methods of cultivation, ventilation and watering.
The sunflower rust (Pnccinia tanuccti IK'.}. This is one of
our most common rusts, occurring in great abundance on almost,
if not all. species of Helianthus and is particular' y abundant up-
on the common cultivated Helianthus animus. In addition, it
174
Minnesota Plant Diseases.
occurs on other more or less closely related plants. The fungus
mycelium gains entrance to the plant in the spring and first pro-
duces cluster cups. These are followed by the summer spores,
throughout the summer months, forming small red-brown patches
FIG. 199. — Leaf rust of roses. The cluster-cup stage on the stems and leaves. On left is
a stem distorted by the cluster-cup cushions. Photograph by H. Cuzner
upon large, dark, red-brown spots in great abundance, on the
lower surface of the leaves. The summer-spores are followed
toward autumn by the winter-spores, which are formed in similar
but darker groups. The winter-spores are two-celled. Where
Minnesota Plant Diseases.
375
the sunflower has been raised in large quanti-
ties, this rust has often proved very injurious.
The leaves and all parts affected by the
fungus should be burned in autumn to destroy
the winter spores and to prevent the recurrence
of the disease in the following spring. (See
Fig. 206.)
The rose leaf rust [Phragmidium subcor-
ticium (Schrk.) ]Vint.'\. This is a very com-
mon disease of both cultivated and wild roses.
All three important spore-forms are formed
upon the same host plant. The cluster-cup
stage appears in early summer, or late spring,
and causes a distortion of the attacked parts.
These are usually swollen and badly bent and
become bright orange in color. The summer
spores appear later and are also brightly col-
ored. The winter spores appear last and are
formed in small, round, blackish patches on the
under surface of the leaf. These spores form
a fine, small, powdery mass. The spores are
long and are divided into a number of cells,
often about seven or eight, arranged in one
row, and have a long club-shaped stalk.
Care should first be taken to prevent the
wintering over of the disease. This can l>e
done by destroying the old leaves, particularly
those of diseased plants. Late fall or early
spring treatment with a strong c<»p|>er sulphate
solution will also aid in destroying the winter
spores. The dormant bushes and the ground
near them should l>e drenched. The spread
of the cluster-cup and summer-spores can be
Fir,. 1M"!.— Leaf rust . . • /• .. | . • .
,,f roses, stem with pre\ eiitcd by spraying atter the buds open with
cup*. Original. lx>rdeaux <>r ammoniacal copper carbonate.
The rose stem rust (Phragmidium spcciosttnt /•>.) This rust
is a near relative of the leaf rust of roses but is not identical with
it. The attacked stem of the rose becomes swollen and distort-
ed, and soon a large winter spore pustule is formed which looks
376
Minnesota Plant Diseases.
not unlike a smut mass. The spore mass is black and powdery
and the spores are, in general features, similar in appearance to
the winter spores of the leaf rust. Infected plant parts should
be destroyed before the spores have a chance to disperse.
The Indian turnip leaf rust [Uromyccs caladii (Schzv.) Farl.].
This rust is sometimes found on cultivated Aroids. (See Dis-
eases of Wild Plants.)
Golden-rod and aster leaf
rust \Colcosporium sonchi-ar-
vcnsis ( Pcrs.} Lev.]. The
golden-rod rust is an exceed-
ingly abundant disease upon
almost if not all of the spe-
cies of golden-rod, asters and
their allies, found in the state.
The bright orange-red summer
spores appear in great numbers
chiefly on the under surface of
the leaves, and form a bright-
colored powder. Often the en-
tire lower surface of the leaf
will be covered with the spore
groups. The winter spores
arise later in light-colored,
crust-like groups. These
spores remain attached to the
leaf throughout the winter and
germinate in the following
spring. They do not germi-
nate in exactly the usual way
for rust winter-spores for they
do not send out a thread in the ordinary manner. Four spores
are, however, produced from each winter spore and each is borne
on a stalk which comes directly from the spore which has been
previously divided up into four cells by cross walls. The cluster-
cup spores are probably formed on some coniferous trees.
Cultivated plants may be treated with ammoniacal copper car-
bonate, early in spring, and the treatment should be continued
every two to four weeks. (Fig. 205.)
;. 201. — Leaf rust of roses. 1. Rose
branch and leaves infected with cluster-
cup stages of the disease. 2. Leaf
with clusters of winter spores. 3. Win-
ter spores. 4. Summer spores. 3 and 4
highly magnified. After Massee.
Minnesota Plant Diseases.
377
Cedar apples of red cedar (G\innos/>orangiinn macro pus Link,
and G. globosum Far/.). See Leaf Rust of Apples. Diseases of
Orchards and Vineyards.
The powdery mildew of lilac [Micros f>hccra alni (ll'allr.)
ll'int.]. This is the very common blight of lilacs which, in the
fall, covers lilac leaves with a conspicuous white mycelial coating.
The same blight is apparently found on many other plants, as
alder, birches, high bush cranberry and others. Summer spores
are produced in the usual manner for powdery mildews and the
FIG. JOi — Powdery mildew of lilac, showing the white patches of the- fui'.m
Original.
sac capsules appear in the fall. 'Hie latter are furnished with
appendages similar in shape to those of the apple jxwdery mil-
dew. L'nlike this blight, however, the sac-capsule of the lilac
mildew contains more than one sac. The presence of the blight
on the lilac, though it undoubtedly draws some nourishment from
its host, does not seem to exert any serious influence ujxni it.
Burning of the fallen leaves in the autumn has l>een recom-
mended. Spraying is usually not practiced since the disease or-
dinarily does no serious injury. Ammoniacal copper carbonate
or potassium sulphide would probably prove effective against it.
378 Minnesota Plant Diseases.
The powdery mildew or blight of the rose \S phaerotheca
pannosa (Wallr.*} Lev.~]. An enormous amount of damage is sus-
tained yearly by the ravages of this blight in gardens and green-
houses. The leaves of the attacked rose bushes become covered
with a fine white coat of the fungus mycelium and often become
distorted or stunted in
various ways. The
young leaves and buds are
especially damaged, and
many leaves are killed.
The mycelium sends suck-
er-like branches into the
interior of the epidermal
cells of the host and from
these draws its nourish-
ment. This of course re-
sults in a drain upon the
host plant. During the
summer erect threads are
produced on the surface
of the leaves and these
form chains of spores,
which are carried about
by the wind and rapidly
spread the disease from
leaf tO leaf and from plant FlG 203.-Powdery mildew of 'roses. A leaf of a
tO plant These Summer rose attac^e(^ by the disease. After Clinton.
spores, therefore, act in a manner similar to those of the wheat
rust. Toward late summer and fall small black bodies about
the size of a pin-point are formed on the mycelium, and these
are the closed sac-capsules. They are yellowish-white, when im-
mature, becoming black when mature ; they are attached to the
mycelium by special brownish appendages. They have a more
or less membranous wall, which is divided into polygonal areas.
The sac-capsule, when broken, shows a single, spherical, colorless
sac, in which are found eight oval spores. The sac-capsule does
not open until spring, when the wall decays, setting the spores
free. These spores, therefore, function as winter spores. In the
spring they germinate, by sending out a fine tube, which again
Minnesota Plant Diseases.
379
infects a rose plant. The mycelium, thus produced, soon com-
mences the formation of summer spores. It is the abundance of
the latter spores, and the rapid infection by their means, that
makes the rose mildew dangerous.
Flowers of sulphur dusted on the leaves of the plant are chief-
ly employed to prevent the germination of the summer spores.
The mycelium is also killed by the sulphur treatment. "For
greenhouse treatment paint hot water pipes with mixture of sul-
FlC. 3M. — Powdery mildew of roses, showing the su)>erncial mycelium ami summer scores
on the leaves. A germinating sjH»re is seen in the foreground. (On a |>cach leaf.)
Aftor Tulasne.
phur and oil. Potassium sulphide or an ammoniacal solution of
copper carbonate can be sprayed on the foliage. Spraying out of
doors can be done with bordeaux, if there is no objection to the
sediment on the leaves." (Conn. Ag. Ex. Sta. Bull. 142 — 1903.)
Powdery mildew of chrysanthemums (Oulinm chrysanthemi
Rabh.). The powdery mildew is an occasional destroyer of
chrysanthemum plants in homes and greenhouses. As in the
other powdery mildews, the mycelium is superficial and forms a
cobwebby or mold-like growth on the surfaces of the leaves.
From this mycelium arise necklace-like strings of spores in a
3^o Minnesota Plant Diseases.
fashion typical for the summer spores of the powdery mildews.
These spores give to the surface of the leaf a powdery appear-
ance. The relationship of this summer spore to its proper win-
ter-spore form, has not been determined, but it is probably con-
nected with the very common powdery mildew of wild com-
posite flowers (Erysiphe cichoracearum) or some closely related
species. It has never been reported as appearing in dangerously
large numbers in any greenhouse in this state. It would proba-
bly yield to the common treatments for powdery mildews and
other superficial parasites, e. g., ammoniacal copper carbonate or
potassium sulphide sprays.
The drop of lettuce (Sclerot'mia libertiana Fckl.\ This fun-
gus has been found very destructive in eastern greenhouses. It
attacks many kinds of lettuce and has been found to be the chief
enemy of lettuce culture under glass. The fungus is also remark-
able in that it is identical with the cause of a rotting-disease of
cucumbers. The drop fungus is a cup fungus. The mycelium
is parasitic on the lettuce leaves and stem and attacks the plant
very vigorously, producing complete collapse and quick rotting.
As the rotting of the leaves proceeds, the fungus threads com-
mence to form small storage organs, usually on the lower sides
of the fallen leaves. These storage organs or sclerotia are about
the size of a large pin head, or slightly larger, and are composed
of densely woven masses of fungus threads, stuffed with nutrient
material. There are sometimes produced considerably larger
sclerotia, and these give rise to the cup form of fruiting body,
which bears the sacs on the upper surface. Usually, however,
the small sclerotia only are produced in greenhouses and these do
not produce the cups. They are, however, very resistant bodies
and will survive very unfavorable conditions for a considerable
length of time. Thus they carry the disease from one crop to
another. Freezing or drying, instead of killing them, accelerates
their development when conditions are again favorable. In the
latter case the sclerotium fungus threads resume growth and a
fine mold-like mass of threads issues from it. These threads are
vigorous and can immediately infect the lettuce plants. The fun-
gus thrives best under conditions most favorable to the growth
of the lettuce and the greatest amount of damage is done when
the lettuce is about mature. Ordinary methods of prevention.
Minnesota Plant Diseases. 381
such as spraying, are not available for reasons that poisonous
substances cannot be used on the lettuce and also that the ordi-
nary sprays do not affect the sclerotia. The most effective rem-
edy is a complete or at least partial sterilization of the soil. A
coating of five-eighths or three-fourths inches of sterilized sand
or earth will materially reduce the effect of drop, while four
inches has in certain experiments completely destroyed all of the
disease. The drop can also be greatly reduced by treating the
soil with hot water which will raise the temperature of the sur-
face to 176° F. to 1 86° F. Lime, sulphur and charcoal applica-
tions and coatings of saw-dust and coal ashes have been found to
be ineffective against drop. Good ventilation and good drainage
will help to keep it in check.
The grey mold of lettuce (Botrytis rulgaris Fr.). This fu:i-
gus appears on greenhouse lettuce, causing a leaf rot. The fun-
gus has been described as a saprophyte and it is claimed by recent
investigators that it is net at all parasitic The supposition that
ft is the summer stage of Sclerotinia libertiana has also been
denied. The grey mold of lettuce appears as a fine greyish mold
on the rotting leaves. When dry the moldy growth, if shaken,
throws off a fine dust of spores which may rapidly spread the
disease. The grey mold is probably not responsible for so much
damage as is the drop fungus (Sclerotinia lil>ertiana) with which
it has l>een confused. It can Ix? controlled by the same treatment
as the drop fungus.
Leaf spots of violets (riiyllostichi t-iolijc 7V.?;;/. uiul Csrco-
spom 'I'iolae Sacc.). This is a very common and destructive dis-
ease of greenhouse violets. There are two kinds of fungi pro-
ducing two kinds of spots, which are. however, not very easily
distinguished from each other. The Cercosj>ora sjx»t is. in gen-
eral, a cleaner cut spot, while the Phyllosticta may be more dif-
fused. Both are whitish and have dark centers where the spores
are formed, in the former cnse. in a loose weft, in the latter, in
dark spherical receptacles or capsules <»f very minute size. The
two diseases may l>e intimately associated. When the sjx)ts are
numerous, the leaf may be killed off. and the entire plant some-
times dies. The fungi are both plants of the Imperfect Fungi.
Bordeaux has l>een found useful in combating the leaf spots,
though it does not entirely prevent them. A quarter strength
382 Minnesota Plant Diseases.
has been recommended for plants under glass — the weak solution
will obviate the injurious effects of stronger solutions in retard-
ing flowering. Plants in the open field should be sprayed
throughout the summer with one-half strength bordeaux every
ten days.
The downy mildew of seedlings (Phytophthora omnivora
DcBy.}. This fungus pest is a parasite on seedling trees of
many families of plants. It is especially destructive in nurseries
where it may destroy seedlings of conifers and many other plants.
It is not dangerous to older plants but confines its attack to young
seedlings which have produced only a few leaves. It appears
first on the stem, cotyledons, or first leaves, as brown or blackish
patches. On these patches develops a very delicate film of spores
produced in a manner very similar to those of downy mildew of
potato. These spores may germinate directly to an infection
tube or they may produce swimming spores, just as do the spores
of the potato mildew. The parasite shows little choice of host
except in the selection of young plants. It is therefore amateur-
ish in its style of parasitism, but it is nevertheless very de-
structive. In a few days' time it may destroy whole beds of
seedlings. It produces winter spores by a breeding act, as is
common among the downy mildews.
When the pest appears in nurseries, if only on a few plants,
these can be destroyed. The most effective methods are, how-
ever, those of ventilation and drainage. The fungus thrives best
in very moist situations and in moisture-laden atmospheres and
in shaded positions. By avoiding as far as possible these condi-
tions the fungus may be kept in check. As the winter spores are
very resistant, diseased plants should be carefully removed and
destroyed and plots which have been infected with the disease
should not be used for the same purpose for several years.
The damping-off of seedlings (Pythium debaryanum Hesse.}.
Seedlings of plants of the mustard family are particularly liable
to become infected with this disease. Many other paints, how-
ever, as clovers, corn and a great variety of others, have also been
known to suffer from it. Potato plants and potato tubers in
storage may be attacked, if the moisture is excessive. The dis-
ease usually appears where seedlings are too densely crowded to-
gether, or in shady places and where there is excessive moisture.
Minnesota Plant Diseases. 383
The evidence of the presence of the disease is seen in the falling
over of the seedlings and their subsequent death and decay. The
fungus requires a great deal of moisture and attacks the stem of
the seedling at the surface of the ground. It is very destructive
in its attack and kills off the tissues at this point, causing the fall
of the seedling. The spores are formed only in the presence of
moisture and the plant is able to live in a saprophytic manner.
It is a primitive, but directly destructive, parasite. Under favor-
able conditions the fungus will spread very rapidly and cause
great destruction to beds of seedlings. The summer spores are
of two kinds. One germinates usually very soon after forma-
tion, producing directly an infection tube. The other is some-
what like the so-called summer spores of downy mildew, but un-
dergoes a resting period, after which it breaks up into swimming
spores. Each of the latter is provided with two lash-like pro-
cesses, which aid in its swimming about in the water. When
these swimming spores come to rest they germinate into an in-
fection tube which attacks new seedlings or builds up an aquatic
mycelium. The winter spore is formed by a breeding act and
is provided with a very thick wall so that it can undergo long
periods of rest. When it develops further it produces swimming
spores, just as do some of the summer spores.
Plenty of sunshine and good drainage will keep the fungus
in check. Soil which contains many winter sjxjres, or resting
summer spores, should be avoided. (Fig. 34.)
The damping-off of prothallia(f ythium intermedium DeBy.}.
This fungus is a very close relative of the damping-off of seed-
lings and its behavior is somewhat similar. The host plant is.
however, the sexual plant of the ferns, commonly known as the
prothallium. The fungus is a common enemy of fern culture in
greenhouses, when ferns are raised from spores. The fungus
permeates the tissues of the prothallium and the latter wilts. In-
comes dark in color, dies and decays. The fungus produces sum-
mer spores in a manner, in general, similar to that of the damp-
ing-off of seedlings. The so-called spores form, under proper
conditions of moisture, numerous swimming spores, and these
behave in a peculiar manner: for. when they cease to swim, they
move in an amoeboid manner until they finally come to rest and
germinate.
384 Minnesota Plant Diseases.
"If the pots or vessels in which the prothallia are grown are
rested on sphagnum, a layer of which can be placed in the bottom
of the Wardian case, and after the young prothallia have started,
all of the watering be applied through this, the prothallia will do
much better than if surface watering is practiced, and far better
than where the pots are rested in a vessel partly full of water.
The air of the Wardian case or of the house should not be kept
too damp." (Cornell Ag. Ex. Sta. Bull. 94 — 1895.)
The downy mildew of violet (Pcronospora viola DeBy.).
This disease is well known in Europe, where it attacks cultivated
violets and pansies, both in greenhouses and in gardens. It is
also known in the United States, though it has not been reported
from Minnesota. The summer spores are borne on threads,
which come out of the leaf on its lower surface and form there
greyish, downy masses of mildew. They are produced on
threads in a manner similar to those in the downy mildew of
mustards.
Good ventilation and abundant sunlight and the avoidance of
damp conditions will keep the fungus in check. It thrives only
in moist conditions.
