EXPERIMENTAL POLLINATION
AN OUTLINE OF THE
ECOLOGY OF FLOWERS AND INSECTS
BY
Frederic E. Clements and Frances L. Long
QK926 |
Q £ Published by the Carnegie Institution op Washington
Washington, 1923
Oty* B. 31 Mi ffitbrara
Nortlt (Carolina &tatp Inineraitij
olina State Library
^["CAROLINA STATE UNIVERSITY L
THIS BOOK IS DUE ON THE DATE
INDICATED BELOW AND IS SUB-
IECT TO AN OVERDUE FINE AS
POSTED AT THE CIRCULATION
DESK.
19 1980
MAY
/yyy
CLEMENTS & LONG
Edith S. Clements I
Painted flowers of Aconitum and Delphinium, showing
the method of experiment.
North Ca(J$i* S'aLe Library
# Raleigh
EXPERIMENTAL POLLINATION
AN OUTLINE OF THE
ECOLOGY OF FLOWERS AND INSECTS
BY
.aca
Frederic E. Clements and Frances L. Long
North Q£M!ina State Librarv
Published by the Carnegie Institution of Washington
Washington, 1923
CARNEGIE INSTITUTION OF WASHINGTON
Publication No. 336
Copies of this feoek
NOV 6 1923
CONTENTS.
1. Introduction and Methods
Introduction
Objectives
Methods
General principles
Normal pollination
Experimental pollination
Organization of experiments
Change of position or place
Concealing or disguising flowers. .
Mutilation
Artificial and painted flowers ....
Addition of parts or substances . .
Competition
Manipulation of insects
Life-history methods and records .
Life-history record of a represen-
tative species
2. Normal and Experimental Pol-
lination
Aconitum columbianum
Page
3
3
4
4
4
6
6
7
7
Normal pollination 15
Structure
Behavior
Experiments
Change of position
Horizontal racemes
Racemes inverted
Mutilations
15
15
1(3
16
16
16
17
Cotton plugs 17
Stamens removed 17
Hood split 17
Hood removed 17
Hood and nectaries removed 17
Lower sepals removed 17
Side petals removed 18
Competitive relations 18
Artificial and painted flowers. . 18
Normal colors 18
Artificial flowers 19
Painted flowers 20
Addition of honey and odor. . . 21
Honey 21
Perfumes 22
Summary 22
Delphinium scopulorum 22
Normal pollination 22
Habit and structure 22
Behavior 22
Experiments 23
Change of position 23
Inverted racemes 23
Horizontal racemes 23
Mutilation 23
Cotton plugs 23
Petals removed 23
Spur removed 23
Landing-platform removed. . 24
Artificial and painted flowers . . 24
Crepe-paper corollas 24
Crepe-paper corollas with
spurs 24
Painted flowers 25
2. Normal and Experimental Pol-
lination {Continued).
Delphinium scopulorum (Continued).
Addition of odor
Perfume
Summary
Rubus deliciosus
Normal pollination
Habit and structure
Behavior
Variation in visits
Experiments
Mutilation
Petals split or shortened ....
Stamens covered
Artificial and painted flowers . .
Crepe-paper corollas
Painted corollas
Addition of honey or odor ....
Honey
Summary
Rubus strigosus
Normal pollination
Habit and structure
Behavior
Experiments
Mutilation
Floral envelopes or stamens
removed
Rosa acicularis
Normal pollination
Habit and structure
Behavior
Experiments
Mutilation
Corolla shortened
Stamens masked
Artificial and painted flowers . .
Crepe-paper corollas
Addition of honey and odor. . .
Honey
Honey and talcum powder. .
Camphor
Summary
Geranium caespitosum
Normal pollination
Habit and structure
Behavior
Calendars
Experiments
Change of position
Flowers vertical or inverted
Mutilation
Cotton over nectaries
Excision
Artificial and painted flowers. .
Crepe-paper corollas
Addition of honey and odor. . .
Honey
Summary
Chamaenerium angustifolium
Normal pollination
Habit and structure
25
25
26
26
26
26
26
27
29
29
29
29
30
30
30
31
31
31
32
32
32
32
33
33
33
33
33
33
33
34
34
34
35
35
35
36
IV
CONTENTS
Page
2. Normal and Experimental Pol-
lination (Continued).
Chamaenerium angustifolium (Cont.).
Behavior 45
Experiments 48
Change of position 48
Racemes inverted 48
Mutilation 48
Floral envelopes removed. . . 48
Upper petals and the in-
cluded sepal removed .... 49
Stamens and style removed . 49
Artificial and painted flowers. . 51
Crepe-paper corollas 51
Painted corollas 51
Addition of honey and odor. . . 52
Honey 52
Odor 52
Perfumes 53
Flavoring extracts 53
Summary 54
Pachylophus caespitosus 54
Normal pollination 54
Habit and structure 54
Behavior 55
Experiments 56
Artificial flowers 56
Crepe-paper flowers 56
Petals obscured 56
Mentzelia multiflora 56
Normal pollination 56
Habit and structure 56
Experiments 56
Crepe-paper flowers and com-
petition 57
Crepe-paper corollas 57
Summary 58
Frasera speciosa 58
Normal pollination 58
Habit and structure 58
Behavior 58
Experiments 59
Mutilation 59
Types 59
Artificial and painted flowers. . 59
Crepe-paper corollas 59
Painted corollas 60
False corollas 61
Addition of nectar and odor. . . 61
Nectar 61
Summary 61
Mertensia pratensis 62
Normal pollination 62
Behavior 62
Experiments 63
Mutilation 63
Changes of corolla 63
Castilleia miniata 63
Normal pollination 63
Habit and structure 63
Behavior 63
Experiments 64
Mutilation 64
Upper lip removed, spike in-
verted 64
Painted flowers 64
Painted bracts 64
Page
2. Normal and Experimental Pol-
lination (Continued).
Pentstemon glaber 65
Normal pollination 65
Habit and structure 65
Behavior 65
Calendars 66
Experiments 68
Change of position 68
Racemes inverted 68
Racemes horizontal 70
Mutilation 70
Cotton at the corolla mouth. 70
Styles, stamens, and stami-
node removed 70
Corolla split 70
Corolla lips separated and
staminode raised 71
Upper lip removed at the
throat 71
Lower lip shortened half. ... 71
Lower lip removed 71
Lower lip and part of the
tube removed 71
Lips removed except lower
lobe 71
Corolla tube shortened half. 71
Petals separated 71
Lower lip split into three
petals 71
Tube end of a corolla slipped
over the staminode 72
Comparative relations 72
Artificial and painted flowers. . . 72
Crepe-paper corollas 72
Corolla painted with water-
colors 72
Honey and odor 72
Sirup added 72
Pentstemon gracilis 73
Normal pollination 73
Habit and structure 73
Behavior 73
Calendars 74
Experiments 75
Change of position 75
Racemes inverted 75
Racemes horizontal 75
Mutilation 75
Landing-platform removed. . 75
Brush of staminode removed 75
Anthers and recurved por-
tion of upper lip removed 75
Upper lip partly removed. . 75
Lobes of upper lip separated 75
Petals split to the base 76
Pentstemon glaucus 76
Normal pollination 76
Normal behavior 76
Experiments 76
Mutilation 76
Upper lobes split to base ... 76
Lower lip removed 76
Outer lobes of lower lip re-
moved 76
Staminode removed 76
CONTENTS
Page
2. Normal and Experimental Pol-
lination (Continued).
Pentstemon glaucus (Cont.).
Middle lobe of the lower lip
removed 77
Upper lip removed 77
Pentstemon secundiflorus 77
Normal pollination 77
Behavior 77
Calendar 77
Experiments 77
Odor 77
Powders and extracts 77
Cotton wads sprinkled with
peppermint 78
Summary 78
Monarda fistulosa 79
Normal pollination 79
Habit and structure 79
Behavior 79
Experiments 80
Mutilation and competition. . . 80
Plan 80
Summary 88
Resume 89
Variation in number of visits. ... 89
Changes of position 90
Masking with cotton 90
Mutilation 91
Artificial flowers 92
Painted flowers 92
Honey and odor 93
3. Competition and Constancy 94
Significance 94
Competition 94
General plan 94
Rubus strigosus 95
General relations 95
Rubus strigosus and Rubus deliciosus 95
Comparison 95
Experiments 95
Summary 97
Rubus strigosus and Rubus deliciosus 97
Comparison 99
Summary 99
Competition of Rubus with Frasera,
Cleome, etc 99
Comparison 97
Experiments 99
Summary 99
Rubus strigosus and two or more
competitors 99
Comparison 99
Summary 100
Rubus deliciosus 101
Experiments 101
Summary 101
Rosa acicularis 101
Comparison 101
Experiments 102
Summary 102
Competition with normal and
mutilated Aquilegia 105
Geranium 105
Comparison 105
Experiments 106
Summary 109
Page
3. Competition and Constancy (Con-
tinued) .
Chamaenerium angustifolium 110
Comparison HO
Experiments HO
Summary HO
Pentstemon HO
Comparison HO
Experiments 113
Summary 113
Monarda fistulosa 115
Comparison H5
Experiments 115
Summary 115
Weight and composition of pollen
loads 119
Value and methods 119
Discussion 127
Constancy 128
Definitions 128
Early observations of constancy 129
Bennett's studies of constancy 130
Christy's studies of methodic
habits 130
Mueller's results 130
Bulman's studies 131
Ord's conclusions 131.
Plateau and Perez 131
Constancy in Bombus 132
Lovell's conclusions 132
Kranichfeld's observations 133
Origin of oligotropism 133
Resume 134
Experimental results in compe-
tition 134
Effects of competition 134
Constancy as shown by pollen
loads 135
4. Principles and Conclusions 136
Introductory 136
Early experiments of Plateau and
others 136
Artificial flowers 136
Nectaries 137
Color sense of bees 138
Response to detached petals. ... 139
Color preferences of nocturnal
moths 140
Response to color without anten-
nae '. 140
Perception of form 140
Response of wasps to color 143
Response of wasps to odor 145
Main researches of Plateau 145
Masked flowers 145
Removal of corolla 147
Response to different colors 148
Addition of honey to vivid nectar-
less flowers 149
Anemophilous flowers 150
Entomophilous flowers of dull
color 150
Artificial flowers, second series . . . 150
Artificial flowers of green leaves . . 151
Conclusions as to artificial flowers 152
General summary 152
Role of vexillary organs 153
VI
CONTENTS
Page
4. Principles and Conclusions {Con-
tinued),
Main researches of Plateau (Con-
tinued).
Choice of colors by insects 154
Errors made by Anthidium 155
Admiration of syrphids for bright
flowers 156
Attraction of colored cloths and
brilliant objects 156
Constancy among bees 157
Mistakes made by bees 157
Removal of the antennae of bum-
ble-bees 158
Evidence of the attractive role of
odor 159
Decorollate poppies and insect
visits 159
New experiments with artificial
flowers 160
Conclusions as to artificial flowers 162
Macroglossa and false flowers. ... 164
Entomophilous flowers little vis-
ited by insects 165
Related studies and critiques 166
Comparative importance of odor
and color 166
Perez's critique of Plateau's work 167
Effect of colors at the hive 168
Critiques of Kienitz-Gerloff 168
Knuth's critique 169
Reeker's experiments with arti-
ficial flowers 171
Decorollate poppies 171
Response to color and odor by a
hawk-moth 175
Vexillary nature of the plume in
Muscari 175
Forel's experiments with covered
dahlias and with artefacts .... 176
Response of Syritta 178
Andreae's experiments with arti-
ficial flowers 178
Andreae's conclusions 181
Andreae's criticisms of Plateau's
work 182
Plateau's criticisms of Andreae's
work 182
Wery's experiments with decorol-
late and artificial flowers 183
Plateau's criticisms of Wery's
experiments 185
Experiments of Weismann and
Errera 186
Orientation of the honey-bee at
flowers of the same species .... 186
Discrimination between similar
species of flowers 187
Orientation of the bee within the
flower 188
Chance observations of visits to
imitations 189
Knoll's critique of Plateau's
study of Macroglossa 193
Recent investigations 193
The color sense of the honey-bee 193
Can bees distinguish colors? .... 194
Page
4. Principles and Conclusions (Con-
tinued) .
Recent investigations (Continued).
The pollination of green flowers . . 195
Conspicuous flowers rarely visited
by insects 196
Response of honey-bees to colored
artefacts 197
Pattern vision in the honey-bee. . 198
Experiments with cotton blos-
soms 198
Color sense and memory in the
honey-bee 199
Frisch's researches — sense of color
and form in the honey-bee .... 200
The supposed color sense of the
honey-bee 201
Seasonal changes in response to
honey 202
The sense of smell in the honey-
bee 203
Bombylius and the colors of
flowers 205
Vision and flower behavior of
Macroglossa stellatarum 206
Response of bees to spectral bands 207
Evaluation of Plateau's researches 208
Forel's estimate 208
Contradictory nature of Plateau's
later conclusions 212
Conclusions as to Plateau's views 213
Senses of insects 213
Sight 213
The mosaic theory 213
Criticisms of Plateau's views as
to vision 215
Sensibility to color 215
Perception of form and move-
ment by insects 215
Discrimination of form 216
Vision in honey-bees 216
Vision in ants 217
The role of ultra-violet in at-
traction 217
The homing faculty in bees and
wasps 217
Fabre's experiment with bees
and wasps 217
Lubbock's and Forel's critique
of Fabre's conclusions 218
Homing faculty of bees 220
Sense of direction in ground-
wasps 220
Disturbance of memory in
wasps 221
Observations on the homing of
Bembex and Pampilus 221
Memory of place in Osmia. . . . 222
The field and nest flights of the
bumble-bee 223
The homing of the mud-dauber
wasp 223
Experiments on the orientation
of bees in homing 224
Homing abilitv in Polistes .... 224
Smell 225
CONTENTS
Vll
Page
4. Principles and Conclusions (Con-
tinued).
Smell (Continued) .
Sense of smell in insects de-
prived of antennae 225
Forel's criticisms of Graber's
results 226
Hauser's experiments 227
Olfactory pores 228
Experiments with antennse
removed, mutilated, or
coated 228
Experiments with wings, legs,
and stings mutilated 229
Mclndoo's experiments with
deantennate insects 229
Present status as to the seat of
the olfactory sense 230
Intelligence 232
Relation between the senses
and mental faculties of in-
sects 232
Memory and general intelli-
gence of wasps 233
Memory of place in bees 233
Memory of time and asso-
ciation of impressions. ..... 235
Memory of time and memory
association in honey-bees. . . 236
Intelligence of honey-bees. . . . 236
The psychic powers of insects 237
Page
4. Principles and Conclusions (Con-
tinued).
General resumS 238
Treatment 238
Attraction 238
Color 238
Mutilation 238
Artificial flowers 239
Painted flowers 240
Inclosing flowers in glass 241
Green flowers and showy nec-
tarless flowers 241
Color preference 241
Odor 244
Masking or covering flowers
to conceal color 244
Odor of honey 244
Effect of added odors 245
Relative value of color and
odor 245
Form 245
Distinction and role 245
Attraction at a distance and near
at hand 246
Learning and habit 247
Memory and intelligence 247
5. Pollinators and Flowers Visited 249
6. Flowers and their Visitors 256
Bibliography 268
Index 273
Description of Plates 276
EXPERIMENTAL POLLINATION
AN OUTLINE OF THE
ECOLOGY OF FLOWERS AND INSECTS
BY
Frederic E. Clements and Frances L. Long
LIST OF PLATES.
Plate Page
1. Painted flowers of Aeonitum and Delphinium Frontispiece
2. Life-history of the flowers of Aeonitum columbianum and Delphinium scopulorum, 272
3. Life-history of Rubus strigosus and Potentilla gracilis 272
4. Life-history of Heracleum lanatum and Sedum stenopelatum 272
5. Life-history of Galium boreale and Saxifraga bronchialis 272
6. Life-history of Campanula rotundifolia and Erysimum asperum 272
7. Life-history of Geranium caespitosum and Dodecatheon meadia 272
8. Life-history of Chamaenerium angustijolium 273
9. Life-history of Pachylophus caespitosus 273
10. Life-history of Pirola elliptica, Frasera speciosa, and Gentiana amarella 273
11. Life-history of Gilia aggregata and pinnatifida, Mertensia sibirica, and Lithosper-
mum multiflorum 273
12. Life-history of Pentstemon glaber 273
13. Life-history of Castilleia miniata and Monarda fistulosa 273
14. Life-history of Allium cernuum and Zygadenus elegans 274
15. Mutilated and inverted flowers of Aeonitum 274
16. Mutilated flowers of Aeonitum, Delphinium, and Monarda 274
17. Mutilated flowers of Geranium, Chamaenerium, and Pentstemon glaber 274
2
1. INTRODUCTION AND METHODS.
INTRODUCTION.
The original plan for the development of quantitative ecology con-
templated two series of monographs, one dealing with the plant in its
vegetative relations, the other in its reproductive aspects. The first has
received attention in a number of monographs, some of which deal with
the individual and some with the community, but the factors and processes
involved in the behavior of the flower were necessarily somewhat neglected
for a time. Studies of the life-histories of flowers were first begun in 1910
and these were followed by observations and experiments upon the relations
of flowers and insects. These served to disclose the nature of the problem
and to indicate the methods needed for a comprehensive experimental
attack upon it. The main investigation was begun in 1918 and has been
carried on actively during the succeeding summers. As a consequence
the limits of the field have expanded greatly and the present treatment is
to be regarded as a preliminary endeavor to organize it upon an adequate
experimental and quantitative basis in nature.
The study of the relations between flowers and insects, begun effectively
by Kolreuter (1761) and Sprengel (1793), underwent an enormous expansion
at the hands of Delpino (1867), Hildebrand (1867), Mueller (1873), Darwin
(1876), Kerner (1876), and Knuth (1894) without becoming experimental
in even a small degree. The first investigator to recognize that the great
mass of observational results needed to be refined by means of experimental
methods was Plateau (1877, 1895), and practically all other experimental
studies have been a direct or indirect consequence of his work.1 The present
investigation constitutes the exception, as it was begun with a different
objective and with contacts sufficiently slight to permit an independent
development of methods. This was of especial importance in view of the
comprehensive nature of the plan, as well as in affording a detached view
of the methods already employed. This appears to have been justified
by the outcome, not only in the matter of methods but also with respect to
results and conclusions. Moreover, the difference in objectives has made
it possible to plan experiments and interpret results without a bias in favor
of Plateau's views or those of his critics. While the relative values of
color and odor in attraction constitute one of the most interesting phases of
the general problem, they have too long held the center of the stage as a
consequence of Plateau's dramatic challenge. However, even in the present
case, the adequate analysis and evaluation of the work that has been done
make it necessary to treat attraction as the paramount theme.
This investigation has been carried out at the Alpine Laboratory, which
is situated at an altitude of 8,500 feet in the montane forest climax on
Pike's Peak. It is perhaps unique in dealing with an insect fauna in exclu-
sive contact with a native flora, though some of the experiments have
1 Since this was written, the admirable monographs of Frisch and of Knoll have become
available. These deal almost exclusively with intensive control researches into the response
of one or two species to color, odor, or form, and are indispensable to students of experimental
pollination. While it is now impossible to abstract them as fully as they deserve, a general
account of the methods and results will be found in Chapter 4.
3
4 EXPERIMENTAL POLLINATION.
concerned species that are probably outside the normal experience of the
visitors. Some studies have also been made in the plains grassland at
the base of the range, and in the alpine meadows on the summit of Pike's
Peak, as well as a few preliminary ones in Arizona and California, but these
are reserved for the most part for a later treatment.
For the flowers the nomenclature is that employed in Clements and
Clements' "Rocky Mountain Flowers," while the names of the Lepidoptera
are those found in Holland's "Butterfly Book" and "Moth Book." In the
other groups the determinations have been made by the following specialists,
to whom grateful acknowledgment is made: Dr. J. M. Aldrich, Bureau of
Entomology, Washington, D. C; Professor T. D. A. Cockerell, University
of Colorado, Boulder, Colorado; Professor C. Howard Curran, University
of Kansas, Lawrence, Kansas; Dr. F. E. Lutz, American Museum of Natural
History, New York; Professor S. A. Rohwer, U. S. National Museum,
Washington, D. C; Professor 0. W. Oestlund, University of Minnesota,
Minneapolis, Minnesota; Professor M. W. Swenk, University of Nebraska,
Lincoln, Nebraska; Professor C. T. Vorhies, University of Arizona, Tucson,
Arizona; Professor H. L. Viereck, Biological Survey, Washington, D. C.
Objectives. — As already indicated, the primary object of the present
investigation is to place the study of the flower in relation to its environ-
ment on the basis of experiment and measurement. At the same time it
is intended to give the fullest value to the synthetic nature of the problem
by placing the chief emphasis upon the mutual relations of flowers and
insects. The life-history of the flower has been given greater attention
than heretofore and it is felt that the life-history of the insect in the broader
ecological sense must receive similar study. The central theme is attraction
and the behavior of the insect at the flower, and in spite of the work already
done, this offers an enormous opportunity for quantitative research. The
efficiency of both flower and insect is susceptible of much greater accuracy
of measurement and it appears probable that this will disclose a new field
of correlations. In this connection the experimental study of competition
is especially significant and promises to throw a flood of light upon reciprocal
adaptation, as is likewise true of mutilation experiments. This leads to
the consideration of the evolution and phylogeny of flowering plants under
the influence of insect and wind pollination, as well as a re-examination
of the effectiveness of cross and self pollination. With respect to the
insects the major queries concern the respective roles of the senses, the
acquisition and fixity of habits, and the relation between instinct and
intelligence.
METHODS.
General principles.— An endeavor has been made to develop a compre-
hensive system of research, based primarily upon experiment and measure-
ment. This has been made as complete as possible, though it is fully
recognized that the further development of this great field will reveal new
objectives and new methods of attack. The great majority of the methods
have been tested in the present study, others are now being used in the work
under way, and a few are still to be applied. Most of the latter have been
employed by other investigators and hence are considered for the sake of
INTRODUCTION AND METHODS. 5
completeness. The observational method has necessarily been continued
in connection with normal pollination and the life-history of the flower,
but it has been made as quantitative as possible and has frequently been
supplemented by experiment. The experimental methods have been made
as simple and direct as possible and have been applied chiefly to attraction,
behavior at the flower, and competition between flowers in this first series.
Most of them have been subjected to repeated check and the results are
thought to be fairly conclusive for the region and the time concerned.
The conditions have differed materially from those obtaining in practically
all other studies in this field, in that both flowers and insects were in the
natural relations that have existed for a long period. While gardens yield
behavior results of as much interest as those of natural habitats, it is obvious
that their essentially exotic nature renders them of little value in questions
of adaptation and evolution. This difference is also to be taken into account
in other respects; for example, artificial flowers appear to be much more
readily visited in gardens than in nature, as would be expected from the
difference in the habits of the insects.
Moreover, it is thought that the experimental investigation of a native
insect fauna in the midst of its natural floral environment, and the con-
verse, furnishes a norm to which can be referred other studies that are
artificial in some degree. Some such standard appears indispensable,
since it is evident that many of the contradictions and discrepancies in the
results of various investigators are to be explained by differences in con-
ditions and setting rather than by faults of method or observation. This
is certainly true of many of the points at issue between Plateau and his
critics. The effects of time, place, weather, grouping, etc., are often
decisive, as shown in the next chapter, and they need always to be checked
by actual trial, or, much better, eliminated by simultaneous observations
in contiguous areas in so far as possible. The time of day, week, or season
not only has an effect due to lapsed time, but also one especially of differ-
ence in sun, cloud, temperature, wind, condition of flowers, habit of insects,
etc. Even the weather of the previous day may have a profound effect,
if it has been rainy, unusually cold or warm, or windy. Differences of
location and particularly region usually produce decided effects, owing to
changes of conditions as well as of flower and insect populations. In fact,
marked differences of behavior have been noted in spots a yard apart
where no differences of sunlight, temperature, or wind were demonstrable
at the time, but where the behavior of the insects had been determined by
earlier shade, exposure, by nearness to their nests, etc. The kinds, number,
and grouping of the species and individual flowers naturally have a pro-
nounced effect, as do also the time of blooming, the position in the flowering
period, the nectar flow, and the rate of nectar production. It is equally
evident that the composition of the insect fauna as to orders and species,
the number of individuals, the sexes, social habits, age, etc., will greatly
affect the results. Finally, it has been found that the position and nearness
of the observer, as well as his clothing (cf. Lovell, 1914:407), produce
effects to be taken into account, while an increase in the number of observers
in the same spot may completely change the response. Still other factors
enter into the problem, thus completing the certainty that researches
6 EXPERIMENTAL POLLINATION.
widely removed in time and space will differ much in detail and often in
principle as well.
Normal pollination. — This is primarily a matter of observation and
is important in experimental studies chiefly because it furnishes a back-
ground of normal behavior against which departures may be measured.
The methods are simple and have long been exemplified in the works of
Delpino, Hildebrand, Axell, Mueller, Darwin, Kerner, Knuth, Loew,
MacLeod, Robertson, and others. For the more exact results needed in
connection with experiments, it has proved necessary to enter into finer
details as to behavior, to deal with a larger number of individuals, and
especially to record the number of visitors of each species, as well as the
number of flowers visited by each individual. The failure to note the
number of visitors of each species deprives practically all of the observa-
tional studies of any quantitative value, in spite of the contention of Knuth
(1906:195) that the "statistical" method of Mueller has greater possi-
bilities than one would be inclined to believe and that the reproach of
affording an inaccurate idea of the number of pollinators because it counts
the visits of species and not of individuals is of no importance. This is
contradicted by the earlier statement that 'a disadvantage is involved,
though one that can hardly be avoided, as it is almost impossible to count
all the individual visits to a conspicuous flower.'
In a critique of Knuth's "Bliitenbiologie," Roberston (1922:148) states
that anthecological data "are lists of insect visitors made to show the
species, their frequency, their efficiency as pollinators, and the possibility
of their having some influence in determining the characters of the flowers.
Mueller's lists show these details. In the case of the bees he indicated
the sexes, and whether they were sucking nectar or collecting pollen. To
note the sexes is important, because female bees fly longer than males and
are more likely to make repeated visits. To note the fact of pollen-
collecting is also important. A female bee will carry pollen all day from
flowers on which the male rarely occurs. From observations at Carlinville
the females of nest-making bees average 20.6 visits to the males 10.3. The
inquiline bees show females 8.8 to males 8.0. In anthecology Mueller's
lists are valuable as regards species and visits, but they fail to indicate the
frequency. In 1908 I rejected Mueller's method and adopted the practice
of capturing the individuals as they came, noting species and counting
individuals It is impossible to indicate the importance of insects to flowers
by lists of species, because efforts to increase the lists involve an exaggera-
tion of the importance of rare and exceptional cases."
Experimental pollination. — This includes practically all the experi-
mental methods that deal with the relations of flowers and insects, though
competitive methods are considered separately for the sake of convenience.
No sharp line can be drawn between these and the methods that make use
of colored objects or odorous substances, but it seems better to consider
the latter in a separate section. Experiments may be devised to show
the role of different parts in attraction, landing, or guidance, the behavior
of insects in securing nectar or pollen, or their efficiency in the transfer of
pollen. However, in many cases two or more of these processes are affected
INTRODUCTION AND METHODS. 7
by the same change, and for this reason the various experimental methods
are organized with respect to the change concerned. There is almost no
limit to the number of changes and combinations that ingenuity can devise,
but the following discussion is restricted essentially to changes that have
been used or are now in process of being used.
Organization of experiments. — All experiments have been made in
the field under natural conditions. Controls have been regularly employed
and the results checked by repetition. Comparative values have been
secured by using a definite number of flowers, an equal area, or an equal
number of them. The latter method alone seems to be entirely without
error and has completely replaced the others, since it yields exact and
directly comparable expressions of choice. For the same reasons experi-
ments should be observed at similar times and for periods of the same
length in so far as possible. For the best results it is often necessary to
have two or three observers, so that the time difference can be eliminated
and the same group of competing insects followed under the same condi-
tions. The grouping of the plants and the relative position of the flowers
are matters of much importance and must be considered with reference to
the habits of the insects and the type of behavior to be tested. All experi-
ments carried on with a plant or group that insects have been in the habit
of visiting must reckon with the effect of the habit itself. While such
results are dependable as to behavior, they do not permit an exact analysis
of the factors entering into it. On the other hand, advantage may be taken
of habit to insure certainty in regard to a response, as when artificial or
mutilated flowers are alternated in the cluster with normal ones. It must
also be recognized that the reactions of mature insects contain a large
element of habit and that the real response to certain stimuli can be obtained
only by using young ones that have just emerged. Moreover, it has become
more and more desirable to deal adequately with individual behavior,
and this can be done only by working with marked bees.
Plateau has more than once pointed out that experiments with flowers
and insects demand the greatest patience and almost unlimited time, and
that one must expect to have many of them rendered incomplete by changes
of weather and other hazards. The problem is the same as in all experi-
mentation in nature and must be met in so far as possible in the choice of
the region, the detailed organization of plans, and the introduction of the
maximum degree of control.
The modifications brought about for experimental purposes may be
grouped as follows: (1) changes of place, grouping, or time; (2) concealing
or disguising flowers or clusters; (3) removal or mutilation of flowers,
parts, markings, etc.; (4) artificial or painted flowers or parts; (5) addition
of flowers, parts, substances, etc. ; (6) combinations of two or more changes.
The distinctions between the different types of modification are far from
absolute and certain changes might well be placed in another group.
Change of position or place. — These may concern the plants or flowers
of one species, or of two or more species. In the latter case they have to
do primarily with competition and are considered later under that heading.
Changes that have to do with the time of blooming or the grouping may be
8 EXPERIMENTAL POLLINATION.
utilized to hasten or retard flowering or to increase the total attraction of
a group of individuals. Changes of position are especially valuable in
connection with the study of normal behavior and in determining the
correlation between habit and intelligence in different species and indi-
viduals. They may deal with the cluster, the flower, or the flower part,
but in the last case the change is essentially a mutilation and is considered
as such. The simplest method is to change the entire cluster in position
by 90 or 180 degrees, either by bending and fastening it in the position
desired, or by cutting it off, placing the end in a vial or in wet cotton, and
attaching it alongside a normal inflorescence. The use of single flowers
permits a wider range of changes, as these can be turned through two circles
with the assumption of very different positions. Such changes not only
affect the appearance of the flower with respect to attraction, but they
necessitate a different behavior in one or more of the successive processes
of landing, guidance, obtaining nectar, collecting pollen, and departure.
A completed visit thus becomes a new problem in the solution of which
species and individuals exhibit striking differences.
Concealing or disguising flowers. — This may operate upon the plant
or cluster, a single flower, or a part of it, such as the petals or stamen-mass.
When the nectary is obstructed by a cotton plug, the effect is essentially
one of mutilation, while the use of green leaves to mask the corolla or
the disguising of the rays of one species with those of another produces
an artificial flower in effect. Masking is primarily a device to conceal the
color and thus permit the determination of the role of odor, but it must
always be done with the effect of habit in mind. Clusters or single flowers
may be covered with pots, boxes, wire cages, or other objects, or they may
be variously disguised by means of paper, cloth, leaves, etc. The perianth
may be similarly covered on either one or both faces, one or more of the
petals covered, the anthers or nectaries masked with paper, cotton, or
foreign petals; in short, any part or parts may be concealed in any manner
that seems desirable. This is similarly true of the rays and disks of com-
posites, and of all vexillary organs, such as spathes, colored bracts, etc.
Painting the petals or other parts is also a type of masking. Finally, odor
may also be masked by means of glass globes, tubes, etc., permitting color
and form to act alone as attractive factors.
Mutilation. — By this is understood the removal of flowers or parts,
the splitting or cutting of parts, and such changes of position as result in
a different form. The removal of flowers is chiefly significant in such
definite inflorescences as the umbel and head with show-flowers or ray-
flowers, in which all or part of either kind of flower may be cut out to dis-
close the role of the other. With respect to other changes a radiate head
resembles a single flower to a considerable degree. In regular flowers the
most important mutilations arise from the removal of corolla or perianth
in whole or in part, the shortening of the petals, or splitting them into
parts of various forms. The mutilation of irregular flowers may also be made
to throw light upon attraction, but it is particularly valuable in revealing
the role of the specialized parts, as in the larkspur, peas, and mints. Hoods,
spurs, standards, keels, and lips may be removed wholly or partly, or they
INTRODUCTION AND METHODS. 9
may be variously split to increase the attractive surface. In the interior
of the flower any or all of the stamens, staminodes, or pistils may be removed
or modified, one or more of the nectaries excised or otherwise changed, and
the protective hairs of various sorts trimmed or cut as desired. All vexillary
organs external to the flower may be treated in the same manner as petals.
Decisive changes in form may be effected by bringing petals together or
turning them back, or by treating them to produce an artificial zygomorphy,
while the internal arrangement of the flower may be modified by changing
the position of stamens, staminode, style, scales, etc. It is obvious that
the nectar may be completely removed and the odor also modified in various
ways. Two or more mutilations may be combined in the same flower or
progressive mutilation may be carried out in a series, ranging from normal
flowers through those with more and more parts removed until the pedicel
alone is left. Finally, mutilation may be applied to the guide lines, stripes,
grooves, etc., but these are usually best modified by masking them with
water-colors.
Artificial and painted flowers. — Between the purely artificial flower
at one end of the series and the painted natural flower at the other lie many
forms, which differ chiefly in the degree to which artificial or foreign
materials are used. Artificial flowers proper may be made of paper, cloth,
wax, or other materials, and may be either crude or accurate copies of
natural flowers, according to the purpose intended. Plateau has raised
many objections to those used by his critics (p. 163), but these seem to have
little weight (p. 239). Flowers with one or more artificial parts are termed
composites and usually consist of the natural center of a flower or head
supplied with artificial petals or rays. In some cases the entire flower
or head is used and accessory colored parts added. Artificial stamens,
staminodes, or pistils may be added in special cases to replace the natural
ones, but such uses are limited. Imitations may be made of green leaves,
with or without natural centers, and they are also fashioned by using the
centers or disks of one species with the petals or rays of another. One
modification of particular value consists in replacing the nectaries or anthers
of one species with those of another. The best results have been obtained
with natural flowers painted with water-colors, since these are artificial
only in color. Such paints may also be employed to mask stripes and spots
or to supply new markings to test the directive value of the guide lines.
In certain cases natural flowers may be killed by the vapors of osmic acid
or otherwise, or they may be used in the dried form when the petals or rays
are papery in texture. Bits of colored paper or cloth, or detached petals,
have something of the value of artificial flowers, but belong properly in
the category of colored objects that can be employed to test color vision.
Addition of parts or substances. — Additional parts, such as petals,
rays, stamens, etc., may be supplied from flowers of the same species or
from those of different species. Perhaps the most interesting change of
this kind is where the number of nectaries is doubled, and especially when
those of another species are alternated. In flowers where the nectar
accumulates in considerable amounts in tube or spur, it may be withdrawn
and exchanged with that of a different species. Pollen may similarly be
10 EXPERIMENTAL POLLINATION.
transposed or the same result obtained by the exchange of stamens. In
the great majority of cases, however, addition deals with honey or sugar
solutions on the one hand or odorous substances on the other in order to
determine the role in attraction. The results with odors depend largely
upon whether these are natural ones to which the insects are accustomed
to respond and the best method is to employ fragrant flowers or parts
regularly visited.
Competition. — Competition is regarded as natural when plants of two
or more species grow so close or intermingled that their flowers compete for
the same group of visitors. It is brought about artificially when plants,
clusters, or flowers are transferred in such manner as to result in com-
petition. The distinction practically disappears when individuals are
transplanted or seeds sown in such a way as to form a competition group.
Natural competition groups are also constituted when the flowering period
of one species is retarded by pruning or cutting back, or accelerated in
various ways to cause it to overlap in some degree the period of an associated
species. However, when one or more species are transplanted to a different
climax or region, the resulting group is more or less artificial in its relations.
As a rule, the simplest method is by the transfer of inflorescences or single
flowers, which are kept fresh in bottles of water or by means of wet cotton.
Clusters have the advantage in saving time and effort and in exerting a
stronger attraction for visitors. The best results are obtained when two
species are employed reciprocally as bouquet and plant at the same time,
but this demands two observers. Mixed bouquets of two or more species
or separate bouquets of the same often give good results with a single
observer. When visitors are not too abundant, as many as a half-dozen
species may be followed at one time if the flowers are close together and not
too numerous. Most mutilation experiments are essentially studies of
competition between normal and mutilated flowers and it is often profitable
to combine these with competition tests between normal flowers of several
species. It is especially desirable to have the number of flowers or heads
the same for each competitor, and this is secured by basing the number
in bouquet or cluster upon that in the group to be used, or by removing
flowers to the number desired. Since the standard or species in the natural
position is regularly favored in consequence of the habit of the visitors, it
is desirable to scatter the competitors through the group, as they may other-
wise remain unnoticed.
Manipulation of insects. — As has been indicated, it is felt that the
greatest advance in the study of insect behavior can now be made by
dealing with individuals. This not only permits greater accuracy in
organizing the results for orders, genera, and species, but it also opens up
a new and fertile field scarcely touched as yet. A prerequisite for such work
is a simple and rapid method of catching and marking individuals, such
as the one devised by Giltay (1906:468). While this will demand still
more time and patience, the gain in detail and accuracy over present
methods will be as great as that secured by replacing lists of species by a
record of visitors and visits. In fact, the actual number of visitors, espe-
cially in terms of flight from the nest or hive, can be determined in no other
INTRODUCTION AND METHODS. 11
way. Many new facts are revealed as to flight, speed of working, constancy,
seasonal adjustment in relation to changing maxima of flowering, and so
forth.
The analysis of behavior rests upon three factors — instinct, habit, and
individual adjustment. Instinct is here regarded as fixed habit, and can
be largely evaluated by investigating the comparative behavior of related
species and genera. It is probable that habit is constantly passing over
into instinct, as seems well illustrated by the perennial adjustment made
by groups of species and individuals in the particular floral environment
to which their round of activities is restricted. As both observation
and experiment have shown, visits to flowers are largely determined by
habit, and it is impossible to secure conclusive evidence as to the senses
and mental powers of insects without eliminating this actor. The best,
though hardly the simplest, way of doing this is to base all studies of
attraction, for example, upon the use of individuals that have just hatched
and hence have had no opportunity to form habits. This demands the
location and control of nests and the marking of individuals as they emerge.
It can be done in a less exact manner by transferring nests or hives to a
different climax, as from the plains at the foot of Pike's Peak to the montane
or alpine zone, but even here marking or cages must be employed for
accurate results, except where a species peculiar to the plains is used.
Pollination cages afford the best means of complete control, but those so
far employed have separated nest and flower group, with the result that
the caged bees finally became panic-stricken. Cages several meters long
and high enough to accommodate an observer when seated, into which nests
are introduced before the young emerge, furnish an almost ideal installation
for the study of initial responses to color, form, and odor and the gradual
fixation of habits. These can then be removed with their occupants to a
totally different group of species, or the flowers to which they are accus-
tomed can be mutilated to call forth new responses and the consequent
adjustment of habits to new conditions. Here, as in all experimental
ecology, the basic problem is to secure laboratory control under field
conditions, and the pollination cage appears much the best solution.
However, there will always remain certain experiments that can be carried
on best or solely in the laboratory, where maximum control, uniformity,
and accuracy can be secured. The requisite technique has been so
carefully developed by Frisch (1914, 1919) and Knoll (1921, 1922) that
their methods will serve as the point of departure for all such work in
this field (cf. also Porsch, 1922:485).
The most conclusive evidence as to the role of color in attraction has
been furnished by insects with the antennae coated or amputated, even
Plateau admitting its cogency. The relatively small number of experi-
ments made with anthophilous insects indicate the desirability of extending
such work, and the questions raised by Mclndoo's researches render this
imperative. Owing to the injury usually caused by the amputation or
excision of the antennae or other organs, the chief task is to discover a
substance that will coat them with litt'.e or no injury and that can not be
readily removed. All substances that contain alcohol, turpentine, essential
oils, etc., must be avoided and the preference given to mixtures of paraffin
12 EXPERIMENTAL POLLINATION.
and vaselin with the lowest possible melting-point and corresponding
penetration. The individuals must be marked and observed from day to
day, and only those utilized which are essentially normal. The tests
should be made under natural conditions with materials to which the insect
has been accustomed, and should meet the requirement laid down by
Forel, namely, that the insect recognize a certain substance and dis-
tinguish it from others in a constant and indubitable manner when normal
and not when mutilated. The application of such tests to normal insects,
those with the antennae coated and those with the olfactory pores cov-
ered, should be decisive. The results can be rendered even more decisive
by covering the insects' eyes and contrasting the response of insects with
either the antennae or the olfactory pores coated to fragrant flowers that
are habitually visited. Many other modifications of insects are possible
and can be developed as need arises, such as removing the scopa, attach-
ing artificial ones, filling the corbiculse with wax, etc. In connection with
determinations of efficiency, constancy, etc., it is helpful to stain the
pollen of various species with particular dyes and thus simplify reading
the pollen record of its behavior. One of the most interesting series of
experiments contemplated deals with the reversal of the characteristic
habits of diurnal and nocturnal pollinators.
Life-history methods and records. — In the endeavor to determine the
exact relation of the flower and its behavior to the habitat, simple methods
have been devised for following and recording all changes in minute detail.
Quite apart from yielding a complete account of the development of the
flower, such records have proved indispensable in correlating floral changes
with physical factors and insect behavior, as well as in connection with
competition and autogamy. The methods are essentially observational,
though the subject affords an increasing opportunity for the use of experi-
ments in the correlation of flowers or parts. The essential features are:
(1) labeling flowers in the order of development; (2) visiting the plants
sufficiently often to obtain a detailed record; (3) recording changes on a
tabular form that permits ready checking against the preceding observation.
The usual plan has been to mark two or three adjacent plants and to follow
the development of 10 flowers on each simultaneously. This furnishes an
adequate check on individual behavior, and it is practically impossible to
follow a larger group when a number of species is concerned. When the
buds are sufficiently large, a label is attached to each and the flowers
are numbered in the order of their appearance. Ordinary price-tags are
employed and the size determined with respect to the flower. In the case
of minute flowers, especially those of umbellifers and grasses, the smallest
tags are too large for individual flowers, and other devices must be employed.
Tags may be placed at every third or fifth flower in large umbels or at
corresponding spikelets in panicled grasses, but in the smaller inflorescences
this often produces great distortion. Diagrams with the flowers numbered
sometimes afford the best solution, while with the smaller radiate heads
of composites the rays may be numbered in ink and thus furnish divisions
that enable one to follow the disk-flowers accurately. In large heads and
umbels and such spikes as those of Phleum, the inflorescence is labeled and
INTRODUCTION AND METHODS. 13
threads are used to mark divisions sufficiently small to permit following
the florets with accuracy.
Visits are regularly made once each day, except during the rapid develop-
ment of the warmest days, when morning and afternoon visits are often
necessary. Once or twice during each series, records are taken in the early
morning, at noon, and in the evening in order to obtain the finest details
in the changes. Similarly, one or two visits at sunrise and sunset are
necessary to determine the times of opening and closing of many species.
The regular visit is made in the morning, preferably at the same hour,
though this must often be modified as a result of weather or by other duties.
The use of two persons, one to observe and the other to record, effects a
great saving of time, but when this is impossible, the entire record should
be made by the same individual. The record sheet for each species is
ruled to hold the entries for 20 flowers, extra sheets being employed when
all the flowers of a head or umbel are to be taken into account. The same
form is used for both the field and the final typewritten record and an
endeavor is made to enter the observations so that the field sheet can be
copied directly. This necessitates a fixed set of abbreviations in order to
save both time and space. The entries for each visit are made beneath
the preceding one, the space being left blank when no change has occurred,
as this permits ready comparison with the last condition. The date and
the hour are entered in the first column for each species, the round of visits
always being made in the same order to allow the same interval, especially
when two or three visits are made in one day. A record is kept of periods
of cloudiness and rain, in addition to the usual records of temperature and
humidity. The striking differences in the rate of floral development in
sun and shade ecads of the same species have been the subject of a special
study, in which temperature and humidity were also determined under
the forest canopy.
Life-history record of a representative species. — The detailed life-
histories have been recorded for about 100 species of the Pike's Peak region.
For the majority of these this was first done in the summer of 1912 and has
been repeated in 1921 and 1922, two simultaneous sets of readings being
taken in 1921 by different observers. Because of the limitations of space,
the detailed table (table 1) is given for a single species only, and this is
restricted to 10 flowers on two different plants, taken from the 1921 observa-
tions. The main features of the life-history of 26 species are illustrated
in plates 2 to 14, and the stages described in the corresponding legends.
14
EXPERIMENTAL POLLINATION.
Table 1. — Aconitum columbianum.
Plant I.
Plant II.
Date.
1
2
3
4
1
5 6
7
1
2
3
July 23, 3 p.m. 02
24, 10 a.m. 0 4
4 p.m. 0 6
25, 10 a.m. op
4 p.m. 1
26,10 a.m. 1
1
4 p.m. . . .
27, 11 a.m. 1
6
5 p.m. . . .
28, 5 p.m. . . .
29, 11 a.m. . . .
30, 11 a.m. . . .
4 p.m. 6
18
31, 11 a.m. 18
4
4 p.m. 4
8t
mm 0 2 mm
mm 0 4 mm
mm 0 6 mm
en open
as 2 a s
ad 2 a d
as 3 a s
... 3ad
... 2 as
ad 2 a d
as las
... lad
4 a s
... 4ad
... 10 a s
... 10 ad
... 8 as
ad 8 a d
as st rec
ad
0 2 mm
0 2 mm
0 2 mm
0 2 mm
0 2 mm
open
open
open
open
4 a s
0 4 mm
open
0 4 mm
0 6 mm
0 4 mm
0 6 mm
0 4 mm
0 6 mm
2 as
2 ad
10 as
10 ad
8 as
Sad
4 a 8
4ad
12 a a
12 ad
st rec
p falls
las
lad
9 a s
9ad
2 a s
2 ad
8 as
Sad
8 a s
10 a d
st rec
p falls
8 a s
8 a d
4 a s
4 ad
4 a s
4 ad
4 a s
4ad
8 as
Sad
st rec
p falls
2 a s
open
4ad
4 a s
4ad
12 a s
12 a d
10 a s
10 ad
st rec
2 ad
2 a s
2 ad
4 a s
4 a d
19 a s
19 a d
6 a s
6 ad
las
1 ad
2 a s
2ad
2 a s
c enl
open
open
4 a s
4 a d
4 a s
2 a s
4ad
10 as
10 a d
4 a s
4 ad
3 a s
3 ad
las
1 a d
4 a s
4 a d
st rec
2 ad
2 a s
2 ad
2 a s
2 ad
10 a s
10 a d
6 a s
ad c enl
c enl
2, 10 a.m. c <
;nl c brwn
... p falls
c brwn
p falls
3, 6 a.m. c b
c brwn
11 a.m. p f
alls
p falls
Gad
8 a s
st rec
4 a s
4 a d
26 a s
aborts
c brwn
p falls
pfllg
o open,
a anther.
st stigma.
c carpels.
Contractions.
shedding. rec receptive. brwn turning brownish.
d shed.
enl enlarging.
fllg falling.
2. NORMAL AND EXPERIMENTAL POLLINATION.
Treatment. — In the following treatment the species have been arranged
in general accordance with their phylogenetic sequence, beginning with
the buttercups and terminating with the mints. The discussion of each is
divided into two sections, the first dealing with normal pollination, the
second with experimental pollination. The experiments are considered
under four headings: (1) change of position; (2) mutilation; (3) artificial
and painted flowers ; (4) addition of honey and odor. Those that deal with
competition and constancy are reserved for the following chapter. Refer-
ences are given to the European and American observations on the pol-
lination of the same or related species, accompanied by a brief abstract
where it seems warranted. Each table or group of tables is summarized
in detail and a rSsume' of the general results is given at the end of the chapter.
These are further discussed in connection with the conclusions of other
investigators in the final resume1 at the end of the fourth chapter.
ACONITUM COLUMBIANUM.
NORMAL POLLINATION.
Structure. — The hood in Aconitum is formed of two colored sepals
united, the other two sepals making a landing-platform for insect visitors.
Two petals are modified into nectaries, while two form the sides of the hood.
The sepals and petals are colored alike, increasing the amount of color in
the flowers and making them more easily seen and attractive. The sepals
that constitute the landing-platform are smaller than the other sepals
and petals, but large enough to support the weight of the visitors. The
side petals arch above the stamens and protect them to some extent from
the rain, but do not interfere with the access of pollinators. However,
they hide the stamens from view when the flowers are seen from certain
positions. The nectaries are long and stalked, with a crested hood at
the top. To secure nectar, the visitors must have a proboscis 10 mm.
long in order to reach through the stalk to the hooded portion containing
the nectar (plate 2).
Behavior. — The most frequent visitors to Aconitum are Bombus juxtus
and bifarius, of which the former is far more frequent, evidently because
this species is more numerous in the region. It is larger than bifarius
and covers more of the flower. It lands on the two lower sepals, with its
head toward the base of the nectaries, and the hind legs curve around the
small sepals, while the front pair grasp the side ones. The under part of
the thorax rubs back and forth against the anthers and stigmas as the bee
sucks nectar. It pushes the proboscis into both nectaries and often stops
to brush the pollen from its sides on to its legs, as it leaves the flower.
B. juxtus visits the flower for nectar, but in getting this, pollen is brushed from
its hairy thorax on the stigmas, and at the same time pollen is dusted on the
bee. When sucking nectar, the tip of the abdomen reaches to the three
styles. The bee scrapes pollen from its head parts as it leaves the flower.
It usually goes from the lower flowers on the raceme to the upper ones
and then down again.
15
16 NORMAL AND EXPERIMENTAL POLLINATION.
Bombus bifarius lands on the sepal platform with its head above the group
of stamens and pointing toward the base of the nectaries. It then moves
up to such a position that its thorax is above the stamens and its head is
at the base of the nectaries, the hind legs resting upon the two front sepals.
As it sucks nectar, its body moves back and forth, thus rubbing the lower
side of the thorax and abdomen against the anthers and stigmatic surfaces.
None of the North American species of Aconitum has previously been
studied with respect to its pollination. In Europe, A. napellus and
lycoctonum have received the most attention, and Kronfeld has pointed out
that the species of this genus are almost exclusively bumble-bee flowers,
the areal limits of Aconitum and Bombus coinciding in a remarkable way.
In addition to Bombus, Knuth cites only visits by Macroglossa and Lycaena
(1908:50); in the Pike's Peak region the sole visitors are bumble-bees.
EXPERIMENTS.
CHANGE OF POSITION.
Horizontal racemes. — Racemes were placed in a horizontal position
and attached to the normal ones by thread. Since the flowers of Aconitum
are fastened at various points around the stem, the tip of the hood on
some pointed sidewise and in others it pointed up or down. Both Bombus
juxtus and bifarius easily went into flowers with the hood pointing down-
ward, using the side petals instead of the lower sepals as a landing plat-
form. They then secured nectar without taking an uncomfortable position.
B. juxtus hovered over the hood in flowers where it pointed sidewise.
Finally, it went to the open end where the stamens were exposed, pushed
its proboscis about as if exploring, and then found the nectary. The next
flower had the tip of the hood pointing up, and B. juxtus landed at once
on the side petals and took nectar without any inconvenience. In another
case where the hood pointed sidewise, the bee hovered over the spur first,
apparently trying to find a place to land. It then went to the side of the
flower and attempted to land, but slipped off the edge of the side petal,
succeeding only on the second attempt. The next flower was horizontal
with the hood directed upward. The bee hovered at the spur, went to
the other end, and landed easily. It did not learn by one experience that
it could find the nectar at this end when the flower was in the horizontal
position. In each case it hovered where it would normally expect to alight,
before going to the place where landing was possible.
Racemes inverted. — Racemes were cut off and tied to the plant in
an inverted position and a piece of moist absorbent cotton was placed
around the cut end to prevent wilting. Some individuals of both Bombus
juxtus and bifarius found the nectar readily, while in other cases they were
frightened away or gave up too soon. The former passed over some flowers
without attempting to land, and merely hovered near others. A few
individuals started to alight and then flew away as if bothered by the
change. Some bees landed at the lower sepals, which now pointed up and
occupied the position usually taken by the hood, turned around, and
quickly walked into the flower upside down. The next flower was normal
and B. juxtus went to this as usual. The third was inverted and the bee
^^
;. ~
ACONITUM COLUMBIANUM. 17
proceeded exactly as in the first inverted flower, apparently noticing the
change of position before landing. One B. bifarius mastered the situation
readily and went to five inverted flowers in succession, turning upside
down just after alighting at each one. Another B. juxtus landed three
times at a group of inverted flowers, tried to push its proboscis into the
hood without turning upside down, and in each case failed to find the
nectary.
MUTILATION.
Cotton plugs. — When absorbent cotton was placed in the nectary,
Bombus juxtus landed, pushed out its proboscis to find the opening, and tried
repeatedly to make a way through the cotton into the nectary. At the
next flower it hovered but did not land. When the styles and stamens were
hidden by a cotton wad, B. bifarius made the same unsuccessful effort to
find the nectary opening. Another individual jerked back as it was about
to land, and then quickly flew away to the next flower. A third hovered
above the flower and departed without landing, as did several others of
both species.
Stamens removed. — Bombus juxtus noticed the change as readily as
when the flowers were covered with cotton wads, while B. bifarius either
hovered above the flower before alighting, or landed directly and flew away
at once without projecting the ligule or trying to find the nectar.
Hood split. — The hood was split longitudinally in some flowers, thus
making them more conspicuous, as it then exhibited a pair of wings ascending
behind the nectaries. In some cases this change had no effect upon landing,
as it appeared neither to frighten the bees nor to attract them in increased
numbers, but in others it greatly increased the attraction. They landed
in tHe usual manner, but had a very hard time hanging on to the stamens.
Because they were unable to find a suitable position, they often went away
without getting nectar.
Hood removed. — The hood was removed, leaving the two nectaries to
project above the remaining flower-parts. This made the nectaries con-
spicuous and changed the general aspect of the flower very much. The
effect on the visiting bees was not uniform. Bombus juxtus sometimes
hovered above the flowers, but did not land, or stopped without pushing
out its ligule. Some exposed the ligule, then noticed the change, and flew
away. Others were more persistent, for they landed, at once found the
slit down which the nectar runs, and emptied each of the nectaries, repeating
this performance at the next flower.
Hood and nectaries removed. — An individual of Bombus juxtus
alighted as usual, and explored in all directions with its tongue, in the
unsuccessful endeavor to find the opening. One adventurous individual
crawled between the side petals as if expecting to find the nectary. When
it got through, it turned around, crawled over the stamens, and flew away.
Lower sepals removed. — Since this is the part of the flower on which
Bombus usually rests its hind legs, it found difficulty in balancing properly
while seeking the nectary, but finally succeeded in reaching the nectar.
18
NORMAL AND EXPERIMENTAL POLLINATION.
Side petals removed. — Some bees evidently noticed the changed appear-
ance brought about when these were removed, and hovered above the flowers
without landing. However, most of them seemed to observe no change, for
they landed and sucked nectar as if the flowers were normal, and even came
back a second time. The second pair of legs in these cases was crowded
closer to the base of the stamens and rested there. Flowers with side
petals removed were also placed in the horizontal position with the hood
pointing upward. One bifarius treated these flowers as it did Rosa and
tumbled about on the stamens, collecting pollen and making no effort to
get nectar. Another followed and did the same thing. This was in marked
contrast to all other observations on normal Aconitum, in which Bombus
had never made any effort to collect pollen. Ordinarily, the pollen was
collected accidentally as the body moved back and forth across the stamens
in the act of gathering nectar.
Competitive relations. — The five types of mutilation were represented
by 5 flowers each, and these were arranged with 25 normal ones (plates
15 and 16). Table 2 gives the results; mere inspections are indicated
by an i.
Table 2. — Visits to normal and mutilated flowers.
Date.
Time.
Species.
Normal .
Side
petals
off.
Nectary
and hood
off.
Hood
off.
Hood
split.
Cotton
over
stamens.
July 27
July 28
3 to 5
9 to 11
Bombus juxtus. . . .
Bombus bifarius. . .
Bombus juxtus. . . .
5
35
o
0
2: 16 i
2:3i
a: Hi
3
6
14
14
8
32
0
1 i
li
Total
67 9 9:30i 23 54 2i :95
The number of visits to the mutilated flowers was nearly a half greater
than those to the normal, due chiefly to the response to the flowers with
the hood split. This greatly increased the extent of the color surface and
the attraction even to a greater degree, as each flower received 4 times as
many visits as a normal one. Since those with the hood off averaged
nearly twice as many visits as the latter, the exposure of the nectaries
evidently played a part in the attraction. The other mutilations were
visited about the same as the normal flowers, except where cotton was
present, this change being noted even in rapid flight. Individual differences
in behavior were especially noted in the case of the flowers with the hood and
nectaries removed. Three bees inspected these flowers to one that landed,
and of the latter some flew away at once, while others extended the ligule
several times in the endeavor to find the opening to the nectary.
ARTIFICIAL AND PAINTED FLOWERS.
Normal colors. — The flowers of Aconitum columbianum are either
blue-purple, or white. The plants studied grew along brook-banks and
were lighted by sunflecks, which made the purple flowers more conspicuous
than the white ones, though the two were equally numerous. The response
ACONITUM COLUMBIANUM.
19
of Bombus to the two colors is shown by table 3, which records the number
and order of visits, each time given representing a different bee.
Table 3. — Visits to white and purple flowers.
Time.
Speoies.
Visits.
llh00m a.m
3 W, G P.
3 W.
G W.
4 P.
2 W, 1 P, 3 W, 14 P,
3 W, 3 P.
2 P, 2 P, 2 P.
2 W, 9 P, 2 W.
4 W.
11 10 <i. m. . .
11 12 a.m. . ,
11 27 a.m. .
11 30 a.m
11 40 a.m
4 P.
During the 40 minutes, 9 bees visited 75 flowers, of which 26 were white
and 49 purple. On another day, 63 flowers each of purple and white were
observed for half an hour. During this period Bombus juxtus visited 64
purple and 68 white flowers, and B. edwardsi 1 purple and 3 white ones. The
total number of visits was 65 to the purple and 71 to the white.
Artificial flowers. — To obtain further evidence as to color preference,
other colors were tried. This was done in two ways: (1) by replacing
the corollas and calyxes with crepe-paper floral envelopes, leaving stamens,
pistils, and nectaries intact, or surrounding the natural corollas by crepe-
paper disks, and (2) by painting the perianth with water-colors. Artificial
corollas and calyxes of crepe-paper were made to resemble those of the
natural flowers as nearly as possible, the effect being essentially lifelike.
Yellow, green, white, red, pale blue, and purple were the colors used. The
artificial corollas were not attached until after the bees had visited all
the flowers under observation, in order to make sure that nectar was pres-
ent and that nothing about the flowers was objectionable. In placing the
artificial flowers the following combinations were used:
(1) A colored crepe flower was paired with a normal one at various points on the stem.
(2) A raceme was left with as many normal as crepe flowers of the various colors, and
these were scattered in no definite order.
(3) Flowers of a single color of crepe-paper, but as numerous as the normal flowers,
were scattered at various points on the stem.
(4) One half the raceme was left normal and artificial corollas of one color of crepe-
paper were used on the other half.
These experiments were tried on several days during the season for four
different years, with essentially the same results. Bombus would fly
within 2 cm. of the crepe flowers, but would then pass without landing.
The only two exceptions to the above were the flowers with the pale-blue
and white perianths. Bombus stopped at the white ones and worked as
if noting no difference, while pale-blue flowers were visited at 7 different
times by as many individuals of juxtus. In two cases after visiting the
flower and taking nectar, this species returned for another visit.
20
NORMAL AND EXPERIMENTAL POLLINATION.
To render the natural flowers more conspicuous, strips of crepe-paper
were cut a half-inch wide lengthwise of the roll. Fine wire was run through
this strip along one edge, making a ruffled disk which was placed around
the stamens and nectaries. An equal number of normal flowers and of
those with red, green, white, yellow, or blue crepe ruffles were used. The
flowers appeared very showy and the nectaries and stamens were con-
spicuous. Bombus juxtus visited only normal flowers to a total of 29,
while bifarius stopped at but 5 normal ones. It hovered low over green,
white, and blue modifications, but did not land on them.
Painted flowers. — In further experiments, flowers were treated with
water-colors. The white flowers were usually painted, as they took the
colors better than the purple. The perianths were washed on the outside
alone. Ten natural flowers and 5 of each color were used, making a total
of 30 colored ones, or 3 times as many painted as normal (plate 1).
Table 4.-
-Visits of Bombus juxtus to painted fl
Date.
Time.
Normal.
Red.
Vermilion.
Green.
Yellow.
Blue.
Indigo.
July 27
10h50m to llh45m
29
4
1 11
6
4
8
10
July 28
10 50 11 15
11
0
4
2
3
7
2
Do.
1 00 2 55
4
0
4
3
2
3
3
Do.
2 55 3 55
13
2
7
9
6
4
8
July 30
10 00 11 30
Total
9
0
0
0
0
5
0
66
6
26
20
15
27
23:117
While this species visited nearly twice as many painted as normal
corollas, the actual ratio was 39 : 66, indicating a distinct preference for the
natural flowers. Among the painted ones, blue, vermilion, and indigo were
sought most, green, and yellow less, and red by far the least.
The response to the colored flowers varied at different times, but the
general behavior of visitors is shown by the following field calendar, derived
from another experiment:
9h22m Bombus juxtus at a blue flower as if
noting no difference, but passed
by flowers painted yellow, red,
and green; bifarius passed by all
the painted flowers, but hovered
as if inspecting them.
9 35 Bifarius passed over the painted
flowers, but flew slowly as it
looked them over.
9 45 Juxtus, purple, orange-red.
9 50 Juxtus took nectar, then hovered above
red and then purple flowers.
9 55 Juxtus, green, and then flew past a
brown and a green one, after
hovering above each for a short
time.
llh15n
11 17
11 20
11 21
11 23
11 24
11 26
11 27
11 35
11 37
11 39
Juxtus, green.
Juxtus, orange-red for 45 seconds.
Bifarius, red, red.
Juxtus, blue, purple.
Juxtus, yellow.
Juxtus, blue.
Juxtus, blue.
Juxtus, blue, purple.
Bifarius, purple, orange, red, purple,
blue, purple; passed over brown
and yellow.
Juxtus, yellow.
Juxtus, purple, blue; passed by yellow,
red, and green.
Bifarius, purple, blue, green, purple,
red, white.
During the time of the above observations, Bombus visited normal
flowers as well as the colored ones listed. A summary shows that the bees
visited flowers of all colors used except brown. Of the 32 visits recorded,
ACONITUM COLUMBIANUM. 21
10 each were made to blue and purple, 4 to red, 3 each to green and orange-
red, and 2 to yellow.
Both the inside and outside of 10 perianths were painted with each of
the following colors: red, blue, yellow, green, purple, and 10 normal flowers
were used for comparison. The following short record shows the resulting
behavior, each line indicating a different visitor:
Bombus juxtus, 6 normal, low over blue, and then flew away,
normal, low over blue, and then flew away.
2 normal, blue, 2 normal, blue, normal,
normal, blue, normal, blue, normal,
normal, normal,
blue, normal.
ADDITION OF HONEY AND ODOR.
Honey. — In order to throw light on the role of nectar in attraction,
four kinds of sweets were used, viz., honey, diluted honey, diluted white
Karo sirup, and beet-sugar solution. These were put on the side petals of
some flowers, on the stamens and styles of others, and in the nectary opening
of still others. In some cases, Bombus juxtus went directly to the nectary
of flowers with honey at the sides of the petals, sipped as usual, and flew away
without discovering the honey. In other cases, it flew down to these flowers,
almost landed, and then flew away as if frightened, perhaps by the unusual
appearance. When the various sugar solutions were put into the nectary
openings, Bombus took nectar as usual, but stayed longer at each flower, owing
to the increased supply. When Karo sirup or sugar solution was put on the
stamens, B. juxtus and bifarius did not notice it in some cases, for they went
past to the nectary and then flew away. Other individuals of B. juxtus
landed in such a way that the mouth-parts accidentally touched the sirup.
After taking sirup from such a flower a bee flew to a normal one, pushed its
ligule around the stamens as if looking for more sirup, then advanced to the
nectary opening, and obtained nectar as usual. In the next flower, where
the stamens were covered with honey, it proceeded to take this supply and
fly away without trying for nectar.
The procedure of Bombus juxtus was various in the flowers where the honey
drop was placed on the stamen group. One bee landed without noticing
the honey on the anthers, but pushed its head into the hood and took nectar.
Another alighted in such a way that its head touched the honey. It
obtained honey in 3 flowers of this type, without paying any attention to the
nectary. A third did not notice the honey drop, but secured nectar in the
usual manner. As it started to fly away its thorax stuck to the anthers,
and it scraped the honey from its front legs, without even discovering that
it was sweet or edible. B. bifarius went in succession to 6 flowers with drops
of honey on the anthers; it did not notice the honey, but took nectar as usual.
B. juxtus landed on the lower sepal of a flower in such a way that its head
touched the honey on the anthers, and it sipped until the drop was all gone.
Instead of pushing its ligule into the nectary, it flew to the next flower,
where a drop of honey was in the same position, and proceeded to suck all
of it. When it started to fly away, its tongue stuck in the honey and it had
a difficult time to free itself.
22 NORMAL AND EXPERIMENTAL POLLINATION.
Perfumes. — Sachet powders and perfumes of various sorts were also
tried, but without positive results. Bombus juxtus and B. bifarius hovered
above the flowers without landing in many cases, and in others flew about
as if not noticing them at all. In one case juxtus alighted at a flower with
arbutus sachet and took nectar as if noting no change. In general, if
Bombus noticed the odor at all, it seemed repelled rather than attracted by it.
SUMMARY.
In general, the bumble-bees had less trouble with horizontal than with
inverted racemes, though there were marked individual differences. Some
bees passed readily from normal to inverted flowers, adjusting their behavior
to each without apparent difficulty. The use of cotton usually prevented
landing, and this was frequently the case also when the stamens were
removed. In spite of individual departures the other mutilated flowers
were usually visited about as much as normal ones. In the competition
study, however, those with the hood split or removed received many more
visits, while those with the hood and nectaries gone received 3 inspections to
one visit, and those with cotton over the stamens obtained but rare inspec-
tions.
No distinction was made between white and purple in the normal flowers,
but blue and purple were given a decided preference over the other colors in
the case of artificial and painted ones. Since white-crepe corollas with
natural centers were visited normally, the choice appears to have been
determined largely by the colors regularly present in the species. With
the exception of white and blue, none of the artificial flowers yielded visits,
though some of these were inspected. Painted flowers, on the other hand,
received a third to a half as many visits as normal ones. The addition of
honey did not render the flowers more attractive, and no positive results
were obtained with perfumes.
DELPHINIUM SCOPULORUM.
NORMAL POLLINATION.
Habit and structure. — The anthers are very conspicuous in young
Delphinium flowers. They become erect when mature, taking a position
very near the opening into the nectary and after dehiscence they bend down
again. The two petals, which have the tips deflexed, then close together
over the shrunken anthers. As the stigmatic surfaces mature, the styles
bend up, bringing the stigmas near the opening of the nectary (plate 2).
Behavior. — Bombus edwardsi and juxtus are the most frequent visitors
to Delphinium. When both species are present, edwardsi visits many more
flowers than juxtus. The latter uses the two lower sepals for a landing-
platform, the forelegs resting on the front spur of the petals or on the sides
of the sepals. After landing, it moves the head forward above the stamens,
pushes the ligule down the spur, and takes nectar. While it comes for
nectar alone, at the same time pollen collects on the legs and thorax. The
flow of nectar in these flowers must be rapid, as one individual went twice
to 15 flowers on the same plant and to 9 flowers three times in succession
while on one trip, and another individual visited 22 flowers twice on the
DELPHINIUM SCOPULORUM. 23
same trip. B. juxtus sometimes visits withered flowers, stopping to seek
nectar at those in which the lower side petals have dropped off. B. edwardsi
and morrisoni land and take nectar in the same manner as juxtus. As
Thanaos martialis lands on the lower sepals, the delicate ligule is pushed
into the nectary and the hairs on the under side of the head come in contact
with the anthers.
Robertson (1889:120) states that the white upper petals are a sure guide
to the nectar in Delphinium tricorne, in which the lateral petals serve to
protect the pollen. It agrees with D. datum and D. consolida in being
protogynous and especially adapted to bumble-bees. In Europe these
species are exclusive bumble-bee flowers (Knuth, 1908:44), but Robertson
notes several other genera of bees and a number of butterflies and moths.
EXPERIMENTS.
CHANGE OF POSITION.
Inverted racemes. — Bombus juxtus hovered above 6 flowers which
were inverted, but apparently noticed that something was wrong and
did not land. At the seventh flower it made an attempt at landing, but
found the pointed front part of the spur too narrow. After slipping off
twice when it tried to put its hindlegs in this spur, it flew away. Other
individuals flew above these flowers, but did not alight.
Horizontal racemes. — In these flowers the hood pointed down and
Bo?nbus juxtus was not bothered by the change. It landed and found the
nectar easily, using a side sepal and one of the lower ones for a landing
platform.
MUTILATION.
Cotton plugs. — Absorbent cotton was placed in the opening to the spur,
which serves for the nectary. Bombus juxtus stopped, but when it found
no opening did not attempt to probe around the cotton, but went to the
next flower. A slender cotton roll was placed in the nectary in such a way
that it projected 1 cm. in front of the flower and changed the whole aspect
of the latter. This bee landed on the cotton projection and tried to find
the opening to the nectary, but failed. It repeated the performance on
the next flower with the same results.
Petals removed. — The petals, which recurve and protect the stamens,
were removed, thus making the black group of anthers very conspicuous.
The curved white filaments showed above the anthers, and the nectary
openings were visible above the filaments, thus changing the aspect of the
flower materially. On the first day of this experiment, Bombus juxtus
took no notice of the change and found the nectary without difficulty.
On another day the results were quite the reverse and 5 individuals passed
by these flowers during a period of 15 minutes. B. edwardsi went to 7 of
the mutilated flowers, apparently without noticing the difference (plate 16).
Spur removed. — Bombus juxtus pushed its tongue back and forth 9
times in one of these flowers, the tongue projecting 6 to 7 mm. beyond the
cut end. In another instance, the tongue was rapidly pushed back and
forth 4 times through the opening. A third individual noticed the change
in the flowers and did not land.
24
NORMAL AND EXPERIMENTAL POLLINATION.
Landing-platform removed. — The landing-platform in this flower
consists of the lower two sepals. When these were removed, juxtus hovered
above two flowers without landing. At the third flower it landed success-
fully by placing the hind pair of legs on the sepals of an adjoining flower.
A comparison was made between 25 normal and 25 mutilated flowers,
consisting of 5 of each type. In the fifth type of mutilation, pieces of grass
culms 2 cm. long were used to close the nectary openings and to change the
appearance of the flowers (table 5).
Table 5. — Visitors to normal and mutilated flowers.
Species.
Normal.
Lower
sepals
off.
Side
sepals
off.
Upper
petal and
spur off.
Spur
off.
Grass culm
in nectary
opening.
Total.
Bombus edwardsi
juxtus
Total
14
15
7
1
7
2
6
2
9
1
2
2
31
8
29
8
9
8
10
4
39
The mutilated flowers were visited somewhat more frequently than the
normal ones, the kind of mutilation making little difference, except when
the grass section was present. However, the two species exhibited a marked
difference in behavior, Bombus edwardsi visiting twice as many mutilated
flowers as normal ones and juxtus but half as many. In the case of the
grass section, two individuals of each species of Bombus tried hard to push
the ligule into the nectary, but did not succeed, their persistent efforts at
the proper spot indicating that they knew where the nectary was.
ARTIFICIAL AND PAINTED FLOWERS.
Crepe-paper corollas. — In order to give Delphinium the same general
form as Rubus deliciosus, disk-like corollas of red, white, green, yellow,
or blue paper were placed around the pedicels after the floral envelopes
had been removed. This did not change the odor or the essential parts of
the flower, but increased the size in addition to changing the color. There
were 147 open flowers under observation, 10 of each of the 5 colors, and 97
normal ones, approximately twice as many normal as changed flowers.
During the hour and a half of observation, Bombus juxtus was the only
visitor, going to 93 normal flowers and to one with a green paper corolla.
During this time it visited 4 normal flowers on one branch where the majority
were blue, and 5 normal ones on a branch where most of them were white,
but in neither case did it venture to try the artificial flowers.
Crepe-paper corollas with spurs. — In order to study the response to
color without change of form, life-like crepe corollas with spurs were used
to replace the floral envelopes. In addition to 27 normal flowers, 4 of each
of the five colors, red, blue, green, yellow, and white, were used for com-
parison, with the following results. Three individuals of Bombus juxtus
visited 3, 2, and 3 normal flowers respectively, not even stopping to inves-
tigate those with crepe corollas. Two B. proximus visited 2 normal flowers
each and no crepe ones. This group of flowers was covered over night with
DELPHINIUM SCOPULORUM. 25
a paper sack to protect the crepe-paper from the rain, this also preventing
'bees from securing the nectar until the time of observation. B. juxtus was
the only visitor and the several individuals went to 9, 3, 2, 3, 5 normal
flowers respectively, some flying low over the colored ones as if inspecting
them, but not alighting.
Painted flowers. — A further study of the reaction of pollinators to
color was made by means of water-colors (plate 1). Three colors, green,
red, and yellow, were represented by 1 1 flowers each, and these were arranged
so that each one adjoined a normal flower. The first visitor was Bombus
juxtus, which went to all the green flowers once and to some twice, but
visited no others. B. proximus visited 3 normal flowers in one group, 4
flowers in a nearby cluster, and then 2 green flowers. The last visitor
was a very persistent individual of juxtus, which came to the flowers in
the following succession: 10 normal, 3 yellow, 2 green, 1 green, 3 green,
25 normal, 21 normal, 3 normal, 3 normal, 2 green, 4 normal, 4 green, 4
yellow. In the next experiment, 12 normal flowers and 6 each of red,
yellow, green, and brown, were used, but without being arranged in any
definite order. Three visitors came during the hour of observation with
the following results: 2 individuals of juxtus visited 17 and 19 normal flowers
respectively and edwardsi 3 normal ones, none paying attention to the colored
flowers. Five days later, when the same number of colored and normal
flowers were used in the same type of arrangement, the results were quite
different. The first visitor stopped at a normal flower only, but the next
one visited the flowers as follows: normal, green, blue, and normal, while
edwardsi visited 2 normal flowers alone. The last juxtus went to normal,
blue, yellow, normal, normal, red, blue, red, and blue flowers in order.
In the next experiment 5 flowers each were painted red, green, blue, yellow,
or purple, on both sides of the corolla, and 25 normal flowers were left on
the same stalk for comparison. B. edwardsi visited 127 normal and 3 blue
flowers, but no red, yellow, purple, or green ones, flying low enough over all
those painted to distinguish the colors. B. juxtus visited 116 normal, 4
blue, 2 green, and 1 yellow, but no red flowers.
The total number of visits to painted flowers was 51, in contrast to 323
to normal ones, the ratio being 1 : 7. The individual range in behavior was
of the greatest, one juxtus visiting green flowers alone and another none but
normal ones, while a third did not discriminate between them and a fourth
went to twice as many painted as natural flowers. When the colors em-
ployed were red, yellow, and green, the latter was given a marked preference,
but when blue was added, this was visited more than all others combined.
ADDITION OF ODOR.
Perfume. — Rose perfume on absorbent cotton was wrapped around the
pedicels under the flowers on one-half of the stalk. The flowers perfumed
were on the side away from the wind, in order to make the odor more notice-
able on the one half. Bombus juxtus visited 9 normal and 2 perfumed
flowers, these being the only visits during 2 hours of observation. On
another day, carnation perfume was placed on cotton wads wrapped around
the pedicels of one-half of the stalk. Nearby, powder made from camphor
balls was sprinkled at the center of the stamens on flowers in a similar
26 NORMAL AND EXPERIMENTAL POLLINATION.
arrangement. The two odors were on stalks near enough together for obser-
vation, but not so close that the odors were likely to mingle. B. juxtus
visited 30 normal flowers and 29 with the carnation odor on one plant and
15 normal and 20 with camphor odor on the other. B. proximus went to
27 normal and 14 with carnation odor, but none with camphor odor. Thanaos
martiales visited 1 normal on the carnation stalk, but none with the car-
nation odor, and 1 normal and 3 with the camphor odor on the other stalk.
B. juxtus and proximus both went from normal to flowers with carnation
odor and from those to normal flowers. All told, 83 visits were made to
normal and 68 to perfumed flowers, the number to carnation being twice
that to camphor.
SUMMARY.
The experiments with flowers in changed positions indicate that the
bumble-bee not only perceives such changes readily, but also distinguishes
between the two positions with respect to the ease of landing. In general,
mutilated flowers were visited as readily as normal ones, even the removal
of the landing-platform causing but temporary difficulty. Individuality of
behavior was more or less marked as usual, the removal of the petals having
no effect on one day and leading to such flowers being completely ignored on
another. As a rule, the bees were quick to learn the significance of the
different changes, solving the problem of landing after a few attempts.
The response to paper flowers with natural centers was in sharp contrast to
that to painted flowers; the former received but one visit to 125 for normal
flowers, while the latter yielded one to each 7 for the normal. This suggests
that the eyes of the bumble-bee are even more accurate than our own in
perceiving small differences of color and form. The figures in the case of
visits to perfumed flowers are not decisive, though they indicate that the
bees found the added odor somewhat disturbing.
The experimental results with Aconitum and Delphinium are essentially
in harmony, as might be expected from the ecological similarity of the
flowers. Changes in position and form produced much the same response,
as did paper flowers and added perfume. In the case of painted flowers of
Aconitum, however, there were more than half as many visits as to the normal
ones, the ratio being 1:1.7 in contrast to 1 :7 for Delphinium.
RUBUS DELICIOSUS.
NORMAL POLLINATION.
Habit and structure. — The bushes of this species are tall and spreading,
the branches profusely laden with flowers which are the showiest in bloom
during its period. With respect to attraction the flower consists essentially
of a mass of yellow stamens surrounded by very large white petals, and
possesses a pleasant odor. The corolla is widely expanded and the stamens
fully exposed. The nectar is formed at the base of the stamens, where it
appears as a circle of tiny drops.
Behavior. — Bombus juxtus collects pollen chiefly with the hind legs
as it tramples about, packing it in large masses on them, the hairs of the
body becoming well dusted in the process. As it moves about, pollen is
RUBUS DELICIOSUS.
27
transferred to the stigmas from the under parts, or autogamy results as
the stamens are spread and brought in contact with the stigmas. This
bee drives Halictus out of the flowers and occasionally enters a flower
with dried anthers. Apis mellifica walks around the margin of the flower,
apparently because the anthers mature there first, and then across the
center, ignoring those with brown stamens. While it is trampling about
and collecting pollen, the ligule is sipping the nectar found around the edge
of the petals at the base of the stamens. Monumetha albifrons works around
the margin in similar fashion, collecting pollen in smaller amounts on the
under side of the abdomen, legs, and head. Andrena crataegi pushes its
head under the anthers, bites them open, and shakes the pollen out in
order to pack it on the hind legs. Vespa germanica sucks ■ nectar in
various positions, often entering flowers in which the anthers are quite dry.
Variation in visits. — In order to determine the effect of time and place
on visits, detailed calendars were made on several different days and in
several places. Since these are too long to be given, the results are sum-
marized in tables 6 to 9. In the first series the time alone was varied
by making use of three different days close together, while in the second
the two days were taken at different parts of the flowering period.
An hour and a half of observation at the Alpine Laboratory on June 10,
11, and 13 yielded the list of visitors to 100 flowers (table 6), the second
figure, as usual, indicating the number of flowers visited.
Table 6. — Visitors on different days in early season.
Species.
Apis mellifica 22:127
Andrena crataegi 0:0
sp 0:0
Bombus morrisoni 1:1
juxtus 0:0
Bombyliad 0:0
Halictus pulzenus 0:0
Monumetha albifrons. ... 1:1
June
5:5
2:2
0:0
1:1
June
0:0
1:1
2:2
0:0
4:4
0:0
0:0 10:10
0:0 I 0:0
Musca sp
Osmia melanotricha.
densa
bruneri
Papilio turnus
Prosopis elliptica. . . .
Syrphus americanus.
Total 29:134
June
10
1:1
0:0
2:2
1:1
0:0
0:0
1:1
June
11
0:0
0:0
0:0
0:0
0:0
0:0
June
13
8:8
1:1
0:0
0:0
2:2
1:1
0:0
23:23.29:29
Table 7-
-Visitors in mid and late season.
Species.
June 23.
July 6.
Species.
June 23.
July 6.
62
10
7
4
7
0
6
3
2
0
1
0
0
0
8
5
0
0
29
7
Eristalis arbustorum . . .
Musca domestica
Diptera (other)
0
1
8
0
0
1
0
1
0
1
0
0
1
4
3
1
0
1
Halictus (Evylaeus) sp.
pulzenus
(Lasioglossum)
Prosopis basalis
elliptica
wootoni
Andrena crataegi
madronitens. . .
vicina
Sphex vulgaris
Bombua juxtus
occidentalis. . . .
Pseudomasaris vespoides
Total
112
61
28
NORMAL AND EXPERIMENTAL POLLINATION.
The most significant variation was that of Apis, indicating the possible
fluctuations from day to day, but similar differences of less degree are to
be noted for practically every species.
The visitors noted at the same time of day, 8h30m to 9h30m a.m., at the
same location, with 65 open flowers in bloom and under observation in
each case, are shown in table 7. The first list represents the visitors at
about the middle of the flowering season and the second those at the end.
There were no plants of Rubus deliciosus in bloom lower down in the canyon
at the time the second list of visitors was made.
Apis and Halictus, the two most important pollinators of the middle of
the flowering period, were almost completely absent at the end, but the
situation was exactly reversed for Bombus and Prosopis. On the contrary,
Andrena maintained its number throughout, though the three species showed
as many types of distribution.
Table 8. — Visitors to adjacent areas on different days.
Species.
June 5.
June 7. Species.
June 5.
June 7.
12
35
37
4
10
1
1
0
14
4
4
4
2
1
5
5
1
1
2
1
2
0
0
0
1
2
0
1
0
0
0
1
3
Bombus occidentalis. . . .
juxtus (worker)
juxtus (queen) .
bif arius
edwardsi
2 Osmia bruneri
0 phaceliae
1 melanotricha. . . .
0 Pseudomasaris vespoides
morrisoni
Andrena canadensis. . . .
madronitens. .
crataegi
prunorum. . . .
vicina
2 Syrphus americanus ....
0 Systoechus vulgaris ....
0 Coleoptera
3
1 Total
146
94
0
Table 9. — Summary by genera
Station 1.
Station 2.
Genus.
Species.
Visitors.
Species.
Visitors.
1
6
5
6
12
88
15
12
1
3
3
4
77
5
4
4
Reciprocal checks at the two stations showed that the differences recorded
were due to location and not to time. Since they were situated in the same
canyon and but 150 meters apart, it is probable that the contrast between
the numbers for Apis and those for Bombus, Andrena, and Osmia is to be
ascribed to the difference in the associates of Rubus in the two places.
In station 1 it was grouped with Prunus demissa and P. pennsylvanica,
while at station 2 it was associated with Geranium especially. However,
it is quite possible that the difference was due to habit rather than to any
difference in conditions.
RUBUS DELICIOSUS.
29
EXPERIMENTS.
MUTILATION.
Petals split or shortened. — When each petal was cut lengthwise into
four ribbons, giving a daisy-like appearance to the flowers, Bombus juxtus,
B. morrisoni, and Andrena vicina visited them just as they did normal
flowers. In order to reduce the attractive surface, the petals were clipped
to half their length, giving the corolla a rotate form, with no spaces between
the petals. The flowers used were at the same stage of development, the
number of normal and mutilated ones being the same on each day. Table
10 shows the effect of this reduction in attractive surface.
Table 10. — Visits to normal and mutilated flowers.
Species.
June 26.
June 27.
Normal.
Corolla reduced.
Normal.
Corolla reduced.
Visited.
Inspected.
Visited.
Inspected.
60
22
0
2
11
1
3
1
2
2
1
0
0
1
1
13
9
3
2
13
15
5
0
1
1
1
0
1
2
0
0
0
3
2
0
4
4
1
1
3
5
5
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
25
8
7
0
0
0
0
0
0
0
4
3
0
0
3
7
0
0
0
3
1
2
0
0
0
0
0
0
0
0
0
0
0
0
2
4
0
1
0
2
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Andrena crataegi
Halictus pulzenus ,
(Lasioglossum) sp . . .
Megachile wootoni
Prosopis basalis
Systoechus vulgaris
Pseudomasaris vespoides
Eristalis arbustorum. . .
Muscidae
Anthrax lateralis
Diptera (other)
Total
147
44
10
58
13
4
The number of visits to the normal flowers was nearly four times as
great as to those with the petals shortened. Since conditions were other-
wise identical, this not only proves the importance of the corolla in attrac-
tion, but also shows that its effectiveness is related to its expanse. The 14
inspections were made by Apis and Bombus and indicate that about one-
fourth of the visits failed because of the disturbance of the usual perception.
This was especially true of B. juxtus, which flew away in 7 different cases
when only a centimeter from the flower. Moreover, Apis was forced to
change its method of working, since it could no longer walk around the
stamen mass on the petals.
Stamens covered. — The stamens were covered with absorbent cotton
in 30 flowers and an equal number of normal ones taken for comparison.
Apis visited 25 of the latter, but found the stamens in only one of those
30
NORMAL AND EXPERIMENTAL POLLINATION.
covered, though it hovered low over 3 others. Bombus occidentalis went to
7 normal flowers and hovered over 2 of the changed ones, while for B. juxtus
the numbers were 8 and 1 respectively.
ARTIFICIAL AND PAINTED FLOWERS.
Crepe-paper corollas. — In all the flowers employed the anthers were
just beginning to dehisce, as flowers at this stage had been found to be most
attractive to insects. Other open flowers nearby were removed, so that
they would not attract visitors from the group under observation. After
the petals and sepals were removed, artificial corollas of red, blue, yellow,
or white crepe-paper were wired below the anthers. A normal flower
was left for comparison near each artificial one, 3 flowers of each color
being used in the experiment, making a total of 15 for each of the two lands.
Table 11 shows the response to them, as well as the color preferences.
Table 11. — Visits to natural and paper flowers.
Species.
Normal.
Red.
Green. 1 White.
Bombus juxtus
morrisoni. . . ,
Andrena vicina
crataegi
prunorum . . ,
Acmaeops longicornis .
Osmia bruneri
phaceliae
Prosopis wootoni
varifrons . . .
basalis
Pipiza sp
Diptera
100
7
25
2
1
17
18
1
14
10
2
1
Total .
4:31
The visits to normal flowers were six times as many as to the artificial
ones. While the bees clearly avoided the imitations as a whole, there
was a great difference in response to the various colors. The visits to green,
white, and red were negligible.
Artificial corollas similar to those used in the previous experiment were
made of crepe-paper, but with the petals fringed by cutting them length-
wise. Four artificial flowers of each color and 16 normal flowers were used.
Observations from 8 to 10 a.m. on the first morning and from 8 to 9 a.m.
on the second gave the results shown in table 12.
Of 222 visits, only 18 were made to the artificial flowers, chiefly by Bombus
and Osmia, a fly being the only other visitor to them. It is significant
that Apis did not go to a single imitation. While the numbers are too
small to be of much value, it is interesting to note that blue and yellow
were again the preferred colors.
Painted corollas. — When the petals were painted blue, green, or yellow
with water-colors, Bombus juxtus visited as many painted as normal flowers,
in contrast to the ratio of 11:1 for natural and paper flowers. Andrena
crataegi went only to the blue flowers, in addition to the normal ones.
RUBUS DELICIOSUS. 31
Table 12. — Visits to natural flowers and flowers with fringed paper corollas.
Species.
Normal. Red. Yellow. Green. Blue
Apis mellifica
Bombus bifarius . .
juxtus. . .
proximus .
Andrena crataegi .
Osmia phaceliae . .
Musca sp
Total.
Bombus proximus. . . .
bifarius
Andrena crataegi ....
madronitens.
Syrphus amerieanus. .
Halictus pulzenus. . . .
Prosopis elliptica
Musca sp
Total .
106
39
12
0
o
1
0
0
0
0
0
0
0
0
0
2
0
2
1
ADDITION OF HONEY AND ODOR.
Honey. — In this installation one-third of the flowers were supplied with
a drop of honey at the base of the filaments, another third with a drop at the
center of the stamen mass, and the remainder were left normal. Halictus
pulzenus visited 4 normal flowers and 10 with honey at the filament base.
Andrena crataegi visited but one flower of this sort; it actually landed at
others but flew away at once, as did Bombus proximus. The total number
of visits to normal flowers was 46, in contrast to 11 for those with honey
added, giving a ratio of 4:1.
SUMMARY.
A comparison of the tables obtained from the various calendars not only
reveals the differences arising out of time and place, but also throws light
upon discrepancies between the results of different observers and investi-
gators, making it clear that comparison is often misleading if not impossible
when different years and regions are concerned. There was much difference
in the number of visits on successive days in the same spot, and a marked
one when different portions of the flowering period were concerned, arising
chiefly out of the period of flight for the various genera. Neighboring
areas likewise showed a distinct divergence, which was strikingly evident in
the ratios of visits for the bees, namely, Apis 1:6, Bombus 17:1, Andrena
7:1, and Osmia 3: 1.
The decisive effect of cutting the petals back to half their length is espe-
cially significant in connection with the question sometimes raised as to
the value of the corolla in attraction. Covering the stamens excluded
visits entirely and suggests that insects distinguish clearly between the
corolla and the stamen mass, or at least readily recognize that the latter is
changed. Although 49 visits were made to paper flowers of various colors,
32
NORMAL AND EXPERIMENTAL POLLINATION.
this was less than one-eighth of the number paid to natural ones at the same
time. All the colors received visits, as follows : red 3, yellow 22, green 3,
blue 17, white 4. In accordance with the general rule, painted flowers
were visited much more than paper ones, doubtless owing to the fact that
they differed but little from the normal ones, as shown especially by the
behavior of Bombus. The attractive power of honey was again found to be
slight, flowers with honey receiving but one visit to 4 for the normal ones.
RUBUS STRIGOSUS.
NORMAL POLLINATION.
Habit and structure. — These flowers open later than those of Rubus
deliciosus, but the two are in bloom together for a considerable period.
They are quite inconspicuous because of their small size and recurved
petals and the scattered position among the leaves. However, the large
amount of easily available nectar makes this species very attractive to
several kinds of insects. The nectar is formed within the stamen circle
at the base of the ovaries. It oozes out in drops and if not kept lapped up
by the bees, the depressed ring becomes filled with it. In order to find out
how rapid this flow of nectar is, 4 plants profuse with flowers were covered
with paper bags in the evening, so that no visitors could get nectar until
the flowers were examined. At 9 the next morning, when the visits of the
bees were becoming numerous, the bags were removed. Flowers outside
the bag, which had been receiving the morning visitors, showed only the
glistening droplets of nectar, while a full nectar ring was very conspicuous
in all the bagged flowers mature enough to produce it (plate 3).
Behavior. — A pis mellifica hangs suspended from the flowers while
sucking nectar. It scrapes pollen from its head and thorax with the
second pair of legs on to the corbiculse of the third pair. One individual
flew half an inch above flowers with dry anthers and discovered without
landing that there was no nectar. Prosopis episcopalis goes to open flowers
for nectar and lands on the petals. If the petals are closed, it goes around
the edge of the bud and inserts its ligule between the petals. The normal
visitors on 3 successive days during periods of 2 hours to 100 open flowers
are listed in table 13.
Table 13. — Visitors on three successive days.
Species.
June
29.
June
30.
July
1.
Species.
June
29.
June
30.
July
1.
34
0
0
2
0
1
118
6
8
8
3
0
47
15
15
7
3
0
Andrena crataegi
0
0
1
2
0
2
4
0
1
0
2
0
Bombus bifarius
juxtus
proximus
Andrena vicina
madronitens. .
Prosopis episcopalis. . . .
Monumetha albifrons. .
Total
40
149
90
Rubus strigosus is primarily a honey-bee flower, as is shown by the fact
that 199 of the 279 visits were made by Apis; of the remaining 80 visits,
61 were made by Bombus.
ROSA ACICULARIS. 33
No previous floral study of Rubus has been made in America, but several
European species have received much attention (Knuth, 1908:352).
EXPERIMENTS.
MUTILATION.
Floral envelopes or stamens removed. — Apis mellifica started to
land at a flower with the stamens removed, but flew away. The nectar
was clearly visible, but the excision of the stamens changed the appearance
of the flowers so much that it seemed to frighten this bee. Andrena
madronitens worked at flowers with the calyx and corolla or stamens gone
as at normal flowers. Prosopis episcopalis stopped at one with the stamens
and corolla removed and worked as usual, while Osmia bruneri visited a
flower with the perianth gone. These results are opposed to those obtained
with Rubus deliciosus, but this is readily explained by the difference in
the size and visibility of the petals. In strigosus these are not only several
times smaller than in deliciosus, but their position further decreases their
attractiveness.
ROSA ACICULARIS.
NORMAL POLLINATION.
Habit and structure. — The corolla of Rosa is pink in color and widely
expanded, forming a broad landing- platform and a bright disk of color,
evidently visible to insects from some distance. The stamens are numerous
and the pollen abundant. A mild sweet odor adds to the apparent attrac-
tiveness of the flower.
Behavior. — Bombus edwardsi tumbles about the stamens very rapidly,
collecting pollen in the corbiculae, on the mouth-parts, and the hairs of
the abdomen. Pollen was gathered at Rubus deliciosus in much the same
manner, and this bee goes from Rosa to Rubus or the reverse without
showing a preference for either. It did not stop at flowers in which the
stamens and pistils were covered by the unfolding petals, but went on to
the next open flower. The anthers in Rosa are not mature when the petals
are unfolding and the bee has perhaps learned by experience that the pollen
is not available until the petals are broadly expanded. One individual of
Bombus flavifrons endeavored to open a half-expanded flower, landing on
the lower petal and trying to push its head in, but after making several
unsuccessful attempts it flew away. B. bifarius tramples back and forth
among the stamens collecting pollen, the tip of its abdomen at the same time
rubbing the stigmatic surfaces and depositing pollen previously collected.
B. proximus collects pollen on the rose; it files low above flowers which are
opening but lands only on those with dehiscing anthers.
Andrena crataegi collects pollen most industriously, even visiting flowers
with petals gone and stamens brown, trying to get pollen from the withered
anthers. Andrena vicina tramples rapidly over the stamen mass, going
round and round with its head buried among the anthers. The first two
pairs of legs gather pollen and pack it on the third pair. A. madronitens
arches the tip of its abdomen downwards toward its head, inclosing a
group of stamens. While in this position, it collects pollen rapidly with
34
NORMAL AND EXPERIMENTAL POLLINATION.
the front legs and stores it on the hind ones. Prosopis elliptica works
very rapidly with its mouth-parts and with the front pair of legs. It
opens the anther with the front legs, scrapes out pollen, and also picks
it up from the corolla. Anthophora simillima poises 7 to 15 cm. above the
flower, meanwhile buzzing loudly, and then makes a dive for it. While
diving, head and abdomen tip are together, and as it lands it grasps the
stamens with its front legs and slides down the bunch of filaments. When
the anthers are reached, a struggling movement takes place, during which
pollen is put on the third pair of legs, when it buzzes into the air again and
dives for another flower. It often darts repeatedly into the same flower,
apparently getting some nectar during this process. Monumetha albifrons
tramples around on the stamens with its head buried in the mass. It moves
very rapidly, working all three pairs of legs and storing the accumulated
pollen on its ventral scopa. The latter also rubs rapidly against the anthers
and collects pollen. Osmia bruneri tramples over the stamens in the same
manner as Bombus. Megachile wootoni moves around very rapidly while
on the stamens, the first two pairs of legs scraping out the pollen and passing
it to the third pair, which place it on the scopa. This is raised in the air
and usually does not come in contact with the anthers.
Table 14 shows the visitors observed during 30 minutes on 42 flowers of
Rosa, 14 of which were just opening and the anthers beginning to dehisce.
The lists were made on successive days, and exhibit the difference often to be
expected.
Table 14. — Visitors to normal flowers.
Species.
Visitors.
Visitors
and visits.
Species.
Visitors.
Visitors
and visits.
Bombus bifarius. . . .
proximus . . .
juxtus
occidentalis.
Andrena crataegi. . .
vicina
18
7
0
0
14
1
0:0
0:0
3:5
1:2
4:4
0:0
Halictus pulzenus. . .
Prosopis elliptica. . .
Megachile wootoni. .
Syrphus sp
Total
3
2
0
2
0:0
1:2
3:3
0:0
47
12:16
The pollination of the rose appears to have received no attention in this
country, but several species have been studied in Europe (Knuth, 1906:348).
These are chiefly visited by beetles, though several genera of bees have
been taken on R. canina, and two species of Bombus on rubiginosa.
EXPERIMENTS.
MUTILATION.
Corolla shortened. — The petals of Rosa were cut to half their length,
giving the corolla a rotate form. This made them paler in color, as the
petals are almost white toward the base. Since the flower is smaller, the
stamens also become more conspicuous. At such flowers, Bombus juxtus
landed, collected some pollen and then passed on to the next, never securing
all of the available pollen at any flower. Monumetha albifrons remained
at each flower a long time and collected much pollen. In order to determine
ROSA ACICULARIS.
35
the comparative effect of reducing the attractive surface of the corolla,
10 such flowers were grouped with 10 normal ones. Table 15 shows the
visitors during an hour of observation.
Table 15. — Visitors to normal and reduced flowers.
Species.
Normal.
Reduced.
21
8
8
3
1
1
0
9
1
2
0
0
0
occidentalis
Anthophora simillima
prunorum
Total
42
13
In accordance with the rule, the reduction of the corolla surface greatly
decreased the attractiveness of the rose, since there were three times as
many visitors to the normal flowers.
Stamens masked. — The stamens of 10 flowers were masked with a
veil of cotton and 10 normal blossoms left for comparison. Two hours of
observation gave the results shown in table 16.
Table 16. — Visits to normal and masked flowers.
Species.
Normal.
Masked.
Andrena madronitens
2
2
3
1
1
1
0
0
0
0
0
0
0
Anthophora simillima
Syrphus americanus
Total
12
1
Andrena madronitens landed on the veil of cotton, walked over it, and
finally slipped under the edge to the stamens. A second bee tried the
same method, but failed to find them. Bombus proximus and 3 individuals
of B. bifarius inspected the masked flowers, but did not stop at them.
Where the cotton had slipped a little at the edge exposing the stamens,
proximus landed in the flower, but its legs became tangled in the cotton
and it flew away as though frightened.
ARTIFICIAL AND PAINTED FLOWERS.
Crepe-paper corollas. — The corollas were replaced by artificial ones
of red, green, and yellow crepe-paper, resembling the normal in size and
form. The crepe flowers were paired with normal ones in the various
positions on the bush. Bouquets of flowers in bottles of water were sus-
36
NORMAL AND EXPERIMENTAL POLLINATION.
pended from the branches to increase the number of normal flowers under
observation. One Halictus pulzenus went to all flowers, making no dis-
tinction between the normal and those with artificial corollas. Another
individual visited one yellow, two green, and many normal flowers. Bombus
proximus went to 118 normal flowers and only 18 with crepe corollas,
Syrphus americanus to 3 yellow, 2 green, and 11 normal, and Clisodon
terminalis to 18 normal and 1 white crepe flower.
The results of observations made on another day are given in table 17,
which shows the visits to normal and crepe flowers during an hour. Eight
natural flowers were used, together with 4 of each color, making 20 artificial
flowers in all.
Table 17.
—Visits to natural and artificial flowers.
Species.
Normal.
Violet.
Red.
Blue.
White.
Green.
20
19
19
2
0
0
0
1
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
Total ...
60
1
1
0
1
0:3
Later, Bombus proximus and juxtus visited these bushes several times,
but stopped only at the natural flowers, passing by the artificial corollas.
The first stopped twice at a petal lying on some leaves and examined it,
but did not land at any of the artificial flowers in passing from one natural
flower to others more distant.
ADDITION OF HONEY AND ODOR.
Honey. — Diluted honey was placed in the center of the stamen group,
so that visitors coming for either pollen or nectar would be sure to come in
contact with it. This glistened in the sunlight and was distinctly visible
3 meters away from the flowers. In general, Bombus proximus avoided
flowers treated in this way, and when it did land usually paid no attention
to the honey. When this was noticed, the bee flew away suddenly, or
avoided it and trampled among the anthers on the other side of the flower.
One individual landed at a flower with diluted honey, commenced at once
to sip nectar, and stayed for a long time. It flew away for a second, came
back again, and took more nectar. This bee went to the next flower which
was normal and trampled among the stamens in the usual fashion. No
pollen was collected in the next two flowers with honey- drops, but the bee
secured nectar. Three normal flowers were then visited in succession and
at each it trampled among the stamens and collected pollen. Monumetha
albifrons sipped honey for 60 seconds on a flower that had pure honey-drops
on the stamens. It also went to those in which the honey-drops were
diluted, but showed no preference for either kind.
Twenty flowers of each kind were used in the following experiment to
find out whether honey would prove an added attraction to visitors; the
period of observation was an hour.
ROSA ACICULARIS. 37
Table 18. — Visits to normal flowers and those with honey on the stamens.
Species.
Visitors.
Normal
flowers.
1
Honey flowers.
Pollen.
Nectar.
15
4
3
2
1
54
1
0
2
1
36
4
3
0
0
5
0
0
0
0
Total
25
58
43
5:48
The results indicate that the honey did not constitute an added attraction,
except possibly to Prosopis and Andrena.
Diluted honey was put on the stamens of half the flowers employed in
experiment 1, while in experiment 2 the honey was placed in a circle around
the base of the filaments and an additional drop at the center of the stamen
mass; 10 normal and 10 honey flowers were used in each case, and the obser-
vation period was 2 hours.
Table 19. — Visitors to normal and honey floivers.
Species.
Experiment 1.
Experiment 2.
Normal
flowers.
Honey
on
stamens.
Normal
flowers.
Honey
under
stamens.
17
0
1
0
6
0
3
0
0
0
0
1
13
5
0
1
0
0
27
1
0
2
0
0
Total
24
4
19
30
Placing honey on the stamens reduced the number of visitors very greatly,
the ratio being 24 : 4. This was due to interference with the usual collection
of pollen. When the honey was placed at the base of the filaments, the
visits of Bombus juxtus were likewise reduced, but those of B. proximus
were doubled, without an evident reason. However, it landed and took
honey in but 10 of these, leaving the others immediately after alighting,
as though disturbed by the presence of the honey.
Honey and talcum powder. — Flowers were modified by the addition
of pure or diluted honey, or talcum powder of the "Love me" and "Arbutus"
brands. There were 10 of each type of modified flowers used and 40 normal
ones were paired with them for comparison. Of the 49 visitors, 30 went to
normal flowers, 4 to flowers with pure honey, 8 to flowers with diluted
honey, 5 to those with "Love me" sachet, and 2 to those with "Arbutus"
NORMAL AND EXPERIMENTAL POLLINATION.
sachet. Clisodon terminalis flew above the flowers scented with "Arbutus"
powder for some little time before landing, projecting its ligule, which was
not its normal procedure when hovering above flowers. One Bombus
juxtus landed on flowers powdered with both kinds of sachet, but quickly
flew away. Syrphus opinator alighted on some with "Love me" sachet
on them and worked as usual. It also landed on flowers with honey-drops
but did not find the honey.
Camphor. — The response of the various species to flowers in which
powdered "moth balls" had been sprinkled on the stamens and to normal
flowers is shown in table 20.
Table 20. — Visitors to normal flowers and flowers scented with camphor.
Species.
Normal
flowers
Scented
flowers
Species.
Normal
flowers.
Scented
flowers.
Bombus proximus
35
2
6
2
5
23
1
1
1
3
Halictus pulzenus
Monumetha albifrons ....
Anthophora simillima ....
Syrphus opinator
Total
3
2
1
1
0
2
0
0
Prosopis elliptica
Andrena crataegi
57
31
It is somewhat surprising to find that the flowers with an unpleasant
odor attracted half as many visitors as the normal ones, but this is probably
to be explained on the basis of habit.
Cotton perfumed with anise was wound around the pedicels under the
sepals in 8 pairs of flowers, normal flowers adjoining the scented ones
in each case, and the observations covering an hour. The response to
anise was essentially the same as that to camphor.
Table 21. — Visitors to normal and anise-scented flowers.
Species.
Normal.
Anise.
Species.
Normal.
Anise.
27
9
5
5
4
3
14
4
0
0
5
2
2
0
0
1
0
occidentals
Monumetha albifrons. . . .
Andrena crataegi
Syrphus americanus
Prosopis elliptica
Eristalis latifrons
Total
58
28
SUMMARY.
As would be expected from their similar size and structure, the rose and
salmonberry yielded much the same experimental results. The reduction
of the corolla decreased the visits to the one 3 and to the other 4 times, while
in both cases flowers with stamens masked obtained but few visits. The
visitors to paper flowers were much more numerous in the case of Rubus,
but this was probably due in part at least to the more extensive experiments
with it. The reverse was true in the case of flowers with added honey, the
GERANIUM CAESPITOSUM. 39
roses thus treated receiving a relatively large number of visitors. The
difference between the two, however, was almost wholly a consequence of
the preference of Bombus proximus for the honey-flowers of the rose. The
addition of various odors to flowers of the rose regularly decreased the
number of visitors about half, quite irrespective of whether the odor was
one ordinarily regarded as pleasant. It seems evident that this decrease
was due to the strange odor disturbing the habitual response of the pol-
linators.
GERANIUM CAESPITOSUM.
NORMAL POLLINATION.
Habit and structure. — The flowers of Geranium are regular and the
five nectaries are so placed that the nectar in all is equally exposed and
accessible. All the visitors except Halictus sp. usually come for nectar.
The inner row of anthers dehisce first, followed by the outer row from
10 to 24 hours later (plate 7).
Behavior. — Bombus juxtus lands on the disk-shaped corolla and proceeds
to circle the stamen group, taking nectar at each of the nectaries. It
secures nectar from flowers in which all the anthers have dropped off,
indicating that the flow continues while the stigmatic surface is receptive.
A few individuals are satisfied to suck nectar from only one or two nectaries
at each flower, and B. bifarius usually stops likewise at only a few of those
in each flower, instead of making the complete round. Halictus pulzenus
comes for both nectar and pollen. It visits each of the 5 nectaries, some-
times going around the circle twice in succession. After getting all the
nectar available, it walks up the anthers, scrapes out pollen with its front
legs, and packs it on the hind ones. This bee is so small that it can stand
under the outwardly curved anthers. When in this position, pollen falls
on its back, but it touches the stigma only as it flies away. Halictus was
seen to pick up the pollen that had fallen on the corolla, brush its head well
with the front legs, and then eat the pollen. Prosopis elliptica has a shiny
body on which pollen does not collect easily. It is so small that in dipping
into the nectaries only the lower shorter row of anthers or the recurved
styles touch its abdomen. This species is probably not a very effective
pollinator on this account.
Andrena madronitens is a pollen collector. It hangs suspended from the
styles and filaments, and moves around them repeatedly, gathering pollen.
It collects with its mouth and front legs and places the pollen on the hind
ones. Monumetha albifrons lands with its head pointing toward the nec-
taries. It tips its abdomen upward as it goes from nectary to nectary, and
this gives it the appearance of standing on its head. The tip of its abdomen
rubs the anthers as it sucks nectar. A pis mellifica stops at all the nectaries
and makes no effort to get pollen. The thoracic hairs become covered with
the latter and scrape the anthers and style, dusting them with pollen as it
moves about the nectar circle. Osmia bruneri and Sphex vulgaris also visit
each nectary, where they appear to be standing on their heads. The head
of the latter is hairy and serves to collect and deposit pollen. Pseudomasaris
vespoides likewise goes to each nectary, the dorsal surface of the bee touching
the anthers in one flower and the stigmas in the next.
40
NORMAL AND EXPERIMENTAL POLLINATION.
Merritt (1896:149) has studied the pollination of the closely related
Geranium richardsoni in California, where the most frequent visitors are
able to secure nectar without touching anthers or stigmas. However,
larger bees also visit the flowers, namely, Apis, Anthophora, Coelioxys,
Osmia, and Bombus californicus, and these readily effect pollination as they
cling to the anthers or styles. Robertson (1889:229; 1893:272) briefly
describes the behavior of the flower in G. maculatum and G. carolinianum
and gives a list of the visitors to each. The insect visitors of a large number
of European species are given by Knuth (1908:218).
CALENDARS.
Fifty flowers were under observation on each of the five days for which
the visitors are given in table 22.
Table 22. — Visitors to normal flowers.
Species.
June 28,
30 min.
June 29,
120 min.
Aug. 17,
80 min.
Aug. 19,
60 min.
Aug. 20,
45 min.
Apis mellifica
Ancistrocerus sp
Bombus juxtus
Coelioxys maesta
Colletes sievisiti
Halictus pulzenus
(Lasioglossum) sp
Monumetha albifrons
Prosopis basalis
varifrons
wootoni
Pseudomasaris vespoides. .
Sphex vulgaris
Thanaos martialis
Muscidae
Coleoptera
Total
Table 23. — Visitors and visits to normal flowers.
Species.
July 16. July 16
July 25.
Bombus bifarius
juxtus
proximus. . . .
Andrena madronitens
Colletes sieverti
Halictus pulzenus. . . .
Megachile texana. . . .
Monumetha albifrons
Prosopis elliptica
varifrons. . . .
Syrphus opinator
Total
10:186
6:44
4:45
22:97
1:1
2:5S
0:0
0:0
0:0
3:3
2:2
2:2
0:0
2:2
0:0
0:0
0:0
1:1
9:13
1:1
1:1
1:1
27:24S
0:0
5:36
0:0
1:2
0:0
0:0
0:0
1:1
0:0
0:0
0:0
7:39
GERANIUM CAESPITOSUM.
41
In the columns for July 16, 40 flowers were under observation for the two
successive hour periods. On July 25, only 26 flowers were in the group
observed during an hour period.
As would be expected, the records for two successive hours resemble
each other closely, but depart much more widely from that made a number
of days later. This record contains but three of the species present on
July 16, and the number of visitors and visits is very low. The inversion
of the number for Bombus bifarius and juxtus is the most striking feature of
the two successive records. In table 23 the most important fact is the
change of dominance from Prosopis at the opening of the flowering period
to Bombus and Halictus near the close. This is to be explained by the
fact that the latter were working on preferred species earlier and went to
Geranium in abundance only when their choice became more restricted.
This is likewise the explanation of the doubling of the average number of
visitors per hour period in the later observations.
EXPERIMENTS.
CHANGE OF POSITION.
Flowers vertical or inverted. — When the face of the flower was turned
so that it was vertical, Bombus juxtus found no difficulty in hanging on,
and its behavior was practically the same as at a normal flower. In the
case of inverted flowers, however, it experienced much trouble in keeping a
foothold. One individual landed on the bottom of the flower, which was
then uppermost, went over the edge to the face, but finally flew away with-
out securing nectar. Another went to an inverted flower that was half- open,
but did not succeed in opening it. It next went to another half-open
inverted flower, landing on the calyx and looking for the opening to the
nectaries among the sepals, and departed unsuccessful.
MUTILATION.
Cotton over nectaries. — A circle of cotton was placed at the base of the
filaments so that it covered the opening to the nectaries. One individual
of Prosopis varifrons flew around above the flowers without landing. Another
individual alighted and poked around the edges of the cotton, but did not
find the nectaries. A fly also landed and pushed out its ligule, but was
unable to locate the nectar. Bombus juxtus secured nectar from 7 flowers
by pushing aside the edge of the cotton until the nectary was exposed.
Table 24. — Visitors to normal and mutilated floivers.
Specie?.
Normal
flowers.
Petals
removed.
Petals
and
sepals
removed.
Stamens
removed.
Stamens
and
style
removed.
15
5
0
10
1
0
0
0
1
1
0
0
15
4
3
0
12
3
2
5
Apis mellifica
Total
30
1
2
22
22:47
42
NORMAL AND EXPERIMENTAL POLLINATION.
Excision. — The results of the experiments with the various types of
mutilation are presented herewith. Flowers with the corolla gone closely
resembled old flowers with the petals fallen and were probably mistaken for
them (plate 17). Tables 24 to 28 give the results of observations in which
25 normal flowers and 5 flowers of each kind of mutilation were used,
with the exception of the last, in which the numbers were equal. The
period of observation was one hour in all cases but the second.
Table 25. — Visitors to normal and mutilated flowers.
Species.
Normal
flowers.
Petals
removed.
Petals
shortened.
Petals
split.
Stamens
and
style
excised.
Cotton
over
stamens.
Cotton
under
stamens.
Bombus juxtus ....
Prosopis basalis. . . .
Halictus pulzenus. .
Total
23
1
0
0
0
0
12
0
0
17
2
2
17
1
1
6
0
0
7
0
0
24
0
12
21
19
6
7:65
Table 26. — Visitors to normal and mutilated flowers.
Species.
Normal
flowers.
Petals
shortened.
Style and
stamens
excised.
6.6
0:0
5:6
1:4
1:1
0:0
0:0
4:4
1:1
0:0
0:0
0:0
0:0
1:1
2:5
7:7
4:10
0:0
2:3
2:6
0:0
Total
13:17
6:6
17:31
Table 27. — Visitors to normal and mutilated flowers.
Species.
Normal.
Petals
\i width.
Stamens
removed.
20
15
9
8
3
7
4
6
2
2
1
2
1
7
12
2
3
0
1
5
0
0
0
1
0
1
1
3
0
0
1
0
0
0
0
0
0
0
Total
80
32
6:38
GERANIUM CAESPITOSUM.
Table 28. — Visitors to normal and mutilated flowers.
43
Species.
Normal.
Corolla I c,
, . , | Species,
shortened. |
Normal.
Corolla
shortened.
Apis mellifica
Bombus juxtus
occidentalis. .
Prosopis basalis
elliptica. . . .
Megachile wootoni. . .
Andronious sp
16
21
8
15
13
10
2
10
9
1
15
17
10
2
Adrena prunorum
crataegi
Osmia melanotricha. .
Halictus pulzenus ....
Anthophora simillima.
TotaJ
1
1
3
1
3
0
0
0
2
0
94
66
In all cases where there were two or more mutilations, these received
relatively twice as many visitors as the normal flowers. The removal
of the petals practically eliminated visits, while shortening them decreased
the number markedly. The excision of the stamens, or of these and the
style, led to the greatest increase as a rule, probably because of the exposure
of the nectar. The use of cotton to mask the stamens or nectar openings
reduced the number of visitors in comparison with many of the other
mutilations, but not below that for the normal flowers.
ARTIFICIAL AND PAINTED FLOWERS.
Crepe-paper corollas. — The corollas were replaced by crepe-paper ones
of the same size and form as the normal and of the colors indicated in
table 29. Four of each color or a total of 20 crepe corollas were used,
together with 4 flowers with normal corollas.
Table 29. — Visitors to normal and crepe-paper flowers.
Species.
Normal.
Red.
Blue.
Yellow.
White.
Green.
34
7
4
7
4
3
2
1
1
0
1
0
0
0
0
0
1
0
0
1
6
0
0
0
0
0
1
0
0
3
0
0
0
0
0
6
0
0
5
5
0
0
1
0
0
0
0
0
1
2
0
0
0
0
0
2
0
0
0
Halictus pulzenus
Monumetha albifrons
Syrphus americanus
Total
63
3
9
14
7
4:37
In spite of the fact that the table shows 37 visits to artificial flowers to
63 for normal, the latter were only one-fifth as numerous and hence appear
to have been about ten times as attractive. The contrast between red and
green on the one hand and yellow, blue, and white on the other suggests
that the bees were influenced in some degree by the brightness of the colors.
ADDITION OF HONEY AND ODOR.
Honey. — A drop of honey was put on the petals of half of the flowers.
Bombus juxtus landed at a normal flower and then at one with the honey-
44
NORMAL AND EXPERIMENTAL POLLINATION.
drop in such a position that its head was just above the drop. It first
walked around the filament column, then commenced to suck honey and
continued for 90 seconds, until the drop was two-thirds gone. While
sucking, it supported itself on a petal with the front and hind pairs of legs.
Diluted honey was placed in drops at the base of the filaments. Halictus
pulzenus went from one nectary to the next, sucking nectar, as usual, and
did not notice the honej^. Bombus juxtus came and crowded Halictus
away, but did not stay long enough to secure all the honey. At the next
flower there was a drop at one point and it sucked at this until the honey
was all gone. This took a minute; it then walked around the flower and
dipped its ligule into each nectary. One individual stayed at a honey drop
for more than 3 minutes. After this it walked around the flower, back to
the honey-drop, and sipped more of it. The end of the ligule did not reach
the nectary, as the tip was visible in the honey, moving in all directions.
This bee flew to another flower that had a drop of honey in a similar position
and walked around the column of anthers without stopping for nectar.
A circle of diluted honey was placed around the base of the filaments.
Bombus juxtus took a few sips of this, but did not stay long. Another
juxtus landed with its head pointed toward the outside of the flower and
sucked honey from a drop that had run half way down the petals. It then
went to the next flower which had honey in a similar position, took a sip,
and flew away. When Bombus bifarius came to a flower on which there
was diluted honey, it stayed and sipped, instead of trying to push the ligule
into the nectaries. However, it did not remain until all the honey was
gone, but flew to normal flowers and took nectar there. Halictus pulzenus
went to a flower with a honey-drop, but worked at all the nectaries without
finding it.
Diluted honey wab put around the base of the stamens of 10 flowers,
which were placed beside 10 normal ones. The results of an hour's observa-
tion are shown in table 30.
Table 30. — Visits to normal and honey flowers.
Species.
Normal
flowers.
Honey
flowers.
13:101
2:13
2:2
3:4
10:12
0:0
0:0
0:0
juxtus
Prosopis varifrons
Halictus pulzenus
Total
20:120
10:12
While there were one-half as many visitors to the honey as to the normal
flowers, these averaged but one visit each in contrast to 6 each for the
normal. In addition, 7 bumble-bees inspected the honey flowers. The
effect of added honey in disturbing the normal response is well shown in the
case of Bombus bifarius. The honey flowers received nearly as many visitors
as the normal ones, but practically all of these made single visits, in contrast
to an average of 8 for the normal flowers.
CHAMAENERIUM ANGUST1F0LIUM. 45
SUMMARY.
Complete inversion of the flower did not deter bees from landing, but
it did prevent their finding the nectaries. As a rule, they also alighted on
flowers with the nectaries concealed by cotton, but Bombus alone succeeded
in finding the nectar. The total number of visitors to the mutilated flowers
was twice as great as the normal. This was due chiefly to the greater
attractiveness of the flowers with stamens excised, since the removal of
the petals almost completely destroyed the attraction and shortening
them greatly reduced it. Paper flowers received a considerable number
of visitors, but they were only about a tenth as attractive as the normal
ones. The effect of honey on the flowers was to reduce the number of
visitors a half and the number of visits six times.
CHAMAENERIUM ANGUSTIFOLIUM.
NORMAL POLLINATION.
Habit and structure. — These plants were present in the open spaces
along Ruxton and Jack Brooks, where the communities are often so dense
and extensive that they practically crowd out all other species where
they exist. The blooming period is continuous from the beginning of July
until the first of September, the lower flowers on the stalk maturing first,
and then as the stalk elongates, the flowers above come into bloom. The
long period of blooming and the numerous flowers that mature at any one
time make this an admirable plant for study. The great number of visitors
always present on bright days indicates that the bees find it a very desirable
species. Nectar is abundant and there is a large amount of pollen. The
pollen grains are large and of a blue-green color, and are held together by
the sticky threads characteristic of the Onagraceae.
The corollas of the flowers lie in a more or less vertical plane with the
style recurved and its branches held closely together, protecting the stig-
matic surfaces, or in the later stage with the style projecting in front of the
corolla and the stigmatic surfaces exposed on the outwardly coiled stylar
branches. The stigmas are covered with blue-green pollen soon after they
recurve. A large number of seeds develop, indicating that the method of
pollination is unusually efficient. The petals of the flowers are about the
size of the Bombus workers and so form a very convenient landing- platform
for most of the visitors (plate 8).
Behavior. — Bombus juxtus is by far the most frequent visitor, although
other species of Bombus and Apis are abundant. The former comes for nec-
tar chiefly, although it usually collects some pollen in the process, while a
few individuals collect pollen alone. Juxtus lands on a petal, pushes out
its proboscis, and finds nectar at the openings between the bases of the two
upper stamens. While sucking nectar, the hind legs move back and forth
in such a way that much pollen accumulates in the corbiculae. This motion
shakes the whole flower, and pollen from anthers and from the hairs covering
the bee's body falls on the recurved stigmatic surfaces. The hairs on the
dorsal and ventral sides of Bombus become dusted with pollen. One
Bombus juxtus marked with white paint was found to return to the same
group of flowers a number of times each hour, as well as day after day.
46 NORMAL AND EXPERIMENTAL POLLINATION.
It followed the same route each time among the flowers. The capacity to
visit many flowers in succession varies in the different species. B. juxtus
visited an average of 36 flowers in succession, while proximus came to an
average of 17. One individual of juxtus visited 116 flowers in one circuit,
and other individuals went respectively to 95, 62, and 52 flowers.
The queen of Bombus proximus lands and takes nectar, but it is so large
that the under tip of the abdomen rubs the style branches and in that way
leaves pollen on them. Much of the pollination is done, however, when the
stamens are shaken. This queen goes from flower to flower for nectar
without making any effort to get pollen. The drone of this species poises
in the air and then lands on the stamens; it takes no nectar, but collects
pollen alone. It scrapes this off with the second pair of legs and from these
on to the third pair, where a heavy load of pollen soon accumulates. When
poised in the air in front of the flowers, it is scraping pollen from the sides of
its abdomen and putting it in the corbiculae. It works very nervously
and rapidly at each flower, but flies deliberately from one to another.
Bombus bifarius, upon landing at a flower, takes a position in which the
tip of the abdomen is between the style and the petals. It comes for nectar
only and seldom touches the recurved styles because of the position of the
abdomen. Apis mellifica lands below and then has to crawl to the opening
of the nectary. It comes for both pollen and nectar, depending upon its
needs at the time. Megachile pugnata, although a much less frequent visitor
to these flowers, is a very effective pollinator. Its fewer visits are doubtless
due to the fact that this species is not so common in this locality. The
abdominal brushes are large and yellow and consist of unusually long, stiff
bristles. It lands in the proper place for sucking nectar and straddles the
style. This places the mouth-parts directly above the opening to the necta-
ries. It pushes out its proboscis and sucks nectar, while the hind legs move
rapidly and scrape pollen on to the abdominal brushes. Halictus (Lasioglos-
sum) sp. hangs on to the anthers with its front legs in some flowers, but
usually twists its abdomen around the base of the filaments while sucking
nectar. This places it in a position to have pollen fall on it, and as the bee
flies away, pollen is jarred loose and falls on the stigmatic surface of the
flower. The brushes on the legs collect pollen as when it hangs on the
stamens. Vespa germanica stands on the petals, reaches in to the nectary,
and sucks nectar. While sipping, Andrena madronitens elevates the tip
of its abdomen in such a way that the scopa rubs the style branches in some
flowers and the anthers in others. This makes it a very effective pollinator
and one that uses the scopa in a different manner from other bees. There
are also long blue-green pollen loads on its legs. Argynnis atlantis comes
for nectar, the tip of its abdomen rubbing the recurved stigmas as it works.
The normal visitors to Chamaenerium are given in tables 31 to 33. In
the first case, 120 flowers on 20 racemes were observed for 30 minutes, in
the second 80 flowers on 12 racemes for an hour, and in the third 140 flowers
on 25 racemes for two successive hour periods.
For an hour period the number of visitors varied from 28 to 4, and the
number of visits from 158 to 728, the average number of visits per insect
ranging from 6 to 50. Bombus contributed 45 of the total of 60 visitors,
and these made 1,391 of the 1,424 visits. A calendar of the normal visitors
CHAMAENERIUM ANGUSTIFOLIUM.
Table 31. — Visitors and visits to normal flowers.
47
Species.
Visitors.
Visits. I Species.
Visitors.
Visits.
Bom bus juxtus
bifarius
appositus. . .
Megachile wootoni . . .
pugnata. . .
Prose-pis basalis
Monumetha albifrons.
Syrphus americanus . .
Total
4
1
1
2
1
3
1
1
56 | Megachile wootoni. . .
3 Prosopis elliptica. . . .
1 Syrphus americanus. .
2
2
1
9
2
1
3
4
3
1
Total
21
413
Bombus juxtus
bifarius
proximus. . .
Syrphus americanus. .
Thanaos martialis . . .
Total
9 to 10
a. m.
12:586
1:27
6:113
1:1
1:1
10 to 11
a. m.
2:173
0:0
2:31
0:0
0:0
14
79
Bombus juxtus
bifarius
proximus. . . .
6
6
4
163
124
114
21:728
4:204
to Chamaenerium during a half-hour period is given below, 9 stalks bearing
85 open flowers being observed.
Calendar 1. — Visits to normal flowers.
8h58m Apis mellifica 3.
9 00 Megachile relativa 8.
9 02 Bombus juxtus 20.
9 06 Megachile vidua 6.
9 08 Megachile texana 15; Bombus occiden-
tals 11.
9 09 Megachile texana 3; relativa 16;
wootoni 10.
9hllm Apis mellifica 4; Bombus occidentalis 15.
9 13 Apis mellifica 3.
9 15 Bombus juxtus 3 ; hunti 5.
9 17 Bombus juxtus 18; Selasphorus platy-
cercus 7; Apis mellifica 5.
9 18 Apis mellifica 4; Bombus hunti 6.
9 35 Bombus bifarius 11.
A summary of the above visitors is given in table 32.
Table 32. — Visitors to normal flowers.
Species.
Visitors and
visits.
Species.
Visitors and
visits.
5:19
3:41
2:24
2:18
2:16
1:6
1:7
occidentalis
2:26
2:11
1:11
Selasphorus platycercus
Total
21:179
All the individuals of Bombus working on one group of flowers during an
hour were collected, with the results given in table 33.
Table 33.
Species.
Workers.
Drones.
4
11
6
32
Total
15
38
48
NORMAL AND EXPERIMENTAL POLLINATION.
These results show that the drones of some species of Bombus gather
nectar, while among the honey-bees this is not the case.
Merritt (1897:4) found the floral structure as described by Mueller
(1883:261), except that she noted no lengthening of the style as the flower
expanded. The style seemed unduly long, to such an extent that the lobes
were often so high that the bee missed them. Only 1 honey-bee in 5 touched
a stigma. Honey-bees and Osmia californica were the chief visitors.
Knuth (1906:441) records a number of variations in the flower mechanism,
and gives lists that show this to be primarily an apid flower.
EXPERIMENTS.
CHANGE OF POSITION.
Racemes inverted. — When the flower-stalk of Chamaenerium is in-
verted, the parts are reversed with respect to the position in which the
bee is accustomed to find them. The style and the stamens now project
upward, leaving only the petals and sepals of the lower half of the flower
as a place to land. These often project backward in a such a way that it is
difficult for an insect to stay on them. Three individuals of Bombus juxtus
went to inverted flowers at different times and tried to discover the nectar,
but flew away without finding it. In another experiment wet cotton was
tied over the cut end of three racemes to keep the flowers from wilting, and
each one inverted was fastened alongside a normal cluster. Table 34
gives the results of an hour's observation on two different days, an equal
number of normal and inverted flowers being used in each case.
Table 34. — Visitors and visits to normal and inverted racemes.
Species.
Experiment 1.
Experiment 2.
Normal.
Inverted.
Normal.
Nectar
found.
Nectar
not found.
Inverted.
Horizontal.
Bombus juxtus
proximus. . .
Halictus pulzenus.. . .
6:33
0:0
2:1
3:8
1:2
0:0
3:8
0:0
0:0
3:8
0:0
0:0
6:30
0:0
0:0
8:48
1:1
0:0
Total
8:34
4:10 3:8
3:8
6:30
9:49
In the first experiment as many individuals of Bombus juxtus visited
inverted as normal stalks, but the number of flowers visited was only half as
great. In the second, the visitors to the changed clusters were four times
as numerous and the number of flowers visited almost 10 times as great.
However, this was due largely to the presence of the horizontal racemes,
the visitors and visits to the inverted ones being much the same for the
two cases.
MUTILATION.
Floral envelopes removed. — This mutilation makes the whole raceme
much less conspicuous even than when in bud, and gives it a pale, feathery
appearance not at all like the normal one. The 24 mutilated stalks were
4 feet away from those bearing normal flowers (plate 17).
CHAMAENERIUM ANGUSTIFOLIUM.
Table 35. — Visitors to flowers with floral envelopes removed.
49
Species.
Visitors.
11:136
1:1
1:1
1:1
Total
15:140
Bombus juxtus readily distinguished between buds and these mutilated
flowers, for it never stopped at the former.
Upper petals and the included sepal removed. — This sepal is just
behind the opening to the nectary and looks as if it might be a guide to
it. Bombus juxtus went to flowers with these parts removed and to normal
flowers indiscriminately, just as they happened to be in its path.
Stamens and style removed. — Bombus juxtus visited flowers with
these parts removed and found the nectar at once. It went to three
flowers in succession, but had some difficulty hanging on.
The following notes made during 5 minutes of observation indicate that
Bombus juxtus took little notice of all the above changes. An equal number
of normal and mutilated flowers were under observation.
10h20m Bombus juxtus flew over flowers with
the corolla removed, but stopped
at 2 with the stamens alone gone.
A second one stopped at 2
flowers with the petals gone and
at 3 normal ones.
10 21 B. juxtus, 2 flowers with stamens gone.
10h22m B. bifarius, 3 flowers with the upper
3 petals gone and 3 normal.
10 23 B. juxtus, 4 normal and then 2 flowers
with the upper petals gone.
10 24 B. juxtus, 3 flowers with the upper
petals gone and 2 normal.
10 25 B. juxtus, 5 normal.
The relative numbers of visits made by the various species of bees to the
different kinds of mutilated flowers, as well as to the normal ones, are shown
in table 36. On July 17 and 18, 10 normal flowers and 5 mutilated ones of
each type were used, one or more of each being placed in each raceme; the
time of observation was 1 hour. For the next two periods of an hour and
a half each, 4 flowers of one kind were arranged on each stalk.
The results obtained in this experiment relate chiefly to the behavior
of Bombus, as the other 4 genera made but 17 of the 210 visits recorded.
Of the 193 visits by bumble- bees, B. juxtus made 173 and B. bifarius but
20. The actual number of visits to normal and mutilated flowers is nearly
equal, but the normal flowers were a third as numerous and hence about
twice as attractive. However, the contrast between the different types of
mutilated flowers is so sharp as to indicate an intentional selection. Thus,
flowers with the perianth, stamens, and styles removed received but 6
visits out of a total of 114 for mutilated flowers, while those with either
stamens or styles excised obtained less than half as many as those with
petals or both sepals and petals removed. On the other hand, the visits
to both the latter were a third less tnan to the flowers with the stamens and
styles excised but the perianth intact. While the results are not entirely
50
NORMAL AND EXPERIMENTAL POLLINATION.
in accord, it is significant that 166 visits were made to flowers with corollas
in contrast to 44 to those without.
Table 36. — Visits to normal and mutilated flowers.
Time.
Species.
Normal.
Petals
off.
Sepals
and
petals
off.
Stamens
excised.
Styles
excised.
Stamens
and styles
excised.
Perianth,
stamens,
and styles
off.
July 17
July 18
July 21
July 25
13
55
1
0 12
12 0
1
7
7
0
12
17
0
0
Do
Total
68 | 12 12 j 8 7 29
0:68
2
4
1
0
0
0
2
1
0
0
1
0
0
0
0
2
3
0
3
0
0
Monumetha albifrons . . .
Megachile wootoni
Total
Bombus juxtus
bif arius
Andrena madronitens . . .
Halictus pulzenus
7 | 0 | 3 1
0 5
3:12
18
1
0
2
5
1
1
3
0
0
0
0
0
0
0
0
0
0
0
2
15
2
0
3
0
0
Total
Grand total
21 | 8 |. 3 | 0 | 0 20
3:34
96 j 20 1 18 ! 9 j 7 54
1
6:114
In the following experiments one raceme was left normal and one mutilated
by each of the various types of excision. In the tables the first number
in each column represents the number of visitors, the second the number
of flowers visited. The first observations were made on July 19 from
9h05m to 10h05m a.m. and the second on the same date from 10h05m to
12h05m a.m.
Table 37. — Visits to normal and mutilated flowers.
Species.
"3
g
o
B T3
Petals
and
sepals
excised.
l]
S "2
Stamens
and
styles
excised.
Ovary
alone
left.
Bombus juxtus
proximus
Megachile wootoni ....
Total
43:157
3:6
2:3
20:89
0:0
0:0
22:99
0:0
1:2
40:165
2:12
0:0
49:143
4:10
0:0
38:132
1:2
0:0
212:785
10:30
3:5
48:166
20:89
23:101
42:177
53:153
39:134
225:820
Bombus juxtus
proximus
Megachile wootoni ....
Monumetha albifrons. .
Total
27:179
3:18
2:8
1:3
14:211
1:2
0:0
0:0
33:208
15:213
Bees flying to the community usually alighted upon flowers with corol-
las. Once landed, they passed on to the flowers in order, with little
CHAMAENERIUM ANGUSTIFOLIUM.
51
regard to the type of mutilation. It is significant that the removal of the
petals or the perianth reduced the number of visitors more than half in
every case, and with a single exception had a somewhat similar effect
upon visits. The flowers with stamens or styles or both excised were treated
essentially as normal ones, but those with ovary and nectary alone left
received practically five times as many visitors and visits, probably owing
to the greater fragrance and accessibility of the nectar.
ARTIFICIAL AND PAINTED FLOWERS.
Crepe-paper corollas. — Red, blue, green, white, or yellow corollas
were made to simulate and replace the normal ones, leaving the stamens
and style intact. No bees went to the flowers with crepe corollas, not
even to those in which a drop of honey was placed on the nectary. At
another trial of crepe corollas no visitors were attracted until a drop of
diluted honey was put on the nectary, and even then but one bee, Bombus
juxtus, came to the flowers for a chance visit. In another experiment,
half of the flowers on the raceme were left normal and paper corollas were
alternated, as it was thought that the habit of going from one flower to
the next would cause some of the bees to stop at those with artificial corollas.
In spite of this, not one bee stopped at a flower with crepe corolla, although
they flew low to inspect them.
Painted corollas. — Natural corollas were painted with water-colors
on the upper side. While the texture of the petal is such that the colors
do not spread uniformly over the surface, they show up very well. Table 38
gives the results of these experiments, 5 flowers of each color and 10 normal
ones being used in each case. The first observations were made on July 21
from 8 to 10 a. m. and the second on the following day from 9 to 10 a. m.
Table 38. — Visits to normal and painted flowers.
Species.
Normal. Red.
White.
Yellow.
Green.
Blue.
51
0
0
0
10
0
0
0
10
1
1
1
10
0
0
0
16
0
0
0
10:56
0
0
0
Syrphus americanus
Thanaos martialis
Total
51
10
13
10
16
10:59
48
3
1
0
0
10
0
0
0
0
6
0
0
0
0
6
2
0
1
7
0
0
0
0
19:48
0
0
0
0
Megachile wootoni
Monumetha albifrons
Syrphus americanus
Total
52
10
6
10
7
19:52
103
20
19
20
While there were a few more visits to the painted than to the normal
flowers, the former were 2.5 times more numerous and the actual ratio of
normal to painted is 103:44. Bombus juxtus made 203 of the total of 214
visits to all kinds of flowers. It showed no pronounced color preference,
52
NORMAL AND EXPERIMENTAL POLLINATION.
though blue led with 29 visits, followed by green 23, red 20, white and yellow
16 each. Oddly enough, white and yellow were the only colors sought by
the other species, but the numbers are too small to be significant. The
behavior of one Bombus juxtus was noted as it worked from flower to flower
and the following course was observed: blue, normal, hovered over green,
normal; next stalk, blue; third stalk, blue, normal, blue, normal.
ADDITION OF NECTAR AND ODOR.
Honey. — When a drop of honey was placed at the opening to the nectary
in a group of normal flowers, Apis mellifica found it at once and stayed at
the flower 6 minutes. In another experiment, honey was placed on every
flower on one plant, but the number of visitors was no more numerous than
to the normal plants adjoining. The bees merely happened to visit it and
were not especially attracted by the honey. However, when Bombus
juxtus did find the latter, it stayed at the drop until this was consumed.
When the drop of honey was put on the style branches, Bombus sucked
it up as readily as when it was over the openings to the nectaries.
Odor. — Flower perfumes were put on cotton-wads and these then
wound around the several pedicels under the calyx. The groups of flowers
on which the different odors were placed were arranged with respect to the
direction of the wind so as to make the odor in each case as distinctive as
possible. Twelve flowers of each odor were used in addition to 24 normal
ones. The two sets of observations were made during succeeding hours on
August 9.
Table 39. — Visitors and visits to perfumed flowers.
Species.
Normal.
Violet
perfume.
Carnation
perfume.
Crab-apple
perfume.
8:75
7:51
4:40
1:3
7:26
3:10
4:18
0:0
1:3
1:5
1:3
0:0
Total
20:169
14:54
3:11
15:111
11:52
9:86
0:0
5:30
2:3
0:0
0:0
16:71
8:29
4:14
1:2
1:2
9:24
1:1
0:0
Total
35:249
7:33
29:116
11:27
55:418
21:87
32:127
11:27
The flowers with carnation were shaded more than those with violet in
the first part of the experiment, which probably accounts for the few visits.
During the next hour of observation, carnation was in a different location
and many more visitors came to it. The number of visitors per flower was
practically the same for normal and for perfumed stalks, but these averaged
only 4 visits each to the perfumed flowers in contrast to 8 each for the
normal ones, indicating again something of the usual disturbance caused
by strange odors.
CHAMAENERIUM ANGUSTIFOLIUM.
53
Perfumes. — Either "Love me," "Three flowers," "Poudre azure," or
camphor-ball powder was sprinkled over the nectaries on half of the flowers
on each of four stalks. Bombus juxtus was the only visitor during the
hour of observation (table 40).
Table 40. — Visits of Bombus juxtus to scented flowers.
Scented powder.
Normal.
Scented.
Inspections
of scented.
6:9
2:6
1:3
0:0
1:2
0:0
0:0
0:0
4:6
3:8
1:1
1:1
Total
8:18
1:2
9:16
The difference in behavior as compared with that shown in table 39 is
probably to be explained by the fact that the appearance of the flower was
visibly changed by the powder. This also seems to furnish the reason for
the large number of inspections indicated in the last column.
Flavoring extracts. — Extract of vanilla, lemon, almond, or peppermint
was poured on absorbent cotton and a small wad wrapped around the ovary
under the calyx. This changed the odor of the flower, but did not affect
its appearance. Visitors to normal flowers were recorded only for the first
experiment. All the observations were made on August 8, the first two
Table 41. — Visitors and visits to flowers scented with extracts.
Species.
Normal.
Vanilla.
Peppermint.
Lemon.
Almond.
9:30
7:18
1:2
1:5
0:0
1:1
5:20
1:5
1:1
3:12
3:12
1:1
3:10
0:0
1:1
Total
17:50
2:6
7:26
7:25
4:11
1:2
0:0
1:1
1:2
0:0
0:0
0:0
0:0
0:0
4:9
2:4
2:3
Total
2:3
1:2
0:0
8:16
3:7
2:5
0:0
0:0
0:0
1:1
1:2
0:0
0:0
8:10
9:10
1:2
Total
5:12
1:1
1:2
18:22
2:3
0:0
0:0
1:2
2:4
3:7
0:0
0:0
0:0
1:2
0:0,
6:6
Total
2:3
6:13
0:0
7:8
11:24
15:42
8:27
37:57
54 NORMAL AND EXPERIMENTAL POLLINATION.
for hour periods from 9h35m to llh35m in the morning and the next two for
an hour period from 2 to 4 in the afternoon.
Both visitors and visits were slightly though not significantly greater
to the scented flowers. The grand totals for the different odors are much
alike, except in the case of almond. While visited least in the first experi-
ment, its total was 2 to 4 times greater than for the others.
SUMMARY.
The inversion of the flower resulted in about half of the visits being
fruitless at first, but later both inverted and horizontal flowers received
many more visits than the normal. Mutilated flowers in general were about
half as attractive as normal ones, but they differed greatly among them-
selves. The removal of the corolla reduced visits from a half to a fourth,
in spite of the marked habit of Bombus in visiting Chamaenerium flowers
in order from the bottom upwards. On the other hand the removal of all
flower parts except the ovary and the nectary increased the visits 5 times
over the normal, doubtless because the nectar was more fragrant and
accessible, thus permitting the bees to work more rapidly. Artificial
flowers of paper were often inspected, but they received only a single visit,
in spite of the addition of honey. Painted ones were about half as attractive
as normal flowers, suggesting that the neglect of artificial flowers was due to
small differences in form and texture, since the colors were unnatural in
both cases. Blue was the preferred color, but not decisively so. Honey
did not attract greater numbers of bees, while scented powders almost
eliminated visits, the number of inspections equaling the visits to normal
flowers. The number of visitors was the same for blossoms perfumed with
other flower odors and normal ones, but the visits were about half as many
to the former. Flavoring extracts seemed to increase attraction slightly,
but the significant fact was the marked effect of almond in augmenting the
number of visitors.
PACHYLOPHUS CAESPITOSUS.
NORMAL POLLINATION.
Habit and structure. — This species possesses the largest and most
fragrant flowers of any in the region. It is white in color the first evening,
becoming pink the next morning. When the calyx
is normal, the flowers open between 5 and 7 in the
evening and the process usually requires but 2 to 7
minutes, the unfolding of the petals being so rapid
that the movement is easily seen. The style and
stamens are covered with very small black diptera
when the flower opens. At this time the anthers are
dehiscing and the stigmas are receptive. The under
surface of the stigma lobes is covered with pollen, but
the receptive surface is free from it. The tube of
the calyx is about 10 cm. long and is filled with nectar
for more than half its length at the time of opening
(plate 9). The amount of nectar varies considerably,
as is shown by its weight in several flowers. These were picked at 7
Weight of
nectar.
gm.
1
0.0135
2
.0430
3
.0065
4
.0280
5
.0475
6
Av
.0355
.0290
PACHYLOPHUS CAESPITOSUS. 55
o'clock in the evening just after opening, but before visitors were ob-
served. The absence of pollen on the stigmas furnished additional evidence
that they had not been visited. The nectar was blown out of the tube on
a glass slide and weighed immediately.
Robertson (1892:272) has given a list of visitors to Oenothera biennis
and 0. fruticosa, and described the structure of the latter. The stigma
exceeds the anthers and is inclined to the lower side so that it strikes the
ventral surface of visiting bumble-bees. The tube measures 14 to 20 mm.
and can be drained only by the largest bees, though shorter-tongued ones
can reach a little of the nectar when the tube is fullest. Hitchcock (1893:
362) has observed that the stigma in Oenothera missouriensis may protrude
from the bud as early as 2 p. m., though the flower opens fully only during
the latter part of the afternoon. The narrow calyx-tube, about 11 cm.
long, is often half filled with nectar. With the exception of ants, the
only visitor was a sphinx-moth, Celerio lineata, which came in abundance
just before 8 p. m., but ceased its visits at dark. The insect pushed its
head into the throat as far as possible, but was able to reach only the upper
portion of the nectar, and was caught in the flower by its endeavor to secure
more. Merritt (1897:4) has noted that the flowers of 0. biennis open
about 6 p. m. and close about 9 a. m. While the stigmas are 2 to 6 mm.
beyond the anthers, a slight breeze is sufficient to bring them into contact.
By 7h30m p. m. pollen was found on nearly all the stigmas, though no night
moths were seen. The odor is faint, but the large, pale flowers are con-
spicuous at night. In 0. californica the flowers at 6,000 feet are always
fully open by 5 p. m. and remain conspicuous and fragrant throughout
the night. Honey-bees collect pollen as soon as the flowers open and
usually strike the stigmas first, since the latter slightly exceed the anthers.
Nectar is not abundant at night, but by morning it is sometimes an inch
deep in the tube; the stigmas are visibly pollinated and the pollen is gone
from the anthers. Longyear (1909: 105) has described the opening of the
flower and its pollination in Oenothera pinnatifida.
Behavior. — Three species of large hawk-moths come to the flowers
very soon after they open each night, namely, Protoparce quinquemaculata,
Hyloicus separatus, and Celerio lineata. The first two have a proboscis
9.5 to 10.5 cm. long, which enables them to reach to the bottom of the deepest
tube. It was found that each moth stays at a newly opened flower until
it obtains all the nectar that it can reach. Protoparce worked as long as
38 seconds at such flowers, but only 3 to 10 seconds at those that had been
previously visited. Celerio has a much shorter proboscis, about 4.5 cm.
long, and is limited to the nectar-supply in the upper half of the tube.
These moths fly swiftly through the air to a group of evening primroses,
when they stop over them, unroll the proboscis and hover in this position,
gradually descending until the tip of the ligule is above the opening to the
tube. After a few trials, the proboscis is gradually pushed down the tube
Until it reaches the nectar, after which it moves downward slowly as the
nectar is sipped up. When it has exhausted the nectar, the moth rises above
the flower and passes to the next. While poised in the air above the
flower after a visit, its proboscis is covered with large masses of pollen
and viscin threads at the point of contact with the anthers. When it dips
56
NORMAL AND EXPERIMENTAL POLLINATION.
into the next flower, these usually come in contact with the stigmatic
surface, which acquires more and more pollen with each visit. The hawk-
moths continue to come for an hour or so after dark, and perhaps later if
nectar is still available. They are not frightened by lights being thrown
on them and in consequence their movements can be readily followed by
means of a flashlight.
EXPERIMENTS.
ARTIFICIAL FLOWERS.
Crepe-paper flowers. — Artificial flowers were made of crepe-paper
and provided with calyx-tubes of glass. Some of these were coated with
paraffin to stiffen them and others were shaped by stretching the paper.
The calyx-tube was filled with a sirup made of beet-sugar, and a drop of
nectar drawn from a flower placed at the top. The calyx-tubes of natural
flowers from which the nectar had been taken were then filled to the top
with sugar solution. In no case were the crepe-paper flowers visited or
even inspected, a fact difficult to explain, since the moths stopped to
inspect a white net and white pieces of paper lying near. The normal
flowers filled with sugar sirup were popular, and this was sipped as far down
as available.
Petals obscured. — Flowers were covered with disks of green crepe-paper
with a hole cut at the center to allow the stamens and style to project and
also to permit access to the nectary. Thus, while the disk covered the white
petals, it did not confine the odor. No moths or other visitors stopped at
these flowers, although the calyx-tube in each case was well supplied with
nectar, while they came regularly to all the normal flowers among which
the experimental ones were located. They also stopped at the disks of white
paper that were grouped among the normal flowers. As the supply of flowers
became greatly reduced at the end of the season, frequent inspections were
made of the white-paper flowers.
MENTZELIA MULTIFLORA.
NORMAL POLLINATION.
Habit and structure. — This species differs from most of the others
studied in that the flowers open at about 4 o'clock in the afternoon and
close about 8 at night. There is a distinct advantage in opening at this
time, since the nectar supply is running low in most of the flowers visited
during the day. About the time these flowers should open, several species
Table 42. — Visitors and visits to normal flowers.
Species.
First
day.
Second
day.
4: 42
6: 55
2: 16
3: 9
5: 11
5: 60
7:172
2: 9
occidentalis
Total
15:122
19:252
MENTZELIA MULTIFORA.
57
of Bombus and Apis are seen hovering around them, landing at the buds
and inspecting them carefully. When the flowers open, the visitors appear
at once in fairly large numbers and immediately commence collecting
both pollen and nectar. The number grows less as the sun goes down, but
persistent visitors are present and working until dark. This is particularly
true of Bombus occidentalis. Table 42 gives the list of visitors to normal
flowers on succeeding days, the first from 5h00m to 6h40m and the second
from 5h00m to 5h55m in the afternoon.
EXPERIMENTS.
CREPE-PAPER COROLLAS, AND COMPETITION.
Crepe-paper corollas. — Red, white, yellow, green, and blue paper
corollas were fastened below the stamens after the petals were cut off.
This was done about 4 p. m., when the buds were beginning to open. Indi-
vidual flowers of Chamaenerium and Geranium were also paired with these of
Mentzelia in the group under observation, so that competition studies could
be made at the same time. Before the calendar given below was made
the flowers were observed as they opened. At that time the visitors were
already in the vicinity, keeping watch of the flowers. In putting on the crepe
corollas the stamens were exposed, and nectar and pollen made accessible.
As a consequence, paper flowers of all colors were visited, yellow more than
the others and green less often, doubtless because of the resemblance to
the leaves. The yellow flowers so closely resembled the normal ones
Calendar 1. — Visits to
S'W Apis mellifica 1.
5 01
5 15
5 16
521 B
5 25
5 30
Bombus juxtus 1.
B. juxtus 1.
B. occidentalis 2 Mentzelia of Gera-
nium pairs, 6 Mentzelia of
Chamaenerium pairs,
juxtus 4 Mentzelia of Chamae-
nerium pairs.
B. occidentalis 1.
B. bifarius 32; inspects all crepe and
paired flowers.
B. bifarius 27; inspects paired Chamae-
nerium.
normal and crepe flowers.
5h45m B. bifarius 50; 7 Mentzelia of Chamae-
nerium pairs.
Apis 3.
B. bifarius 48; inspects all crepe and
paired flowers.
B. bifarius 1.
B. juxtus 1; red crepe 1, Mentzelia
21, 33.
Apis 5.
B. bifarius 15.
5 52
5 55
6 02
6 15
Table 43. — Summary of Mentzelia calendar.
Species.
Normal.
Geranium
pair.
Chamae-
nerium
pair.
Crepe
corollas.
3:9
6:173
5:57
1:1
0:0
2 (i all)
0:0
2 Mentz.
0:0
3 (i all)
7 Mentz.
4 Mentz.
6 Mentz.
0:0
2 (iall)
lr
0:0
Total ,
15:240
2 Mentz.;
2 (i all)
17 Mentz.;
3 (i all)
1 r:2 (i all)
i = inspected; r = red.
58 NORMAL AND EXPERIMENTAL POLLINATION.
that they were hard to find after these had opened, and this similarity
doubtless explains the attraction of more visitors to them. After the normal
flowers opened, those with artificial corollas were practically deserted, as
the following calendar shows. Visits to normal flowers are indicated by
the numeral alone.