Mildew of mushroom (Sporodinia graudis Link.). (See Dis-
eases of Wild Plants.)
Chapter XXII.
Diseases of Wild Plants.
Gall disease of the blueberry, cranberry and other heaths
[Ejfobasidium vaccinii (Fckl.) IT or.]. Plants of the heath fam-
ily, e. g., cowberries, blueberries and true cranberries, may be at-
tacked by a fungus which produces malformations of branches
and leaves. Flowers and flower-stalks are also attacked in some
cases, and the formation of fruits prevented. Sometimes the leaf
swells up into enormous kidney-shaped, fleshy taxlies which are
many times thicker than the normal leaves. The hypertrophied
portions, where exposed to the light, are colored red. A cut
through such a leaf shows it to be composed of a fleshy mass,
through which the branching veins can lie clearly seen. These
veins are much reduced in structure from the normal and contain
but a small amount of woody material. The fleshy portions have
almost completely lost the power of starch-making, as is shown
by the small amount of leaf-green present and by the entire ab-
sence of large air-spaces. The fungus threads are very fine and
are found only in the attacked regions. They run between the
cells of the host, and at the surface of the leaf form a rather
dense weft, just underneath the cuticle of the external layer of
cells. From this weft numerous spores are produced on basidia.
which are arranged in a palisade. The s|>ores can l>e seen with
the naked eye as a tine, white powder on the surface of the leaf.
Under the microscope the s|x»res are seen to l>e produced on small,
finely-pointed stalks, four arising from a single cell. When these
spores fall on the young leaves or stems of the host-plant they
germinate into fine germ-tubes, which penetrate into the leaf
through an air pore, or directly through the walls of the outer
row of cells, and from this point spread into the mature mycelium.
The presence of the mycelium immediately stimulates the leaves
to the above-described abnormal growth, which takes place at
the expense of the neighboring parts. All diseased plant parts
should be burned. (See Fig. 37.)
25
386 Minnesota Plant Diseases.
Rust of Pyrola \Chrysomyxa pirolae (DC.} Rostr.]. On all
species of Pyrola found in the northern part of the state occurs
a Pyrola rust. It is found chiefly in the spring and often occurs
in great abundance. The cluster-cup stage is not yet known, but
is probably to be found upon some needle-leaved evergreen tree.
The summer spores are by far the most abundant and appear in
early summer. Their spore groups often completely cover the
lower surface of the leaves with a golden-orange powder-mass.
The winter spores form darker, crust-like masses, which are much
less abundant. See Leaf Rust of Pines, Chapter XVI.
The rust of milkweeds [Cronartium asclepiadeum (Willd.)
Fr.~\. This rust is very well known in Europe as a parasite upon
many species of the milkweed family. It seems to be very rare,
or entirely wanting, on milkweeds in this state, but what is prob-
ably the same rust has been found upon the leaves of the oak, not,
however, in great abundance. The winter spores, preceded by
the summer spores, are formed on the above-named hosts, and
the cluster-cups probably on the pines. It is the disease which is
produced upon pines that is of chief importance. See Leaf
Rust of Pines, Chapter XVI.
Cluster-cup rust of various wildflowers (Species of Aecid-
iuni). Many of our spring wild flowers, such as buttercups, may-
flowers, columbines, squirrel-corn, Dutchman's breeches, Old
Man's beard, white cohosh, Solomon's seal, false Solomon's seal,
lilies, evening primrose, elder, violet, etc., are attacked by the
cluster-cup stages of rusts. In comparatively few cases is the
connection between these and the winter-spore stages known.
These cluster-cups are found, often in great abundance, from
early spring until midsummer and are usually found on yellowish
spots, on the under surface of the leaf. On the upper surface of
the same spots are formed the little accessory spore-capsules
known as pycnidia. These are flask- or pear-shaped bodies,
opening in small yellow or black dots, onto the upper surface of
the leaf. They often exude a sugary solution. Their behavior
is problematical but they are probably vestiges of former func-
tional male, reproductive cells.
A few of these cluster-cup diseases, such as the cluster-cup
rust of gooseberries and currants, have been considered in detail
Most of them are of minor importance economically, so that pre-
ventive means need not be considered.
Minnesota Plant Diseases. 387
Cluster-cup of gooseberry and currant (Aecidium grossu-
larice Schnm.). This is very common on wild gooseberries and
currants. See Diseases of Garden Crops. See also Rust of
Sedges (this chapter).
Cluster-cup rust of composites (Species of Accidium). A
number of cluster-cup rusts attack wild and cultivated plants be-
longing to the composite family, e. g., sunflowers, asters and
goldenrods. Very little is known of their relationships with the
other spore-forms. They occur in abundance, throughout early
summer and midsummer, and are usually found on yellow spots,
accompanied by the pycnidia or accessory spore capsules, as in the
rusts of wild spring flowers. These cluster-cup rusts must be
distinguished from the golden-rod rust, which is caused by a dif-
ferent fungus and is even a different spore-form. A close ex-
amination, even with the aid of a hand lens, will serve to dis-
tinguish between them. The cluster cups are very easily recog-
nized. v
Leaf rust of golden rod and aster. See Diseases of Green-
house and Ornamental Plants.
Rust of sunflowers (Puccinia tanaceti DC.). See Diseases of
Greenhouse and Ornamental Plants.
Rusts of ferns [Hyalopsora polypodii (/'.) Mugti.]. Our
common wild ferns are subject to a rust disease, which is not un-
common in this state. The fragile fern is frequently attacked.
Summer spores are produced on the under surface of the leaves.
The winter spores are scattered through the fern tissues. They
are not as conspicuous as the summer spores. The latter occur
in dark, rust-like patches, often covering considerable areas.
Stem and leaf rust of cowberry (Culyptospora gocppcrtiana
Kilhn). An interesting disease of plants of the blueberry family,
similar in some of its effects to those of the fungus leaf gall of
the same plants, is caused by a rust fungus. This attacks
chiefly the cowberry and other related species. The young
shoots are attacked and the affected branches become much
larger than the healthy and are swollen to several times their
normal thickness. This swelling takes place the year following
the infection of the plant. The parasite lives in the tissues
for several years and the formation of fruits is usually pre-
vented on such affected shoots and the latter are finally killed.
;88
Minnesota Plant Diseases.
FIG. 205. — Golden-rod rust. Shows black spots, which are clusters of winter spores
occurring in crust-like cakes. Original.
Minnesota Plant Diseases.
389
The fungus threads, which are found in the swollen parts of
the host plant and which cause the stimulation, whereby the
increase of growth or swelling of the stem takes place, form
their winter rust-spores inside of the cells of the epidermis of
FlC. 21*5. — Sunflower rust. Winter ami summer spore clusters on
the leaf of a sunflower. ( iri^na).
the host. This epidermis is much altered on account of the
action of the fungus. Its cells have thin, instead of thick,
outer walls, and are much increased in size. These spores
germinate in the spring in the usual way, except that they
390
Minnesota Plant Diseases.
remain in the cells of the host. The cluster-cups are found on
the leaves of some coniferous tree. Spruces in the neighbor-
hood of affected cow-
berry plants often show
an abundance of cluster
cups and are usually most
seriously attacked in the
lower branches. It has
not been proven in our
American plants that
these two stages are con-
nected, but there seems
to be considerable proba-
bility that such is the
case.
Rust of an emo n e
(Puccinia fuse a Relh.\
Anemone, Thalictrum
and allied genera are sub-
ject to the attack of
anemone rust. In this rust
only the winter spores
are produced. The af-
fected plants are consid-
e r a b 1 y deformed. The
leaf stalks are longer and
the leaf blades are thick-
ened. The spore groups
are found on the lower
surface of the leaves. The winter spores of the anemone rust
pass the winter in a resting condition on the dead leaves of the
host and germinate in the spring.
Rust of wild sarsaparilla (Triphragmium clavellosum Berk.).
Although found only rarely in some places, this rust is very com-
mon in others. It is particularly abundant in the northern part
of the state, but is exceedingly rare or entirely wanting in the
middle and southern parts. It forms blackish, winter-spore
groups on the under surface of the leaf. These groups are
almost smut-like in their appearance. The spores are com-
FIG. 207. — The stem rust of cowberry (a plant of
the blueberry group). The fungus spores are
formed in the skin cells of the host, several in
each cell ; they have germinated sending out
short, divided threads, each division of which
produces a short-stalked basidiospore. Highly
magnified. After Hartig.
Minnesota Plant Diseases. 391
posed of three cells arranged in clover-leaf fashion. The spore
clusters are usually very dense and vary in size from a pin-
head's width to three-quarters inch broad. The leaf under the
spores colors black, so that the groups can readily be seen
from the upper surface of the leaf. Cluster cups and summer
spores are not known for this rust.
Rust of sedges [Pnccinia caricis (Sc,hum.) Reb.]. This is
an exceedingly common rust on many Minnesota sedges. The
summer and winter spores are produced on the sedge plant and
the cluster-cup form is very common on the vacant lot weed,
stinging nettle. The attacked nettle-
plant parts are usually deformed and
swollen, where the mycelium of the
rust develops. When the stem is at-
tacked, it is usually much bent and a
swollen cushion arises on one side.
Similar cushions arise on the leaf stalks
and on the leaf blades. On these
cushions which are usually orange to
yellowish in color are found the clus-
ter cups in great abundance. The
winter-spores are found on the sedge
leaves in long black rows, similar to
the black rust of wheat. Not all of
the rusts on sedges are of the same
F,C. 208. RuMaf^iMsarsaparma^P^ieS. TllOUgll tllC winter
•hows ciustcn of the winter spores. mav j^ so similar in appearance that
Original. .
they can scarcely be distinguished
from each other, even with the microscope, they may form their
cluster cups on different host plants. The common rust of
sedges, however, is that one which forms its cluster cups on the
nettle. The white cluster cups of wild black currant arc forms
of another sedge rust.
Rust of the dark green rush (Pnccinia angnstata Pk.). One
of our commonest broad-leaved marsh rushes is frequently at-
tacked by a rust, which occurs in great abundance on the leaves
of the plant. The winter spores are particularly conspicuous,
forming long, black lines, in which are found the densely crowd-
ed winter-spores. The latter are two-celled.
392 Minnesota Plant Diseases.
Rust of Indian turnip [Uromyccs caladii (Schw.) Farl.~\.
This rust is very abundant in Minnesota. It is found in the
wild state, chiefly on Indian turnip, but is also known on the
dragon root and on other cultivated aroids. All three rust
stages grow upon the same host plant. The cluster cups ap-"
pear in the spring and are evenly distributed over the lower sur-
face of the leaf. In early summer, the summer spores are pro-
duced in small, round, yellowish pustules and these are followed
by the winter spores. The latter are brownish and single-
celled. The mycelium is capable of wintering over in the swol-
len, underground, bulbous stem, so that a plant, once infected,
cannot be rid of the fungus. Infected cultivated plants must
therefore be destroyed as soon as the disease appears.
Cedar apple of red cedar (Gymnosporangium macro pus Lk.
and Gymnosporangium globosum Farl.). See Leaf-rust of
Apples and Pears. Diseases of Orchards and Vineyards.
Leaf rust of plums (Puccinia pruni Pers.}. On many wild
cherries. See Diseases of Orchard .Plants.
Leaf rust of juneberry. See Birds-Nest Rust of Red Ce-
dar. Diseases of Orchards and Vineyards.
Club rust of juniper [Gymnosporangium clavariaeforme
(/a/.) Rees.]. See Diseases of Orchards and Vineyards.
Rust of mints (Puccinia menthac Pers.}. See Diseases of
Garden Plants.
Rust of violets [Puccinia violae (Schum.} D. C.]. See Dis-
eases of Greenhouse Plants.
Rust of rose leaf \Phragmidium subcorticium (Schrk.)
Wint\ See Diseases of Greenhouses and Ornamental Plants.
Smut of anemone [Urocystis anemones (P.) Schroet.]. This
is not an uncommon smut upon a great number of our spring
wildflowers of the crowfoot family. It is often found upon the
liver-leafed anemone or hepatica. The smut forms upon the
leaves, stems or petioles and produces large, black, sack-like
pustules of spores. The pustule is at first covered with a thin,
greyish membrane, which later breaks and releases the spores
in a powder. The spores are not formed and liberated singly
as in ordinary powdery smuts, but are grouped together into
small spore-balls. Each ball consists of a number of spores of
two kinds : there are one to several large, central spores sur-
Minnesota Plant Diseases.
393
rounded by a protective coat of smaller, lighter spores, which
have lost their power of germination. The spore balls escape
intact as the smut powder.
Carnation smut \Ustilago vwlacea (P.) Fckl.]. This smut
is often found on wild plants of the pink family; e. g., on chick-
weeds, starworts, catch-flies, soapworts and corn cockles. See
Diseases of Greenhouse and Ornamental Plants.
Fir.. 3»9. — Mint rust. Winter sport- cluster* <>n the leaves, iiii^in.il.
Smut of violet [L'rocystis rioluc (Soic.) I:isch.]. One oc-
casionally meets with this smut on wild violets. It may occur
on leaf-blades, petioles, stems or flower stalks. Definite pus-
tules are formed which, when broken, disclose a black, powdery
spore-mass. The flowers do not seem to be attacked and the
anthers are not smutted, as in the carnation smut. The smut
spores are formed in ball-like masses of cells, the outer of which
394 Minnesota Plant Diseases.
form a protective coat to the inner cells, which are the func-
tional spores.
Diseased plants should be removed and burned.
Smut of pigeon grass (Ustilago neglecta Niessl.). There
are several smuts which attack the common pigeon grass.
Commonly the grains are replaced by the smut-spore-mass,
which is at first covered by a thin wall. These closed masses
have often a purplish tinge. The spore-mass is black.
Smut of bromes (Ustilago bromivora Fisch.~). See Diseases
of Field Crops.
Root smut of sedge (Schinzia cypericola Magn.). This is
an uncommon smut and would not be readily recognized as a
member of the smut family. Indeed it is very possible that it
does not belong to this group. It is moreover of no economic
importance but is of interest on account of its root-inhabiting
character, a very rare phenomenon in smuts. It attacks sedge
roots forming tuber-like swellings which are often branched in
finger fashion. The spores are produced internally on the ends
of short threads of the mycelium. This smut occurs in Minne-
sota, though very rarely.
Honey dew fungi (Apiosporium, Capnodium and other re-
lated genera). These fungi constitute a group of plants with
peculiar habits, which have already been partially explained.
They belong to the burnt-wood fungi, producing a mycelium of
charcoal-like texture and fruiting bodies of the same nature.
They are not true parasites, but are saprophytes, which prefer
to live on the excreta of various insects. As these excreta are
found largely on living leaves the fungus mycelium comes to
spread over the surface of the leaf and often to completely en-
close it in a dark mycelium. This position may slightly inter-
fere with the light, though the leaf is seldom injured in conse-
quence. These fungi do not effect any important losses to agri-
cultural plants in Minnesota though a number of them are
found in the state.
Mold of honey-colored mushroom [Endomyces decipiens
(Tul.) Reess.]. One sometimes finds upon the "mushrooms" of
the honey agaric (Agaricus melleus), which is so common in
Minnesota in late autumn, a mold-like parasite. The mycelium
threads of the parasite permeate the tissues of the mushroom.
Minnesota Plant Diseases. 395
The spores are formed usually in fours, inside of small sacs,
which are formed on the ends of branches of the mycelium.
These little sacs or asci are not enclosed in any special covering
but are free upon the mycelium.
The red disease of mushrooms [Hypomyces lactiflnorum
(Schw.) TuL']. This is a conspicuous though not very abundant
disease of wild mushrooms. It is usually found on the milk
mushrooms. The disease-fungus is a member of the burnt-
wood fungi, though it has not the black color of most of these
plants. An attacked milk mushroom becomes greatly modified
in structure. It does not form gills as under normal conditions
but the entire surface of the mushroom is smooth. It is there-
fore roughly top-shaped with the peg in the ground. The sur-
face is colored a very brilliant red (scarlet to orange red), which
makes the diseased plant a very conspicuous object in the
woods. This color is imparted to it by the parasitic fungus.
All over the surface one sees the slightly protruding tips of the
sac-spore-capsules which are spherical to pear-shaped and are
partially embedded in the tissues of the host. Through an
apical opening the sac spores escape in enormous numbers so
that if the diseased mushroom be placed under a bell jar for
several hours, and left undisturbed, a dense white powder of sac
spores from the parasite will fall on the underlying glass.
These spores are presumably again capable of causing infection.
Powdery mildew of hazel [Phyllactinia suffttlta (Rcb.)
Sacc.]. Hazels are very commonly attacked by a blight, which
occurs also on many other trees, such as birch, oak and ash.
though not so abundantly on these. A fine, white, cobwebby
mycelium is formed on the leaves, upon which the sac-capsules
arise in the fall. The sac-capsules are readily recognized among
the powdery mildews by the peculiar appendages which are
colorless and straight, and when mature have a swollen bulb
at the point of attachment to the capsule. The appendages are
not very numerous. The capsules contain a number of sacs,
each of which encloses eight spores. Although the disease is
very common, the damage done is usually slight and does not
call for combative measures.
Powdery mildew of vetch and crowfoot [Erysiphc com-
nutnis (U'all.) /•>.]. This blight is an exceedingly common para-
396
Minnesota Plant Diseases.
site on many wild plants and is also found on cultivated plants.
It is found in great abundance on plants of the crowfoot and
pea families. It appears on wild vetches as an extensive, fine,
white mycelium, which bears the summer spores as a starchy
powder, typical for the powdery mildews. The spore-sac-cap-
sules are formed in the late summer and fall and appear as small
black bodies about the size of a very small pin-point. The cap-
sules have unbranched, brown appendages, which are inter-
woven with the mycelial hyphae. They contain a number of
sacs, each enclosing eight spores. This mildew, though com-
mon on wild plants, is apparently not very destructive to culti-
vated plants.