SUMMARY.
In spite of the numerous visits to the normal flowers, but one crepe flower
received a visit after the normal ones opened. Not a single one of the paired
Geranium or Chamaenerium flowers was visited, though 19 Mentzelia flowers
of such pairs were. Bombus bifarius was the only species to inspect the
artificial or competing flowers, Apis not even visiting Mentzelia when
paired with these. This experiment also included false flowers made by
pasting petals of Geranium or Chamaenerium over those of Mentzelia, but
as these were noticed only by one bifarius, which stopped at a false Chamae-
nerium, they were not included in calendar or table.
FRASERA SPECIOSA.
NORMAL POLLINATION.
Habit and structure. — The plants are 3 to 4 feet tall and wand-like,
growing on sunny slopes or in open woods. The flowers form a close
cluster often 2 feet long, but the number of those open at any one time is not
large and they must be sought throughout the inflorescence. When the
flower opens, the petals are curved so that the corolla is cup-shaped, but
as the anthers mature, they are flattened. At first, the filaments are
vertical or bend outward slightly, but they diverge as the anthers shed
singly or by pairs; Two rows of hairs on a tongue-like projection extend
over the nectaries and protect them (plate 10).
Behavior. — Bombus juxtus lands on the petals with its head pointing
toward the pistil. Its ligule is pushed under the hairs above the nectary,
and it sips in turn from each. In doing this the anther which extends
between the two petals touches the side of its abdomen. Occasionally this
bee stands with the abdomen over the style and its head pointing toward
the outside of the flower. When the anthers are about through dehiscing,
the petals close up, the corolla becomes cup-shaped again, and the stamens
project between the closed petals. Nectar is still being produced, and in
order to get it B. juxtus walks up the outside of the petals and dips its head
into the inside of the cup. In doing this, the side of the abdomen and head,
which have collected pollen from the dehiscing anthers, rubs pollen against
the now receptive stigmas. Halictus pulzenus walks over the pistils, then
up the filaments, and with its front legs and head collects pollen from the
individual anthers. Clisodon terminalis also comes to this flower for pollen
rather than nectar. It stands on its hind legs and collects with the front
legs and head. Apis mellifica lands in such a manner as to reach and empty
the nectaries in rapid succession. In one case a honey-bee took hold of the
dehiscing anthers with the front legs, and, while suspended, opened each
one, scraping out the pollen and placing it on the hind legs.
Fifty flowers were under observation on the three days recorded in
table 44.
FRASERA SPECIOSA.
Table 44. — Visitors to normal flowers.
59
Visitors,
35 min.
Visitors,
90 min.
Visitors,
90 min.
Apis mellifica
Bombus juxtus. . .
Andrena crataegi.
Halictus pulzenus
Total
97
Robertson has discussed the pollination of Frasera carolinensis (1893:48)
and given a list of visitors (1895:142).
EXPERIMENTS.
MUTILATION.
Types. — Flowers were modified in the following ways: (1) by removal
of the stamens; (2) removal of petals to the nectary; (3) removal of nectary
hairs; (4) removal of hairs and pads, leaving only the nectar pit; (5) removal
of pistil; (6) by splitting the petals. Observation during an hour on July 28
gave the results shown in table 45 when 30 normal flowers and 5 of each
type of mutilation were used.
Table 45. — Visits to normal and mutilated flowers.
Species.
Normal.
Nectary
intact ;
petals
off.
Stamens
off.
Pistil
off.
Hairs
and
sepals
off.
Hairs
off.
Petals
split.
Apis mellifica
8
6
0
1
2
2
0
0
3
5
0
1
1
0
0
0
0
0
0
0
3
1
3
0
2
1
0
0
occidentalis
Andrena madronitens. . . .
Total
»
4
9
1
0
7
3:24
While the number of visits is too small to permit definite conclusions,
mutilation increased them somewhat, probably in consequence of making
the nectar easier of access and allowing the odor to escape more readily.
ARTIFICIAL AND PAINTED FLOWERS.
Crepe-paper corollas. — The flowers of Frasera are gray-green with
blackish lines on the surface. In color and form they are not conspicuous,
though the upright brushes of hairs above the nectaries help to make
them somewhat so. Crepe-paper corollas of red, green, blue, yellow, or
white were used to disclose whether bright-colored petals would make
them more attractive. The petals of the flowers were removed before the
crepe- corollas were added, and the latter made to resemble them as closely
as possible. The hairs above the nectaries were left intact, so that the
general form of the flower was the same, although no nectar was present.
Bombus juxtus stopped at the yellow crepe flowers and put out its proboscis
60
NORMAL AND EXPERIMENTAL POLLINATION.
at the place where the nectar should be. It felt around for the nectary,
went to the next petal and did the same thing, then to a red-crepe flower
and repeated this behavior. Apis mellifica avoided the artificial flowers
altogether.
Painted corollas. — Flowers were painted blue, yellow, red, green, or
purple with water-colors. The following calendars show the flowers
visited by the different bees; visits to normal flowers are shown by number
alone.
Calendar 1. — Visitors to painted flowers.
10h45m Apis mellifica, 1, blue, 1.
10 51 Apis mellifica, yellow, yellow, 2, blue, 1.
Andrena crataegi, 1, red, 3.
Apis mellifica, 1; Bombus juxtus, 1,
10 54
10 58
llh05m Apis mellifica, 2, blue.
11 10 A. mellifica, 1, blue, 3, blue; Bombus
juxtus, 1, 3, 2 yellow, 1, red, 2,
green, 1, blue, green, blue, 1,
green, 1.
11 20 Bombus juxtus, 1; Apis mellifica, red, 1.
On the next day the same experiment was repeated with the following
results :
Calendar 2.
11 00 Apis mellifica, yellow, red, 1.
10h47n
10 49
10 52
10 56
10h27m Apis mellifica, blue, 4.
10 28 A. mellifica, 6, 1, red, 3.
10 30 A. mellifica, blue, 5; Bombus juxtus, 6.
10 38 Bombus juxtus, yellow, blue, 1 ; Apis
mellifica, 6, blue, 1, blue, 4.
10 41 Apis mellifica, green, red, 1.
10 43 Apis mellifica, 3.
10 44 Halictus pulzenus, 3; Apis mellifica,
blue, 5.
The results shown by these two calendars are summed up in table 46.
The first section represents the visits during a 35-minute period and the
second those made on the next day, but covering a period of 90 minutes;
20 normal flowers and 5 of each color were used.
Bombus juxtus, 1; Apis mellifica,
yellow, green, 1.
Apis mellifica, red, yellow, 1; Halictus
pulzenus, 1.
Apis mellifica, 1, blue, 1, red, 1.
Apis mellifica, red, yellow, 8; Bombus
juxtus, 6, 6, red.
10 58 Apis mellifica, 1.
Table 46. — Summary of visits to painted flowers.
Species.
Normal.
Red.
Blue.
Purple.
Yellow.
Green.
14
11
2
1
5
2
0
0
0
0
3
2
0
0
4
0
4
Total
29
4
7
0
5
4:20
53
20
4
6
1
0
6
1
0
0
0
0
3
1
0
2
0
0
Total
77
7
7
0
4
2:20
106
11
14
0
9
6:40
The total number of visits to the painted flowers was less than half that
for the normal. The behavior was decidedly different for the two days,
the bees making two-thirds as many visits to the painted as to the normal
on the first, and only a fourth as many on the second. The most striking
FRASERA SPECIOSA. 61
fact with reference to the selection of colors was that red stood next to blue,
while purple, which often occupies this place, was completely ignored.
False corollas. — Blue corollas were made from petals of Campanula,
which were cut to shape and glued on the sepals. The nectaries and pro-
tecting hairs were left intact, but the remaining portions of the Frasera petals
were removed. Fourteen modified and 14 normal flowers were grouped on
the stalk under observation. The first Bombus juxtus to visit the blue
flowers had great difficulty in finding the nectary, as well as a place on which
to stand. The next one landed on the blue petals and thrust out its ligule.
At 9 successive flowers it pushed back the petals and tried to find the
nectary between these and the sepals. At each flower visited it eventually
found the nectar, but not readily, as it was accustomed to standing on the
petal and facing the pistil, while with the normal petal cut away from around
the nectary the visitor had to stand on a sepal. In three cases it finally
straddled the pistil and dipped its ligule into the nectaries. Bombus juxtus
showed no objection to the modified flowers, but Apis mellifica merely
inspected them without landing.
Calendar 3. — Visits to flowers with Campanula petals.
9h30m Bombus juxtus, 1 blue.
9 42 Apis mellifica, 4; Bombus juxtus, 3.
9 43 Bombus juxtus, 3 blue.
9 48 Bombus juxtus, 4; Apis mellifica, 6.
9 51 Apis mellifica inspects blue, 3, inspects
blue, 2.
9 55 Bombus juxtus, 4 blue.
10 00 Bombus juxtus, 6 blue, 1. This bee
had trouble finding the nectar;
it stood on the blue petal and
sipped at the adjoining nectar,
then walked around the pistil,
taking nectar from each of the
others.
10 02 Bombus juxtus, 2, 6; Apis mellifica, 3.
10h05m B. juxtus, 2 blue; Apis mellifica, 1.
10 12 B. juxtus, 2, 9, 6 blue, 4; Apis mellifica
inspects blue.
10 17 B. juxtus, 2, 5 blue.
10 23 Apis mellifica, 6, inspects blue, 3.
10 27 A. mellifica; Bombus juxtus, 3.
10 38 Bombus juxtus, 5 blue, 5, 3 blue, 4.
10 42 B. juxtus, 2, 4 blue, 1.
10 45 B. juxtus, 5 blue, 2.
10 54 B. juxtus, 6 blue, 1, 2 blue.
10 58 B. juxtus, 3, 2 blue, 6, 2 blue; Apis
mellifica 1, inspects blue.
11 04 Apis mellifica inspects blue.
11 06 A. mellifica 4.
A summary shows that Bombus juxtus visited 60 normal and 56 blue
flowers, while Apis mellifica visited 37 normal and inspected 6 blue flowers,
but stopped to visit none of them.
ADDITION OF NECTAR AND ODOR.
Nectar. — Honey-drops were placed where the nectaries would be in
normal flowers, and were also added to those with crepe corollas. Bombus
juxtus and Apis mellifica were working constantly on the flowers in this
location. In normal flowers they went directly to the nectaries, sipping
nectar from all four, but the paper flowers were avoided, even though they
had honey-drops on them. The honey-drops on normal flowers were
visited by 2 Apis mellifica and 1 Bombus juxtus, but they were not sufficiently
attractive to bring about a return visit.
SUMMARY.
Mutilation increased visits somewhat, owing chiefly to the behavior
at the flowers with the stamens or the nectary hairs removed. The response
of Bombus and Apis to artificial flowers was fairly typical, the one working
on them industriously, the other ignoring them entirely. In the case of
62
NORMAL AND EXPERIMENTAL POLLINATION.
painted flowers, both went readily from these to the normal or the reverse,
the ratio for Apis being 27:67 and for Bombus 12:31, or almost identical
in value. The false flowers made of Campanula petals were treated like
the paper ones, Bombus visiting practically as many of them as the normal
and Apis merely inspecting them without landing. Honey received little
attention from either, the paper flowers with honey-drops being entirely
ignored.
MERTENSIA PRATENSIS.
NORMAL POLLINATION.
Behavior. — The flowers are pendant and have a tubular corolla with
a bell-shaped expansion below (plate 11). The corolla-tube is only about
15 mm. long, but both Vespa germanica and Bombus juxtus often bore holes
at the base of the corolla and steal nectar. They land on the corolla-tube
with their hind legs toward the corolla mouth. Juxtus carries yellow pollen
on its legs, probably from Fragaria or Rubus strigosus previously visited,
but it does not gather pollen at Mertensia. It comes to this for nectar,
and upon landing it hangs on to the pendant corolla-tube, pushes out its
ligule, and at once takes nectar. Edwardsi enters the flower, resting on the
lower lobe of the corolla, and its head is pushed into the tube for the nectar.
While the stigma comes in contact with the abdomen and receives the
pollen found there, its head brushes against the dehiscing anthers and col-
lects pollen. Osmia pentstemonis is so eager for nectar that it opens buds
and pushes its head into the corolla-tube to secure it. Andrena madronitens
usually rifles flowers of nectar when a hole has already been made. Other-
wise, it pushes its head directly into the tube, bending at the thorax
so that the abdomen is outside the corolla-tube and pointing upward.
Halictus pulzenus lands at the corolla mouth, eats pollen, and then goes to
the base of the corolla to puncture it for nectar. Other species of Halictus
push far into the corolla tube, where they scrape pollen so vigorously with
the hind legs that it flies out of the opening. While doing this, the head
is very near the nectar, probably sipping it, and the hind legs are resting on
the anthers. Halictus (Evylaeus) sp. bends over the edge of the corolla -tube,
while its head is in contact with the stamens, and touches the stigma as it
leaves the flower. Dejeania vexatrix lands and rests its legs on the lower
edge of the petals, while it pushes its head into the corolla-tube and sucks
Table 47. — Visitors to normal flowers.
Species.
Observation.
Species.
Observation.
1
2
1
2
49
6
4
3
1
2
0
0
0
4
0
3
0
1
Halictus (Evylaeus) sp
Monumetha albifrons
0
0
0
0
0
Pseudomasaris vespoides
Total
70
8
CASTILLEIA MINIATA. 63
nectar. Acmaeops longicornis enters the corolla and eats pollen, which it
also collects and deposits as it moves slowly about. Selasphorus platycercus
visits and pollinates Mertensia as it flies very rapidly from flower to flower.
In table 47 two lists of visitors are given. The first represents those
present during a two-hour period in the midst of the flowering season, the
second those for an hour period at the end of the season. In each case 100
flowers were under observation.
During another hour's observation toward the end of the season, 15
individuals of Bombus juxtus made 167 visits to 140 flowers. The only
other visitors were two wasps that robbed the flowers.
EXPERIMENTS.
MUTILATION.
Changes of corolla. — The petals were split apart, the corolla made
irregular, or the upper petals were removed in various flowers. The only
visitors during the period of observation were 4 individuals of Halictus sp.,
which went to the flowers with the front half of the petals removed. They
paid no attention to the exposed stamens and nectar, but pierced the small
corolla-tube in the usual place, as when robbing normal flowers.
CASTILLEIA MINIATA.
NORMAL POLLINATION.
Habit and structure. — The bracts inclosing the flowers are vermilion
in color and arranged in a closely massed spike. As the individual flowers
mature they elongate rapidly and take an ascending position. The first
pair of anthers ripen while the flower is still very small, about one-third
the mature size. The lower lip is much suppressed and serves to open the
slit when pulled down. When the anthers are about through dehiscing,
the style elongates, grows through the tip of the corolla-tube, and then
bends downward. To obtain nectar, visitors must push into the slit of the
corolla and reach to the base of the tube. In doing this the head comes in
contact with the anthers in young flowers, while in the more mature ones
the stigma bends downward so that it rubs the back of the visitor (plate 13).
Behavior. — Halictus (Evylaeus) sp. transfers pollen from the under part of
its abdomen to the receptive stigma as it lands on the green tip of the corolla.
It then turns upside down, opens the corolla, and exposes the stamens.
With its front legs it scoops out the pollen and places it on the ventral
surface of the abdomen. One individual stood with its head at the lower
lip of the corolla and took out pollen with its front feet and mouth-parts.
A second landed with the head toward the style and tried to open the corolla
slit without success; it then turned toward the other end and scraped up
the pollen on the outside with its front legs, placing it on the rear legs and
abdomen. After turning again, it repeated its unsuccessful attempt to
open the corolla, then turned its head downward, and at the lower lip
succeeded in opening the corolla. It went into the latter until only the
abdomen tip was visible outside the flower. A third bee of this species
landed at the tip of the corolla and ate pollen found on the outside. The
slit of this flower was inverted, i. e., faced up. The bee walked to the under
64 NORMAL AND EXPERIMENTAL POLLINATION.
side to the position in which it was accustomed to work, looked around, and
found no slit. It had difficulty in holding on to the under side in the absence
of the slit. It then moved to the dorsal side and found a few grains of
pollen, but did not seem satisfied. Again it tried the ventral side of the
corolla and looked all around for the slit and the lower lip. It went to the
dorsal side again, but failed to locate the slit. For a third time it moved
to the under side of the corolla, but not finding what it was looking for,
flew away to a flower in a normal position and located the slit at once.
A fourth one landed with its head toward the style, walked to the end of the
latter and over it, the style touching the pollen loads on its legs, and then
walked back again. It worked for several seconds with its head and the
first pair of legs in the attempt to open the slit, and finally succeeded.
A fifth individual alighted on the lower lip and immediately went down into
the corolla and sucked nectar. Then it turned around, walked out to the
end of the style, which swayed under its weight, and around it. It returned
to the end of the corolla and then backed out onto the stamens, where it
collected pollen, placing it on the hind legs before flying away.
Selasphorus platycercus landed upon a low tree branch and sucked
nectar from the nearby Castilleia flowers, while resting its wings. Normally,
it keeps its feet close to the body and sustains itself in the air by rapid wing
motion while sucking nectar. In one flower the corolla tube was too small
even for its slender bill. The bird found no trouble in thrusting the bill
into the corolla, but was unable to pull it out again. It then lowered
itself so that the corolla tube became pendant and sipped more nectar,
finally freeing itself after further effort.
The normal visitors to Castilleia are not numerous, observations for a
period of 2 hours and 20 minutes yielding only the following: Halictus
pulzenus 6, Sphecodes sp. 2, Selasphorus platycercus 3.
Merritt (1897:21) states that the flowers of Castilleia affinis have abun-
dant honey, and that pollination is usually effected before the flowers attain
their full length. The exserted capitate stigma is struck by the visiting
humming-bird, while the bill receives a fresh supply of pollen from the
anthers just below in the galea. Longyear (1909:79) has described the
structure and pollination of the flower of C. linarifolia.
EXPERIMENTS.
MUTILATION.
Upper lip removed, spike inverted. — The upper lip of the corolla
was cut off even with the lower, the bract cut back to the same length,
and the cluster then inverted so that the lower lip of the flower was turned
up. Halictus pulzenus landed and remained quiet at the lower lip for
some time, with its head inside the corolla. It was probably sucking
nectar, but there was no movement of the abdomen to indicate this. It
then walked out on the filaments to the anthers and ate the pollen that
was still there. It next went to the end of the style, arching its body over
in such a way that the stigma rubbed against the abdomen.
PAINTED FLOWERS.
Painted bracts. — The bracts of various clusters were painted purple,
green, or yellow with water-colors. A humming-bird sucked nectar from
PENTSTEMON GLABER. 65
such flowers in the normal fashion and Halictus pulzenus likewise gave no
evidence of being disturbed by the change.
PENTSTEMON GLABER.
NORMAL POLLINATION.
Habit and structure. — The plants of this species usually grow in small
communities on warm gravel-slides. The stems are about a foot high,
several in number and ascending. The flowers are arranged in brilliant
secund clusters. This is one of the large-flowered species, with not only a
comparatively large corolla mouth, but also a tube of nearly the same size.
Hence, its nectar is the most accessible of all the species of this genus in the
region. The staminode is broadly spatulate and covered for nearly half
its length with long hairs in two rows. The flowers are protandrous, the
anthers on the longer filaments maturing first and arching above the entrance
to the corolla mouth. The young stigma is straight, extending forward
just behind the front pair of anthers. When the stigmas become receptive,
the four anthers are nearly through dehiscing and the style elongates, its
tip arching sharply downward between the front pair of anthers and almost
touching the staminode. In older flowers the staminode coils inward,
coming in contact with the stigmas (plates 12 and 17).
Behavior. — Osmia phaceliae works persistently at the tip of the bud,
trying to gain entrance to the corolla. When the flower is about ready to
bloom, the bee succeeds in opening it. In mature flowers it stands at the corolla
entrance and scratches the dorsal surface of its thorax on the anthers,
and then goes into the corolla-tube and secures nectar. Osmia pentstemonis
lands where the lobes of the lower lip bend downward ; it usually comes for
pollen and enters the flower to the point where the anthers brush against the
thorax. The latter is first well rubbed on the front pair of anthers and then
on the rear ones. Its dorsal surface rubs back and forth against the anthers
until the stigmas as well as the scopa become white with pollen. It rarely
if ever seeks both pollen and nectar, but some individuals pass the anthers
and take nectar only. Osmia melanotricha collects pollen in the same manner,
ignoring the nectar, in spite of the fact that the corolla-tube is nowhere so
narrow that it could not obtain this with its short tongue. Osmia densa
is so large that its body fills the entire corolla, the tip of the abdomen reaching
to the corolla mouth. It comes for nectar and the under surface of its
abdomen rubs the staminode while it is sipping. In more mature flowers
with a curved style, the stigma brushes closely against its back. In seeking
nectar, Osmia coloradella lands on the lower petals and stands upright,
bringing about pollination by contact with its dorsal surface.
Vespa germanica stands at the angle of the corolla mouth and rubs the
thorax against the anthers so hard that a scratching sound is heard, while it
moves back and forth 5 to 10 times during the process. The hairs on its head
touch the anthers and stigma as it sucks nectar. Just before leaving the
flower, it stands at the edge of the corolla mouth and with the front legs
scrapes off and eats the pollen that has fallen on its head. Andrena madro-
nitens goes into the flowers upside down and collects pollen only, while A.
vicina enters for nectar alone and remains for a long time at each flower.
NORMAL AND EXPERIMENTAL POLLINATION.
Prosopis varifrons is very small in comparison with the size of the tube, and
some individuals go directly to the nectary and depart without touching the
anthers. Others work upside down and eat pollen as they hang suspended
from the anthers, without making any attempt to find the nectary. Halic-
tus pulzenus lands on the lower lip, then walks to the upper one and stands
upside down on the anthers. The tip of its abdomen is just below these
while it is removing pollen with its front legs. It also picks up and eats
any pollen that has dropped on the lower lip.
Bombus juxtus lands in the normal way, turns upside down, and takes a
position such that the anthers rub the thorax as it moves back and forth.
It also scrapes pollen from the anthers with its front legs and transfers it to
the hind ones. This bee often tries very hard to open buds and turns over
and around in the attempt to do this. Bombus bifarius goes into a corolla-
tube, turns upside down, and scrapes pollen from the anthers with its front
legs, placing it on the hind ones. Monumetha albifrons lands and goes
directly to the nectar. Its thoracic hairs brush the anthers as it sucks
nectar and some pollen is collected accidentally, but it makes no effort to
gather it. Titusella pronitens works on the anthers only, standing upside
down as it collects pollen on its scopa.
Table 48. — Visitors to normal flowers.
Species.
Observations.
1
2
3
4
5
6
63
48
3
1
1
3
0
0
1
0
42
10
0
0
0
1
3
0
0
1
1
7
0
0
0
0
2
0
0
0
6
34
0
0
0
4
0
1
0
1
2
17
0
0
0
0
1
0
0
1
2
4
0
0
0
0
4
0
0
1
Total
120
57
10
46
21
11
COMPARATIVE VALUES.
21
16
16
3
2
14
4
22
4
34
1
3
Total
40
21
20
31
40
8
Calendars. — Table 48 contains the results of observations on six dif-
ferent days. There were 150 open flowers under observation on the first
date, 172 on the second, and 100 on the others. The records were made
at the following times: (1) June 25, 8 to 10 a. m.; (2) June 27, lh40m to 3h18m
p. m.; (3) June 28, 10h35m to llh04ra a. m.; (4) July 13, 10 to llh30m a. m.;
(5) July 24, llh06m to llh40m a. m.; (6) July 1, 9h15m to 10h40m a. m.
PENTSTEMON GLABER.
67
While the first part of table 48 contains the actual record of visits, the
exact significance of these can be obtained only by reducing them to the
same basis as to length of observation and number of flowers. This reveals
a variation of five times in the total number of visits per hour. More
suggestive, however, is the balance between Pseudomasaris and Osmia;
the decrease of the one with the increase of the other indicates the effect
of competition for the same species, either actually in progress or wrought
out in the seasonal behavior.
Observations 1 and 2 in table 49 give the lists of visitors from 10 to
10h40m on two mornings a week apart with 50 flowers concerned in each
case. There were 19 flowers in number 3, which was made on June 27
from llh20m to 12 a. m. Observation 4 was taken on July 10 from 9h47m
to 10h26m on 20 flowers. 50 flowers were used for 5, which was on July 12
from 10 to llh30m a. m. Number 6 was made July 18 from 10h4m to
llh40m and 50 flowers were in the group under observation. As usual,
the first number in each column indicates the visitors, the second the
visits made.
Table 49. — Visitors and visits to normal flowers.
Species.
Observation.
Osmia phaceliae
bruneri
Pseudomasaris vespoides
Clisodon terminalis
Melissodes fremonti
Andrena vicina
Prosopis varifrons
elliptica
Apis mellifica
Bombus juxtus
Halictus pulzenus
Thanaos martialis
Total
26:65
2:2
6:18
6:25
2:4
2:3
2:2
2:2
1:2
1:32
0:0
0:0
17:20
0:0
3:4
3:9
0:0
2:2
2:2
1:1
0:0
4:9
8:51
0:0
0:0
0:0
1:1
0:0
0:0
2:2
0:0
0:0
0:0
1:8
5:113
0:0
0:0
0:0
1:1
0:0
2:2
1:1
1:1
0:0
0:0
27:71
4:17
6:25
2:2
0:0
2:2
0:0
1:2
1:30
0:0
0:0
15:63
11:126
43:149
0:0
17:20
4:4
1:8
0:0
1:5
0:0
0:0
0:0
4:4
0:0
0:0
27:41
COMPARATIVE VALUES.
Osmia phaceliae
bruneri
Pseudomasaris vespoid
Clisodon terminalis . . .
Bombus juxtus
Total
39:87
3:3
9:27
9:37
1:48
25:30
0:0
4:6
4:13
0:0
18:40
36:225
0:0
9:0
75:233
45:64
66:282
0:0
4:36
22:510
0:0
4:4
48:570
0:0
18:47
3:12
4:17
1:20
30:103
0:0
25:40
2:16
The reduction in the number of visitors and the great decrease in the
visits made by them shown by the second observation were due entirely
to the wind, the other factors being essentially the same. A similar decrease
68
NORMAL AND EXPERIMENTAL POLLINATION.
in the number of visits particularly occurred toward the end of the flowering
period, as shown in columns 5 and 6. The dominance of the species of
Osmia alternates in a striking and suggestive manner. A similar alternation
occurs in the case of Pseudomasaris and Clisodon, and the whole summary
shows the extent to which the maxima for different species tend to fall at
different times. The varying effectiveness of the genera is revealed by a
comparison of Bombus and Osmia; 2 individuals of the former visited 30
and 32 flowers respectively on the same days that those of Osmia averaged
but 2.5 visits each.
Merritt (1897:19) found that Pentstemon palmeri, P. barbatus labrosus,
and P. bridgesi all have abundant nectar secreted by the bases of the two
upper stamens. The filaments of these curve inward to meet each other
and the other pair of filaments, and then rise to the upper wall. The
staminode crosses the tube above this junction and lies for the rest of its
length on the lower wall, thus excluding short-tongued visitors from the
nectaries. Dehiscence of the anthers is not simultaneous, and it is continued
for some time, the style lengthening only toward its close. The latter
lies against the upper side, but is curved to bring the stigma down to the
entrance, but out of the line of falling pollen. P. palmeri is constricted
in the tube where the 4 filaments meet about 4 mm. above the base, and the
sterile filament crosses just above this. The throat and limb are wide
enough to admit the largest bees. The anthers lie against the upper wall
and the heavily bearded staminode forces insects against them, though one
frequent guest, Osmia densa, appears to get nectar without touching them.
The vivid scarlet of P. barbatus labrosus stamps it as a humming-bird
flower. The anthers are exserted but protected by the upper lip, and serve
to guard the entrance, as the stigma does later. Honey-bees and Antho-
phora sometimes collect pollen from the anther-slits. In P. bridgesi honey-
bees attempted to reach the nectar, but in vain, while the pollen is dis-
charged too slowly to tempt bees.
EXPERIMENTS.
CHANGE OF POSITION.
Racemes inverted. — Table 50 gives a summary of the results of an
experiment in which 23 racemes in the normal position and 3 inverted
ones were under observation.
Table 50. — Visitors to normal and inverted racemes.
Specie3.
Normal.
Inverted.
Relative No.
inverted.
Osmia phaceliae
bruneri
Bombus juxtus
Apis mellifica
Pseudomasaris vespoides
Melissodes f remonti ....
Prosopis varifrons
Total
118
PENTSTEMON GLABER. 69
Since there were about 7 times as many flowers in the normal position
as inverted, the latter were relatively about a third more attractive, the
ratio being 118:169.
In another series of observations the behavior of certain individuals
was noted in detail, especially for Osmia, Vespa, and Apis, The first
individual of Osmia phaceliae landed on the new lower lip, then climbed to
the upper, went in upside down, and scratched its thorax back and forth
on the stamens. At the next inverted flower it landed in the same way,
looked around, and backed out. The second went to 4 inverted flowers,
where it scraped its thorax against the inverted staminode and then pushed
in to where the nectar should be. The third went straight in and tried
to find the opening to the nectary, but did not succeed. The fourth indi-
vidual entered the inverted flowers just as the normal ones and stayed the
same length of time, while the fifth attempted to enter 3 inverted flowers
without success. The sixth went into 3 inverted flowers and obtained
nectar with but little more difficulty than in normal ones, but the seventh
entered upside down, hence in its usual position with respect to the flower
parts, and consequently worked as usual. Four others then did the same
in succession. Osmia phaceliae often went into inverted flowers and
scratched its thorax against the staminode, evidently without realizing
that it was not touching the anthers. Some of this species at once recog-
nized that the flowers were inverted and landed accordingly. Osmia
melanotricha also went into such flowers upside down and secured nectar.
It entered and scraped pollen as in normal flowers.
Vespa germanica twice tried unsuccessfully to find nectar in these flowers.
It landed, but before entering noticed something different and went to the
next flower, which was also inverted, where it behaved in the same way.
A second individual entered hesitatingly in such a manner that it was upside
down and then took nectar. A third one flew above and examined 6 inverted
blossoms but did not land, while a fourth wasp entered the flower, and
reached into the nectary, but did not stay long enough to get nectar. It then
flew past the mouths of other inverted flowers, but did not land. Apis melli-
fica went into 2 inverted flowers, but departed at once. It stopped several
times at such flowers later, but noticed the difference and flew away.
Finally, it came back to a stem bearing inverted flowers and obtained pollen
without standing upside down. Another individual stood upright and
gathered pollen from the anthers underneath these flowers instead of
standing upside down. Clisodon terminalis visited 10 normal flowers
and 4 inverted ones, but obtained nectar in but 2 of the latter, while Andrena
vicina secured it as usual.
When the two lobes of the lower lip in an inverted flower were cut into
separate petals, Osmia melanotricha landed easily, but the stamens and style
which projected in front of the flower confused it so that it could not find
the entrance to the nectar. Osmia pentstemonis likewise landed on the in-
verted upper lip, but did not find the anthers and nectar. In the case of
inverted flowers with the corolla mouth closed by wilting, it succeeded in
opening the corolla with difficulty, but failed to find the anthers and so
flew out at once.
70 NORMAL AND EXPERIMENTAL POLLINATION.
Racemes horizontal. — Bombus juxtus landed at the corner of the
mouth, turned sideways, and then sucked nectar in the normal position with
relation to the flower. Osmia pentstemonis tried to enter 3 flowers with the
corolla tip pointing up, but after landing and starting in, it backed out
each time without finding the anthers. The next individual went into these
flowers apparently without noticing the change in position. 0. melanotricha
was puzzled by those that had the corner of the mouth pointing up.
It landed by placing the right legs on the lower outside lobe of the upper
lip and the left legs on one of the lower, thus straddling the angle of the
mouth, which pointed down. The bee then moved back and forth, trying to
rub, and some time elapsed before it discovered that the anthers were
missing, when it flew away.
MUTILATION.
Cotton at the corolla mouth. — Absorbent cotton was placed in the
corolla mouth, thus obscuring the anthers and blocking the entrance to
the nectaries. The amount of cotton used was small and it was placed in
position lightly, so that insects could easily push it aside and gain entrance
to the flowers if they made any effort to do so. Half of the racemes were
left normal and those with obstructed corollas were arranged at various
places in the cluster. Two individuals of Osmia pentstemonis hovered at
the corolla mouth, but did not try to force an entrance. Osmia phaceliae
attempted repeatedly to get in past the corolla mouth but did not succeed,
while Vespa germanica noticed the change just as it landed and did not try
to enter.
Styles, stamens, and staminode removed. — In flowers thus modified,
Bombus juxtus started to enter one, but before turning upside down noticed
the difference and went to the next flower. Osmia bruneri flew to the
corolla mouth, but noticed the change and did not enter, while 0. phaceliae
reached the point of getting its head in position to suck nectar before
flying away. Another individual went into the flower, worked as usual,
and left, apparently without having noted the change.
Corolla split. — When the corolla was deeply split between the lips,
Andrena vicina visited 3 flowers without noting the difference. The first
Halictus pulzenus that arrived walked around the flowers, but without
entering. Another landed on the lowest lobe of the corolla and wandered
back and forth over the edge. It then walked over the lowest lobe 5 times,
trying to find the way into the corolla, and then flew away without entering
at all. Some individuals of Bombus juxtus stopped and sucked nectar as
if they noted no change, while others flew away at once as if frightened.
Clisodon terminalis worked in the normal way, and both Vespa germanica
and Pseudomasaris vespoides went directly to the nectary, took nectar,
and departed. One Osmia pentstemonis landed and went at once to the
nectary, but flew away without sipping. Another alighted on the lower
petal and walked around, but since the anthers were projecting in front of
the flower and the corolla lips were somewhat reflexed, it failed to find the
anthers and the tip of the staminode, which it usually uses as a guide to the
nectary. Osmia phaceliae went to 9 flowers, among which was one with
the corolla lips separate. This bee advanced to the nectar, but suddenly
PENTSTEMON GLABER. 71
flew away as if aware of the change. Another individual went into 3 of
these flowers and inserted its ligule into the nectary, but left without taking
nectar (plate 17).
Corolla lips separated and staminode raised. — In flowers of this
type, Osmia phaceliae tried repeatedly to get on the lower lip of the corolla,
but slipped off. Finally it landed and then bumped into the staminode.
After doing this twice it went in at the side and obtained nectar. In
normal flowers 0. melanotricha has the habit of rubbing its back against the
anthers, but in these it failed to find them, and went instead to the nectary.
Upper lip removed at the throat. — Osmia bruneri landed as usual
and secured nectar, the style touching its back in the process.
Lower lip shortened half. — The lower lip constitutes the landing-
platform, and this experiment was devised to find out the response of visitors
when it was removed. Clisodon terminalis went into a flower without noting
the change; it then flew to a normal flower, and afterward to one with the
corolla mouth obstructed with cotton. When it did not succeed in entering
this, it flew away. Vespa germanica sipped some nectar, but did not stay
the usual time. Osmia phaceliae landed on the staminode, finding difficulty
in balancing itself, but finally made its way along the staminode until it
obtained a better foothold on the corolla-tube and was able to reach the
nectar.
Lower lip removed. — Osmia melanotricha entered these flowers by
straddling the staminode and was able to secure nectar.
Lower lip and part of tube removed. — The lobes of the lower lip
were removed, as well as the tube for a distance of 4 mm. Osmia bruneri
succeeded in landing after repeated attempts by taking hold of the anthers
with the front legs, turning upside down, and walking a short distance into
the flower; it then turned right side up with the front legs on the remaining
part of the lower lip. This gave it a sufficient foothold for gathering nectar.
Lips removed except lower lobe. — The median lobe thus left formed
a landing-platform, so that Osmia phaceliae was able to obtain nectar in
the usual fashion.
Corolla tube shortened half. — Clisodon terminalis poised in the air
before these flowers, but did not land. Melissodes fremonti, Osmia phaceliae,
and Andrena vicina entered them and obtained nectar. Some individuals
of Pseudomasaris vespoides landed, but could not hang on and suck nectar,
as too little of the corolla was left to serve as a platform for them.
Petals separated. — When the petals are separated to the base, they
are long, slender, and recurved, since they lack mutual support. The
stamens consequently spread out in all directions. Osmia phaceliae went
directly to the nectar, instead of first standing at the corolla mouth and
rubbing its thorax, as in the normal flower.
Lower lip split into three petals. — Osmia bruneri stood on the middle
petal and continued to suck nectar, in spite of the fact that its weight
caused this to bend down vertically. It did not come in contact with the
anthers and style at all in these flowers.
72
NORMAL AND EXPERIMENTAL POLLINATION.
A second corolla slipped over the staminode. — This gives the flower
an unusual appearance, as though it were doubled, and interferes with
entrance to the corolla. Osmia melanotricha and 0. pentstemonis landed
and tried to enter, but failed.
Comparative relations. — An experiment in which normal, mutilated,
and inverted flowers were placed in the same group was devised to determine
the effect of competition. Three spikes of each type of mutilation and an
inverted one were used with 11 normal spikes for comparison. Table 51
shows the results.
Table 51. — Inverted and mutilated flowers.
Species.
Normal.
Inverted.
Style
removed.
Corolla
removed.
Corolla
2-divided.
51
1
28
19
18
0
1
9
0
3
4
1
3
2
2
0
1
0
0
0
0
2
0
0
1
0
1
0
2
0
0
1
0
0
0
Apis mellifica
Pseudomasaris vespoides. . .
Melissodes fremonti
Prosopis varifrons
Total
118
22
3
4
3
ARTIFICIAL AND PAINTED FLOWERS.
The flowers of this species are bright blue in color and stand out conspic-
uously against the buff of the gravel-slides on which they grow. The
racemes are 6 to 12 inches long and each plant has several, so that the color
mass is large and conspicuous from some distance.
Crepe-paper corollas. — The corollas of half the flowers of 4 racemes (25
flowers) were removed and replaced by tubular paper corollas in red, blue,
green, white, or yellow. Although the normal flowers were visited as usual
during the morning, no insects even attempted to enter the artificial ones.
Corolla painted with water-colors. — Half of the flowers on 5 racemes
were painted red, yellow, or green. One Vespa germanica passed by red and
yellow to work on the normal ones adjacent. Another Vespa observed
went to 2 flowers painted yellow, but passed by the neighboring red ones.
Clisodon terminalis entered the normal flowers, but ignored the painted ones.
Osmia pentstemonis was less discriminating and different individuals visited
the yellow flowers repeatedly. They flew from yellow to normal flowers
and then to red ones, etc., as they found the flowers in a convenient order,
but they avoided the green ones to some extent. One individual inspected
the green, but passed to work at yellow and red, and then returned to the
green. It next went to yellow, to red, to a normal flower, and then back to
red.
HONEY AND ODOR.
Sirup added. — Diluted Karo sirup was placed in various positions on the
flower. One individual of Osmia pentstemonis entered blossoms with a drop
PENTSTEMON GRACILIS. 73
of diluted Karo on the anthers without noticing its presence, and went
directly to the anthers as usual. Another twice visited a flower with a
drop at the right corner of the corolla mouth, and rubbed the anthers without
discovering the sirup. Halictus pulzenus entered flowers with Karo on the
anthers as it did normal ones, that is, upside down. It walked through
one drop, turned around, and sipped it up before flying away. Vespa
germanica visited every flower on the stalk except those with the Karo
drop. Osmia melanotricha entered a flower with Karo at the right corner
of the mouth, straddling the staminode in the usual manner, but before
reaching the nectar turned around and came out at the left corner.
Bombus juxtus almost entered such a flower, but suddenly flew to the next
one.
PENTSTEMON GRACILIS.
NORMAL POLLINATION.
Habit and structure. — This is the smallest flowered species of Pent-
stemon found in the Pike's Peak region. The corolla-tube is narrow and
comparatively long, 1 to 2 cm., and the limb extends at right angles to the
tubular portion. The racemes are erect, the color varying from delicate
pink to pale blue. It grows on warm slopes and blooms earlier than the
other species in the locality, and is sought particularly by various species
of Osmia.
Behavior. — Osmia bruneri and pentstemonis push the head into the
corolla-tube, the anthers and stigma rubbing against the hairs on the
dorsal surface of the thorax as the bee sucks nectar. 0. phaceliae rests
on the lower lip, and then enters the flower in a normal position. Its
hind legs hang over the lip and the front pair rest in the corolla-tube.
It goes from one flower stalk to the next and enters flowers at about the
same level, in preference to visiting all the open flowers on one stalk. The
same flower is visited repeatedly by different individuals and sometimes
one bee returns several times. Prosopis elliptica enters in the normal
position and turns so that it either stands upside down or sidewise within
the corolla while collecting pollen. Halictus (Chloralidus) sp. lands on
the lower lip in the normal position, and then turns upside down, hanging
suspended from the upper lip. The tip of the abdomen touches the outer
pair of anthers as it scrapes pollen on to the hind legs.
Bombus juxtus lands, thrusts its head in and places its front legs around
the two outer lobes of the lower lip as it sips, the hairs on its head rubbing
against the stigma meanwhile. It enters the flower upside down as well
as in the normal position. This bee visited pink and blue flowers without
discriminating between the two. In one plant with unusually small flowers,
it could not get its head into the corolla-tube. However, it inspected
these and tried to enter, even splitting the corolla-tube in the attempt.
B. juxtus did not accumulate the heavy pollen loads exhibited by B. bifarius.
The latter pushes its ligule into the flowers for nectar, the recurved part
of the lobes extending past the thorax to the base of the abdomen. As it
sips, the anthers rub against the dorsal side of the thorax. Most of the
individuals carried heavy pollen loads on their legs, but they were not col-
74
NORMAL AND EXPERIMENTAL POLLINATION.
lecting pollen at the time. As B. bifarius leaves the flower, it scrapes
pollen from the dorsal surface of its thorax with its front legs and places it
on the hind ones. One individual started to suck nectar in the normal
position, and then turned upside down and scraped pollen. Another
individual behaved in the same manner on one flower and then visited the
next flower in the normal way. The third landed, at once turned upside
down, and commenced scraping pollen, working in the same fashion
on three flowers in succession. The assumption of the normal or inverted
position by B. bifarius apparently depended on whether it came for nectar
or pollen.
Apis mellifica is so large that only its head and half of its thorax can
enter the corolla-tube. These parts are hairy, and after sucking nectar
the bee comes out dusted with pollen. Titusella pronitens stands with its
hind legs on the lower recurved petals and the front ones on the corolla-
tube, while it pushes out its ligule and takes nectar. Anthophora simillima
inspects these flowers, but none land. Systoechus vulgaris has a tongue as
long as the corolla-tube, so long indeed that the head usually does not touch
the anthers or stigma in sucking nectar. If pollination is accomplished
by this fly, it is done by the ligule as it enters and leaves the corolla. Selas-
phorus platycercus is a very persistent visitor. In the course of a morning's
observation the same bird sucked nectar once or twice from every open
flower on the whole slope. This species worked so rapidly from flower to
flower that even when there were only one or two visitors every flower
in the locality was reached.
Table 52.-
-Visitors to normal flowers.
Species.
Observations.
1
2
3
4
5
6
1
7
12
0
0
7
2
0
1
1
0
0
4
0
15
2
0
1
0
1
1
1
1
1
3
1
15
5
0
3
0
0
1
0
0
0
0
0
0
1
12
0
0
0
0
0
0
0
0
0
0
0
0
13
1
0
0
14
0
0
0
0
0
0
0
1
20
6
0
0
10
2
0
0
1
0
0
0
Pseudomasaris vespoides
Halictus (Lasioglossum) sp
(Chloralictus) sp
Total
Relative total
35
9
27
2
24
24
13
13
28
19
40
26
Calendars. — The normal visitors to this species as observed during an
hour period on six different days are grouped in table 52. The first list
was made at the entrance to Englemann Canyon on June 13, when the
plants were past their prime and 212 open flowers on 30 spikes were in the
group. The second list was made on 82 spikes, bearing 526 open flowers,
PENTSTEMON GRACILIS. 75
found at Long's Ranch on the Ute Trail on June 19. The last four lists
were made in the vicinity of the Alpine Laboratory; 50 flowers were under
observation on the first two days, June 15 and 16; 85 open flowers on 169
spikes on the third, June 17; and 72 flowers on 175 spikes on the fourth,
June 18.
EXPERIMENTS.
CHANGE OF POSITION.
Racemes inverted. — Bombus juxtus entered the inverted flowers as if
it did not notice the difference. It stayed in the corolla for a shorter time
than with normal flowers and probably did not find the nectar. Osmia
phaceliae pushed into the corolla, thrust out its ligule, and, not finding the
opening to the nectary, went to the next flower. It also failed to obtain
nectar here and then visited a third flower that was in the normal position.
The hairy thorax rubbed the mature pair of anthers, regardless of whether
this was the front or rear pair. It also visited flowers with the pollen
practically shed, the deflexed stigma scraping the thorax as the bee sipped
nectar. 0. pentstemonis ate the pollen that had fallen on the floor of
the corolla, as also that on the staminode and anthers. Prosopis varifrons
turned upside down in order to gain entrance to the flowers.
Racenie horizontal. — Bombus juxtus turned to take a horizontal
position and entered at once in the usual relation to the parts.
MUTILATION.
Landing-platform removed. — The lower lip of the corolla was removed
to destroy the landing-platform and in consequence Bombus and Apis were
not able to enter such flowers. Osmia phaceliae did not need the lower lip
for support, but straddled the staminode in such a position as to take nectar.
Brush of staminode removed. — There was no difference in the behavior
of the visitors to these flowers.
Anthers and recurved portion of upper lip removed.— Halictus
pulzenus entered the flowers upside down in the usual way and rubbed the
upper surface of its body against the filaments, as if noting no change.
Upper lip partly removed. — This exposes the anthers to full view, but
leaves the lower lip unchanged as a landing-platform. It also gives the
observer a much better opportunity to view the interior of the flower while
the bee is securing nectar. As Clisodon terminalis sucks nectar, it moves
its head back and forth once or twice and the upper parts become covered
with pollen, which is then removed by the stigma in older flowers. In the
case of Bombus juxtus, the first pair of anthers rub the top of the abdomen
and the second the top of the thorax, but only when mature. In these
flowers the bee did not go to the exposed nectary directly, but always passed
under the arch made by the stamens and style, as is its custom in normal
flowers. When the style is mature, it is in position to touch the back of the
abdomen.
Lobes of upper lip separated. — Osmia phaceliae goes into these flowers
apparently without noticing any difference, the whole procedure being
76 NORMAL AND EXPERIMENTAL POLLINATION.
exposed to view. As the bee sucks nectar, the hairs of the thorax are
brushed against the anthers or the stigma.
Petals split to the base. — Osmia phaceliae usually stands on the lower
lip, and a single petal suffices to support it when the lobes are split. 0.
bruneri, on the contrary, is so heavy that a single petal will not support its
weight, and hence it was unable to obtain a foothold. Bombus juxtus
had even greater difficulty in landing because of its weight. It finally
found a position in which it was supported by the two outer petals. It
then felt around with its ligule until it found the arch under the stamens and
went to the nectar in the usual manner. Vespa germanica entered these
flowers, but stayed only a very short time, acting as though uneasy because
of the unsteady foothold.
PENTSTEMON GLAUCUS.
NORMAL POLLINATION.
Normal behavior. — Thanaos martialis lands on the lower lip of the
corolla, where it feels around with its ligule until it finds the nectar, the
anthers and stigma rubbing against the hairs of its back meanwhile.
Bombus proximus and edwardsi enter the flowers by landing on the lower
lip and going directly to the nectary. One bee tried to turn around and
enter a half-open bud upside down, but was not successful. Osmia pent-
stemonis works on the anthers upside down, so that the ventral scopa rubs
them. It comes out of the normal flower head first and, as it starts to fly,
the back of its head comes in contact with the anthers or stigma tip.
EXPERIMENTS.
MUTILATED.
Upper lobes split to base. — Osmia pentstemonis, after trying to land
on the projecting staminode, placed its front legs on the outer lobes of the
lower lip and the others on the middle lobe and worked easily, reaching
the nectar readily. The corolla mouth is so large that the bee does not
usually come in contact with the anthers and the stigma. Its scopa rubs
the hairs of the staminode, but pollination is not often effected by this
visitor. Bombus morrisoni landed on some of the flowers, but flew away
at once, while in other cases it inspected them without landing.
Lower lip removed. — Osmia pentstemonis had difficulty in landing,
slipping back and forth and its head rubbing the anthers.
Outer lobes of lower lip removed. — Thanaos martialis normally
places the front pair of legs on the outer lobes and the weight of its body on
the middle one. With the outer lobes removed it finally succeeded in landing
by putting its front legs at the edges of the middle lobe and the weight of its
body on a bud under the flower.
Staminode removed. — Bombus juxtus landed, then moved from side
to side, and backed out. It started into the flower again, stopped, and
went directly to the nectar. In normal flowers it follows the staminode to
the nectar at once.
PENTSTEMON SECUNDIFLORUS.
77
Middle lobe of the lower lip removed. — Bombus morrisoni went into
3 flowers of this type, apparently without noting any change, and B. juxtus
behaved similarly.
Upper lip removed. — Bombus morrisoni noted no change.
PENTSTEMON SECUNDIFLORUS.
NORMAL POLLINATION.
Behavior. — Bombus proximus alights on the lower lip of the corolla
and then turns around on to the upper lip, standing upside down while
working. It flies from one open flower to another in a cluster and then
to the next cluster. Vespa germanica stands on the lower lip and pushes
its head far into the flower for nectar. It transfers the pollen collected on
the head to its hind legs with the front ones. After visiting many flowers,
it rests on the ground before going to others.
Calendar. — A calendar is given below of visits during a 42-minute period
to 24 spikes bearing 125 open flowers. Holes had been bored by robbers
at the base of the corolla on the upper side of many of these flowers. Pseudo-
masaris vespoides went to many flowers twice, collecting in the usual way
from those previously robbed by some other insect. Anthophora simillima
stopped at only 2 or 3 flowers at a time and was easily frightened. Sys-
toechus vulgaris was a persistent visitor, going to as many as 59 flowers in
rapid succession.
Calendar 1. — Visits to normal flowers.
llh06m Anthophora simillima, 1.
11 10 Osmia melanotricha, 1; Prosopis
wootoni, 1 ; Pseudomasaris ves-
poides, 15.
11 13 Anthophora, 1.
11 15 Anthophora, 2.
11 16 Bombus juxtus, 1.
llh20m Osmia, 1.
11 21 Bombus, 1; Systoechus vulgaris, 59.
11 27 Anthophora, 5; Megachile wootoni, c
11 30 Anthophora, 1.
11 34 Osmia pent3temonis, 4.
11 45 Andrena, 1.
11 48 Monumetha albifrons, 1.
The variety of visitors to this species is shown by table 53, column 1
giving the visitors during a 40-minute period and column 2 during 48
minutes.
Table 53. — Visitors to normal flowers.
Species.
1
2
Species.
1
2
Systoechus vulgaris
Andrena madronitens
Anthophora simillima
7
6
0
0
0
0
1
1
1
4
1
1
2
1
1
0
0
1
1
2
1
1
0
0
Pseudomasaris vespoides . . .
Monumetha albifrons
Osmia melanotricha
pentstemonis
Selasphorus platycercus ....
Total :
..17
15
EXPERIMENTS.
ODOR.
Powders and extract. — Flowers were sprinkled with four kinds of
talcum powder. Many individuals of Bombus juxtus landed on such flowers,
78
NORMAL AND EXPERIMENTAL POLLINATION.
but flew away immediately. Between such visits they stopped at normal
flowers and sipped nectar. Halictus pulzenus behaved in a similar manner.
Flowers sprinkled with talcum one day lost their odor during the night and
the following day were visited normally by both Bombus juxtas and Halictus
pulzenus for nectar.
Cotton-wads sprinkled with peppermint or almond essence were
placed below the calyxes of 28 mature flowers, and 28 noimal ones were
left for comparison, with the results shown in table 54.
Table 54. — Visitors to normal and scented flowers.
Species.
Normal
flowers.
lint
Peppermint Almond
scented. scented.
Bombus juxtus
bifarius
proximus. . . .
Prosopis basalis
Andrena madronitens
Osmia bruneri
Total
8:38
6:27
0:0
3:4
1:1
1:1
5:5
0:0
1:1
0:0
0:0
0:0
19:71
0:0
0:0
0:0
0:0
0:0
0:0
SUMMARY.
Practically all visitors solved successfully the problems involved in
changes of position, inverted flowers being visited as much as normal ones
at least. On the other hand, a light plug of cotton rendered all visits
unsuccessful. When the styles, stamens, and staminode were removed
in Pentstemon glaber, most of the visitors left without securing nectar, while
in the case of P. glaucus with the staminode excised, Bombus juxtus entered,
backed out, and then went in again to the nectar. When the lips were
separated in P. glaber, about half the visitors flew away as if disturbed.
With the lobes split to the base, landing was modified to a marked degree,
but it became impossible only in the case of one or two species. The
removal of the upper lip produced no effect, but with the lower lip shortened
or removed, the larger bees, such as Bombus and Apis, were unable to land
on the small flowers of P. gracilis, while Osmia was obliged to make use of
the staminode for landing. Splitting the upper lobes to the base in P.
gracilis caused Bombus to inspect merely or to fly away without securing
nectar, while splitting the lower ones in P. glaber caused difficulty in alighting
even to smaller bees such as Osmia. When the interior of the flower was
disarranged by slipping a corolla over the staminode, Osmia failed to find
an entrance.
Artificial flowers of P. glaber secured no visitors whatever, but natural
flowers painted with water-colors were well visited. The addition of honey
had practically no effect, while essences greatly reduced the visits to P.
secundifiorus. Flowers scented with peppermint received one-third as
many visitors and one-twelfth as many visits as the normal ones. Those
scented with almond were completely shunned, in marked contrast with the
behavior in Chamaenerium.
MONARDA FISTULOSA. 79
MONARDA FISTULOSA.
NORMAL POLLINATION.
Habit and structure. — This species grows in fairly dense groups on
warm half-gravel slides, the numerous stems of each plant making a brilliant
mass of color. This attractiveness is due in large measure to the capitate
clusters of bright pink-purple flowers. The latter are erect or ascending,
and consist of a slender tube with two long lips. The upper lip is subulate
and protects the anthers and stigmas when young, while the lower is strap-
shaped and forms a landing-platform. The anthers are reduced to two,
and the nectar is abundant, so that the flowers are visited almost wholly
for nectar. Since the flowers bloom late in the summer, they constitute
the chief attraction to the butterflies and larger bees at this time (plates
13 and 16).
Behavior. — Bombus juxtus lands on the lower lip of the corolla and
sucks nectar through the tube, pollinating the flower as its head rubs against
the anthers or stigma. One B. juxtus was observed stealing nectar from
the base of the corolla-tube, but this was not the normal procedure for the
species. B. bifarius, proxirnus, and pennsylvanicus robbed Monarda through
holes at the base of the tube during several seasons in succession, but in
1922 all the individuals observed secured nectar in the normal way. The
year previous Bombus proxirnus was observed puncturing the corollas in
one group without making a single normal visit, while in a second group a
few yards away it just as regularly obtained nectar in the proper manner.
Andrena crataegi is unable to make holes easily in the corolla-tube and con-
sequently takes advantage of those made by other species. Prosopis
elliptica stands on the lower lip of the corolla and eats the pollen fallen from
the stamens. Halictus pulzenus alights, walks around on the anthers,
and then goes down the filaments to the nectary. It gathers pollen from
the anthers, but it does not come in contact with the stigma, except by
accident.
Erynnis leonardus snowi alights on the corolla lip, unrolls its ligule, and tries
to find the nectar. The ligule often slips along the outside of the tube, and
even when it starts down the tube it is withdrawn occasionally as if the
butterfly were uncertain. The latter does not have very good control of the
ligule and its eyes are apparently so placed that it can not see down the tube
to guide this by sight. The difficulty experienced by Erynnis is probably
due to its landing at the margin of the head. This is indicated by the fact
that Argynnis atlantis regularly alights in the center, the angle of the ligule
approaching that of the corolla-tube and thus rendering the insertion of
the ligule much easier. The control of the larger butterfly is perhaps
greater also, as it has little difficulty in inserting the tongue in shortened
corollas on the first trial. As a consequence, this species works on Monarda
with something of the rapidity of Bombus. Selasphorus platycercus is a
frequent visitor to these flowers, where it poises in the air in front of the
flower-head and works very rapidly. It pushes its bill into every flower
and is a very effective pollinator. The fluttering motion rubs the bill and
feathers on the front of the head against the stigma and also collects pollen
from the anthers.
80
NORMAL AND EXPERIMENTAL POLLINATION.
The visitors to normal flowers as observed for an hour on July 5 and 8
are given in table 55. There were 50 Monarda heads used on the first date
and 80 on the second.
Table 55. — Visitors and visits to normal flowers.
Species.
July 5.
July 8.
35:35
13:13
0:0
25:25
16:16
9:9
2:2
0:0
0:0
2:2
40:70
6:6
1:1
0:0
3:6
0:0
0:0
5:24
1:3
0:0
Bombus proximus
morrisoni
Clisodon terminalia
wootoni
Total
102:102
56:110
As would be expected from the form of the flower, more than half the
visitors belonged to the two genera of butterflies, Erynnis and Argynnis.
While all four species of Bombus are able to secure nectar in the proper way,
this is sufficiently difficult so that they often avoid Monarda when Geranium
or Aster are near, or they steal the nectar by puncturing the corolla at the
base, as was done by all the visiting individuals of Bombus proximus and
morrisoni in the present observations.
Meehan (1892:449) found that the anthers of Monarda fistulosa burst as
the lips expand and while the stigma is still infolded by the curved portion
of the upper lip. By nightfall of the second day the stamens begin to wither,
the upper anther-cell shriveling first. In the morning the styles grow out
beyond the upper lip and the stigmas separate. Keller (1892 : 452) observed
that the anthers shed their pollen and the stigmas diverge widely in the
closed buds, but this was probably a case of cleistogamy due to cold, as
the observations were made in November. Longyear's observations (1909:
84) are in accord with those of Meehan, as is the detailed life-history (plate
13, figs. 11 to 16).
EXPERIMENTS.
MUTILATION AND COMPETITION.
Plan. — In order to permit a wider range of selection, mutilation and
competition experiments were combined in the case of Monarda. The
flowers of this plant lend themselves with especial readiness to studies of
the effect of mutilation, owing to the pronounced zygomorphy. Moreover,
the arrangement of the flowers in heads affords an opportunity to vary the
kind of competition. Paper disks and paper composite flowers were also
employed in some of the series. In order to determine in some degree the
effect of place and time, two observers were employed to record the behavior
in two separate clumps, distant 1 to 3 meters from each other, and the
calendars were repeated a week apart and on two successive days. In
consequence of the closing of the flowering period for many plants, the
MONARDA FISTULOSA.
81
number of species and individuals visiting Monarda was large, comprising
representatives of the three great groups. For the sake of brevity the clue
name alone is given in the calendars, and the species are listed here:
Hymenoptera:
Andrena madronitens
Apis mellifica
Bombus appositus
bifariua
edwardsi
hunti
juxtus
morrisoni
occidentalis
Hymenoptera — continued.
Clisodon terminalis
Colletes sp.
Halictus lasioglossum
puJzenua
Monumetha albifrons
Prosopis varifrons
Diptera:
Anthrax nigra
Aristatus montanus
Eristalis arbustorum
Syrphus americanus
Lepidoptera:
Argynnis atlantis
Atrytone taxile3
Chrysophanus sirius
Erynnis leonardus snowi
Gnophaela vermiculata
In these more complicated calendars it seems desirable to use "normal"
for such flowers, the number then indicating the number of flowers visited
in each head. Visits were for nectar, unless otherwise indicated, but in the
case of Clisodon, p. and n. are employed to denote those for pollen or nectar
respectively. When the time is given in seconds or minutes, it applies to
all the visits that precede.
First series. — The two records were made on August 8 in two adjacent
clumps of Monarda. The installation consisted of approximately the
same number of normal and modified heads. Crepe-paper corollas of the
size of those of Rubus deliciosus were fastened below Monarda heads, making
a composite; there were 2 each of red, yellow, blue, white, and green. The
Calendar 1.
8h45m Clisodon upper lip off 4, normal 6.
8 47 Argynnis lands and inspects Chamae-
nerium.
Prosopis Chamaenerium 2
Clisodon normal 2, inspects Chamae-
nerium, normal, 1, 1,1, corolla
split 1, normal 2, corolla shortened
3n, inspects Chamaenerium.
Bombus occidentalis Geranium 4, in-
spects crepe Geranium.
Prosopis Chamaenerium 3.
Argynnis Chamaenerium 1, normal 2.
Bombus bifarius Geranium 5, inspects
crepe Geranium.
Argynnis inspects most of the objects.
Atrytone normal 8, 2, Chamaenerium
2, normal 3, upper lip off 1, Cham-
aenerium 1, normal 3, rests on
8 48
8 49
8 51
8 53
8 55
8 58
9 00
9 04
9h07n
9 11
9 13
9 14
9 17
9 22
9 26
yellow composite, but does not
take nectar.
Atrytone blue composite 1, upper lip
off 1.
Argynnis corolla shortened 1, normal
1, upper lip off 1.
Argynnis Geranium 2.
B. appositus normal 3; Atrytone blue
composite 4, white composite 3,
normal 5, Chamaenerium 3.
B. bifarius Geranium 2; Atrytone
normal 3, lower lip off 4, rests on
normal, normal 2.
Erynnis rests on yellow composite;
Clisodon normal 3p, upper lip off
4n.
Erynnis normal 2.
Calendar 2.
9h29m Atrytone, blue composite 1, white
composite 1, normal 1.
Atrytone, lower lip off 1.
Monumetha, normal 2; Syrphus, nor-
mal 1.
Clisodon, normal 4, lower lip off 2p;
inspects both yellow composites
and normal 3.
Gnophaela, normal 4, 3; Atrytone,
normal 1, red composite 1.
9 30
9 31
9 34
9 37
9h44m B. bifarius, Geranium 2; B. occi-
dentalis, Geranium 4, inspects
crepe Geranium; Clisodon, nor-
mal 7n, lp; B. appositus, normal
4, lower lip off 1.
Clisodon, normal 2p, 2n.
B. occidentalis, Geranium 3; Atrytone
normal 2, corolla shortened 3.
Atrytone, lower lip off 3, normal 3.
Atrytone, rests on yellow composite.
9 50
9 51
9 52
9 55
82
NORMAL AND EXPERIMENTAL POLLINATION.
corollas were removed from 2 heads and flowers of Chamaenerium sub-
stituted. Heads were also mutilated by shortening the corolla to half its
length, leaving the stamens intact in one case and removing them in another,
Table 56. — Summary of calendars.
Calendar 1.
Species.
Norm.
Mon.
Upper
Hp
off.
Lower
lip
off.
Cor.
short.
Cor.
short,
stam.
Cor.
split.
Mon.
comp.
Chamae.
head.
Norm.
Ger.
Crepe
Ger.
16
3
0
0
3
26
2
0
8
0
0
0
1
2
0
0
0
0
0
0
0
4
0
0
3
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
5b:3w
0
0
2i
0
0
0
l:li
6
0
5
0
0
7
4
2
0
0
0
0
0
li
li
0
0
0
0
Bombus appositus. .
bifarius
occidentalis
Total
50
11
4
4
0
1
5b:3w
12:3i
13
2i
Calendar 2.
Clisodon
Bombus appositus. .
bifarius
occidentalis
Monumetha
16:3i
4
0
0
2
1
7
7
0
0
0
0
0
0
0
0
2
1
0
0
0
0
4
0
0
0
0
0
0
0
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
yi
0
0
0
0
0
bwr
0
0
0
0
0
0
0
0
0
0
0
2
7
0
0
0
0
0
0
0
li
0
0
0
0
Total
Grand total. .
37:3i
0
7
3
0
0
bwr : yi
0
9
li
87:3i
11
11
7
0
1
6b4w
r:yi
12:3 i
22
3i
Table 57. — General summary.
Species.
Normal.
Muti-
lated.
Other
flowers.
Species.
Normal .
Muti-
lated.
Other
flowers.
16
3
0
0
3
26
2
0
12
0
0
0
2
6
0
0
0
0
7
4
3
6
0
5
16
4
0
0
2
1
7
7
2
1
0
0
0
0
7
0
0
0
2
7
0
0
0
0
Bombus appositus. . . .
bifarius
occidentalis. . .
Bombus appositus
bifarius
occidentalis . . .
Total
Total . .
50
20
25
37
10
9
Grand total
87
30
34
MONARDA FISTULOSA.
83
by removing the lower lip or the upper one, and by splitting the tube for
its entire length, each type being represented by 2 heads. The corollas
of 5 Geranium flowers were replaced by crepe-paper ones representing the
colors red, yellow, blue, green, and white, and these were grouped with
5 normal flowers.
Second series. — The two records were made on August 14 from 8h20m
to 10h40m a. m., in two clumps of Monarda 3 meters apart. The number
of normal and modified Monarda heads and normal Geranium flowers was
approximately the same. Five heads were mutilated by shortening the
corollas of one to half the normal length, by removing the upper lip in the
second, the lower lip in the third, upper lip and stamens in the fourth, and
both lips in the fifth. The flowers of one head and half of those of another
were replaced by corollas of Gilia aggregata, while flowers of Chamaenerium
angustifolium were substituted for half of those of a third head. In addition,
two racemes of the latter species were inserted in bottles of water and placed
in the clump.
Calendar 1.
8h20m
8 22
8 24
8 26
8 29
8 38
8 40
8 42
8 44
8 45
8 48
8 53
8 54
8 55
8 56
8 57
8 59
9 00
9 03
9 14
9 15
9 19
Erynnis, normal 2.
Erynnis, normal 1, 7, 2, 1; 70 seconds.
Clisodon, normal 7, 1, 4, 14.
Erynnis, normal 3, 2; Chamaenerium
2, 9; 80 seconds.
Erynnis, normal 3; 60 seconds; Gera-
nium 2, 2, 1.
Erynnis, normal 3, 1, 4.
Erynnis, normal 4, upper lip off 4;
Clisodon, normal 1.
Bombus juxtus, Chamaenerium 1.
Clisodon, normal 4, 5.
Erynnis, normal 1, 2, 3, 3, 5.
Bombus morrisoni, normal 8.
Erynnis, normal 2, touched Chamae-
nerium.
Clisodon, normal 1, 5, 3, 2.
Erynnis, upper lip off 3.
Erynnis, visits Chamaenerium 2, but
takes no nectar, upper lip off 2,
normal 2, lights on leaf.
Clisodon, normal 6.
Bombus appositus, 3 to 4 flowers each
of 3 heads (total normal 10).
Erynnis, normal 3, upper lip off 2, leaf.
Erynnis, normal 2, 1, 1, 3; 55 seconds;
upper lip and stamens off 4,
upper lip off 5; B. juxtus, normal
5, shortened corolla 3, both lips
off 1, upper lip off 1.
Erynnis, upper lip off 12; 2 minutes;
Geranium, normal 2, 3; 30
seconds. Clisodon, normal 8,
10, 12, 10; upper lip off 5; 40
seconds; normal 5, 40 seconds.
Clisodon, normal 6, 6, inspected
Chamaenerium.
Erynnis, normal 3, Gilia 1, Monarda,
1 in mixed head, tries Chamae-
nerium vainly.
Erynnis, Chamaenerium 3.
9h21D
9 23
9 25
9 30
9 33
9 35
9 59
10 04
10 09
10 13
Erynnis, Chamaenerium 2, normal 2"
Erynnis, normal 2, 1, Chamaenerium 1.
Erynnis, normal 4, Chamaenerium 1,
normal 5, Gilia 2.
Bombus morrisoni, normal 5; Argyn-
nis, normal 12, 30 seconds;
Chamaenerium 6, 20 seconds.
Erynnis merely lands on 2 horizontal
Monarda.
Erynnis, normal 3, Chamaenerium 2,
both lips off 2, upper and stamens
off 9; Clisodon, normal 10, 12,
3, 9, 5, 6.
Clisodon, normal 2, 3, 2, 4, 6, 7, 3, 5,
8, 6, 1, 3.
Bombus appositus, normal 6, 8, 5, 4,
7, 8, 5, 8, 4, 4, 3, 8; second
individual normal 4, 4, upper lip
off 12, 2 minutes; third indi-
vidual normal 8, 10, 12, 6
Monarda flowers of mixed Gilia
head, normal 4, 8, Chamaenerium
8; Clisodon most flowers of 3
heads (total normal 25), all
flowers of 4 heads, often twice
(total normal 60), 5 heads some
twice (total normal 53), 6
heads (total normal 58).
Bombus juxtus, normal 2, 1, 5, 6,
1, 3, 6, 5.
Bombus juxtus, normal 6, 2, 1, 1, 1,
2, 2, 2, 8, 1, 2, 10, 2, upper lip
and stamens off 6, then goes
vainly to shortened corollas;
second individual normal 3, 2.
Bombus appositus, normal 3, 2, 2, 4,
4, 1, 1, 2, 2, 2, 3, 9, 4, 2.
Bombus appositus, both lips off 4,
upper lip and stamens off 7,
upper lip off 5, normal 11, 6, 1,
4, 1, 4, 5, 6; 1 minute.
84
NORMAL AND EXPERIMENTAL POLLINATION.
10h15m Bombus appositus, normal 4; Erynnis,
normal 11; 2 minutes.
10 20 Erynnis, Gilia 2, 7, 2.
10 23 Argynnis, normal 1.
10 25 Bombus juxtus, normal 3, 4.
10 29 Bombus appositus, normal 5, 1, 1;
Erynnis, normal 8, Chamae-
nerium 1, 5.
10 31 Bombus juxtus, normal 2, 6.
Calendar 1 — Continued.
10h32m Clisodon, upper lip and stamens off 6,
normal 11, 5, 5, Gilia 1, normal
9, inspects Chamaenerium, nor-
mal 4, 3, 4, 4, 15, inspects
Chamaenerium and Gilia, nor-
mal 6, 14, thrice (total normal
60), shortened corolla 1, upper
lip and stamens off 3 vainly,
upper lip off 3, inspected 6 for
pollen; 4 minutes for all.
Calendar 2.
9h10m Bombus juxtus, Chamaenerium 1 in
mixed and 3 in pure head;
Erynnis, Monarda 2 in mixed
Chamaenerium head.
Erynnis, lower lip off 1.
Halictus pulzenus, normal 1.
Halictus pulzenus, normal 1.
Halictus pulzenus, normal 2; Clisodon,
upper lip off 3.
Bombus edwardsi, normal 1.
Bombus appositus, normal 1.
Bombus hunti, 9 normal on 3 heads,
Chamaenerium 10 normal on
3 racemes, upper lip off 3 (total
31), normal flowers on 4 heads.
9 23
9 27
9 29
9 40
9 50
9 54
9 58
10h00m Bombus appositus, 26 normal flowers
on 5 heads; Clisodon, normal 9;
B. appositus inspects 2 Geranium.
10 20 Bombus juxtus, Geranium 5.
10 24 Halictus (Lasioglossum) sp. Geranium
2; Halictus pulzenus, Geranium 1.
10 26 Bombus juxtus, normal 13, Geranium
15; P. varifrons, Geranium 1.
10 35 Bombus occidentalis, Geranium 14.
10 36 Bombus juxtus, Geranium 2.
10 41 Bombus morrisoni, Geranium 1.
Table 58. — Summary of calendars.
Calendar 1.
.ft
.ft
ft
8
T3
6
3
6 T3
. ®
§ a
3
O
Species.
°*2
ft«8
o. °
O °
ft m
m
&
a
.2
.5
a. a
| a
a 1
03 ?
a
s
K%
U
h^l
&
PQ
0
O
O
o
O
£
621:6i
220
8
17
0
0
6:3i
7
0
4
i
0
0
6Mon.
1:11
0
0
0
2i
8
0
0
Bombus appositus
juxtus
94
1
0
40
1
3
0
0
0
1
0
morrisoni
13
0
0
0
0
0
0
0
0
0
0
13
100
0
28
0
0
0
13
0
2
0
0
0
1 Mon.
0
14
0
0
6
26:3i
0
10
Total
l,061:6i
54
0
66:3i
7
4
7 Mon.
15:li
0
41:5i
10
Calendar 2.
Clisodon
9
3
0
0
0
0
0
0
0
0
0
Bombus appositus
27
0
0
0
0
0
0
0
0
0
2i
juxtus
13
0
0
0
0
0
0
0
1
3
22
edwardsi
1
0
0
0
0
0
0
0
0
0
0
40
0
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
10
0
0
14
occidentalis
morrisoni
0
0
0
0
0
0
0
0
0
0
1
Halictus(Lasioglossum)sp
0
0
0
0
0
0
0
0
0
0
2
pulzenus
4
0
0
0
0
0
0
0
0
0
1
Prosopis varifrons
0
0
0
0
0
0
0
0
0
0
1
Erynnis
Total
0
0
1
0
0
0
0
0
2 Mon.
0
0
94
6
1
0
0
0
0
0
1:2 Mon.
13
41:2i
Grand total ......
1,155
60
1
66:3i
7
4
7 Mon.
15:li
1:2 Mon.
54:5i
51:2i
MONARDA FISTULOSA.
Table 59. — General summary.
85
Species.
Normal .
Total
muti-
lated.
Total
other
flowers.
Species.
Normal.
Total
muti-
lated.
Total
other
flowers.
621
220
94
13
13
100
15
28
45
0
0
43
1
8
1
0
6
50
Bombus edwardsi
hunti
occidentalis. . .
morrisoni
Halictus (Lasioglossum)
1
40
0
0
0
4
0
0
0
3
0
0
0
0
0
1
0
10
14
1
2
1
1
0
Bombus appositus. . . .
juxtus
morrisoni. . . .
Total
pulzenus
Prosopis varif rons
1,061
131
66
9
27
13
3
0
0
0
0
26
Total
Bombus appositus. . . .
juxtus
94
7
55
Grand total
1,155
138
121
Third series. — The two calendars were recorded on August 15 between
8 and 11 a. m., the labor involved in installation causing the second to begin
and end a half hour later than the first. The equipment consisted of
8 normal heads of Monarda, 3 racemes of Chamaenerium and 2 of Gilia,
8 heads of Aster bigelovi, and 8 flowers of Geranium caespitosum. The
flowers of one head of Monarda were entirely replaced by those of Chamae-
nerium and of a second head by those of Gilia. In addition, there was one
head of each type of mutilation, viz, upper lip removed, upper lip and
stamens removed, lower lip removed, both lips cut off, corolla cut back
to half its length in all but the marginal row. Finally, a few paper corollas
of Geranium were still in place at some slight distance. The normal and
mutilated heads of Monarda and the clusters of Chamaenerium and Gilia
were intermingled, while Geranium and Aster were at one edge.
Calendar 1.
8h18n
8 22
8 30
8 32
8 35
8 36
8 37
8 48
8 50
8 51
Clisodon, normal 1, 1, 1.
Bombus appositus, normal 5, 2, 2, 8, 1 ;
lands on Gijia merely.
Bombus juxtus, normal 1; Clisodon,
normal 4, 2, 4.
Argynnis, normal 12, 16, 10, 12, 14, 11;
Erynnis, normal 4, 5.
Bombus juxtus, normal 4, Geranium 2;
Clisodon, normal 2, 1.
Clisodon, upper lip off 8; unable to
land on flower with upper lip
and stamens off; upper lip off 2;
normal 3, 8; touches Gilia;
Chamaenerium 1.