If necessary,
treatment as
against powdery
mildews in gen-
eral would prob-
ably be effective.
Powdery mil-
dew of compos-
ites (Erysiphe ci-
choracearum DC.\
This is perhaps
the most com-
mon of all our
powdery mildews.
It is exceedingly
abundant upon a
great number of
wild plants, be-
longing chiefly
to the composite
family. The bo-
rage and other
families are less
frequently
FIG. £10.— Powdery mildew of composites, on the leaf of the
great ragweed. The white felt of the superficial mycelium
is shown and the numerous black dots are the sac-spore- t cl C K 6 Q. It
capsules. Original.
at-
is
found on s u n-
flowers, rag-weeds, verbenas and a host of other plants. It
forms a more or less dense and conspicuous, white, cottony
Minnesota Plant Diseases. 397
coat over the leaf surface. The sac-capsules appear in the fall,
but in some cases do not mature until the following spring.
They have appendages somewhat similar to those of the pow-
dery mildew of grasses are unbranched, dark in color and inter-
woven with the mycelial threads. The capsules contain nu-
merous sacs, in each of which are produced eight spores.
See also Powdery Mildew of Cucumbers. Diseases of Gar-
den Crops.
Powdery mildew of mints (Erysiphe galeopsidis DC.}. This
mildew occurs on many wild plants of the mint family. The
mycelium appears as a superficial whitish film on the leaves and
stems. The fungus is very similar to the powdery mildew of
vetches and peas. It differs from this fungus in the form of its
sucker threads. The sac-capsules are formed in the fall, but
do not mature until the following spring. The fungus is not
known extensively on cultivated plants. In case of a serious
attack the usual methods against powdery mildews would prob-
ably be effective.
Witches'-broom of cherry [E.voascns cerasi (Fckl.) Sad.]
See Diseases of Orchards and Vineyards.
Witches'-broom of birch (Species of EMUSCIIS). See Dis-
eases of Timbers and Timber Trees.
Plum pockets and cherry pockets (Species of E.voascus,
chiefly E.roascus pruni FckL). See Diseases of Orchards and
Vineyards.
Black-knot of plum and cherry [Plourightia morbosa
(5Y//7C1.) Sacc..]. See Diseases of Orchards and Vineyards.
Mold of mushrooms (Sporodinia grand is Link.). Mush-
rooms of various kinds, wild as well as cultivated, are attacked
by a mold of the bread- or black-mold group. The mold is
particularly abundant on mushrooms that have been picked and
kept in moist situations for some time. It lives chiefly as a
saprophyte and forms on the mushroom a dense, white, moldy
felt which is composed of comparatively coarse threads. This
white felt later turns brown and then black. When in the
brown state one usually finds an abundance of spore-cases, each
containing several to many spores. When the felt has become
black the sexual reproductive bodies are produced, similar to.
but in much greater abundance than in. the ordinary bread
mold. Their fusion results in the production of a thick-coated.
398
Minnesota Plant Diseases.
resting spore. Shortly after the mold has become established
decay of the mushrooms sets in and the latter may soon be de-
stroyed. The trouble can usually be obviated by avoiding too
moist conditions. There are several other molds of the bread-
mold group which attack picked mushrooms.
Gall fungus of the wild peanut (Synchytrium decipiens
Farl.). This disease has no economical importance in Minnesota,
since its host is an unused wild flower, but is of interest on ac-
count of the fungus producing it. It is an exceedingly com-
FIG. 211.- — Gall fungus on the wild peanut. Minute galls can be seen on the petioles and
leaflets. Original.
mon disease and is often found in great abundance. The host
plants then appear covered as with a yellow rust, not unlike the
cluster-cup stages of a rust fungus. The fungus is a single-
celled plant and lives in the cells of the host which it stimulates
to an increased growth resembling tiny yellow galls. Swim-
ming spores are produced in a manner similar to those of the
seedling disease of cabbages. Winter spores are also formed
in a similar manner to those of the cabbage disease. The fun-
gus is abundant in rainy seasons.
Fungus gall of wood anemone [Synchytrium anemones
(DC.) Wor.}. This fungus is a similar plant to that of the wild
Minnesota Plant Diseases. 399
peanut. It is single-celled and produces swimming spores in
the early summer months. It forms small, dark, reddish galls in
the tissues of the host plant, quite like those formed by the gall
fungi of dandelion, wild peanut and cranberry, but the galls are
colored red as in cranberry. This fungus is very common in
Minnesota and is especially conspicuous in late spring and early
summer. It can be readily recognized by the dark, reddish col-
or of the host plant leaves and the small wart-like excres-
cences.
Leaf wart of dandelion (Synchytrium taraxaci DcBy. et
Wor.\ This fungus is closely related to the fungus of the seed-
lingi disease of cabbages. It attacks the leaves of the dandelion
and stunts and distorts them. The fungus is a single spherical
cell and lives in one of the epidermal cells of the host. The
latter cell swells to many times its original size and produces
the simplest kind of a plant gall. The leaf when badly infected
contains many of these galls, so that the surface is more or less
roughened by the abundance of warts. Swimming spores are
produced in a manner similar to those of the seedljng cabbage
disease and spread the infection under moist conditions. Thick-
coated winter spores are also produced. This disease, though
not uncommon, is never serious enough to assist materially in
getting rid of the dandelion pest.
Cranberry scald (Undetermined fungi). The life stories of
the fungi which cause this disease have not yet been worked
out. There are probably several kinds producing what is com-
monly known as scald. Small soft spots arise in the cranberry
and these soft spots enlarge rapidly until the whole berry is af-
fected and it now has the appearance of a scalded berry. The
skin remains intact but the contents are watery and soft. In
the diseased tissues one can find abundant threads of the fun-
gus. The berry in later stages turns dark brown, finally shrivels
and becomes black. On the surface are produced minute black-
spots appearing somewhat like the capsules of certain parasitic
burnt-wood fungi. The disease appears in July and August
and affects also cranberries in storage. Excessive moisture
seems to favor the disease. Sanding of the bogs, an inch in
depth, and draining in summer, so that they shall remain fairly
drv, have been recommended.
Index*
JST
Absorption, in fungi, 10
in parasites, 12
system of parasites, 10
threads, 61
Acetate of copper, 220
Acid of rancid butter, in potato
wet rot, 34°
Aecidium elatinum (Fig. 23),
grossulariae, 317, 38?
species of, 3$
Agaricacerc (see gill fungi), 178
Agaricus campestris (Fig. 89), 179
melleus (Fig. 128), 260,261.262
melleus, mold on, 394
Age, of mycelium, 19, 20
old. predisposition of, 95
old, relations of. 91
stimulation, 83
Aid of state in disease preven-
tion, 208
Albugo Candida, 330
Alcohol, in apple blight. 364
Alder, hairy pore fungus of. 259
powdery mildew of. 377
root tubercles of, 50
witches'-broom on, 121
Alfalfa, bacteria of, 196
leaf spot, 309
Alga-, absence of rusts in, 165
blue green, 7
causing disease in plants, 198
flower pot, 104
partnership with fungi ( Fig.
2l), 48. 49. 145. / ff>
pill box, host to Chytn-
dities, 105
pond scums. 105
Algal fungi. 103. 104
destruction of small areas. 78
list of groups in, 104
lowly (Fig. 41), 104.105
on animals, 66
on fruits, 65
-t;
Algal fungi, on insects, 67
Aluminum sulphate. Hassel-
man's treatment, 239
Ammonia in blue water, 219
Ammoniacal copper carbonate, 219
for apple rot, 357
for aster leaf rust. 376
lor black rot of vine. 366
for blight of ro«' 371
for downy mildew 01 Deans. 33;
for leaf blight of cdcr;, 321
for mildew of chrysanthe-
mum, 380
for powdery mildew of ap-
ple, 361
for powdery mildew of cu-
cumber, 325
for powdery mildew of
hops. 325
for powdery mildew of
strawberry. 324
for powdery mildew of
vines, 366
for rose leaf rust. 375
substitute for bordeaux. 220
Amu-ba stage of slime moulds, HJ~
Amphibia, parasites on, 7-'
fish molds on. 107
Amphispore of I'uecinia
vexans, 15*1
Anatomy of host, effect of
parasite on, 87
Ancotry of plants. 8
Anemone, cluster-cup on ( Fig.
74>. 161
cup fungi on, 145
gall fungus of. 398, 3'W
host to Chytridines, 105
host to downy mildews. 112
rust 01, 390
smut of, 392
Animals, burrowing, wounds
caused by, 4"
parasites on. 66
402
Minnesota Plant Diseases.
Antagonisms of bacteria, 193
Anther-inhabiting parasites, 65
Anthers, smuts in, 158
Anthracnose, 151
of bean, 327
of currant and gooseberry, 327
of vines, 367, 368
Ants, parasites of, 71
Apiosporium, 394
Apparatus, fixings for spray
(Fig. in), 228
Apples,
bitter or ripe rot of (Fig. ,
190), 356,357
black rot of (Fig. 194), 363, 364
blight of (Fig. 195), 364,365
brown rot of, 357, 358
cedar, of red cedar (Figs.
181, 182), 347,348, 349
leaf rust of (Figs. 181, 182),
347, 348, 349, 350
powdery mildew of, 361
ripe rot of, 152
rot (Fig. 190), 356,357
rusts, 1 66
scab (Figs. 183, 184, 185, 186,
187), 138, 351, 352, 353, 354
slime flux of, 271
Arcyria serpata (Fig. 100), 197
Armillaria mellea (Figs. 6, 128),
260, 261, 262
Aroids, rust of, 392
Arsenic mixtures 213, 214
Attack, methods of, in parasites, 61
Auriculariineae (see Jew's ear
fungi).
Ascomycetes, 117
Ash,
leaf rust (Figs. 75, 76),
162, 163, 277
powdery mildew of, 395
Asparagus,
rust of (Fig. 161), 166, 318, 319
spray pump for rust of
(Figs. 109,110), 222,224
sterile fungus rot of, 329
Aspergillacea% 122
Aster,
china, sterile fungus rot of, 329
Bacillus, a bacterial form, 190
amylovorus (Fig. 97),
193- 364, 365
of wet rot (Fig. 172), 340
Bacillus,
sorghi, 314, 315
tracheiphilus (Fig. 173), 341
Bacteria (Fig. 96), 189 to 196
air-loving and air-shunning, 191
and iron ore, 191
apple and pear blight, 364, 365
assisting in fermentation, 119
assisting in wood rot, 40
bean leaf blight, 342
black rot of cabbage, 342
cause of disease, 189, 193
cause of plant disease, 192
classification of, 190
colorations by, 194
coloring matters of, 189
diseases in plants, 191
dye-forming, 194
fermentation by, 194
forms and sizes of, 189
general characters, 189
heat-loving, 192
in beer and wine, 196
in bread and beer making, 195
in cheese, 196
in slime exudations, 120
in slime flux, 271
in tanning, 196
influence of light, etc., on, 192
light and heat forming, 194
multiplication of, 190
nitrifying, 195
nodules of (Fig. 98), 195
of fire-blight of apples (Fig.
97), 193
of hay-curing and ensilage, 195
of rancid butter, 191
of root nodules (Fig. 99), 196
of vinegar, 191
partnerships and antagon-
isms, 193
partnerships with plants, 50
pathologic, 193
phosphorescence of, 194
physiology of, 191
relationships, 189
rennet, 196
reproduction of, 190
sorghum blight, 314
spores of, 191
vinegar, 195
wet rot of potato (Fig. 172), 340
wilt of cucurbits (Fig. 173), 341
Minnesota Plant Diseases.
403
Bacteria,
zooglcea, 190
Bacterial purple, 194
Ball-throwing fungus, explosive
apparatus, 33
Balsam fir,
green cup-fungus rot, 267
canker of stem, 268
Jews' ear fungus on (Fig.
79), 167
witches'-broom of (Fig. 23),
53, 277, 278
Barberry, rust spores on leaf
(Fig. 73), 159
pycnidium on leaf (Fig. 74), 161
wheat rust on (Fig. 145),
283, 285, 290
Bark, tree, smooth shelves on, 171
Barley, covered smut of, 300, 302
ergot on, 130
naked smut, 300
rust (see rust of wheat).
Barrel pumps (Figs. 104, 105),
213, 214. 230
in action (Fig. 107), 217
Basidiomycetes, 153
Basidium. of Jews' ear fungi
(Fig. ;8). 166
of palisade fungi (Fig. 8l), 170
of rusts (Fig. 73). 159
of trembling fungi (Fig. 78), 166
of weeping fungi (Fig. 78), 166
true. 155
Basidium-bearing fungi,
153. 154- 155- >7«
Bean, anthracnosc of, 327
bacterial nodules of ( Fig.
98). 195
downy mildew of. 112.330.337
leaf blight. 342
rust (Fig. 162), 166, J/9
sterile-fungus rot of. 329
Bear's head fungus, 175
fruiting bodies of. 23
rot of timber, -'44
Beef-teak fungi. 177
Beer, bacteria in. i</>
Beer-making (see yeasts).
bacteria in. 195
Bees' nest dwelling habit. 42
Bees' nest, fungi on. 122
Beet, damping-off of. 109
downy mildew of. 112. J^p
Beet,
leaf spot of, 328
scab, 327
sclerotium disease of roots, 322
slime mold parasite of, 108
sterile-fungus rot of, 329
Beetle fungi, 139, 140
on insects (Fig. 30), 68.69
origin of, 140
Beetles, parasites of, 71
Biologic species, 88
of rusts, 289
Birch, fungi on branches. 139
gill fungus on (Fig. 86). 177
green cup-fungus rot, 267
hairy pore fungus, 257
leaf rust, 279
parchment pore-fungus rot. 258
powdery mildew of.
125, 272, 377. 395
sapid fungus rot (Fig. 131). 265
shelf fungus. 175
slime mix of. 271
witches'-broom on, 56, 121. 271
Birch-fungus rot (Fig. 126). 254,255
Birds, parasites on. 7^
Bird's-eye rot of grape. 367
Bird's-nest fungi (Fig. 13). 186
fruiting bodies, 23
spore distribution. 29
Bird's-nest rust of red cedar. 350
BirdVnc-t witches'-broom
( Figs. 2<>, 57). 54. 55
Bitter rot of apples (Fig. 190),
356. 357
Blackberry, orange ru-t of
( Fig. 100), 310,317
Black haw. powdery mildew of
(Fig. 51 >. 125
Black knot (Fig. 5«/>. U5- '36
allies of. 135- >3r>
fruiting bodies of. 23
on plum and cherry I Fig.
191.). 358. 359- 3<*>
Black fungi. 123
apple -cab, 35 l
black roi of tomato. 329
black rot of vine. 3"5
early blight of potato. 329
imperfect fungi of. '4'J
red disease of mushrooms. 395
red knot rot. 271
404
Minnesota Plant Diseases.
Black mold of clover (Fig.
153),
Black molds (Fig. 46), 113,
dung-dwelling habit (Fig.
16),
on food,
on mushrooms,
parasites on,
soft rots of fruits,
Black rot of apple (Fig. 194),
363,
of cabbage (Figs. 174, 175,
1/6, 177, 178), 342, 343,
of tomato,
of vine, 365,
Black rust of wheat (see rust
of wheat),
Black spot, on elm leaf,
on grasses,
Blight, early, of potatoes,
Blight, fire, of apples (Fig.
195), 364,
Blight, leaf, of celery,
Blight, of apples and pears (Fig.
195), 364,
of bean leaf,
of potato (Figs. 39, 166, 167),
99, no, in, 112, 331, 332,
of potato, epidemics,
of potato, inoculation by,
of potato, spores of (Fig.
44),
of rose (Figs. 203, 204), 378,
of sorghum, 314,
of willow (Fig. 134), 272,
Blister of oak leaf,
Blow guns,
Blueberry, cup fungi on,
gall disease of,
gall fungi on,
galls on,
rust of.
Blue green alg;e in slime flux,
Blue molds (Fig. i),
allies of,
assisting in fermentation,
half saprophytes,
on food,
on mammals,
parasites on,
relatives of, on bees' nests,
soft rots of fruit (Figs. 188,
189),
Blue molds,
305 spore resistance to drying,
114 Blue water,
Board, pine, attacked by dry rot
37 (Figs, 121, 122), 248,
43 Boletus, species of (Fig. 85),
397 176,
114 Bones, fungi on, 42,
353 Borage family, powdery mildew
of,
364 wheat rust on,
Bordeaux (see bordeaux mix-
344 ture), dry, 218, 227,
328 for anthracnose of currant,
366 for apple orchards,
for apple rot,
for apple scab,
for asparagus rust,
for bean anthracnose,
for bean rust,
for black knot,
365 for black rot of tomato,
328 for black rot of vines,
for blight of rose,
365 for brown rot of plums,
342 for carnation rust,
for downy mildew of cu-
333 cumbers,
100 for downy mildew of onion,
98 for early blight of potatoes,
for leaf blight of celery,
109 for leaf blight of strawberry,
379
315 for leaf rust of apple,
273 for leaf spot of beets,
272 for orange rust of rasp-
232 berry, etc.,
145 for plum pocket,
385 for plum scab,
170 for plum leaf rust,
56 for potato blight,
387 for powdery mildew of ap-
271 pie,
122 for powdery mildew of
123 hops,
119 for powdery mildew of
35 vines,
43 for rose leaf rust,
73 for rust of mallows,
115 tor violet leaf spot,
42 Bordeaux mixture,
213, 215, 216, 217,
353 stock solutions of, 216.