Erynnis, normal 4; B. juxtus, normal
3, 2, 4, 1 ; Chamaenerium, 2,
normal 1 ; Erynnis, normal 3,
upper lip off 4, both lips off 1,
upper lip and stamens off 1;
Argynnis merely lights on flower
with upper lip off.
Erynnis, normal 4, 5, leaf, normal 4, 8;
Chamaenerium 1, leaf.
Erynnis, normal 2, 3, 1.
Erynnis, upper lip and stamens off 1,
normal 1, 3.
Erynnis normal 4, 1, 1, 2.
8h53m Clisodon, normal 1, 3, 7, 8, 4; inspects
Chamaenerium head, 4 normal
flowers of head with middle
flowers shortened, upper lip off 3,
inspects Chamaenerium.
8 55 B. appositus, normal 8, 5, 8, 3, 8, 3, 9,
1 , rim flowers of shortened head
3, Chamaenerium 1.
8 57 Clisodon, normal 6,
normal 2.
9 00 Erynnis, normal 6
Geranium 1.
Erynnis, normal 2, 1.
1 ; B. juxtus,
white paper
9 01
9 04
B. juxtus, normal 7, 2, Chamaenerium
5, probing 1 from the bottom,
normal 2, Chamaenerium 2,
normal 6, 1, upper lip off 5,
normal 3; Erynnis, normal 3,
Gilia 1, 1, upper and stamens
off 8, upper off 3.
9 07 Erynnis, normal 8, 4, 2 normal and 1
shortened corolla of the same
head, upper lip and stamens off 9.
9 10 B. appositus, normal 10, 9, 8, 7, 4, 4,
3, 1 ; Erynnis, shortened corolla 1,
normal 12, Chamaenerium 2;
normal 5, rests on Gilia.
86
NORMAL AND EXPERIMENTAL POLLINATION.
Calendar 1
9h15m Clisodon, normal 2, 1, 4, 1 p. n., 7p,
7p, 3n; Chamaenerium 2, in-
spects 2 mutilated heads, normal
4, 6 p, 12 p twice (total 24),
2, 4 p, shortened 1, 5 p, 2 p;
B. juxtus, normal 3, Chamae-
nerium 1, shortened 7, inspects
flowers with both lips off,
normal 1,3, 1, Chamaenerium 2,
normal 6; Erynnis, upper and
stamens off 4, normal 3.
Clisodon, normal 2 p, upper lip off 1,
normal 3 p, 1 n, 10, inspects
heads with upper lip and with
this and stamens off, shortened
1, normal 3 p, 3, 4, 6, 2.
Argynnis, upper off 8.
Apis lands on 3 normal heads but is
unable to reach nectar; B. juxtus,
normal 2, Chamaenerium 3,
lower lip off 9, working very
rapidly, normal 3; B. appositus,
normal 1, 3, 2, 5; Erynnis,
upper lip off 7.
Erynnis, normal 2.
Argynnis, normal 2, upper lip off 6.
Clisodon, normal 12, 12, 13, inspects
Chamaenerium, shortened 3, 15
normal of shortened head, Cha-
maenerium 3, normal 1, 5, 8, 2, 4;
B. juxtus, normal 10, 11, 14,
Chamaenerium 6, Chamaenerium
1 (next stalk), shortened 6,
Chamaenerium head 2.
9 35 Argynnis, normal 3, 1, 14, 2, 4, 4;
Erynnis, normal 1, touches Gilia
and Chamaenerium, lower lip
off 8, leaf.
9 39 Erynnis, Chamaenerium 1; normal 1,
lower lip off 3, shortened 2,
Chamaenerium 1.
9 40 Erynnis, normal 5, 3, 4; Argynnis,
normal 5, Chamaenerium 1.
9 42 Argynnis, normal 2 ; Erynnis, shortened
1, upper lip and stamens off 2,
upper lip off 12, normal 1,
Geranium 1, lower lip off 2,
Chamaenerium 2.
9 22
9 25
9 26
9 30
9 31
9 33
■Continued.
9h45m Argynnis, normal 4.
9 47 Argynnis, upper lip off 12, normal 8,
tries all buds of young head,
lights merely on Chamaenerium*
9 49 B. juxtus, normal 1, 2, 1, 3, Chamae-
nerium 2; Clisodon normal 12,
13; B. appositus, normal 4, 5,
shortened 4, both lips off 3.
Erynnis, Gilia 1, normal 3, 2; Argynnis,
normal 2, 5.
B. appositus, normal 2, 2, 1, 1, 3, 3.
B. juxtus, small individual tries 4
heads but can not reach nectar.
Erynnis, normal 3, Gilia 1, normal 3,
lower lip off 4, normal 1.
B. appositus, normal 10; Erynnis,
normal 10, 11.
Clisodon, normal 4 p, 2 p, 3 p, 3 p,
2 p, 3 n, 3 n, 2 p, Chamaenerium
1, lower lip off 2 p, normal 2 p,
upper lip off 2 p, 1 n, 1 p, 3 p,
2 p, 1 n.
Erynnis, normal 2; Clisodon, normal
2 p, 1 p, 4 p, lower lip off 1 p, In,
normal 1, 5, 1 p, 1 p, shortened
1 and 3 normal of the same head,
Aster 1, normal 4, 4.
Erynnis, upper lip and stamens off 1;
B. morrisoni, Chamaenerium
head 4, shortened 1, normal 2,
Gilia 3; B. juxtus, normal 2,
upper lip and stamens off 3,
upper lip off 4, upper lip and
stamens off 3, 2 normal of short-
ened head, Chamaenerium 1,
normal 4, 1, 6.
10 06 Clisodon, upper lip and stamens off 3,
shortened 3, normal 3, 4 p, 3,
lower lip off 3 p, normal 4, 1 p,
7, 2, shortened 1; Argynnis,
normal 10, 4, 5; Erynnis, normal
3, 4, 3.
Argynnis, normal 14, 10, shortened 3.
Erynnis, 8 normal of shortened head,
upper lip off 2 ; Argynnis, normal
7, 6, shortened 2, lower lip off 4.
50
9 52
9 54
9 55
9 56
59
10 01
10 03
10 12
10 14
Calendar 2.
8h40m Bombus hunti, Chamaenerium raceme
68, inspects Aster, Chamae-
nerium raceme 16, Atrytone
normal 2, 2, Chamaenerium
raceme 2.
Erynnis, normal 2, upper lip off 6.
Erynnis, upper lip off 2, normal 3.
Erynnis, normal 10.
Aristatus, normal 1; B. morrisoni
queen, Chamaenerium raceme 2;
Erynnis normal 6, Gilia 1, nor-
mal 5.
Erynnis, normal 3.
Eristalis, Chamaenerium raceme 1;
Erynnis normal 2.
8 45
8 46
8 50
8 53
8 58
8 59
9h00n
9 02
9 08
9 14
9 26
Erynnis, upper lip off 7.
Erynnis, upper lip off 6.
Erynnis, Chamaenerium raceme 1;
Clisodon, upper lip off 3, normal
4, lower lip off 9, normal 1,
shortened 5, upper lip off 10,
normal 3, 13, inspects mixed
Gilia head, normal 6, 4, 5.
Erynnis, normal 1 ; Clisodon, normal 1 ;
Argynnis inspects 1.
Erynnis, normal 1.
Erynnis, normal 4, upper lip off 3;
H. pulzenus, normal 2, Aster 30
florets in 1 head.
Erynnis, Chamaenerium raceme 3.
MONARDA FISTULOSA.
87
Calendar 2 — Continued.
9h27m Erynnis, normal 6, upper lip off 5,
normal 8; H. pulzenus, Aster
16 florets in 1 head.
Erynnis, upper lip off 10.
Erynnis, Aster 12 florets in 1 head,
Chamaenerium raceme 20; Ar-
gynnis, upper lip off 2.
juxtus, Chamaenerium raceme 9;
Andrena same Chamaenerium
raceme 9.
Erynnis, normal 2; H. pulzenus, Aster
2 florets 1 head.
Argynnis, normal 5, 2, upper lip off 4.
B. morrisoni, normal 2.
Erynnis, normal 4, 3, leaf; B. bifarius,
Chamaenerium raceme 25, Gera-
nium 1, normal 6, 2.
10 05 B. morrisoni, normal 3; Syrphus,
normal 4, 8, 5; Erynnis, normal 6.
9 34
9 37
9 44 B.
9 50
9 53
9 56
9 58
10 14
10 17
10 19
10 20
10 22
10 24
10 26
10 29
10 30
10 34
10 35
10 38
10 42
Erynnis, upper lip off 2.
Erynnis, normal 4.
Argynnis, normal 4.
Argynnis, upper lip off 2; B. morrisoni,
normal 4, 7.
Clisodon, normal 1.
Argynnis, normal 5.
H. pulzenus 3, Aster florets in 1 head;
Erynnis, normal 2.
Erynnis, normal 4, 4, 2, 2; B. hunti,
Chamaenerium raceme 6.
Andrena, Aster 7 florets in 1 head.
Erynnis, normal 2, 3, 4.
Erynnis, normal 6.
Erynnis, normal 3; Colletes, Aster 2
florets in 1 head.
B. hunti, Aster 1; Erynnis, normal
8, 3, 5, 6; Argynnis, normal 5.
Erynnis, normal 1.
Table 60. — Summary of calendars.
Calendar 1.
II
a °
l«S
s a
a <»
a o
Clisodon. . .
B. appositus
juxtus. . .
morrisoni
Erynnis
Argynnis
Total
151
113
2
161
187
0
28
26:1
923
78:2i! 37
22:lsh
li
3
2
0
10:lsh
0
3:2i
0
o
26
0
0
0
3
3:2i
0
7:2i
1
25
0
7:1 i
1
37:2sh 4:li35:2:
li
43
i:2i
6:1
41:2i
0
0
0
lw
0
lw
Calendar 2.
Clisodon
B. juxtus. . . .
morrisoni . .
bifarius. . .
hunti
H. pulzenus. .
Andrena
Colletes
Erynnis
Argynnis
A try tone
Syrphus
Aristatus
Eristalis
Total
Grand total.
38
13
0
0
16
0
8
0
0
0
2
0
0
0
0
0
125
41
21:1 i
8
4
0
17
0
1
0
0
0
232:1 i 62
1,155: 1 il 140:2 i; 46 37:2sh 4:li'35:2i 48
6:li203:2;
1
0
0
0
0
0
1
0
0
1:1
0
51
0
7
0
2
0
12
0
0
0
0
0
0
0
0
0
0
1 73:li
4 74:1 i
88
NORMAL AND EXPERIMENTAL POLLINATION.
Table 61. — General summary.
Species
Normal
Total
muti-
lated.
Total
other
flowers.
Species
Normal
Total
muti-
lated.
Total
other
flowers.
309
151
113
2
161
187
51
7
37
1
77
35
8
1
29
7
11
1
Bombus hunti
Halictus pulzenus. .
0
2
0
0
125
21
4
17
1
0
0
0
0
0
41
8
0
0
0
0
91
51
16
2
37
0
2
0
0
1
Bombus appositus. .
juxtus
morrisoni. .
Colletes
Total
923
208
57
38
0
16
8
27
0
0
0
0
9
2
26
Bombus juxtus
morrisoni . .
bifarius. . . .
Total
Grand total .
232
76
237
1,155
284
294
Table 62. — Summary of tables; mutilations and totals.
Species.
Norm.
Mon.
Upper
lip
off.
Upper
and sta.
off.
Lower
lip
off.
Both
lips
off.
Corolla
short.
Total
mutila-
tions
Total
compet-
itors.
1,009
405
8
1
40
220
0
31
0
0
0
6
2
0
388
224
37
7
1
0
18
56
17
0
0
3
10
0
0
0
0
0
0
0
0
97
35
2
0
0
0
0
18
1
0
0
0
9
0
0
0
0
0
0
0
0
18
4
8
0
0
0
0
9
7
0
0
0
46
0
0
0
0
0
0
0
0
39
0
0
0
0
0
0
0
7
0
0
0
1
0
0
0
0
0
0
0
0
3
0
0
0
0
0
0
25
4
1
0
0
16
0
1
0
0
0
0
0
0
4
6
3
0
0
0
0
110
36
1
0
3
82
0
1
0
0
0
0
0
0
162
45
13
0
0
0
0
9
9
35
0
101
65
25
10
16
2
2
52
0
6
98
10
8
0
0
1
0
Bombus appositus. . .
bifarius
edwardsi . . .
hunti
juxtus
occidentalis .
morrisoni . . .
Colletes
Halictus (Lasioglos-
sum) sp..
pulzenus. . .
Monumetha
Eristalis
Grand total. .
2,397
220
58
101
11
60
453
449
SUMMARY.
Although the flowers of Monarda are in heads, they are sufficiently
separated that bees and the smaller butterflies must fly from one to another,
and are thus fairly comparable with those of other species. However, the
detailed consideration of the relation to competing flowers is deferred to
the succeeding chapter, the totals only being taken into account here for
the sake of a view of the entire experiment. The number of visits to muti-
RESUME. 89
lated flowers of Monarda and to flowers of other species was practically the
same, though this is doubtless only a coincidence. The normal flowers
were about thrice as attractive as these two groups, due in part to habit
and in part to the mutilated ones being often less conspicuous and demanding
unusual methods of approach.
The number of visits to the various mutilations were determined by
four factors, namely, conspicuousness, ease of landing, accessibility, and
exposure of nectar. Flowers with the upper lip removed were visited,
most, since they were least changed in essential respects, the lower lip
constituting the landing-platform and the attractive banner. The removal
of the stamens in addition diminished the visits more than half, by affecting
landing and eliminating the attraction of pollen, in the case of Clisodon
especially. Visits to flowers without the lower lip were about a fourth as
numerous as to those with the upper lip removed, due to their being less
conspicuous and deprived of the landing-platform. Blossoms with the corolla
shortened to half its normal length received an equal number of visits, a
puzzling fact when taken in conjunction with the response to flowers with
both lips cut off. The difference here is evidently to be explained by the
greater readiness with which the odor of the nectar escapes, as well as by the
greater ease of access for certain bees. The respective values of the upper
lip, stamens, lower lip, and both lips in attraction and guidance are probably
well indicated by the number of visits, viz, 220, 101, 58, and 11.
While Monarda exhibits a wide range of visitors, only 8 of these are
frequent and 5 important, namely, Clisodon, Bombus appositus, B. juxtus,
Erynnis, and Argynnis. Clisodon paid nearly as many visits to the normal
flowers as the total for the other four species, but it made only 1 visit in 10
to the mutilated flowers in contrast to about 1 to 2 for Erynnis and 1 to 3
for B. juxtus. Its large number of visits is to be explained chiefly by the
fact that many of them were made for pollen alone and did not involve
landing. It is interesting to note that the longer-tongued B. appositus
visited nearly twice as many normal flowers as juxtus, while it went to only
1 mutilated flower in 9 to 1 in 3 for juxtus. Among the butterflies, Erynnis
visited more than a half again as many normal flowers as Argynnis, but four
times as many mutilated ones. In spite of its apparently less accurate
movements, Erynnis was considerably more successful than B. juxtus and
several times more so than Argynnis in solving the difficulties presented by
the mutilated flowers.
RESUME.
Variation in number of visits. — The special studies of the abundance
of visitors and the frequence of visits made with Rubus deliciosus, Geranium
caespitosum, Chamaenerium angustifolium, and Pentstemon glaber show that
time, place, and conditions produce great fluctuations in the species and
numbers of visitors and visits. Considerable differences in these respects
between early, mid, and late season would be expected, but almost as great
differences may be found between successive days or hours, as, for example,
in the case of Chamaenerium, where the number of visitors and visits for
two successive hours were 21:728 and 4:204, or of Rubus deliciosus, for
which the figures for Apis were 22:127 and 5:5. The effect of even a
90 NORMAL AND EXPERIMENTAL POLLINATION.
small distance is shown in the Monarda calendars, which were made in
areas but 3 meters apart. The flower group was essentially similar in both,
but one calendar gave 1,061 visits to normal Monarda, 131 to the mutilated,
and 66 to other species, while the other made simultaneously yielded 94
normal visits, 7 mutilated, and 55 to competing flowers. Essentially
similar results were obtained the next day, the first area giving 923, 208,
and 57 visits respectively, and the second 232, 76, and 237. It is thus
evident that a single record or calendar can not give an accurate or com-
prehensive picture of the numerical relations between a group of flowers
and insects. It is evident also that similar variations must be more or
less universal, and that they often explain the discrepancies between the
results of different investigators.
Changes of position. — In general, the problem of alighting and securing
nectar from flowers in inverted, horizontal, vertical, or other changed
positions was solved with more or less readiness by the various bees. The
general behavior is well illustrated by the response to such changes in
Aconitum. Bombus juxtus and B. bifarius readily entered flowers with the
hood pointed downward, though this involved using the side petals instead
of the lower sepals as a landing platform. When the hood was turned to
the side, B. juxtus first hovered over such flowers for a moment before landing
successfully; in one case it slipped off, but tried again and succeeded. In
the case of inverted flowers, some individuals passed over them, others
hovered, and still others attempted to light and then flew away as
though disturbed by the change. Some landed at the lower sepals, turned
around, and entered upside down; at other inverted flowers they behaved
in exactly the same way, apparently recognizing the changed position before
landing. One individual landed three times at a group of inverted blossoms,
tried to reach the nectary without turning upside down, and failed in every
case. One B. bifarius mastered the problem readily and went to five
inverted flowers in succession, turning upside down just after alighting.
A scrutiny of the behavior of various species of bees when confronted
by changes in the position of flowers makes it certain that they usually
recognize such changes at once. Since these are essentially changes in
form, they demonstrate that such insects at least do distinguish forms.
Differences in specific behavior are shown by table 50, in which Apis paid
relatively almost twice as many visits to inverted as to normal flowers,
Pseudomasaris about half as many, and Bombus went about equally to the
two. Differences in individual behavior are exemplified by the instances
given above for Bombus and they are revealed as well by practically all
studies with changes of position. They permit no doubt of the remarkable
intelligence of bees in problems that arise in situations with which they are
familiar. It seems obvious also that many of the individual variations in
response are not the result of differences in intelligence, but rather in what
is called temperament in man.
Masking with cotton. — When the center of the flower was masked with
cotton, or cotton plugs put over or in the nectaiies, the bees were usually
unsuccessful in reaching the nectar or pollen. Most of them landed and
probed where the nectary or stamens should be, but were unable to reach
RESUME. 91
these except where they found an entrance at the edge. After making vain
attempts at one or two masked flowers, they usually hovered over others,
apparently inspecting them in the light of their previous experience. The
presence of a strange substance in the flower changed the relations so greatly
and offered an obstancle so foreign to the experience of the bee that it could
be solved in but few cases. Their behavior demonstrated the good memory
of bees for position in the flower, and their ignoring of the masked flowers,
both with and without experience of the cotton as an obstacle, indicated
their perception of form.
Mutilation. — In more than three- fourths of the experiments mutilated
flowers were visited to a greater extent than the normal ones, the outstanding
exception being Monarda, to which the normal visits were five times more
numerous than those to the mutilated flowers. The advantage enjoyed
by the mutilated flowers as a whole was due chiefly to those in which both
stamens and styles were excised or all parts removed but the ovary and
nectaries. These changes not only permitted the odor of the nectar to
escape more freely, but also made the nectar itself more readily accessible,
with the consequence that the bees could work more flowers in the same time,
and were also led to return to them sooner. Increasing the attractive surface
of the perianth also augmented the number of visits; for example, splitting
the hood of Aconitum and turning the sepals back rendered such flowers
more than four times as attractive as the normal ones. On the contrary,
reducing the expanse of the corolla to a half diminished its attraction from
one-half to a tenth in practically all cases and demonstrated its paramount
importance even in the case of habituated bees. When both lips were
removed in Monarda, the number of visits was reduced to a fortieth of the
total for all mutilations, though the difficulty of landing obviously played
some part in the result. The removal of the lower lip alone decreased the
visits to a fourth of those to flowers with the upper lip alone removed and to
a tenth of the total visits to mutilations.
The accounts of the behavior of the different species and of the individuals
of each species to the various mutilations naturally reveal similar specific
and individual differences to those found for changes of position, and these
are shown most clearly for Monarda in table 62. Clisodon paid only 1 visit
in 10 to the mutilated flowers in contrast to about 1 to 2 for Erynnis and
1 to 3 for Bombus juxtus. In contrast to the last, B. morrisoni made 1 visit
in 30 to mutilated ones, while B. occidentalis went to neither normal nor
mutilated Monarda, but only to flowers of competing species. There was
no striking difference between the general behavior of Bombus on the one
hand and the butterflies on the other. With respect to the type of mutila-
tion most visited, Erynnis, B. appositus, and B. juxtus went to each of the
5 types, Clisodon to 4, and Argynnis to but 3. Of the mutilated flowers
Clisodon gave the preference to those with the upper lip removed, as did
B. appositus; B. juxtus preferred those with the upper lip and stamens cut
away, while both Erynnis and Argynnis likewise went most often to the
flowers without an upper lip, the removal of the latter obviously interfering
least with attraction and access.
The evidence of this table, as well as that from the mutilation experi-
ments as a whole, leaves no doubt that these pollinators were able to dis-
92 NORMAL AND EXPERIMENTAL POLLINATION.
tinguish the form of the different types and to adjust themselves to the
changes with a great deal of ingenuity. What is now most needed is quanti-
tative studies of marked individuals, both old and young, to determine
differences in normal response and learning power.
Artificial flowers. — The artificial flowers employed were always com-
posite in nature, consisting of crepe-paper corolla or perianth surrounding
the natural center of the flower concerned, or more rarely of a natural
flower or head with a paper disk below it. These imitations were at once
rather more crude than those used by Plateau, Andreae,Wery. and others,
in so far as the attractive corolla was concerned and much more natural
with respect to stamens and pistil. As a rule, they were visited little or
not at all, receiving but 257 visits in comparison with more than 2,000 to
normal flowers, and a fifth of these were paid Frasera flowers provided
with Campanula petals. In more than a half of the installations the
imitations were completely ignored or received but 2 or 3 visits. The
best success was obtained with Rosa, in which the relation between visits
to natural and artificial flowers was 257 : 78, Rubus deliciosus, where it was
254:49, and Geranium, where it was 63:37, though the imitations were
5 times more numerous. In the case of the Frasera-Campanula composite,
this received 56 visits to 97 for the normal, proving that the use of natural
tissues was much less disturbing than that of paper. However, it is certain
that the paper corollas did not in themselves actually repel the bees, since
Bombus in particular went readily to paper Mentzelias in the early evening
before the natural ones were open.
There was the usual wide range in the behavior of the various genera.
Halictus pulzenus went indifferently to paper and natural roses, Bombus
juxtus visited practically as many Frasera flowers with Campanula petals
as normal ones, and B. bifarius went to more than half as many artificial
as natural Geranium flowers. Osmia was likewise a frequent visitor to the
imitations. On the other hand, no honey-bees were seen to visit artificial
flowers, though they often were deceived until they came near, as shown by
the fact that such flowers were much inspected. Prosopis and Andrena
made very few visits to the paper flowers. Very few flies and butterflies
were present in these experiments and the visits were too infrequent to
indicate their response.
The significant fact is that crude paper composites were visited freely
by a few species and that some flowers were frequently visited as imitations
and others not at all. While the results as a whole approach more nearly
those of Plateau and Forel than those of Andreae, Wery, Giltay, Detto,
and others, it is clear that they constitute the explanation of the discrepancy
between them, as is shown more fully in the final resume1 in Chapter 4.
The artificial flowers were sufficiently plausible to cause a large number
of inspections, which signifies that the marks differentiating them could not
be distinguished until the insect was within a few centimeters. The case
of Mentzelia shows that they did not repel visitors and that the difference
is rather one of habit.
Painted flowers. — These were much more successful than artificial
flowers in attracting visitors in competition with natural ones, receiving
RESUME. 93
420 visits to 845 for the latter. In the case of Aconitum they obtained
154 visits to 116 for the normal flowers, though they were more numerous
in the installation. This was likewise true of Chamaenerium, the numbers
being 111 to 103, though on the basis of the number of each the relation
is 44 : 103. The painted flowers of Rubus deliciosus were visited as frequently
as the natural ones, while in the case of Frasera the visits were a half and in
that in Delphinium a fifth as many as for the natural.
The outstanding visitor to the painted flowers was Bombus juxtus, which
made more than half the total number of visits. However, in two experi-
ments it was exceeded by the honey-bee, which made 27 such visits to its 12.
The 27 visits were in contrast to 67 for the normal flowers, thus showing
clearly how much more natural the painted flowers appeared than the paper
ones, since Apis did not visit a single one of the latter. Of the four colors
most employed, blue obtained a distinct preference, the visits being, blue 98,
green 84, yellow 55, and red 43.
The painted flowers were approximately five times as successful in
attracting bees as the paper ones. This was due to their identity with the
natural ones in everything but color, and indicates that the artificial flowers
were distinguished as such chiefly by small differences in form and by the
texture, thus demonstrating an acute perception of form and texture by
Bombus and A pis especially. The significance of this is further discussed
in the final r6sume\
Honey and odor. — In the majority of the species where it was employed,
honey actually decreased the number of visits, often tenfold, while in a few
it had no discernible effect. In no case did it increase the number of visits
to natural flowers, and it had practically no effect upon those to artificial
ones. The significant result of these experiments was to confirm the evi-
dence of the exceedingly poor sense of smell in bees for honey. Often they
would not discover the drop at a distance of a few millimeters and in some
cases they even became entangled in it without recognizing it. This may
have been due to the odor of the flower itself, but as it was true of all
the flowers employed, it suggests that the odor of nectar plays a very small
part in the attraction exerted by many species.
The addition of perfumes derived from other flowers or of other odorous
substances decreased the total of visits 50 per cent in comparison with
normal flowers. Even when honey was also added, a similar relation
obtained, though it is certain if the bees had been trained to come for
honey on flowers with a certain perfume that the latter would have seemed
attractive. With odor, as with color, form, and texture, habit is the con-
trolling factor, and this probably explains why the various perfumes ap-
peared to repel. They disturbed the habitual response of the bee, and
this was true whether perfumes, essences, or odors unpleasant to us were
employed. The results certainly do not strengthen the role of odor in
attraction, though undoubtedly it often plays a part in forming the habit
of guidance.
3. COMPETITION AND CONSTANCY.
Significance. — Although a number of studies have been made with
special reference to the constancy of a particular species of pollinator to
one species of flower, there has been little or no experimental work in this
field. Competition between different species or genera of plants for the
visits of insects has received practically no attention and no experiments
are known that bear directly upon this problem.1 The early view that the
bees in particular are constant or nearly so has been shown to be only partly
true by Bulman, Plateau, and others, and the whole subject of habit in
pollinators has been found to be much more complex than supposed. The
idea that constancy was essential to the effective cross-pollination of a
species, as well as to the prevention of hybridization, has necessarily been
modified, and is now rather to be regarded as a matter for investigation
in terms of habit and efficiency. Moreover, there have been several dif-
ferent concepts of constancy, as discussed later. In the present treatment,
the experimental results of competition studies are first considered. This
is followed by an account of the composition and weight of the pollen loads
of various species, and the chapter is concluded with a resume of the work
of other investigators and a summary of the general principles involved.
COMPETITION.
General plan. — The methods employed in competition experiments
have been discussed in detail in the introduction, the one most used in the
present study being that of reciprocal bouquets. The primary objectives
have been to throw light on the degree of habit fixation on the one hand
and to furnish evidence as to the relative attractiveness of different flowers
on the other. At the same time, questions of efficiency have been taken into
account. For the most part, the species with regular corollas were used in
order that visitors might not be excluded or handicapped by structural
features, but a few zygomorphic flowers were employed in order to disclose
the effect of structure.
The bouquet method was the one regularly used, though occasionally
normal plants grew sufficiently close to each other that equal areas or equal
numbers of flowers could be marked off for comparison. In all cases the
natural plant was regarded as the standard, and the comparison was made
by means of a bouquet placed in its midst or attached to the branches.
The bouquet consisted in some cases of a mass of flowers or a group of
branches and in others of single flowers or branches put in vials and attached
to the stems. In practically all cases where this method was used, the
records were made in the normal habitat of the standard plant. The
bouquets were arranged among the stems or branches so that the insects
would necessarily pass them in moving about. In a few instances the
bouquet consisted of several species from other localities, in order to deter-
mine the reaction to species probably not seen previously but similar to
those regularly visited.
1 Knoll has made an incidental study of competition, which has just come to hand (1922:
215); he employed Pelargonium zonale or Satureia nepeta in competition with Linaria vulgaris
in experiments with Macroglossa stellatarum.
94
RUBUS STRIGOSUS. 95
RUBUS STRIGOSUS.
General relations. — The raspberry is especially well fitted to serve as
a standard plant for competition studies, owing to its abundant nectar and
pollen, the duration of the flowering period, and its exceptional attractiveness
for the honey-bee. While it is employed as the standard plant for the
majority of the following experiments, certain reciprocal comparisons were
made in which it was the bouquet. The various species with which it
competed practically all possess open flowers, but exhibit a wide range in
the size and color of the latter and the amount of nectar and pollen, as well
as in the degree of relationship. With respect to the latter, Rubus deliciosus
represents a related species, Rosa a related and Opulaster a more distant
genus of the same family, while Geranium, Cleome, and Frasera are succes-
sively more remote, exemplifying a progressive decrease in the number of
stamens and pistils, as well as striking differences in the nectaries. Mer-
tensia and Pentstemon afford more pronounced differences, though these are
still within the range of effective competition. The order of treatment in
the following pages is essentially that of degree of relationship, though the
effect of size, color, and amount of nectar or pollen often obscures the signi-
ficance of this.
RUBUS STRIGOSUS AND RUBUS DELICIOSUS.
Comparison. — The flowers of the raspberry are small and inconspicuous
and more or less hidden by the leaves, so that they are hardly noticeable,
while those of the salmonberry are large and showy and stand out clearly
from the leaves on most of the branches. The flowers of both are white,
but the corolla of Rubus strigosus is masked to a large degree by the green
sepals. The flowers of the latter are often more numerous in an equal
area, but they are so scattered as to be quite ineffective. Pollen is naturally
abundant in both species, but there is approximately eight times as much
in R. deliciosus. The petals of the latter are expanded at right angles to
the pedicel, leaving the stamens much exposed, while in R. strigosus the
petals are more or less erect and the pollen consequently less accessible.
The nectar of R. deliciosus is formed at the base of the stamens and appears
as minute drops in a circle; it is produced in the same place in R. strigosus,
but much more abundantly, sometimes accumulating to an appreciable
depth in the stamen-tube (plate 3).
Experiments. — Of the five studies made with these two species, Rubus
strigosus was employed as the standard plant in the first three, and R.
deliciosus in the last two. Two observers recorded the visitors in each
case, and the numbers consequently are not only exact, but they are also
maximum. In all cases where two figures are separated by a colon, the
first indicates the number of insects and the second the number of visits
made by them.
The differences arising out of the time-factor are revealed by the totals,
the number of visitors being nearly twice as great in the first experiment.
During the third period, Rubus deliciosus received several times as many
visitors, due in part to the presence of the two species of flies. All told,
Apis furnished 171 visitors to the raspberry in contrast to 5 for the salmon-
96
COMPETITION AND CONSTANCY.
berry, while Bombus yielded 7 and 6 respectively. The total number of
visiting bees was 212 for the one and 21 for the other, while the flies went
to R. deliciosus alone to the number of 6.
Table 63. — Competition of Rubus strigosus and R. deliciosus.
Experiment 1, one hour, 10 to 11 a.m., July 6.
Experiment 2, one hour, ^SO" to 10h30m a.m., July 7.
Experiment 3, one hour, lO^O"1 to llh10m a.m., July 6.
Species.
Plant, R.
strigosus.
Bouquet, R.
deliciosus.
Species.
Plant, R.
strigosus.
Bouquet, R.
deliciosus.
First experiment:
73
5
4
2
2
2
1
7
0
7
0
0
1
1
0
0
0
0
1
0
Second experiment — Cont.:
Ancistrocerus sp
Calliphora vomitoria . . .
Syrphus americanus. . . .
Total
1
0
0
0
4
2
Andrena crataegi
vicina
proximus
Colletes oromontis
Halictus (Lasioglossum)
62
48
1
2
1
2
2
18
2
2
2
0
0
0
One juxtus visited a
flower of deliciosus
thrice in succession
and later returned.
Third experiment:
Prosopis basalis
varifrons
Total
103
50
2
2
3
4
3
3
3
4
2
0
Halictus pulzenus
Second experiment:
Pseudomasaris vespoides
Ancistrocerus sp
Total
Halictus pulzenus
56
6
Pseudomasaris vespoides
Table 64. — Competition of R. deliciosus and strigosus.
First experiment, one hour, 9 to 10 a.m.,
June 27.
Second experiment, one hour, 9 to 10 a.m.,
June 28.
Species.
Plant,
R. deli-
ciosus.
Bouquet,
R. stri-
gosus.
Species.
Plant
R. deli-
ciosus.
Bouquet,
R. stri-
gosus.
Apis mellifica
Andrena crataegi ....
vicina
Bombus bifarius
juxtus
proximus. . . .
Halictus evylaeus. . . .
Monumetha albifrons.
Osmia bruneri
melanotricha . .
Melitaea sp
Total
4
4
1
10
0
1
2
0
6
1
1
50
0
3
7
1
6
Apis mellifica
Bombus juxtus
morrisoni. . .
Syrphus americanus. .
12:53
6:26
2:77
1:1
6:39
3:26
0
0
Total
21:157
9:65
0
1
10
0
0
30
78
In spite of the fact that it was the bouquet and hence out of place, the
total number of visitors to R. strigosus was 87 in comparison with 51 for
R. deliciosus. These were all bees, the single fly and butterfly going to
RUBUS STRIGOSUS. 97
R. deliciosus, as would be expected. Of Apis, 56 individuals went to the
raspberry and 16 to the salmonberry, the preponderance of the former
being reversed in the second experiment. The number of visitors belonging
to Bombus was nearly the same for both experiments, viz, 17 and 19, and
they were also more abundant on R. strigosus in the first case and on R.
deliciosus in the second. The ratio of attraction to bees was almost exactly
the reverse in the two instances. It is also interesting to note that they made
an average of 7 visits to the raspberry to 4 for the salmonberry.
Summary. — Rubus strigosus is evidently much more attractive than
R. deliciosus, as shown bj' the fact that the total number of visitors in the
five periods was four times greater. However, this was true only for the
bees, though they furnished nearly the entire number, since the flies and
butterflies went only to the more visible and accessible flowers of the salmon-
berry. The raspberry held its advantage, whether used as the standard
plant or the bouquet, except in the last experiment, where twice as many
bees went to R. deliciosus. The constancy of the honey-bee was high in
the first four cases, viz, 221 visitors for R. strigosus to 9 for R. deliciosus,
but it was in abeyance in the last, in which twice as many went to the latter
as to the former. As a whole, Bombus was inconstant, 24 going to the one
and 23 to the other, while the numbers for the other bees were too small
to be significant, twice as many preferring R. strigosus, however.
RUBUS STRIGOSUS AND OPULASTER.
Comparison. — The flowers of Opulaster are about half as large as those
of the raspberry, but this is more than offset by their grouping in corymbs
and the position of the latter at or near the ends of the branches. The
spreading petals make the corymb verjr conspicuous, and at a distance it
assumes a uniformly white appearance. The nectar is less abundant in
Opulaster, but this is somewhat compensated by the large number of flowers
in a cluster and by the open nature of the cup. The stamens are also
less numerous and the amount of pollen available is considerably less.
Summary. — The total number of visitors was 138 for Rubus and 137
for Opulaster, indicating that they are equally attractive. However, the
former was more than twice as attractive to bees, the ratio being 137:64,
and overwhelmingly so to honey-bees, 85 of which visited the raspberry and
only 1 the nine-bark. Andrena crataegi was the only bee that exhibited
a marked preference for Opulaster, the ratio being 46:7. The behavior of
the flies was exactly opposite to that of the bees, 73 going to the nine-bark
and one to the raspberry. This appears to be readily explained by the
fact that the flowers of the former were more easily seen and the nectar
more accessible. The smaller amount of nectar and the ease with which
it can be obtained make clear the reason why the bees and Apis in particular
preferred the raspberry with its less conspicuous flowers and larger store
of nectar less accessible to flies.
COMPETITION OF RUBUS WITH FRASERA, CLEOME, ETC.
Comparison. — The flowers of Jamesia americana resemble those of the
raspberry, but differ in forming conspicuous white clusters at the ends of
branches, and in having much less pollen and much more perfume. Those
98
COMPETITION AND CONSTANCY.
of Cleome serrulata are smaller, pink in color, and grouped in conspicuous
spike-like racemes; nectar is abundant, but the odor of the plant is strong.
The flowers of Geranium richardsoni are white and occur scattered at the
ends of branches; they are somewhat larger than those of the raspberry,
but contain much less nectar and pollen. Those of Chamaenerium angusti-
folium are about the same size, of a deep-pink color and arranged in a bril-
liant raceme often 2 or 3 feet long; the value in both nectar and pollen closely
approaches that of the raspberry. The single flowers of Frasera speciosa
are fairly inconspicuous, but the massive spike-like clusters are visible
at considerable distances. The nectaries are highly differentiated and the
flow abundant. Mertensia sibirica differs from all the others in having
tubular flowers of a blue color; they produce a scanty amount of pollen
and nectar (plates 3, 7, 8, and 10).
Table 65. — Natural and bouquet competition.
Experiment 1, \]4 hours, 10h30m to 12 a.m., June 27.
Experiment 2, 1 hour, 10h10m to llh10m, July 6.
Experiment 3, 1 hour, 8h30m to 9h30m, July 7.
Experiment 4, 1 hour, 8h30m to 9h30m, July 7.
Experiment 5, 1 hour, 9 to 10 a.m., July 12.
Species.
Plant, R.
strigosus.
Plant,
Opulaster.
Species.
Plant, R.
strigosus.
Plant,
Opulaster.
First experiment:
Apis mellifica
Andrena crataegi. .
madroni-
tens
vicina. . . .
Bombus bifarius. . .
proximus. .
Osmia bruneri
Prosopis elliptica. .
25
0
0
2
6
2
4
3
0
0
20
1
2
0
0
0
0
7
Third experiment —
Continued:
Pseudomasaris
vespoides
1
0
0
0
41
1
Lepidoptera
Total
Fourth experiment:
Apis mellifica
Andrena crataegi . .
Halictus pulzenus. .
Monumetha albi-
42
Bouquet,
R. strigosus.
4
1
0
1
0
0
50
Plant,
Opulaster,
1
3
3
0
1
9
Total
Second experiment:
Andrena crataegi . .
Halictuspulzenus. .
Osmia bruneri
42
Bouquet,
R. strigosus.
6
1
1
30
Plant,
Opulaster.
18
1
0
16
Pseudomasaris ves-
Total
Fifth experiment:
Apis mellifica
Andrena crataegi. .
Bombus bifarius. . .
juxtus. . . .
proximus. .
Osmis densa
Prosopis varifrons. .
Total
Total
Third experiment:
Apis mellifica
Andrena crataegi . .
Bombus juxtus ....
Megachile wootoni.
Osmia bruneri
densa
6
Plant, R.
strigosus.
20
0
14
1
0
3
1
17
Opulaster
in vials.
0
1
0
0
2
1
1
9
Plant, R.
strigosus.
36
0
3
0
0
2
35
Bouquet,
Opulaster.
0
5
0
1
2
0
39
5
RUBUS STRIGOSUS.
99
Experiments. — In the first case all three plants were rooted in position,
affording a test of natural competition. In the others, Rubus strigosus
was the standard and its competitors were arranged in bouquets or vials.
Table 66
. — Rubus and Frasera, Cleome, etc.
Expt. 1, 1 hour, 11 to 12 a.m., June 23.
Expt. 2, 2 hours, 10 to 12 a.m., July 13.
Species.
Plant, R.
strigosus.
Plant, M.
sibirica.
Plant, J.
americana.
Species.
Plant, R.
strigosus.
Geranium
in vials.
Bombus
bifarius. . .
Colletes
oromontis .
Diptera
Total
5
0
3
1
1
4
1
0
1
15
14
2
5
0
0
0
0
proximus
Prosopis varifrons
36
0
8
6
2
26
37
1
Chamae-
nerium in
vials.
0
0
0
Prosopis varifrons
Total
64
0
Expt. 3, 1 hour, 10 to 11 a.m., July 14.
Expt. 4, 1 hour, 11 a. m., to 12 m., July 18.
Species.
Plant, R.
strigosus.
Bouquet, F.
speciosa.
Species.
Plant, R.
strigosus.
Bouquet, C.
serrulata.
Apis mellifica
57:62
1:1
0:0
0:0
1:1
8:9
11:16
6:6
2:2
1:1
37:62
0:0
2:5
1:2
3:3
0:0
2:2
1:1
4:4
1:1
22
2
0
1
0
3
4
2
3
0
1
0
1
0
0
0
0
ronitens. . . .
Bombus juxt>
Colletes ororc
Halictus pulzenus
(Lasioglossum)
ontis
enus
Megachile wootoni
Pseudomasaris vespoides. .
melanotricha
Prosopis elliptica
Pseudomasaris vespoides. .
Total
Protothyreopus dilectus . .
Total .
87:98
51:80
37
3
Summary. — The total number of visitors to Rubus was 232, in contrast
with 62 to all its competitors, though the raspberry was undoubtedly favored
by being the plant in each case. With the flowers in vials, Geranium and
Chamaenerium exerted no competition whatever and that of Cleome was
negligible. Mertensia approached Rubus in attractiveness and Frasera
apparently exceeded it, as suggested by the relatively greater number of
visits per insect. This was especially true of the honey-bee.
RUBUS STRIGOSUS AND TWO OR MORE COMPETITORS.
Comparison. — The flowers of the two species of Pentstemon are much
larger than those of the raspberry, but they contain much less pollen and
100
COMPETITION AND CONSTANCY.
nectar. P. secundiflorus possesses a pink-purple corolla with a wide throat,
while that of P. barbatus is a flaming scarlet with a narrow throat and hence
excludes the larger bees. The flowers of Scrophularia nodosa are small
and of a dull mottled color, but these disadvantages are offset by the
abundant nectar. Those of Aquilegia coerulea are large and showy, the
sky-blue color making them exceedingly conspicuous; they contain much
pollen and nectar, but the latter is unavailable to many of the visitors.
The deep-blue flowers of Mertensia alpina are relatively small, with a narrow
throat, and are borne in small clusters. However, they possess a delightful
fragrance, which is indicated by their local name, "forget-me-nots." Table
67 contains the record for 1 hour 15 minutes, from 10h45m a. m. to 12 m. on
July 4, and table 68 for an hour, 10h20m to llh20m a. m. on July 12.
Table 67. — Rubus, Pentstemon, and Scrophularia.
Species.
Plant, R.
strigosus.
Bouquet, P.
secundiflorus.
Bouquet, P.
barbatus.
Bouquet, S.
nodosa.
Many.
0: 0
1: 4
0: 0
1: 2
0: 0
2: 5
4:12
1: 1
1: 3
0: 0
4:12
0: 0
2: 3
5:14
4: 5
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
1: 3
0: 0
0: 0
0: 0
0: 0
0: 0
4:21
Total
8:23
17:38
0: 0
5:24
Table 68. — Rubus, Aquilegia, and Mertensia.
Species.
Plant, R.
strigosus.
Bouquet, A.
coerulea.
Bouquet, M
alpina.
Apis mellifica
Andrena crataegi
madronitens
Andronicus sp
Bombus juxtus
Halictus pulzenus
Megachile texana
Monumetha albif rons
Osmia densa
Prosopis sp
Pseudomasaris vespoides
Muscidae
Atrytone taxiles
Total (Apis)
Countless.
1: 1
16:20
1: 1
0: 0
0: 0
1: 1
20:66
7: 9
1: 1
1: 2
0: 0
0: 0
0: 0
4: 4
1: 1
36:85
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
1: 1
6: 6
0: 0
2: 2
1: 1
10:10
Summary. — In both cases the honey-bees were so numerous that they
could not be counted at the same time that the other visitors were noted.
In the first experiment Pentstemon secundiflorus was nearly twice as attrac-
RUBUS DELICIOSUS — ROSA ACICULARIS. 101
tive to the other bees as the raspberry and Scrophularia was about equal to
the latter. It is interesting that P. barbatus received neither visits nor
inspections from bees to most of which it was new, but this probably is to
be ascribed partly to color and partly to habit. In the second experiment
the honey-bee was again almost perfectly constant to Rubus, while the other
bees preferred Aquilegia in the ratio of 2:1. Bombus juxtus showed a
decisive preference for the latter, as Prosopis did for Mertensia; on the
contrary, the wasp Pseudomasaris went only to the raspberry. Taking all
bees into account, Rubus was much the most attractive, but, ignoring the
honey-bee, the attractive features of Pentstemon secundifiorus and Aquilegia
coerulea proved more potent than the control exerted by habit.
RUBUS DELICIOSUS.
Experiments. — In the studies with this species it was compared with
two plants of the same family, viz, Rosa acicularis and Prunus demissa.
The flower of the rose resembles that of the salmonberry closely in form,
size, and grouping, but contrasts sharply in color. On the other hand,
the flowers of the chokecherry, though white, are several times smaller
and arranged in close racemes. The color area is much the same in the
three, but in Prunus it is broken by the spaces between the flowers; the
raceme is much the most fragrant and produces more nectar, while the
amount of pollen appears to be much the same as in the single flowers of
the other two species. Since the plants grew in juxtaposition, it was only
necessary to bring the branches together to form an effective competition
group, though in the last case a bouquet of Rubus was used (table 69).
Summary. — Of the total of 434 visitors, 302 went to Prunus, 120 to
Rubus, and 12 to Rosa. While this indicates the relative attractiveness,
it must be considered with reference to the fact that 387 of the total were
contributed by Andrena and Diptera. Had either Apis or Bombus been
abundant in the area at this time, the results would have been very different.
The marked preference of Andrena for Prunus is shown by the fact that
the latter obtained 225 visitors to 43 for Rubus and 4 for Rosa, all of the four
species exhibiting the same behavior. The preference was less marked in
the case of the flies, 75 going to Prunus and 40 to Rubus. The honey-bee
was all but perfectly constant to Rubus, 26 visiting this in contrast to one
to Rosa and none to Prunus. All told, the rose received less than a tenth of
the total number of visitors in the experiments concerned, affording clear-cut
evidence of the effect of habit in the face of greater total attraction.
ROSA ACICULARIS
Comparison. — Of the competitors employed, Rubus deliciosus most
nearly resembles the rose in size and form, but contrasts sharply with
its white color. Rubus strigosus and Opulaster opulifolius, though likewise
belonging to the same family and white in color, differ greatly in form, size,
and arrangement. Geranium caespitosum and Chamaenerium angustifolium
approach closely in color, but they are much smaller and yield much less
pollen, and this is largely true also for Cleome serrulata. Aquilegia coerulea
equals the rose in pollen production and excels it in the attractiveness of the
bright blue corolla, while the flowers of both species of Mertensia are rela-
102
COMPETITION AND CONSTANCY.
tively small and produce little pollen, but are readily visible by virtue of
their deep blue color (plates 3, 7, 8, and 11).
Table 69. — Rubus, Rosa, and Prunus.
Expt. 1.2 hours, 9h45m to llh45ma.m.June23.
Expt. 3, 1 hour, 10 to 11 a.m., June 28.
Species.
oq
3
. B
c ®
s
Species.
|
tf .2
o
03 13
S
W 3
-w °
a "3
03 03
03
3 oj
03 -O
First experiment:
Andrena madronitens ....
prunorum
0
0
5
3
21
7
4
25
0
45
Andrena crataegi
madronitens. . . .
10
0
0
0
0
1
0
1
3
0
1
2
1
0
1
0
85
2
2
1
0
0
0
3
proximus
Total
29
81
Total
12
8
93
Two hours, 8h30m to 10h30m a.m., June 25.
6
1
6
1
0
5
22
6
12
0
1
23
madronitens
Expt. 4, 2 hours, 9h48m to lh48m a.m., July 3.
Pseudomasaris vespoides . . .
Species.
o
3
tf.2
. o
a •
OJT3
W 3
03 03
Total
19
64
Expt. 2, 1 hour, 10 to 11 a.m., June 28.
Species.
« i
23
2
2
1
2
1
1
3
4
3
1
1
1
2
0
0
0
0
0
0
0
0
.. 03
3 .2
05
Halictus pulzenus
Pseudomasaris vespoides .
13
2
1
1
54
6
0
4
Anthrax lateralis
Eristalis latifrons
Syrphus americanus
Systoechus vulgaris
madronitens
Total
Total
17
64
43
4
Experiments. — In order to save space some of the less important
details of installation are omitted and others are given in the discussion
that follows tables 70 and 71. As always, an equal number of flowers was
used as a rule or an endeavor was made to have the attractive surfaces equal.
Summary. — Rosa acicularis proved to be less attractive than its com-
petitors taken collectively, the ratio being 327:420. Rubus strigosus
ROSA ACICULARIS.
Table 70. — Rosa, Rubus, Geranium, etc.
103
Expt. 1, 1 hour, 8h45m to 9h45m a.m., July 6.
Expt. 3, 1 hour, 8h50m to 9h50m a.m., July 6. ■
Species.
Plant, R.
strigosus.
Bouquet, R
acicularis.
Species.
Bouquet, R
acicularis.
Plant, O.
opulifoliua.
50
1
2
1
0
3
4
0
0
3
0
0
0
1
5
0
2
1
Andrena crataegi
madronitens. . . .
Halictus pulzenus
Prosopis varifrons
0
0
0
0
0
20
1
2
1
26
Andrena crataegi
Halictus pulzenus
Osmia coloradella
Pseudomasaris vespoides. .
Total
0
50
Expt. 4, \y2 hours, 9h30m to 11 a.m., July 8.
Total
61
12
Species.
Plant, R.
acicularis.
Plant, G.
caespitosum.
Expt. 2, 1 hour, 10h40m to llh40m a.m., July 7.
Species.
Plant, R.
strigosus.
Bouquet, R.
acicularis.
Prosopis episcopalis
elliptica
10:10
0:0
1:1
9:15
1:4
9:30
4:13
4:15
4:4
1:1
1:1
5:11
4:9
5:16
1:1
1:1
5:5
33:36
2:2
0:0
0:0
0:0
0:0
0:0
0:0
1:1
8:8
0:0
0:0
0:0
0:0
0:0
0:0
0:0
42
1
2
2
5
0
0
0
4
0
0
2
Andrena crataegi
occidentalis
Anthophora simillima. . . .
Halictus (Evylaeus) sp.. . .
pulzenus
( Lasioglossum ) sp.
Megachile texana
wootoni
Monumetha albifrons. . . .
Megachile wootoni
Pseudomasaris vespoides. .
Total
52
6
Expt. 3, 1 hour, 10h40m to llh40m a.m., July 7.
sp
Species.
Bouquet, R.
strigosus.
Plant, R.
acicularis.
Eristalis latifrons
Total
65:137
44:47
Anthophora simillima ....
Apis mellifica
2
0
1
1
1
2
0
4
1
0
0
0
Expt. 5, 2 hours, 10h05m to 12h05m a.m., July 18.
Halictus (Evylaeus) sp. . .
Monumetha albifrons ....
Species.
Plant, R.
acicularis.
Bouquet, C.
serrulata.
Syrphus americana
Total
8:15
0:0
5:6
1:1
1:1
1:4
1:1
2:2
1:3
7
5
15:22
1:4
2:2
0:0
2:3
1:2
0:0
5:8
0:0
occidentalis
Andrena madronitens. . . .
Prosopis elliptica
Megachile wootoni
Syrphus americanus
Total
26:41
20:33
104
COMPETITION AND CONSTANCY.
Table 71. — Rosa, Chamaenerium, Aquilegia, etc.
Expt. 1, IK hours, 10h30m a.m. to 12 m., July 11. Expt. 4, 1)4 hours, S^O™ to 10 a.m., July 12.
Species.
Plant,
R.
acicularis.
Vials,
C.
angusti.
Species.
Plant, R.
acicu-
laris.
Bouquet,
A. coer-
ulea.
Bouquet,
M. al-
pina.
5
2
0
1
1
0
0
1
0
0
Adrena crataegi
madronitens. . .
1:1
2:2
4:4
1:1
12:16
1:1
1:1
2:2
1:1
0:0
7:7
0:0
5:5
2:5
0:0
29:61
0:0
4:5
1:1
0:0
1:1
11:11
0:0
1:1
0:0
0:0
0:0
1:1
0:0
0:0
0:0
2:2
3:3
Bombus occidentalis . . .
juxtus
Halictus pulzenus
Monumetha albifrons . .
Prosopis basalis
Anthrax lateralis
Eristalis arbustorum . . .
Muscidae
Total
Total
9
1
Expt. 2, 1^ hours, lO^O™ a.m. to 12 m., July 12.
Species.
Plant,
Rosa.
Vials,
Rosa.
Vials,
Chamae.
32:36
53:89
7:7
Expt. 5, 1 hour, 8h30m to 9h30m a.m., July 20.
Bombus proximus
bifarius
juxtus
Halictus pulzenus
man'tonellus..
Megachile wootoni ....
Total
72
2
1
3
1
1
41
2
1
1
1
0
7
0
0
0
0
0
Species.
Bouquet,
Rosa.
Bouquet,
Aquil-
legia.
Bouquet,
Rubus d.
80
46
7
0:0
7:9
23:31
5:17
2:10
5:6
0:0
10:14
11:11
2:2
1:1
0:0
13:25
0:0
1:1
3:3
1:2
1:1
1:1
0:0
0:0
0:0
6:7
0:0
0:0
2:2
0:0
3:3
1:1
0:0
Andrena crataegi
Bombus juxtus
occidentalis. . .
Clisodon terminalis ....
Halictus pulzenus
Monumetha albifrons . .
Prosopis basalis
elliptica
Expt. 3, 3 hours, 7h30m to 10h30m a.m., June 27.
Species.
Plant, R.
acicularis.
Plant, M.
sibirica.
0
3
2
9
0
5
0
1
2
23
0
0
1
1
0
60
0
0
Total
65:100
21:34
12:13
Total
22
85
greatly exceeded it in attractive power, in the ratio of 120:23, though this
was due chiefly to the habitual preference of the honey-bee. When
Rosa was the standard and Rubus the bouquet, the difference was slight,
owing to the fact that Apis then visited the first alone. In competition
with Opulaster, the rose received no visitors, a consequence explained by the
fact that practically all the visitors present were flies and species of Andrena.
The rose was most effective in competition with flowers of similar color
but smaller size, the ratio being 65 : 44 for Geranium, 26 : 20 for Cleome. and
GERANIUM.
105
9:1 for Chamaenerium. When a flower of rose or of fireweed in a vial was
paired with rose flowers on the bush, the latter yielded 85 visitors to 49 for
the first and 7 for the second. When Rosa as the standard competed with
Aquilegia, the latter received nearly twice as many visitors and more than
twice as many visits, but when both were in the form of bouquets, the num-
ber of visitors and visits to the rose was thrice as great. This exception to
the general rule for standard and bouquet was due chiefly to the reversal
of the behavior of Bombus juxtus and the greater abundance of Prosopis.
The success of Mertensia sibirica in securing nearly four times as many
visitors as the rose was the result of the constant preference of Andrena
madronitens and Osmia phaceliae for it, all the other species choosing the rose.
The small number of visitors for Mertensia alpina is partly to be explained
by its being removed a long distance from its native habitat in terms of
climate and vegetation.
Competition with normal and mutilated Aquilegia. — In this
experiment were employed 50 normal flowers of the rose and columbine,
and 10 flowers of each of the three kinds of mutilation. In addition, a
pile of loose petals 6 inches in diameter was placed on the ground. The
period of observation was one hour, 9h15m to 10h15m, July 13.
Table 72. — Competition of Rosa with normal and mutilated Aquilegia.
Species.
Normal.
Mutilations.
Plant,
Rosa.
Bouquet,
Aquilegia.
Sepals and
petals off.
Petals
off.
Petals and
spurs off.
Loose
petals.
Bombus juxtus
occidentalis . . .
Andrena crataegi
Halictus pulzenus
Megachile texana
w. calogaster
Monumetha albifrons . .
Osmia densa
Prosopis elliptica
5
6
9
0
0
5
1
1
1
0
0
0
5
9
10
0
0
5
1
1
1
0
0
0
28:31
1: 1
0: 0
1: 1
1: 1
0: 0
1: 1
0: 0
0: 0
0: 0
1: 1
1: 1
7:10
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
6: 6
0: 0
1: 1
0: 0
0: 0
0: 0
0: 0
0: 0
1: 1
1: 1
1: 1
1: 1
5:6
0:0
0:0
0:0
0:0
1:1
0:0
0:0
0:0
0:0
0:0
0:0
2:2
0:0
0:0
0:0
0:0
0:0
0:0
0:0
0:0
0:0
0:0
0:0
Syrphus americanus. . . .
Muscidae
Total
28:32
34:37
7:10
11:11
6:7
2:2
While the rose was more attractive to Bombus occidentalis, Andrena
crataegi and Megachile w. calogaster, the greater number of visitors of
B. juxtus gave the preference to the columbine. The mutilations were
relatively more visited than the normal flowers, this exception. to the rule
for decorollate flowers being explained by the bright-colored stamen mass
and the blue color of the sepals.
GERANIUM.
Comparison. — The flowers of Geranium caespitosum and G. richardsoni
are almost identical except for the color, the former being pink-purple and
106 COMPETITION AND CONSTANCY.
the latter practically white. In nature, G. caespitosum is much more visited,
as it is a plant of open sunny slopes. Its flowers are larger and much more
conspicuous than those of Rubus strigosus, but are only about one-fourth
the size of the rose. They are also much smaller than the flowers of Aqui-
legia coerulea and the color somewhat less attractive, while the pollen is
much less abundant. Mertensia alpina possesses the advantage of blue
flowers, but the cluster is rather less conspicuous than a single geranium.
In the group of natural competitors, the heads of Aster bigelovi resemble
the flowers of geranium in size and color, but they yield more nectar and
pollen. Campanula rotundifolia, in spite of its deep blue color, produces
little pollen or nectar and moot pollinators ignore it. In both Allium
recurvatum and Heracleum lanatum, the smallness of the flowers is com-
pensated by their grouping in umbels, though even this is little effective
in Heracleum. The pink flowers of Allium produce an amount of nectar
and pollen that is out of proportion to their size. Of the competitors
with zygomorphic flowers, Pentstemon secundiflorus and P. barbatus have
larger and more brilliant flowers, and the cluster is larger and more vivid
in Castilleia miniata, while the chief asset of the small, dull flowers of
Scrophularia nodosa lies in the abundant nectar (plates, 3 7, 11, 12, 13,
and 14).
Experiments. — Table 73 deals with the competition between the two
species of Geranium in various installations, table 74 with competition be-
tween Geranium and other genera, and tables 75, 76, and 77 with group
competition.
Although Geranium caespitosum yielded 277 visitors to 155 for G. richard-
soni, in competition with each other, they are more nearly equal in attrac-
tiveness than this would indicate. This difference is more than accounted
for in the behavior of Prosopis, which preferred caespitosum in the ratio of
184:28, chiefly when this species was the standard. The two were practi-
cally equal when both were used in the form of bouquets, and they changed
rank in two successive periods in which they alternated as standards, the
respective ratios being 88:9 and 83:10. This equality is further indicated
by their behavior in competition with Rubus strigosus, though the conditions
were not precisely comparable in the different experiments. When plants
were compared, A pis was perfectly constant to the raspberry, but in all
other cases it exhibited a practically exclusive preference for the standard
plant, going to richardsoni, caespitosum, or strigosus as each took this role.
Between richardsoni and strigosus as plants, Prosopis gave a ratio of 42:1,
while between bouquets of G. caespitosum and Rosa the ratio was 28:0.
The honey-bee behaved similarly in the latter choice, while for Bombus the
preference was reversed, namely, 0:29, as it was likewise for Megachile
and Anthophora. However, Aquilegia in a mixed boquet was as attractive
as standard G. caespitosum, while the associated Mertensia alpina received
but one visit. It is interesting to note that Andrena crataegi was the only
visitor to both Geranium and Aquilegia in this experiment.
The size of the flowers differs so much in this group that exact comparisons
are difficult. In spite of the size of the clusters, however, the pinkish or
white flowers of Allium and Heracleum were obviously at a disadvantage.
The flowers of Geranium and Campanula and the heads of Aster are somewhat
GERANIUM. 107
Table 73. — Competition of Geranium caespitosum and G. richardsoni.
1
Expt. 1,1% hours, lO^O" a.m. to 12 m., July 14.
Expt. 4, 2 hours, 8 to 10 a.m., July 9.
Species.
Plant,
caespitosum.
Bouquet,
richardsoni.
Species.
Caespitosum,
vials.
Richardsoni,
plant.
Andrena madronitene . . .
Halictus pulzenus
Megachile wootoni
Monumetha albifrons. . .
Prosopis elliptica
varifrons
0
14
5
3
46
57
1
2
5
0
0
0
3
7
0
0
0
2
2
0
5
0
49
2
15
3
18
1
Andrena madronitens . .
Bombus bifarius
proximus
Halictus pulzenus
Prosopis varifrons
Total
9
88
128
15
2 hours, 10 a.m. to 12 m., July 9.
Exp. 2, half-hour, 9h25m to 9h56m a.m. July 14.
Apis mellifica
0
1
0
1
1
0
1
3
1
1
1
1
Vials
Vials
Halictus pulzenus
Osmia phaceliae
Prosopis elliptica
5
1
0
13
1
55
6
1
2
0
0
1
0
0
6
2
0
1
Anci trocerus sp
Bombus juxtus
Halictus pulzenus
Monumetha albii'rons. .
Prosopis elliptica
varifrona
Sphex vulgaris
Total
3
8
Expt. 3, half-hour, 8h45m to 9h15m a.m. August 5.
Species.
Bouquet,
caespitosum.
Bouquet,
richardsoni.
Total
83
10
Bombus bifarius
Foenus perplexus
Halictus pulzenus
(Chloralictus)
2
2
8
1
4
0
1
2
5
0
5
1
4
1
0
5
2 hours, 1 to 3 p.m., July 9.
Andrena madronitens. .
Ancistrocerus sp
7
6
1
2
5
12
1
7
2
0
2
1
2
0
(Lasioglossum)
sp
Osmia penstemonis ....
Prosopis elliptica
wootoni
Total
Megachile relativa
Prosopis elliptica
varifrons
Protothyreopus dilectus
Total
20
21
34
14
Expt. 6, 1 hour, S^O00 to 9h30m a.m., July 23.
Species.
Plant,
caesp.
Bouquet
caesp.
richard.
1
1
1
1
2
2
1
0
0
1
0
0
0
1
0
1
0
0
Andrena madronitens . .
Bombus occidentalis . . .
Halictus (Lasioglossum)
sp
pulzenus
Prosopis varifrons
Total
8
2
2
108
COMPETITION AND CONSTANCY.
Table 74. — Geranium, Rubus, Rosa, Aquilegia, etc
Expt. 1, 1 hour, O^O" to lO^O* a.m., July 2.
Expt. 3, 1 hour, 2h50m to 3h50m p.m., July 11.
Species.
Plant, G.
richard.
Plant, R.
strigosus.
Species.
Mixed bouquet.
Ger. caes.
Rosa acic.
0
0
1
1
40
2
1
1
1
1
29
1
0
0
1
0
0
0
0
0
16
15
13
0
0
0
0
2
0
0
3
1
0
0
0
8
21
8
3
0
1
1
0
0
Andrena madronitens . .
Osmia bruneri
Prosopis basalis
elliptica
Bombus occidentalis . . . .
juxtus
Megachile wootoni
Anthophora simillima. . .
Prosopis basalis
elliptica
Psammophila violace-
Sphex vulgaris
Andrena crataegi
prunorum
Osmia melanotricha . . . .
Halictus pulzenus
48
31
50
42
Expt. 2, 1 hour, 11 a.m. to 12 m , July 10.
Expt. 4, half-hour, ll^O™ a.m. to 12 m., July 12.
Species.
Plant, G.
caespitosum.
Bouquet, R.
strigosus.
Species.
Plant, G.
caesp.
Mixed bouquet.
11
2
0
0
0
0
1
1
Halictus pulzenus
A. coer.
M. alp.
Prosopis basalis
Total
13
2
Andrena crataegi
madronitens. .
0:0
3:3
0:0
0:0
0:0
0:0
0:0
1:1
1:1
1:1
1:1
4:4
2:2
1: 1
1: 1
1: 1
1: 1
2: 2
4: 4
1: 1
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0:0
0:0
0:0
0:0
1:1
0:0
0:0
0:0
0:0
0:0
0:0
0:0
0:0
1 hour, 11 to 12, July 11.
Bombus juxtus
occidentalis. . .
Halictus pulzenus
Monumetha albifrons . .
Prosopis episcopalis ....
Protothryreopus dilec-
48
2
0
0
0
0
1
1
Halictus pulzenus
Prosopis basalis
Total
50
2
Arctophila flagrans. . . .
Eristalis latifrons
Symmorphus sp
Syrphus americanus. . . .
Total '
1 hour, 10 to 11 a.m., July 8.
Species.
Bouquet, G.
caespitosum.
Plant, R.
strigosus.
13:13
11:11
1:1
0
4
1
1
24
0
1
1
Ancictrocerus sp
Prosopis basalis
Total
6
26
GERANIUM.
109
similar in color and size. As there were 25, 10, and 5 respectively, the
corresponding numbers for visitors and visits are 11:26, 45:90, and 10:10,
the much larger nectar supply of Aster giving it a great advantage.
Table 75. — Natural competition: Geranium, Aster, Allium, Campanula, Heracleum.
1 hour, 10h15m a.m. to llh15m a.m., August 2.
Species.
G. caesp-
itosum.
A. big-
elovi.
A. recur-
vatum.
C. rotund-
ifolia.
H. lan-
atum.
0: 0
1: 1
1: 2
1: 1
6:11
2:11
0: 0
0: 0
0: 0
0: 0
1: 2
0: 0
0: 0
0: 0
2: 2
0: 0
4: 4
3: 7
3: 8
6:14
0: 0
0: 0
2: 4
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
2: 2
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
1: 1
0: 0
Total
11:26
19:37
2: 4
2: 2
1: 1
Summary. — In these two experiments the preferences of most of the
visitors were so pronounced that the usual difference between plant and
bouquet is hardly to be seen. Anthophora, Bombus, and Osmia were the
only visitors to work on both standard and bouquet, the first two giving
preference to the rose and the last to Pentstemon secundiflorus. Andrena
and Megachile likewise preferred the rose, while Apis selected Geranium.
The competition between Geranium and Castilleia was conclusive as to the
marked specialization of the latter, the broad-tailed humming-bird being
the regular pollinator and Osmia the only insect to visit it. As in former
experiments, Pentstemon barbatus was entirely ignored, perhaps because of
its narrow vermilion corolla, and the difference between P. secundiflorus
and Scrophularia was less than would be expected from the size and color
of the former. In both experiments more individuals of Pseudomasaris
went to Scrophularia, but they made a larger number of visits to Pentstemon.
Osmia, however, showed an all but exclusive preference for the latter.
In the second experiment the bouquet was later turned so that the flowers
of P. barbatus were in the position formerly occupied by Scrophularia.
Pseudomasaris returned to the original position of the latter, recognized
its mistake, and then flew through the red flowers of the Pentstemon to the
figwort. Andrena crataegi flew 7 times within 0.5 cm. of Scrophularia
and 4 times around P. secundiflorus, but ignored P. barbatus; it then flew to
Rosa and alighted.
Since there were four times as many roses and twice as many castilleias
as geraniums, the latter was relatively as attractive as the others, receiving
more visitors but fewer visits than the rose. The three species in the
bouquet were represented by an equal number of spikes. Pentstemon
secundiflorus was about 50 per cent more attractive than Scrophularia,
probably owing to its much larger size and brilliant color.
110
COMPETITION AND CONSTANCY.
The results are interesting only in showing the behavior of Bombus
juxtus on two successive and similar mornings. On the first the bouquet
of Chamaenerium approached the Geranium plant in attraction, but there
was a great discrepancy on the second day. Monarda received a few
visits on one and inspections only on the other, in spite of the fact that
B. juxtus can reach the nectar when it chooses. Gilia was not even inspected,
the visitors evidently knowing that the nectar is inaccessible to them.
Table 76. — Plant and bouquet competition of several species.
Expt. 1, 2 hours, 8 to 10 a.m., July 3.
Species.
Plant.
Geranium Rosa
Mixed bouquet.
Pent. sec. Pent. barb. Scroph. nod
Andrena crataegi
madronitens. . .
prunorum
Anthophora simillima . . .
Apis mellifica
Bombus juxtus (worker) ,
(queen) . .
occidentalis
Colletes sp
Megachile w. calogaster .
Osmia sp
Prosopis episcopalis. . . .
Peeudomasaris vespoides
Total
0: 0
0: 0
0: 0
0: 0
9:27
0: 0
0: 0
1: 1
0: 0
0: 0
0: 0
0: 0
1: 2
0: 0
1: 1
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
2:10
0: 0
5:59
0: 0
0 0
0: 0
0: 0
1: 7
0: 0
0: 0
1: 1
0: 0
8:54
13:34
31:156
0: 0
10:62
Expt. 2, 2 hours, 10 a.m. to 12 m., July 3.
Species.
Geranium
Castilleia
Mixed bouquet.
Apis mellifica
Bombus juxtus
Osmia melanotricha . . .
pentstemonis . . .
Prosopis elliptica
Pseudomasaris vespoides
Vespid
Selasphorus platycercus .
Total
6:16
1: 1
0: 0
0: 0
1: 2
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
1: 2
0: 0
0: 0
0: 0
19:39
0: 0
0: 0
6:19
6:21
0: 0
6:75
0: 0
0: 0
8:19
20:41
18:115
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
0: 0
8:39
2: 9
0: 0
10:48
CHAMAENERIUM ANGUSTIFOLIUM.
Comparison. — The flowers of Geranium caespitosum resemble those of
the fireweed in form and color, but are somewhat larger. Perhaps the
chief difference between them lies in the fact that they are scattered in
the one and grouped in a conspicuous raceme in the other. The fireweed
produces more nectar, and the pollen is not only more abundant but is also
PENTSTEMON.
Ill
available in each flower for a much longer period. Both Aconitum colum-
bianum and Delphinium scopulorum afford a striking contrast to the fireweed
in the form and color of the flower. The blue or purple color and the great
abundance of pollen would seem to make them more attractive, but this is
offset by the more constant flow of nectar in Chamaenerium. Frasera
speciosa is similar to the latter in the form and size of the flower, but the
corolla is dull green. It would seem to be greatly handicapped by the
color and the small number of stamens, but the nectar is abundant and
apparently very palatable, a fact that more than compensates for the
larger size, brighter color and more abundant pollen of Aquilegia coerulea
(plates 2, 7, 8, and 10).
Table 77. — Plant and bouquet competition of several species.
Expt. 1, 1 hour, 47 minutes, 8h10m to 9h57m a.m., August 15.
Species.
Plant.
Bouquet.
Geranium.
Monarda.
Aster.
Chamaener-
ium.
Gilia.
Bombus juxtus
Halictus pulzenus. . . .
Erynnis 1. snowi
Total
34:107
1: 2
1: 1
2:5
0:0
0:0
6:8
0:0
0:0
23:77
2:14
0: 0
0:0
0:0
0:0
36:110
2:5
6:8
25:91
0:0
Expt. 2, 2 hours, 15 minutes, 8h15m to 10h30m a.m., August 14.
Bombus juxtus
bif arius
Total
Grand total . . .
24:151
2: 8
15i
0
7:34
0
26 :159
15i
7:34
62:269
2:5:15i
6:8
32:125
0:0
Experiments. — In table 78 the first record is one of natural competition
between fireweed and geranium, the next two are experiments in which
the former was the standard plant and the last is an isolated one with
Frasera, a flower of similar form but very different color.
Summary. — Chamaenerium proved many times more attractive than
either Aconitum or Delphinium; it received fewer visitors than Geranium,
though this was only exceptionally true, and was due to the absence of
Bombus. The usual efficiency of the columbine was lacking in competition
with Frasera, in consequence of the great attraction of the latter for Apis
and Bombus.
PENTSTEMON.
Comparison. — Of the five species of Pentstemon employed, P. glaber,
glaucus, and gracilis grow native in the area, barbatus and unilateralis were
brought from the foothills, and halli from the alpine meadows. The
112
COMPETITION AND CONSTANCY.
flowers of all are variously blue or blue-purple in color, with the exception
of P. barbatus, in which they are vermilion. The flowers of P. glaber are
the largest, decreasing through unilateralis, glaucus, and halli to gracilis;
those of P. barbatus have a narrow tube as in the last, but they are much
longer. The secund clusters are most conspicuous in P. unilateralis and
P. glaber and the open few- flowered one of P. barbatus is the least so, in spite
of the brilliant flowers. The pink-purple corollas of Elephantella groen-
Table 78. — Natural and bouquet competition of Chamaenerium, and Frasera.
Expt.l, half-hour, Hh23m to llh53m a.m., July 15.
Expt. 3, 1 hour, 10h35m to llh35m a.m., July 24.
Species.
Plant
Chamae.
Plant
G. caesp.
Species.
Plant
Chamae.
Bouquet
Aconitum.
Apis mellifica
Megachile relativa . . .
texana. . . .
Osmia phaceliae
Prosopis elliptica
wootoni
Protothyreopus dilec-
tus
Sphex vulgaris
Atrytone taxiles
Total
0: 0
4:13
2: 6
1: 1
6: 6
2: 2
0: 0
0: 0
1: 1
0: 0
0: 0
1: 4
13:13
1: 1
2: 4
1: 1
0: 0
Bombus appositus . . .
juxtus
proximus
Megachile pugnata. . .
texana ....
Vespa germanica ....
Atrytone taxiles
Total
42
140
7
4
10
2
47
0
4
0
0
0
0
0
252
4
16:29
25:32
Expt. 4, 1 hour, QHOF* to 10h40m a.m., July 14
Expt. 2, 2}i hours, 8 to 10 and 10 to 11 a.m.,
August 17.
Species.
Plant,
Frasera.
Bouquet,
Aquilegia.
Species.
Plant,
Chamae.
Bouquet,
Delphin.
Apis mellifica
Andrena madronitens
Bombus juxtus
morrisoni. . . .
73
3
30
1
0
0
0
1
2
101
4
49
1
0
0
0
1
2
0
1
1
0
1
1
1
0
0
0
2
1
0
3
3
1
0
0
n
Bombus bifarius
juxtus
Prosopis varif rons ....
Total
133
46
3
11
0
0
Osmia bruneri
melanotricha .
Prosopis episeopalis .
182
11
Bombus Justus
bifarius
Monumetha albifrons
Total
121
16
4
1
0
0
Totals
114:162
5:10
141
1
landica are individually inconspicuous, owing to the slender coiled tube,
but they are massed in a compact cluster that has a considerable degree of
visibility. The amount of both nectar and pollen is much less than in the
various species of Pentstemon. The flowers of Dodecatheon meadia are
bright pink and of about the size of the smaller pentstemons; usually but
one or two are in bloom in a cluster at the same time and the amount of
nectar and pollen is small. The other species concerned have been pre-
viously described (plates 7, 8, and 12).
PENTSTEMON.
113
Experiments. — These dealt largely with single and mixed bouquets,
though both natural and plant-bouquet competition were also concerned.
Table 79
— Bouquet competition of species of Pentstemon.
Separate bouquets.