33
219
249
177
122
229
327
347
357
352
319
327
319
360
329
366
379
358
373
336
334
329
328
317
362
363
351
333
325
366
375
373
38i
218
217
Minnesota Plant Diseases.
405
Bordeaux mixture,
test of, 216, 217
Bordeaux resin mixture, 218
stock solutions, 218
Botrytis vulgaris, 381
Brand of wheat, 297
Bread-making, bacteria in, 195
yeasts in, 36, 119
Bread molds (see black molds),
113, 114, 122
allies of, 66
on food, 43
on mushrooms. 397
Breeding act,
in basidium -bearing fungi, 154
in fungi, 103
in rusts, 164
in sac fungi, 1 17
in water molds (Fig. 42), 106
in yeasts, 119
Bremia lactuc.f, 337, 339
Brewing, with yeasts, 36
Broccoli, black rot of. 342
Brome smut, 303
Broom (see witches'-broorn).
Broom corn smut, 300
Broom rapes, parasitic seed
plants, 200
Brown rot of apples and plums.
357- 35^
Brussels sprouts, black rot of.
Bucket pumps (Fig. 1021, 211.
Buckthorn, wheat rust <>n ( Fig.
144'. 283.285. 28S
Building paper, fungi on. 137
Bulbs, bacteria in. i«jj
cup fungi <>n. 145
sclerotium disea-e of. 32.'
Burls on trees, 50
Burning of refuse, method of
cure. jo >
Burning. t«> prevent spread of
disease. 207
Burnt-wood fungi. i.V)
apple rot.
fruit rots,
honey dew fungi. 394
on honey dew. 4_'
on loaves, 41
on log ( Fig. 83). 17.;
on stems. <>4
saprophytes on dung. jS
wound parasites. 47
Burreed elder (Fig. 45), in
Butter, bacteria of rancid, 191
Buttercups, rust of, 386
Butterflies, parasites of, 69
Butyric acid in apple blight, 364
Cabbage,
black rot of (see black rot
of cabbage).
club root of (Fig. 180), 345-346
downy mildew of, 331
host to Chytridines, 105
seedling disease of, 339, 34°
sterile-fungus rot of, 329
white .rust on, 330
Cake, molds on, 113
Calyptospora gttppcrtiana (Fig.
207), 387. 3«9. 390
Canary grass, ergot on (.Figs.
5-J. 155). 1 -'8.308
Cancer roots, parasitic seed
plants, 200
Cane sugar, yeasts in. 1 ly
Canker of balsam fir stem, 268
Caper plants, white rust on, 330
Capillitium of slime mold (Fig.
100), 197
Capnodium, 394
Caps, reducing, for spray ap-
paratus (Fig. in), 228
Carbonate, ammoniacal copper, 219
Carnation.
ru.st. 373
MIHU. isS. .?;;. 393
Carrion fungi (.Fig-, i.'. <>4. 05 i.
29. /.V;. 188
earth-dwelling habit. 39
fruiting bodies. 23
-pore distribution. 29
-torage organ- < Fig. 3), 15
-•rands of ( Fig. 31. 10
Carrots,
downy mildew oi. 112
-terile-fungu> rot ..:. 329
Catch llies. smut oi'. 371
Caterpillar fungi (,Fig. 50).
130. 131, 132
allie- of. 133
germinating -pore (Fig. 15.1. 34
• in animal-. 60
• IP. butterflies < Fig. 311. (><>. 70
' ii> in-ect-. O.S
-torage organs. 15
Caterpillar-, mold on. 1 15
406
Minnesota Plant Diseases.
Cats, fungi on, 73
Cattle, fungi on, 73
wounds caused by, 47
Cauliflower,
black rot of, 342
sterile-fungus rot of, 329
Cause, immediate, of disease, 2
Cedar apple, of red cedar (Figs.
181, 182), 347, 348, 349
rusts of, 160, 164, 166
Cedar, red,
bird's-nest broom of, 165
bird's-nest rust of, 350
Cedar, white,
Jews' ear on, 167
Celery,
leaf blight of, 328
sterile-fungus rot of, 329
Cells of wood tissues, 85
Cellulose, in cell walls, 85
Cercospora apii, 328
beticola, 328
viols, 381, 382
Cereal rusts (see rust of wheat).
Cereal smuts, 158
Cereals, rust-proof varieties, 289
Chffitomiaceas '(Fig- 60), 136, 137
Cheese, bacteria in, 196
green mold on, 118, 122
Cherry,
black knot of (Fig. 191),
135, 136, 358, 359, 36o
broom on, 56
brown rot of, 357
leaf rust of, 350
pockets of, 120, 361
powdery mildew of (Fig.
192), 360, 361
scab of, 363
stunting by pocket fungi, 82
witches'-broom of, 121, 271, 363
Chickens, parasites on, 73
Chickweed, rust of balsam fir, 278
Chlorosplenium reruginosum, 267
Chondrioderma difforme (Fig.
100), 197
Chrysanthemum, powdery mil-
dew of, 379, 380
rust, 371, 372
Chrysomyxa pirolae, 386
Chytridine;c (Fig. 41), 1-04, 105
Cladosporium carpophilum, 363
Clamps, hose (Fig. in), 228
Clams, parasites of, 67
Classification of diseases, i
Clavaria, species of (Fig. 83), 173
rots of wood, 244
Clavariacese (Fig. 83), 172, 173, 174
Claviceps purpurea (Figs. 154,
155), 306,307,308,309
Cleanliness in prevention of
spread, 207
Clover, bacterial nodules of, 195
black mold of (Fig. 153), 305
cup fungi on, 145
cup fungus leaf spot, 309, 310
damping-off, 109, 382
dodder on, 200
downy mildew of, 112, 314
leaf rust, 292
leaf spot of, 309, 310
rotation of crops and bac-
teria, 196
rusts, 166
Clothes, mildew of, 43
Club fungi (Fig. 83), 172, 173, 174
earth-dwelling habit, 39
edible forms, 174
fruiting bodies, 23
rots of wood, 244
Club root of cabbage, radish,
etc. (Figs. 179,180), 345,346
Club root of beets, 198
Club rust of juniper, 349, 350
Cluster-cup,
of ash-leaf (Figs. 75, 76),
162, 163
rust of composites, 387
rust of gooseberry and cur-
rant, 317, 386, 387
rusts of wild flowers, 386
Coal spot diseases, 151
Coccus, a bacterial form, 190
Ccelenterates, parasites of, 66
Coffee rusts, 166
losses by, 201
Coleosporium sonchi-arvensis
(Fig. 205), 376, 388
Collards, black rots of, 342
Colletotrichum lindemuthianum, 327
Collybia rot, velvet stemmed
(Fig. 130), 264. 265
Collybia velutipes (Fig. 130),
264, 265
Colorations of bacteria, 194
Columbines, rust of, 386
Minnesota Plant Diseases.
407
Common gemmed puff-balls
(Figs. 90,91), 181,
Composites,
powdery mildew of (Fig.
210), 396,
powdery mildew of hops on,
rust of,
Cone-bearing trees, ring disease
of,
Conifers, cup fungi on.
downy mildew of seedlings,
rust of cowberry,
sulphur fungus on,
Contract of parasitism in plants
and animals,
Conversion of wood into punk.
Co-operation of state in disease
prevention,
Copper acetate (dibasic).
substitute for carbonate.
Copper carbonate ammoniacal.
Copper saccharate,
Copper salts, effect on roots.
Copper sulphate.
for apple orchards.
for apple seal).
for powdery mildew of
vines.
for rose leaf rust,
in blue water.
in bordeaux.
in Hasselman's treatment,
in saccharate of copper.
Coprinus comatus (Figs. 87,88).
I78,
Coral fungus (Fig. 84), 174.
rot of \v<»<x!s (Fig. 119). 244.
Coral root orchid.
partnership with fungus,
Cordyceps (Fig. 15).
Cordyceps militaris (Fig. 31).
stylophora ( Fig. 31 ).
Coreopsis, sterile-fungus rot of.
Corn, broom, smut of.
Corn cockles, smut of.
Corn, rust,
Corn, simit (Figs. I4S, 149).
»56. .'97.
formalin not effective.
poisonous to cattle,
proficiency of parasitism.
stimulation bv.
182
397
325
387
270
MS
382
390
253
75
19
208
2JO
220
219
220
213
219
347
352
366
375
-'15
215
239
_'2O
5°
34
70
70
329
300
393
292
223
295
>S
Corrosive sublimate, 226
for potato scab, 326
on knife in pruning, 365
steep, 226
Cottonwood, leaf curl fungi on, 121
powdery mildew of, 272
red knot of, 134
rust of, 279
Couplers, hose, for spray ap-
paratus (Fig. in), 228
Covered smut of barley, 300, 302
Cowberry, gall disease of, 385
rusts, 160
stem and leaf rust (Fig.
207), 387. 389- 390
Crabs, parasites of, 6"
Cranberry, fungus galls on, 171
gall disease of, 385
high bush, powdery mildew
of, 377
scald, 399
Creeping pore fungus, wood
rot, 258
Creosote, against timber rots, 235
to cover wounds. .05
r.se to prevent rot. -'37. 23<)
Creosoting of timbers.
Cress, white rust on. 330
Cronartium asclepiadeum, 386
Crops, rotation of. -'05. 2CG
Crowfoot, powdery mildew of.
395' 390
smut of. 302
Crown rust (see rust of wheat).
Cruciferir. club root of. 345
Cucumber, downy mildew of
(Figs. 168. it*), 170. 171).
II.'. 334. .?.?.-;. 3,&. 33$
epi'iemic of mildew ( Fig.
40*. lot
powdery mildew of. 3-J4. 325
-cliTotium disease of. 320
wilt of. 341
Cucurbits, wilt of (Fig. 173). 34'
Cultures, pure, of crops. 205.206
Cup fungi (Figs. 4. 10. 14. 61
to 65). 117. /./o, /.//. 142
brown rot of plums. 358
canker of bnl-ain fir, 2<>H
drop oi lettuce. 322. 380
earth-dwelling habit. 39
explosive apparatus. 31
fruiting bodie-. 23
408
Minnesota Plant Diseases.
Cup fungi,
green, rot of,
imperfect fungi of,
leaf spot of alfalfa,
leaf spot of clover, 309,
on dung,
on fruit,
on two hosts,
ring disease of conifers,
sclerotium disease of cu-
cumbers,
sclerotium disease of let-
tuce,
storage organs of (Fig. 4),
tar spots of willow and
269,
143,
386,
maple,
transition to,
true (see cup fungi),
Currant, anthracnose of,
cluster-cup rust of,
fall of leaves,
pore fungus rot,
red knot of, 322,
root rot of (Fig. 163),
rust of,
Currant, wild black, sedge rust
of,
Cure of disease, 201, 202, 200,
Cure, mechanical means in
methods of,
methods of,
Curl of leaf, 120,
Cystidia,
Doedalea quercina,
Dahlia, sclerotium disease of
roots,
Damping-off fungi, 45, 108,
degree of parasitism,
of prothallia, 383,
of seedlings (Fig. 34).
Dandelion, Chytridines on,
leaf wart,
stunted leaves,
Daphne, parasites of,
Dacryomycetinea-, 153, 154.
Darnel, age stimulation,
infection of,
Dasyscypha resinaria,
Dead stick fungi,
Death of plants,
Deer, wounds caused by.
Degeneration of structure in
animals.
267
149
309
310
38
65
145
270
320
322
14
270
139
144
327
387
152
320
323
321
317
391
210
2O9
2O9
121
171
257
322
384
77
105
399
Si
67
769
83
94
268
139
90
47
10
Degeneration of structure in
plants, 10
Destroyers of organs, 80
of small areas (Fig. 35), 78, 79
of whole plants, 80
of host, immediate, 78
Diphtheria, bacteria of, 193
Dictyophora duplicata, 188
ravenellii (Figs. 3, 94), 187
Disease, bacteria causing, 193
cure of, 202, 209, 210
difficulty of definition, i
distinction between health
and, 90, 91
economics of, 201
factors of, 92
inheritance of, 94
in plants, 90
in plants, bacterial, 192
losses by, 201
of birds, 73
of field and forage crops, 282
of fis'h and lower vertebrates
(Fig. 32), 71
of garden plants, 316
of greenhouse and orna-
mental plants.
of insects, 67
of lower animals, 66
of lower mammals, 73
of man, 74
of mushrooms, red, 395
of orchards and vineyards, 347
of plants, bacterial, 196
of plants, organic, I
of plants, museum of, 209
of plants, inorganic, I
of timber and shade trees,
235, 260
of trees, prevention of,
237. 238 239, 240
of vineyards, 365
prevention and state aid. 208
prevention of, 202 to 209
Discomycetes (Figs. 4, 10. 14,
61 to 65), 140. 141- M2
Distribution of spores, 26
Docks, smuts in, 158
Dodder, 10
a parasitic seed plant. 203
Dogs, fungi on. 73
Douglas fir, ring scale on, 256
Minnesota Plant Diseases.
409
Dothideacea? (black knot),
(Fig. 59), 135, 136
Downy mildews (Fig. 44),
80, 109, no, III
of beans, peas, etc., 336, 337
of beets, 339
of burreed elder (Fig. 45), in
of clovers, 314
of cucumber, melon, etc.
(Figs. 168 to 171),
334- 335- 336, 338
of grape on leaf (Fig 196), 368
of lettuce, 337, 339
of mustards, cabbage,, etc., 331
of onion, 333. 334
of potato (Figs. 1 66, 167)
no, in. 112, 331, 332, 333
of seedlings, 365. 382
of spinach. 339
of vines (Figs. 196, 197,
I9«), 368.369.370
of violet, 384
sucker threads of (Fig. 2). n
Dragon flies, parasites of. 71
Drain pipe molds (Fig. 43). 101, 108
Drop of lettuce, 322. 380. 381
Dry bordeaux powder, 218, .'.'7. 2<W
Dry rot (Figs. 120, 121, 122),
245. 247, 248. 249, 250
Dry rot fungus. 175
strands of (Fig. 5). 15
Duckweed, alga: in, 198
Dung, bird's-nest fungus on. 187
constituents of. 137
cup fungi on. 144
-dwelling fungus (Fig-, id.
17*. 37-3*
-dwelling fungus, sapro-
phyte. 37
fungi, spore distribution, 30
fungi and allies ( Fig. 60).
136. i.?7
gill fungi on. 17^
Dusts, method of cure. _>ixj, _>io
powders for. _'_'7
Dutchman's breeches, rust of. 380
Dye-forming bacteria. i<>4
Early blight of potatoes u<>
Earth, basidium-bearing fungi
on. 154
-dwelling fungi (Fig. iS). 38,39
gill fungi on, 179
hard -kinned puff-balls on, 183
Earth,
long stalked puff-balls on, 182
pore fungi on, 178
Earth-stars (Fig. 93), 185, 186
Earth tongues, 147
Eau celeste, 219-
Economics of diseases, 201
Edible gill fungi (Fig. 8)), 179
pore fungi, 178
puff-balls, 186
Effect of disease on anatomy of
host, 2, 87
of host on parasite, 88
of parasitic fungi on tissues. 84
Egg, hen's, fungi on, • 73
-inhabiting fungi, 44
of carrion fungi, 188
Elder, rust of. x
Electricity, effect on bacteria. 192
use in timber treatment. 240
Elm. black spots on leaves, 136
I'leurotus rot ( Fig. 2O>.
40, .'65. 266
powdery mildew on ( Fig.
135^- 1-5- -77
slime llux of. 271
velvet Clemmed Collybia on, 265
Elynuis. orange leaf rust on, _><)i
Endomyces decipiens. 394
in slime rlux. .'71
Endomycetacear, 120
Endophytic fungi. (n
spraying of. 21 I
Endophytic parasite in cells of
grass grain (Fig. 28). 60
Ensihgc, bacteria of. i<>5
Entomophthorinea- < inject
molds), (Fig. 47). 115. 116
F.pichlu- typhina, 306
Epidemic*. 100. 101. lo_>
and pure cultures of iT"ps, 206
checked by spraying ( Fig.
40), 101
condition.- and cau.-e> of. IO_'
examples of (Fig. 3<;l. 99
]o-*e- by. -'01
i if downy niihk w-. I IM
i-f lish molds. 107
of mildew "ii cuc;;mber-
i l-'ig. 40 i.
of iowder ihiKlew-.
J>re\ elltioll
Mate aid in
101
I_'5
f. JO_'. -'07
ombating. 208. 2oj
4io
Minnesota Plant Diseases.
Epiphytic fungi, 60
spraying of, 211
Ergot disease of grasses (Figs.
154, 155), 306 to 309
Ergot fungi (Figs. 53, 54),
128, 129, 130
fruiting bodies and spores
(Fig. 55), 130
inoculation by, 98
Ergot of grasses (Figs. 53, 54),
127, 128
of rye, 64
of rye, spore distribution, 28
of rye, storage organs, 14
storage organs (Figs. 53,
54), 127, 128, 129
Ergotism, 309
Erysiphacese (Figs. 50, 51, 52),
124. 125
Erysiphe cichoracearum (Fig.
210), 324, 325, 380, 396, 397
communis, 395, 396
galeopsidis, 397
graminis (Fig. 152), 304
Exoascacea; (Fig. 49), 120, 121
Exoascus cerasi, 363
pruni (Fig. 193), 361, 362
species of, 271
Exobasidiinere, 170, 171
Exobasidium (Fig. 37), 83
vaccinii, 385
Explosive apparatus. 31
ball-throwing fungus, 33
for spore distribution (Fig.