Single bouquet.
Expt. 1, 1 hour, 9 to 10 a.m., June 19.
Expt. 4, 2 hours, 9 to 11 a.m., July 21.
Species.
Glaber.
Halli.
Gracilis.
Species.
Glab.
Hall.
Glauc.
Eleph.
Anthophora simillima. .
Halictus pulzenus
Monumetha albifrons. .
Osmia bruneri
0
1
0
3
10
1
0
1
1
0
0
15
14
3
0
0
1
2
2
13
9
Bombus bifarius
juxtus
Halictus (Chloralictus)
sp
Osmia bruneri
melanotricha . . .
pentstemonis . . .
Prosopis elliptica
Pseudomasaria vespoi-
22
1
1
2
5
8
5
21
0
0
1
0
7
0
1
0
1
0
0
0
4
0
0
0
25
0
0
0
3i
0
Hi
0
phaceliae
Prosopis basalis
Total
15
34
:7
Expt. 2, 1 hour, 10 to 11 a.m., June 19.
Total
65
9
5
25:14i
Species.
Glaber.
Unilat-
eral.
Bar-
batus.
Expt. 5, 1 hour, 9 to 10 a.m., July 14.
Anthophora simillima. .
Bombus juxtus
Halictus pulzenus
Monumetha albifrons. .
Osmia phaceliae
Vespa germanica
Atrytone taxiles
Total
1
4
2
1
2
1
2
0
2
0
0
0
0
0
0
0
0
0
0
0
0
Species.
Pent,
glab.
Geran.
caesp.
Dodoc.
meadia
Anthophora simillima . .
2
1
0
1
5
1
0
19
1
0
0
0
0
0
0
0
0
0
Halictus (Chloralictus)
13
2
0
pentstemonis. . . .
Prosopis varifrons
Total
Expt. 3, 1 hour, 11 a.m. to 12 m., June 19.
Bombus juxtus
Halictus pulzenus
Osmia phaceliae
Prosopis varifrons
Vespa germanica
Total
6
0
3
1
1
10
3
3
0
1
0
0
0
0
0
10
20
0
11
17
0
There were no visitors to the P. secundiflorus flowers when that bouquet
was placed 6 inches from the P. gracilis plants. However, when these
flowers were mixed in the same cluster, Osmia went from P. gracilis to P.
secundiflorus and behaved in the same way at both species. It probably
visited P. secundiflorus in this case without noticing that it had gone to a
different flower. Although the corolla mouth of the P. secundiflorus flower
is very large, Halictus went into it upside down just as in P. gracilis.
Summary. — In the competition with separate boquets, Pentstemon
halli and gracilis were about twice as attractive as glaber, owing to the pref-
erence shown by Osmia and Prosopis. P. barbatus again received no visits,
while the ratio between P. glaber and P. unilateralis was 24 : 19, this similarity
being suggested by the resemblance of the flowers. The extra-regional
114
COMPETITION AND CONSTANCY.
species, P. halli and P. unilateralis, fared as well or better than the others,
the neglect of the third, P. barbatus, obviously being due to its color or
shape. When combined in one bouquet, P. glaber was several times more
attractive than both P. halli and P. glaucus and about twice as attractive
as Elephantella. While Osmia and Prosopis were both attracted by the
latter, the one merely hovered and the other was unable to probe the
Table 80. — Natural and bouquet competition of Pentstemon gracilis.
Expt. 1, 8 to 10h50m a.m., July 1.
Expt 3, 9 to 10 a.m., June 17.
Species.
Plant, P.
gracilis.
Plant, G.
caespito-
sum.
Species.
Plant, P.
gracilis.
Bouquet, R.
deliciosus.
Bombus juxtus
1
7
0
16
9
5
0
0
0
4
1
1
0
0
1
1
Halictus pulzenus
Osmia pentstemonis
Prosopis varifrons
Syrphus americanus
Total
5
1
1
2
0
0
0
0
Halictus pulzenus
Monumetha albifrons ....
Osmia densa
phaceliae
Prosopis basalis
9
0
Pseudomasaris vespoides. .
Total
Expt. 4, 10h35m to llh35m a.m., June 17.
38
8
Expt. 2, 8 to llh20m a.m., July 6.
Species.
Bouquet, P.| Plant, R.
gracilis. 1 deliciosus.
Apis mellifica ....
0
o
4
; 1
Colletes oromontis 0 24
Ancistrocerus sp. . .
juxtus j 5
0
1
1
1
1
Total . .
0
25
Monumetha albifrons ....
Osmia densa. .
4
0
0
0
Expt. 5, 2 to 3 p.m., July 12.
SP
Muscidae
Total
Species.
Plant, P.
gracilis.
Vials, C.
angustif.
16
16
1
10
8
7
0
0
0
1
Osmia melanotricha
Prosopis elliptica
Total
26
1
tightly coiled beak. Though P. glaber attracted more species than gera-
nium, the preference of Apis for the latter gave it the lead. In the natural
competition of Pentstemon gracilis and Geranium caespitosum the ratios
were 38:8 and 16:16 on days about a week apart. This was due chiefly
to the practical dropping out of Osmia and Prosopis in the second case. The
results with bouquets and vials followed the rule, neither Pentstemon nor
Rubus being visited when it was the bouquet and Chamaenerium flowers in
MONARDA FISTULOSA.
115
vials receiving but 1 visit to 26 for those of P. gracilis in the natural position.
The latter as the standard was about twice as attractive as P. secundi-
florus, P. barbatus, and Scrophularia in a mixed bouquet.
Table 81. — Competition of Pentstemon gracilis standard and a mixed bouquet.
Expt. 1, 1 hour, 11 a.m. to 12 m., July 3.
Species.
Plant,
P. gracilis.
Bouquet,
P. secund-
iflorus.
Bouquet,
P. barbatus.
Bouquet,
S. nodosa.
0: 0
0: 0
6:25
6:45
1: 4
2: 3
1: 3
3: 9
0: 0
2: 4
1: 3
0:0
0:0
0:0
0:0
0:0
0:0
0: 0
0: 0
0: 0
0: 0
1: 4
3:18
Total
15:77
8:20
0:0
4:23
Expt. 2, 1 hour, lO^O™ to ll^O™ a.m., June 22.
0: 0
1: 1
8: 8
1: 1
1: 1
1: 1
1: 1
1: 1
0:0
0:0
0:0
0:0
0: 0
0: 0
0: 0
1: 1
Syrphus opinator
Total
10:10
4: 4
0:0
1: 1
25:87
12:24
0:0
5:23
MONARDA FISTULOSA.
Comparison. — A large number of species were used in competition
with Monarda, in natural, bouquet, and group installations. The only one
to resemble it at all closely was Gilia aggregata, with long, tubular pink
corollas in an elongated cluster. The gamopetalous flowers of Gentiana
parryi and Campanula rotundifolia departed widely in shape, color, and
arrangement, as did also the zygomorphic Delphinium and the actino-
morphic Geranium, Chamaenerium, and Calochortus gunnisoni. This was
essentially true also of the three composites Achillea millefolium, Aster
bigelovi, and Erigeron macranthus, the first with white rays and the last
two with purple ones (plates 6, 7, 8, and 10).
Experiments. — These include natural and bouquet competition, and
the competition results of the Monarda calendars given in the preceding
chapter.
Summary. — In natural competition with Geranium caespitosum, Cam-
panula rotundifolia, and Achillea millefolium, Monarda was slightly less
attractive than Geranium, owing to the decided preference of Bombus and
Halictus for the latter. When Monarda was the standard in competition
with a bouquet of Gentiana, Erigeron, and Calochortus, it was about twice
116
COMPETITION AND CONSTANCY.
Table 82. — Natural and bouquet competition.
Expt. 1, \\i hours, 8 to 9h30m a.m., July 3 .
Expt. 3, 2 hours, 8h57m to 10b57m a.m., July 20.
Species.
Plant,
Mon.
Plant,
Ger.
Species.
Plant,
Mon.
Bouquet,
Chamae.
Bombus juxtus
bifarius
proxiruus. . . .
Colletes oromontis. . .
Argynnis atlantis. . . .
Thanaos martialis. . . .
Total
17:44
0
0
0
1: 1
1: 1
74
85
5
2
0
0
Anthophora smithi. . .
Bombus juxtus
appositus. . .
Megachile pugnata. . .
texana. . . .
Vespa germanica. . . .
Dejeania vexatrix. . . .
0
12:169
0
0
0
1: 3
0
0
1: 3
1: 2
35:222
3: 8
2: 4
1: 2
0
1: 9
3: 4
0
19:46
166
Argynnis atlantis. . . .
Total
Expt. 2, 1 hour, 11 a.m. to 12 m., August 17.
14:175
46:251
Species.
Plant,
Mon.
Bouquet,
Delph.
Bombus proximus. . . .
morrisoni. . . .
edwardsi ....
juxtus
bifarius .....
Total
134
19
46
14
11
0
96
17
6
0
224
119
Table 83. — Natural competition of a group.
One and one-half hours, 9 to 10h30m a.m., August 2.
Species.
Monarda.
Geranium.
Campanula.
Achillea.
0
4
0
30
0
0
0
2
0
0
0
4
33
50
0
9
1
13
10
2
0
2
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
3
0
0
Halictus (Lasioglossum) sp
Total
73
88
0
3
as attractive. In a test of plants of Monarda and Geranium, the latter was
more than three times as attractive, Bombus bifarius going to it alone, and
B. juxtus giving it a marked preference. Similar behavior of B. bifarius
was the chief factor in causing a bouquet of Chamaenerium to be preferred
MONARDA FISTULOSA.
117
to a plant of Monarda. However, while the latter obtained only a third as
many visitors, these averaged 12 visits to it in contrast to 6 for the former.
In the three related series, the total number of visits to normal Monarda
flowers was 2,397, to mutilated ones 452, and to the various competing
flowers 449. There were outstanding differences between the different
Table 84. — Bouquet competition of a group.
Two and a half hours, 9 to llh30m, August 5.
Species.
Plant,
Monarda.
Bouquet,
Gentiana.
Bouquet,
Erigeron.
Bouquet,
Calochortus.
0
26
24
0
1
0
1
2
16
0
0
0
0
0
0
0
0
0
0
0
3
0
0
9
1
0
2
0
2
11
0
0
0
9
2
1
0
0
0
0
Pseudomasaris vespoides
Total
70
0
28
12
Table 85. — Competition of normal and mutilated Monarda and other species.
First Series.
Species.
Normal
Monarda.
Total
mutilated
Monarda.
Monarda
composite.
Chamae-
nerium
Normal
Geranium.
Total
competi-
tors.
Clisodon
Bombus appositus. .
bifarius. . . .
occidentalis
Argynnis
Atrytone
Erynnis
Prosopis
Total
Clisodon
Bombus appositus . .
bifarius ....
occidentalis
Monumetha
Syrphus
Atrytone
Gnophaela
Total
Grand total . .
87
0
0
0
0
0
5b:3
0
0
5b:
0
0
0
0
0
0
bwr
0
bwr
b:4 w:r
12
13
34
118
COMPETITION AND CONSTANCY.
Table 85- — Competition of normal and mutilated Monarda and other species — Continued.
Second Series.
Species.
Normal
Monarda.
Total
muti-
lated.
Gilia
heads.
Chamae.
head.
Total
heads.
Norm.
Chamae.
Norm.
Ger.
Total
competi-
tors.
621
220
94
13
13
100
15
28
45
0
0
43
0
6 Mon.
0
0
0
1 Mon.
14 p.
0
0
0
0
0
0
0
6 Mon.
0
0
0
1 Mon.
0
8
1
0
6
26
0
0
0
0
0
10
1
8
0
6
50
Bom bus appositus . . .
juxtus
morrisoni . . .
Total
1,061
131
7 Mon.
0
7 Mon.
41
10
66
9
27
13
1
40
0
0
0
4
3
0
0
0
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
2 Mon.
0
0
0
0
0
0
0
0
0
2 Mon.
0
0
3
0
10
0
0
0
0
0
0
0
0
22
0
0
14
1
2
1
1
0
0
0
26
0
10
14
1
2
0
Bombus appositus. . .
juxtus
edwardsi. . . .
hunti
occidentalis .
morrisoni. . .
H. (Lasioglossum) sp.
P. varifrons
Erynnis
s
Total
94
7
0
1:2 Mon.
1:2 Mon.
13
41
55
Grand total. . .
1,155
138
7 Mon. Jl:2Mon.
1:9 Mon.
54
51
121
Third Series.
Species.
Nor-
mal.
Total
muti-
lated.
Gilia
head.
Chamae.
head.
Total
heads.
Norm.
Chamae.
Norm.
Ger.
Norm.
Aster.
Total
competi-
tors.
309
151
113
2
161
187
51
7
37
1
77
35
0
0
0
3
3
0
0
0
2
4
0
0
0
0
2
7
3
0
7
1
25
0
7
1
0
0
2
0
1
0
0
0
0
0
0
8
1
29
7
11
1
Bombus appositus. . . .
juxtus
morrisoni. . . .
Total
923
208
6
6
12
41
3
1
57
38 27
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
9
2
25
90
0
9
0
24
0
2
0
0
1
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
51
7
2
12
0
0
0
0
0
0
9
2
26
91
51
16
2
37
0
2
0
0
1
Bombus juxtus
morrisoni. . . .
bifarius
hunti
0
16
8
0
2
0
0
125
21
4
17
1
0
0
0
0
0
0
0
0
41
8
0
0
0
0
Total
232
76
1
0
1
162
1
73
237
Grand total . . .
1,155
284
7
6
13
203
4
74
294
POLLEN LOADS.
119
series as well as between the two calendars made at the same time, as shown
in table 86.
The greatest difference is shown by the two calendars of series 3, in which
the marked constancy of Clisodon and Bombus appositus and their vastly
greater abundance in the one place furnishes the explanation. Corre-
sponding differences may also be noted with respect to the response to the
several competitors. Normal Geranium flowers and composite heads of
Chamaenerium were twice visited equally, though as a rule these artificial
heads were neglected. A marked exception occurred in the second series,
where 14 flowers of a pure Gilia head were visited by Argynnis. As between
normal Chamaenerium and normal Geranium, the former was thrice as
attractive all told, though the relative positions were reversed in the cal-
endars of the second series. In this competition B. bifarius and B. hunti
were partial to Chamaenerium and B. occidentalis to Geranium, while B.
juxtus preferred Geranium in one series and Chamaenerium in the other.
Table 86. — Summary of normal and competing flowers by series and calendars.
Series 1.
Series 2.
Series 3.
Nor-
mal.
Com-
peting.
Ratio.
Nor-
mal.
Com-
peting.
Ratio.
Nor-
mal.
Com-
peting.
Ratio.
50
37
25
9
2:1
4:1
1,061
94
66
55
16:1
2:1
923
232
57
237
16:1
Total
87
34
3:1 lis*
121 Q-i
1,155
294
1:4
COMPOSITION AND WEIGHT OF POLLEN LOADS.
Value and methods. — While occasional observations of the purity of
pollen loads have been recorded (Bennett, 1874; Perez, 1903), no previous
microscopical analysis of loads seems to have been made. The latter were
undertaken in the first place as a check upon the habits observed in the
field, and were extended to include the weight of the bee and its pollen load
as a measure of its efficiency in collecting and in flight. Unfortunately, it
was not until these preliminary studies were practically finished that it was
realized that the time of flight should have been recorded, since the degree
of constancy varies much between morning or evening on the one hand
and mid-day on the other. There is also an evident difference in indi-
vidual efficiency, which can be determined only by the use of marked bees.
As a rule the bees were weighed immediately after being caught, the
load completely removed by means of a needle, and the body weighed
again. In a few cases the bees were dry, and corresponding allowance must
be made with respect to the percentage weight of the load. In the tables
the name of the species on which the insect was captured is given first in
each case; when the bee had collected none of this pollen, it is indicated.
For a number of specimens previously collected (designated by a letter),
the pollen was examined, but the weight of the load was not determined.
120
COMPETITION AND CONSTANCY.
Table 87.
-Composition and weight of pollen loads.
Apis mellifica.
Date.
Catalogue
No.
Weight of
bee.
Weight of
load.
Load, p. ct.
of bee's
weight.
Composition of load.
gm.
gm.
p. ct.
June 21
1
0.0780
0.0168
21.4
Rubus deliciosus, pure.
Do.
2
.0800
.0190
24.0
Do.
Do.
3
.0710
.0188
26.5
Do.
Do.
4
.0858
.0210
24.5
Do.
Do.
5
.0930
.0120
13.0
Do.
Do.
6
.0820
.0190
23.2
Do.
Do.
7
.0738
.0120
16.2
Do
Do.
8
.0800
.0250
31.2
Do.
Do.
9
.0725
.0235
32.4
Do.
Do.
10
.0670
.0200
30.0
Do.
Dry.
June 7
49
.0262
.0113
44.0
Do.
Do.
50
.0315
.0125
39.0
Do.
Do.
51
.0250
.0095
38.0
Do.
Do.
52
.0250
.0120
50.0
Do.
Do.
99
.0250
.0200
8.0
Do.
Do.
100
.0275
.0145
52.0
Do.
Do.
101
.0300
.0108
36.0
Do.
Do.
102
.0275
.0135
49.0
Do.
Do.
103
.0280
.0145
52.0
Do.
Do.
104
.0230
.0045
19.0
Do.
Do.
105
.0260
.0040
16.0
Do.
Do.
106
.0335
.0065
19.0
Do.
July 23
123
.0750
.0085
11.0
Geranium caespitosum, pure.
Do.
125
.1020
.0090
9.0
Geranium caespitosum, 1 p. ct.
Holodiscus dumosus, 99 p. ct.
July 28
167
.0760
.0190
25.0
Chamaenerium angustifolium,
pure.
Do.
169
.0900
.0080
9.0
Do.
July 30
170
.1015
.0185
18.0
Do.
Do.
171
.0950
.0245
26.0
Do.
Do.
172
.0950
Number
examined.
.0130
14.0
Do.
A
1
Geranium caespitosum, 99 p. ct.
R. acic. and P. gracilis, 1 p. ct.
B
1
Solidago, 95 p. ct.; ?5.
C
1
Petalostemon purpureus, 99 p. ct.
Andrena
2RATAEGI.
gm.
gm.
p. ct.
June 22
30
0 . 0469
0 . 0058
12
Rubus deliciosus, 99.5 p. ct. ; ?.5.
Do.
31
.0537
.0053
10
Rubus deliciosus, pure.
Do.
40
.0520
.0075
14
Do.
Do.
41
.0687
.0095
14
Do.
July 3
68
.0520
.0090
17
Rosa acicularis, pure.
July 6
78
.0490
.0070
5
Rubus deliciosus, pure.
(Rubus deliciosus, 25 p. ct.
\ Rubus strigosus, 75 p. ct.
Do.
79
.0470
.0055
11
Do.
80
.0500
.0050
10
Rubus strigosus, pure.
July 23
128
.0395
Number
examined.
.0035
8
Geranium caespitosum, 10 p. ct.
Holodiscus dumosus, 90 p. ct.
A
B
2
7
Prunus demissa, pure.
Rubus strigosus, pure.
1
POLLEN LOADS.
Table 87. — Composition and weight of pollen loads — Continued.
Andrena edwineae.
121
Date.
Catalogue
No.
Weight of
bee.
Weight of
load.
Load, p. ct.
of bee's
weight.
Composition of load.
C
gm.
1
gm.
p. ct.
Jamesia americana, pure.
Andrena madronitens.
July 23
July 24
July 25
127
135
148
D
gm.
0.0320
.0365
.0380
2
gm.
0.0045
.0050
.0080
p. ct.
14
14
21
Geranium caespitosum, 1 p. ct.
Holodiscus dumosus, 97 p. ct.
Oenothera biennis, 2 p. ct.
Frasera speciosa, 97 p. ct.
Geranium caespitosum, 3 p. ct.
Frasera speciosa, 5 p. ct.
Sedum stenopetalum, 95 p. ct.
Rubus deliciosus, pure.
Andrena vicina.
June 23
Do.
28
29
E
F
gm.
0.1045
.0700
Number
examined.
2
1
gm.
0.0065
.0100
p. ct.
6
13
Rubus deliciosus, pure.
Do.
Rosa acicularis, 99 p. ct. ; ?1.
Rubus deliciosus, 99 p. ct. ; ?1.
ANTHOPHORA SIMILLIMA.
June 23
July 3
July 8
32
62
94
A
B
gm.
0.1555
.1275
.1400
- Number
examined.
1
1
gm.
0.0079
.0095
.0110
p. ct.
5.0
8.0
8.0
[Rosa acicularis, 90 p. ct.
1 Dodocatheon meadia, 8 p. ct.
(Pentstemon gracilis, 2 p. ct.
28 conifer grains.
(Rosa acicularis, 99 p. ct.
\Pentstemon gracilis, 1 p. ct.
Rosa acicularis, pure.
(Lithospermum canescens, 98 p.ct.
\ Rosa acicularis, 1 p. ct., ?1 p. ct.
fCapnoides aureum, 98 p. ct.
\Aragalus lamberti, 2 p. ct.
» BOMBUS APPOSITUS.
A
Number
examined.
1
p. ct.
Petalostemon purpureus, 70 p. ct.
Compositae, 30 p. ct.
122 COMPETITION AND CONSTANCY.
Table 87. — Composition and weight of -pollen loads — Continued.
BOMBU8 BIFARIUS.
Date.
Catalogue
No.
Weight of
bee.
Weight of
load.
Load, p. ct.
of bee's
weight.
Composition of load.
No.
gm.
p. ct.
B
1
Pentstemon glaber, pure.
c
2
(Geranium caespitosum, 2 p. ct.
\ Pentstemon gracilis, 98 p. ct.
D
1
Pentstemon gracilis, pure.
E
1
fPentstemon gracilis, 99 p. ct.
1 Geranium sp., 0.1; ?.9 p. ct.
[Pentstemon gracilis, 90 p. ct.
F
1
\ Rosa acicularis, 5 p. ct.
iGeranium caespitosum, 5.
G
.
(Pentstemon gracilis, 99 p. ct.
\Rosa acicularis, 1 p. ct.
gm.
July 22
120
0.0800
0.0220
27.0
Jamesia americana, pure.
July 23
124
.0780
.0060
7.0
(Geranium caespitosum, none.
\ Holodiscus dumosus, pure.
Do.
126
.0640
.0295
46.0
fGeranium caespitosum, 1 p. ct.
\Holodiscus dumosus, 99 p. ct.
July 24
136
.0825
.0065
7.0
Frasera speciosa, pure.
July 26
137
.0875
.0050
5.0
Campanula rotundifolia, pure.
Do.
145
.0755
.0140
11.0
Sedum stenopetalum, pure.
Chamaenerium angustifolium, 1
July 31
173
.0670
.0090
13.0
p. ct.
Holodiscus dumosus, 99 p. ct.
BOMBUS
JUXTUS.
gm.
gm.
p. ct.
June 23
33
0.1124
0.0231
20.0
Rubus deliciosus, pure.
Do.
34
.0295
.0045
19.0
fRubus deliciosus, 30 p. ct.
\ Pentstemon gracilis, 70 p. ct.
Do.
35
.0427
.0021
5.0
fRubus deliciosus, 99 p. ct.
\Rosa acicularis, 1 p. ct.
Do.
36
.0228
.0022
10.0
Rubus deliciosus, pure.
Do.
37
.0225
.0025
11.0
Do.
Do.
38
.0090
.0021
24.0
Do.
Do.
39
.0075
.0018
24.0
Do.
Do.
45
.0860
.0025
26.0
Do.
4 conifer grains.
July 3
61
.0870
.0255
29.0
fRosa acicularis, pure.
\ conifer grain.
Do.
71
.0820
.0130
16.0
fRosa acicularis, pure.
\ 4 conifer grains.
[Rosa acicularis, none.
Do.
72
.1150
.0200
17.0
j Rubus deliciosus, 50 p. ct.
| Rubus strigosus, 50 p. ct.
1 2 conifer grains.
July 6
73
.0725
.0315
43
fRubus deliciosus, pure.
|6 conifer grains.
Do.
74
.0700
.0210
30.0
fRubus deliciosus, pure
1 2 conifer grains.
Do.
75
.0940
.0365
39.0
fRubus deliciosus, pure.
\3 conifer grains.
June 5
110
.0900
.0555
61.0
Rubus deliciosus, pure.
Do...
111
.1000
.0390
39.0
Do.
Do.
112
.1370
.0130
9.0
Do.
July 17
113
.1000
.0150
15.0
Rosa acicularis. pure,
POLLEN LOADS.
123
Table 87.-
-Composition and weight of pollen loads — Continued.
Bombus juxtus — Continued.
Date.
Catalogue
No.
Weight of
bee.
Weight of
load.
Load, p. ct.
of bee's
weight.
Composition of load.
firm.
gm.
p. ct.
July 17
114
0 . 0850
0 . 0050
3.0
Rosa acicularis, pure.
fHolodiscus dumosus, 70 p. ct.
July 21
116
.0915
0.0110
12.0
\ Rosa acicularis, 29 p. ct.
(Oenothera biennis, 1 p. ct.
July 22
117
.0880
.0125
1.0
fPotentilla sp., 85 p. ct., ?10 p. ct.
\ Chamaenerium angustifolium, 5
p. ct.
Campanula rotundifolia, pure.
July 26
138
.1010
.0045
4.0
July 25
147
1
.0955
.0135
14.0
fCarduus hookerianus, pure.
\ 1 conifer grain.
f Aconitum columbianum, 99 p.ct.
\Chamaenerium angustifolium, 1
p. ct.
fPentstemon gracilis, 99 p. ct.
\Rosa acicularis, 1 p. ct.
m
n
Astragalus drummondi, pure.
fPentstemon gracilis, 99 p. ct.
[Geranium caespitosum, 1 p. ct.
0
Bombus ]
CIRBVELLUS.
July 3
70
0.5940
0.0275
4
Frasera speciosa, pure.
July 25
149
.2395
.0065
12
Castilleia p. occidentalis pure.
Do.
150
.1000
.0200
20
Do.
Do.
151
.1470
.0190
13
Do.
Do.
152
.1030
.0100
9
Do.
Do.
153
.0720
.0140
20
Do.
Do.
154
.0700
.0100
13
Do.
Do.
155
.1480
.0140
9
Do.
Do.
156
.2700
.0380
14
fPedicularis parryi, none.
\Castilleia p. occidentalis, pure.
Do.
157
.0600
.0050
8
Castilleia p. occidentalis, pure.
Do.
158
.1020
.0315
30
fPentstemon glaber, 95 p. ct.
\Potentilla pulcherrima, 5 p. ct.
Do.
159
.1045
.0095
9
Castilleia p. occidentalis, pure.
Do.
160
.0800
.0220
20
Do.
Do.
161
.1200
.0090
8
f Castilleia p. occidentalis, 90 p. ct.
\Potentilla sp., 10 p. ct.
Do.
162
.1450
.0250
17
Castilleia p. occidentalis, pure.
fTrifolium dasyphyllum, 50 p. ct.
Do.
163
.1800
.0200
11
i Castilleia p. occidentalis, 48;
1 ?2 p. ct.
Do.
164
.1050
.0220
12
fTrifolium dasyphyllum, 50 p. ct.
\ Castilleia p. occidentalis, 50.
Do.
165
.0805
.0085
11
fTrifolium dasyphyllum, 97 p. ct.
\Composite, 3 p. ct.
E
OMBUS OCC
DENTALIS.
June 30
48
0.1400
0.0250
18.0
fRosa acicularis, 99 p. ct.
\Geranium caespitosum, 1 p. ct.
July 3
63
.1330
.0530
40.0
Rosa acicularis, pure.
Do.
64
.1400
.0390
28.0
fRosa acicularis, 95 p. ct.
\Rubus deliciosus, 5 p. ct.
124
COMPETITION AND CONSTANCY.
Table 87. — Composition and weight of pollen loads — Continued.
Bombus occidentalis — Continued.
Date.
Catalogue
No.
Weight of
bee.
Weight of
load.
Load, p. ct.
of bee's
weight.
Composition of load.
gm.
gm.
p. ct.
July 6
76
0.1060
0.0080
7.0
Rubus deliciosus, pure.
July 8
90
.1650
.0420
25.0
Rosa acicularis, pure.
June 5
107
.1385
.0650
47.0
Rubus deliciosus, pure.
Do.
108
.1620
.0727
45.0
Do.
Do.
109
.1590
.0730
46.0
Do.
July 22
119
.2450
.0625
25.0
Jamesia americana, pure.
July 23
122
.1750
.0465
26.0
/Geranium caespitosum, 5 p. ct.
\Holodiscus dumosus, 95 p. ct.
July 22
134
.1580
.0300
19.0
Mentzelia multifiora, pure.
Chamaenerium angustifolium, 1
July 31
174
.0955
.0045
4.0
p. ct.
Holodiscus dumosus, 99 p. ct.
Aug. 5
175
H
.1435
.0355
24.0
fGeranium caespitosum, 2 p. ct.
(Allium recurvatum, 98 p. ct.
Linaria vulgaris, pure.
/Calochortus gunnisoni, 95 p. ct.
^Geranium caespitosum, 5 p. ct.
I
J
(Delphinium scopulorum, 7 p. ct.
jCalochortus gunnisoni, 93 p. ct.
K
f Delphinium scopulorum, 35 p. ct.
1 Composite, 65 p. ct.
Bombus occidentalis:
Cat. No. L
?10
?2
Percentage
composition
of load.
(Delphinium scopulorum 95
[Composite 5
M Delphinium scopulorum 85; ?15
N Delphinium scopulorum 99 ; ? 1
O Chamaenerium angustifolium 98; ?2
p /Chamaenerium angustifolium 95
\Composite 5
Q Chamaenerium angustifolium 90 ;
■p /Chamaenerium angustifolium 95
\ Composite 5
o j Chamaenerium angustifolium 80
\Composite 20
T Carduus hookerianus 98;
Bombus centralis:
^ XT TT /Delphinium scopulorum 10
Cat- No- U \ Composite 90
Bombus edwardsii:
Cat. No. V Petalostemon purpureus i 99;
w /Petalostemon purpureus 90
\Composite 10
■^ /Calochortus gunnisoni 40
(Composite 60
Bombus fervidus:
Cat. No. Y Petalostemon purpureus 98;
Bombus flavifrons:
p -IJ „ fCalochortus gunnisoni 45
\ Composite 45
Chamaenerium angustifolium 10
Bombus hunti:
Cat. No. a Chamaenerium angustifolium 75;
Bombus kirbyellus:
Cat. No. b Rubus deliciosus 99;
POLLEN LOADS.
125
Table 87. — Composition and weight of pollen loads — Continued.
Percentage
composition
of load.
fChamaenerium angustifolium 1
[Rosa acicularis 99
Bombus morrisoni :
Cat. No. c
Bombus proximus:
p, . xt j (Rosa acicularis 99
Uat. No. d \Chamaenerium angustifolium 1
e Rosa acicularis pure
f Rubus strigosus pure
J Rosa acicularis 99
g [Rubus strigosus 1
Bombus rufocinctus:
pi f XT i, /Solidago missouriensis 10
• \Petalostemon purpureus 90
Chamaenerium angustifolium 50
Petalostemon purpureus 50
Calochortus gunnisoni 90
j -j Geranium caespitosum 2
Composite 2 ;
( Solidago missouriensis 10
' ' Petalostemon purpureus 90
Clisodon terminates
Date.
Catalogue
No.
Weight of
bee.
Weight of
load.
Load, p. ct.
of bee's
weight.
Composition of load.
July 17
115
gm.
0.1010
gm.
0.0040
p. ct.
4.0
(Rosa acicularis, 70 p. ct.
i Mertensia sibirica, 29 p. ct.
[Geranium caespitosum, 1 p. ct.
COLLETES OROMONTIS.
July 23
133
gm.
0.0045
gm.
0.0015
p. ct.
33.0
fGeranium caespitosum, 1 p. ct.
\Holodiscus dumosus, 99 p. ct.
HaLICTUS MEDIONITEN9.
June 23
July 8
July 8
July 23
46
96
97
130
gm.
0.0011
.0320
.0058
.0060
gm.
0 . 0003
.0030
.0012
.0020
p. ct.
27.0
9.0
21.0
33.0
Rubus deliciosus, 70 p. ct.
■ Rosa acicularis, 25 p. ct.
Potentilla pulcherrima, 5 p. ct.
J Rosa acicularis, 95 p. ct.
\Rubus deliciosus, 5 p. ct.
Rosa acicularis, pure.
/Geranium caespitosum, none.
\Holodiscus dumosus, pure.
Halicttjs pulzenus.
A
B
C
D
fGeranium caespitosum, none.
\Unknown, pure.
Geranium richardsoni, pure.
Rosa acicularis, pure.
Rubus strigosus, pure.
126
COMPETITION AND CONSTANCY.
Table 87. — Composition and weight of pollen loads — Continued.
Megachile pugnata.
Date.
Catalogue
No.
Weight of
bee.
Weight of
load.
Load, p. ct.
of bee's
weight.
Composition of load.
gm.
p. ct.
Petalostemon purpureus, 13 p. ct.
A
Geranium caespitosum, 2 p. ct.
B
Carduus hookerianus, pure.
Megachile wootoni calogasteb.
gm.
gm.
p. ct.
June 29
47
0.0900
0.0048
5.3
fRosa acicularis, 95 p. ct.
1 Rubus deliciosus, 1, ?4 p. ct.
July 3
65
.1110
.0075
7.0
JRosa acicularis, 99 p. ct.
\ Rubus deliciosus, 1 p. ct.
Do.
66
.0980
.0095
10.0
Rosa acicularis, pure.
July 8
91
C
D
.0995
.0080
8.0
Do.
Do.
fPentstemon glaber, 99 p. ct.
\ Rosa acicularis, 1 p. ct.
[Rosa acicularis, 99 p. ct.
E
4 Chamaenerium angustifolium, 1
[ p. ct.
F
Rubus deliciosus, pure.
Megachile texana.
gm.
gm.
p. ct.
[Chamaenerium angustifolium, 80
G
J p. ct.
iRosa acicularis, 10 p. ct., ?10
[ p. ct.
June 22
24
0.1160
0.0125
11.0
Rubus deliciosus, pure.
Megachile sp.
gm.
gm.
p. ct.
July 3
67
0.0915
0.0035
3.0
Rosa acicularis, pure.
July 26
139
.1090
.0045
4.0
Campanula rotundifolia, pure.
Do.
140
.0850
.0190
22.0
Campanula rotundifolia, 50 p.ct.
?50 p. ct.
Do.
141
.0820
.0085
10.0
Campanula rotundifolia, pure.
[Campanula rotundifolia, 50 p.ct.
Do.
142
.1125
.0135
12.0
\ Chamaenerium angustifolium, 49
[ p. ct., ?1 p. ct.
[Campanula rotundifolia, 33 p.ct.
Do.
143
.1185
.0105
9.0
\ Chamaenerium angustifolium, 33
( p. ct., ?34 p. ct.
July 28
168
.0585
.0030
5.0
Chamaenerium angustifolium,
pure.
[Geranium caespitosum, 5 p. ct.
Aug. 5
177
.0940
.0060
6.0
\ Erigeron macranthus, 90 p. ct.
[Oenothera biennis, 5 p. ct.
Do.
178
.1040
.0005
0.4
Campanula rotundifolia, pure.
Do.
179
.1070
.0080
0.7
Do.
POLLEN LOADS.
127
Table 87. — Composition and weight of pollen loads— Continued.
MONUMETHA ALBIFRONS.
Date.
Catalogue
No.
Weight of
bee.
Weight of
load.
Load, p. ct.
of bee's
weight.
Composition of load.
June 22
July 8
Do.
26
92
93
gm.
0.1135
.0995
.0800
gm.
0.0035
.0055
.0050
p. ct.
2
5
6
Rubus deliciosus pure; 1 conifer
grain.
Rosa acicularis, pure.
Do.
08MIA MELANOTRICHA.
July 8
95
A
gm.
0.0247
gm.
0 . 0023
p. ct.
9.0
Rosa acicularis, pure.
Pentstemon gracilis, pure.
Panurginus sp.
A
Calochortus gunnisoni, pure.
PROSOPI8 varifrons.
July 23
131
gm.
0.0045
gm.
0.0015
p. ct.
33.0
("Geranium caespitosum, 10 p. ct.
\Holodiscus dumosus, 90 p. ct.
PSITHYRUS CONSULTUS.
A
Solidago missouriensis, 95 p. ct.,
?5 p. ct.
Discussion.— Of the total of 207 bees, 121 carried pure loads of pollen,
i. e., from a single species of flower, while 86 had mixed loads. Three-fourths
of the latter consisted of 2 species, and one-fourth of 3 species, a single load
containing as many as 4 species. Pollen grains of conifers are not considered
as constituting a mixture, since they were purely incidental. They may
have been taken with the pollen sought or picked up separately, but in no
case did they involve a visit to the species from which they originated.
With the exception of Halidus pulzenus, no species represented by 4 or
more individuals was perfectly constant in its choice of pollen. Apis
mellifica and Andrena crataegi were the most constant of these, Bombus
occidentalis and Anthophora simillima among the least so. The 4 genera
represented by 2 or more species gave the following ratios between pure
and mixed loads: Andrena 19:10, Bombus 50:36, Halidus 6:2, Megachile
12:10. Each of these contained species that were largely or entirely con-
stant on the one hand, and those that were 50 per cent or more inconstant
on the other.
128
COMPETITION AND CONSTANCY.
The only bees able to carry a pollen load amounting to approximately
half of their own weight were species of Bombus; Apis, Colletes, Halictus,
and Prosopis coming next with a load a third of their body-weight.
Table 88. — Summary.
Species.
Maximum
load.
No.
bees.
Pure
load.
Mixed load.
2 spp.
3 spp.
4 spp.
Total.
p. ct.
32
14
32
18
1
4
5
5
1
14
27
26
1
3
1
1
1
1
4
4
18
1
1
4
4
2
2
8
10
3
2
1
1
1
28
15
3
3
1
2
3
3
1
5
6
17
1
3
1
4
3
madronitens
21
13
8
1
2
1
1
3
3
4
Anthophora simillima
1
46
61
47
7
19
9
2
2
7
8
17
occidentalis
1
1
1
2
3
4
morrisoni
2
1
1
1
1
1
4
5
30
4
33
33
13
Clisodon terminali3
Colletes oromontis
Halictus madronitens
2
4
4
6
3
2
1
1
2
"*3
1
1
1
3
11
10
22
6
9
w. cologaster. . . .
4
4
Monumetha albifrons
Osmia melanotricha
33
1
Total
207
121
67
18
1
CONSTANCY.
Definitions. — Loew (1884) employed the term monotropic to designate
those apids that visit flowers of a single species, oligotropic for those visit-
ing only a few allied species, and polytropic for those that go indifferently
to very diverse flowers. Robertson further restricted the terms, designat-
ing as oligotropic only those bees the females of which collect pollen
from a single species or from those of the same genus or family and as
polytropic those that secure pollen from flowers of different families.
Following the English naturalists, Plateau (1901) denoted by constancy
the behavior of a polytropic hymenopter such as the honey-bee, which
visits various species of flowers during the season, but limits its activity
HISTORICAL. 129
to the flowers of a single species during one journey from the hive or nest.
Detto (1905) pointed out that constancy may be used to refer to the fact
that a bee visits only flowers of one species on a journey, or to fidelity to
one species until it obtains nothing more from it, when it goes to another.
It must also be recognized that single individuals seem to visit only certain
portions of very large or very floriferous plants and that they do not go to
other plants of the same species, but to a new species when a particular
portion has been exhausted. Moreover, nothing is known as to whether a
bee gives the preference to flowers of the same color or shade as those upon
which it began to collect. The term "monodrome constancy" may be
applied to the cases where the bee visits the flowers of but one species during
a single flight, and "polydrome constancy" to those where successive
flights are always directed to the same species as long as this yields nectar
or pollen. An insect that then goes to another species is "temporarily
constant" in contrast to one that confines itself chiefly to one species.
Early observations of constancy. — Two chance observations only
have been recorded for the period before Darwin, one by Aristotle and the
other by Dobbs (1736). Aristotle stated that during each flight the honey-
bee does not settle upon flowers of different kinds, but flies, as it were, from
violet to violet and touches no other species till it returns to the hive.
With respect to constancy, Darwin (1876:415) says:
"All kinds of bees and certain other insects usually visit the flowers of the same
species as long as they can, before going to another species. It may be observed by any
one, both with hive and humble bees, in every flower garden; not that the habit is
invariably followed. Humble and hive bees are good botanists, for they know that
varieties may differ widely in the color of their flowers and yet belong to the same
species. Some species of diptera or flies keep to the flowers of the same species with
almost as much regularity as do bees, and when captured they are found covered with
the pollen. I do not know whether lepidoptera generally keep to the flowers of the
same species, but I once observed many minute moths apparently eating the pollen
of Mercurialis annua. I then went to a female plant some yards off and saw three of
these moths light on the stigmas. It must not be supposed from these several state-
ments that insects strictly confine their visits to the same species. They often visit
other species when only a few plants of the same kind grow near together. That
insects should visit the flowers of the same species as long as they can is of great
importance to the plant, as it favors the cross fertilization of distinct individuals of
the same species, but no one will suppose that the insects act in this manner for the
good of the plant. The cause probably lies in the insects being thus enabled to work
quicker; they have just learnt how to stand in the best position on the flower, and how
far and in what direction to insert their proboscides."
Kerner (1876) stated that the bumble-bee always devotes itself to the
plunder of a single species at one time, but in commenting on this, Weed
(1884) said that he had observed one bumble-bee fly back and forth from
Pedicularis canadensis to Vicia americana, another from hyacinth to col-
umbine, a third from Solomon's seal to dandelion, and a fourth from vetch
to honeysuckle. Forbes (1878) recorded 30 visits in succession of Bombus
to Lamium, during which it ignored all other flowers, while Syrphus visited
Rubus to the complete neglect of Lamium. Kronfeld (1888:785) observed
a honey-bee that returned for 10 visits to a bed of cucumbers after being
130 COMPETITION AND CONSTANCY.
driven off, though many species were in bloom in the adjacent beds. Three
other individuals worked solely on Zinnia, though the same bed contained
7 other species in bloom, while a bumble-bee visited exclusively 28 heads
of Tragopogon in a 10-minute period, in spite of the competition of 10
other kinds of flowers.
Bennett's studies of constancy. — Bennett (1874, 1884:175) was
apparently the first to make an extensive study of the visits made by an
insect in one journey from the hive, in the hope of confirming or confuting
Aristotle's statement. The 66 observations made concerned only the butter-
flies, the syrphids, and apids, and they appeared to indicate very different
degrees of constancy. On the whole, the butterflies manifested but a small
degree of fidelity; they preferred yellow or pink flowers and showed a
marked tendency to adhere to one of these colors after starting with
it. In the case of Eristalis, it exhibited little constancy in two instances,
while in two others it confined its visits to a single though different flower.
On the other hand, four observations of Syrphus gave only one case of
constancy.
Of 33 observations made on various species of Bombus, 4 showed visits to
3 distinct species, while in 6 others the number of species noted while the
insect was in sight was 2. In 23 instances the bumble-bee visited but a
single species while under observation, but these were of the most diverse
kinds and colors. It was quite obvious that at the same spot different bees of
the same species were visiting different kinds of flowers. Pollen masses
were examined. in two cases and found to consist wholly of the pollen of the
flower on which the bee was taken. The honey-bee was constant to one
species for 5 out of 6 observations, the exception consisting of 1 visit to
Scabiosa and 9 successive ones to Centaurea. It was concluded that the
butterflies exhibit little constancy, the flies greater constancy, while this
is much greater for the bumble-bees and all but absolute in the honey-bee.
Constancy appeared to increase in proportion to the part performed by the
insects in carrying pollen from flower to flower.
Christy's studies of methodic habits.— Christy (1884:186) adopted
Bennett's methods and corroborated his general results. The honey-bee
was found to be perfectly methodic, not one individual changing from one
species of flower to another, even in mixed groups. Among the bumble-
bees one individual was seen to visit no less than 5 different species, 3 visited
4 species, 4 went to 3 species, 18 to 2 species, and 29 were constant to a
single species. The Lepidoptera were found to be much more constant
than in Bennett's observations, only 3 of the 12 individuals going to a
second species. It was observed that bees were less constant in early
spring and autumn, probably because fewer flowers were out, a honey-bee
in spring going twice from Anemone to Ranunculus. Bumble-bees proved
more methodic when visiting blue flowers than those of other colors, though
the results were not regarded as conclusive.
Mueller's results.— Mueller (1876) reached the same conclusions as
Darwin with reference to the causes of constancy. With respect to the
differences in the behavior of male and female bees (1881), he found that
HISTORICAL. 131
pollen flowers are visited almost solely by the females. Many fragrant
honey-flowers are visited by the males of certain bees with especial fond-
ness, but little or not at all by the females of the same species. In cases
where the females of a certain species have restricted themselves to a par-
ticular flower form or even species for the sake of rapid and certain profit,
the males are not affected by such restriction but visit also other flowers.
Among those species of bees that visit many flower forms, the females go
to the most profitable flowers, the males to the easiest or most fragrant.
His demonstration of the presence of the greatest individual differences
in color preference also revealed one of the factors involved in constancy
(1883:275).
Bulman's studies.— In a series of papers (1890, 1892, 1897, 1899)
Bulman dealt especially with exceptions to the supposed rule of constancy.
"It is pretty generally believed that the bee is very constant in its visits to flowers,
and that when it begins with any particular species it keeps to that until it has obtained
its load. But while it is true that bees do show a considerable amount of constancy
and often visit a large number of flowers of the same species in succession, they are
far from possessing that amount of constancy required by the theory. But it is a
well-established fact that bees pass readily from variety to variety of the same species
in our gardens. They do not even confine themselves in a single journey to varieties
of the same species. In numerous cases I have seen bees visit two, three, or even four
species in the course of a minute or two. Hive bees are much more constant than wild
bees, yet they pass freely from variety to variety, and not by any means rarely from
species to species. As to the latter, take any wild bee, and if you can follow its move-
ments for twenty visits or more, the chances are something like ten to one that it will
be seen to change its species of flower."
Among the numerous cases of inconstancy cited, the most striking were
those of a bee that made 10 changes in 27 visits to four different species
of geranium and of a group of bees that passed from Lavandula to Geranium,
Leycesteria, Epilobium, Antirrhinum, and Oenothera.
Ord's conclusions. — Ord (1897) observed the following routes for two
honey-bees: (1) Cytisus 2 visits, Primula 1, Tremandra 1, Eupatorium, rose
2, white 2; (2) Caltha 7, Ficaria 2, Caltha 3, Ficaria 2, Caltha 3. Bombus
made the following journeys: (1) red Tropaeolum 1, yellow 2, red 1, Viola
1, red Tropaeolum 2, yellow Calceolaria 1, red 2; (2) Geum rivale 2, inter-
medium 1, rivale 1, intermedium 2, urbanum 2, rivale 6, rivale 6, intermedium
3, urbanum 1. The majority of the apids observed seemed constant to a
single species, though this was not true of all the individuals followed for a
long time. Few bees were able to resist the temptations offered by a garden.
The hive-bee appeared to be fully as inconstant as the wild humble-bees.
The most remarkable examples of constancy were observed for Salix, Tilia,
Calluna, Mercurialis, and Ajuga. The transfers seemed especially frequent
when a number of related plants grew together.
Plateau and Perez. — The general results of Plateau's studies of con-
stancy (1901) have already been given (p. 157). Anthidium and Apis were
found to be very constant, the latter affording but 14 examples of incon-
stancy during three summers, while Bombus often flew from one species to
another and even to a third. P6rez (1903:24) objected to Plateau's re-
132 COMPETITION AND CONSTANCY.
striction of the term constancy to polytropic hymenoptera and he extended
it to apply to polytropic and oligotropic bees that visit but one species of
flower during a flight. For the honey-bee constancy is the usual rule at any
moment, as it is for the social bees generally, a fact shown by the pollen
stored up in the hives. It is likewise the rule that the pollen-baskets of
bumble-bees contain the pollen of a single species. The fidelity of bees in
general to a single species of flower is far from absolute, but it may be very
frequent. Within the limits of observation it appears only with respect
to the collection of pollen and not at all with that of nectar. Consequently,
it rarely exists with the males. For the same reason, doubtless, it is hardly
to be found in hymenoptera other than the bees. It appears to exist in
relation to the gathering of pollen because the larva is less tolerent to dif-
ferences of food than the adult (cf. also Peiez 1889, 1894.)
Constancy in Bombus. — Wagner (1907:38) has recorded the following
observations which show an exceptional degree of constancy in several
species of Bombus. Four individuals of Bombus lapidarius made respectively
31, 28, 34, and 20 visits to Vicia sepium without going to other flowers, and
a fifth sought Lamium album exclusively. Bombus terrestris flew 15 times
to Dianthus carthusianorum to the neglect of Vicia, another individual
ignored all flowers but those of red clover, and four others paid attention
only to those of Scabiosa; while the last visited similarly Melampyrum
nemorosum. Bombus muscorum went only to Salvia pratensis on one day,
in spite of the presence of Melampyrum, while on the next it flew back and
forth from Trifolium to Melampyrum. For a whole day Bombus terrestris
and silvarum worked only on species of lilac-colored flowers, ignoring all
others. As a result of his study of the detailed path followed by the
bumble-bees in these and other visits, Wagner reached the conclusion that
at a certain distance they are guided to flowers by vision exclusively, the
distance at which the species can be discriminated being determined by the
size of the flower, the inflorescence, or the plant group itself.
Lovell's conclusions. — Lovell (1914:202) reaches the following con-
clusions as to the various types of constancy:
"There are still in existence many intermediate stages between mono-tropic, oligo-
tropic and polytropic bees. While many bees visit a great variety of flowers, others
visit only one family, as the Compositae or Nymphaeaceae, others only a single genus,
as Salix, and others only a single species, as the violet, strawberry or spring beauty.
Many exceptions no doubt occur and will be recorded when the habits of these bees
have been more carefully observed. For instance, I have often seen the loosestrife
bee on the umbels of the prickly sarsaparilla. It is evident that if a monotropic bee
extends into a region where the flower it visits elsewhere does not occur, it must of
necessity visit other flowers. Evidently this habit did not originally exist among
bees, but has gradually been acquired.
"We may sum up the matter as follows. All bees including the honey-bee show a
strong tendency in collecting both nectar and pollen to be constant to one species of
flower. This is manifestly for the advantage of both insects and flowers. In the case
of a number of bees flying for only a small part of the season, this habit has become so
specialized that they visit only one or a few allied species of flowers, which offer an
abundance of pollen and nectar. As the honey-bee for a time restricts its visits to
HISTORICAL. 133
the white clover, so in like manner a monotropic bee visits but a single kind of flower.
But in the former case the bee flies throughout the whole season, while in the latter
when the flower fades the bee's period of flight is over."
Kranichf eld's observations. — Kranichfeld (1915:39) has carried out
two series of field observations on the constancy of the honey-bee to color
and species. Of the 18 fields studied, 15 were being visited by honeybees
and 10 of these contained plants of Cirsium oleraceum. In these Cirsium
was sought exclusively in five cases and chiefly in all the others, the only
visits to other flowers being to Lathyrus in one case, Cirsium palustre in
another, and to Centaurea and Heracleum in the third. As the flowers were
almost wholly white or dull in color, it was concluded that color was not
decisive in the choice of the flowers. In the second series the constancy
was greater, both as to color and species, the exceptions being regarded as
due to the behavior of the young and inexperienced bees. The other cases
of inconstancy appeared to be due to the confusion of the honey-bees and
bumble-bees by the presence of the same color in two or three species.
While the results were not entirely harmonious, they strengthened the
probability that sense of color serves to guide bees and hence is a factor in
constancy.
Origin of oligotropism. — Robertson (1914) ascribes the assumption
of the oligotropic habit to competition, maintaining that "the bee fauna
is all that the flora will support, that there is constant competition between
bees, and that natural selection favors those which are the least competitive
in food habits. The early maximum flight, the non-competitive pheno-
logical distribution, and the frequent oligotropic habits indicate that these
bees have managed to hold their own only by dividing up the remaining field
and occupying the most favorable corners left by their polytropic compet-
itors." On the contrary, Lovell (19142) believes that only a part of the
available flower food is gathered by bees, many plants producing nectar
far in excess of the needs of the tributary bee population. If severe com-
petition were to occur, the oligotropic habit would be undesirable, since
such a bee would be at a disadvantage in comparison with polytropic spe-
cies, unless it were always certain to find the requisite food supply. In the
genus Perdita, the tube-length of the flower, and not competition, is the
factor that limits the visits of the various species. It is concluded that
"certain bees have become oligotropic because of the direct advantage
gained, combined with the fact that their flight was S3mchronous, or nearly
so, with the period of inflorescence of the plant to which they restricted
their visits. This theory offers an explanation of the rise of oligotropism
by the observation of existing conditions. There may be and often are
accessory factors, but they are of secondary importance." It appears
fairly certain that Lovell is correct in assigning the chief importance to the
limiting action of structure and to the coincidence of flight and flowering
period, though there are doubtless cases in which competition enters to
some degree, as apparently he would admit. Special studies are greatly
needed in the case of each oligotropic species to determine the exact relations,
and these will afford further opportunity for the use of experiment.
134 COMPETITION AND CONSTANCY.
RESUME.
Experimental results in competition. — In the case of adult insects,
especially bees, habit is the controlling factor in competition. This is
shown by the fact that the standard plant, which is the one that the insect
was in the habit of visiting, was favored in 36 cases, while the bouquet,
consisting of flowers out of their natural position, had the advantage in
but 11 cases. Moreover, the difference between the number of visitors in
each experiment was regularly much greater when the plant was preferred
than when the bouquet was. The reversals of choice were caused by flowers
with a large amount of nectar, mostly members of the rose family, such as
Rubus strigosus, Prunus demissa, and Opulaster opulifolius, or by regular
flowers well-supplied with nectar and pollen, such as Chamaenerium, in
competition with specialized ones such as Monarda. In a few cases, the
abundance of pollen was the deciding factor, as when Rubus deliciosus or
Rosa acicularis proved more attractive, doubtless owing to a shift in the
nutrition requirements at the time. Flowers in vials obtained very few
visitors, even in comparison with bouquets, probably because of the strange-
ness of the vial itself. The effect of the vial is well exhibited in the experi-
ment where the two species of Geranium were employed reciprocally as
standard plants and in vials. With G. richardsoni as the standard the re-
spective figures were 88 and 9; withG. caespitosum as the standard, 83 and
10. When standard roses were in competition with roses and with Cha-
maenerium in vials, the figures were 85, 49, and 7. The vials alone reduced
visits nearly a half, and a strange flower in addition further decreased them
seven times. In the case of natural competition, or competing bouquets,
habit is partly eliminated, and the relative attractive power of the species
is the chief factor. This varies, however, with respect to the composition
of the visiting population, and a decisive test is possible only with young
insects in which habits have not yet been fixed.
Apis mellifica gave the preference to the standard plant in 24 instances
and to the bouquet in 4; in 15 experiments it went to the plant alone.
The total number of visitors to the standard was 972, to the bouquet, 153.
Bombus bifarius preferred the standard in all of the 9 experiments where
it was an important visitor, and went to it alone in 6 cases, the total number
of visitors to standard and bouquet being 206 and 20. B. proximus chose
the plant in 7 experiments out of 8, visited it alone in 6 instances, and 222
bees went to it in contrast to 48 to the bouquets. B. juxtus was far less
faithful to the standard, giving it the preference in 13 cases out of 19,
visiting it exclusively but twice, and yielding 564 visitors to the bouquets
for 920 to the standards. The preference as to species naturally shifted
with the progress of the season, but during the respective flowering periods
the marked preferences were as follows: Apis for Rubus strigosus, Bom-
bus for Rubus deliciosus, Rosa, Geranium, and Chamaenerium, Clisodon
for Monarda, Andrena for Opulaster and Prunus, and Osmia for Pentstemon.
Effects of competition. — The final outcome of competition for pollin-
ators in terms of the setting of fruit and the production of seeds is difficult
to determine in nature, owing to the wide range of preferences among the
many species of insects usually present. The only direct study of this so
RESUME. 135
far made seems to be that of Dodel-Port (1882:294), though Lovell (1912,
1914) mentions a number of observations by bee-keepers, which belong in
this general category. Dodel-Port found that two beds of the scarlet-
runner bean, though blooming profusely, failed to set fruits with the excep-
tion of a single legume, in spite of the fact that elsewhere in Zurich it fruited
abundantly. During this period repeated observation failed to reveal a
single pollinating insect on these flowers, though honey-bees, bumble-bees,
butterflies, wasps, and flies were numerous on the adjacent flowers of
Cerinthe, Calendula, Centaurea, Bidens, Cichorium, etc., which exercised a
greater selective power upon them. Just as long as these flowers that were
richer in honey continued to bloom, the bean was at a complete disadvan-
tage in the competition, but after the middle of August they began to
disappear and the brilliance of the beans then brought the visitors to them
and fruits began to develop frequently. A comparison with the plants of
this species in other gardens led to the inevitable conclusion that it formed
no fruits in the Botanical Garden as a direct consequence of the diversion
of the bumble-bees through the other more attractive flowers.
Constancy as shown by pollen loads. — The composition of pollen
loads can only reveal the behavior of bees in the collection of pollen. Too
little is known of the detailed habits of the various species of bees with
respect to the gathering of pollen and nectar, and more exact knowledge
of constancy must await upon this among other matters. The analysis of
pollen loads showed that 86 individuals carried mixed loads in comparison
with 121 carrying pure pollen. With respect to species, none represented
by 5 or more individuals was characterized by pure loads, the latter being
found only on 4 bees belonging to Halictus pulzenus, on 3 of Monumetha
albifrons, and 2 of Osmia melanotricha. In Apis the relation of pure loads
to mixed was 28:3, in Andrena crataegi 15:3, in Bombus juxtus 19:6, and in
bifarius 7:5. Variation in behavior within a genus is shown by the fact
that for B. occidentalis the ratio was 9 : 17, Andrena madronitens 1 : 3, and
A. vicina 2:3, while for Halictus medionitens it was 2:2. It is clear that
bees in general are no more constant in the collection of pollen than in the
gathering of nectar.
Determination and designation of constancy. — Our present know-
ledge of the habits of bees is inadequate to a comprehensive and accurate
treatment of constancy. Nearly all those interested in the subject have
defined constancy in different terms and the studies that bear directly on
this relation have been so few and fragmentary that further advance must
await special investigations which are at once extensive and intensive.
These must take account of behavior with respect to both pollen and
nectar, the differences between individuals, sexes, ages, species, etc.,
single flights and those made on the same day, and on different days
and at different parts of the flowering period of preferred species. Further-
more, they must employ experiment to vary conditions in a definite manner
in order to test habit under new circumstances and to furnish quantitative
results, which will permit the expression of the degree of constancy for
individual or species in numerical terms.
4. PRINCIPLES AND CONCLUSIONS.
INTRODUCTORY.
Nearly the entire history of experimental pollination is reflected in the
writings of Plateau and the papers called forth by his results. His were the
first researches in this field and for thirty-five years his classic experiments
were the outstanding features of its development. Indeed, he and his
critics occupied the stage until the last decade, which has been marked by
researches not genetically related to his. Thus, while Plateau is the dom-
inant figure almost throughout, it is helpful to divide the period of develop-
ment into four stages, as follows; (1) early experiments of Plateau and others,
(2) main researches of Plateau, (3) related studies and critiques, (4) recent
investigations. In the hope of providing a comprehensive and exhaustive
account of experimental pollination, abstracts are given in detail of all
experimental studies, and of such critical discussions as those of Knuth,
Kienitz-Gerloff, and others. Because of their significance and their frequent
inaccessibility, the papers by Plateau have been summarized with especial
fullness. The historical section is followed by an extended resume of results
and conclusions, examined in the light of the present researches.
EARLY EXPERIMENTS OF PLATEAU AND OTHERS.
Artificial flowers. — The stimulus for Plateau's first experiments came
from an observation reported by Vallete (1875), according to which an
individual of Macroglossa stellatarum, which had entered through the
window, tried vainly to plunge its tongue in the flowers of a tapestry,
"passing from one bouquet to another and choosing skillfully the flowers
that it sought to probe." The unfavorable comments called forth by this
statement led Plateau to come to its defense with his study of response to
artificial flowers (1877:535). The latter consisted of red and yellow roses,
yellow Ranunculus, and variegated Convolvulus, which were made to resem-
ble natural flowers as closely as possible. They were placed in the garden
among plants of Viola, Pulmonaria, Primula, Fritillaria, Crocus, Hyacinthus,
and Arabis, of which the latter was almost alone in being visited by
insects, chiefly Vanessa and A pis. During two hours of observation no
visitor came to the artificial flowers, though a butterfly passed near one.
When the same artificial flowers were placed in a bed of Hyacinthus or of
Arabis, or the latter mixed with artificial flowers of its own kind, the results
were the same, only a single honey-bee hesitating for a moment above them.
Moreover, when a drop of honey was placed in the center of each false
Arabis, no visitors alighted on the flowers, although Anthophora frequently
poised above them as though drawn by the odor. Two showy beds of arti-
ficial flowers of violets, pansies, marsh marigolds, roses, buttercups, etc.,
were placed in a sunny sward, but of the Anthophora, Apis, Bombus,
Pieris, and Vanessa flying about, only the latter noticed them in the least
and then but momentarily. On the same day branches of a cherry in full
bloom were provided with flowers made to resemble the cherry and white
lilac, but the bees visited only the natural ones. When imitation roses,
white, pink, and red in color, were mixed with natural ones, Apis,
Bombus, Trichius, and various flies showed complete indifference to the
136
EARLY EXPERIMENTS OF PLATEAU AND OTHERS. 137
former, though Syrphus poised for some time above a false rose and Pieris
wheeled to make a small circle above a group. A shoot of Aucuba without
natural flowers was furnished with artificial ones of a lively color, but
drew no visitors during a half-hour of observation. In the final experiment,
a large number of brilliant artificial flowers was placed in one group in the
center of a lawn surrounded by a garden in full bloom. Although many
bees, butterflies, and flies were working on the latter, but two individuals
of Pieris came to inspect the imitation flowers.
In conclusion, Plateau stated that the bright colors of flowers attract but
a small number of insects, chiefly diurnal Lepidoptera, a group in which
instinct is but feebly developed. Insects are able to perceive differences
between natural and artificial flowers that escape the observer who is not
forewarned, differences sufficiently great to permit no error and even to
excite distrust. In their flight from a distance to the flower sought, insects
are probably guided by some other sense than sight alone. Thus, he was
led to draw conclusions which were exactly the opposite of what he expected.
He disclaimed any desire to render a final judgment, but regarded the meth-
ods employed as worthy the attention of those engaged in the study of
pollination.
Nectaries. — Bonnier (1878:5) challenged the prevailing view of the
fundamental importance of floral nectaries in pollination, scrutinizing
in detail the evidence adduced by the enthusiastic students of floral biology.
He pointed out that the development of spurs in flowers is not necessarily
in accord with the presence of nectar, and that this is likewise true of
scales, hairs, and other devices for protecting the nectar. A considerable
list was given of flowers of inconspicuous color that are abundantly visited
by insects, and a reciprocal list of bright-colored flowers little or not at all
visited because of the lack of nectar. The view of Mueller that the vis-
ibility of the flower is proportional to insect visits and to the development
of floral adaptation was tested by means of related species of different
color. The greenish-white flowers of Teucrium scorodonia were visited
by 13 honey-bees in the same time that 3 went to the red ones of T. chamae-
drys, while 4 species of Allium with a nearly equal attractive surface re-
ceived respectively 6, 4, 5, and 15 visits. In the case of Althea rosea an
equal number of red, rose, and white flowers gave 14, 13, and 13 visits
by honey-bees and 4, 3, and 4 visits by bumble-bees respectively. Ob-
servations were reported for a number of other species, and a special test
of response to color was made by means of rectangles colored red, green,
yellow, and white, provided with an equal amount of honey and placed at
equal distances from the hives. The maximum number of visits for any
one minute was 78 for yellow during the ninth minute, 90 and 93 respec-
tively for red and green during the tenth minute, and 85 for white during the
eleventh minute, the totals being 549, 621, 640, and 652. The conclusion
was reached that there is no agreement between the development of colors
and that of nectar, that in the same conditions the flowers with brightest
colors are not the most visited by insects, and the visibility of flowers
is not proportional to their adaptation to cross-fertilization; in short,
insects go in greatest number where the nectar is most abundant, the rich-
est in sugars, and easiest to obtain.
138 PRINCIPLES AND CONCLUSIONS.
The view that the male flowers are more visible than the female in
diclinic nectariferous flowers was tested by observations of Salix, Ribes,
Asparagus, and Bryonia. The number of visitors was so nearly equal that
it was stated that in such flowers the bees do not go first to the staminate
and then the pistillate, and that the former do not possess a greater vis-
ibility. The development of spots and stripes on the corolla was thought
not to be correlated with the nectar or the presence of a large corolla,
which is independent of the frequent visits of insects. The development
of perfume in the flower and that of nectar are not in agreement. The same
flower can be visited in several different ways by the same insect, indicating
that there is no reciprocal adaptation between them, as is shown also
by the fact that insects continue to visit flowers after the corolla has fallen.
Insects are able to secure nectar from the flower without effecting fecund-
ation, as is especially true of the large number of flowers that are robbed by
bees. The visitors to the same species differ in accordance with the var-
iations in the amount of nectar. Furthermore, undesirable visitors are not
excluded by odor, form, or by the time or place of blooming. In sum-
marizing it was stated that it is impossible to admit that all the features
of flowers are designed to attract insects in furnishing them nectar, and
thus bringing about cross-fertilization. One can not admit that there may
be reciprocal adaptation between flowers and insects, since the observed
facts do not accord with the imaginary hypotheses. Finally, the modern
theory as to the role of the nectary seems to be inadequate.
It is obvious that Bonnier's conclusions were much more sweeping
than his evidence warranted, and hence it is not strange that he should
have been severely criticized by Mueller (1880:219), who declared that
Bonnier, in his blind and presumptuous endeavor to destroy one of the
most comprehensive and best-grounded of theories by childish weapons,
had only succeeded in bringing to it new support. In spite of this, however,
he deserves much credit for pointing out some of the serious weaknesses
of a theory which attempted to explain the most insignificant features
of the flower as both cause and effect of insect pollination.
Color sense of bees. — Lubbock (1882:291) studied the response of
honey-bees to color by means of paper slips and glass slides provided with
honey. The latter was placed on blue and on orange paper and a bee
brought to the former. After she had returned twice the papers were
transposed, but she still went to the blue paper, as she did also when
the papers were again transposed after three visits to the blue. Similar
results were obtained two days later, in which, as the bee returned to
the usual place, now occupied by the orange slip, she started to alight
and then darted off to the blue. Experiments of the same sort were made
at various times, and agreed in showing that bees return to the color to
which they have been accustomed.
To determine whether there was a preference for one color over another,
Lubbock made use of microscope slides on which were pasted slips of paper
colored respectively blue, green, orange, red, white, and yellow. These
were placed on a lawn about a foot apart and on top of each was put a
second slide with a drop of honey; with them was also placed a slide of
plain glass with honey. After a marked bee, trained to come for honey,
EARLY EXPERIMENTS OF PLATEAU AND OTHERS. 139
had sipped for a quarter of a minute, the slide with honey was moved so
that she flew to another slide. This was next taken away, and so on, until
she was induced to visit all the drops before returning to the hive. While
she was absent, all the upper glasses with honey were transposed and the
colored slips also moved, so that position could not influence selection
by the bee. The record was made by noting the order in which the bee
went to the different colors. The experiment was repeated a hundred
times with the use of two different hives at different places and the obser-
vations extended over some time in order to work with different bees and
under varied conditions. The first day's results gave a decided preference
for blue; white, yellow, and green were nearly equal, followed by orange
and red also about equal, with the plain glass last. In the next series,
bees had been trained for three weeks to come to a particular spot on the
lawn by placing honey on a piece of plain glass. In spite of the advantage
thus given the latter, blue was again first, followed at some distance by
white, and this by yellow, red, green, orange, and plain glass.
Bonnier's results to the contrary were regarded as inconclusive, since
the colors were largely covered up by the bees and since the presence of
so many would attract their companions. Moreover, he omitted blue and
his squares were all colored, the absence of colorless checks being especially
serious.
Response to detached petals.— Mueller (1883:273) regarded Lubbock's
results as inconclusive, since he did not use the natural colors of the flower
and did not give the bee a distinct choice between two plates differing in
color alone. To obviate these difficulties Mueller made use of detached
petals placed between glass slides which were cemented at the edges,
so that the odor could not be effective. A drop of honey was placed on
each test-object thus prepared. As a rule, petals of two distinct colors
were submitted to the choice of bees that had been marked and accustomed
to coming for honey on glass slides. In their color preference different
honey-bees exhibited marked individual response, one showing equal
liking for both colors, another a preference for one, and a third for the other.
Thus, while the total number of visits made by a group of 6 bees to the purple
of a rose and the blue of a cornflower was the same for each, only three
bees were equally sympathetic to them, the other three visiting them
in the following ratios: 10:14, 5:3, and 3:1. In the case of the fire-red
of nasturtium and the violet of the pansy, seven of eight bees preferred the
latter, most of them very decisively, and but one the former, also very
distinctly, viz, 10:3. Individual bees also differed in the constancy of
their response to related colors, two preferring honey-yellow to brilliant
yellow throughout the period of experiment, and the other two choosing
the one in the first half and the other in the second. Bright colors, bril-
liant yellow and orange, fire-red, scarlet, are less pleasing to the honey-
bee than the softer colors with which the bee-flowers are adorned, viz,
white, honey-yellow, rose, pink-red, violet, and blue. The preference
for bright yellow and honey-yellow was 48:78, for the former and white
21:48, for brilliant orange and rose 22:71, and 26:77, for fire-red and
violet 29:80, for scarlet and rose 9:55, for scarlet and pink 34:69, and for
scarlet and blue 13:78.
140 PRINCIPLES AND CONCLUSIONS.
The least attractive of all the colors of true bee-flowers is glaring yellow,
the ratio between this and yellow-white being 35:68, with pink-red 27:74,
with purple 42:62, with indigo-blue 28:56, and with violet 24:78, while
chrome-yellow and cobalt-blue gave 11:40. White and yellowish- white
were visited about as readily as many shades of purple or even more so,
but less readily than blue or violet; for example, white against dark-
purple gave a ratio of 7:30, and against sky-blue 36:64, while yellowish-
white and purple gave 52:49, with blue 18:25, and with violet 11:24.
Blue is either preferred to red, or the two are equally attractive, in accord-
ance with the particular shades employed; thus, violet-blue in competition
with dull-purple gave 61:31, sky-blue and bright purple 45:36, sky-blue
and rose 57:54, cornflower blue and purple 52:52, and impure violet-blue
and dark-purple 57:57. A pure deep blue excels violet in attraction in
the proportions, 50:35 and 81:67. In its attraction for the honey-bee
violet excels all other flower colors except blue. Among the brilliant flower
colors, bright yellow is the most attractive to bees, giving with scarlet
the ratio 50:29, and with bright orange 42:31. The green of leaves is less
pleasing to honey-bees than the colors of bee-flowers, giving in competition
with rose 75:33, but it is more attractive than scarlet, 45:40 or orange
57:46. As a result of field observations, Kranichfeld (1915:40) has come
to the conclusion that the color preference demonstrated by Mueller's
experiments does not obtain in the normal visits of bees to flowers (see
p. 133).
Color preference of nocturnal moths. — Gratacap (1883:791) made
cylinders of variously colored tissue-papers and drew them over common
kerosene lamps with gas chimneys in order to test the color perceptions
of night-flying insects. The colored lights were first placed in a row at long
distances from each other, but this arrangement seemed defective by reason
of the fact that the brilliancy of the light first visited interfered with the
visitor's freedom of choice between that color and another that reached
it but dimly. The lights were next arranged in a square, at first in such
manner that the circles of light touched each other, but later so that they
overlapped. Since this did not permit an exactly equal choice, the final
plan was to make use of but two lamps at a time. The need of causing the
insect to choose instantly between the colors before it reached either arose
from the infatuation produced by the lights, preventing the insect from
freeing itself except in an accidental manner. The results indicated the
absence of marked preference for certain colors over others, and demon-
strated the almost invariably greater charm of the white lantern, which
on account of its translucency appeared more brilliant than the colored ones.
Response to color without antennae. — Forel (1886:24) considered
that the ingenious and patient studies of Lubbock had demonstrated the
ability of bees and wasps to distinguish colors and at the same time a feeble
sense of smell in the former. While this seemed to be contradicted by
the experiments of Plateau with artificial flowers, such negative results
were regarded as of less value, especially since other factors rendered the
investigation incomplete. Above all, it is possible and even probable
that an imitation exact to our eyes may affect those of an insect so that
EARLY EXPERIMENTS OF PLATEAU AND OTHERS. 141
it will perceive differences not apparent to us. Moreover, Plateau failed
to take odor into account, though this is of less importance, and finally,
Lubbock has shown that bees and wasps are so controlled by habit that
new flowers would attract them less than those to which they were habit-
uated. To determine the attraction exerted by color, Forel cut the antennae
of 6 individuals of Bombus terrestris at the base and released them. At the
end of 5 minutes a male returned and visited 10 flowers of bindweed in
succession, each time flying directly to the flower without hesitating a
second. It was caught, the antennae examined to confirm their complete
absence, and then released, when it made a single circuit in the air and
returned immediately to the flowers, to visit them as before. In the case
of other bumble-bees the front of the head was cut away as far as the com-
pound eyes and the remainder of the lower lip and the entire pharynx
removed. Nevertheless, the bees thus mutilated flew actively, saw, and
moved their antennae; when released they returned to the flowers, but
remained only an instant in each, since they were unable to suck nectar.
At the same time several of the bees without antennae came again to the
bindweeds, flying from one to the other with more precision if possible
than those with the antennae intact. Two days later several of the mutilated
bees were again found on the flowers, visiting them with an astonishing
rapidity and precision. When the antennae, the front part of the head
and the pharynx were removed from males of Bombus pratorum, one of
these made a turn and flew directly back to the Veronica it had been visit-
ing, seeking vainly to secure nectar from it as well as from the bindweed.
A second shortly returned and behaved in the same manner, while the small
females thus treated did not come back, apparently because of their greater
intelligence. A wasp, Polistes gallicus, treated in the same way, behaved
similarly, returning to the mignonette in a fruitless quest.
Forel noted that the loss of the antennae in these cases seemed to increase
instead of decreasing the precision of flight. The insects no longer balanced
to the right and left before alighting, but flew in a straight line to the
flower and landed immediately, the difference in behavior before and after
the removal of the antennae being especially striking in Vespa. All this
seems to indicate that the balancing in flight enables these insects to smell
certain substances with their antennae, which explains why this movement
is more marked with the wasps which smell readily and see less well than
with the bees, where the reverse is true. The experiments were regarded
as demonstrating clearly that it is the compound eyes alone that direct
flies, butterflies, beetles, dragon-flies, bumble-bees, and wasps in their
flight. It is by means of these organs alone that these insects distinguish
colors on the wing, as well as objects, especially when they are moving,
distances, and pathways through the air. Odor can attract certain winged
insects in a certain direction, but without eyes they could not find their
way.