14)- 3^
External fungi, spraying of, 211
Exudations, fungi in, 120
Factors of disease, 2, 92
Fairy rings (Fig. 8), 18, 20
False tinder-fungus rot, 250
False truffles, 123
Fatty Pholiota rot (Fig. 129),
262, 263
Feathers, blue mold allies on, 123
fungi on, 42, 121
Fermentation, bacterial, 194
caused by yeasts, 119
Ferns, damping-off of prothallia, 383
molds on sexual plants of, 116
rusts of, 165, 387
Fermvorts, 198
Fertilizers and prevention of
disease. 206
Field crop diseases, 282
Fire blight of apples (Fig.
195), 364, 365
Fish eggs, fungi on, 72
Fish hatcheries, Chytridines in, 105
Fish molds (Figs. 32, 42),
71, 72, 105, 70(5, 707
distribution of spores, 27
half saprophytes, 37
on crabs, 67
saprophytic habit, 36
spore case of. (Fig. 33), 72
Fish oil, in resin bordeaux, 218
Fish, parasites of (Fig. 32), 71
Fixings for spray apparatus
(Fig. in), 228
Fixation of nitrogen by bacteria,
195
Flattened pore fungus rot
Fig. 123), 251,252
Flax wilt (Figs. 156, 157, 158,
159), 3io to 315
Flies, parasites of, 68
spore distribution by, 188
water molds on, 107
Flowering plants, 7
Flower-pot alg;e, 9, 49
Flowers of sulphur, for dusting, 227
Flowers, smuts on, 65
Flux slime, on trees, 271
Fly cholera, caused by molds
(Fig. 47), 115
explosive apparatus, 31
Fly wood, wood rot, 240
Fodder grasses, smothering
fungus of, 306
Fomes applanatus (Fig. 123),
251,^52
fomentarius, 251
igniarius, 250
ribis, 320
Food mold habit, 43
stuffs, destroyed by molds, 122
Forage crop diseases, 282
Formalin, a steep, 221, 223
for fruit soft rot, 356
for onion smut, 320
for oat smut and stinking
wheat smut
221, 223, 293, 294, 296
for potato scab. 223, 326
prevention of timber rot, 240
Formula; for sprays. 215
Minnesota Plant Diseases.
41 i
Fox tail grass, rust on, 287
Fragile fern, rust of, 387
Frogs, parasites on, 72
Frost, cracks caused by, 47
Fruit rots, imperfect fungi, 152
Fruiting bodies of fungi, 22, 24
Fruit-inhabiting parasites, 64
Fruits, molds on, 114
mold rots of, 122
preserved, fermentation of, 36
preserved, molds on. 122
ripe rots or storage rots
of, 44- 353
soft rots of (Figs. 188, 189),
353, 355. 356
sphere fungi on, 138
spraying of. 214
yeasts in juices of, 119
Fungi,
algal, 103. 104
allies of caterpillar, 133
basidium-bearing, 153, 154. 155
bird's-nest, 186
beetle, 139, 140
black, 123
breeding act in, 103
carrion (Figs. 94,95). 187,188
caterpillar (Fig. 56), 130. 131, 13.'
club (Fig. 83), 172, 173, 174
cup (Figs. 4. 10, 14. 6 1 to
65), 140, 141. 14.'
damping-off, 108, lot)
dead stick and burnt wood, 13*;
definition of, 7
descent from alga-, 8. 103
distinction between groups. 103
dung (Fig. 60). 136. 137
food of, 7
gall, 105
gall producing. 170. 171
gill (see gill fungi),
honey dew. i_'5. 394
imperfect (Fig. 70),
117. ijy, 150, /j/, /j.»
inhabiting clung, 38
Jew's ear (see Jew's ear
fungi).
kinds of, 103
lichen-forming, 145. 140
loose weft (Fig. 49). ui
mold palisade, 171
mycelium of. 7
Fungi,
nutrition and general char-
acters, 9
on mushrooms, 133
palisade (Fig. 81), 153, 154, 170
partnership with alg;e. 145
pore (see pore fungi).
sac, 117
saddle (Fig. 67). 146, 147, 148
sewer and drain pipe (Fig.
43). 107, 108
sphere, and allies, 137, 138
sphere-throwing, 183, 184
slime flux, 120
smooth shelf (Fig. 82), 171
smothering (Fig. 82), 172
smothering, of seedlings, .243
spraying of, 21 1
strangling (Figs. 57, 58), 132. 133
tar spots, 14-'
tooth (Fig. 84), 174. 175
trembling (see trembling
fungi).
weeping (Fig. 78), 153. 154, 169
Fungicides (see also sprays).
action of. _'i i
defined. _MI
effect on cattle, horses, etc., 213
effect on fungi. -'13
effect on host. -'13
effect on man. .'13. 214
Fungus, animals. 7
-dwelling habit. 4.;
fruiting bodies. j.j
Balls. 171
life methods. 35
method of reproduction. ji
partnership with alga. 4')
root hairs of puff-balls, 180
rot-, dub. _'44
:»hoe string-. 10
starch. 15
starch in ergot. uo
Fu-arium culm-irmn. 310
lini (Fig>. 150. 157, 15.*.
!.;«>). 310 to 314
Gall disease of blueberry. 3X5
Gall fungi, 105
Gall fungus of wood anemone.
3< 3'J*
us of wild peanut (Fig.
3<jS
Gall fungu
211 )
Gall-producing fr.ngi
412
Minnesota Plant Diseases.
Galls, fungus (Fig. 37), 78,82,83
on blueberry and heaths, 56, 171
on Labrador tea (Fig. 37), 83
Garden plants, sterile-fungus rot
of, 329
truck diseases, losses by, 202
Gasteromycetes (Figs. 90 to
95), 153, 154- 181, 182
Gear power pump (Fig. 106), 216
Geaster triplex (Fig. 93), 185
Gelatinous pore fungi, 175
Gemmed puff-ball (Figs. 90,
91), 181, 182
Germination of a spore, 18
of spores, physiology of, 19
Giant puff-ball, 186
Gill fungi (Figs. 86, 87, 88,
89), 178, 179, 1 80
elm Pleurotus rot. 265
fatty Pholiota rot, 262
fruiting bodies, 23
honey-colored fungus, 261
on railway ties (Fig. 116), 236
on stems, 64
on sticks (Fig. 86), 177
pine Lenzites, 266
scaly Lentinus rot, 267
scurfy Pholiota rot, 263
shoestring fungus, 260
timber rots and wound
parasites, 235
velvet stemmed Collybia
rot, 265
wound parasites, 47
Gills of gill fungi, 178
Ginger beer plant, bacteria of, 193
Glccosporium ribis, 327
Glomerella rufomaculans (Fig.
190), 356
Golden-rod and aster leaf-rust. 376
Golden-rod rust (Fig. 205), 160, 388
Gooseberry, anthracnose of, 327
cluster-cup rust of, 386, 387
pore-fungus rot, 320
powdery mildew of, 125, 325
rust of, 317
Goosefoot family, downy mildew
of, 339
Gourds, downy mildew of (Figs,
i 68, 169, 170, 171),
334. 335. 336, 33-^
Grain smut of sorghum (Fig.
150, 299
Grains, smuts on, 155, 158
Grape sugar, yeasts in, 119
Grape, anthracnose of, 367, 368
black rot of, 365, 366
diseases, losses by, 201
downy mildew of (Figs. 196,
197, 198), 1 10, 112, 368, 369, 370
powdery mildew of, 125, 366, 367
root disease of, 138
Grass, canary, ergot on (Fig.
54), 128
ergots (Figs. 53, 54), 127, 128
family, downy mildew of, 112
pigeon, smut of, 394
rusts. 160
Grasses, ergot disease of (Figs.
154, 155), 306,307,308,309
powdery mildew of (Fig.
152), 304
rusts of (see also rust of
wheat), 165, 166
smothering fungus of, 306
smuts on, 158
strangling fungus of (Figs.
57, 58), 132, 133
Grasshopper, losses by, com-
pared with wheat rust, 201
Green cup fungus rot, 267
Green felts, 9
Green islands, 84
Green molds, 122
Green mold, allies, 123
amateur parasites, 78
disease in man, 75
fruit rots, 44
on animals, 66
on food, 43
on cheese, 43, nS
rot of timber, 270
Greenhouse plants, diseases of, 371
Grey mold of lettuce, 381
Ground, Boletus on (Fig. 85), 176
cup fungi on, 142
puff-balls under, 184
morel allies on, 148
tooth fungi on, 175
Grubs, fungi on, 130, 131, 132
Guignardia bidwellii, 365, 366
Gynmoascaceie (Fig. 49), 121
Gymnoconia interstitialis (Fig.
160), 316,317
Gymosporangium clavarircforme,
349, 350
Minnesota Plant Diseases.
-M
Gymnosporangium,
globosum (Figs. 181. 182),
347. 348, 349
macropus (Figs. 181, 182),
347, 348, 349
nidus-avis (Fig. 26), 57, 350
Habit, bee's-nest dwelling, 42
dung-dwelling, 37
food mold, 43
fungi on eggs, 44
fungus-dwelling, 42
honey-dew dwelling. 42
leaf-dwelling, 41
of parasites on anthers, 65
of parasites on fruit. 64
of parasites on leaves, 62
of parasites on stems, 63
of root parasites, 64
water mold, 36
wood dwelling, 40
yeast, 36
Hag fishes, degeneration in. 10
Hailstones, wounds caused by, 47
Hairy pore-fungus rot, 259
Half saprophytes, 35, 44
Hard-skinned puff-balls, 183
Hard woods, dry rot of, 245
Hasselman treatment of tim-
bers, 239
Hausschwamm, 245
Haw, black, powdery mildew
of (Fig. 51), 125
Hay-curing, bacteria of. 195
Hazel powdery mildew. 395
Head smut of sorghum (Fig.
150). 208, 299
Heat-forming bacteria, 194
Health, and disease, 2
improvements of. 91
in plants, denned, 90.91
Heath family, partnership with
fungus, 50
Heaths, gall fungi on. 170
gall disease of. 385
Helianthus. rust on. 373
Helvetia lacunosa (Fig. 67), i4S
Helvellinca- (Fig*. <'"• 08).
146. 147. i4S
Helotium citrimim (Fig. 65). 145
Hepatica, smut of. 392
Hole, shot, IT I
Hollyhocks, rust of. 37-', 373
Honey-colored mushroom, mold
of. 394
rot (Fig. 128), 260,261,262
strands of (Fig. 6), 17
Honey dew, fungi, 125. 394
fungi, spore distribution, 29
-dwelling habit, 42
spores (Fig. 55), 128. 130
spores of ergot, 307
Honey mushroom, strands of, 16
Hoofs, blue mold allies on, 123
fungi on, 42
Hops, powdery mildew of, 324, 325
Horizontal pumps (Fig. ic8),
220. 231
Horn, blue mold allies on, 123
fungi on, 42
Hornbeam, hairy pore fungus
on, 259
Horseradish, white rust on. 330
Horses, parasites of, 74
Host, effect of parasite on, 77
effect of parasite on anat-
omy of, 87
effect on parasite, 88
infection, 97.9$
influence on spore germina-
tion. 89
stimulation, 82
Hot water method, for loose
smut of wheat. 297
for millet smut. 303
for naked and covered
barley smut. 300, 303
for oat smut. 157
lor sinut>. 22s\ 22(1
for sorghum grain smut,
299. 300
Hou>e iiingu- rut t M-C dry rot).
Hyalopsora polypodii. 387
Hydnace.i- < Fig. 84). 174. 175
Hydnum coralloidcs ( F:g>. *4.
119.'. 174. -'4')
Hymenogastracea,- (Fig. 81), 170
Hypochnace;e, 171
Hypocreace:e (caterpillar fungi),
(Fig. 50), 130. 131. 132
i ergot fungi). (Figs. 53. 54).
128. 129. 130
i strangling fungi). (Figs.
57. 58). 132. 13.5
(in part). 133
Hypomyces lactitluorum. 395
414
Minnesota Plant Diseases.
Hysteriinese, 142
Immersion in solutions, methods
of cure, 209, 210
Immunity and variation, 96
from disease, 93, 206
Impatiens, orange leaf-rust on, 291
Imperfect fungi (Fig. 70),
25, 26, 117, 149, 150, 151, 152
anthracnose of currant and
gooseberry, 327
anthracnose of vines, 367, 368
bean anthracnose, 327
black rot of apple, 363, 364
flax wilt, 310
leaf blight of celery, 328
leaf habit of, 62
leaf spot of beets, 328
plum scab, 363
potato scab, 326
violet leaf spots, 381
wheat scab, 310
Impregnation of timbers to pre-
vent rot, 239, 240
Increase in size, effect of para-
sitism, 82
Indian, corn smut, tubercles of, 56
pipe, partnership with fun-
gus, 50
turnip leaf-rust, 3/6, 392
Individtiation, 51- 56
Infection, and prevention of dis-
ease, 204
by wounds and prevention,
204. 205
conditions favoring, 98, 99
conditions of, 62
in parasitic fungi, 61, 62
in timber rots, 249
of grass leaf by a rust
(Fig. 29), 61
of host, 97,98
Inflorescences, smuts in, 158
Inheritance of disease, 94
Inky gill fungus (Figs. 87, 88),
178, 179
Inoculation of host, 97, 98
Insects, agents of spore distri-
bution, 29
beetle fungi on, 140
carrying slime mold of
malaria, 198
carrying spores of bird's-
nest fungi, 186
Insects,
carrying smut spores, 65
carrying spores of ergot
fungi, 128
causing witches'-brooms, 56
conditions of parasitism on
(Fig. 30), 67,68
degeneration in, 10
distribution of spores by, 162
factor of disease, 92
fungi on (Fig. 56), 130, 131, 132
injuries to apple fruits, 355
molds (Fig. 47), 68, 115, 116
molds, on animals, 66
molds, on butterflies, 69
prevention of wounds by, 205
production of honey dew, 42
ravages by, 201
spore distribution in car-
rion fungi, 187, 188
water molds on, 107
wounds caused by, 47
Interior-dwelling fungi, 61
parasites (Fig. 28), 60
Internal^ fungi, spraying of, 211
Iron ores, relation to bacteria, 191
Iron sulphate and sulphuric
acid, 221
for anthracnose of grape, 367
for downy mildew of grape, 370
in Hasselman's treatment, 239
Isaria (Fig. 31), 70
Iva xanthiifolia, downy mildew
of (Fig. 45), ill
Jells, molds on, 122
Jew's-ear fungi (Figs. 78, 79),
153. 154, 166, 167
Juniper, club rust of, 349. 350
Kainit, in Hasselman's treat-
ment, 239
Kale, black rot of, 342
Kephir, bacteria in, 193
yeasts in, 119
Killing tissues, methods of, 79
Kinds of fruiting bodies of fungi
(Fig. 10), 24
Kinds of fungi, basidium-bear-
ing fungi, I53> i/o
sac fungi, 117, 135
Knapsack pumps (Fig. 103),
212, 230
Knot black (Fig. 59), 135. U6
Minnesota Plant Diseases.
Knot, black,
of plum and cherry (Fig.
191), 358,359,360
Knot of pine (Fig. 136), 275, 276
Knot, red, of currants, 322, 323
Kohlrabi, black rot of, 342
Kumys, yeasts in, 119
Labrador Tea, galls on (Fig.
37), 82,83,171
Laboulbeniinese, 139, 140
Larch, canker, European, 268
killed by parchment pore-
fungus (Fig. 36), 81
parchment pore-fungus rot, 258
weeping fungi on, 169
Larva-, molds on, 115
Lead arsenate, for apple orch-
ards, 347
Leaf blight of celery, 328
of strawberry, 323, 324
Leaf blister of oak, 272
Leaf curl. 120
fungi, and plum pockets. 362
fungi, witchcs'-broom of
cherries, 363
fungi, leaf habit of, 62
Leaf, destroyers of, 80
-dwelling habit, 41
-dwelling fungi, agents of
disintegration of debris. 41
fall of, caused by imperfect
fungi, 152
green, absent from fungi, 7
-inhabiting parasites, condi-
tions of, 02. 103
rust of apple and pears
(Figs. iSi. 182.). 347,348.349
rust of ash. 277
rust of birch. _'7>;
rust of clover, 20,2
rust of pine. 270. _'77
rust of plum. 350. 351
rust of rose ( Figs. lot). 200,
-'oi >. 375
ru-t of willow ( Fig. 138), 270
Leaf stmu of onion. 320
of rye, 303
Leaf spot (Fig. 70). 149. 150. 151. i5_>
de>troyer of small areas
(Fig. 35). 78, 79
diseases. 138
habit of. 62
of alfalfa, 309
415
Leaf spot,
of beets, 328
of clover, cup fungus, 309, 310
of strawberry (Fig. 35). 79
of violets, 381, 382
Leaf wart of dandelion. 399
Leaves, rusts on. 164
tar spots on, 142
Leguminous plants, bacteria of, 196
Lentinus lepideus (Fig. 116),
236, 26?
scaly, rot, 267
Lenzites abietina, 266
betulina (Fig. 86), 177
of pine. 266
Lepiota (Fig. 8), 20
procera (Fig. 18), 39
Lettuce, downy mildew of.
H2, 337, 33v
drop. 322.380.381
grey mold of. 380
sclerotium disease of. 322
sterile-fungus rot of. 320,
Lice, plant, molds on, nt>
Lichen ( Fig. 21 ). 48
-forming fungi. 145. 146
Life methods of fungi. 35
processes in plants. 91
Light-forming bacteria. 194
influence on bacteria. 192
Lightning, wounds caused by, 47
Lignin. 40
action upon, by wood-dwell-
ing fungi. 40
disintegration of. 8;
in wood walls. 85 8'i
Lilac, powdery mildew ( Fig.