Perception of form. — An individual of Vespa germanica was placed by
Forel on a circle of white paper 3 cm. wide, spread with honey. After
taking its fill, the wasp flew away, but returned at once directly to the
white circle and again sipped the honey. The white paper was then re-
142 PRINCIPLES AND CONCLUSIONS.
placed by one without honey, while it was moved to one side at a distance
of 2 inches. The wasp returned to the original place occupied by the disk
without honey, and finding nothing there, rose a little, balanced two or
three times, and went to the paper with honey. During its absence honey
was placed upon a cross of white paper about 11 cm. long, and this with
the empty white disk was placed near the spot last visited. Upon returning
the wasp soon found the honey, probably because the cross was not suf-
ficiently different, and it was replaced by a white band. On the next,
visit the wasp flew direct to the white disk and searched a long time for
honey, and then went to the original place in vain. It repeated this before
it was able to find the honey in consequence of repeated searching. On the
morrow the wasp came twice to take nectar from the cross, when it was
caught and the antennae removed. It flew away, but returned in a half-
hour to sip upon the same cross. After its departure a similar cross with-
out honey was placed at one side, and on the other a band with honey,
the original cross then being taken away. The wasp returned, flew directly
to the cross, and alighted in the middle, hunting vainly during a rather
long time. Then it began to search, apparently remembering that the papers
had been frequently transposed, and after passing two or three times
within a few millimeters of the honey, finally found it after the tongue
practically touched it.
A bumble-bee, trained to take honey from a blue disk, first flew to one
without honey, but taken again to the former, returned to it several times
without error. The blue disk was next replaced by a blue band, and a
disk alone put at a distance of three inches. The bee then flew straight
to the disk, but made only one turn before going to the band with nectar.
He was returned to the disk with nectar, which he visited several times.
Two hours later this was replaced by the band with honey, and a disk without
was put at 6 cm. This time the bee came first to the original place now occu-
pied by the band, but scarcely hesitated, failing to note the honey, and flew
to the empty disk, which he searched thoroughly two or three times, finally
going to the band with the honey. When a red disk with honey was sub-
stituted for the blue, and an empty blue one placed at 4 or 5 inches, the bee
each time went straight to the latter and could not find the honey on the
red disk, even though it was in the original place. Once found by chance,
he hardly tasted it, so much was he obsessed by the association of "honey
and blue," before he again began his search upon the blue disk, without
returning to the honey on the red one. This was explained by the fact
also that bumble-bees have much poorer memories than wasps, since
several visits are necessary to enable them to find a place without hesi-
tation, while one suffices for the wasp.
Consequently, the influence of color was regarded as of the greatest
significance. The bee did not know enough to find the honey on the red
disk when he was brought to touch it; he still sought it on the blue with
a perseverance but little intelligent. It is evident that he perceived
the color in a fashion infinitely more intense than the form of the paper.
On the contrary, as Lubbock has shown, while the bumble-bees and honey-
bees distinguish colors especially well, wasps pay little attention to them,
but recognize places admirably, the one employed going direct to a red
EARLY EXPERIMENTS OF PLATEAU AND OTHERS. 143
disk in the place formerly occupied by the blue one, and paying no heed
to the latter at one side. On the other hand, when the disk is moved a
foot from the former place, the wasp is usually unable to find it, while
the bee locates it quickly by the color. The fact that wasps guide them-
selves so well when deprived of antennae, without distinguishing colors
very clearly, is one of the best proofs that they see the forms and contours
of objects, further evidence being afforded by the fact that they can not
direct themselves when their eyes are covered with varnish.
Response of wasps to color. — In their classic experiments with wasps
(1887:105), the Peckhams carried out experiments upon the response to
color, largely with the idea of verifying Lubbock's conclusions. Their
results were somewhat at variance with his, however, as they tended to
prove that wasps rely very greatly upon color for their guidance. This
divergence may be explained in part by the fact that they worked with
large numbers, 500 sometimes passing into and out of the nest in 5 minutes,
and that the presence of two observers increased the accuracy. At the
outset a hole 4.5 inches in diameter was cut in a sheet of bright-red paper
about 24 by 20 inches in extent, and the latter was placed above the nest
in such a way that the entrance was not at all impeded and could be plainly
seen from above. The returning wasps did not enter, but circled over the
paper, seeming greatly excited, until one more intelligent or venturesome
flew in and the others gradually followed. In the course of 3 hours all of
them became accustomed to the paper and worked as usual. Two days
later a blue paper was substituted and this produced as much confusion
as before, though the wasps became used to it in a little more than 2 hours.
The next day the blue paper was removed and a cage full of wasps released
at some distance; an hour afterward 25 or 30 wasps were found buzzing
about, apparently not knowing how to get into the nest, though they en-
tered at once as soon as the blue paper was replaced. When a yellow paper
was substituted for the blue, 130 wasps noticed the change within a period
of 10 minutes, circling around the nest several times before entering, while
8 seemed not to notice it. After an hour's exposure, 70 out of 100 wasps
recognized the change, but after the paper had been over the nest for 3
working hours, only 8 out of 200 hesitated before entering. The sub-
stitution of a light-green paper with yellowish reflections for the yellow one
produced a response, but it was not nearly so marked, 100 out of 172
wasps noting it, but to a smaller degree.
When three dark-red nasturtiums were placed on yellow paper 2 inches
from the hole, 46 of 146 wasps noticed them by flying to them and almost
alighting during a period of 5 minutes, while 29 of 126 noticed them in
the next 5 minutes. With the substitution of California poppies of a yellow
color for the red nasturtiums, the number was much smaller, being but
5 per hundred for 10 minutes instead of 28 per hundred, the previous
rate. Replacing the dark-red flowers brought the rate again to 18 per
hundred. To eliminate the effect of perfume, 3 light yellow nasturtiums,
which matched the paper even more closely than the poppies, were em-
ployed; these received but 3 notices per hundred, proving that the dif-
ferences observed were due to color and not to odor.
144 PRINCIPLES AND CONCLUSIONS.
Being satisfied that the wasps distinguished colors and were disturbed
by a change from one to another, an endeavor was made to determine
more exactly the impression made by a particular color. After the red
paper had been over the nest for 24 hours, it was moved a foot and half
to the south and a blue one put in its place, in order to determine whether
any of the returning wasps would enter the hole in the red paper, to which
they were accustomed, instead of going to the real entrance through the
blue paper. For convenience the blue was designated as the true and the
red as the false entrance. In the first 10 minutes, 76 wasps went into the
true entrance, of which 54 first hovered over the false and about half of
which actually entered it and explored the grass below. Some of the lat-
ter, not finding the entrance here, flew away entirely, and most of those
that entered the true one directly did not pass above the red paper in so
doing. In the next 5-minute period 50 of 78 wasps went first to the false
entrance and afterward found the true, but after 4 hours only 15 out of
125 were deceived. The blue paper was then left over the nest for 48 hours,
when it was moved a foot and a half to the west to put it directly in the
line of flight and its place taken by a yellow paper, which gave a more
decided contrast than the blue had to the red. In the first 7 minutes 270
wasps returned, none of which flew straight into the true entrance, al-
though many passed directly over it; all hovered first over the false,
many of them going in and some going in and out seven or eight times,
so closely was the blue color associated with the idea of the nest. Three
minutes later, during a 5-minute period, 205 wasps first entered the false
and then the true hole; not one flew straight to the true, though 6 hesi-
tated over it and then entered without going to the false. An hour later
184 went into the false hole and 202 into the true one, but after 2 hours
more, only 76 entered the false hole to 191 for the true one, while 5 hours
later still only 5 out of 49 visited the false entrance. The next morning only
an occasional wasp entered the false hole, though one came and searched
in the grass after the blue paper was finally removed.
A similar test was made with yellow paper, one of slightly darker color
being substituted after an exposure of 3 days. During the first period
nearly a third of the wasps were deceived, but during the 4 succeeding
ones only about one-eighth of them, while 2 hours later this dropped as
low as one-twentieth. The original paper was replaced and 2 days later
it was moved 10 inches to the south, leaving the ground about the nest
exposed after it had been covered with different papers for 16 days. During
the first 5 minutes not one flew straight to the hole, but of the 130 that
entered the false hole 61 finally found the true one. When the false paper
was moved 2 feet to the south, 107 entered the true hole and 103 the false,
but when the opening in the yellow paper was put 6 inches from the hole
and a red one placed over the latter, three or four times as many entered
the true hole as the false one. Somewhat similar results were obtained
when green paper was substituted for the red, the mistakes growing fewer
with increasing experience. When the green paper blew over the hole
and the wasps could not get in, at least 100 gathered and many settled
in the false hole. The green paper was taken away, exposing the ground
about the nest, but only 3 or 4 entered. As soon as it was replaced with
EARLY EXPERIMENTS OF PLATEAU AND OTHERS.
145
the hole above the entrance, they swarmed in 6 or 7 at a time and in a
moment all had disappeared; it was plainly the color that had directed
them.
Response of wasps to odor. — In studying the attractive effect of
odor, the Peckhams surrounded the nest with paper saturated with oil
of peppermint or wintergreen. When the latter was employed, a third
to a fourth of the wasps noticed the odor, as shown by starting back and
circling about. A plate of maple sirup placed 6 inches from the nest re-
ceived no attention from the wasps, though visited by many ants and flies
and one bumble-bee. Fresh warm chicken bones were wrapped in several
thicknesses of gauze of the same color as the paper around the nest and
placed 4 inches to one side of the entrance, while a control bundle without
bones was put on the other side. In 15 minutes 25 different wasps visited
the first bundle, some working over it for a minute or two, but none went
to the second. This test was twice repeated with the same results; in the
last case 3 wasps worked on the bundle with bones for 15 minutes and then
had to be driven away. When the bones were cold, fewer wasps noticed
them and only 2 alighted, and 2 days later after they had become dry and
relatively inodorous, but 2 out of 129 wasps landed on them. A dead wasp,
hidden completely in the grass, attracted 5 others, one of which carried it
away. Three or four others afterward visited the spot, probably attracted by
the scent of blood. At another time 2 were killed and the ground smoothed
over after they had been thrown away; in 15 minutes 9 wasps came to
the spot. It was concluded that wasps have a strong sense of smell, but
that they pay little attention to odors, however powerful, that do not
indicate food.
MAIN RESEARCHES OF PLATEAU.
Masked flowers. — In the first paper of the main series (1895:466),
Plateau set himself the task of evaluating the attractive power of color
and odor by masking simple heads of Dahlia with colored paper or green
leaves. The dahlias grew in a garden with petunias, stocks, nasturtiums,
morning-glories, zinnias, phlox, marigolds, etc., all of which were being
visited by species of Bombus, Megachile, Vanessa, and Pieris. In the pre-
liminary experiments the ray-flowers were covered with squares of paper,
red, violet, white, and black in color, the yellow disk projecting through a
hole in the center. During an hour the 4 masked heads, which were on
different plants, received visits as follows:
Table 89.
Red.
Violet.
White.
Black.
Total.
2
8
1
0
6
0
9
3
0
0
1
0
11
18
1
Total
11
6
12
1 30
146
PRINCIPLES AND CONCLUSIONS.
While the heads with red and white squares seemed to be much more
attractive, this was shown not to be wholly true by the next test, in which
the application of white or green disks to the center of the heads resulted
in masking the latter entirely. In spite of this, a total of 29 visits was re-
corded, of which the black square with white disk received 7. However,
the red square with white disk still yielded the largest number, and a direct
comparison between black and white was lacking, as no white square
was employed in this series. Similar results were obtained with a disk
masking the tubular flowers alone, and with a central cylinder and a black
square.
In order to avoid objections arising from the use of paper, the latter
was replaced by leaflets of Ampelopsis in the remaining experiments.
When the rays of 20 heads much sought by insects and well distributed
among normal heads were covered with leaflets, with only the yellow disk
in evidence, 36 visits were noted in an hour, 18 by Bombus, 11 by Vanessa,
and 7 by Megachile. To determine whether the yellow disk still furnished
the necessary attraction, this was effectively concealed in each of the 20
heads by a smaller leaflet. In spite of this an hour period yielded 58 visits,
of which 28 were made by Bombus, 6 by Vanessa, 5 by Pieris, and 1 by
Megachile. The following day the small leaflet was placed in contact with
the disk-flowers in 16 heads and these were disposed among a larger number
of normal heads. Of the 30 visits made, Bombus afforded 19, of which 13
were successful and 6 in vain, while the butterflies made 6 unsuccessful
to 3 successful ones. In the fourth series 37 heads were completely covered
with leaflets and the remaining ones were removed. In an hour's time 70
visits were recorded, distributed as follows.
Total.
Suc-
cessful.
Unsuc-
cessful.
36
21
13
29
10
2
7
11
11
Total
70
41
29
The author contended that the experiments of Bert, Lubbock, and
others gave misleading results, since it was impossible to give two dif-
ferent colors the same absolute intensity. This conclusion was derived
from the researches of Graber (1884), who found that leucophile, i. e.,
light-seeking, invertebrates preferred the more refrangible rays, while the
leucophobe chose the less refrangible, red producing to them the effect
of obscurity. He also cited the observations of Forel (1887) and others to
the effect that the sense of smell is much better developed among insects
than in man, and that the perception of odors is very different. From these
facts he reached the conclusion that nothing in our present knowledge
proves that insects distinguish colors as the human eye does, and also that
they perceive odors that can not be recognized by the olfactory nerve
of man. His final conclusions were as follows:
MAIN RESEARCHES OF PLATEAU. 147
(1) Insects visit actively heads in which form and color are masked by green leaves.
(2) Neither the form nor bright colors of flower heads seem to possess attractive power.
(3) The colored ray-flowers of simple dahlias, and in consequence those of other
radiate composites, do not have the vexillary, or signal, role attributed
to them.
(4) Since form and color appear to have no attractive role, insects are evidently guided
to composite heads by another sense than sight. This is probably the
sense of smell.
Removal of corolla. — Plateau removed the corolla or ray-flowers in
several species in order to determine the role in attraction (1896:505)
The first experiment was made with Lobelia erinus, with which Darwin had
already made a test of this response (1876:420). The latter cut off all the
petals of certain flowers and only the lower striated lip of others and found
that not a single honey-bee visited them, although bees were abundant on the
normal flowers. The removal of the small upper lip had no effect. Plateau
used two pots of this species, one with 30 and the other with 40 flowers.
These were placed near groups of Dahlia, Petunia, and Tagetes in order to
afford a wider choice to visitors. The corollas of one pot were cut back to the
tube, and the behavior recorded for three different periods of 1 to 2 hours.
The total number of visitors to the whole flowers was 33 against 25 to the
mutilated ones, Eristalis tenax giving much the largest number, while
there were 29 inspections to the former and 16 to the latter. Thus, while
there was a larger number of visitors to the normal flowers, it was pointed
out that the suppression of the corolla did not prevent them, as in Darwin's
results. In the case of Oenothera biennis, one honey-bee was seen to take
nectar from 14 mutilated flowers in succession, and other individuals made
respectively 10, 3, and 15 visits to them, the last one returning to flowers
already visited. When the corolla of Ipomoea purpurea was cut back to
the sepals, Bombus muscorum visited successively 5 mutilated flowers, and
B. terrestris in like manner 2, 3, and 5 respectively.
Kurr (1833:135) removed the floral envelopes of Delphinium ajacis and
D. consolida and found that the flowers produced seeds, a fact that aston-
ished Darwin (1. c). Plateau made a similar test with D. ajacis, removing
all the petaloid parts except the nectary, but the only visit was made by a
bumble-bee. In the next test only part of the flowers of a spike were
mutilated; B. terrestris visited the intact flowers and two of the mutilated
ones. The mutilation experiment made by Bonnier (1878:61) with Digi-
talis purpurea was also repeated, 5 out of 19 clusters having the corolla
cut back to a tube 1 cm. long, and the plants being intermingled. Anthid-
ium and Bombus made 12 and 1 visits and 11 and 5 inspections respectively
of the mutilated flowers. With 3 mutilated spikes out of 5, 4 individuals of
B. terrestris merely inspected the cut flowers, while 2 visited 5 and 6 of them
respectively. The next day the same setting was visited by 4 bumble-bees
of the same species, the first going only to intact flowers, the second merely
inspecting the mutilated ones, the third visiting 6 of the latter in succession
after normal ones, and the last, 9 in similar manner. Antirrhinum majus
was mutilated by cutting the corolla back to 1 cm. in 8 spikes out of 25.
Of 5 bumble-bees observed, 3 merely whirled about the cut clusters, while
the other two flew near them and then left for the entire flowers. The
148 PRINCIPLES AND CONCLUSIONS.
author remarked that if he had worked only with Antirrhinum he would
have been persuaded of the attractive role of the corolla, but regarded this
difference in response to two related genera to be due to the fact that the
cut flowers of Digitalis are still directed downward, while in the snapdragon
the stub is erect and much more difficult to reach.
One experiment was carried out on Centaurea cyanus to determine the
value of the sterile marginal flowers of the head, which were regarded as
attractive parts by Mueller and others. The show flowers were removed
from 10 heads scattered among many normal ones. During an hour and
a half, 1 honey-bee visited a mutilated head, while Megachile revisited them
to a total of 19 heads, behaving exactly as at the normal ones, and pass-
ing readily from one kind to the other. Observations of Darwin, Mueller,
Bonnier, and Van Tieghem were cited to show that insects visit flowers
of which the corolla has fallen, while Van Tieghem had similar results with
Nicotiana, from which he had cut the upper part of the corolla. The con-
clusion of Errera and Gevaert (1878:141) that bees are guided by the odor
of the nectar was extended to include all pollinating insects and to be true
even when there were no normal flowers to assist in the attraction.
The effect of masking flowers was further tried on a very fragrant Hera-
cleum, the single plant available being several kilometers from any others
and thus apparently eliminating the possible action of habit. An umbel
was covered with leaves of rhubarb, but in spite of this received 7 visits in
a half-hour. Several umbels were brought close together and covered with
leaves in a similar fashion, receiving 45 visits during the period of obser-
vation. The evidence furnished by this umbellifer was in entire accord
with that obtained from Dahlia and was regarded as proving that the
insects were guided by the sense of smell.
Response to different colors. — In connection with his experiments on
color, (1897:17), Plateau emphasized the importance of the work of Graber
(1884,1885). In the case of the honey-bee, the latter found that the choice
of color depended upon the degree of refrangibility. When the bee was
given a choice between bright red and deep blue, it went to the latter,
which is more refrangible though less luminous; between bright red and
deep yellow it chose the latter, which is likewise more refrangible. Be-
tween dark green and bright yellow it exhibited no preference, owing to
the similar refrangibility of the two colors, in spite of the fact that the
yellow is more luminous. In consequence, Plateau concluded that insects
do not see color as such at all, in the way that we do, but that they respond
to the different ones merely in relation to differences in refrangibility. His
observations as to choice of color were made upon several species with
flowers of various colors. In the case of Centaurea cyanus he grew blue,
rose, white, and dark-purple varieties in mixture. Both Apis and Mega-
chile were observed to pass readily from one color to another, though 22
of the 30 visits were to blue or purple, and this was explained by the greater
number of the blue heads. Unfortunately, the number of each kind was
not counted, and no endeavor was made to arrange the installation so that
the number of each would be the same. With Dahlia variabilis the colors
were scarlet, purple, rose, salmon, and white, among which the visiting
MAIN RESEARCHES OF PLATEAU. 149
bees, butterflies, and syrphids showed not the least choice, though no
figures were given. During one period of observation pollinators went more
frequently to purple heads of Scabiosa purpurea and during another to the
rose ones, the explanation being that this was due to the greater number
of heads in each case. Observations by Darwin, Bonnier, and Errera and
Gevaert were also cited in confirmation of these results, and the conclusion
was reached that, contrary to the general view, insects exhibit the utmost
indifference to the diverse colors to be found in the same species or the same
genus.
Addition of honey to vivid nectarless flowers. — In the same paper were
reported the results of experiments made upon showy flowers with little
or no nectar, in confirmation of the views of Darwin, Bonnier, and Pe'rez,
who had found that nectar brought visitors in abundance. The flowers of a
border of Pelargonium zonale were observed to be completely disdained by
Apis and Bombus. A drop of honey direct from the hive was placed in each
flower of 17 umbels on plants arranged in a continuous series and marked to
prevent confusion with normal ones. Bombus terrestris made 8 visits in an
hour to the honeyed flowers, entirely neglecting the neighboring nasturtiums.
After sipping at several, he would fly toward the normal flowers, but only
to inspect them without alighting. The next day honey was taken from
these flowers by 3 A pis, 5 Bombus, and 3 Vespa, as well as several Diptera,
and a little later by 18, 5, and 5 individuals respectively of the same genera,
but no further visits were seen for the normal flowers. Flowers of Phlox
paniculata, which were but little visited by diurnal insects, were provided
with honey, a drop being placed in 20 flowers of the violet and white varie-
ties. The latter, being in the shade at the time, received no visits, while
6 were made to the former by A pis, Pieris, and Vespa, the two bees also
making 9 visits during the next period to both colors. Honey was placed
on 6 out of 29 white flowers of Anemone japonica, which were ordinarily
little visited except by Diptera. During the hour 100 visits were made to
intact flowers and 94 to those with honey, making an average of 4.5 for each
of the former and 15.6 for the latter. A single flower of Convolvulus sepium,
which had been completely neglected, received 29 visits after being supplied
with honey, though few of these were made by bees.
The effect of removing the supply of nectar was determined in Dahlia by
excising the disk-flowers of 8 heads and replacing them by a small disk cut
from a yellowed leaf of cherry. No insect alighted on the mutilated heads,
though Bombus and Megachile inspected them frequently. This behavior
determined, the disks were coated with honey and the visitors immediately
returned, Bombus making 26 visits, Vespa 12, and Megachile 2 during a
half-hour. Two days later the artificial disks were dry and the mutilated
heads were again entirely neglected. The disks were removed and a little
honey placed in the greenish cup of the receptacle, when visitors came in
abundance. The summary stated that insects go without hesitation to
flowers habitually neglected by reason of the absence or paucity of nectar,
when they are supplied with artificial nectar in the form of honey. They
cease their visits, even in the presence of the showy ray-flowers, when the
nectariferous part is removed, and begin them again when honey is added.
150 PRINCIPLES AND CONCLUSIONS.
Anemophilous flowers. — In his study of the attraction of anemophi-
lous flowers (1897:601), Plateau enumerated Chenopodium album, Rumex
obtusifolius, Corylus avellana, Carex, Anthoxanthum, Agrostis, Poa, Festuca,
Bromus, Brachypodium, and Secale as already known to be visited by insects
for their pollen, and cited also a number of cases in which extrafloral nec-
taries and fruits were visited by bees and butterflies. His own experiments
were carried out on green or brownish flowers belonging to the Chenopo-
diaceae, Urticaceae, Polygonaceae, Typhaceae, Juncaceae, Cyperaceae,
and Poaceae, to which honey was added. The great majority of the visitors
were Diptera, which usually came within a few minutes, while the bees
appeared much later. It is perhaps significant that Apis went to 12 of the
17 species, the wasps Odynerus and Vespa to but 4, and Bombus to but 1.
Rheum tataricum, which combines the two methods of pollination to some
degree, gave somewhat similar results with honey, but Apis was entirely
absent and 2 species of Bombus made one visit each.
Entomophilous flowers of dull color. — After citing the frequent
neglect of such flowers by Darwin and Mueller, and the emphasis upon
their significance by Bonnier and MacLeod, Plateau (1897:613) gave a
complete summary of his own and other observations upon flowers of this
type, grouped as green, greenish, brown, or brownish. In the first group
he listed 43 species belonging to 18 families, frequented chiefly by Diptera,
especially the muscids; 8 species were visited by Apis, 4 by Bombus, and 8
by other bees, usually the same ones. In the group with greenish flowers or
inflorescences were placed 38 species belonging to 20 families, of which 10
were visited by A pis, 4 by Bombus, and 6 by other bees, the vast majority
of visitors being flies. The flowers with brown or brownish color numbered
12 and were distributed in 9 families, 6 of the species being visited by honey-
bees.
In the matter of anemophilous flowers the conclusion was reached that
it was only necessary to add honey in order to attract insects in large
numbers. Moreover, insect visits were abundant to 91 species of ento-
mophilous plants that lack striking color in the corolla. In short, insects
concern themselves little with the presence or the absence of bright floral
parts; what they desire is pollen or nectar. They are guided to these in
a very secondary degree by sight, but on the contrary in a sure manner
by another sense, which can only be that of smell.
Artificial flowers, second series. — The first experiments of Plateau,
made by means of artificial flowers in 1876, were augmented 20 years later
by studies with the flowers of 8 different families (1897:847). In all cases
the flowers were copied with the utmost fidelity, even to the details of
stamens, calyx, etc. With Ribes sanguineum 10 clusters of artificial flowers
were placed among normal ones, but of 5 individuals of Bombus, 3 of Apis,
and 3 of Osmia, not one was seen to pay the slightest attention to them.
Two branches of artificial flowers of the peach were suspended among the
natural ones and observed for three different periods two days apart. The
bees showed complete disdain for the imitation flowers, even when they
were supplied with a drop of honey, as on the last day. With flowers of the
cherry the results were the same, bumble-bees and honey-bees both passing
MAIN RESEARCHES OF PLATEAU. 151
them without the slightest notice. Similar results were obtained with the
apple, except that the flowers with a drop of honey were visited by one
wasp and many flies. No visitors came to the artificial flowers of Myosotis
alpestris, even with the addition of honey, while with those of Saxifraga
umbrosa 2 individuals of Apis and 1 of Andrena gave them a hurried in-
spection.
A more comprehensive study was made of Digitalis purpurea, in which
the habit of the inflorescence, the form of the corolla, its color, and markings
were copied from nature with great care. Among 6 natural spikes were dis-
posed 3 artificial ones, on one of which honey was placed in the flowers. On
its two visits Megachile paid no attention to the false flowers, while 4 of 10
individuals of Bombus inspected them, 1 repeating this three times. In the
second experiment, 3 natural spikes were interspersed with 3 false ones, 1
of which was provided with honey. Anthidium ignored the artificial flowers
on 38 visits, but inspected them briefly during 11 others, while one Oxybelus
actually entered a false corolla containing honey, as did one Odynerus also.
In the next test, made when the natural flowers were few, Megachile again
ignored the false flowers, Anthidium inspected them on 9 visits out of 31, and
two individuals of Musca alighted, but without entering the corolla. To
eliminate the competition of the natural flowers of Digitalis, 3 clusters of
artificial ones were placed at a distance, but among Dianthus and Tagetes.
Of the many visitors to the latter, but 3 individuals inspected the false
flowers for an instant. To check this behavior an old trunk of a conifer,
a few feet in height, was placed in the spot occupied before by the imitation
clusters, with the result that 3 different insects were observed to inspect
it on two different occasions, indicating the precautions that must be taken
in interpreting mere inspections.
Three clusters of false flowers were suspended in a mass of normal ones
of Lathyrus latifolius, the mimicry being so close that it would not have been
suspected by one not forewarned. One individual of Stelis and one of Bombus
gave an instant's attention to an artificial cluster, while Megachile inspected
it in 10 of 17 visits. To test the significance of this, 3 pieces of pole were
placed where artificial clusters had been, when it was found that Megachile
made 9 inspections of them in the course of 36 visits. When the imitation
clusters were placed 4 dm. in front of the main group, Bombus ignored them
and Odynerus merely alighted for a moment on one of the artificial leaves.
In 50 visits Megachile hovered above the false flowers in but 8 cases, paying
no attention whatever to them in the others.
Artificial flowers of green leaves. — To avoid the objection arising from
the use of something other than vegetable tissue and to further test the
response to green objects furnished with honey, leaves of Ribes rubrum and
Acer pseudoplatanus were rolled into cups, the free edges trimmed, and
honey placed in the center. Six flowers of this type were attached to several
branches of Symphoricarpus racemosus, where they were almost invisible
in the mass of foliage. In a half-hour the leaf flowers had received 19 visits,
chiefly from flies; the bees were represented by two visits of Apis. In the
next test Apis made 8 visits, 1 more than by the other insects, and in the
third, Bombus furnished 2 of the 15 visits, again chiefly due to flies. The
152 PRINCIPLES AND CONCLUSIONS.
bumble-bees attempted to pierce the leaf with their mandibles, but desisted
after several minutes, as the thickness was too great. Finally, two leaf
flowers were fastened to the peduncles of simple heads of Dahlia, the one
made from the leaf of maple being erect, the other from the currant,
hanging. The first received 14 visits, of which 5 were by Bombus, and the
second but 4 visits, none of them from bees.
Incidentally, Plateau made a series of tests with various essences, such
as lavender, sage, thyme, mint, etc., but found that they exerted little
attraction. Thyme and sage alone afforded a feeble attraction, while the
effect of mint was to repel the insects.
Conclusions as to artificial flowers. — From the above results, Plateau
came to the following conclusions :
(1) In general, the insects observed paid no attention to artificial flowers of bright
color, whether empty or provided with honey; they even seemed to avoid them.
(2) In the few cases where they seemed to notice the presence of the artificial flowers,
they merely hovered about them, a behavior also exhibited before other bodies
without any resemblance to flowers.
(3) The insects did not attempt to enter the flowers made of paper or cloth, even when
furnished with honey.
(4) On the contrary, the leaf corollas, marked by the natural plant odor, and normal
green color, and provided with honey, received numerous visits.
(5) The attractive influence of bright artificial colors can consequently be regarded
as practically null.
General summary. — In completing the series of five papers on the way
in which flowers attract insects, Plateau enunciated the following prin-
ciples.
Insects seeking pollen or nectar are guided to the flowers that contain
these substances in only a subordinate degree by sight. In fact:
(1) Neither the form nor the bright colors of flowers seem to have an important
attractive role.
(2) Insects visit actively the heads of composites and the umbels of umbellifers not
mutilated but with the forms and colors masked by green leaves.
(3) Insects continue to visit flowers or inflorescences in which practically all the bright-
colored organs are removed, such as petals, corolla, disk-flowers, etc.
(4) They exhibit neither preference nor antipathy for the different colors afforded
by the flowers of different varieties of the same species or of related species,
passing from a white flower to a blue one, then to purple, rose, etc., without
appreciable choice.
(5) Insects easily discover and actively visit numerous green or greenish flowers,
which are but slightly visible in the midst of the leaves.
(6) They ordinarily pay no attention to artificial flowers of paper or cloth, even though
brightly colored and well-executed, and provided with honey. They even seem
to avoid them.
(7) On the contrary, artificial corollas made of green leaves receive numerous visits
when provided with honey.
Insects are guided in an accurate manner to flowers with pollen or nectar
by some other sense than vision and this can only be the sense of smell :
(1) They go without hesitation to those flowers habitually neglected because of the
lack or paucity of nectar, just as soon as one provides them with an artificial
nectar in the form of honey.
MAIN RESEARCHES OF PLATEAU. 153
(2) Insects cease their visits when, without disturbing the bright-colored parts, one
removes the nectar-bearing part of the flower, and they begin them again if
the missing nectar is replaced by honey.
(3) It is sufficient to put honey in or upon inconspicuous green or brownish anemoph-
ilous flowers rarely visited, to attract numerous insects.
(4) The r61e of the sense of smell is also demonstrated by leaf flowers filled with honey.
Role of vexillary organs. — The attractive value of colored bracts
and show-flowers furnished the theme of the first investigation in a new
series of studies on the relations between insects and flowers, begun by
Plateau in 1897 (1898:339). The vexillary role of the terminal group of
vivid bracts of Salvia horminum was first studied, making use of a bed of this
species more than a square meter in extent. This resembled a rose carpet
as seen from above, while the flowers themselves were hardly visible, except
at the edge. The numerous bees present, chiefly Apis and Anthidium,
went directly to the flowers upon their arrival, noticing the colored bracts
only as they flew upward from flower to flower or when the folded bracts
simulated the flowers. The butterflies were more easily deceived, 1
Pieris and 3 Rhodocera landing on the bracts and trying to probe them with
the proboscis. Six honey-bees were observed to make but one visit and one
inspection of the bracts to 388 visits to the flowers. In order to eliminate
the possibility that this behavior was due to habit arising from the fact
that Salvia had been grown for several years in the same spot, plants were
transferred to another garden more than 2 km. distant, where they were
placed in a circle within another of Dianthus barbatus. Thus, the visiting
insects were offered three choices, between the flowers of Dianthus, those of
Salvia, and the bracts of the latter, the last two being presumably new to
them. The insects that hovered without landing on either Dianthus or
Salvia were 106 in number, all butterflies or moths, with the exception of 3
individuals of Bombus. During the period, 26 individuals of bees, 49
butterflies, 48 flies, and 16 beetles visited Dianthus alone, without paying
any attention to Salvia. Of 21 individuals that visited Dianthus and were
also confused by Salvia, all were Lepidoptera, with the exception of one
Andrena. Three out of 6 individuals of Macroglossa hovered over the
colored bracts of Salvia, one making this mistake 3 times. In the case of
the insects visiting Salvia alone, the bees observed numbered 250, but only
24 of these made even a slight mistake, while there was on an average one
error for each butterfly and each fly.
With reference to the attraction exerted by show-flowers, Plateau em-
ployed two species of Hydrangea, the one native and with a clear distinction
between the small fertile flowers of the center of the umbel and the large
sterile ones of the margin, the other cultivated and exhibiting umbels with
large sterile flowers alone. The number of visitors to the native species
was small, a few bees and syrphids coming for pollen alone. The behavior
of these was characteristic, for, instead of alighting first on the large mar-
ginal flowers as demanded by the theory of their attractive rdle, they flew
by or above them as though they did not exist, in order to land directly on
the fertile central ones. The number of mistakes made was but 1 for the
bees out of 79 visits, while for the less intelligent flies it was 1 for 18 umbels
visited. In the case of the cultivated species neither the brilliance of the
154 PRINCIPLES AND CONCLUSIONS.
umbels nor their large number served to attract honey-bees, bumble-bees,
or butterflies, except for rare visits or inspections. The sole visitors were
Syrphus and Melanostoma, which went almost exclusively to the flowers
with stamens. The total number of errors for the bees was 5 in 397, for the
flies 5 in 93. The author dismissed the possibility that this was due to
habit, partly because of the short life of the individuals and partly because
of the way he assumed this would affect the numbers found on the umbels.
He regarded these results as proving conclusively that the vexillary organs
studied actually attracted the majority of insects so little and the higher
bees to such a minimum degree that the fertilization of these species would
in no wise suffer by their absence, and that they could no longer be consid-
ered as organs of attraction.
Choice of colors by insects. — The first half of this second paper of the
series (1899:336) is devoted to a critical resume" of experiments by others
made by means of colored objects and by means of natural intact flowers,
together with an account of desirable and undesirable methods to be em-
ployed in such studies. The first experiments were made with the two
varieties of Salvia horminum, one of which had pale-rose flowers and bright-
rose bracts, while the other possessed violet-blue flowers and deep-blue
bracts. These grew in contiguous beds and were trimmed back to give the
same dimensions to the two groups. The observations were made during
an hour each day for 12 days, a representative record giving 125 visits to
rose and 131 to blue, with 5 abrupt changes from rose to blue and 7 from
blue to rose. The addition of the numbers series by series gave the predom-
inance alternately to rose and blue, the final totals being 1,085 rose and
847 blue, and this was regarded as explaining the preference obtained by
Lubbock for blue and Bennett for rose. The equality of the two colors
was further shown by the fact that Anthidium and Megachile flew suddenly
from rose to blue in 64 cases and from blue to rose in 75, while one individual
of the former visited first 5 blue, then 2 rose, 4 blue, 4 rose, 1 blue, and 4 rose.
For a number of insects and flowers the percentages of each color and
of the visits were computed and the results expressed in table 90.
In further experiments it was found that the honey-bee went to scarlet
without the least repugnance. Pieris brassicae eagerly visited the red
and yellow heads of Zinnia, while the related Goniopteryx seemed to neglect
these colors. One individual of Pieris visited indifferently the red, rose, and
yellow heads of Zinnia, but another went only to rose heads of Scabiosa.
In his conclusions, Plateau emphasized the fact that he had at no time
said that insects did not see the colors of flowers. He affirmed, however,
that we have no practical means of assuring ourselves that they perceive
colors and that this perception is the same as with man. The results of all
experiments made with colored papers, cloths, or glass, or with isolated petals
or normal flowers can be explained either by differences in the amount of
light reflected, or by differences in the refrangibility of the rays transmitted
or reflected. Whatever may be the visual perception of insects, the
question whether the insects that visit flowers are guided in their choice by
the colors that flowers present to the human eye must be answered in the
negative. In studying the response of insects to varieties of the same
MAIN RESEARCHES OF PLATEAU.
155
species, which eliminates the effect of differences of form, perfume, and
the abundance and accessibility of nectar or pollen, it has been seen that
they show a complete indifference to color, when the relative number of the
flowers of each color available is taken into account. Finally, it was ad-
mitted that insects perceive flowers from a distance, either because they
see colors as we do or because they perceive a certain contrast between
the flowers and their surroundings, and that concurrently with the sense
of smell, although to a considerably smaller degree, this visual perception
can direct them toward the mass of flowers. Once arrived there, however,
if the flowers differ from each other in color alone, they are perfectly indif-
ferent whether the corollas are blue, red, yellow, white, or green.
Table 90. — Color preferences.
Species.
Color.
No. of
flowers.
No. of
visits.
White
p. ct.
60.9
39.0
55.2
44.7
p. ct.
60.1
39.8
49.1
50.8
Bom bus terrestris : Delphinium ajacis
Blue
Color.
Heads.
Visits.
Bombus terrestris : Scabiosa atropurpurea. . .
p. ct.
56.4
33.8
9.6
69.6
12.9
8.9
8.4
70.6
18.6
10.6
27.8
54.0
18.0
p.ct.
52.6
42.1
5.2
76.4
13.5
7.3
2.7
75.0
21.8
3.1
25.0
42.8
32.0
White
Blue
Violet
White
Yellow
Wrhite
Red
Yellow
Errors made by Anthidium. — Plateau (18992:452) concluded that
the female of Anthidium manicatum was directed to the flowers of Salvia
horminum by the odor, since these were much smaller and much less con-
spicuous than the group of terminal bracts. In following her behavior it
is seen that she makes many mistakes ; she often returns to a flower already
visited, goes to partly faded flowers with the upper lip brownish, and even
to completely faded ones which fall with her, and finally alights uselessly
upon the buds. The male is frequently unable to see the female when the
latter is immobile, but perceives her instantly when she flies. Moreover,
he is often unable to recognize the same individual again, sometimes return-
ing to her twice. So much does he depend upon movement that more than
once he was seen to fly to females of other genera even, such as Megachile,
Anthophora, Apis, and an ichneumon fly. However, he did not disturb
156 PRINCIPLES AND CONCLUSIONS.
females of Pieris, recognizing them as different by their staccato flight and
large white surface. It was concluded that the observations given for this
one species, belonging apparently to those better endowed mentally, show
how necessary it is to distrust statements as to the perfect clearness of the
vision of Hymenoptera.
Admiration of syrphids for bright flowers. — In the third and last
paper of this series (1900:266), Plateau discussed the current views as to
the admiration exhibited by syrphids for bright-colored flowers. To refute
this view he listed 35 species with green or greenish flowers for which charac-
teristic visits by syrphids were recorded, and gave a large number of obser-
vations in which species of Syrphus in particular hovered in the usual
fashion over leaves and other objects. In addition, he showed by experi-
ment that these flies could be made to respond as usual by means of a
variety of objects, such as a finger, the tip of a cane, etc., His conclusions
were as follows:
(1) The number of cases clearly described of supposed shows of admiration for the
color of flowers is very limited and may be reduced to seven altogether out of the
thousand described by naturalists.
(2) The only insects noted are the dipterous syrphids, with limited faculties inferior
to those of the bees.
(3) The syrphids regularly exhibit their so-called admiration before flowers not only
without bright colors, but also before green and greenish ones.
(4) They frequently hover before other plant parts than flowers, such as green leaves,
green buds, and fruits, green and brown stems.
(5) Syrphids also exhibit their characteristic stationary flight before objects having
no resemblance to flowers, such as a finger, a cane, a marble, or a string.
(6) As a consequence, admiration for the color of flowers does not exist among insects.
Attraction of colored cloths and brilliant objects. — Plateau em-
ployed banner-like pieces of colored cloth to determine the attraction of
color when not associated with flowers (19002: 174). In the first experiment
the colors used were bright red, yellow, bright violet, and sky-blue, the
cloths being suspended on leafy branches at about a meter above the soil.
The sole response to the banners was made by a single individual each of
Musca, Calliphora, and Megachile, which seemed to rest on the yellow cloth
as on any object. However, 7 individuals of Eristalis and 1 honey-bee
hovered over a fringe of blue wool. The position of the colors was then
changed, but the results were similiar; Pieris was attracted slightly by the
blue, one Eristalis and Bombus rested on the violet piece, while 11 Eristalis,
4 Syrphus, and 1 Pieris hovered over the blue fringe. Two further tests
were made with much the same results, the entire series yielding 30 cases
of probable and 8 of doubtful attraction. All but 2 of the first were caused
by the blue fringe, as well as 4 of the latter. Of the total, 5 visits were made
by bees, 29 by flies, chiefly syrphids, and 4 by buttei flies.
To determine the effect of brilliant objects, four spheres of metallic
luster and 4 to 6 cm. in diameter were employed. One of these was red
above and blue below, the second had these colors reversed, while the other
two were glass silvered within. These were suspended on stakes at the
usual height of the flowers visited. All told, there were 24 cases of evident
attraction and 10 doubtful ones, the silvered spheres furnishing 14 of the
MAIN RESEARCHES OF PLATEAU. 157
former. The bees comprised 19 of the evident attractions, of which Apis
and Bombus each made 4 to the silvered spheres, and Bombus 7 to the
colored ones.
Plateau repeated the experiment of PeVez, who found that insects were
attracted to pieces of colored cloth when these were hung among masked
flowers. Pieces of the colored cloths and the blue fringe previously used
were hung among 13 masked heads of Dahlia and 3 of Rudbeckia and at the
same level. The visiting insects paid practically no attention to the shreds
of cloth, in spite of the fact that they hovered over both buds and fruits. One
honey-bee and 2 Eristalis inspected the blue fringe, and two of the latter
and one Lucilia alighted for a moment on the yellow piece.
In general, brightly colored pieces of cloth attracted so few insects that
it is impossible to deduce from this an argument in favor of the attraction
of insects by the colors of flowers. Pieces of colored cloth suspended near
flowers masked with leaves attracted no more insects than when they were
placed near normal flowers. Brilliant objects with metallic luster seemed
to exercise a slightly greater attraction than colored cloth. From this
it may be concluded that the attraction produced by certain objects other
than flowers is probably related to the amount of light reflected. In certain
flowers supposed to be without odor, such as Dahlia for example, a real odor
can be disclosed by a simple process.
Constancy among bees. — After citing the observations of Bennett,
Christy, Bulman, and Ord on the constancy shown by insects as to the
flower visits made during each flight; from the nest or hive (1901:56),
Plateau gave'the results obtained from his own studies. A tabular expo-
sition was made" of the visits of 42 individuals belonging to 4 species of
Bombus, in which the bee flew from one species to another and in 13 in-
stances to a third, showing complete indifference to structure and color.
In contrast to Bombus, Anthidium was found to be very constant, and it
was only with difficulty that 8 cases of inconstancy were observed, two of
them comprising 3 species. As shown by the results of earlier investiga-
tors, the honey-bee proved also very constant, though not completely so.
In three successive summers Plateau found only 14 instances of incon-
stancy, and but 2 of these concerned a third species.
None of the apids observed exhibited an absolute constancy. Bombus
was much the most inconstant, rarely remaining faithful even for a short
time to the same species. Anthidium and Apis presented a remarkable
fidelity, which, however, suffered certain clear exceptions. In all the cases
observed, the bees passed from the flowers of a certain species and color
to those of other species, often of a different color and family, thus giving
proof of a complete indifference to flower structure and coloration. The
acquisition of pollen and nectar is their sole motive.
Mistakes made by bees. — Plateau recorded in detail the mistakes
made by 7 species of Hymenoptera in visiting 37 species of flowers belonging
to 19 different families. The time involved was rather more than 6 hours
scattered through 22 days. The results are given in table 91.
It was concluded that probably no pollinating hymenopter is exempt
from error and that the honey-bee is deceived as frequently as others.
158
PRINCIPLES AND CONCLUSIONS.
Table 91.
Species.
No. of
individuals.
No. of
errors.
Proportion per
individual.
Apis mellifica
Bom bus hortorum
muscorum
lapidarius
Megachile centuncularius
ericetorum
Odynerus quadratus
Total
107
186
1.8
1.5
2.2
1.0
1.0
1.0
1.0
Removal of the antennae of bumble-bees. — In the introduction to
this paper (19022:414), Plateau stated that up to that time he had attributed
a secondary role to sight and a preponderant one to smell, and likewise
called attention to the results of many investigators, including Forel and
himself, who had shown that with the insects the sense of smell resides
chiefly if not exclusively in the antennae. Forel (1901:53) cut the antennas
of 6 individuals of Bombus at the base and set the bees free again. At the
end of 5 minutes a male returned to visit 8 to 10 flowers of Convolvulus
in succession, each time flying directly to the flower without a second's
hesitation. He was caught to confirm the complete absence of the antennae
and then released, when he made a single turn in the air and came back
at once to the flowers to visit them as before. At the same time, several
of the bumble-bees deprived of their antennae returned to the bindweed
flowers, flying from one to the other with even more precision if possible
than those with the antennae intact. Two days later several males and
small females with the antennae cut were found flying from flower to flower
with an astonishing rapidity and precision.
Plateau repeated the experiments of Forel on two occasions. In 1899
the antennae were cut from 10 individuals of Bombus terrestris and 1 ot B.
muscorum, on four nearly successive days. These at once flew away, but
one returned the first day to the same flowers, and on the following days,
and in 3 cases shortly after the operation, 6 bees without antennae were
captured, including the B. muscorum. Although more than half of the
multilated bees had found their way back to the flowers, the experiment
was repeated in 1902 to remove certain doubts, especially with respect to
the thoroughness with which the antennae were removed. The latter were
consequently cut at the level of the head and the bees released. The results
were as follows: 4 neuters of B. terrestis never returned; of 11 B. hortorum,
10 females and 1 neuter, only 1 female returned; 1 male and 1 female came
back out of 7 individuals of B. lapidarius; finally, of 8 B. hypnorum, 5 re-
turned shortly after the operation. Thus, 8 bumble-bees out of 30 returned
accurately to the preferred species of flower after the antennae had been
completely removed and guidance by smell was impossible.
MAIN RESEARCHES OF PLATEAU. 159
Evidence of the attractive role of odor. — Plateau properly insisted
that the above results did not indicate that the sense of smell played no
part in attraction, and he brought forward a number of facts to prove this
and in particular the investigations of Mayor and Gorka.
(1) Flowers that seem to man to have no odor may be shown to possess it by the
proper method, and these would be perceived by insects with the sense of smell
well developed.
(2) Many champions of the importance of the corolla in attraction have adznitted that
in certain cases odor can attract insects more strongly than color.
(3) The apids are much more attracted by odor than is ordinarily believed. Honey-
bees and bumble-bees seek actively the extrafloral nectar of stipules, petioles,
and leaves, while the former, with many flies and wasps, visit fallen and dry
fruits.
(4) The olfactory sense of many insects is extraordinary and guides them from con-
siderable distances to objects that frequently they can not see, as in the case of
saprophilous flies and beetles. Wasps readily find such desired food as cooked
meat, and, like bees, are often attracted in great numbers to fruits, preserves,
etc. Numerous observations have been made of the attraction from the fields
of male moths by a captive female inclosed in a room or in a box.
(5) Moths are captured at night by means of perfumed sugar solutions placed on
tree trunks, cords, apples, etc.
Mayor (1900) clearly demonstrated the unique importance of the sense
of smell in connection with the sex attraction in Callosamia promethea.
Males of this species when released more than 30 meters from a glass vase
covered with mosquito netting and containing 5 females, flew directly to
the vase and hovered about the opening. When the vase was inverted in
sand so that the females could be seen but no emanation could escape, the
males flew away, only to return when the vase was placed again in the
original position. When the female was wrapped up in loose cotton, the
males flew to the latter and gathered on it. After the females were inclosed
in a box with a paper chimney at one end and a lattice at the other, the males
flew to the opening of the former, through which the odor was drawn. When
the abdomens of the females were detached and placed on a table and the
winged thorax placed near by, the males went only to the former. If the
antennae of the male were covered with varnish, glue, paraffin, or other sub-
stances capable of excluding the odor, it no longer sought the female or
even noticed it at a distance of a few centimeters. Plateau pointed out that
the experiments of Gorka (1900:57) seemed to demonstrate that odor
should be taken into account as well as sight, since the individuals of Deili-
phila with the eyes covered with black varnish immediately found the
flowers of Borrago and Malta, and shortly afterward, the preferred ones of
Phlox. He further stated that, if he had been incorrect in assigning an
exaggerated importance to smell, his many observations and experiments
proved, as Knuth had admitted, that the sense of smell played a much
more important role in the attraction of insects by flowers than had been ad-
mitted up to that time.
Decorollate poppies and insect visits. — In repeating Giltay's experi-
ments with flowers of Papaver from which the petals had been removed
(p. 171), Plateau pointed out two errors in the method that he regarded
160 PRINCIPLES AND CONCLUSIONS.
as serious (19023:657). In order to remove the petals before the flowers
were visited by insects, Giltay excised them before the corolla expanded,
which led to the flowers being handled for too long a time. He also paid no
attention to the behavior of the insects on the mutilated and on the intact
flowers. Hence, Plateau took precautions to work on Papaver orientate,
a species more abundantly visited and easier to observe than P. rhoeas,
to remove the petals with the minimum of disturbance, and to observe the
number and behavior of the insects in minute detail. In addition some
buds were enclosed in netting and the stems tied to stakes to prevent the
access of insects and the transfer of pollen in consequence of being shaken
by the wind. During a typical period there were 1 fresh and 18 old de-
corollate and 13 normal flowers under observation. The single fresh muti-
lated flower received 20 visits, of which 17 were made by Apis and 3 by Halic-
tus. During this time the 13 normal flowers yielded 56 visits, or an average
of 4.3 to 20 for the mutilated one. While frequent visits were made to old
decorollate flowers, these were always brief, the insect quickly recognizing
its error. The total number of visits to 30 multilated flowers was 137, Apis
making 97 and Halictus 19, while 70 normal flowers received 172 visits,
of which Apis contributed 121 and Halictus 18. The former received an
average of 4.5, the latter of 2.4 visits. As to the weight of seed, the 70
capsules of the intact flowers produced 21.07 gm., and those of the mutilated
ones 6.5 gm.; the respective averages per capsule were 0.30 and 0.21 gm.,
giving a ratio of 1:1.39 in favor of the normal flowers. In the matter of
germination no difference was found between the two kinds of flowers.
In conclusion, the removal of the petals reduced the number of seeds
per flower, as Giltay had shown. This result probably did not come from
the removal of the attractive corolla, since the mutilated flowers received
as many or even more visits than the normal ones. It was really due to the
different behavior of the insects on the two flowers in their quest for pollen.
They hang from the stamens of the decorollate flowers and pull them below
the ovary, with the consequence that they neither carry pollen to the stigmas
nor shake any upon it. On the contrary, in the normal flower they pass
between the corolla and the crown of stamens, which they shake vigorously
by the movements ; they also wander over the stigmatic disk. As a conse-
quence, the mutilated flower is reduced to the less effective autogamy, while
the normal benefits by the action of allogamy.
New experiments with artificial flowers. — In reply to a number of his
critics, Plateau performed a much more comprehensive series of tests with
artificial flowers in 1904 and 1905, in the course of which he made 66 experi-
ments of an hour's duration with 10 different genera, 5 of which were
composites (19062:3). His criticisms of the methods of Andreae, Reeker,
Wery, and others are considered later under the authors concerned, and the
present account is restricted to his own investigations and the consequent
conclusions. In making the artificial flowers especial pains were taken to
avoid the use of any attractive material whatsoever, as well as to copy the
flower faithfully as to habit, size, and color. Translucid colored papers of
the usual kind were employed alone for the flowers of thinner texture, while
for others the paper was first pasted upon tarlatan cloth, but without alter-
MAIN RESEARCHES OF PLATEAU. 161
ing the transparence. For an adhesive, pure gum arabic alone was used,
since it never attracts insects, and for stuffed parts, only cork, wadding, or
tow. Paste anthers were avoided and all delicate parts, such as disk flowers,
were made of paper cut into a fringe. At the time of each experiment, all
artificial flowers were provided with natural foliage.
When 21 artificial flowers of Crocus, 10 yellow and 11 white, were placed
in a bed of normal flowers of C. luteus and vernus, they received but one
visit, that of a muscid, and two inspections from Osmia, in the course of
three experimental periods, in spite of abundant, visits to the normal flowers.
In the case of Viola odorata, the imitations received two visits from Vanessa
and 11 inspections from Osmia in 47 visits, while Apis ignored them entirely.
Paper flowers of Althea rosea were provided in one series with stamens of
commerce, afterwards found to contain much starch and some dextrin-
like substance, while in the second series, fringed paper was employed for
the stamens to avoid the possibility of attraction by the starch. Two art-
ificial stems with 6 white and 7 rose flowers were attached to 2 out of 4
plants with the buds still closed. Eight insects landed on the imitation
flowers, 7 merely inspected them, and 15 ignored them. When the arti-
ficial clusters were placed near natural ones the latter yielded 55 visits
to 3 inspections of the former in one case and 50 visits to but 4 inspections
in the other. In the experiment given from the second series an artificial
cluster of 6 flowers was placed 4 meters in front of natural ones bearing
20 flowers. One Apis and Bombus and 5 Prosopis inspected the false clusters.
Three cloth flowers of Papaver orientalis were arranged among unopened
buds, but out of 45 insects, only 3 individuals of Pieris inspected them.
When placed in competition with a bed of Myosotis alpestris, 3 such flowers
secured no attention from the honey-bee. A mixture of 4 normal flowers
with 3 artificial ones yielded 51 visits to the former and 1 visit and 4 in-
spections by Apis to the latter, while in the five experiments there were
but 10 inspections or visits to the artificial flowers as compared with 198
visits to normal ones. Six artificial heads of Scabiosa atropurpurea were
placed at the edge of a cluster containing more than 60 natural heads,
receiving 4 inspections to 53 visits to the latter. When the imitations
were placed a meter in front of the cluster, they received 5 inspections
to 36 visits. When imitation heads of Dahlia variabilis were attached
at the proper level to stalks not yet in bloom, 4 individuals of Apis, 1 of
Megachile, 4 small bees, 2 muscids, and 1 Lucilia inspected them, out of
the host of insects in the garden. The 9 artificial heads were next fastened
on stalks bearing 3 normal heads in full bloom, with the result that 28
insects visited the latter directly and 10 passed near the imitations without
noticing them. Twelve insects went directly to the latter and 3 visited
them after a normal head, all of these merely making an inspection, with
the exception of 3 butterflies. The same 9 imitations were placed 2 meters
before 8 plants bearing 18 heads, and the number of inspections was con-
siderably decreased, namely, to 4 out of 51, as would be expected from
the distance between the two groups.
The effect of grouping on the response to artificial flowers was especially
well shown by the experiments with Zinnia elegans. When 20 imitations
were placed 3 meters from a plot of this plant, they received 2 inspections
162 PRINCIPLES AND CONCLUSIONS.
and 11 visits, at 2 meters 1 inspection and 9 visits, while the mixture
of artificial and natural heads yielded 23 visits. When 2 imitation heads
of Helianthus annuus were placed on stems with closed buds, they received
2 inspections by Bombus and 13 incidental visits from muscids chiefly,
while 33 insects ignored them entirely. The number of inspections was
increased when the 2 imitations were placed among 15 normal heads,
9 insects coming to inspect and 2 to alight, among them being Apis and
Bombus. With 3 normal and 2 artificial heads, 27 insects ignored the latter
as they flew past, and 5 inspected them. In order to test the attraction
exerted by the materials used in ordinary artificial flowers, a head bought
in a store was added to the two previously used. The result was that the
10 inspections observed either took place before this one head or began
with it, indicating that the starch or dye employed in it served as the
attraction. Twelve heads of Leucanthemum vulgare bought in the trade
were attached to a plant bearing 1 open head and 25 to 30 buds, but re-
ceived a single incidental visit and no inspections. The next experiment
was organized by placing 5 imitations among 30 open heads of the same
plant and putting a group of 7 artificial heads at a distance of a meter.
No visits were made to the latter, in contrast to 3 to those on the plant
and 53 to the normal ones, thus indicating that the natural flowers furnished
the attraction for the others.
The most comprehensive series of experiments was made with Centaurea
cyanus, in which both bought and specially constructed artificial flowers
were employed. Six clusters of 3 heads each of the former were attached
to plants with the buds still closed, which grew near groups of Melandrium
and Anchusa actively visited by bees. Apis and Bombus inspected the
false heads 30 times and extended the ligule before them 5 times. When
artificial heads made for the purpose were employed, Apis made 1 inspection
and Bombus 5 only. However, these were made a year later and under
different conditions of weather and competition. The author admitted
that the bees frequenting the adjacent flowers gave evident attention
to the imitation heads, but stated that they perceived them only from a
short distance, attraction from a distance seeming not to exist or to be
very feeble so far as the artificial heads were concerned. When 18 of the
commercial flowers were put at 2 dm. from a group of normal ones, they
obtained 15 inspections and 2 extensions of the ligule in comparison with
54 visits to the latter, while the special imitations when placed in and
about a nearly equal number of natural heads received but 9 inspections.
In a series of 5 comparative studies with both kinds of artificial heads
the figures were essentially similar, though the inspections were more marked
with the commercial heads. Altogether, the cornflowers attracted insects
somewhat more than the other artificial flowers.
Conclusions as to artificial flowers. — Because of their value in sum-
ming up the results of his three investigations with artificial flowers and giving
his final views on the subject, Plateau's conclusions are here stated in detail :
"With respect to the solution of the question whether insects are or are not seriously
attracted by artificial flowers, these new and extensive experimental studies are
almost useless, since they serve only to confirm in full the results of my earlier re-
MAIN RESEARCHES OF PLATEAU. 163
searches. They confirm these all the more, since, advised by the criticisms, I have
endeavored to avoid everything that could lead to objections: it has been said that
the imitations employed were too few in number compared with the normal flowers;
this time I have used numerous examples and in several cases the numbers of the real
flowers and of the copies were essentially the same; it has been objected that I have
not tried the attraction of imitations completely isolated; I have now done this repeat-
edly; the erroneous objection has been made that my artificial flowers have been
nothing but gross imitations; I have continued to use only the most careful imitations
possible and have frequently employed the very same species utilized by my critics.
"I can then only repeat the conclusions that I have formulated earlier, modifying
the words alone a little in order to avoid all ambiguity, and emphasizing the necessity
of good experimental conditions:
"1. In much the greater number of cases insects pay no attention to artificial flowers
of vivid color and frequently treat them merely as obstacles in their way.
"2. In the relatively small number of cases where they perceive the presence of the
imitations, they usually show only a brief hesitation, which is revealed by a
turn or a crochet before or around them.
"3. Insects never seek pollen or attempt to suck nectar in a flower truly artificial and
containing no attractive material of any sort.
"4. The attractive influence of bright artificial colors can in consequence be regarded
as nearly null.
"However, if this laborious study has ended only in the demonstration of the accur-
acy of my earlier results, it has permitted what is perhaps more important, the dis-
covery of most of the errors committed by my opponents and the reasons why they
have believed in good faith in the actual attraction of artificial flowers. Such errors
are as follows:
"A. To cover, conceal, cut or suppress in any manner the natural flowers and to
replace them with artificial ones. In this case, insects, and especially the
bees, not finding pollen or nectar where it was on former visits, fly in seeking
it about any object occupying the place or located near it.
"B. To place artificial flowers near or among natural ones. Under such conditions it
happens occasionally . that insects which start by going directly to the real
flowers, in passing from one flower to another or in leaving, hesitate before
an artificial one as one sees them stop before faded flowers or even closed buds.
"C. To make studies with artificial flowers in places where they have already been
performed with natural ones, since such places might have become habitually
visited by bees, for example.
"D. Not to have taken into account the significant difference between a direct flight
and simple turns or crochets of inspection.
"E. To disregard the well-known details of behavior, thus to forget that syrphids
may hover before any object whatsoever, that the muscids alight constantly
upon the most diverse surfaces, chiefly to expose themselves to the sun, that
Pieris whirls about all kinds of plants and projecting objects, that small Hymen-
optera such as Stelis and Prosopis fly about and land upon anything; finally, to
take for visits the momentary or accidental presence upon artificial flowers of
carnivorous insects or others that are not attracted by real flowers.
"F. To employ the artificial flowers of commerce or those made by florists. Such
imitations may contain parts taken from natural flowers; they are nearly
always impregnated with starch; they are sometimes dyed with chlorophyll or
other plant colors ; the stamens and pistils are always represented by small balls
of paste more or less attractive to certain insects, faults whose importance I
do not wish to exaggerate, but which probably explain the cases noted of an
apparent search for pollen, of attempts to suck pollen, and of visits to the flowers
of ladies' hats."
164 PRINCIPLES AND CONCLUSIONS.
Macroglossa and false flowers. — In order to throw light upon the
numerous observations of visits by Macroglossa stellatarum and other in-
sects to artificial and painted flowers, Plateau (1906:141) collected all
the known cases of this sort, commented on them critically, and carried
out several series of experiments to show the slight value pertaining to the
observations. The significance of the latter and of Plateau's objections
is discussed later (p. 189), the experiments alone being taken up at this
point. The flight of Macroglossa is astonishingly swift, Bedel noting an
average of 50 flowers of jasmine visited per minute, and Plateau observ-
ing 301 flowers of Phlox paniculata sought in succession. In the experi-
ments with colored cloths, rectangles of silk, wool, etc., varying in size
from a 12mo. to a 4to. page and ranging from red through yellow to blue,
and rose, were attached to four stakes placed at the corners of a large
bed of Delphinium ajacis. The 7 experiments with varying combinations
gave the following results: (1) the 12 hawk-moths observed always flew
directly to the flowers, never to the cloths; (2) no moth paid any real
attention to the cloths, two only making a rapid exploratory curve about
the blue woollen fringe; (3) none of the other insects noticed the colored
cloths, not even the blue fringe. In the next series, the objection raised
earlier by Perez was met by using small pieces of cloth 4 cm. square, which
were hung near the flowers of Dianthus and Phlox. In no case did the hawk-
moths go to the bits of cloth, even bounding over them as so many ob-
stacles to visiting the flower. Similar results were obtained by employing
pieces of colored paper, 14 by 10 cm., a single Macroglossa, and one of Papilio
and Bombus merely inspecting the papers. When screens covered with
paper on which bright flowers were painted were employed, no hawk-
moth gave them the slightest attention, and this was true of a large number
of bees and butterflies. Two butterflies, two bees, and a wasp merely
alighted on the screen for a moment's repose, as shown by the fact that
one of them landed on the unpainted side, while one Apis and one Vespa
flew up and down along the screen. Four experiments were made with a
large number of artificial flowers, which permitted the study of the behavior
of 6 individuals of Macroglossa. At least 100 such flowers were placed in
two groups near a mass of Anchusa, and at a distance of a meter, and in
the second experiment they were scattered in and about a border of
Dianthus. While 99 flowers of Anchusa and 110 of Dianthus were visited
by hawk-moths, no notice was taken of the imitations, and a similar result
was obtained in the final experiment.
Plateau refrained from giving formal conclusions at the end of this
paper, partly because his studies, though prolonged and laborious, were
rendered incomplete by the destruction of the gardens in the midst of
which he worked.
"New researches, by means of other methods, will be necessary and I hope there
will somewhere be found a serious investigator to undertake them, rather than a super-
ficial observer content with approximations. I have conscientiously endeavored to
deceive Macroglossa by means of colored paper, large and small pieces of cloth, flowers
painted upon wall-paper, artificial flowers, and the colored bracts of Salvia horminum.
MAIN RESEARCHES OF PLATEAU. 165
It is possible, it is even probable that several of my experiments have been defective ;
I believe, however, that it is impossible that all of these observations and experiments,
made during five successive summers, are absolutely bad. A single consideration
diminishes my regret at not being able to carry them further, namely, that the present
work contains a number of documents which it will be neceessary to take into account in
writing the history of Macroglossa stellatarum."
Entomophilous flowers little visited by insects. — The final memoir
by Plateau (1910:3) was devoted to experiments with entomophilous flow-
ers with bright colors but without nectar. The investigations were made
in the spring and summer of 1907, 1908, and 1909, and comprised 55 ex-
periments upon a dozen species. The substances employed to render the
flowers attractive were anisette, composed of very dilute alcohol, sugar
sirup, and a small amount of essence of anise, brown-sugar sirup with rum,
sugary juice of cooked cherries, and sugar sirup with a decoction of An-
gelica. The first two species employed were Fumaria officinalis and Poly-
gonum convolvulus, both with very small inconspicuous flowers. When
anisette was placed upon these by means of a brush, insects were immedi-
ately attracted to them, the visitors being chiefly flies. The experiments
dealt chiefly with large flowers of a vivid color, which are normally little
or not at all visited by insects. When Lilium candidum was supplied with
anisette or brown-sugar sirup, visitors appeared almost at once, the total
number reaching 28 in an hour, of which 25 were honey-bees. As a check,
flowers were supplied with sirup alone, but these were visited by only a
small number of flies, no bees noticing them. A single flower of Passifiora
with the corolla moistened with anisette received 34 visits by flies, while
another was supplied with brown-sugar sirup with rum a few days later
and yielded 40 visits in an hour, of which 1 was by Apis, 2 by Bombus,
and several by Vespa. Five experiments were made with Oenothera speci-
osa, the first one with anisette showing visits by Halictus and Prosopis
chiefly, while the second, on the afternoon of the same day, yielded 20
visits, 19 by Apis and 1 by Prosopis. Similarly treated, Pisum sativum
received 30 visits, chiefly of Bombus and Megachile, and Linum perenne,
15 visits, 11 of which were by flies, 3 by bees, and 1 by a hawk-moth.
The juice of cooked cherries was put in the flowers of 3 umbels of Pelar-
gonium zonale and anisette in those of another two. While the natural clusters
were not visited at all, those treated received a number of visitors, practi-
cally all flies. Clematis jackmanni perfumed with anisette gave 20 visits
in an hour, of which 14 were made by Bombus, and Convolvulus sepium
received numerous visits from 4 genera of Hymenoptera, 5 of Diptera, and
1 of Lepidoptera. In the case of Petunia hybrida provided with cherry
juice, 40 honey-bees came during a period of an hour, and visits continued
actively for a day or more, even to flowers completely faded, as long as
the juice was available. In the second experiment, cherry juice was placed
in the flowers of a group situated at a distance of 5 meters from the first
one, but no visits occurred for more than 4 hours, and the number then was
much smaller than in the previous case.
166 PRINCIPLES AND CONCLUSIONS.
The results of this series of experiments were summarized in the fol-
lowing conclusions:
1. These observations confirm the fact, already known but not sufficiently empha-
sized, of the existence of a considerable number of entomophilous flowers of
large size and bright color that attract diurnal insects little or not at all.
2. Two corollaries may be derived from this fact: the first is that the attractive r61e
of the form and color of the floral envelopes is either null or nearly so; the
second is that other causes than the attraction of colored surfaces is necessary
to bring pollinators to flowers and to cause them to return, such as an odor pleas-
ing to insects and a sugary liquid.
3. The addition of these two attractions to nectarless flowers that are little visited has
the practically certain consequence of causing insects to come to them, fre-
quently in large numbers.
4. This type of experiment, previously made by means of honey, succeeds just as
well when sugar sirup perfumed with an odor properly chosen is employed, a
fact which proves that the criticisms directed against the use of honey are
not well founded.
5. To obtain good results it is necessary to avoid the use of most of the pure essences
of commerce and of artificial perfumes, and to employ substances already known
to attract insects, others of which will doubtless be discovered. It is also
necessary to work on clear days and during the warmest part of the day, as well
as to renew the solution from time to time so that the odor will continue to
attract.
6. The immediate or nearly immediate arrival of insects, not only flies but frequently
bees as well, at flowers thus treated demonstrates clearly the olfactory sensi-
tiveness of insects and, in spite of all the objections raised, proves the import-
ance of the role of smell in the attraction of insects by flowers.
7. In resume^ the present investigation but confirms the thesis advanced in 1S97 in the
following words: "Insects seeking pollen or nectar are guided to the flowers
that contain these substances in only a subordinate degree by sight. They
are guided in an assured manner to such flowers by some sense other than
vision, and this can only be the sense of smell."
RELATED STUDIES AND CRITIQUES.
Comparative importance of odor and color. — As a consequence of
Plateau's first paper, P6rez (1894:245) brought together the results of
a number of observations and several experiments to show that both color
and odor serve for attraction, as Lubbock had already demonstrated.
With reference to the attraction of red flowers, he found that Salvia splen-
dens was not visited by honey-bees while in the shade, but as soon
as the sun reached it a number of visitors came almost immediately. This
was explained as being due to the effect of the sun's rays in favoring the
excretion of nectar or freeing its perfume, and not to the greater visibility,
but the latter seems much more probable. When honey was placed on
the corolla of flowers of a scarlet Pelargonium, honey-bees working on neigh-
boring heliotropes were at once attracted by its odor and went directly
to the flowers, which they continued to visit until evening. They even
returned in the morning, although the honey had been exhausted the eve-
ning before, when they also went to flowers that had not received honey
and examined them thoroughly. Perez concluded that at a distance where
vision could not be an aid, bees and the great majority of insects are di-
RELATED STUDIES AND CRITIQUES. 167
rected by the odors carried by currents of air and thus reach the flowers
that exhale them. As soon as they approach sufficiently near for sight
to intervene, they fly directly to the flowers in response to guidance by
vision. Color likewise serves to attract, in the absence of odor previously
perceived, when the chances of the flight bring them near a flower. They
then visit the latter if the odor is pleasing, or disdain the flower if the odor
is unpleasant.
In a more extensive paper (1903:1), Perez communicated the results of
further experiments and discussed at some length the points of difference
between Plateau and himself. When fallen flowers of Glycine were inter-
spersed with bits of paper of the same color, a honey-bee inspected them,
but flew away before landing, to seek nectar in some of the flowers. Small
balls of rose paper were strung on a pin, which was fixed on the end of a
leafy shoot of Symphoricarpus or on a shoot from which the flowers had
been removed, and in some cases all the open flowers of a cluster were
replaced by similar balls of paper. Two honey-bees inspected the paper-
balls for a moment, while a bumble-bee gave them more extended
attention. When the rose flowers of a currant were hidden by means of
green leaves and bits of cloth of the same color placed near them, several
honey-bees were deceived by the latter, though they finally found the
masked clusters. Similar results were obtained from a small orange tree
ornamented with small pieces of white paper. The addition of honey
to the branches of a laurustine ornamented with squares of white and blue
paper quickly attracted honey-bees, which went first to the colored papers.
Disconcerted, they began an agitated search for the honey and finally
found it.
Perez's critique of Plateau's work. — Perez pointed out that the use
of large surfaces of colored cloth by Plateau to demonstrate the indifference
of insects to color was incapable of furnishing actual evidence on this point,
since insects care nothing for color in itself, but only as a sign of the food
they are seeking. The same failure to recognize the significance of the
resemblance of small bits of cloth to flowers in contrast to large pieces was
regarded as vitiating Plateau's results with bright standards placed near
masked composite heads. A just criticism of the latter's statement that
all the results obtained with colors were illusory because of Graber's dis-
covery, was based upon the fact that this showed insects, like man, to
receive different impressions from the light of different parts of the spec-
trum, and that it is immaterial whether their perceptions are the same as
ours, since they possess a scale of luminous sensations. Experiment based
upon the use of colored objects is legitimate in every respect and to proscribe
it would be only to carry one's scruples to excess. Attention was also called
to the obvious discrepancy of Plateau's own conclusions as to the importance
of color, involved in the two statements, "Neither form nor color seems
to have any attractive role" (1895), and "I admit that this vague visual
perception can guide the insect toward the flower mass, concurrently with
smell but to a much less degree" (1899).
In regard to the errors committed by pollinators, P6rez noted that
Plateau invoked smell to explain the attraction of flowers containing nectar,
168 PRINCIPLES AND CONCLUSIONS.
but said nothing about the role of this when it was a question of flowers
already visited, or of faded flowers, buds, or fruits. The mistaken visits
to these were said to be directed by the form, poorly seen, the attraction
of which had been previously denied. In the case of withered flowers it
was thought clear that these were really visited because of the usual similarity
in color and not because of the form, as was likewise true in the case of many
buds. Imperfect vision of form can not serve to explain the majority of the
errors noted by Plateau, and form is to be regarded as the least important
of the features that effect attraction.
Effect of colors at the hive. — Theen (1896:101) summarized the
results of a number of investigators on the color sense of bees, including the
little known ones of Wiist and of Donhoff. In Wust's apiary the thresholds
of the hives were painted with bright colors, which stood out sharply against
the deep-green of the Ampelopsis surrounding them on three sides. On one
occasion the supply of bright colors was inadequate and some thresholds
were painted black, red, or blue. The consequence was that the bees
required a longer time for recognition and were able to recognize the proper
hive at once only after the second day; at first it was necessary for them
to orient themselves for a much longer time in order to determine the right
hive. He also found that queen-bees were best equipped with the sense
of location and color. When a red petal of a poppy was placed on the yellow
threshold of a hive, a returning queen approached ten times as though to
enter and even alighted twice; it then quickly flew back, showing that she
recognized the place accurately, but found something there that was not
present when she flew out. Suddenly she flew away and was lost to view,
and the red petal was removed. After a few minutes she flew directly to
the threshold without hovering about and immediately disappeared. Don-
hoff pasted blue paper before a hive and 14 days later replaced it with a
yellow one. Bees returning from the field hesitated long before flying to the
hive and finally most of them flew to another part of the hive rather than
to the entrance. Theen also cited three observations of Darwin, in which
honey-bees flew directly from a tall larkspur in full bloom to one of another
species at a distance of 10 to 12 feet, though none of the flowers were open
and the buds showed but a tinge of blue.
Critiques of Kienitz-Gerloff. — In a series of four reviews, Kienitz-
Gerloff considered the results and conclusions adduced in the five papers
of Plateau's first series. With reference to the response to masked Dahlia
heads he pointed out that the insects were readily guided by the sense of
smell, and that this did not warrant the assumption that the color of the
normal heads played no part in attraction, especially since no comparative
number of visits was given for the two kinds of heads. He cited the many
and varied experiments of Lubbock and of Mueller, and in particular those
of Forel with insects deprived of their antennae to show that the experiments
with Dahlia were not to be regarded as adequate. In opposition to the
conclusion of Graber that weakly refrangible light gives leucophobe animals
the impression of darkness, he brought forward the fact that all nocturnal
winged animals fly to lighted windows, indicating that they are drawn by
the contrast (1896: 123). In discussing the experiments in which the corolla
RELATED STUDIES AND CRITIQUES. 169
was removed, he emphasized the fact that the mutilated flowers were always
near normal ones and the insects attracted by the latter were guided by
odor to the former. Moreover, control numbers were lacking in most cases
and in that of Lobelia were mostly against the assumption. The fact that
a honey-bee flew to faded flowers and buds, and even to fallen petals, gave
evidence of the effect of color, the fact that it took nectar only from the
mutilated flowers being explained perhaps by the greater odor and accessi-
bility. It was further remarked that the results with flowers of different
colors of the same species indicated just the opposite conclusion to that
drawn, as shown especially in the case of Centaurea. The small number of
experiments were regarded as having little weight in comparison with the
observations of Mueller on 5,674 visits by 841 species of insects to 422
alpine flowers. Whether insects see the various colors as we do or not is
immaterial, if in general they distinguish them (1897:84, 108).