202), 125. .?77
Lilies, rust of. 38(>
Lime and sulphur, for downy
mildew of onion, 334
powder, 227
Lime, for club root. 340
for onion smut, 320
in bordeaux. 215
in dry bordeaux. 227.228
in saccharate of copper. 220
potash of. in resin bordeaux, 218
Liquors, yeasts m. 119
Living together with special
plant parts. 02
Localities, importance of. in
prevention. 205.
416
Minnesota Plant Diseases.
Locusts, molds on, 116
.Log, club fungi on (Fig. 83), 173
coral fungus on (Fig. 84.), 174
pore fungi on, 175
rot of (see timber rots),
-smooth shelves on, 171
trembling fungi on (Fig.
80), 167
weeping fungi on, 169
Lolium temulentum (Fig. 28), 60
Long-stalked puff-balls (Fig.
92), 182
Loose smut of oats (Fig. 146),
293, 294
of wheat, 297
of wheat, formalin treat-
ment, 223
Loose-weft fungi (Fig. 49), 121
Lowly algal fungi (Fig. 41),
104, 105
gall fungus of peanut, 398
leaf wart of dandelion, 399
seedling disease of cabbage,
339, 340
Lucerne, downy mildew of, 314
leaf spot of, 309, 310
Lumber, rots of (see timber rots).
Lumpy jaw of cattle, 73
in man, 75
Lurking fungi, 31
Lycoperdineae (Figs. 90, 91,
93). 184, 185,
Lycoperdon gemmatum (Figs.
90, 91), 181,
Macrosporium solani,
tomato,
Magnesium sulphate, for timber
rot,
Malaria, slime mold of,
Mallow rust, 31. 166,372,
Mammals, diseases of lower,
Man, agent of spore distribution,
fungus diseases of,
wounds caused by,
Manure, fresh, and spread of
c'isease,
Maples, elm Pleurotus rot,
powdery mildew of,
slime flux of,
smothering fungus of seed-
lings,
tar spots of leaf (Fig. 133).
142, 268,
1 86
182
329
328
240
198
373
73
3i
74
47
206
265
125
271
Marsh mallows, 372
Mayflowers, rust of, 386
Meat extracts, fungi on, 122
Mechanical means of methods
of cure, 209
Medicago denticulata, bacteria
of nodules (Fig. 99), 196
Medusa-head fungus rot, 244
Melampsora betulina, 279
populina (Fig. 137), 278,279
salicis capreae (Fig. 138), 279
Melons, downy mildew of (Figs.
1 68 to 171), 112,334,335,336
Merulius lacrymans (see dry rot)
(Fig. 5), 15
Mildew powdery (Figs. 50, 51,
52), 124, 125
distribution of spores, 28
of apple, 361
of chrysanthemum, 379, 380
of composites (Fig. 210),
396, 397
of cucumbers, 324, 325
of elms (Fig. 135), 274
of gooseberry, 325
of grasses (Fig. 152), 304
of hazel, 395
of hops, 325
of lilacs (Fig. 202), 377
of mints, 397
of plums and cherries
(Fig. 192), 360, 361
of rose (Figs. 203, 204), 37§, 379
of strawberry. 324
of vetch and crowfoot, 395. 396
of vines, 366, 367
of willow (Fig. 134)- 272, 273
Milk fungi, 179
sugar, yeasts in, H9
mushrooms, fungi on, 133
mushrooms, red disease of,
395.
Milkweed rusts, 160.386
Millet smut, 3O3
Minnows, fish molds on, 107
Mint, powdery mildew of, 397
rust of (Fig. 209),
160, J/7- 3i8, 393
Method of attack in germinating
spore, J9
of inspect-inhabiting fungi, 19
of parasites, 61
Minnesota Plant Diseases.
417
Methods for smut treatment,
hot water, 225, 226
Methods of cure, 209
cleanliness, 209
prompt action in. 209
Methods of killing tissues, 79
Microsphaera alni (Fig. 202), 377
grossulariae, 325
Mildew downy (Fig. 44),
109, no. in
of beans, peas, etc., 336, 337
of beets, 339
of clovers, 314
of cucumbers, melons, etc.
(Figs. 168 to 171),
334, 335- 336, 338
of lettuce, 337. 339
of mustards, cabbage, etc., 331
of onion, 333. 334
of potato (Figs. 166, 167),
33 '-332. 333
of seedlings, 382
of spinach, 339
of vines (.Figs. 196. 197. 198),
368. 369. 370
of violet, 3&4
Mildew, destroyer of organs, 80
epidemics (Fig. 40; . 100. 101
leaf habit of, 62
of clothes, 43
of grapes. ' '-
Mistletoe, causing witches'-
broom on spruce (Figs. -'4.
25), 54. 55
disease of spruce (Figs. -'4.
-'5. 101 ), 54. 55- 199. "«*>• -'-to- -$'
Modes of life of parasitic fungi, 60
Molasses, in saccharate of cop-
per, -•*>
Molds, 105. 106. 107. 113.
114. 115. !_'_>. U3
Molds, black, of clover (Fig.
153). 305
black or bread (Fig. 46),
113. H4
beginners in parasitism, 57
green, allies of. 123
green and blue. i-'-'
green, rot of timber. 270
grey, of lettuce. 381
of honey-mushroom, 394
of insects (Fig. 471. 115,110
Molds,
of mushrooms, 397
on dung, 38
on eggs, 44
on mushrooms, 42
palisade fungi, 171
parasites of, 114
power of fermentation, 114
power to change sugar to
starch, 114
rots on fruits, 64
sewer and drain (Fig. 43),
107, 108
slime (Fig. 100), 196. 197, 198
soft fruit rots, 353
water and fish (Fig. 42),
105. 106
Morchella esculenta (Fig. 66), 147
Morels (Fig. 66), 146. 14". 148
fruiting bodies of, .'5
Morning glories, white rust of. 112
Mosquitos, molds on, 116
parasites of. 08
Moss, morel allies among. 14.^
parasites on, 198
cup fungi in. 144
Jcw's-car fungi on. i>>6
Mossworts. l(>5
Mucor. 353. 355
Mucorine;e. black molds (Fig.
46), 1 13, 1 14
Mud puppy, fish molds on. 107
parasites on, 7-'
Museum of plant diseases, 2o<j
Mushroom allies, on stems, 04
Mushrooms, basidium-bcaring
fungi. 155
coral fungus (Fig. li<ji. -'44- -4(l
earth-dwelling habit. 3<;
fairy rings, 20
fruiting bodies. 22
gill fungi ( Fig. So) I7'J
group, fungi on. 4-'
group, leaf dwellers, 41
group, wound parasites,, 47
honey-colored, rot (Fig.
i_'S), joo. jo i. 26 j
honey-colored, mold of, 394
milk, fungi on. 133
molds on. 1 14. 3v?
on dung. 38
red disease of. 395
418
Minnesota Plant Diseases.
Mushrooms,
spore distribution, 28
sulphur fungus, 253
true saprophytes, 35
truffles, 148
Muskmelons, downy mildew of
(Figs. 1 68, 169, 170), 334
wilt of, 341
Mustard family, club root of, 345
damping-off of seedlings,
108, 382
downy mildew of, 331
Pythium debaryanum, 45
white rust of, 112,330
Mycelium, definition of, 7, 8
development of, 18
of food mold (Fig. i), 8
of mushrooms, n
physiology of, 17
Mycetozoa (Fig. 100), 196, 197, 198
Mycoplasm theory of rusts, 289
Mycorrhiza of puff-balls, 186
Mycosis, 73
Naked barley smut, 300
Nectria cinnabarina,
271, 272, 322, 323
Needle-cast of pines, 138
Nettles, sedge rust of, 391
Nidulariinerc, 186
Nitrates, formation by bacteria, 195
Nitrifying bacteria, 195
Nitrogen-fixing bacteria, 195
Nodule bacteria, 195
Nozzle, for mist-like sprays
(Fig. 114), 231
for spraying apparatus (Fig.
ill), 228
for spraying plants in rows, 230
for spraying under sides of
leaves (Fig. 112). 230
Nuclear parasites. 66
Nutrition of fungi, 10
Nutritive method, expressed in
structure, 9
Oak, D;edalea on, 257
dry rot of, 245
false tinder fungus on, 250
fatty Pholiota rot of (Fig.
129), 263
fungi on limbs, 139
hairy pore-fungus, 259
leaf blister of, 272
Oak,
leaf curl fungi on, 121
partnership with fungus, 50
partridge wood rot of, 242
powdery mildew on, 125
rust of milkweeds on, 280
slime flux of, 271
Stereum wood rot (Fig.
117), 240
sulphur fungus on (Fig.
124), 252
white-piped and yellow-
piped, 240
Oats, hot water treatment of, 157
loose smut of (Fig. 146),
293, 294
rust (Fig. 141), 285
smut of, 156, 157
smut of, an accomplished
parasite (Fig. 27), 59
smut of, formalin treatment,
221, 223
Oidium, 150
chrysanthemi, 379, 380
Oil, fish, in resin bordeaux, 218
Oil in resin prevention of rot, 240
Oils in ergot, 129
Old man's beard, rust of, 386
Olpidium brassicse, 339, 340
Onion, downy mildew of,
112, 333, 334
smut of, 158, 320
Oospora scabies (Fig. 164), 326
Orange leaf rust (see rust of
wheat).
rust of raspberries, etc. (Fig.
160), 316. 317
Orchard diseases, losses by, 202
spraying, horizontal pump
for (Fig. ioS), 220
trees, red knot on, 134
trees, wounds and preven-
tion, 205
Orchards, diseases of, 347
Organisms causing disease, 189
Organs, destroyers of, 80
Ornamental plants, diseases of, 371
Oxalis, rust of corn, 292
Oyster fungus rot, 266
Palisade fungi (Fig. Si) 170
gall disease of blueberry, 385
wold, i/i
Minnesota Plant Diseases.
419
Pansies, smut of, 371
Paper, building, fungi on, 137
moldy, fungi on, 137
Parasites (see also wound para-
sites), 35, 51
cause development of floral
rudiments, 83
cause increase in size of
host, 82
cup fungi, 142, 144
defined, 9
destroyers of organs, 80
destroyers of small areas
(Fig. 35), 78, 79
destroyers of whole plants, 80
effect of host on, 88
effect on anatomy of host, 87
effect on host, 77
* effect on host tissues, 84
entrance through wounds, 45
formation of new organs. 84
higher seed plants. 199. 200
immediate destruction of
host, 78
leal inhabiting, 62
life methods. 60
low type of (Fig. 34). 77
on animals, 6<i
an anthers, 65
on birds, 73
on fruit. <>4
on insects (Fig. 30), 67. OS
on molds. 1 14
on nuclei. 66
on roots. 64
on special plant parts,
on stems, 03
place, 198
plant. 77
rusts. 164
si/e of. 13
stimulation of ho*t. 82
stimulation of age. S3
surface dwelling. 60
wound. 235
Parasitic fungi, modes of life. oo
life of smut, . 156
Parasitism, an auxiliary proc-
cess, _>oo
aii;l saprophytism, 12, 35
contrast in plants and ani-
mals. 75
Parasitism,
destructive,
in animals,
nutrient,
proficiency in,
51
10
49
57.58
Parchment pore fungus rot, 258
Paris green, 213
for apple orchards, 347
Partnerships, fungi with alga?, 145
of bacteria, 193
of plants, equal (Fig. 21), 48
of plants, unequal, 49, 50, 51
Partridge wood rot (Fig. 118),
242
Pastry, molds on. 113
Pathologist, agent of preven-
tion, 208
Plicaria repanda (Fig. 64), 144
Pea family, powdery mildew of. 325
root tubercles of. 50
Peach, brown rot of, 357
Peanut, wild, gall fungus of
(Fig. 211), 398
Pear blight (Fig. 195). 364.365
leaf rust of (Figs. 181. 182).
347. 348. 349
rusts, 166
Peas, downy mildew of, 336, 337
Penecillium (Figs. 188. 189), 353,355
species of. 270
Peridermium, species of (Fig.
136). 275.276
Permanganate of p<ita>sium. 221
Peronospora alsinearum (Fig.
44 >• IOIJ
etfusa. 339
Icptopcrma (Fig. 44). 109
parasitica, 331
-chachtii. 339
.schleidcni, 333- 334
trifolioruni, 314
\i"l:r. 3«4
lYrono^porinc.'i' (downy mil-
dewo. (Fig. 44), log. no, m
( white rusts,), 112
Pe/i/ine;i- ( -cc cup fungi,), 143,144
Phacidiinc:*.-, 142
Phallinea.- (Figs. 94, 95). 187,188
Pholiota adiposa (Fig. !_'</).
262. 263
fatty, rot ( Ki«. i.'g). 202.263
>curfy, rot. -''13
420
Minnesota Plant Diseases.
Pholiota,
squarrosa, 263
Phosphorescence, bacterial, 194
Phragmidium speciosum, 375, 376
subcorticuim (Figs. 199, 200,
201), 373
Phycomycetes, 104
Phyllachora trifolii (Fig. 153), 305
Phyllactinia suffulta, 395
Phyllosticta violas, 381, 382
Physiology of mycelium, 17
Phytophthora infestans (Figs.
44, 1 66, 167), 109,331,332,333
omnivora (Fig. 44), 109, 382
phaseoli, 336, 337
Pigeon grass smut. 394
Pig-weed, white rust of, 112
Piling of timber, 238
Pilobolus (Figs. 16, 17), 37, 38
Pin worms, parasites of, 66
Pine board, attacked by dry rot
(Figs. 121, 122), 248,249
Pine knot (Fig. 136), 56,82,275,276
Pine Lenzites, 266
Pine stem rust (Fig. 136), 275, 276
Pines, needle cast of, 138
ring scale of, 256
rust of leaves, 276, 277
rusts of wilkweeds and
Pyrola,
stimulation in rusts of,
witches'-broom on (Fig.
22), 52
Pink family, rust of balsam fir, 278
smut of, 371, 393
smut on anthers, 65
stimulation of floral rudi-
ments, 83
stimulation of smuts in, 158
Pipe tongs, for spray apparatus
(Fig. in), 228
Pitch-stemmed pore fungus rot, 259
Plant diseases, 90
lice, molds on, 116
parasites of, 68
parasites, 77
partnerships, 48, 49
Plantain, powdery mildew of, 124
Plasmodiophora brassica; (Figs.
179- i So), 345.346
Plasmodium of slime mold
(Fig. 100), 197
Plasmopara cubensis (Figs 168
to 171), 334,335,336,338
viticola (Figs. 196, 197,
198), 368,369,370
Pleurotus ostreatus, 266
rot of elm, 265, 266
sapidus (Fig. 131), 265,266
ulmarius (Fig. 20), 46, 265, 266
Pliers for spray apparatus (Fig.
in), 228
Plowrightia morbosa (Figs. 59,
191), US, 358, 359- 36o
Plug for spray apparatus (Fig.
111), 228
Plums, black knot of (Fig. 59),
135, 136, 358, 359, 36o
brown rot of, 152, 357, 358
leaf rust of, 350, 351
pockets (Figs. 49, 193),
I2O, 121, 361, 362
pockets, oak leaf blisters, 272
powdery mildew of (Fig.
192), 360, 361
scab of, 363
stunting by pocket fungi, 82
witches'-brooms on, 121
Pockets, of plum and cherry
(Figs. 49, 193), 82, 120, 121, 361, 362
Podosph;era leucotricha, 361
triclactyla (Fig. 192), 360, 361
Poisoning by ergot, 309
Poisonous gill fungi, 179, 186
pore fungi, 178
Poisons, corrosive sublimate. 226
in ergot, 129
smuts of grasses, 295
use in methods of cure, 209
Poles, rot of, 239
Pollen, replaced by smut, 158
Polyporace;e (see pore fungi).
Polyporus betulinr.s (Fig. 126),
254- 255
picipes, 259
rot, zoned, 258
squamosus (Fig. 125), 254
sulphureus (Fig. 124), 252,253
rolystictus hirsutus, 259
pergamenus (Fig. 36), 81, 258
versicolor, 258
Pond scums. 9
Poplar rusts (Fig. 137). 160, 278. 279
Poplars, leaf and fungi on. 121
Minnesota Plant Diseases.
421
Poplars,
powdery mildew of, 121, 125, 272
red knot on, 134
Pore fungi (Fig. 85),
175, 176, 177, 1/8
birch fungus (Fig. 126), 254, 255
creeping wood rot of, 258
currant rot, 320
dry rot fungus, 245, 247 to 250
earth-dwelling habit, 39
false tinder fungus, 250
flattened, rot (Fig. 123),
251,252
fruiting bodies, 23
hairy pore fungus, 259
oak Dredalea, 257
zoned pore fungus, 258
on ground (Fig. 85), 176
on stems, 64
parchment, on larch (Fig.
.36), 81, 258
pitch-stemmed, 259
ring-scale of pine, --'
root-rot of currant (Fig.
163), 32i
scaly (Fig. 125), 254
sulphur fungus (Fig. 124)
252, 253
timber rots and wound
parasites, 235
tinder fungus, 251
trametes radiciperda, 256
undetermined (Fig. 127), 257
wound parasites, 47
Portulaca, white rust of, 112
Potash of lime, in resin
bordeaux, 218
Potassium permanganate, 221
Potassium sulphide, 220, 221, 357
for brown rot of plums, 358
for carnation rust, 373
for downy mildew of onion,
334
for mildew of chrysanthe-
mum, 380
for powdery mildew of
gooseberry, 325
for powdery mildew of
rose, 379
for powdery mildew of
vines, 366
Potato disease, losses by, 202
Potato blight (Fig. 39),
80, 99, no, in, 112
destroyer of leaves, 80
destructive effect, 78
distribution of spores, 27
epidemics, 100
spores of (Fig 44), 109
Potato, damping-off of seed-
lings, 382
downy mildew of (Figs. 166,
167), 331- 332, 333
early blight of, 329
fungus stimulation of
tubers, 50
scab (Fig. 164), 326
scab, corrosive sublimate
treatment, 226
scab formalin treatment, 223
starch, converted to sugar, 114
sterile-fungus rot of, 329
wet rot of (Fig. 172) 340
Powder guns (Fig. 115), 231,232
Powders, dry bordeaux, 227
for dusting plants, 227
sulphur, 227
sulphur and lime, 227
Powdery mildew (Figs. 50, 51,
52), 80. 124, 125
degree of parasitism, 58
fruiting bodies, 23
kinds of spores, 25
of apple, 361
of chrysanthemums, 379, 380
of composites (Fig. 210),
396, 397
of cucumbers. 324, 325
of elms (Fig. 135), 274
of gooseberry. 325
of grasses (Fig. 152), 304
of hazel, 395
of hops, 325
of lilac, 377
of mints, 397
of plums and cherries (Fig.
192), 360, 361
of rose (Figs. 203, 204), 378, 379
of strawberry, 324
of vines, 366. 367
of vetch and crowfoot, 395, 396
of willow (Fig. 134), 272, 273
on limited areas, 79
spores of, 118
422
Minnesota Plant Diseases.
Power pump, gear (Fig. 106), 216
Predisposition and variation, 96
factor in disease, 93
general and special, 93
kinds of 94, 95
Preserves, molds on, 122
Prevention of disease, 201 to 209
and fertilizers, 206
and state aid, 208
and wound infection, 204, 205
by spraying, 212
curative methods, 209
importance of localities, 205
importance of knowledge, 203
importance of co-operation, 203
plant pathologist in, 203
selection of varieties, 206
work of farmer in, 204
Prevention of dry rot, 250
of spread in disease, 207
of timber rots and tree
diseases, 237, 238, 239, 240
Primrose, evening, rust of, 386
Proficiency in parasitism, 57, 58
Promycelium of rust (Fig. 73), 159
Prothallia, damping-off of, 383, 384
Protomyces, sucker threads
(Fig. 2), ii
Pruning, best time for, 205
for apple scab, 352
methods of cure, 209
of trees and protection, 237
wounds and treatment, 205
Puccinia angustata, 391
asparagi (Fig. 161), 318, 319
caricis, 391
chrysanthemi, 371, 372
coronata (see rusts of
wheat).
fraxinata, 217
fusca, 39°
graminis (see rusts of
wheat), (Fig. 73), 159
menth;e (Fig. 209), 317, 318, 393
pruni, 35OJ351
rubigo-vera (see rust of
wheats).
sorghi, - 292
tanaceti (Fig. 206),
373- 374- 375, 3§9
vexans (Fig. 73), 159
vioke, 373
Puff-balls and allies (Figs. 90
to 95), 153, 154, 181, 182
common gemmed (Figs. 90,
91) 181, 182
earth-dwelling habit, 39
fruiting bodies, 23
hard skinned, 183
long stalked (Fig. 92), 182
spore distribution, 28
strands of, 16
true (Figs. 90, 91). 184, 185
underground, 184
Pumpkins, downy mildew of, 334
Pump, barrel (Figs. 104, 105),
213, 214, 230
barrel, in action (Fig. 107), 217
bucket (Fig. 102), 211, 230
complex type of spray (Figs.
109, no), 222, 224
engine power, 232
gear power, 231
gear power force (Fig. 106),
216
horizontal, 231
knapsack (Fig. 103), 212, 230
requirements for, 230, 231
Punk, 40
formation of, 85
Pseudomonas campestris (see
black rot of cabbage).
phaseoli, 342
Pseudopeziza medicaginis, 309
trifolii, 309, 310
Pure cultures of crops and epi-
demics, 206
disadvantages, 205. 206
Pycnidium of wheat rust (Fig.
74), 161, 162
Pyrenomycetinere, 123
(clung fungi), (Fig. 60), 136, 137
(sphere fungi), 137, 138
(honeydew fungi), 125
Pyrola rust, 386
Pythium debaryanum (Fig. 34),
45- 77, 3S2. 383
intermedium, 383, 384
Quack grass, ergots of (Figs.
53, 155), I2/- 308
Rabbits, agents of spore distri-
bution, 30
fungi on, 73
Radish, black rot of, 342
Minnesota Plant Diseases.
423
Radish.
club root of, 345
sterile-fungus rot of, 329
white rust on. 330
Railway ties, gill fungus on
(Fig. 116), 236
rot of, 87
Rag weed, powdery mildew of
(Fig. 210), 396
Raspberries, orange rust of, 316,317
Razoumofskya pusilla (Figs.
24. 25), 54.55.280,281
Red cedar, witches'-broom on
(Fig. 26), 54- 55. 57
Red disease of mushrooms. 395
Red knot. U4
of currants. 322. 323
rot, 271, 273
Red rust of raspberry, etc. (Fijj
160), 3i6.3«7
of wheat (see rust of
wheat), 291
Red sea weeds, 9
Reed grass, ergot on (Figs.
53- 155). 127.309
Reed mace fungus. 306
Refuse, burning of, methods of
cure, 209
Rennet bacteria, 196
Reproduction of Fungi. 21
Reproductive, systems of para-
sites. 10
Resin bordeaux for asparagus
rv.st, 3'9
mixtures, 218
Rhi/ina intlata. 270
Rhizoctonia, species of. 329
Rhubarb, sterile-fungus rot of. 329
Rhytisma acerinum (Fig. 133'.
268.269
salicinum (Fig. 133). 270
Rice, wild, ergot on ( Fig.
155). 130.307.308
Ring disease of cone bearing
trees. 270
scale of pine, 256
Rings, fairy, 18
Ripe rot of apples (Fig. 190),
356. 357
of fruits, 44- 353
Rocks, lichens on, 146
Rcot. hairs, fungus, 186
Root,
-inhabiting parasites of, 64
nodules, bacteria of (Fig.
99), 196
parasites, seed plants, 200
rot of currant (Fig. 163). 321
rot of trametes, 256
smut of sedge, 394
tubercles of pea family. 50
Roots, bacteria in (Fig. 98),
19-2, 195
rust on. 164
sclerotium disease of, 322
sphere fungi on, 138
sucker, of mistletoe. 200
Rose family, powdery mildew
of hops or 32;
leaf rust (Figs. 190. 200.
201). 37$
powdery mildew of ( Figs.
203. 204), 125. J/cV. S7V
stem rust, 375. 376
Rotation of crops and bacteria. iy6
of crops, advantages of, 205, 206
Rot. black, of tomato. 3^8
brown, of potato tubers. 332
flattened pore fungus (Fig.
123). 251.252
method of attack on wood
cells (Fig. 38). 85.86
of apples, and plum, brown.
357- 358
of apples, bitter or ripe
(Fig. 190). 356. 357
of apple, black (Fig. 194)
3'>3- 3' '4
of cabbage, black (see black
rot of cabbage),
of false tinder fungus. 250
of fruits, 44
of fruits, imperfect fungi, 15.'
of fruits, ripe, 353
of fruits, soft (Figs. iHK 189).
353- 355- 356
of fruits, storage, 353
of grapes, bird's-eye. 307
of root, trametes, 256
of scaly pore fungus ( Fig.
125). -'54
of shoe string fungus
(Fig. 128). 260. 261.262
424
Minnesota Plant Diseases.
Rot,
of sulphur fungus (Fig. 124),
252, 253
of timbers, dry (see dry
rot), 235
of timbers, harvesting of
trees, 237
of timbers, prevention of,
237, 238, 239, 240
of timbers, smooth shelf, 172
of timbers, trembling fungi, 169
of timbers, treatment to pre-
vent, .239;
of vine, black, 365, 366
of wood, coral fungus
(Fig. 119), 244,246
of wood, stick fungi, 139
partridge wood (Fig. 118), 242
Stereum wood (Fig. 117), 240
sterile-fungus, of garden
plants, 329
tinder fungus, 251
wet, of potato (Fig. 172), 340
Rush-like plants, smuts in, 158
rust of dark green, 391
Rust, bird's-nest of red cedar, 350
epidemics and pure cul-
tures, 206
club, of juniper, 349, 350
leaf, of apples and pears
(Figs. 181,182), 347,348,349
of anemone, 390
of ash leaf, 277
of asparagus (Fig. 161). 318, 319
of asparagus, spray pump for
(Figs. 109,110), 222.224
of aster leaf, 376
of bean (Fig. 162), 319
of birch leaf, 279
of carnations, 373
of cereals, losses by, 201
of chrysanthemums. ^71, 372
of clover leaf, 292
of coffee epidemics, \oo
of composites, 387
of corn, 292
of cowberry (Fig. 207),
387. 389, 390
of dark green rush. 391
of ferns, 387
of golden rod (Fig. 205),
376, 388
Rust,
of gooseberry and currant,
317, 386, 387
of grasses, destroyers of
leaves, 80
of hollyhocks and mallows,
372, 373
of Indian turnip, 392
of mallow, epidemics, 98, 102
of milkweeds, 280, 386
of mint (Fig. 209) 317, 318, 393
of pine leaf, 276, 277, 351
of pine stem (Fig. 136),
275. 276
of poplar (Fig. 137), 278,279
of Pyrola, 386
of rose leaf (Figs. 199, 200,
201), 375
of rose stem, 375, 376
of sedges, 391
of sunflower (Fig. 206),
373, 374, 375, 389
of violet, 373
of willow leaf (Fig. 138) 279
of wild sarsaparilla (Fig.
208), 390
orange, of raspberries, etc.
(Fig. 160), 3i6,3i7
predisposition towards, 93
-proof varieties of wheat,
289, 290, 291
spores, insect distribution, 29
white, inoculation by, 98
Rusts (Figs. 73, 74, 75, 76, 77),
(see also page 166), 80, 759 to 166
breeding act in, 164
causing rupture of epi-
dermis, 87
causing witches'-broom
(Figs. 23,26), 51,53-57
cedar apples of red cedar
(Figs. 181, 182). 347
cluster cup, of wild flowers, 386
effects of hosts on, 88
effects on tissues. 84
infection of grass leaf (Fig.
29), 6 I
inoculation by spores, 98
leaf habit of, 62
of wheat (Fig. 73), 159
of wheat and other cereals
(Figs. 139 to 145), 282 to 292
Minnesota Plant Diseases.
425
Rusts,
of wheat, differences be-
tween red and black rust,
291, 292
of wheat, epidemics, 100
of wheat, losses in Minne-
sota, 201
of wheat, relation to varia-
tion, 97
on limited areas, 79
producing pine knots, 82
proficiency of parasites, 59, 60
stimulation of new organs, 84
sucker threads (.Fig. 2), 11
white, 112
white, of mustarJs, cab-
bage, etc., 330
wind distribution of spores, 27
Rutabaga, black rot of, 342
club root of (Fig. 179), 345
Rye. ergot of (Fig. 154), 130,307
leaf smut, 303
rust (see rust of wheat).
Sac fungi, ///, 135
causing witches'-broom, 56
general characters, 103
Sac of cup fungus (Urnula),
(Fig. 6.'.), 141
Saccharate of copper, 220
Saccharomycetes (Fig. 48),
1 |8, I 19, I2O
Saddle fungi (Fig. 67), 146, 147, 148
earth-dwelling habit. 39
Sago palms. alg;e in roots of, 108
Sake, yeasts in. 1 19
Sanitation, relation to bacteria,
192. 193
Sapid fungus rot (Fig. 131),
-'05. 200
Saprolegnia thuretii. 71
Saprolegniinex,
105, 100. 107, 108. 109
( Damping-ofT fungi). 108.109
( Fi-h molds). (Fig. 4-'). 105. 100
(Sewer pipe molds). (Fig.
43». 107, 108
Saprophytes. 35
cup fungi. 14.'
definition of. 9
dung-dwelling habit, 37
earth-dwelling habit, 38
water-mold habit. 36
Saprophytes,
yeast habit, 36
Saprophytism and parasitism. 12
Sarsaparilla, rust of wild (Fig.
208). 390-
Scab of apple (Figs. 183. 184, 185.
1 86, 187), 138, 351 to 354
of apple, preparation for
soft rots, 355.
of apple, spores of (Fig.
187) 35-4
of beet, 327
of plum and cherries. 363
of potato (Fig. 164). 326-
of potato, formalin treat-
ment, 223
potato, corrosive sublimate
treatment, 226
of wheat. 310
Scald of cranberry, 399
Scale, ring, of pine, 256
Scaly I.entinus rot. 267
pore fungus rot (Fig. 125), 254
Schinzia cypericola. 394
Sclerodermatacea-, 183
Sclerotinia (Figs. 4. 63). 14, 143
fructigena. 357. 358
libertiana, 320, 322. 380, 381
Sclerotium disease of cucum-
bers. 320
of ergot (Figs. 53, 54. 154.
155). i-'7, 128. 129. 307
Scotch pine (Fig. 130), 270
Scurfy 1'holiota rot. 303
Sea weeds, red. breeding act. 14')
Seasoning of timbers. .-38
Sedge root smut, 304
HIM. 3<jl
Seed plant-, higher, parasites.
199. 200
lower. 198
Seed wheat, from rusted field-. 2</j
Seedling.-, damping-off of. 382, 383
disease of cabbage. 339, 340
downy mildew of (Fig. 44).
109. 382
smothering fungu.- of 243
Selection for special substances, 26
of ho-t-. fungii--. 26
of varieties. 2
of varieties and disease
prevention. joO
426
Minnesota Plant Diseases.
Sewer pipe molds (Fig. 43),
107, 1 08
Shade trees, diseases of, 235, 260
wounds and prevention, 205
Shaggy-mane, fungus (Figs. 87,
83) 178, 179
spore distribution, 30
Shakers, pepper, 232
Shelf fungi, pore, 175
smooth (Fig. 82), 171
spore distribution, 28
Shepherd's purse, club root of, 345
white rust of, 112,330
Shoe strings fungus, 16
rot (Fig. 128), 260, 261, 262
strands of honey mush-
room (Fig. 6), 17
Shot hole diseases, 151
Shut-off for spray apparatus
Fig. in), 228
Silkworms, parasites of, 71
Silver fir, broom of, 278
Slime flux fungi, 120
of trees, 271
Slime molds (Fig. 100),
7, 196, 197, 198
club root of turnips, etc., 345
parasites on plants, 198
plasmodium (Fig. 100), 197
Smooth shelf fungi (Fig. 82), 171
partridge wood rot, 242
smothering fungus of seed-
lings, 243
Stereum rot, 240
Smothering fungus (Fig. 82), 172
of grasses, 306
of seedlings, 243
Smut, covered, of barley, joo, 302
loose, of oats (Fig. 146),
293- 294
loose, of wheat, 297
naked, of barley, 300
of anemone, 392
of brome, 303
of broom corn, 300
of carnations, 371, 393
of corn (Figs. 148, 149), 297,298
of corn, stimulation by, 158
of corn, treatment, 223
of grains, age of mycelium, 20
•of millet, 303
Smut,
of oats, an accomplished
parasite (Fig. 27), 59
of oats, formalin treatment,
221, 223
of oats, hot water treat-
ment, 157
of onion, 320
of pigeon grass, 394
of rye leaf, 303
of sedge root, 394
of sorghum head (Fig. 150),
298, 299
of sorghum grain (Fig. 151),
299
of violet, 393
of wheat, loose (Fig. 72), 157
of wheat, stinking, formalin
treatment, 221, 223
spores, germinating (Fig.
7i), 155
spores, lurking, 31
spores, vitality, 33
spores, wind distribution, 27
stinking, of wheat.
Smuts (Figs. 27, 71, 72, 146 to
151), 155, 156, 157, 158
accomplished parasites, 59
epidemics of, 100, 101
fruit rots, 64
half parasites, 35
host influence in germina-
tion, 89
hot water treatment of, 225; 226
machines for treatment of, 232
on anthers, 65
on limited areas, 79
parasitic life of, 156
parasitic on roots, 64
predisposition toward, 94
proficiency of parasitism, 58
saprophytic life of, 156
treatment of, 33
Soap, in potassium permangan-
ate, 221
Soapworts, smut of, 371
Soda lye, prevention of timber
rot, 240
Sore throat, cause by yeast al-
lies, 120
Soft rots of fruits (Figs. 188,
189), 353. 355, 356
Minnesota Plant Diseases.
427
Soft,
woods, dry rot of, 245
Solomon's seal, false, rust of, 386
Solomon's seal, rust of, 386
Sordariacea? (Fig. 60) 136, 137
Sorghum blight, 3M, 315
grain smut of (Fig. 151). 299
head smut of (Fig. 150),
298,299
rust on, 292
Spartina cynosuroides, 277
Spathula, downy mildew of, 339
Spontaneous combustion, bac-
terial, 194
Sphaceloma ampelinum, 367, 368
Sphace'.otheca reiliana (Fig.
150), 298. 299
sorghi (Fig. 151). 299,300
Sphagnum, for prothallia, 384
Spha-rella fragario.- (Fig 35),
79. 3-'3. J-'V
Sprueriacese, 137, 138
Splucrobolacea-, 183, 184
Sph;eropsis malorum (Fig. 194)
3^3. 3f'4
Spha-rotheca castagnei, 3-'4. 325
mors-uva?, 325
pannosa (Figs. 203. 204).