Plateau was further criticized for not being familiar with Mueller's
results and for opposing a single observation on Listera to the many made by
the latter, as well as for not distinguishing between insects of different
orders and diverse intelligence, although Mueller had frequently empha-
sized the importance of this. Moreover, he should have repeated the experi-
ments of Lubbock and of Mueller, which showed that insects possessed a
clear perception of color, instead of trusting too much to the evidence
drawn from artificial flowers. Likewise, he contradicted himself when he
explained the visit of a cabbage butterfly to an artificial flower on a lady's
hat by saying that it sought the flower for its protective white color and not
for nectar. The critic also found unconvincing the use of artificial flowers
made from leaves and provided with honey, owing to the superior attraction
of honey, irrespective of the object on which it may be placed. The final
conclusion was reached that Plateau had proved nothing against the color
sense of insects, although it was admitted that odor played an important
r61e, as Mueller had long before insisted.
Knuth's critique. — The results of Plateau's first series were reviewed
by Knuth (1898, 1906:204), who pointed out that they permitted another
interpretation than that given. In the case of umbels of Heracleum covered
with green leaves, the visits of a variety of insects were regarded as indi-
cating that insects are attracted also by odor, but that this was alone
effective was not proved, since there was no comparison with the visitors
of the umbels not masked. The evidence that color is not attractive,
afforded by behavior to the differently colored varieties of the same species,
is inconclusive and it can only be concluded that color is immaterial in
flowers of the same form. The experiments in which honey was added to
bright flowers that are normally little visited merely prove the well-known
fact that the odor of honey is a powerful lure. Since both honey-bees and
bumble-bees distinguish readily in many cases between flowers visited and
unvisited, it is not strange that they distinguished the artificial from the
natural flowers in Plateau's tests and left them alone, even when supplied
with honey. Neither the paper flowers nor those made from green leaves
and provided with honey prove that color is unattractive to insects, but
both merely emphasize the powerful attraction exerted by the odor of honey.
170 PRINCIPLES AND CONCLUSIONS.
Since other odors were unattractive or actually repellent, with the exception
of thyme and sage, which were weakly attractive, Plateau's theory is
refuted by his own experiments.
The discovery that bees still visited flowers rendered inconspicuous by
removing the petals or the colored part of the corolla seemed at first to
overthrow the accepted principle of attraction by color. However, careful
consideration of these experiments led to the conclusion that Plateau's
inferences were not justified and that another explanation was permissible.
The mutilation of Digitalis by cutting away the corolla, together with the
stamens and style, to leave a stump only 1 cm. long seemed to warrant the
conclusion that neither color, size, nor form was essential to their attraction.
Knuth argues, however, that the nectar is more exposed and the fragrance
more widely diffused and that this compensates for the loss of the corolla;
moreover, the visits should thus have been more numerous than to the
normal flowers, which was not the case. With other species the mutilated
flowers were visited less than the normal ones, a fact that Knuth regarded
as proving that the corolla also plays a part in attraction. In the case of
Antirrhinum majus the lack of visitors to the cut flowers seems to indicate
that the odor is not effective and that the form and color of the corolla play
the chief part. Moreover, the frequent visits of Megachile to heads of Cen-
taurea cyanus deprived of ray-flowers, explained by Plateau as due to the
odor, may be equally well explained by the memory of the bee as applied to
the honey-bearing disk-flowers.
Plateau has given a one-sided meaning to his experiments, without regard
to the work of earlier investigators. Thus, he has entirely overlooked the
experiments of Forel, who showed that blinded insects are unable to recog-
nize the landing-place of the flower, while those that have the antennae
cut away fly confidently from flower to flower. He further ignores the
results of Mueller, Loew, MacLeod, and Knuth himself, which have estab-
lished the following principles:
1. Other things being equal, a flower is visited by insects in proportion to its conspic-
uousness. Among related species that agree closely in form and color as well as
in floral mechanism, the most conspicuous receive the most visits and the
least conspicuous the smallest number.
2. In a number of cases odor has more to do with the attraction of insects than the
color and size of the corolla.
3. Dull yellow flowers are not visited as a rule by beetles, while nearly related flowers
that are white or of some other conspicuous color attract these insects even
when nectarless. Reddish-blue or violet flowers are preferred by bees, butter-
flies, and hoverflies, which are highly specialized, while the most frequent visi-
tors to white or yellow flowers are less intelligent insects with a short proboscis.
Bumble-bees appear least dependent upon the color of flowers, and as Mueller
indicated, are influenced more by food-value than by the external appearance
of flowers.
4. Strong-smelling flowers attract flies more particularly, while those with sweet
aromatic odors attract bees strongly without excluding other insects. The
delicate odor, strongly exhaled toward evening, of many white flowers with
long corolla-tubes attracts hawk-moths especially, as well as other nocturnal
Lepidoptera.
RELATED STUDIES AND CRITIQUES. 171
"Plateau's experiments only show that the sense of smell perhaps guides insects to a
greater extent than has hitherto been supposed. Apparently there is need of further
experiments to decide questions as to the attraction of insects to flowers by means of
the senses of smell and sight. Meanwhile, the following law may be provisionally
accepted: Attraction from considerable distances is certainly effected for the most
part by the odor of flowers, which fills the air as with invisible clouds and indicates
the direction for flight: when the insects approach near (1 to 2 meters), the colors of
flowers undertake the task of attracting them further, and when they finally settle, the
lines and points long since described by Sprengel under the name of 'Saftmal' (i. e.,
sapmark) serve to point the way to the nectar."
Reeker's experiments with artificial flowers. — Reeker (1898:105)
made a critical review of Plateau's first series of investigations, in which he
brought forward essentially the objections advanced by Kienitz-Gerloff and
by Knuth. Of especial interest was an extract from Graber which showed
that Plateau was not justified in citing Graber 's views in support of his
conclusions, since the latter was actually an exponent of the color sense of
insects (p. 215). In the first experiment Reeker employed artificial
flowers of Centaurea cyanus, 4 of which were grouped in a square against
a green background, at a distance of 6 to 8 meters from other flowers. Dur-
ing an hour of observation, 11 individuals of Pieris inspected the imitations
and 4 actually alighted. Honey-bees were very scarce, only one coming
near the cornflowers, and this landed and probed for nectar for 2 seconds;
3 syrphids came to seek pollen and 6 to 8 small flies flitted from one head
to another in an assiduous search for pollen or nectar. For the second
experiment four artificial flowers of Ranunculus acris were added to the
cornflowers in a fairly compact group, placed at a distance of 12 meters from
natural flowers. Five Pieris made inspections and 3 others alighted, while
one bumble-bee also landed on a cornflower and probed for nectar, and 2
honey-bees visited nearly every flower in the group. A dozen small flies
made long stays at several flowers and flew back and forth from the blue
to the yellow.
Reeker stated that these experiments gave such uniformly positive results
that further investigation seemed unnecessary, an unfortunate conclusion
in view of the much more extensive studies of Plateau. He regarded them
as furnishing incontrovertible proof that the color and form of flowers serve
to attract insects. Granting that the odor of flowers constitutes a very
powerful means of attraction, it must also be conceded that color likewise
has a share in the attraction of pollinating insects. However, Plateau
(1906:87) considered it very probable that the visits noted by Reeker were
due to the materials entering into the composition of the artificial flowers,
such as starch, etc.
Decorollate poppies. — In order to demonstrate the importance of the
corolla, Giltay (1900) grew Papaver rhoeas in two beds of about equal extent
and separated 50 meters from each other, and in a third bed covered by a
screen impenetrable to pollinators. In the first two the number of flowers
was equalized, and in one the flowers were left to develop normally, while
in the other the corolla was removed before the flowers opened. A portion
of the latter were later fertilized artificially with other pollen to determine
whether the mutilation itself could influence the production of seed. The
172 PRINCIPLES AND CONCLUSIONS.
plants in the wire cage produced only a very small amount of seed, viz,
0.004 mg. per flower, although they had been artificially pollinated. The
215 decorollate flowers yielded 10.77 gm. of seed or 0.05 gm. per fruit, while
215 normal ones produced 25.23 gm. or 0.117 per fruit. The 28 decorollate
flowers that had been artificially fertilized gave 0.115 gm. of seed per fruit.
The criticisms of Plateau as to the methods and conclusions of Giltay
have already been given (p. 159). These brought in return a critique of
Plateau's studies, in addition to a new series of experiments with mutilated
poppies, in which especial attention was devoted to the insect visitors
(1904:368). The first emphasized the discrepancy between Plateau's
earlier and later conclusions as to the importance of color, as Perez had
already done, and summarized the experiments of Forel with masked Dahlia
heads, which gave results very different from those obtained by Plateau (p.
145). Papaver rhoeas was again used by Giltay for his studies, owing to its
many advantages, such as complete sterility to its own pollen, the ease of
cultivation, the abundance of flowers and of insect visitors, and the readiness
with which the corolla may be removed. To insure better manipulation
the plants to be used were transferred to pots and kept in a screened cage
until needed. Checks were employed in connection with the removal of the
calyx and corolla to show that this in no wise affected the visits of insects
and that Plateau's fears were consequently groundless. In the first series
of 1902 two potted plants were placed on a greensward 2 meters apart,
and the corollas removed from the flowers of one of them. For an equal
number of flowers the normal ones received 96 visits and the mutilated 9
visits, while the second series with the plants near each other and with but
one or two flowers each gave 38 and 1 visits respectively. In the third
series the intact flowers obtained 34 visits, those with the calyx removed
and the corolla still folded 14, ordinary buds 1, and young fruits 2. When
flowers were so masked by pots that they could not be seen but any odor
present was free to escape, they received no visits, but bees came readily as
soon as the pot was removed. When the pot was so placed that the flower
was visible, it received frequent visits, thus showing that the odor of the
pot was not a factor in the preceding case. The relative importance of
color and odor was further demonstrated by placing petals in a dish and
covering them with a pot so that they were invisible but the odor could
escape. These were never visited, but when the pot was removed, bees
alighted on them, sometimes immediately.
Several additional series of experiments were carried out in 1903, in which
the response to the two kinds of flowers was shown to be greatly influenced
by habit. At first when one or more pots of mutilated flowers were placed
among normal ones, the visitors gave the former practically no attention.
In the case of two flowers of each sort the intact received 15 visits, the muti-
lated, none, while on the next day a honey-bee was seen that went to muti-
lated flowers as often as to normal ones. Three days later an observation
on 4 each of intact and decorollate flowers yielded 12 visitors to the former
and none to the latter, and 1 flower of each on the same plant gave respec-
tively 8 and 4. However, 1 marked honey-bee went to 18 intact and 13
mutilated flowers. When all the flowers in the experimental plot were picked
and 2 pots with equal numbers of the two sorts of flowers were placed at
RELATED STUDIES AND CRITIQUES. 173
a distance of several meters, the bees came first to the habitual place and
flew about it for some time before finding the potted plants, on which they
went only to the normal flowers. When the latter were picked and placed
in water or wet sand near the plot, there were several times as many visitors
to them as to the mutilated flowers. As the visitors to the latter increased,
the two kinds were separated about 2 meters, with the result that 24 honey-
bees and 23 bumble-bees went to intact flowers and 15 and 10 to the muti-
lated ones. When the flower groups were again brought near each other,
the number of visitors to normal flowers alone was 1 honey-bee and 9
bumble-bees, to mutilated alone 16 honey-bees, while 11 bees and 1 Bombus
went first to a normal flower and 2 of the latter first to a decorollate one.
The 12 mutilated flowers were then removed to a distance of 2 meters and
in their place was put a new group of 5 similar ones; the latter received 8
visits, while a single bee alone found the flowers in the new position. Fin-
ally, the position of a single flower of each was changed each time, with
the results that 14 visitors came to the intact flower to 3 for the decorollate
one, the latter being visited first but a single time. When the intact
flower alone was shifted it still received all the visits, but when the two were
again brought together the sole visiting bee went 10 times to the intact
flower and then directly to the mutilated one. The normal flower was
then taken away, and the bee now visited the mutilated one.
In the second series of experiments, Giltay (1906:468) extended the work
of Perez on the response of bees to red flowers, employing geranium and
corn-poppy for this purpose. A special instrument was devised for catch-
ing and marking bees, and practically all the studies were made with bees
so treated. The results of the experiments are expressed in a number of
resume's, as well as in the final summary. Trained bees came to the usual
place even when the plant used was not provided with honey; however,
they did not alight or for but a moment, though they landed in the normal
manner as soon as honey was placed on the flowers. When a plant without
honey was substituted for one with it, and the latter placed at a distance
of 1 to 2 meters, most of the first visits were made at the usual place, but
the honey plant was quickly found again. The honey-free plant was put
2.5 meters to one side of the usual place and the honey-bearing one the
same distance to the other side; several bees flew about the experimental
spot, but visited neither pot, until the honey-bearing plant was replaced,
when Nos. 5 and 4 visited it again. Five leaves were spread with honey and
placed on the ground below the honey-bearing plant. Within a few min-
utes, three visits were made to the latter and later these were repeated,
without the other plant or the honey-bearing leaves being perceived. This
indicated that the odor of the honey was not sufficiently strong to be attrac-
tive at the short distance represented by the height of the geranium plant.
When a cork with honey and a dish of the same were placed near the two
plants, both the latter were frequently visited, but the honey alone was not
noticed. In the next experiment, a blue flower of iris and a bud of poppy
with the calyx removed were put a meter distant on opposite sides of a
honey-bearing geranium, but neither was visited. The iris was then
replaced by a full-blown poppy, which was visited by both bees. When
Brassica was employed, it was also visited, though to a less degree than
the geranium.
174 PRINCIPLES AND CONCLUSIONS.
In the studies with Pelargonium, 22 honey-bees were concerned, 20 of
which were marked and brought to a flower provided with honey, while 2
made independent visits. Of the 22, only 4 returned to the place of experi-
ment and one of these, No. 4, more often than all the others. The visitors
to the honey-bearing flowers clearly exhibited place-memory, as well as a
preference for these over those without honey, and the ability to remember
Pelargonium after they had once learned it. During 14 days of experiment
no case was found of a marked bee bringing others, the only doubtful instance
being that of a bee that seemed to come by mere chance. Perez explained
the visits ultimately made to flowers without honey as due to the memory-
association of honey and color, and Giltay also found such visits to be
numerous. Moreover, he thought that, while form and fragrance might
play a part in this, it was improbable that these could be perceived as
quickly and accurately as was the case. His conclusion was that the
bees saw the flowers of Pelargonium as standing out against the back-
ground of different color and consequently could easily find them at a cer-
tain distance.
The experiments with Papaver were designed to demonstrate the relative
attraction of decorollate flowers or of paper ones, usually with a natural
center, in competition with normal flowers. These were organized in such
a manner as to bring out clearly the effect of memory of place. In all
cases of competition between decorollate and intact flowers, the latter were
always much more visited. The method of exposure exerted an evident
influence upon the ratio, since the decorollate were first sought after the
normal flowers had been brought near them. As in the experiments of
1903, it was found that flowers covered with a pot were not visited when
they were not visible from the outside. In the case of paper flowers with
natural centers, one bee visited practically all of these, independently of
their position, while another was much more timid, flying to some of them,
but rarely alighting. However, in a second series, the first bee behaved
in a wholly inexplicable manner, going to both the normal and artificial
flowers, but stopping at none, until it finally landed on a yellow composite
one. By means of a particular grouping it was possible to bring the bees
to visit decorollate flowers readily, though to see the latter it was
almost necessary for them to pass very close. After the bees had been
attracted to the decorollate flowers, the latter were exposed with an intact
one, but this was then alone visited.
In the case of Papaver, 27 bees were marked, of which 13 returned and 5
served for experimental purposes. These showed place memory in a high
degree. Of their own accord they found the decorollate flowers not at all
or only by chance, when these were not exposed in a most conspicuous
manner. Once attracted to them, they later found them more easily, and
often returned to the spot where the flowers had stood earlier. Likewise,
artificial flowers with natural centers were not readily visited, but they
were frequently sought after the bees had first been attracted to them.
Marked individual differences were exhibited by the bees employed in the
experiments, and the same bee sometimes behaved in two opposite ways.
It was concluded that bees are certainly attracted by the corolla in
Pelargonium and Papaver, and that it is very improbable that a special odor
RELATED STUDIES AND CRITIQUES. 175
constitutes the attraction of this organ. Since a single petal or a bud
deprived of its calyx exerts this attraction, it can not depend upon the form
of the flower. Hence, it must be due to the color, which must also stand
out sharply from the background to the bee's eye, although it can not
be said that they see the color red as we do. Small amounts of honey had
relatively little effect, at equal distances a single corolla exercising a much
stronger power of attraction than a quantity of honey much greater than
that ever found in a single flower.
Response to color and odor by a hawk-moth. — The experiments
performed by Gorka (1900:57), though few in number, are among the most
important of all, as they were carried out with newly hatched moths in
which either the antennse or the eyes were rendered useless. He noted that
Deiliphila elpenor, which was frequent in a garden in upper Hungary,
sought the flowers of Phlox paniculata and drummondi with especial fond-
ness, but ignored the other flowers, such as Dianthus, Malva, Borrago,
etc. As a preliminary test, a butterfly was released from its pupal case,
when it flew straightway to Phlox. On this he based his experiments to
determine whether this flower attracted hawk- moths by means of its color
or its fragrance. For this purpose he had at his disposal about 40 pupae.
The antennae of three hawk-moths that had just emerged were covered with
collodion and thus deprived of the sense of smell. These were freed in the
evening, when they flew directly to the Phlox at a distance of about 2 meters
and at once began to suck the nectar. Four days later the eyes of 4 hawk-
moths just hatched were covered with shellac, but the antennae were not
disturbed. In the evening when released, these flew to the flowers of
Borrago and Malva, which they immediately left; they finally landed on
those of Phlox, where they remained for some time. They then flew away, but
only to return for six different visits. These two experiments were repeated
12 times, and always with the same results. In three cases the blue flowers
of Borrago were sprinkled with essence of jasmine, when it was found they
were no longer disdained, but were visited by several of the moths.
Gorka's results prove conclusively that the hawk-moth is guided by both
sight and smell, and indicate that the former is more directive at a distance.
Taken in conjunction with the similar experiments of Forel (p. 140), and
Mayor (p. 159), they afford convincing evidence of the importance of both
senses in regard to attraction.
Vexillary nature of the plume in Muscari. — In order to test the
value of Plateau's conclusion as to the role of vexillary organs, Ferton
(1901:96) mutilated racemes of Muscari comosum by removing the sterile
flowers, which form a vivid violet-blue plume at the top of the inflorescence.
The fertile flowers are brownish and rather inconspicuous, but they emit a
pleasant fragrance. Andrena vetula flew indifferently to the fertile or sterile
portion of normal clusters, but when the fertile flowers were cut off, it went
to the sterile plume direct, then dropped to the level of the fertile ones,
only to find them gone. It twice hovered for some time before the muti-
lated stem, and also visited two or three such clusters in succession. Bom-
bylius fimbriatus likewise went to the vivid sterile group first and then
descended slowly along the stem, with the ligule extended, but finally dis-
176 PRINCIPLES AND CONCLUSIONS.
appeared as though disconcerted. Osmia tricornis and some males of
Anthophora acervorum were not deceived by the change, but one male
visited in succession four mutilated clusters before flying away. In the
following experiment the colored plume was removed from most of the
plants and placed on the ground near normal ones. A female of this species
passed by the latter in spite of their fragrance and went directly to one of
the detached clusters. However, it quickly recognized its error and de-
parted after visiting one of the fertile flowers. These results were thought
to confirm the vexillary role of the plume, which was regarded as a better
guide than the perfume which diffused in all directions. When the essential
organs were excised from flowers of Cistus, such blossoms were visited by
Anthophora, in spite of the fact that the fragrance had disappeared, one
individual going to three or four after failing to find pollen in the first
(cf. Knoll, 1921).
ForePs experiments with covered dahlias and with artefacts. —
Forel (1901:26, 1904:22) repeated Plateau's experiments with concealed
dahlia heads in order to check his conclusions. A bed of variously colored
dahlias, much visited by honey-bees, contained about 43 heads, of which 28
were covered with grape leaves fastened below by pins; in 4 heads the
yellow center alone was covered, while in a single one the center was free
and the rays masked. Forthwith the bees ceased to visit the completely
concealed heads, but went to the one with the rays covered just as to the
normal. They also flew frequently to the heads with masked disk, but
soon forsook them, though a few succeeded in crawling beneath the leaf.
Just as soon as the leaf was removed from a red dahlia the bees returned
to it, and a poorly covered head was also discovered and visited. Later one
bee found an entrance to a concealed head, to which it repeatedly returned.
Various individuals continued to seek the dahlias that had so suddenly
disappeared and late in the afternoon some of them had discovered the
hidden flowers. They were soon imitated by the others and in a short time
the concealed heads were again regularly visited. As soon as a bee had
discovered the entrance to a masked head, it flew without hesitation to it
on subsequent journeys. Single bees were not noticed by the others, but
a successful visit by several brought the others after them. It was con-
cluded that Plateau's methods were faulty and his results erroneous, due
to the fact that he had failed to reckon with the bee's memory and attention.
Three days later crude imitations of dahlia heads were made by putting
yellow Hieracium heads in Petunia flowers and these were placed among the
dahlias. Neither Petunia nor Hieracium was visited by the bees, though
at first nearly as many flew to the artefacts as to the normal heads. They
left them immediately, however, upon finding their error, obviously through
the sense of smell. They behaved in the same manner at dahlias with the
center replaced by a Hieracium head. As a check a beautiful fragrant
dahlia disk was placed among some white and yellow Chrysanthemums
neglected by the bees. For a half-hour this remained unnoticed by the
many bees, but came to be visited like the normal ones as soon as one
or two had discovered it.
In confirmation of Plateau's results, Forel found that the most carefully
made artificial flowers were entirely neglected when placed among the
RELATED STUDIES AND CRITIQUES. 177
dahlias. He then made a series of crude paper flowers as follows, placing
a drop of honey on each; (a) red, (6) white, (c) blue, (d) blue with yellow
center made from a dead leaf, (e) rose-colored with a dry dahlia disk,
together with an (/) unchanged green dahlia leaf. During the first hour
the honey was removed from the blue flower alone. The red flower was
then brought repeatedly to the attention of a bee resting on a dahlia,
when it began to sip the honey. This bee was marked with blue, and those
led to sip from the white and the rose flower were painted yellow and white
respectively. Upon returning from the hive, the blue bee flew at once to
the red flower and hovered over it doubtfully, then visited the blue, and
went again to the red but not to the dahlias. The yellow bee next revisited
the white flower, then visited the red and the blue, but gave no heed to the
normal ones. It was followed by the white bee, which, failing to find the rose
flower at once, began to work on the dahlias, but remained only a moment
on each. It returned to the artefacts without finding the honey, until
it encountered a corner of the rose-colored flower and began to sip. After
this the three painted bees, and no others, returned regularly to the
artefacts and ceased to visit the dahlias. It is significant that they dis-
covered the other artificial flowers by themselves, doubtless through an
instinctive inference from analogy, in spite of the fact that these were
somewhat distant from each other and differently colored. The blue bee
went to red, white, and both blue flowers, the yellow to white, red, blue,
and blue composite, and the white to rose, red, white, and blue com-
posite, the green not being found, evidently because of its color.
Finally, a new bee came to the blue composite and was marked with
carmine, after which she drove the blue bee from the red flower. Another
bee came to the rose flower and was painted with orange, and still
another to the white flower and was painted green. The experiment had
now lasted more than three hours and but six bees had come to know the
artefacts, the great number continuing to visit the dahlias. Soon, however,
the others began to come and it was necessary to replenish the honey
constantly, a swarm finally removing the last traces and one bee discovering
it on the green leaf. After vainly searching the empty artefacts, the bees
began to return to the dahlias; at this moment the red and white flowers
were replaced by red and white paper entirely free from any odor of honey.
These pieces of paper were visited and examined by various bees, still
possessed with the idea of honey, the white bee carefully searching the
white paper for three or four minutes. This could only be explained by
an association of space, form, and color memories with memories of taste.
When the artefacts were carried away, several bees followed and tried to
alight on them, in response to color and form alone, the space-image having
changed.
This and other experiments were considered to demonstrate the space,
form, and color perceptions of the honey-bee, its memory particularly with
respect to vision and taste, the power of associating gustatory and visual
memories, the instinctive ability to draw inferences from analogy, a poor
olfactory sense, a one-sided and narrow range of attention, the rapid for-
mation of habits, and the limited imitation of bees by each other. Further
experiments designed to lead the bees to distinguish between disks of dif-
178 PRINCIPLES AND CONCLUSIONS.
ferent color were vitiated by the bees' power of memory, the marked bees
placed on the blue disks beginning at once to investigate all the other colors
with and without honey, and being followed by a swarm that even besieged
the paint-box.
Response of Syritta. — Schroder (1901: 181) recorded 12 cases in which
a honey-bee approached to within 2 dm. of heads of Chrysanthemum leu-
canthemum and then flew to a bush of jasmine at a distance of 4 meters,
the strong fragrance of which was carried across the former. He clipped the
rays from half a group of 12 heads and found that Syritta pipiens in the
course of a half-hour visited 37 normal heads, while it completely ignored
the mutilated ones. Syritta hovered over the latter a longer time than usual,
but without alighting. During the afternoon, 4 visits were made to the
clipped heads and 21 to the normal, and on the next day 19 to 46, the fly
no longer showing the hesitation before the former. This indicated that the
insect recognized the difference in the heads in spite of the similar odor, and
that it learned rather rapidly to accustom itself to the mutilated ones. Two
days later the latter were cut off and a flat piece of white paper the size of
the head, provided in the middle with another piece the size and color of the
disk, was fastened on the end of the stem. In spite of visits to the normal
flowers, no Syritta paid the slightest attention to these crude imitations,
which lacked the form and fragrance of real flowers. They were then
furnished with a few drops of an infusion of Chrysanthemum heads, but,
while they were inspected during the next half-hour, no Syritta visited them.
However, when three of them were provided with honey, they received 10
visits during the half -hour to 12 for the normal ones. The other three were
also visited four times, indicating that Syritta had again profited by experi-
ence. Three artificial flowers made of cloth were fastened on the stem ends,
and one received a visit, but it was thought this might be due to the odor
of the adjacent normal heads. To give them a distinctive odor they were
soaked in the infusion of normal heads, dried, and again attached, when
they received 7 visits in comparison to 24 for the normal. Thus, the question
of the means by which flowers attract insects seemed not solved in the direc-
tion of Plateau's views.
Andreae's experiments with artificial flowers.— In a comprehensive
examination of Plateau's results, Andreae carried out many experiments
with artificial flowers, some of these being made at Jena and some at Lake
Como (1903:427). In the first series yellow artificial flowers were placed
2 meters from a bed of Eranthis nivalis and these were visited during an
hour by 10 honey-bees. As a check a bell-glass was put over one plant to
eliminate the influence of odor, but in spite of this 4 honey-bees came to the
glass. When the imitations were replaced they were visited 8 times within
the hour. A further check was obtained by putting 10 decorollate flowers
in one beaker, 10 normal ones in a second, and the detached perianths in
a third. One honey-bee flew into the first glass and 2 hovered about it,
14 into the second and 10 about it, and 9 into the beaker with perianths
alone and 4 about it. When a dark paper was placed upon a small group
of Crocus and an artificial flower placed 2 meters away, bees went to the
latter, to Crocus, and again to the imitation before flying away to the snow-
RELATED STUDIES AND CRITIQUES. 179
drop. A bell-glass was next put over the Crocus flowers and 5 honey-bees
came to it within an hour. At a distance of a meter from a bed of yellow
Crocus was placed a striking artificial flower of the same color and at the
same distance a beaker with 5 normal flowers, while a meter further away
stood one with 10 similiar flowers. The latter was surrounded by dark
paper with a fairly large opening above, so that the odor might easily
escape. However, not a single bee came to this during two and a half
hours, though 10 visited the imitation during the first hour. The open glass
with normal flowers was constantly visible, but only one bee entered it.
The next installation consisted of a beaker filled with blue Crocus 2 meters
from the bed, another with white Crocus at 4 meters, and an artificial flower
at 7 meters. During a quarter of an hour these received respectively 11, 9,
and 2 visits by honey-bees; when the beakers were turned down they still
received 9 and 7 visits respectively.
In the first experiment with Rhododendron ciliatum a large empty beaker
was placed 2 meters from the bush and a smaller one filled with normal
flowers of this species at a distance of 3 meters, the first designed to show
the effect of the brightness of the glass, the second that of color. During
a half-hour but 2 bees went to the empty beaker, while 12 flew to the red
flowers in the other, and 10 flew directly against the glass itself. When
this beaker was inverted, 7 bees went to it in 5 minutes. The second instal-
lation consisted of three beakers placed 8 meters from the bush and likewise
distant from each other, one containing honey, another slightly perfumed
water, and the third was the inverted one with normal flowers, designed
to show the relative attraction of honey, perfume, and color. The visits
made by Musca and Apis were respectively 15 and 4, 12 and 3, and 16 and
10, during an hour. An inverted beaker with normal flowers gave 60 visits
to a single one for an empty beaker. The bush was then shaken and 20
bees flew directly to the normal-flower beaker, and during three repetitions
not a single bee went to the empty glass. This showed conclusively that
the bees were not attracted by the brightness of light but only by the color
itself. Moreover, the honey-bee must be able to see color for a distance
of 8 to 10 meters at least. When the attraction of honey alone was tested,
a single bee came to the beaker as though by accident.
Parallel to a bed of primroses were installed a yellow primrose made
of cloth, an inverted beaker containing blue primroses, a glass of honey, and
an upiight beaker filled with the same flowers freshly picked. The last two
were surrounded with dark-gray paper to conceal their contents, and all
were placed a meter from the bed. The artificial flower received a total
of 18 visits, of which 10 were made by the honey-bee, the inverted beaker 13,
the glass of honey none, and the open beaker 1, giving a ratio of 31:1 in
favor of color. In the check a glass with diluted honey was surrounded with
paper and placed at a meter from the bed, while at 2 meters were located
an imitation flower and an inverted beaker. This yielded 26 visits, 14 by
Apis, to the artificial flower, 2 to the beaker, and 3 to the honey glasses,
or 28 to 3 in favor of color. The second check consisted of four glasses,
one filled with honey and the other three with primroses and all wrapped
with dark paper, placed at a meter from the bed. At 3 meters were located
a false flower and an inverted beaker of red primroses. The imitation
180 PRINCIPLES AND CONCLUSIONS.
received 38 visits, 25 by bees, the inverted beaker 17, and the four "odor"
glasses but one, giving a ratio of 55 : 1 in favor of color. Even when the
artificial primrose was placed 5 meters from the flower-bed, it received 13
visits from bees to none for the more accessible "odor" glasses. To deter-
mine the effect of a difference in form the artificial primrose was re-
placed by a peony of the same material and color, which was placed 7
meters from the bed of primroses. One meter from the latter stood four
glasses, one filled with honey, the other three faintly perfumed with jas-
mine, mignonette, and violet respectively. However, the latter obtained
no visits in contrast to 41 for the imitation flower.
Twelve meters from a bush of Doronicum caucasicum, a yellow composite
actively sought by various insects, was located an artificial flower-bed
composed of the primrose and peony already used and an orange-red and a
dark-red poppy, all of which were a meter apart. As an additional attrac-
tion, artificial cornflowers and snowballs were placed in the center of the
square. The yellow peony received 31 visits, the orange-red poppy 9,
the dark-red one 3, the central group 7, and the primrose but 1, showing
a clear relation between conspicuousness and attractiveness. A further
test of the effect of odor was made by filling an inverted beaker with fresh
primroses, so that they were plainly visible, while a bell-glass was likewise
filled with several hundred fragrant flowers of the same species, but these
rendered invisible by means of dark paper. In spite of the advantages
given the latter, it received but 3 visits to 35 for the former.
When 5 funnels were filled with fragrant flowers of the peony and sur-
rounded with paper, and placed above the bush, now past blooming, they
received but 3 visits in competition with a bell-glass in which several
flowers were visible, this yielding 40 visits. To test the effect of the glass
itself, the same bell-glass full of peonies was placed 15 meters away, while
a small empty one was put but a meter distant. The latter received no
visits to 5 for the former. In the next trial two artificial flowers were made
of bright-yellow and rose-red tissue paper, provided with dark-green below
to furnish a contrast, and attached to stakes 2 meters high. Within a
period of 2 hours 17 visitors went to one and 16 to the other, the total of 33
including 12 bees. When a yellow, a dark-yellow, and a purple-red cloth
flower were employed, the yellow obtained 21 visits and the red 9, during
3 hours. In the next case, 3 flowers of Papaver orientalis were placed in a
funnel so that the odor could escape without their being seen, while to the
single normal flower left on the plant was added a larger artificial one of
cloth, in order to determine whether conspicuous color, color and odor,
or the latter alone would be most effective. The results showed 81 visits
to the imitation, chiefly by Osmia and Apis, 56 to the normal flower, and
none to the funnels. In the control the last normal flower was added to
those in the funnel and this placed 5 meters distant against the wind. In
spite of this it received no notice from the bees, which meanwhile made
43 visits to the imitation.
Experiments with flowers of dull color but nectar-bearing showed that
the color was often attractive, sometimes more attractive than the odor
of nectar or honey. Studies were also made of flowers with dull color and
marked perfume, such as Reseda, Dahlia, etc. When stems of the former
RELATED STUDIES AND CRITIQUES. 181
were put in a dark-brown bag of gauze and hung above the bed, they were
visited by Prosopis and Andrena, but Apis continued to work only on the
plants in the bed. In the case of bell-glasses filled with mignonette and one
of them inverted, Prosopis and Andrena went only to the one with the open-
ing, thus exhibiting the reverse response to odor and color from that of the
higher apids. When artificial flowers of Paeonia and Primula were placed
in a meadow, 8 Apis went directly to the more conspicuous peony and one
each of Apis and Bombus to the primrose. A box was covered on the four
sides with differently colored cloths, through which a large opening per-
mitted the air to move. When linden flowers were placed on the inside,
about 20 individuals of Prosopis went directly in, while 3 Eristalis went first
to the color before entering, and 10 to 20 A pis flew against the color alone,
especially on the lighted side. With buckwheat substituted for linden, the
results were the same, Apis flying to the color and Prosopis entering the
box, but when the latter was empty, Prosopis failed to appear, Apis, how-
ever, behaving as before. In the case of a choice between the colored bracts
of Salvia horminum and artificial cornflowers attached to the plant, the
former received 20 visits to 9 for the latter.
A few weeks later experiments with Dahlia variabilis were made in a
garden at Cadenabbia on Lake Como. Four heads were cut off and laid
in a pot wrapped with green paper, which was kept covered until the odor
had time to collect, and at the same time a large bright-yellow paper flower
was fastened to the stem. The pot received no visits, while 19 were made
to the imitation, and the results were similar when other paper flowers
were employed. When red-brown plums were placed in a pot and also on
the ground, the latter alone were visited by honey-bees; with those on the
ground removed and the pot in full sunshine the odor of the plums attracted
but one bee in the course of an hour. Near a plum tree sought by hundreds
of bees was placed a pot wrapped with bright paper and filled with crushed
ripe plums, and a paper flower with contrast colors. The latter received 16
direct flights, while the former was visited only by young bees that grazed it in
flight. In the last experiment with diurnal insects, 50 paper flowers of
various colors were fastened to stems of Zinnia elegans, and the normal ones
inclosed in wire-gauze to permit the attraction of fragrance alone. However,
the latter received no visits, while the former had 49, of which Apis made
30, Argynnis 14, Pieris 3, and Vanessa 2, showing that the butterflies be-
haved essentially like the higher bees.
Andreae's conclusions. — It is evident that running insects will have
the sense of smell better developed, while flying ones that possess an ex-
tended life-period have sight developed in proportion to their rapidity
of flight. Thus, it is necessary to distinguish between high and low types,
the one characterized by long direct flight, a relatively long life-period,
and a keen sense of sight, the other by short flight, short rife-period, marked
sense of smell and a poorer vision. Consequently, the various inflores-
cences and corollas with bright colors are chiefly adapted to the biologically
highly differentiated insects, and the fragrant flowers without bright colors
are designed to attract the lower ones. Thus, Prosopis and Andrena react
to odors very differently from the higher apids, for, while colors attract
Apis, Osmia, Anthophora, and Anthidium from considerable distances, as
182 PRINCIPLES AND CONCLUSIONS.
can be determined by their direct and rapid flight to them, the flight by the
lower types is quite different. The latter change in direction and each
time toward the side from which the fragrance comes. Such insects also
perceive colors, but only when they are near at hand. Similar differences
also occur among Diptera; Eristalis responds differently to a color than a
gnat does, and Bombylius and Volucella, two highly developed flies, show
but very slight response to odor, as Forel has already shown.
The conclusion that color attracts the biologically higher insects from a
distance and odor when near at hand is supported not only by the experi-
ments recorded, but also by the following facts. A brightly colored object
does not change its position, and, if forced out of it, becomes more or
less conspicuous only as a result of changes in lighting, while odor behaves
very differently. In the first place, its intensity varies from time to time,
in the second its conveyance depends upon a variable wind direction, and in
the third its perception is determined by the amount of humidity in the
air, since the antennae are much more sensitive in moist than in dry air.
There are constantly many odors in the atmosphere which pervade and
replace each other, and are constantly changing their position in response
to the slightest breeze. Thus, the view of Sprengel and of Darwin that
color attracts insects from a distance is rehabilitated.
Andreae's criticisms of Plateau's work. — In connection with Plateau's
statement that we have no means of knowing that the perception of color
by insects is the same as with man, Andreae pointed out that this was
equally true of odor, declaring that the whole question was an idle one and
that the only thing of importance was to determine whether what we call
color exerts an attractive effect upon insects or not. He also emphasized the
fact that many of Plateau's experiments were excellent in demonstrating
choice among colors, but they had no value for the question of the relative
merits of color and odor. The chief error in his investigations lay in the
fact that he failed at the outset to organize his queries properly. In the
first place all possible factors that bring about attraction must be considered,
and in the second as many of these as possible must be tested at the
same time. In this way alone can comparative results be obtained that
will lead to an objective conclusion as to the importance of form, luster,
brightness, and color, honey-odor, or fragrance. Many of Plateau's results
were to be ascribed to the effect of habit, and the others were not organized to
}deld a definite decision as to color and odor. However, Andreae's state-
ment that the greater proportion of visits to the decorollate poppies did
not change the essential facts with respect to the attraction of the corolla
does not seem valid. Finally, it was stated that Plateau had not sufficiently
distinguished the behavior of various insects in regard to color and odor,
since the lower apids gave results directly opposite to those obtained with
the higher ones.
Plateau's criticisms of Andreae's work. — Plateau stated (1906:13)
that it was probable that the artificial flowers of Andreae and of Reeker
would have exhibited the same sources of error as those employed by Wery
(p. 185). With respect to the experiments with Crocus in which the flowers
were covered, it was objected that the bees upon returning to the habitual
RELATED STUDIES AND CRITIQUES. 183
place and not finding the flowers precipitated themselves upon the imita-
tion, as upon any object whatsoever. The same objection was raised to
the experiments with the poppy, the results of which were regarded as
illusory because of this fact, as well as because the flowers were cut off and
handled, and to those with Dahlia. The experiments with Zinnia were
also regarded as demonstrating nothing whatsoever, since the artificial
flowers were attached to the stems to which the bees were accustomed to
come to visit the natural ones. Moreover, it was supposed that the meshes
of the wire-gauze were so small that the odor could escape little if at all.
Both of these objections were also urged against the results obtained with
Salvia horminum, but their validity does not seem to be great, and they
can not apply to the many cases in which the artificial flowers were placed
at distances of several meters.
Wery's experiments with decorollate and artificial flowers. — At
the suggestion of Errera and Massart, and under their supervision, Wery
(1904:1211) made a series of investigations to determine whether color
exerted an attraction upon insects and whether this was greater or less than
that due to odor. An interesting historical introduction is given, but no
direct criticism of Plateau's work is made, except to point out that this
investigator modified his earlier conclusions as to odor and color in 1899,
and in 1902 he admitted that he had ascribed an exaggerated importance
to odor. The first experiments with decorollate flowers demonstrated that
different insects behaved differently in response to color and odor, the higher
bees, Apis and Bombus, visiting the normal flowers in much greater number,
Eristalis showing a marked but slighter preference, and the flies and other
small Diptera exhibiting little difference. This showed that it was not
permissible to group such various insects together in studies of attraction
and consequently the visits of honey-bees alone were taken into account
in these experiments, a fact that explained in part their disagreement with
those of Plateau. A further explanation of this difference was afforded
by the fact that the bouquets were always separated by a distance of several
meters and sufficiently isolated to avoid errors due to any other attractive
object. Moreover, the flowers were changed about in order to eliminate
errors arising from the habits of the bees. The experimental area was stripped
of all other flowers and the space between these and the hive was cleared
of all plants, so that the bees flew straight from the hive in direct response
to attraction and the visits were not the result of hazard. The bouquets
were not exposed between experiments and the artificial flowers were put
away to make sure that the bees would not ignore them in consequence
of vain visits. An endeavor was made to count only the visits of bees coming
from the hive or from a distant flight during which they had gone to other
flowers. In removing the corolla care was taken not to injure the nectaries
and great care was also given to following the precautions laid down by
Plateau, such as washing the hands, avoiding the use of perfume, not touch-
ing the flowers with the hands and using the scissors for no other purpose.
The objection of Plateau that insects would not visit cut flowers was not
confirmed, except when the temperature was unfavorable, as at other times
they were abundantly visited by insects of diverse species.
184 PRINCIPLES AND CONCLUSIONS.
The first experiments were carried out by means of a bouquet each
of normal and decorollate flowers of Epilobium spicatum and Malva silves-
tris, placed 10 meters apart. The normal flowers of these received respec-
tively 14 and 4 visitors, of which 7 and 2 were honey-bees, while the muti-
lated ones yielded 12 and 3, of which 5 and 1 were bees, the totals for the
former being 18 and 9, and for the latter 15 and 6. When Epilobium and
Antirrhinum majus were employed, there were 19 visitors to the intact
and 13 to the mutilated flowers, the number of bees being twice as great
in the former. Symphytum, officinale was added in the next test, which
gave 27 visitors to normal and 24 to mutilated flowers, while the respec-
tive numbers for the bees were 20 and 6. The next installation consisted
of two bouquets of Centaurea cyanus, Papaver rhoeas, and Pyrethrum leucan-
themum separated by a distance of 25 meters and 500 meters from two hives.
The flowers of one bouquet were left intact, while the petals or the ray-
flowers were cut off in the other. The former received 43 visits, 29 of them
by the honey-bee, and the latter 27, of which 10 were made by the bee. The
following year the visits of the honey-bee alone were counted, the instal-
lation comprising two bouquets, one intact, the other decorollate, which
were exchanged after each series. The results of 6 observations gave a
total of 72 bees for the normal flowers to 28 for the mutilated ones. The
total for the two years was respectively 138 and 46, the bees being much
more attracted by the normal flowers, in the ratio of 3: 1.
When a dish of honey was placed at 6 meters from a bouquet of normal
flowers, the latter gave 49 visitors, the former none, while the totals for
two further observations were 25 and 0. When a bouquet of artificial
flowers of Eschscholtzia and Dahlia was placed 6 meters from one of normal
ones, it was visited by 15 bees, to 17 for the latter, the visitors scarcely
landing before perceiving their error. The final results of the series gave
almost equal numbers, showing that the artificial flowers were equally
attractive. Two experiments were made with the normal bouquet in a
closed globe in order to suppress the perfume, resulting in 5 visitors in
contrast to 6 for the artificial one. In competition with a bouquet of
natural flowers deprived of the corolla, the artificial flowers received 11
visitors in contrast to 6. Hiding a bouquet of normal flowers under the
foliage resulted in but 7 visitors to it in comparison with 32 to a similar one
freely exposed. In a check with artificial flowers entirely visible and normal
ones hidden in the foliage, 19 bees went to the first and but 4 to the last,
demonstrating that odor is much less effective than color.
The remaining experiments made use of honey or fragrant flowers, the
installation for the first consisting of bouquets of normal and artificial
flowers fully visible, normal flowers hidden under leaves, and a dish of
honey, all 2 meters apart. The respective numbers of bees were 25, 20,
7, and 1. The check, which differed only in having 2 artificial dahlias stuck
in the honey, gave respectively, 15, 11, 3, and 8 bees, the dahlias having
greatly increased the attractiveness of the dish with honey. When yellow
pollen flowers (Eschscholtzia) were placed in a dish of honey 6 meters away
from honey alone, no bees went to the latter, while 14 flew directly to the
flowers and for the most part to the stamens, only 3 going to the honey.
A bouquet of brilliant flowers with little odor was placed 6 meters from
RELATED STUDIES AND CRITIQUES. 185
another containing mignonette, with marked perfume and dull color; the
former was visited by 35 bees, the latter by 6. When the bouquet of normal
blossoms was replaced by one of artificial flowers, equally brilliant, the figures
were 25 and 6. In the final installation, made first on a day with few bees
flying, 6 bees went to a dish of honey to which natural flowers were added,
4 to one with artificial flowers, and none to honey alone or with green leaves
merely. In the check, the dish with natural flowers gave 14 visitors, that
with artificial ones 15 visitors, and the honey with leaves or honey alone,
none. Finally, the author endeavored to give a numerical expression to
attraction by means of a table of her own results, as well as one for those
of Andreae and Giltay. The conclusions drawn were as follows :
1. Flowers provided with brightly colored parts have a much greater attraction
for the honey-bee than those of the same species when deprived of these parts.
2. Honey attracts bees very little.
3. Under the conditions given, artificial flowers attracted honey-bees readily, to the
same degree as normal flowers placed in a globe.
4. Perfume alone attracts bees but feebly, while bright color and form taken together,
but detached from odor, exercise a very manifest attraction upon them.
5. From the juxtaposition of the three principal factors, form, color, and odor,
associated in the memory, results the most marked attraction.
6. For the honey-bee the attraction exerted by the form and color of flowers is approxi-
mately four times greater than that of their pollen, perfume, and nectar taken
together. Thus, if the total attraction exerted by the most attractive flowers
is taken as 100, that of form and color will be represented by about SO and
that of the other three factors by about 20.
Plateau's criticisms of Wery's experiments. — In discussing the
discrepancy between his results and those of Wery and Andreae in particular,
Plateau (1906:11) thought it probable that this was due to certain dis-
turbing factors. In order to discover these, it appeared necessary to
secure conclusive evidence as to the nature of the materials employed by
his opponents, and to repeat their experiments and add new ones surrounded
by all possible precautions. A preliminary examination showed that certain
artificial flowers of commerce are only partly artificial; thus the yellow
disk of oxeye daisies consisted of the natural receptacle dried and dyed,
the involucre of the cornflower was simply the natural one dried, etc.
Moreover, the stiffness of the petals in artificial flowers for hats is secured
by means of a large amount of starch and the anthers are composed of balls
of paste, which are eaten by small Hymenoptera. He then obtained samples
of the flowers used by Wery and found his suspicions to be confirmed. In
all the flowers their rigidity was due to the presence of starch. The yellow
color of Helianthus and Eschscholtzia was derived from a saffron dye obtained
from the stigmas of Crocus sativus and containing a yellow glucoside ac-
companied by a volatile odor attractive at least to certain insects. The
disk flowers of Dahlia were made of yellow fibers, some of which were covered
with gum and rolled in flour. Balls of wheat flour colored yellow consti-
tuted the yellow center of Aster, and the anthers of Eschscholtzia were
made of similar starchy material colored blue by iodin. Although it was
not supposed that the presence of such substances explained all the dif-
ferences, it was thought to be responsible for them in part. Finally, the
186 PRINCIPLES AND CONCLUSIONS.
artificial flowers used by Miss Wery were regarded as imitations of very
mediocre value.
In the experiments where Dahlia was used, Plateau stated that the
figures probably did not really indicate that the artificial flowers were
practically as attractive as the natural ones, for three reasons. The first
was the error committed in carrying out these tests where a series of 8
experiments with bouquets had been made during the preceding two weeks,
giving an opportunity for the exercise of place-memory by the bees. The
second was the fact that the majority of the insects barely landed on the
artificial flowers, these visits to be interpreted rather as hesitations, curves,
or crochets made in flight, and the third dealt with the materials used in
the artificial flowers.
Experiments of Weismann and Errera. — Weismann (1902:219)
placed an artificial Chrysanthemum in the midst of normal flowers actively
visited by butterflies. He found that most of the latter passed near the
imitation without stopping, but he saw two alight on it and probe actively
with the ligule before flying away. It seemed evident that they sought the
nectar which they had found in the normal flowers and that they flew off
only after having determined its absence. Errera (Wery, 1904:1224)
placed two bouquets made up of the same number of flowers of the same
species in similar vases at a considerable distance from each other in the
midst of an extensive greensward at Brussels. In one the flowers were
normal, in the other they were deprived of their corollas in such a way as
not to injure the nectaries. The decorollate bouquet was still rather con-
spicuous, owing to the colored stamens of Rhododendron, the white calyx
of Hesperis, and the yellow disks of Chrysanthemum. The two bouquets
were visited at the rate of 46 per hour for the normal and 24 for the de-
corollate, the majority of the visitors being flies.
Orientation of the honey-bee at flowers of the same species. —
Detto (1905:424) carried out a number of experiments to determine the
relative importance of color and odor in the attraction of the honey-bee,
as well as to throw light upon the rapidity with which it learned. The
first series dealt with the manner in which the bee is led from one flower to
another of the same plant or different plants of the same species. When
flowers were mutilated by removing the anther mass or half the corolla, they
were visited like the normal ones, but when the corolla was completely sup-
pressed, visits ceased immediately, to begin again as soon as it was replaced.
Visits also stopped at once as soon as the corolla was replaced by one of
yellow tissue-paper, but were resumed when the normal corolla was put in
position again. Shortening the corolla to a third did not affect its attraction,
and finally, after a few hours the decorollate flowers began to receive visitors,
but in a smaller degree than the normal ones. These tests show how im-
portant a guide the colored corolla is in the near-flight of habituated honey-
bees, and the visits to decorollate flowers merely prove that they are able
to form new associations in consequence of the stimulus afforded by the
abundant nectar. If flowers with excised anther column were provided
with a colored paper disk with a hole in the center, thus cutting off the
lower third of the flower, part of the bees avoided such flowers and others
RELATED STUDIES AND CRITIQUES. 187
alighted for but a moment. Many, however, rushed about on the disk
and some succeeded in passing under the edge or through the opening to
the nectaries. In three other flowers the anther column was replaced by a
staminate flower of Bryonia and the results were similar, some bees shunning
the artefacts and others succeeding after persistent endeavor in finding
the nectar. It was concluded that in Anoda triloba the colored corolla is
the guide in the flight from flower to flower and that near-flight is deter-
mined by optical orientation to color.
In the case of Bryonia dioeca, flowers provided with a ring of colored
paper were readily visited, the visits to the different colors being, yellow 12,
blue 8, green 6, and red 1. When the anthers were concealed by colored
disks, the visits were fewer than to normal flowers, yellow again leading,
and visits continued at about the same rate when the anthers were excised.
The complete removal of the perianth greatly decreased the number of
visits. The conical disk of three heads of Rudbeckia laciniata was covered
with a thin glass tube, with the result that numerous bees flew against
the glass, some crawling all over it and others flying about it several times.
In two heads the cone was replaced by the similar one of Heliopsis levis;
some bees hovered over this and others crawled about on it, but none
sipped nectar from it. Heads of Echinacea purpurea placed between those
of Rudbeckia were not visited, but they were sought when the disk was
replaced by that of Rudbeckia. In order to determine the effect of the yel-
low ray-flowers, the cones of two heads were completely removed; bees
coming from higher heads or those on the same level paid little attention
to these, but those coming from below alighted on them for a moment or
darted over the middle. When the disk was covered with blue or yellow
paper, bees arriving on the same level or from below alighted on the paper
before perceiving their mistake. Bees coming from above visited the green
disk after the ray-flowers had been covered with colored paper, but the
visits decreased in cases where the rays were all removed. These results
were considered to prove that visits are determined by optical signals,
and that either ray-flowers or disk suffice for attraction, though the green
disk is naturally less effective in this respect.
From this series of experiments it was concluded that the colored corolla
is the normal guide to the individual flowers of a cluster or group, but other
guides may be utilized with the result that decorollate flowers may continue
to be visited. In consequence no conclusion as to the absence of the color-
sense can be drawn from habituated bees. The means of orientation in the
flight from flower to flower is optical in nature. Since the different at-
tractive parts of the flower can bring about visits when present alone, it
is easily seen that partly concealed flowers may be visited. This also ex-
plains why the differently colored varieties of a species are visited indif-
ferently by bees ; this is possible whenever the flowers agree in the possession
of one important guide for the insects, which may be some other part than
the corolla.
Discrimination between similar species of flowers. — In further
studies Detto placed clusters of Deutzia flowers in umbels of Crataegus.
The bees behaved differently on them, some sipping nectai , others not, but
they all flew or crawled to the neighboring flowers of Crataegus. When
188 PRINCIPLES AND CONCLUSIONS.
umbels of Crataegus were placed between clusters of Deutzia, the behavior
was the reverse. A similar discrimination was found in the case of heads
of Rudbeckia provided with disks from Heliopsis, and these results led to
the conclusion that flowers of similar color are distinguished on near
approach by means of the odor of the nectar or the flower itself. The ap-
proach of bees habituated to a particular species to the flowers of a similar
species intermingled with it attests their color-sense, since they perceive the
difference only in the immediate vicinity of each, through the perception
of the strange odor. Detto considered it unwarranted to ascribe this
ability to discriminate to the perception of form, as was done by Forel,
Buttel-Reepen, and Knuth, but this conclusion is contradicted by his
earlier statement that pistil and anthers serve as guides in decorollate
flowers. He called attention to the conflict between the views of Knuth
and Andreae as to the attraction sequence of color and odor, and agreed
with the latter that far -flight in the case of newcomers is due to color and
near-flight to odor, though this was not true of all groups of insects.
Orientation of the bee within the flower. — In order to determine
whether bees are guided by vision or smell in going from one nectary to
another, Detto made use of flowers of Althea rosea, in which the deep comate
nectaries are about 9 mm. apart. Honey-bees and bumble-bees go from one
nectary to the next with the greatest accuracy, without feeling with the an-
tennae or probing with the ligule. The anther column was removed and a
paper disk put in place in such a manner that it covered the nectaries ; it was
perforated in a way to permit the nectaries to be closed or opened by a turn.
Some bees avoided such flowers, while others entered and quickly found the
nectar through the openings, going to them all in normal fashion. As one
bee went from the first to the second nectary, the disk was turned to
bring the openings between the nectaries; he went to the next perforation.
In repeated trials, some of the insects flew away after the first futile attempt,
others went to several openings, and still others kept probing until they
were able to reach the nectar by oblique movements of the ligule. Finally,
some forced up the edge of the disk and crawled beneath it. When the disk
had no perforations, the bees sought to force the head under the edge at
all points and not merely in the direction of the nectaries. With holes 1 mm.
in diameter directly above the nectaries, the bees made no attempt to reach
the nectar. While these results were not regarded as entirely conclusive,
they seemed to indicate that vision was the decisive factor in directing the
insect to each nectary. An ingenious check was constructed by cutting out
a disk from a hollyhock flower in such a manner that the nectaries were with-
out a bottom and could be brought above or between the nectaries of a
normal flower at will. As a further precaution the false nectaries were
thoroughly washed out to free them of odor in so far as possible. When
the false nectaries were directly above the true ones, the bees visited the
latter in the normal way, but when they were brought into the intervals
the bees continued to go to the false nectaries without success. Although
it was impossible to be certain that the latter were entirely without odor,
it seems highly probable that the nectar journey is controlled by vision.
If odor be regarded as chiefly directive, it must be assumed that its inten-
sity decreases with the distance from each nectary, as otherwise the bee
RELATED STUDIES AND CRITIQUES. 189
could not go directly to each one. However, several facts argue against this
assumption. The bees behave in the normal manner even when the flowers
sway back and forth in a strong wind. Spraying menthol in the nectaries
does not change the behavior, except that the bees fly away after probing
such a nectary or go rapidly to the next. Moreover, the layering and the
concentration of the nectar odor above the nectaries must be obliterated
by its mixing with the odor of the flower itself.
Detto also gave an interesting account of the training of an individual
bee, which was effected by covering a flower cluster with glass. The cluster
was thus changed by the addition of the glass, the greater accumulation
of nectar in consequence of fewer visits, and a corresponding increase of
fragrance. The abundance of nectar appeared to be the chief factor in the
association through which the bee gradually accustomed itself to the new
marks of the cluster and finally came to gather nectar from it almost
exclusively, so that it might be said to know it.
The following general statements were made with respect to the sigifi-
cance of color in the attraction of bees:
1. The assumption of Sprengel, Darwin, Mueller, Buttel-Reepen, and others that the
color of the flower brings about the attraction of the higher bees, Apis and
Bombus, has been established by the investigations of Forel, Andreae, and
Giltay.
2. However, since flowers 'with inconspicuous corollas are often abundantly visited
by honey-bees and bumble-bees (Ampelopsis, Vitis, Rhamnus frangula, Coton-
easter acutifolius, etc., with greenish flowers), the bright color of corolla or
inflorescence is not an indispensable condition. Still, color must play a sig-
nificant part in the competition of species for the visits of the most dependable
pollinators, since striking colors are more easily found than dull ones and since
these insects orient themselves in flight exclusively with their eyes (Buttel-
Reepen, Forel).
3. The return of a habituated bee to the plant is independent of the color signal,
probably indeed after the first visit, since the bees are able to refind the place
of the desired plant through optical orientation to the surroundings (Buttel-
Reepen, Giltay, etc.).
4. Guidance to the individual flowers of an inflorescence takes place by means of
vision. Normally the color of the corolla is the chief factor in guiding the bees
to the single flowers. Sometimes other features of the flower have a share in
this, and the removal of the corolla does not necessarily cause a cessation of
visits.
5. The distinction of flowers of the same color but different species by the honey-bee
is very probably due to the perception of odor when near at hand.
6. It is very probable that honey-bees and bumble-bees locate the nectaries of large
flowers by means of vision.
Chance observation of visits to imitations. — Plateau (1906:148)
has collected the records of the great majority of accidental observations of
visits to artificial flowers on hats, flower designs on tapestry or wall-paper,
and bits of colored paper or cloth. To these a few others are added here to
make the record complete and to permit a discussion of their significance in
the light of Plateau's criticisms. The first recorded instance of such visits
appears to have beeen made by Houzeau (1872:132), who stated that
Trevillian saw an individual of Sphinx convoluta fly along wall-paper orna-
190 PRINCIPLES AND CONCLUSIONS.
merited with brilliant flowers and try to probe the fanciful corollas. A
similar observation by Vallete (1875) had the fortunate consequence of
stimulating Plateau to undertake his first experiments, as already indicated
(p. 136), and this was followed by another one made on artificial flowers:
"After the experiments of Plateau, I watched for an opportunity to renew my
observations, the occasion for this presenting itself while I was at La Roche-sur-Yon
last October. An individual of Macroglossa stellatarum entered the room and per-
ceiving two baskets of artificial flowers, roses, violets and others, that decorated the
mantel-piece, flew precipitately toward them. But I must confess that he had barely
unrolled the ligule before the baskets when he flew away. He had recognized his
error, or at least this seems to be the explanation to be given. Led into error by the
sense of sight, the mistake was rectified by means of the sense of smell" (1878).
Burton recorded a corresponding observation the same year (1878:162):
"In going by steamboat from Como to Maggiore in September, 1875, I saw a
Macroglossa stellatarum dart towards some brightly colored flowers in a lady's hat,
hover a short time above them, and then fly away. It remained long enough to con-
vince me that it had examined the flowers and had recognized its error."
In a discussion of the mistakes made by animals, Romanes (1884:167)
cited the following cases:
"Again, the Rev. Mr. Bevan and Miss C. Shuttleworth write me independently
that they have seen wasps and bees visiting representations of flowers upon the wall-
paper of rooms and Trevillian saw the same mistake made by a sphinx-moth. Swainson
in his 'Zoological Illustrations' gives an analogous case in a vertebrated animal;
an Australian parrot, whose food is taken from the flowers of the Eucalyptus, was
observed endeavoring to feed on the representations of flowers on a cotton-print dress.
Likewise, Professor Moseley, F. R. S., informs me that he has noticed honey-seeking
insects mistake for flowers the bright-colored salmon flies stuck in his hat while fishing,
and Mr. F. M. Burton, writing to Nature, says that he has observed the humming-
bird hawk-moth (Macroglossa steUatarum) mistake artificial flowers in a lady's hat
for real ones. Still more curiously, the naturalist Couch observed a bee mistake
a sea-anemone (Tealia crassicomis) , which was 'covered merely by a rim of water,'
for a flower, darting to the center of the disk, 'and though it struggled a good deal
to get free, was retained till it was drowned and was then swallowed."'
Blanchard (1891), upon entering a hotel room in Adelsberg in September,
1890, found a sphinx- moth fluttering about, apparently deceived by the
seeming twilight. It successively examined each of the flowers, painted
in blue, violet, yellow, and dull red, that formed the cluster at the center
of the ceiling. The proboscis was extended, as though it were dealing
with real flowers. Disappointed by a lack of success, it left the ceiling to
explore, one after another, a large number of the yellowish flowers crudely
figured on the wall. It then went back to the ceiling, but visited only a
few flowers to make sure that it was not deceived the first time, and then
returned to the wall. After a number of fruitless visits to the flowers here,
it sought refuge in the hangings. Blanchard also reported a statement
of Alphonse DeCandolle to the effect that he had frequently seen sphinx-
moths dart to the flowers found on wall-paper.
The studies of J. Pe>ez on Macroglossa led to those of Plateau on the
same insect, which were designed to correct the impression that this was
due to an actual attraction by color. An earlier observation by his brother,
B. Perez, was reported as follows:
RELATED STUDIES AND CRITIQUES. 191
"A diurnal sphinx (Macroglossa stellatarum) entered my room, in which there is a
tapestry with a clear background strewn with bouquets of white and rose flowers
with green stems and leaves. For two minutes the insect flew from bouquet to
bouquet, stopping before 5 of them with the ligule unrolled as if visiting real flowers.
Afterwards he disappeared suddenly, possibly because I moved in the hope of observing
him more closely."
P£rez himself saw an individual of this same species fly abruptly from a
pot of flowers in a window to a small piece of rose-colored paper on the
pavement, but the mistake once recognized the moth disappeared like a
flash (1894). Several years later (1897), he stated that he had frequently
deceived this moth by placing bits of bright-colored paper on shrubs, and
that Eristalis also exhibited a similar response.
Lesne (1895) saw a fly of the genus Bombylius alight without hesitation
on an artificial violet of his sister's hat and insert the ligule in the corolla.
Not finding nectar, it passed at once to a second and then to a third in the
same manner before flying away a few paces to rub its tongue as though it
had been roughly treated. It was concluded that smell in the case of the
Bombylidae does not play the role ordinarily assumed, but that vision alone
enables them to discover the flowers that provide their food. However,
this was not intended in an absolute sense, since it was later stated that the
bee-flies are guided by both senses acting together in most cases. This
discrepancy was pointed out by Gazagnaire (1895) in the paper immediately
following, and it was contended that either or both senses acting together
could enable these flies to distinguish the flowers sought and that errors
would be frequent only when they were flying indifferently and not in
need of food. Schnabl (1896) related an experience of Schuch, who saw
a Macroglossa flying before a tapestry in a hotel room, on which were
represented flowers of Tropaeolum majus. It went to the flowers from time
to time in the endeavor to plunge its ligule into the corolla.
Bedford (1897), while walking down a street in London, noted a
butterfly (Pieris brassicae) following a lady's hat, which was ornamented
with artificial lilies of the valley. It made repeated attempts to light on
the flowers, but was prevented by the abrupt movements of the wearer
and finally gave up the endeavor. Parkin (1897) related the observations of
his friend Winstaley with respect to a honey-bee that entered his room.
This flew at first to some paintings on the wall opposite the window,
passed from one to the other in making the round of the room, stopping
for an instant before those with color, and then disappeared through the
open door. It returned and flew to the gas-globes, returned to the paint-
ings, went again to the globes, visited four glass objects on the mantel-
piece, and finally, after five minutes in all, departed through the window.
Thornley (1897), on one or two occasions when driving a pony whose
head was decorated with blue rosettes, saw a Macroglossa fly straight to
one of the rosettes and hover above it for several seconds, although the
pony had begun to trot.
Knuth (18982) recorded the case of Syrphus that flew to the flowers on
his wife's hat in a railway station at Leipsic. The flowers were greenish-
brown with a velvet sheen, but in spite of their inconspicuous character
and lack of fragrance, the fly hovered over them for several minutes, per-
192 PRINCIPLES AND CONCLUSIONS.
forming its characteristic evolutions. Gorka (1898) noted two individuals
of Deiliphila elpenor that flew along the walls of a pavilion painted with
crude flowers of Phlox and Verbena and attempted to plunge the proboscis
in the corollas. Lack of success did not discourage them, for they returned
after a moment to renew the attempt. In the instance cited by Motelay
(1898), a cabbage butterfly fluttered against the window of a florist's shop,
trying for 10 or 15 minutes at all parts of the pane to reach the flowers
on the inside. It appeared certain that it was attracted by vision and not
by smell, since the door of the shop was open but 6 or 8 feet away, and
especially since the butterfly passed the door as it flew away. Benary
(1900) stated that a bumble-bee, which entered a room through the open
door, flew at first to some natural flowers. After it had examined all of
these, it sought for nearly a minute to insert the ligule in one of the flowers
of the carpet. According to Aigner-Abafi (1900), Langhoffer saw a bee fly
through the open window of his lecture-room and go directly to a colored
botanical wall-chart. It flew to one cluster, working upward and then to
another flower, but finding itself again deceived it flew away.
Charlier observed that the males of Rhodocera rhamni were greatly at-
tracted by a piece of green paper 10 by 20 cm. moving gently in the sun-
shine. They alighted on it several times and moved about in an agitated
manner. Errera noticed a number of Hymenoptera flying about the hat
of a country-woman for fully a half-hour. The hat was trimmed with
artificial flowers, full-blown yellow roses and pansies, but the bees flew to
the former and neglected the latter. They were so numerous and their
behavior so striking that it was remarked by several people. He also
reported an observation communicated by Strasburger, who saw Macro-
glossa stellatarum light on the red oleander flowers of the wall-paper of a
room; the hawk-moth sought to visit the flowers one by one exactly as
though they were natural (Wery, 1904:1224, 1226). Van Bembeke, while
walking in a park at Ghent, saw a cabbage butterfly dart toward a piece
of red paper, light on it for an instant and then depart abruptly (Wery, 1. c).
In supporting his opinion that these isolated observations were without
value, Plateau cited the case of a Rhodocera that appeared to follow a
bicyclist in a dark costume, who was mounted on a wheel without bright
colors, pointing out that the presence of bright colors would have led to the
fallacious assumption of a real attraction. Instances of visits to bits of
paper were regarded as fortuitous and without significance, and it was em-
phasized that butterflies often light on objects having neither the form nor
the color of flowers, but provided with an odor. With respect to attraction
by the colored designs of wall-paper or tapestry, he remarked that several of
the accounts were given at second-hand and that some of these were merely
verbal, while as to those given by the observer himself, the latter was often
taken bj^ surprise. This fact, together with the poor light and the rapid
movements of the insects, made it probable that the findings would be
very different from those of an investigator prepared to follow the insect's
behavior. Moreover, Macroglossa and other insects were found to fly
along vertical walls without flower designs, the extension of the ligule
being without significance, since Breyer stated that this moth and the
sphinx-moths always fly with the ligule unrolled. Furthermore, if paint-
RECENT INVESTIGATIONS. 193
ings of flowers were to attract insects, colored posters bearing flowers
should do this in an evident degree, which is obviously not the case. Finally,
Plateau gave a list of eight objects, mostly dull in color, on which a bumble-
bee alighted in his study. Likewise, as to attraction by the artificial flowers
of hats, he regarded the cases as too isolated to be of value, those of an
actual attraction being explained by the presence of some dye possessing
an odor evident at least to certain insects.
Knoll's critique of Plateau's study of Macroglossa. — Knoll (1922:
363) points out that Plateau's failure to interpret the behavior of Macro-
glossa properly was due largely to not recognizing that the "darkness
flight" of the hawk-moth is a peculiar response of this insect. He was
also in error in thinking that the hawk-moth always flies with the ligule
unrolled, and was thus not in position to observe the finer details of its
behavior. As Perez contended earlier, the pieces of cloth and paper used
by Plateau were too large, as were also his artificial flowers. Moreover, the
colored objects often belonged to a different optical group from the flower
visited shortly before by the hawk-moth, so that the latter had no predi-
lection for them, contrary to the case when the color group was the same.
Since the depth of color plays an important part, it is not strange that the
few moths observed by Plateau did not notice the artificial objects in
which the color was less saturated than in the flowers. This was
especially true in the experiments with Anchusa italica, owing to its remark-
able deep-blue color. Finally, Plateau's arrangement of his test objects was
not a happy one. It has proved undesirable to place artificial objects in
competition with large plants in full bloom, as the insects fly directly to
the latter and visit the artefacts only by chance, and much better results
have been secured by intermingling the test objects and plants with few
flowers. The same effect can be obtained by removing the flowers in
part or, better still, by installing a path of flight in which the artefacts
are placed.
With respect to the vexillary role of the bracts of Salvia horminum, Knoll
remarks that the visits of three out of six hawk-moths to such clusters
constituted a positive result and not an error, and that this is to be explained
by the fact that Dianthus and Salvia belong to the same color group. He
also found these colored bracts without honey to be sought by the moths
in just the same manner as the usual violet honey containers and a similar
response was obtained in nature. He concludes that the bracts greatly
increase visibility at a distance and hence possess a definite vexillary func-
tion, contrary to the views of Plateau (cf. Frisch, 1914:4, 1919:3).
RECENT INVESTIGATIONS.
The color sense of the honey-bee. — Lovell was the first to carry out
extensive experiments on pollination in America, in which he had the un-
usual advantage of bringing to the problem the experience gained by
years of observation in this field. The first three papers of the series deal
with the color sense of the honey-bee, the fourth with conspicuous flowers
rarely visited, and the fifth with constancy. As indicated in the first (1909:
338), his investigations were stimulated by Plateau's conclusions that color
and form are unimportant and odor alone attractive to pollinators. In
194 PRINCIPLES AND CONCLUSIONS.
order to determine whether conspicuousness is an advantage to flowers,
the petals were removed from a cluster of 7 blossoms of Pirus communis,
which had received 8 visits in 15 minutes. No visits were paid to it in the
first 15 minutes after this, and but 2 in the second. When the petals were
removed from one of two adjacent clusters of 8 flowers, the normal received
11 visits in the 15-minute period to none for the mutilated one. Two groups
of flowers of Borago officinalis 6 inches apart received 15 and 13 visits
in 10 minutes; after the corolla and anthers were removed from one,
no bees came to it, while the normal yielded 7 visits. Although bees did
not go to the decorollate flowers, they twice flew to withered corollas on
the ground. In the case of a staminate flower of Cucurbita maxima, 12
visits were made in 10 minutes, 4 of them by Bombus terricola. The removal
of the perianth decreased the number of visits for the unit period to a single
one made by a bumble-bee, although a flower wilted and nearly closed
received 5 visits. Two staminate flowers with their corollas touching were
used in the next test; one received 6 visits, the other, 13 during a unit
period. The calyx-lobes and corolla were cut from the more attractive
flower, which then received no visits in contrast to 12 for the other.
Lovell explains the visits to the mutilated flowers of Digitalis purpurea
in Plateau's experiments as due primarily to memory of place, though
the corolla stump itself was not entirely inconspicuous, and cites in illus-
tration the visits of bees for a month and a half afterward to a window
where they had obtained honey. Bees were trained to visit a red-glass
slide with honey, and this was put in various positions, and a plain slide
added. All of these were found in 6 to 20 minutes as a consequence of
the reflected light, the color, and the odor, and this is regarded as
explaining why bees readily passed under the green leaves used by Pla-
teau for masking dahlia heads. These experiments were not well adapted
to the purpose and afford an insufficient basis for the conclusion that
bright colors are not advantageous to flowers.
Can bees distinguish colors? — In order to test the statement of Pla-
teau that flowers might as well be green as bright-colored and that of Bethe
that bees have no ability to acquire experiences or to modify them, Lovell
has repeated and extended the experiments of Lubbock with colored strips
of paper (1910:673). After a bee had been accustomed to visit a blue
strip with honey, strips of other color were added or exchanged with it
in various ways. Given a choice between blue and red, the bee went 4
times to the former and once to the latter. When blue, red, and yellow
were employed, blue alone was visited. With a wider range of choice the bee
went to blue 8 times, black twice, and once to red, yellow, and white,
the choice of some other color than blue occurring only after the slides
had been exchanged or the color changed. Out of the total of 21 visits,
15 were made to blue and not more than 2 to any other color, the bee en-
deavoring to be constant to blue in spite of loss of time and effort. When
a yellow and a plain slide were used, the bees made 20 visits to the first
in 30 minutes, entirely ignoring the second; flies went alone to the yellow,
and the wasps went to it in all but two cases. These results indicate that
Plateau was in error in assuming that artificial colors appear different
from natural ones to the bee.
RECENT INVESTIGATIONS. 195
Lovell has also repeated the experiments of Mueller with colored co-
rollas, making use of the yellow rays of sunflower, the blue perianth of
larkspur, and the red corolla of balsam. A bee accustomed to the sun-
flower yellow made 9 visits to it and one to blue, and in other experiments
with these slides the bees discriminated readily between the colors. When
bees trained to red were given a choice between a red slide and a plain
one, they made 46 visits to the one and but 8 to the other. To determine
the effect of habit in this case, a blue slide was substituted for the plain one;
the first visits were 8 to red and 2 to blue, but at the end this had changed
to 3 for red and 7 for blue, the respective totals being 22 and 24. A number
of instances are cited from the experience of practical apiarists to show
that bees distinguish colors readily, and it is stated that "it may well be
doubted whether they would ever have been capable of making long journeys
afield for nectar and pollen, if this visual power had been wanting."
When a bee trained to blue was given a choice between seven or eight
colors, it remained constant to blue or purple for several visits, but its
fidelity to them was weakened by repeated transpositions, until similar-
ity of form, honey, and odor prevailed over the difference in color and
visits were then made indiscriminately. In nature a bee usually finds
in one flower only a part of a load of nectar and is compelled to go to other
blossoms; if these are alike in form they will then be visited regardless
of differences in color, especially when a number of bees are present. In
conclusion, Lovell states that bees easily distinguish colors whether arti-
ficial or natural and are more strongly attracted by a colored than a plain
slide. Bees trained to a certain color tend to return to it habitually, but they
quickly learn to ignore the color differences when it is to their advantage.