378. 379
Sphere fungi and allies, 137, 138
apple scab. 351
back rot of vine, 365
leaf blight of strawberry.
3-'3. 3-'4
Sphere-throwing fungi, 183. 184
Spiders, parasites of. 67
Spore, definition of 8. 21
germination of (Fig. 15), 18.34
germination and seasons, 34
resting, germination, 34
succession. 26
Spores, distribution of, 26
distribution by animals, 30
distribution by insects, 28
distribution by water. 27
distribution by wind, 27
distribution, explosive ap-
paratus (Fig. 14), 31
kinds of (Fig. 9), 21.22.25
kinds of, from one fungus
(Fig. ii). 25
numbers of, 14
Spores,
of algal fungi, 33
of apple scab, 354
of ash-leaf rust (Fig. 76), 163
of fish mold (Fig. 33), 72
of food mold (Fig. i), 8
saprophytes, 37, 38
of slime mold (Fig. 100). 197
of smuts germinating (Fig.
70, 155
of water molds (Fig. 42), 106
of wheat rust (Fig. 73), 159
physiology of germination, 19
prodigality of, in fungi, 26
resistance to drying out. 33
resistance to temperature. 34
size and amount of nourish-
ment, 26
swimming, 27
unfavorable conditions in
germination, 26
Sporodinia grandis. 397
Sporidium of wheat rust (Fig.
73 >• 159
Spots, black, of grasses, 136
of leaf, of beets. 328
of leaves (see leaf spots),
of violet leaf, 381, 382
tar. 14-'
Spray apparatus (Figs. 102 to
no), .MI
accessories. 231
fixings, tools, etc. (Fig.
Ill), 2->8
good. 213
selection of. 229. 230
special. 231
Spray pump, complex type (Figs.
109. 1 10) 222. 224
Spraying, a check to epidem-
ics ( Fig. 40). 101
a preventive method. 200
actii >n of, 21 1
of fungi, best time for, 27
of plant*, value of. 212
plants in rows (Fig. 112). 230
under sides of leaves (Fig.
112). 230
Sprays. 215
ammoniacal copper car-
bonate, 219
bordeaux, 21^
218
220
219
2ig
428
Sprays,
bordeaux resin,
copper acetate,
copper sulphate,
eau celeste,
iron sulphate and sulphuric
acid, 22J
potassium permanganate, 221
potassium sulphide, 220
saccharate of copper, 220
Spread of diseases, prevention
Spruce, mistletoe disease of (Fig.
101 )> 199,200,280,281
rust of cowberry, ?g0
witches'-broom on (Figs.
•O 4 0-S\
~t> *sJ> 54, 55
Squash, downy mildew of, 334
wilt of (Fig. 173), 34I
Squirrel, agent of spore distri-
bution, _,Q
corn, rust of, 3gg
tail grass, rust on, 2g7
wounds caused by, 47
Stalked fungi (see basidium-
bearing fungi), IO3
Stalked puff-balls (Fig. 92), 182, 183
strands of (Fig. 3), I^
Starch, molds on, I22
solution of, by fungi, g5
turned to sugar by molds, 114
yeasts in, Iig
Stars, earth (Fig. 93), l8s> l86
Starworts, smut of, o7l
State aid in disease prevention, 208
Steeps, 22I
corrosive sublimate, 226
formalin, 22I 2^,
hot water, -„-
Stem canker of balsam fir, 268
-inhabiting parasites, 6^
rust (see rust of wheat),
rust of cowberry (Fig.
207 )> 387- 389, 390
rust of pine (Fig. 136), 275, 276
rust of rose, 375,376
btems, bacteria in. IO2
dead, cup fungi on, 144
imperfect fungi on, i$2
rusts on, jg.
smuts in, j.g
sphere fungi on, ^g
Minnesota Plant Diseases.
Stereum frustulosum (Fig. n8). 242
hirsutum,
wood rot (Fig. 117),
Sterile-fungus rot of garden
plants,
Sticks, dead, cup fungi on, I44
dead, fungi,
fungi on,
gill fungus on (Fig. 86), 177
tar spot allies on, I42
trembling fungi on, jgp
Stimulation by rusts, rf*
by smuts, j.g
of floral rudiments, g3
of host, g2 J7I
of new organs, g4
Stinking smut of wheat (Fig.
I47)' 295, 296
formalin treatment, 221, 22}
Storage organs (Figs. 3, 4),
13, 14, 15
caterpillar fungi. I3I
food material of, I-
of cup fungi, I4- .
of ergot (Figs. 53, 54),
127, 128, 129
with fruiting bodies (Fig.
qt
Storage rots ot trim,
Strainer brass, for barrel pump
(Fig. 105),
Strands (Fig. 3),
of dry rot (Fig. 5),
of honey mushroom (Fig. 7)
of puff-ball (Fig. 93),
Strangling fungi (Figs. 57, 58),
132,
Strawberry leaf blight, 323,
leaf spot (Fig. 35). 79'
powdery mildew of.
Stumps, rots of (see timber
rots).
Stunting of plants, gx
Sublimate corrosive, a steep,
Sucker roots of mistletoe and
dodder,
Sucker threads of parasitic fungi
^ (Fig. 2),
Sugar, from starch by molds.
yeast in solutions of,
Sulphate, iron, and sulphuric
acid.
353
2II
I3
I5
, 18
'I8-
133
324
I3g
324
6l
114
119
22J
Minnesota Plant Diseases.
Sulphate,
of iron copper and alum-
inum, 239
of magnesium, 240
Sulphide of potassium, 220
Sulphur and lime, 227
for downy mildew of onion, 334
Sulphur for asparagus rust, 319
for onion smut, 320
for powdery mildew of cu-
cumber, 325
for powdery mildew of rose. 379
for powdery mildew of
strawberry, 324
for powdery mildew of
vines, 366
flowers of. 227
fungus (Fig. 124). 175. .'5». >$$
Sulphuric acid and iron sul-
phate, 221
for anthracnose of grape. 367
Sumacs, leaf curl fungi on. 121
Sun scalds wounds of, 47
Sunflowers, downy mildew of, 112
powdery mildew of, 396
rusts of (Fig. 206),
160. 373. 374, s~5. 3*9
Susceptibility toward disease,
Sweet William, sterile-fungus
rot of.
Swimming spores of fish mold
(Fig. 33). 7-'
Synchytrium anemones. 308, 399
decipiens (Fig. 211), 398
taraxaci, 399
Tamaracks, scaly Lentinus rot. 267
Tanning and bacteria. 196
Tape worms, degeneration in. 10
Taphrina, species of, 272
Tar ringing, to prevent in-rct
wounds. 205
spots and allies. 142
spots of maple (Fig. 133").
2;:8. 20 ,1
spots of maple and willow. 136
spots of willow ( Fig. 133.), 270
to cover wounds, 205
used against timber rot. 87
Temperature, influence on bac-
teria. 192
Terfeziace;v, i_>}
429
Texas fever of cattle, slime
molds of, 198
Thalictrum, rust of, 390
Thelephoralaciniatum, 172,243
terrestris, 243
Thelephoracea? (Fig. 82), 171
Thorn trees, leaf rust of, 349
Threads, sterile, in cup of cup
fungi (Fig. 62), 141
sucker, 61
Thrush, caused by yeast allies. 120
Ties, railroad, gill fungus on
(Fig. 116), 236
railroad, rot of (Fig. 116),
87. 236. 239
Tilletia tritici (Fig. 147) 295.29(1
Timber rots, 235, 260
birch-fungus. 254
bird's-nest fungi, 187
club fungus, 244
coral fungus, 244
creeping pore fungus. 25 S
dry rot, 245
elm Pleurotiis, 205
false tinder fungus, 250
fatty Pholiota. 262
flattened pore fungus, 251
gill fungus, 179
green cup fungus, 267
green mold. 270
hairy pore fungus, 250
methods of attack upon
wood cells (Fig. 38), 85.80
Nectria of red knot. 271
oak Da-dalea. 257
parchment pore fungus, 258
partridge wood rot. 242
pine Lenzites, 2Mj
pitch-stemmed pore fungus. 259
prevention of, 237, 238. 239, 240
ring scale of pine,
scaly I.eiitimis,
scaly pore fungus.
>cur;"y 1'hoHota.
shot- string fungus.
Miiooth shelf.
Stereum wood rot.
sulphur fungus.
tinder fungus.
Tramete> wood rot.
use of cresote to prevent.
256
267
-'54
-'63
430
Timber rots,
velvet stemmed Collybia,
zoned Polyporus,
see also Chapter XVI. and
XVII.
Timber trees, red knot on,
disease of,
Timbers, basidium-bearing fungi
on,
conditions of rotting,
creosoting,
dry rot of (see dry rot).
impregnation of, to prevent
rot,
house, rots of, 235, 245,
247, 248, 249,
piling of,
pore fungi on,
seasoning of,
sphere fungi on,
storing of,
tooth fungi on,
treatment of, to prevent rot,
trembling fungi' on,
ventilation of, to prevent
dry rot,
wood-dwelling fungi on,
Tinder-fungus rot, 177,
false,
Tissues, effect on, by parasites,
methods of killing,
Toad flax, parasitic seed plant,
Toad stools, fruiting bodies,
Tobacco plants, downy mildew
of,
Tomato, black rot of,
disease, losses by,
Tomatoes, host to downy mil-
dew,
Tools, fixings, etc., for spray
apparatus (Fig. m)j
Tooth fungi (Fig. 84),' 174,
coral fungus,
Toxins, bacterial,
Trametes pini.
radiciperda,
root rot,
Treatment, for smuts, hot
water, 2^
of apple orchards,
of timbers to prevent rot,
265
258
134
235
154
8?
87
239
250
238
175
238
138
238
175
239
169
250
40
251
250
84
79
200
22
112
328
201
112
228
175
244
193
256
256
256
226
347
239
Minnesota Plant Diseases.
Tree diseases, prevention of,
237, 238, 239, 240
Trees, conifers, cup fungi on, 145
diseases of,
harvesting of,
slime flux of,
Tree trunks, lichens on,
Trembling fungi (Figs. 78,
80 >• 153, 154, 167, 168, 169
basidium (Fig. 78),
Tremella (Fig. 80),
Tremellinec-e (see trembling
fungi).
Trifolium incarnatum, black
mold of,
Triphragmium clavellosum
(Fig. 208),
True puff-balls (Figs. 90, 91),
184, 185
True truffles (Figs. 68, 69), 148. 140
Truffles,
false,
fruiting bodies,
spore distribution,
true (Figs. 68, 69),
Trunk, tree, cup fungi on,
tree, smooth shelves on, 171
Tuber lyoni (Figs. 68, 69), 149, 150
Tuberculosis, bacteria of, 193
Tuberine;e (Figs. 68, 69), 148, 149
Tuckahce Indian bread,
Tulostoma mammosum (Fig.
92),
TulostomacecE (Figs. 3, 92),
Tunbridge nare,
Turnip, black rot of.
club root of (Fig. 179),
Indian, rust of,
sclerotum disease of roots,
white rust on,
Tylostoma (see Tulostoma).
Typhoid, bacteria of,
Uncinula, macrospora (Fig.
135),
nccator,
salicis (Fig. 134),
Underground puff-balls,
Uredineaj (see rusts),
Crnula craterium (Figs 6r
62),
L rocystis, anemones,
235
237
271
146
166
168
306
390
117
123
23,25
30
148, 149
144
15
183
182
267
342
345
392
32-'
330
193
274
366, 367
272, 273
184
140, 141
392
Minnesota Plant Diseases.
Urocystis,
cepulae, 320
occulta, 303
violae, 393
Uromyces, appendiculatus, 319
caladii, 392
caryophyllinus, 373
trifolii, 292
Ustilagine* (see smuts).
Ustilago, avenae (Fig. 146), 293, 294
bromivora, 303
crameri, 303
hordei, 300, 302
maydis (Figs. 148, 149), 297, 298
neglecta, 394
nuda, 300
tritici (Fig. 72) 157-297
violacea, 371, 393
Variation and predisposition, 96
relation to disease, 91
Varieties, rust-proof, 97
selection of and prevention
of disease, 96, 206
Vegetable worms. 16
Velvet-stemmed Collybia rot
(Fig. 130), 264.265
Venturia pomi (Figs. 183. 184,
l85), 35i. 35-'. 353
Verbena, powdery mildew of 396
Vertebrates, degeneration, 10
Vetch, powdery mildew of, 395. 396
spring, bacteria of nudules
(Fig. 99). 196
Vicia saliva, bacteria of nodules
(Fig. 99), utf
Vinegar bacteria. 191. 195
Vines, anthracnose of. 307, 368
black rot of. 365. 366
downy mildew of (Figs. 196.
197. >98). 1 1-'. no.
.?o\v. 369. 370
powdery mildew of. 366,367
Vineyards, disease of. 347. 365
Violet, cluster cup rust of, 386
downy mildew of. 112. jtf/
™>t. 373
smuts of. 1 58. 37 1 . jv.?
spot of leaf, 381, 382
sterile-fungus rot of, 329
Wall tlower, white rust on, 330
Water cress, white rust on, 330
Water,
flea, parasites of,
hot, method for smuts, 225,
molds (Fig. 42), 105,
molds, distribution of
spores,
molds, on animals,
molds, on crabs,
molds, on fish,
molds, saprophytic habits,
Watermelons, downy mildew of
Weeping fungi (Fig. 78).
153- 154, 169,
basidium of (Fig. 78),
Wet rot of potato (Fig. 172),
Wheat, brand.
crop rotation and bacteria.
ergot of. 130.
formalin treatment of stink-
ing smut, 221,
loose smut of (Figs. 71.
7-'). 155- »57.
loosc smut of, formalin
treatment,
Wheat rust (see also rusts of
wheat ).
(Figs. 73. 74). 159. 163 to
and variation,
distribution of spores.
epidemics and pure cul-
tures. loo.
host succession.
infection of grass lea! ( Fig.
29).
kinds of spores (Fig. lit.
scab,
stinking smut of (Figs. 71.
1471. '55- -'V5.
White cohosh. ru>t of,
piped oak,
rusts. formation oi' leaf gree
in petals of hosts tlower.
ru-t> of inu>tards, cabbage.
etc..
Wild (lowers, cluster cup rusts
of.
Wild mushrooms (Fig. 89.1,
Wild rice, ergot on,
Willow blight (Fig. 134). 272.
leaf rust ( Fig. i.^S).
67
226
106
27
66
67
71
36
334
245
166
340
297
196
307
223
223
330
180
Minnesota Plant Diseases
Willow,
powdery mildew of (Fig.
52), 125, 126
rusts, 160
tar spots (Fig. 133), 142,^70
Wilt of cucurbits (Fig. 173), 341
of flax (Figs. 156, 157, 158,
159), 3io to 314
Wind, assistance in infection, 98
spore distribution in puff-
balls, 182
Wine, bacteria in, 196
Witches'-broom (Fig. 22), 51,52
age of mycelium, 20
caused by insects, 56
caused by leaf curl fungi, 121
of rust origin, 164
on balsam fir (Fig.
23), 153, 277, 278
on birch, 56, 271
on cherry, 56, 363
on red cedar (Figs. 26,
57'), 54- 55
on spruce (Fig. 101). 199,200
on white spruce (Figs. 24,
25, 55), 54
stunting in age, 82
Witches' butter, a trembling
fungus, 169
Wood, attacked by fungi, 40
basidium bearing fungi on, 154
bird's-nest fungi on, 186
characters of, 85'
dead, cup fungi on, 142
-destroying fungi, action on
lignin (Fig. 38), 85,86
-dwelling fungi, action on
wood, 40
-dwelling fungi, methods of
entrance, 40
-dwelling fungi, nutrition, 40
-dwelling habit, 40
gill fungi on, i/q
Jcw's-car fungi on, 166
pali>a>k' fungi on, i/i
-]K'ck(.T>. agents of spore
distribution, 31
-pecker>. wounds caused by. 47
rot, coral I'ungus (Fig. 119),
244, 246
rot. destruction of wood
- (Fig. 38), 86
Wood,
rot, creeping pore fungus, 258
rot, partridge (Fig. 118), 242
rot (see also timber rots),
rot, Stereum (Fig. 117), 240
sphere throwing fungi on, 184
tissues, 85
tooth fungi on, 175
trembling fungi on, 167
Worms, degeneration in, 10
true, parasites of, 67
Wound infection and prevention
of disease, 204, 205
parasites (Fig. 20),
45, 46, 80, 235
parasites, birch fungus, 255
parasites, degree of para-
sites, 58
parasites, destroyers of
branches, 80
parasites, false tinder fun-
gus, 250
parasites, gill fungi. 179
parasites, ring scale of pine, 256
parasites, scaly pore fungus, 254
parasites, Stereum (Fig.
117), 241
parasites, sulphur fungus, 253
parasites, tinder fungus, 251
Wounds, cause of, 47
causes of predisposition, 96
in bark, entrance of rots, 41
in bark, causes, 41
Yeast-like fungi on animals, 66
on man, 75
on water flea, 67
Yeasts (Fig. 48), 118, 119, 120
allies of, 120
fermentation, 36
habit of saprophytes, 36
in bread making, 119
in slime exudation, 120
in slime flux. 271
occurrence in nature, 36
power of fermentation, 119
Yellow piped oak, 240
Youth, predisposition of, 95
relation to disease, 91
Zinc chloride, to prevent tim-
ber rot, 239
Zoned Polyporus rot, 258
Zooglcea. 190
Live Music Archive
Librivox Free Audio
Metropolitan Museum
Cleveland Museum of Art
Internet Arcade
Console Living Room
Books to Borrow
Open Library
TV News
Understanding 9/11