The pollination of green flowers. — Lovell (1912:83) discusses the re-
lation of insects to green flowers and points out that the phylogeny of
such flowers as developed by Bessey (1897, 1907) strongly supports the
view that they are not well adapted to pollination by insects. He ad-
mits that bees will collect sweet liquids from green or dull-colored sur-
faces, after they have once been found, but states that this does not prove
that bright colors are not an advantage to flowers. When a bouquet of
Gerardia purpurea was placed in front of a hive, it received little attention,
but when two clusters, one normal and the other decorollate, were provided
with honey, the former received many visits and the latter none, until
later, when the bees discovered the honey on them. In order to vary the
conditions under which the objects were exposed, bees were trained to
visit a small dull-gray board bearing a small quantity of honey, raised
on a support 2 feet high. A slide prepared from the blue perianth of a
larkspur and provided with honey was placed on the grass 3 feet from the
support and honey was also placed on a dandelion leaf 5 feet away and 3
feet from the support. As soon as the honey on the feeder was exhausted,
the bees began to circle in the air. In a few minutes 1 bee had found the
blue slide and in 25 minutes 5 bees found it, though none had discovered
the honey on the leaf. Two days later the experiment was repeated, 3
bees finding the blue slide within 2 minutes after the honey had disappeared
from the feeder. In 7 minutes there were 8 bees on the slide and none on
the green leaf, 1 bee finding the latter 5 minutes later. Two poles 4.5 feet
196 PRINCIPLES AND CONCLUSIONS.
high were then placed 6 feet from the support and 6 feet apart; the top
of one was covered with a large amount of honey, while to the top of the other
was attached a cluster of yellow immortelles many years old. Within 3
minutes after the honey disappeared from the feeder there were 3 bees
and a fly on the flowers, but none on the free honey; later there were 6
bees and 1 fly on the flowers and 1 bee on the free honey, the total num-
ber of visitors to the flowers being three times greater than to the free
honey. When the poles were transposed and a single immortelle placed
on the one that had the supply of honey previously, both being provided
with honey, the cluster showed 10 insects at the same time that the single
flower gave 4.
In later experiments a yellow immortelle with honey was placed 9 feet
from the feeder and a considerably larger apple-leaf with honey at a equal
distance on the opposite side. Three bees came to the flower and none
to the leaf, the small number apparently due to the fact that they were
looking for sugar sirup which they had been eating on the feeder. The
number of visitors was larger in other cases, but in spite of this the leaf
did not receive a single visit. When a head of golden glow and the end
of a spike of Amarantus were used, the head yielded 18 visits to 8 for the
spike, but when they were laid side by side, there were 15 visits to the golden
glow to 3 to the spike in one case, and 18 to 5 in another. In further studies
with a green and bright-colored object placed on a green background
or with conspicuous and inconspicuous objects, which extended over three
seasons, there were no visits to the inconspicuous objects in 6 cases, while
in the others the number of visits to the conspicuous object was usually
two or three times greater. The preference was sufficiently marked to
account for the development of color contrast in flowers and shows that
the experiments and observations of Plateau on green or greenish flowers
were fallacious.
Conspicuous flowers rarely visited by insects. — In testing Plateau's
conclusion that bright color is without significance because certain con-
spicuous flowers are commonly neglected, Lovell (1914:147) made ob-
servations and experiments on some of the same species, in addition to
others. The nectarless flowers of Clematis jackmanni were not only found
to be visited, but the number of visitors was greatly increased by putting
sugar sirup on some of them, showing that the presence of an agreeable
odor was unnecessary, contrary to Plateau's assumption. It was deter-
mined that the real reason for the general absence of visits to the garden
pea and the sweet pea is the inability of most pollinators to depress the keel
and open the flower. In these flowers neither color nor odor will induce
frequent visits, since nothing is to be gained by them, but the addition
of an odorless sirup causes bees to go to them in large number. Similar
results were obtained in the case of petunia, the addition of sugar sirup
bringing many bees and small Diptera, and the honey-bees continuing
to come for many days after the sirup was gone. In the case of a variety
of Pelargonium zonale with neither nectar nor pollen, no insect visits were
observed to the normal flowers, but the application of sugar sirup ultimately
brought them, the bees repeatedly searching the normal umbels after the
supply was exhausted. Later they flew to a bed of Portvlaca grandiflora,
RECENT INVESTIGATIONS. 197
which is habitually ignored, and inspected flower after flower, but rarely
alighting. The use of sugar sirup also brought visitors to other flowers
ordinarily neglected, such as zinnia and the scarlet runner.
Interesting instances are given of the role played by variations in the
length of the corolla of red clover and the amount of nectar in alfalfa
in determining the visits of honey-bees, and many cases are cited to show
that the latter occasionally make careful examination of flowers commonly
neglected. Such visits are infrequent because the bees remember their
inability to obtain food. In the aggregate they waste much time in fruit-
less visits to flowers that yield no booty for one reason or another, but
this waste is reduced to a minimum by their ability to learn from expe-
rience. Thus, insects do perceive the colors and forms of neglected flowers,
and the rarity of their visits is the result of recalling the absence of nectar
or pollen and not because the flowers lack an agreeable odor, which,
moreover, is often not the case.
Response of honey-bees to colored artefacts. — Turner (1910:257)
has carried out investigations —
"To see if, in the field, bees can be trained to respond to colored artefacts, and,
after a bee has thoroughly learned to collect honey from an artefact of a certain color,
to see if it can select those of that color from numerous others of a different color;
first, when the artefacts to be selected contain honey and the others do not; second,
when some of each kind contain honey; third, when none of the artefacts contain
honey; fourth, when the brightness content of the artefact to be selected is changed
without altering the hue. In furthering the first aim, honey was placed on disks of
a certain color and exposed in a field from which a large number of bees were col-
lecting honey. At first these disks were not attended to; but after a lapse of several
hours a few bees began to collect from them. After a few bees had acquired the habit
of collecting from disks of a certain color, three different series of experiments were
conducted; one with disks, one with cornucopias, and one with small boxes, each
provided with a small opening. In each of these series a large number of artefacts of
two colors, half of which were of the color of the disks from which the bees had learned
to collect honey, were scattered promiscuously among the flowers from which the
bees were foraging. The artefacts of the color from which the bees had learned to
collect honey were supplied with honey, the others were not. All of the artefacts
containing honey were visited by numerous bees; no bees visited the others. Control
artefacts of the color from which the bees were collecting honey were well supplied
with the latter and placed in portions of the field where the bees had not been trained
to feed from artefacts. Although the bees were numerous, these artefacts were not
visited. At intervals artefacts of the color from which the bees had not been trained
to forage were supplied with honey and scattered among the others. As a rule these
were not visited. At the close of both the second and third series of experiments,
all of the artefacts were removed from the field; and two artefacts, one of each color,
both new and neither containing honey, were exposed in the field. In a few minutes,
the artefact of the color that had formerly marked those that contained honey was
completely packed with struggling bees. No bees entered the other artefact. In
each series the artefacts were distributed in both the sunshine and the shadow. All
were equally visited by bees. Since the brightness content in the two cases was
different while the color was the same, it was concluded that the bees were reacting
to color as such. It is thought that these experiments prove that bees can discriminate
between colors."
198 PRINCIPLES AND CONCLUSIONS.
Pattern vision in the honey-bee. — In experiments on this subject,
Turner (1911:249)—
"Made use of pasteboard boxes like those employed in his experiments on color
vision in the same insect. He constructed artefacts showing seven different color
patterns. Bees which had been trained to gather honey from one pattern were tested
to see if they could choose this pattern from one or more of the others. In some cases
the artefact of the pattern to be chosen contained honey, while the rest had none;
in other cases there was honey on some of the artefacts of all patterns, and in still
others there was no honey on any of the artefacts. Five hundred and eight correct
selections out of 518 were made, indicating that color patterns are perceived by bees.
Since they can distinguish both color and pattern, no evidence can be drawn from the
visual powers of bees against the hypothesis that colors and patterns in flowers are
adapted to secure the visits of insects."
Experiments with cotton blossoms. — Allard (1911:607) has made
a large number of interesting experiments with single cotton blossoms.
The normal flower, modified flower, and control were disposed at the corners
of a triangle and about 4 feet apart, or in a line in the same row. Petals
pinned to a stem received as many inspections as the normal flower, almost
all of them being made by Melissodes. The number of entrances was less
than one-fifteenth the number of inspections, and at all times the actual
visits were few. When the petals of one of the same group of flowers were
removed, the inspections dropped from 81 to 4, though they actually in-
creased for the other normal flower. Replacing the petals brought the
inspections up to those for the normal, but when cloth petals from an artificial
rose were employed, the number dropped to 4 in comparison with 48 for the
normal control and 65 for the petals alone. Five cotton petals were then
placed over the cloth ones and the number of inspections again rose to
a point slightly above that for the control. The next installation con-
sisted of a normal blossom in situ, one pinned in position, and an
artificial half-opened bud made by pinning normal petals together and
wrapping a piece of green cotton leaf about the base. The latter received
practically the same number of inspections as the most visible control. This
was next modified by concealing one of the normal flowers so that it was
visible only from above; this yielded 1 inspection to 12 for the control
and 40 for the artificial bud. Removing the disguise caused the flower
to be inspected twice as often as the control. The substitution of crepe-
paper petals led to the reduction of inspections to 2 in contrast to 16 for
the control, while placing three real petals on the paper ones increased
them to 11 in comparison to 7 for the control and 21 for the artificial bud.
The following installation comprised a single real petal pinned to a
stem, an artificial bud made by wrapping a portion of a cotton leaf about
the base of 5 petals rolled together and a normal in situ; these received
2, 8, and 3 inspections respectively. A single petal in competition with
a normal blossom alone obtained 16 inspections to 26 for the latter. In
the following experiments the flowers were on 3 consecutive plants in the
same row. The first consisted of a flower of bindweed between two normal
flowers pinned in position, which attracted attention as often as the nor-
mals, but was entered less frequently. When the petals were removed
from one of the controls, this received no inspections to 19 for the bindweed
RECENT INVESTIGATIONS. 199
and 20 for the normal control. When a single petal was placed on the de-
corollate flower, the latter yielded 8 inspections to 9 for a single petal
pinned to the stem and 27 for a normal flower; changing the relative
position of the three gave 27, 8, and 22 inspections. Placing the smaller
brighter yellow blossom of an Asiatic cotton between two normal flowers
of the American variety resulted in 14 inspections for the former and 20
and 29 for the latter in one case, and 10, 16, and 20 in another, while putting
the foreign flower at one end of the series gave 3, 10, and 11 respectively
in one instance and 11, 12, 9 in the other. A day-old blossom of a deep
reddish-purple color received 12 visits to 26 for a recently opened cream-
colored one. Four experiments with two controls and a normal blossom
with honey added at the base of the petals, arranged in varying order,
gave respectively 62, 64, and 66 inspections, the actual visits being but 2
for the flower with honey to 27 for the other two.
The petals of a normal bloom were covered on both sides with cotton
leaves cut to match and a drop or two of honey added. When this was
exposed with a control with honey and one without, the inspections were
respectively 0, 34, and 25, the actual entrances being 0, 2, and 6. In the
next installation the pieces of leaf were removed from the outside of the
corolla and this was exposed with a normal flower and one with the petals
removed. The respective inspections were 9, 11, and 1, while the actual
visits were negligible. When one bud due to open the next day was pulled
fully open and another but partly so, the first was inspected 15 times to
twice for the latter and 24 for the normal, the latter receiving 14 visits
to none for the other two. To entirely eliminate the effect of odor, a glass
plate was fixed before a flower and leaves drawn in about the edges to con-
ceal most of the plate but leave the flower fully visible. This received 18
inspections in contrast to 37 for the normal. When a flower was placed
in a box with a glass face, it was inspected twice to 5 times for the control.
With a crepe-paper blossom of the proper color added, the boxed flower
was inspected once, the normal 8 times, and the imitation 3 times. In the
final experiments, detached petals were usualty inspected, but the numbers
were too small to be very significant.
The simplicity and variety of Allard's experiments, coupled with the
use of single flowers and constant controls, give his results an excep-
tional value. They emphasize the attractive value of the color at the ex-
pense of odor and suggest that the latter merely guides bees from a distance
or from one field to another. The discrimination between artificial flowers
and normal ones is thought to depend upon perceptible differences in color
and texture rather than to the presence of repellent odors from the material
and support the view that bees develop keen powers of discernment as
to the structural details of flowers.
Color sense and memory in the honey-bee. — Dobkiewicz (1912:664)
carried out three series of experiments dealing respectively with the color-
• sense, memory, and learning ability of the honey-bee. The first series
employed crude artificial flowers of yellow or red paper placed at the same
spot in a clover field. No visits were made to installations of 10 yellow or
10 red artefacts without honey, or at first to 5 of each color with and with-
out honey. For the next experiment the blue artefacts were removed,
200 PRINCIPLES AND CONCLUSIONS.
after which a single bee appeared, soon followed by two others. A half hour
later the honey flowers were actively sought, while those without honey
were completely neglected. When the yellow flowers were more widely
separated and the blue ones so interspersed that one with honey occupied
the former position of a similar yellow one, the blue imitations were neither
inspected nor visited, though the yellow were busily probed. Placing the
two kinds of yellow artefacts in pairs caused those without honey to be
often inspected, but the bees quickly learned the position of the honey ones
and paid no further attention to the others. Further experiments likewise
showed that when the bees did not at first know all the honey artefacts,
it was necessary for them to make orienting flights over the two kinds.
However, the flights of inspection over the flowers without honey gradually
diminished to the point of disappearance. With respect to memory, the
second series of experiments indicated that colored objects do not attract
bees that are busily at work if they have had no previous experience with
imitations. However, when they have repeatedly found honey in an arte-
fact of a certain color in one spot, the color continues to exert attraction
even when honey is absent, and small displacements of position are imma-
terial. It was also demonstrated that bees habituated to gather from honey
artefacts at a certain time, namely, 11 to 1 o'clock, did not react to them
at a different time, showing that they take note of time as well as of color
and place. Further experiments showed that the bees were able to make
use of two colors in adjusting themselves to new conditions and that they
utilize their sense of color in different and unexpected relations. In short,
they are not reflex machines, but their behavior has the stamp of purposeful,
intentional acts.
Frisch's researches. — Sense of color and form in the honey-bee. —
Frisch has discussed the color and form sense of the honey-bee in a mono-
graph of fundamental importance (1914), as well as in shorter articles
(1913, 1919). At the present time it is possible only to indicate the scope
of his treatment and the general method, and to give his conclusions. The
original itself must be studied by all those who wish to carry on accurate
work under controlled conditions. The treatise is divided into the follow-
ing main sections: (1) demonstration of a color sense; (2) nature of the
color sense; (3) the color sense of the honey-bee and flower colors; (4) sense
of form and its significance in flower visits ; (5) unsuccessful training experi-
ments with unnatural forms; (6) biological notes; (7) practical significance
of painting hives in color. The method of experiment consisted essentially
in training bees to come to a watch-glass of honey placed on a particular
color and following their behavior when such colored squares were variously
arranged among gray ones, ranging through all possible shades from white
to black and likewise provided with glasses of honey. After two days
training with two papers of dull yellow disposed among 30 gray ones, two
new yellow papers and watch-glasses, unused and hence free from the odor
of bees, were placed in a different position from the first two, which were
removed and gray ones substituted. All the watch-glasses were then filled
with sugar solution, thus making the conditions on all the papers identical,
except for color and brightness. Thus, if the bees were entirely color
blind they would see yellow only as a certain degree of brightness without
RECENT INVESTIGATIONS. 201
color and would visit the corresponding shade of gray in similar number.
If they saw color as such, the yellow papers should receive more visits than
all the gray ones. This is what actually happened. The bees flew without
hesitation to the yellow papers and crowded together on these about the
sugar-solution, while the watch-glasses of this solution on the gray papers
remained neglected. Frisch's conclusions were as follows:
1. Bees possess a sense of color. This is proved by the fact that if they were totally
color-blind they would see each color, for example, blue, only as gray of a certain brightness.
In a series of gray papers that grade insensibly from white to black must occur a gray paper
that would be identical to the bee with a blue one in form, extent, and surface character.
Once trained, however, it is able to distinguish the blue paper with certainty from all the
shades of gray. The gradations of the gray series were sufficiently fine, as demonstrated
by the fact that training for a particular shade of the series was unsuccessful. The objection
that the bees may have recognized the colored paper by means of a particular odor imper-
ceptible to us is removed by the fact that the experiments gave the same results when
the colored and gray papers were covered with a glass plate or sealed in a glass tube.
2. The bee confuses red with black and blue-green with gray. It distinguishes only
"warm" and "cold" colors and mixes orange-red with yellow and with green, blue with
violet and purple-red. Thus, its color sense shows a close agreement with that of a
man color-blind to red and green (protanopic).
3. The colors that are not seen as such by the bee, such as blue-green and pure red, are
extraordinarily rare in the flowers of our flora. This supports the view that the colors of
flowers have developed in adaptation to their pollinators, and all the more since, in exotic
flowers adapted to pollination by birds, scarlet-red blossoms predominate and blue ones
are strikingly infrequent. In many flowers are found several colors combined which
contrast strongly. Such "contrast colors" have been regarded as adaptations to insect
visits, especially when they appear in the form of nectar guides. However, our new
knowledge indicates that color differences which are conspicuous to our eyes can not be
assumed to be such for the eyes of the insects, but closer examination shows that this
presents no serious difficulty. We find that the varicolored flowers combine almost exclu-
sively such colors as stand out distinctly from each other in the bee's eye. On the other
hand, the biological significance ascribed to changes of color during anthesis is not to be
accepted in the fullest sense.
It has appeared a striking fact to students of flower biology that blossoms with the most
complete adaptation to allogamy and particularly fitted to the visits of honey-bees and
bumble-bees should be blue or red-purple. This has been explained by the assumption
that such colors are the favorite ones of bees. On the contrary, my experiments show
that for the bee's eyes blue and red-purple contrast most strongly with the green of leaves,
and hence range themselves readily with the other characters by which the bee flowers
reveal their greater adaptation to insect pollination in contrast with the more primitive
flowers of this kind.
4. From the observations on constancy it follows that bees recognize the flowers of
one species as belonging together and hence distinguish them certainly from those of
another species. Since they possess no finer sense of discrimination for color nuances,
they must consequently utilize other features than flower color. Thus it may be shown
that form and combinations of color serve bees as indicators, and the significance of nectar
guides is partly to be sought in this connection.
5. It is of psychological interest that the training of bees is unsuccessful when it demands
of them the discrimination of forms that are completely unknown to them in nature, e. g.,
geometric figures.
6. The question whether color striping of the hive facilitates the return of the bees
to the proper hive must be answered in the affirmative. How closely the bees observe
hive-color and use it as a guide is shown by the fact that returning bees can all be decoyed
into a wrong empty hive by a change of color. Misled by the color of the hive, they even
seek to enter occupied hives, where they are received in the most unfriendly manner.
The supposed color sense of the honey-bee. — In a series of papers
(1913-1919), Hess has imitated Plateau in challenging all the studies and
202 PRINCIPLES AND CONCLUSIONS.
conclusions as to the ability of bees to distinguish colors as such. It is
now impossible to deal with his experiments and criticisms in detail, and
it must suffice to give the summaries of the two papers that treat this
question directly. These will serve also to reveal the attitude of the author,
who goes far beyond Plateau in rejecting unqualifiedly the results of those
who do not agree with him.
"It has been demonstrated that the earlier conclusions of Lubbock and Forel, as well
as the later ones of Frisch, in accordance with which it is possible to train bees to discrimi-
nate a particular color, are incorrect. If the colors are presented under conditions other-
wise identical, the bees find it wholly impossible to habituate themselves to a certain color
and to respond to it. The errors of the earlier investigators are in part to be ascribed to
the fact that they either ignored the contributing factors emphasized by me or failed to
take them sufficiently into account.
" Up to the present time not a single fact has been adduced that makes even probable the
assumption that bees possess a color sense comparable with ours. On the contrary, my
earlier researches with spectral and other rays as well as the later ones with colored papers
refute this opinion conclusively. In virtue of the results contributed by me, which are
readily demonstrable, the view of Sprengel as to the significance of flower color in insect
attraction can no longer be maintained." (1913: 105.)
"It has been demonstrated that every training experiment with bees, which has been
thought to prove their color sense, affords complete support to my researches which show
their total color-blindness. Moreover, Frisch's record shows, in entire agreement with
mine, that bees supposedly trained to blue or yellow were unable to distinguish the two
colors, but much more frequently confused one with the other or with gray.
"The inadequacy of the method of training experiments is forcibly exhibited by these
new observations and measurements. Furthermore, the objections recently raised from
the zoological side to my investigations are vitiated by the results given here. Finally,
even Frisch himself has removed the last prop from the concept of color sense in the bees
by his training experiments and the Freiburg results." (1918:365.)
Frisch (1919:122) has made an effective rejoinder to Hess's statements,
as is indicated by the following excerpts :
"Hess begins his real objections with the surprising assertion that my record shows
that the bees were unable to distinguish blue and yellow from gray, and also blue from
yellow. I wish to ask him how he can advance such a statement when he must have seen
from my record that the bees trained to yellow discerned the latter and discriminated
between it and all the shades of gray in all seven experiments in which a yellow paper was
exposed in the gray series; that further, the bees trained to blue selected this color and
distinguished it from the gray shades in the entire 15 experiments with blue similarly exposed;
that bees trained to yellow sought this in overwhelming majority in competition with blue
and purple in all eight experiments, and finally that bees trained to blue chose blue and
purple just as decisively in 25 of the 26 tests with the complete color series, the exception
being readily explained by the circumstances (p. 126).
"I have shown that bees trained to blue for two days were able to distinguish with
certainty a blue paper, which, according to Hess, they see as a colorless gray of a particular
shade, from gray papers of any shade. In order to remove the objection that they directed
themselves to the blue paper by virtue of an odor imperceptible to us, all the papers were
covered by a glass plate. When the mass of bees above the blue paper were brought upon
a gray one by moving the glass plate, the mass dissolved within ^ to J^ minute and a new
one formed upon the blue" (p. 135).
Seasonal change in the response to honey. — Zander (1913:711)
found that, while honey exposed in summer stood day after day without
visits from honey-bees, in agreement with the results of Forel, it was sought
by hosts of them in September. This led him to make similar tests at inter-
vals of about two weeks from the end of April to the beginning of October.
RECENT INVESTIGATIONS. 203
The honey was placed in a small porcelain dish covered with gauze, so that
the odor could escape but the honey itself could not be reached and thus
exhausted. This was exposed on the threshold or the top of a hive and
observed for a quarter to a half hour during the period of the best morning
flight, the temperature, humidity, wind direction, and condition of the sky
being recorded, as well as the honey increase of a test hive and the kind and
condition of the flowers available. On June 1 and July 6 no bees were
attracted to the honey, while on April 30, May 15, June 15, July 15, and
August 1, the respective numbers were 7, 3, 6, 7, and 1. On August 15,
13 bees were noted, 23 on August 30, a host on September 16, and 15 to 20
on the 30th. The most striking relation was the inverse one to the number
and abundance of nectariferous species and the nectar flow. The visitors
to the honey were few or none until the flowers decreased greatly or dis-
appeared altogether, when they increased from two to several fold. Zander
regarded the observations of June 1 and July 6 as the only ones that sup-
ported Forel's view as to the bee's feeble sense of smell for honey, but it
would appear that all the observations that yielded but 1 to 7 visits should
also be considered as evidence for this, if those that gave 20 to many vis-
itors be adduced in proof of a keen sense of smell. Interesting as the
experiments are, they fail to reckon sufficiently with the effect of habit
on the one hand and the tendency of bees to attract others on the other,
to be entirely conclusive. They do show, however, that the sense of smell
is psychic as well as physical, in that the stimulus of the odor of honey is
much less effective in the midst of the obsession produced by an abundant
flow of nectar.
The sense of smell in the honey-bee. — Frisch has supplemented his
studies of the attraction exerted by color by a second outstanding research
on the sense of smell in the honey-bee (1919:1). As this likewise became
available only after the present book was in type, it must suffice to
indicate the main heads of his treatment and to give the essence of his
summary. The main divisions of his treatise, which has the proportions
of a book, are as follows: (1) exposition of the experimental technique, and
discussion of the question whether bees are attracted by the odor of flowers;
(2) ability of the honey-bee to discriminate between different odors; (3)
odor and color; (4) memory of the honey-bee for odor and color; (5) do
scentless inconspicuous flowers that are much visited by bees have a fra-
grance imperceptible to us? (6) the odor of honey; (7) the fineness of the
sense of smell in the honey-bee (the "minimum perceptibile ") ; (8) experi-
ments with mixed odors; (9) the biological significance of the fragrance of
flowers; (10) experiments with odorous substances of different chemical
composition but similar odor; (11) training with lysol, skatol, etc., a con-
tribution to the psychology of the honey-bee; (12) summary.
The first questions to be decided were whether the honey-bee perceives
the odor of flowers and whether it is guided by such perception in its visits
to flowers. The answer in both cases is affirmative, since training for flower
odors has always met with complete success. But in addition to odor
itself, its quality must be taken into account. Bees trained to the fragrance
of acacia visit this alone and are not in the least attracted by the odor of
the rose or lavender. Bees trained to the odor of the oil from orange-peel
204 PRINCIPLES AND CONCLUSIONS.
distinguish this by smell from 43 other essential oils with the greatest
certainty, and are attracted only by a similar oil of different origin and by
bergamot and cedar oils. It is not especially noteworthy that the essential
oils which are similar to our sense of smell should be the very ones confused
by the bees, since they are related in origin and chemical composition.
Comprehensive experiments with paired odorous substances of different
chemical constitution but smelling alike to us have shown that many of
them are also confused by the bee, and that a similar grade of likeness
appears to exist also for it. This indicates that the physiological basis of
the sense of smell in man and in bees has more in common than has pre-
viously been supposed for organs that are anatomically so different. How-
ever, in detail the two show considerable departures. Many odorous sub-
stances, very similar to us but easily distinguishable, were mixed by the
bees, and on the contrary the latter distinguished with great accuracy others
that can not be discriminated by us.
When bees trained to both odor and color were exposed to the two sepa-
rately, the behavior was complex, but it was regularly the case that the color
was perceived at considerable distances and the odor only near at hand,
even when strong odors were borne toward the bee by a gentle wind.
This and other observations support the assumption that the sense of smell
in bees is not materially keener than in man. It might be supposed that
the perception of odors related to their life activities would be greatly en-
hanced in bees, and that they would perceive the odor of nectar or honey
at great distances. However, this is not supported by the results. A
honey fragrance that is little or not at all perceptible to man also gives no
positive results with bees. With a stronger honey odor an actual training
can be effected, but the observations of other investigators that have led
to the assumption of its attractive effect at a distance can be otherwise
explained. The honey odor is probably nothing more than the fragrance
of the flower that has been absorbed by the nectar, and it is understandable
that it should affect the bee like any weak fragrance of this sort.
Some evidence exists for the assumption that many flowers which are
scentless for us have a strong odor for bees, and this has been assumed for
the wild grape especially. However, it can be demonstrated that these
flowers have just as little odor for bees as for us, and this is true likewise for
the bilberry and the red currant. Outside of these three species there are
but few whose blossoms are both inconspicuous and scentless, and yet
visited by bees. These are trees or shrubs, or plants that grow in extensive
closed masses, with the consequence that they are easily found by bees.
The experiments with mixed odors show that the fragrance of scattered
flowers, even when marked, can be effective only in the immediate vicinity,
where it is pure and unmixed.
While fragrance has been regarded as a means of attracting pollinators,
this is not wholly correct; at least, it does not fully characterize its function.
When a bee has found the food desired in a particular species, it brings its
companions with it and these then haunt the plant with great persistence,
distinguishing it with the greatest assurance from all others. Inasmuch as
they see only "yellow," "blue/' and white flowers out of the entire series of
shades, they must make use of other characters to discriminate between
RECENT INVESTIGATIONS. 205
the various species. Thus, flower fragrance is a distinguishing mark for
bees, and perhaps the most important one that the flower possesses. In
the light of this fact, it is readily understood how bees can remember for
days or even weeks an odor to which they have been trained for a short time
only.
It seems significant of the psychic processes in these highly organized
insects, which are able to perceive flower odors so quickly and to make use
of them, that they refuse almost completely to respond to training experi-
ments with foul-smelling substances, and that certain other odorous sub-
stances give only poor training results. There seems no other explanation
of this than the assumption that there are odors which had been without
significance for bees through countless generations and to which they
habituated themselves not to respond. In like manner they readily learn
to distinguish forms which suggest those of flowers, while training them to
geometric figures is completely unsuccessful.
In their entire behavior bees show in their sense of smell an agreement
with that of man which is as far-reaching as it is unexpected. All of the
32 odors to which they were trained are effective for them, as for us. All
the substances tested that are inodorous for us are equally so for them. Sub-
stances with strong odor for us are likewise strong for bees and the reverse,
just as those that are similar for the one are alike for the other. Thus, it
is possible to evaluate the biological significance of flower odors with far
greater certainty than heretofore.
Bombylius and the colors of flowers. — Knoll has presented the
results of his investigations of the behavior of Bombylius and Macroglossa
in two comprehensive monographs, which must be ranked with those
of Frisch with respect to the detail and accuracy of the treatment. The
first deals primarily with the response of Bombylius fuliginosus to the flowers
of Muscari, under the following headings: (1) main objects of the experi-
ments; (2) experiments, (a) choice and preparation of the experimental
area, (b) determination of the optical attraction of flowers, (c) studies of
the chemical attraction of flowers, (d) experiments with Frisch's methods,
(e) near-by attraction of Muscari; (3) constancy of Bombylius in its visits
to certain flowers and the behavior of other species of the genus to the same
flowers; (4) general considerations on the color sense of Bombylius and that
of the honey-bee. The experimental results showed that the flowers of
Muscari attracted this fly at a distance by color and form and that fragrance
had no part in this. It was also found that Bombylius possessed the ability,
though probably in smaller degree than in the honey-bee, to associate the
color of a flower and the presence in it of an easily accessible store of nectar.
Further, since this fly visits the brightest or pure white flowers as well as
the less bright ones of the blue group, but ignores the deep yellow, which
are also very bright, it seems that the attraction is determined by the quality
of the color rather than by its intensity. It may be assumed that the
color vision of insects and of vertebrates has been developed independently
on the basis of the independent evolution of the sense organs and the related
nerve systems. A consideration of the structure of the sensory apparatus
and the central organ of the two groups confirms us in the assumption that
206 PRINCIPLES AND CONCLUSIONS.
a more or less different expression of physiologically similar functions must
result from organs so differently constituted.
As a consequence of what has been said, a part of the teaching of Sprengel
as to the ecological significance of the color of flowers can be accepted by
modern flower biology without modification. One reservation must be made,
however, to the effect that the two insects so far investigated, the honey-bee
and the bombyliad, possess a different optical perception of what appears
to us as pure red or blue-green in color and that in consequence neither of
these colors can exert an attractive action on these insects in connection
with pollination. However, the questions as to the nature of insect vision
and the ecological significance of the details of color and marking in flowers
can not be conclusively answered with our present knowledge.
Vision and flower behavior of Macroglossa stellatarum. — The sec-
ond half of Knoll's monograph on insects and flowers treats of the response
of the hawk-moth to light and color, as well as to flowers, under the follow-
ing main captions: (1) observations on the life-history of Macroglossa; (2)
experiments on the vision of Macroglossa; (3) the food instinct in Macro-
glossa and its evaluation for the study of the color sense; (4) experiments
with freshly hatched moths; (5) the behavior of the female during the period
of egg deposit; (6) flower visits and fragrance; (7) critique of the experi-
ments of Plateau (p. 164); (8) notes on other Lepidoptera; (9) summary.
In its flights for nectar, Macroglossa observes objects of a certain optical
quality, but not those of a different one. In addition to the dark colors,
it often visits also the paler ones and pure white, but takes no notice of
green plant parts, and just as little of the gray, black, or brown objects of
its environment. With the hawk-moth, as with the honey-bee and the
bombyliad, two groups of colors come into especial consideration, namely,
blue and yellow. When it has obtained its nectar for some time solely
from an object of a definite optical character, under certain conditions
there appears an association with such an object. In the attraction of this
moth from a distance the fragrance of flowers plays no part, as this appears
to be true also for the immediate proximity of the flower. This result was
entirely unexpected, as it has been generally assumed in flower biology
that the marked fragrance of many flowers was a direct adaptation to the
hawk-moths. However, this particular species does not lack the faculty of
perceiving plant odors, since the odor of Galium leads the female to deposit
her eggs upon it.
A newly hatched hawk-moth flies directly to certain flowers, in spite of
the fact that it has had no individual experience with them. In doing
this it distinguishes the color of the blue and yellow groups from green and
the various grays. Thus, there is present in the inexperienced moth a
predilection for objects of a certain optical effect. This effect is given in
nature only by flowers, so that the young insect may go quickly to its food
in consequence. The action of certain optical stimuli in the process of
flying to the flowers and the consequent possibility of acquiring experience
by means of vision furnishes the basis for a part of the constancy of the
hawk-moth. This utilization of animal experience has already been made
by other investigators in this field, notably by Frisch with the honey-bee.
A comparison of the results shows that there is no essential difference be-
RECENT INVESTIGATIONS. 207
tween the color sense of the honey-bee and that of the hawk-moth, as is
equally true for the latter and Bombylius.
Since attraction from a distance is a matter of vision, the hawk-moth
will regularly visit only those flowers that belong to its particular color
groups. This is supported by the records of visits, which show that the
flowers commonly sought are blue or purple in color, though in southern
Europe the yellow flowers of Linaria vulgaris may be exclusively visited.
This difference in behavior in various regions may be regarded as a passing
stage of the natural association, and therefore as a consequence of the insect's
experience. To effect pollination it is desirable that the hawk-moth visit
the flowers of one species for as long a period as possible. Therefore, all
the features of the flower are of significance that produce and fix the associ-
ation of the moth with this particular species. Of paramount importance
in this are those optical features which guide the moth to adequate supplies
of nectar. In connection with such optical associations the nectar guides
may play an important role.
The above results confirm in large measure the views of the earlier
flower biologists as to the significance of the optical features of flowers for
the visits of the hawk-moth. The importance of nectar guides was some-
what overemphasized by them, though the essential facts of the older con-
cept can be maintained. However, no support has been found for the
view that the odor of flowers plays the important part in the attraction
of the hawk-moth heretofore assigned to it.
Response of bees to spectral bands. — The studies of Kuhn and Pohl
(1921:738) mark a distinct advance in the technique employed for the
analysis of color vision in insects. They have utilized the spectral bands
obtained by means of the mercury spectrum in order to extend their experi-
ments into the region of the ultra-violet and have consequently had the
advantage of working with pure colors. The bees were habituated to fly
in a room in which a Hg spectrum was thrown on a horizontal table-top,
upon which it could be turned and shifted at will. To human eyes the
lines at 578 mm (yellow), 546 (jl/jl (green), and 436 nn (blue) appeared brilliant;
405 ^n (violet) was distinctly and 492 nn (blue-green) still noticeably to be
seen in the daylight of the room. The line 365 nn (ultra-violet) could be
recognized in weaker light as a sensible bluish glow on the white paper of
the table. In training the bees all the lines were eliminated except one,
which was directed upon a small elongated combustion dish filled with
sugar solution. In doing this the position of the line was frequently shifted
to avoid any association with a particular portion of the table. In the
tests without food a new sheet of paper was spread and the particular wave-
length presented in proper sequence with the remaining lines of the spectrum.
After a training period of an hour the bees always gave a constant response.
After training to 578 ixn (yellow) the bees concentrated regularly upon
this band. When this was covered, they went in almost equal number to
546 uti (green). Lines of shorter wave-length were not noticed, and varia-
tions in the brightness within wide limits had no effect. After feeding upon
436 ij-h (blue) a dense mass of bees formed on this; violet (405 nn) was
equally strong in effect after uncovering from 436 n/x. After eliminating
436 nn and 405 nn, there was a marked movement to the ultra-violet line
208 PRINCIPLES AND CONCLUSIONS.
365 mm- The region of greater wave-length was completely avoided after
training to 436 nn and 405 nn. The wave-lengths of ca. 400 to 440 nn on
the one hand and ca. 540 to 580 nn on the other were consequently dis-
criminated from each other by the eyes of the bee. The flight to the ultra-
violet line 365 fin after training to 436 fifi or 495 nn (blue or violet) may be
explained by the action of the weak bluish fluorescence or by a sensitivity
of the bee's eye to this part of the spectrum. Further studies indicate a
particular specific sensitivity to ultra-violet. When trained to 365 fifi, the
bees sought ultra-violet alone out of the entire spectrum, and even after
concealing this line, blue and violet were without effect. Unbroken light
rays received no visits, but the interpolation of an ultra-violet filter which
cut out wave-lengths above 400 fifi and removed the disturbing influence
of whiteness brought about many visits. Light-waves in the region of
365 hijl, or ultra-violet, were distinguished qualitatively from unrefracted
light as well as from the regions of ca. 400 to 440 fifi and ca. 540 to 580 fifi.
Further experiments showed that the line 492 fifi (blue-green) was also
distinguished from the other lines of the Hg spectrum as well as from unre-
fracted light. The bees were then trained to a bright band from a continu-
ous spectrum between 480 fifi and 500 fifi. Checking with the Hg spectrum
gave a massing upon the blue-green mercury line of 492 fifi, which is faint
to our eyes and which always remained free in the training to all the other
wave-lengths. In order to test the discrimination of the region 480 to 500 fifi
from unrefracted light, a "white" band of the same size was exposed
alongside of or instead of the "blue-green" one. The bees left this un-
noticed, even though its brightness was varied greatly, and gathered always
on the blue-green strip (480 to 500 fifi). To this region of the spectrum
corresponds Hering's paper No. 10 approximately for our eyes. In the
experiments of Frisch the bees were unable to distinguish this pigment from
the shades of gray, but the explanation of this discrepancy seems obvious.
Pigment No. 10 has been measured photo-electrically and found to reflect
from 492 fi/i to 365 fifi downwards in increasing measure. Consequently,
there must have been present for the bee's eyes a marked veiling by white.
EVALUATION OF PLATEAU'S RESEARCHES.
Forel's estimate. — The most comprehensive critique of Plateau's
work was made by Forel (1901, 1908:142). As a complete summary of
this would involve too much repetition of Plateau's results, it appears
best to quote Forel's general statements and conclusions, and to deal with
certain contradictions which affect the significance of some of his criticisms.
"It is with reluctance that I have decided to undertake the criticism of this author,
not, indeed, that it will be difficult, but because of the space it demands, and because
it is painful to me to have to bring to light the false conclusions of a colleague whose
patience, work, honour, and good faith I esteem. But the considerable confusion
that Plateau has thrown on the question which occupies us, in spite of and in part by
his long and patient researches, and the fact that his conclusions have been accepted
all too easily by certain authors who consider themselves to be very superior to all
that has preceded them, demands that we examine the matter closely.
"Before starting, I must, to simplify matters, lay down in anticipation certain
general theses at which I have long arrived and which agree in short with the results
EVALUATION OF PLATEAU'S RESEARCHES. 209
of Darwin, Romanes, Lubbock, and all investigators who have gone deeply into the
psychology of insects. But these theses require to be definitely formulated.
" (a) Granted that there is often a principal directing sense, the rule is nevertheless
that insects combine the impressions of several senses for their own guidance.
"(b) Attention plays a considerable part in the manner in which insects guide
themselves. When it is strongly directed toward a goal or object, they are often
profoundly oblivious of everything else, somewhat like an absorbed savant (bee
eating honey; ants fighting).
" (c) The memory of insects varies much according to the species. It is connected
with various sensory impressions. It is much better than one would imagine a priori
in insects with complicated instincts and especially in social hymenoptera, but it is
extremely weak in the small-brained forms.
"(d) As Lubbock and H. Mueller have shown, impulse plays a great part. At-
tracted by the sensations of sight or of smell or of both combined, the insect ends by
fixing its attention on an object or on an instinctive coordinated act, connected with
a purpose. When this fact is accomplished it may be seen to repeat its journey or
other instinctive acts with a rapidly increasing precision.
"(e) Insects have sentiments or emotions more or less developed according to the
species, genera, and families. Rage, fright, discouragement, jealousy are very marked
among the social hymenoptera; similarly affection and temerity based on success.
It is necessary to take them into account accurately to judge their acts. Emotional
states of the nerve centers are very general in the animal series and are therefore
related to danger, success, defeat, fruitless efforts, pain, attack, defence, as much in
the individual as in the society.
" (/) Nothing is so dangerous as premature generalizations, or (g) to draw illegitimate
conclusions from experiments."
"Attraction of insects by flowers. — Color preferences. — It is well known that
Hermann Mueller has insisted on the part played by the colors of flowers as a cause of
attraction, and has upheld the opinion that certain lively colors of flowers of themselves
attract insects, i. e., that the attraction for such and such a lively color will tend to
direct the insect towards them rather than towards less apparent colors. These
preferences of color thus serve indirectly for the fertilization of flowers by insects,
so that selection will induce the flowers for this reason to become more and more
colored. Lubbock has made experiments whence it resulted that bees and bumble-
bees had, for example, a marked preference for blue. Let us say once for all that this
question is extremely complex, and that the results of observations made without
prejudice are not of a nature to confirm in a satisfactory manner the theories of Mueller.
The results of Lubbock are similarly not very conclusive on this point. It has often
appeared to me also that blue was especially apt to attract and to direct bees and
bumble-bees to a spot; they find honey placed on blue more easily, for example, than
if on red. But as insects distinguish the colors on the side of the ultra-violet better
than those on the side of the infra-red, the preference might thus be accounted for.
White attracts them in my opinion as much as blue, everything else being equal.
In this question, distinction of colors must not be confounded with preference for one
or another color. Though the distinction of colors is useful to insects which visit
flowers, to enable them to distinguish and find them rapidly, the attraction of a special
color will be equally detrimental to them in preventing them from going to flowers
quite as rich in nectar or pollen, but differently colored, or in attracting them toward
flowers or other objects colored with the hue of predilection, but offering neither
nectar nor pollen, or even having poisonous qualities. For these simple reasons,
self-evident to the common-sense of a practical entomologist, I have never been able
to participate in the theories of Mueller and Lubbock on this subject.
"I am happy to find myself in perfect agreement with Plateau on this point; his
numerous experiments all tend to prove clearly what would be expected, i. e., that
210 PRINCIPLES AND CONCLUSIONS.
insects direct themselves toward flowers which provide them with the nourishment
that they need, and that they find them as well when they are as green as the leaves,
as when they are blue, red, or yellow. Inversely, they ignore the most beautiful
flowers with striking colors, when these have nothing to give them. Plateau gives
himself unnecessary trouble to show that there are green flowers and that insects
visit them as much as others. Every one knows the first of these facts, and the second
has escaped no entomologist; in my opinion, his long comparative tables refute Mueller.
Nevertheless, do there exist any preferences of color beside the fundamental fact
that we have enunciated? This is so difficult and so delicate to decide that I dare not
express an opinion.
"But Plateau has completed his old experiments on another very interesting point.
I refer to artificial flowers. He has taken enormous trouble to obtain the best and most
artistic imitations of natural flowers. To one who knows modern art in this branch
this means much, for even man needs all his attention to enable him to distinguish
these artificial products from true flowers. Here again I am pleased to be able to
confirm Plateau by several experiments that I have been able to make. That which
deceives us never deceives insects, or hardly ever, and then only for an instant. The
insect passes to one side of artificial flowers without paying them attention, without
stopping at them, without hesitating, and goes straight to natural flowers situated
beside them, and which we do not distinguish from them. Ought we to conclude
therefrom that the colors which we use, and which are not chlorophyllic, are dis-
tinguished by insects from chlorophyllic colors? This appears very probable from
Plateau's experiments, and I shall believe it until I have proof to the contrary. That
which to our eyes is a good imitation of color appears not to be so to the insect eye.
These facts will appear less astonishing to us if we remember that among men some
are color-blind, while others are artists who render and appreciate colors in many
various shades. Then we must not forget that artificial imitations of flowers are made
by the help of human vision and for it.
"I shall not enlarge upon the researches of Mueller, Bennett, Bonnier, Gratacap,
Christy, Bulman, Scott Elliot, Delpino, Kuntze, Knuth, and Plateau on the truly hair-
splitting question regarding the possibility of insects having preferences for certain
colors or not. Here I am in agreement, as I have said, with Plateau (and Bulman).
What is astonishing is that so many authors can waste so much ink in proof of the
obvious, clearly summed up by Bulman when he saj^s, 'It matters not one iota to
a bee whether the flower is blue, red, pink, yellow, white, or green, so long as there is
honey, that is sufficient.' Only the fact that any color does not attract specially by itself
some insect is no proof that the latter cannot distinguish other colors.
"But here my agreement with Plateau ceases. Here again he has drawn erroneous
conclusions from his experiments. In the case of masked dahlias, he concludes that
shape and color do not attract, but forgets that the insect remembers the place where
the flower was. Plateau's observations and inferences are both faulty. First, his
dahlias were insufficiently masked, being covered only in the upper part; bees flying
around a group of flowers must perceive the uncovered colored sides by their
peripheral vision. This seems to be evident from the figures of Plateau, which
shows the vine leaf lying flat on the flower. In the second place his bees had conse-
quently discovered his trick sooner than mine; he probably took no account of their
behavior at the beginning of his experiment, or had not noted it. But it is only at
such a time that conclusions can be drawn as to vision alone, independently of
memory. Further, our results show that bees have a poor sense of smell at a distance.
"Plateau also worked with bees that were visiting Oenothera biennis with its beautiful
yellow petals. On September 3rd he cut the corollas, leaving only the stamens.
I give the results in his own words: — 'The bees visiting the plant flew in every direction,
toward the faded flowers, towards the buds, even to the fallen petals on the ground,
which they examined with some attention in walking over them; nevertheless,
EVALUATION OF PLATEAU'S RESEARCHES. 211
they alighted to forage only on the mutilated blossoms deprived of corollas.' [The italics
are Plateau's!] And Plateau concludes that it is smell and not vision that guided
them! Is it possible to prove better to oneself the contrary of what his experiment
says? That bees do not forage where there is nothing, is obvious to a child. But
that they should seek the flowers, wherever they perceived them, by their bright
yellow color, that they should see the dry rudiments or the buds on the plant, this
agrees so admirably with our experiments that I pass no comment.
"The last conclusions of Plateau are somewhat curious. He begins by declaring
that he has 'never said that insects do not see the colors of flowers; that would be
absurd' (jievertheless, he uses the title: On the so-called distinction of colors by insects).
Then he adds that the differences in the quantities of reflected light or in the refran-
gibility of luminous rays transmitted or reflected by the transparent media can explain
the results hitherto obtained. And finally he pretends that the question to be solved
U: do the insects which visit flowers allow themselves to be guided in their choice
by the colors which these flowers present to the human eye? I protest against the man-
ner in which Plateau now puts the question. I do not believe any more than he does
that insects see colors subjectively as we do, and I believe further with him that there
are objective differences in the manner in which their eyes and ours are stimulated
by the different forms of light, i. e., by colors and shades. But the experiments of
Lubbock, of Peckham, of other authors, and my own indicate that certain insects
distinguish not only flowers, but colored objects, by their coloration, i. e., by the kind
of refrangibility of the luminous rays which they reflect or transmit, and recognize
them in this particular when the other senses are eliminated, and even when such
objects are found surrounded by light of the same intensity.
"In saying that bees distinguish colors, We have never wished to assume that they
see them exactly as man does, and so much the less since, as I have already emphasized,
all men do not see them absolutely the same.
"In recapitulation, we see that the facts are very complex, and this is why I abstain
from general conclusions on 'all insects' seeing or not seeing 'forms and colors, etc.,'
for such generalization would necessarily be false. If one wishes to understand it,
one must take the trouble to follow the details. Nevertheless, I am constrained to
repeat that Plateau's interpretation of his so-called non-distinction of forms among
insects, after the restrictions which he has himself gradually introduced, finally
approaches more or less to the opinion of Exner, which has always agreed with my
own. The greatest error of fact into which Plateau falls, is that by which he attributes
what really belongs to vision in certain insects (in bees in particular) to their
sense of smell. Nevertheless, in the final paper of the series, he finally recapitulates
the way insects guide themselves, in a manner which in its general characteristics
approaches nearly to the truth. As we have seen, the causes of the erroneous judg-
ments with which Plateau has obscured the question at issue are errors of interpreta-
tion, inadmissible and continual generalizations, and the almost total neglect of the
psychical faculties of the insect, especially with regard to memory and association."
Although Forel's criticisms of Plateau's work are often too severe,
they are on the whole fairly well justified. They err in making the dif-
ferences between their general conclusions greater than it actually was,
as Plateau himself pointed out (19022:424). Moreover, Forel was not
free from the contradictions for which he takes Plateau to task, and it
is evident that his own knowledge of the behavior of anthophilous in-
sects was much smaller than for many other groups. After dismissing
the views of Mueller and Lubbock on color preference as unsatisfactory
or inconclusive, he states that "this problem is so difficult and delicate
to decide that I dare not express an opinion," only to express a very positive
212 PRINCIPLES AND CONCLUSIONS.
one a moment later (p. 210) and to rebuke Mueller, Plateau, and others
for proving the obvious. He is far from clear as to the practical difference
between the distinction of colors and the preference for certain ones, and
fails to realize that the marked constancy of many bees indicates that
distinction and preference are often the same thing. He apparently did
not know the careful work of Mueller as to color preferences for petals,
which, like that of Lubbock, is corroborated by the later researches of
Lovell, Turner, Frisch, and others. Lovell in particular has shown that
green flowers and green objects are visited much less than bright-colored
ones and often not at all, and this has been confirmed by Allard in his work
with cotton blossoms. The results of Plateau and of Forel with respect
to artificial flowers are contradicted by those of Andreae, Wery, Detto,
and others, and it is evident that time, place, and other factors often
play a controlling part in the behavior of insects to such imitations. Move-
over, if insects can distinguish chlorophyllic colors from others in the case
of artificial flowers that deceive human vision, it is impossible to believe
that they are unable to distinguish the strikingly different forms of various
flowers. The evidence for the perception of form by bees is given later,
and it is only necessary to point out here that Forel himself speaks of their
seeing the dry remains of flowers and the buds of Oenothera.
Contradictory nature of Plateau's later conclusions. — While several
critics have pointed out that Plateau materially modified his earlier state-
ments as to the relative r61e of color and odor in attraction, the greater
contradictions involved in his later ones have been overlooked. These
are contained in the four extracts that follow, which represent the last
ten years of his work, 1899 to 1910.
"I have never said, in my previous studies or the present memoir, that insects do not
see the colors of flowers. This assertion would be absurd. But I insist that we have no
practical means of assuring ourselves whether there exists a perception of color and
whether this is the same as our own. The question to be resolved is this: whatever
may be the visual perceptions of insects, are those that visit flowers guided in their choice
by the colors that the flowers present to the human eye. The reply can only be negative
[1899:368]. I admit fully that the insect can perceive flowers at some distance,
whether it be because he sees their colors in the same manner that we do or because
he perceives a certain contrast between the flowers and their surroundings, I admit
that concurrently with the sense of smell, although to a much less degree, this vague
visual perception can guide the animal to the whole floral mass; but once arrived
there, if the flowers differ among themselves by color alone, he will prove by his be-
havior that it is entirely indifferent to him, as Bulman says, whether the corollas are
blue, red, yellow, white, or green" (370).
As a result of his experiments with bumble-bees deprived of their an-
tennae (1902*: 418), Plateau said:
"The results of A. Forel are thus shown to be accurate; I state it with the satis-
faction of having been able to contribute to the demonstration of a scientific truth.
However, it is not necessary to draw from this the exaggerated conclusion that the
sense of smell plays no part in the attraction of insects by flowers." "What is to be
drawn as a conclusion from all this? It is that, if I have been wrong in attributing
an exaggerated preponderance to the sense of smell in the relations between insects
and flowers, my numerous observations and experiments prove, as Knuth admitted,
that the olfactory sense plays a much more important r61e in the search for flowers
by insects than has hitherto been admitted.
SENSES of insects: sight 213
"I could quote further from the work of Forel, but limit myself to the preceding.
I thank him for giving me the opportunity to prove that, even in supposing all the
criticisms of which he is not sparing to be absolutely well founded, the results of my
studies on the relations between insects and flowers are not as worthless as some pre-
tend and that they do lead to the refutation of this part of the floral theory of Hermann
Mliller and his school, who attribute to the brilliance of flowers, to their colors more
or less striking, an important role in the attraction of insects and consequently in
fecundation (1902:424).
"Two corollaries may be derived from this fact: the first is that the attractive
r61e of the form and color of the floral envelopes is either null or nearly so; the second
is that other causes than the attraction of colored surfaces is necessary to bring pol-
linators to flowers and to cause them to return, such as an odor pleasing to insects
and a sugary liquid." "In r6sum£, the present investigation but confirms the thesis
advanced in 1897 in the following words: 'Insects seeking pollen or nectar are guided
to the flowers that contain these substances in only a subordinate degree by sight.
They are guided in an assured manner to such flowers by some other sense than vision
and this can only be the sense of smell' " (1910:51).
Conclusions as to Plateau's views. — The admiration felt for Plateau's
frank admission that he had been wrong in assigning an exaggerated im-
portance to the sense of smell in attraction is more or less eclipsed by the
fact that this was never again referred to in his later papers, in which
he returned finally to his original view that the attractive role of color
is null or nearly so. In spite of Plateau's originality, industry, and patience,
the bias in favor of odor and against color pervaded all his researches,
blinding him to many faults of execution and leading him to unwarranted
conclusions. How dominant this prejudice was is shown by the fact that
within six pages after his apology for exaggerating the r61e of smell in at-
traction, he states that his studies refute the view of Mueller that color
plays an important part in this process. This also led him frequently
to overlook facts and results that were not in accord with his views, and to
make gratuitous assumptions as to the work of other investigators. A
second great fault of his experiments was the failure to insist upon the
regular use of controls, with the consequence that the results were often
open to any interpretation desired. With this went the failure to realize
that time, place, and conditions work great differences in response, and
that this was usually the explanation of the discrepancies between his
results and those of his critics, rather than carelessness or lack of thought
on their part. Finally, as Forel in particular insisted, he paid practically
no attention at first to the importance of habit and memory, and gave
them too little consideration throughout. In spite of all this, he deserves
great credit as the pioneer in experimental pollination, as an indefatigable
investigator, and a good-natured and courteous opponent.
SENSES OF INSECTS.
SIGHT.
The mosaic theory. — Forel (1886:10) emphasized the fact that the
structural studies of Grenacher (1874) and the physiological ones of Exner
(1875) led them to revive the earlier theory of Muller. This was not
that each facet formed an image, as Gottsche thought to have demon-
strated, but that the insect perceives a more or less clear image of the
214 PRINCIPLES AND CONCLUSIONS.
object in the form of a mosaic, due to the fact that each facet receives a
different part of the light rays coming from the object. It follows necessarily,
as Muller pointed out, that, since the clearness of vision, the localization
of the light rays, is rendered possible only by the combination of the separate
action of each facet, it is the number of facets that will determine the
degree of definition. The smaller the facet, the longer the crystalline, the
fewer the rays the retinule will receive and the smaller or more localized will
be the external object from which the rays proceed. On the contrary, the
larger the facet and the shorter the crystalline, the more light the retinule
will receive and it will see in a manner more intense and diffuse, that is, less
clearly. Thus, many small facets will diminish the intensity of the light,
but will increase the clearness of vision. When in addition the entire eye
is not flat but strongly convex, it will receive light from more diverse
points, which increases the common field of vision. If this be true, it ought
to be possible to prove by observation that insects with many small facets
and with the compound eyes strongly convex have the best vision.
Forel brought forward a number of observations to support this view,
the most significant, perhaps, being with reference to eyes of male and female
ants. The eyes of the former are more convex and may contain twice
as many facets, since they require greater vision to discern and follow
the females in flight. He also confirmed the opinion of many investigators
that the loss of the ocelli was without effect, but that this was not the case
with the compound eyes. When the latter were varnished in the case of
flies, these no longer flew if placed on the ground and once in the air they
flew about aimlessly. Wasps and bumble-bees similarly treated behaved
in like manner, flying even more rarely and finding their way on the ground
more slowly. They searched for cracks in which to hide, as though it
were night.
The following summary was given of the existing knowledge of vision
in insects.
1. Insects guide themselves almost wholly in flight and partly on the ground by
means of their compound eyes. The antennae and the sensory organs of
the mouth can not serve for direction in the air, their extirpation in no wise
diminishing the ability to guide themselves on the wing.
2. The mosaic theory of vision proposed by Muller is alone sound. Each retinule
of the compound eye does not receive an image, but merely a pencil of light
rays more or less distinct from that of its neighbors.
3. The greater the number of facets and the length of the crystallines, the more dis-
tinct the sight, as well as further.
4. Insects perceive the movements of objects particularly well, that is, the displace-
ments of the visual image relative to the compound eye. They thus see better
in flight than at repose, for the image of immobile objects is then displaced
with respect to the eye. Perception of the mobility of objects decreases as the
distance becomes greater.
5. Insects distinguish the contours and form of an object only in a manner more or
less indistinct, as much more indistinct as the number of facets is less, the crys-
tallines shorter, the object more distant or smaller. Those insects that have
large eyes with several thousand facets see quite distinctly.
6. In flight insects recognize the direction and distance of objects very clearly by
means of their compound eyes; at least this is true for short distances. Even
when in repose they can also recognize the distance of immobile objects.
SENSES of insects: sight 215
7. Certain insects, the honey-bee and bumble-bee, clearhy distinguish colors and they
recognize colors better than forms. With the wasps on the contrary the per-
ception of colors appears to be very rudimentary.
Criticisms of Plateau's views as to vision. — Forel stated (p. 43) that —
"Plateau began by assuming that the theory of Muller as to mosaic vision is finally
rejected and this in consequence of the work of Exner of which we have spoken!
This is completely in error. On the contrary we have seen that Exner, as well as
Grenacher, has entirely rehabilitated the theory of Muller. Plateau appears to have
failed to understand the works of Exner, because he also adds that this author has
concluded theoretically that insects do not see the form of objects, which is wholly
inexact as well. Plateau says in the text, 'The earlier hypothesis of J. Muller, con-
sisting in the production of a mosaic image formed by the juxtaposition of a series
of minute partial images each of which occupies the base of one of the distinct elements
of the compound eye is definitely rejected.' But this is the theory of Gottsche and not
at all that of mosaic vision of Muller. The theory of mosaic vision does not admit
of minute images in each facet, but a single image in mosaic formed by the juxta-
position of light rays of different quality perceived by each facet."
As to the experiments of Plateau upon the perception of form by in-
sects, Forel declared that these did not in the least demonstrate that
they could not distinguish form, but merely that they would fly to the
more luminous of the two orifices without regard to the form. He also
pointed out that while Plateau first spoke only of the non-perception
of form, he concluded by saying that "insects do not distinguish the
form of objects or distinguish it very badly."
Sensibility to color. — Graber said (1875):
"I understand very well that a brain relatively small and simple in construction
is in general less capable than a more highly differentiated central organ and that
both the number and the coordination of perceptions is limited by the simplicity of
structure, but I can not admit offhand that when an animal, let us say a bee for ex-
ample, exhibits actual color perceptions, these must necessarily be different from ours,
or that we then know, since the sensory organ for color perception in the bee is essen-
tially different than with us, that the nerve tissues concerned can not call forth the
same sensations that they do with us. Disregarding the fact that insects possess
very complex eyes and that they appear to react clearly to small differences of color,
such as orange, yellow-green, etc., other evidence testifies to the great sensibility of
their sense of color. I have especially in mind the fact that many insects have no
other means of recognizing their own species than certain differences in color and it
is well known that related species often differ outwardly only in coloring or marking.
Moreover, it is hardly to be assumed that mutual recognition takes place by means of
other attractions, imperceptible to us, such as odor or sound. But if I ascribe a very
delicate sense of color to certain insects on the basis of these relations, I do not how-
ever go so far as Allen, who asserts that the ability of insects to distinguish color
may be more marked than with man."
Perception of form and movement by insects. — In a series of six
papers appearing from 1885 to 1888, Plateau dealt with a comprehensive
investigation of vision in the Arthropoda. Some of these were made upon
other groups than the insects and others had little or no relation to
the problem of insect attraction. In consequence, the following account
of his conclusions is confined to those that have to do with the perception
of form or movement. Diurnal insects require a fairly strong light and
216 PRINCIPLES AND CONCLUSIONS.
are unable to direct themselves in semi-obscurity. Insects with com-
pound eyes pay no heed to differences of form existing between two illum-
inated openings and are deceived either by excess of luminous intensity
or of apparent surface. In short, they do not distinguish the forms of
objects at all, or do so very poorly (1885:251).
Plateau (1888:437) stated that Exner, Notthaft, Carriere, Forel, and
Bleuler had all concluded from theoretical considerations, often sup-
ported by observations, that the majority of insects see the movements
of bodies much better than they do the bodies themselves. He regarded
his own experiments as fully confirming this opinion and permitting the
following conclusions. The faculty of perceiving the displacement of
mobile objects is very well developed in many insects with compound
eyes, those best endowed in this respect being the Lepidoptera, Hymen-
optera, Diptera, and Odonata. However, the distance at which the move-
ments of an object of small volume are perceived does not exceed 2 meters.
On the average it is 1.5 meters for the butterflies, 58 cm. for the bees, and
68 cm. for the flies. The perception of movement plays a great r61e as
the determining cause in the behavior of insects. It explains how, with-
out a clear vision of form, the dragon-flies pursue their victims in the
air, how different insects fly about among leaves moved by the wind, and
why those with slow movement often escape their enemies. On the other
hand, insects may be readily touched or caught if the movements are suf-
ficiently slow. For them an object that ceases to move merges at once
into the vague background.
Discrimination of form. — As a result of simple experiments with a
spider, bee, and fly, Dahl (1889:243) found himself in agreement with
Lubbock and Forel as to the ability of insects to distinguish forms, and in
opposition to the conclusions of Plateau. He regarded the statement of
the latter that insects often deceive themselves by flying to unopened
flowers as indicating that they are attracted primarily by color rather
than form, and not that they are unable to distinguish forms. He also
observed (Knuth, 1898:45) that in spring young bees light on flowers
whose nectar is too deep-seated for them and make vain endeavors to reach
it, while the older bees merely come near and fly away without landing.
This indicates that the latter recognize the flower on sight as one with
unavailable honey, since guidance by odor would make it unnecessary
for them to approach the flower.
Vision in honey-bees. — Buttel-Reepen stated that bees do not find
their way home when thrown up into the air at dusk, not far from the
hive; they make several small circles and fall to the ground completely
lost. Their flight is often strongly influenced by dark clouds, especially
during the honey-flow, when the approach of a storm sends thousands
of bees scurrying back to the hives. In their haste many blunders are
made in entering, which would not be true if they were drawn to the proper
hive like a magnet by the "unknown force." It was also observed that
when they went to the wrong hive, they tried to enter as at their own,
even when no entrance was present, showing that they had a memory
picture of their hive, though they had mistaken it. He also cited an in-
HOMING FACULTY. 217
6tance of bees flying against a gable painted sky-blue that they had regu-
larly avoided before, and one of young bees issuing from a blue hive and
flying on their return to other blue ones by mistake, but never to those
painted in other colors.
Vision in ants. — Fielde (1902:599), whose studies of vision in ants
were in agreement with those of Lubbock and Forel, stated that —
"The ants manifested no liking for any of the rays of light. If obliged to stay in
light rays of some sort, the rays of longer wave-lengths are preferred to those of shorter
wave-lengths. Dividing the spectrum, as we know it, into red, green, and violet,
we may say that to the ants' eyes red and green are most like the darkness that they
prefer and that violet is to them most luminous; or that the red and green are less
visible to them than is violet. In this regard the eyes of the ant appear to be the re-
verse of our own. Our eyes perceive in the spectrum three fundamental colors — red,
green, and violet. The eyes of the ant perceive there only two fundamental colors —
one made up of the red and green rays, the other of the violet and ultra-violet rays.
"It appears that the eye of the ant is not well adapted to the reception of light-rays
whose wave-length is longer than in the violet rays ; that it receives blue and indigo
more perfectly than red, orange, yellow, and green; and that there is a sudden in-
crease of luminosity in the light rays at that point in the spectrum where violet be-
gins for our eyes. The ants may discern colors, and yet have no preferences among
the colors discerned. Color is determined by the wave-length in the light-ray, and
since ants discriminate between rays of different wave-lengths, they probably perceive
color in the rays. Sensitivity to the length of the wave indicates perception of color."
The role of ultra-violet in attraction. — Richtmyer (1922) has de-
termined the ultra-violet reflection of a number of Colorado flowers with
reference to a possible influence in attraction. He considers that the effect
of ultra-violet in attraction involves two questions: (1) do insects "see"
ultra-violet in the sense that they seem to "see" the rays visible to us?
(2) is the ultra-violet reflected by flowers present in sufficient degree to
play an important part in rendering flowers visible to insects? It was
found that few of the flowers reflected any considerable proportion of
ultra-violet, only 4 of the 25 studied reflecting more than 10 per cent of
radiation shorter than 0.38 wi. These were Laciniaria punctata, Oenothera
biennis, Rudbeckia laciniata, and Solanum rostratum. Certain yellow flow-
ers showed a distinct ultra-violet reflection band, particularly well marked
in Rudbeckia, but others such as Solidago and Ratibida gave no trace of
such a band. The flowers differed from each other in the reflection of ultra-
violet just as much and as erratically as in that of the visible spectrum.
It might be expected that a white flower, which reflects the visible rays
in approximately equal proportions, would also reflect a considerable
amount of ultra-violet, but this is not the case. They gave a high reflection
of light longer than 0.42 or 0.43 n, but none of them reflected more than 4
per cent of 0.39 /j.. The most striking case was that of Argemone platyceras,
with a relative coefficient of reflection of more than 75 per cent at 0.41 n
and of only 4 per cent at 0.39 ju.
THE HOMING FACULTY IN BEES AND WASPS.
Fabre's experiments with bees and wasps. — In his "Souvenirs Ento-
mologiques" (1879:299, 1882:99), Fabre recounted his studies of the horn-
218 PRINCIPLES AND CONCLUSIONS.
ing of bees belonging to two species of Chalicodoma. In the first series
the insects were released at 4 km. from their nests; of the first 2, one returned
the next morning, but the other never reappeared, while in the second case,
3 of the 5 were noted the following morning. In the third experiment 40
bees were freed, but only half of these flew away from the spot. Once
free, the bees fled as though frightened, some in one direction and some in
the other. The first 2 returned to the nests in three-quarters of an hour
and 3 others toward sundown, while 10 more were observed the next morn-
ing, making a total of 15 to return out of the 20 released. All told, 19 found
their way home out of 27, disregarding those thought to be injured. These
were supposed to have found their way back in spite of the contrary winds
and their ignorance of the places to which they were carried. It is obvious,
however, that the assumption that the bees had never wandered so far
from home and had never seen these places was a gratuitous one. It
afforded exceedingly tenuous support for the conclusion that they were
certainly not guided by memory on the homeward journey, but by some
special faculty, not to be explained but recognizable by its astonishing
effects.
In the second series, 10 bees of the same genus were placed in a bag and
carried a kilometer distant, where the bag was whirled rapidly about.
They were then taken in the opposite direction to a distance of 4 km.
from their home and again whirled around before they were released one
at a time. The first bee traversed the distance in a quarter of an hour
and 2 others returned several hours later, but the remaining 7 did not re-
appear. The following day the first bee reached home in 5 minutes and 2
more in about an hour, while the other 7 failed to appear. When 49 bees
were released, the majority started in the right direction, the first arriving
in 15 minutes and 11 within an hour and a half; 6 more appeared within
the next 5 hours, making a total of 17 out of 49, while in the next test 7
bees out of 20 found the way back. The bees in the next experiment were
taken over 2 miles away, 2 returning in an hour and a half and 7 more in
3 hours and a half, making 9 out of the total of 40. Finally, 15 bees were
marked with rose and carried by a roundabout route of over 5 miles, while
a second 15 were marked with blue and taken directly to the spot, a distance
of a mile and a half. All were released at noon, and by 5 o'clock 7 "rose"
and 6 "blue" bees had returned, the long detour making no appreciable
difference. Fabre regarded these results as conclusive, neither the whirling
of the sack, the obstacles of hill and forest, nor the devious route being
able to hinder Chalicodoma from returning to the nest.
Lubbock's and Ford's critiques of Fabre's conclusions. — Lubbock's
discussion of Fabre's results is so detailed and conclusive that quotation
alone can do it justice (1888:264):
"I am not ashamed to confess that, charmed with M. Fabre's enthusiasm, dazzled by
his eloquence and ingenuity, I was at first disposed to adopt his view. Calmer considera-
tion, however, led me to doubt, and though his observations are most ingenious and are
very amusingly described, they do not carry conviction to my mind. There are two
points especially to be considered: (1) the direction taken by the bees when released;
(2) the success of the bees in making good their return home.
"As regards the last point, it will be observed that the successful bees were in the following
proportion, viz, 3 out of 10, 4 of 10, 17 of 49, 7 of 20, 9 of 40, 7 of 15, or a total of 47 out
HOMING FACULTY. 219
of 144. This is not a very large proportion. Out of the whole number no less than 97
appear to have lost their way. May not the 47 have found theirs by sight or by accident?
Instinct, however inferior to reason, has the advantage of being generally unerring. When
2 out of 3 bees went wrong, we may, I think, safely dismiss the idea of instinct. Moreover,
the distance from home was only \x/% to 2 miles. Now, bees certainly know the country
for some distance around their home; how far they generally forage I believe we have
no certain information, but it seems not unreasonable to suppose that if they once came
within a mile of their nest they would find themselves within ken of some familiar landmark.
Now, if we suppose that 150 bees are let out 2 miles from home and that they flew away
at random, distributing themselves equally in all directions, a little consideration will
show that some 25 of them would find themselves within a mile of home and consequently
would know where they were. I have never myself experimented with Chalicodomas,
but I have discovered that if a hive-bee is taken to a distance, she behaves as a pigeon
does under similar circumstances; that is to say, she flies round and round, gradually
rising higher and higher and enlarging her circle, until I suppose her strength fails or she
comes within sight of some known object. Again, if the bees had returned by a sense of
direction, they would have been back in a few minutes. To fly \Yi or 2 miles would not
take 5 minutes. One bee out of the 147 did it in that time, but the others took 1, 2, 3, or
even 5 hours. Surely, then, it is reasonable to suppose that these lost some time before
they came in sight of any object known to them.
"Fabre observes that the great majority of his Chalicodomas at once took the direction
home. He confesses, however, that it is not always easy to follow bees with the eye.
Admitting the fact, it seems to me far from impossible that the bees knew where they were;
and at any rate, this does not seem so improbable that we should be driven to admit the
existence of a new sense, which we ought to assume only as a last resource. Moreover,
Fabre himself says: 'When the rapidity of flight permitted me to note the direction taken,'
which seems to imply doubt. Indeed, some years previously he had made a similar experi-
ment with the same species, but taking them direct to the point rather over 2 miles from
the nest and not whirling them round his head. In this case some went in one direction,
some in another. It certainly would be remarkable if bees which were taken direct missed
their way, while those which were whirled round and round went straight home. Moreover,
it appears, after all, as a matter of fact, that they did not fly straight home. If they had
done so, they would have been back in 3 or 4 minutes, whereas they took far longer. Even
then, if they started in the right direction, it is clear that they did not adhere to it.
"Romanes's experiments, likewise, as he himself says, entirely confirm the opinion I
have ventured to express, that there is no sufficient evidence among insects of anything
which can justly be called a 'sense of direction.'"
Forel (1900, 1908:72, 215) also emphasized the discrepancy between
Fabre's results and his conclusions.
"Instead of attributing these facts to an instinct of direction, I explain them as follows:
aerial insects and aerial beings in general, soaring above terrestrial objects ought to have, —
and have, a knowledge of places very different from that of wingless ones. If we reflect
on the geographical coup d'oeil 'as the crow flies' that one obtains on the summit of a hillock,
we shall have a feeble idea of what the vision of an aerial being can be, with this difference,
that in the twinkling of an eye it moves and alters its horizons, which we can not do. In
20 minutes the Chalicodoma of Fabre had travelled over their 3 kilometers! This experi-
ment simply proves to me the very instructive and interesting fact that the Chalicodoma
knew the places within a radius of a league, at any rate. Those which did not find their
way were probably newly hatched and had not pushed their reconnaissances so far.
"If a mysterious sense of direction had guided them, all that started would have returned.
Weismann thinks rightly that the bees, set free in this unknown and to them distasteful
place, would have been attracted by the sight of the hill. Once there, the oldest, those that
knew the surroundings best, would have found a landmark and a road. Indeed we see
even pigeons often go off in various directions at first. Is it not significant thus to see
mason-bees, placed under the same conditions, conduct themselves in miniature like
carrier-pigeons, without possessing however any vestibular or otolithic apparatus? The
circle of their knowledge of places does not appear to go beyond 4 kilometers; that of
highly trained pigeons appears to reach 500. There is no striking disproportion therein.
220 PRINCIPLES AND CONCLUSIONS.
"I hope to prove that any mystic or mysterious theory of special sense, sixth sense,
magnetism, etc., is as superfluous as false for the whole animal series. The known senses,
their variations, and the memories which are derived from them explain everything"
(p. 196).
As a result of experiments of his own (1895; cf. Rau, 1918:278), Weis-
mann concluded also that "the only correct solution of the enigma of
path-finding by Chalicodoma is that the insects find their way back with
their eyes." (See also Perez, 1895.)
Homing faculty of bees. — Romanes (1885:630) conducted observations
to determine whether honey-bees find their way home by means of land-
marks or by means of a mysterious sense. A hive of bees was placed in a
basement room of a house situated several hundred yards from the coast,
with flower gardens on each side and lawns between the house and the sea.
A definite number of bees was used in each experiment and those that
returned were caught by means of birdlime. The first score of individuals
were taken out to sea, whence none of them returned; the second lot was
liberated on the shore, but none returned. The same result was obtained
when the next lot was released on the lawn between the shore and the
house, although the distance to the hive was not over 200 yards. Finally,
when bees were freed in different parts of the garden, they were always
found stuck in the birdlime within a few minutes, often arriving before
the observer could reach the hive. As the garden was a large one, many
of these bees had to fly a longer distance than those released on the lawn
and their uniform success in reaching home quickly was due to their special
knowledge of the garden. The results convinced Romanes that bees de-
pend entirely upon their special knowledge of a district or landmarks and
not upon any general sense of direction.
Sense of direction in ground-wasps. — The Peckhams (1887:113)
performed a number of experiments to determine whether wasps possess
a mysterious sense that enables them to fly in a straight line to any desired
point, even though they have never been over the fine before. When 63
workers were carried 200 yards west to the top of a hill in sight of the nest
and 10 released, they flew off in all directions, not taking the east toward
the nest oftener than the other directions. Three, after circling about,
settled again on the stump, but after some hesitation started off. When
20 wasps, 10 of which were marked, were set free on a lake, nearly all
flew in the direction of the wind, toward the nest, but in the next test
with 26 individuals, 6 took a direction opposite to that of the nest, 10
returned to the boat and seemed loath to leave, while several seemed to
change their minds and altered their courses. Two days later 32 wasps
were released on the lake a half-mile north of the nest; 8 of these returned
to the boat, some of them twice, 6 or 7 flew in a straight fine against the
wind and over the lake to the nest, while 17 or 18 flew toward the shore.
A second group of 40 was released, to fly in all directions, but most of them
returned to the boat. Of the 135 wasps set free, it seemed fairly certain
that they did not fly toward their nest as frequently as in an opposite
direction. It also appeared that they were at a loss to know which way to
go, since they often returned once or twice for a new start. Of 55 wasps
released in a later experiment, 39 returned to the nest in about an hour's
time. When 38 workers were set free in a room with opposite windows,
HOMING FACULTY. 221
22 flew through the window away from the nest, 16 through the one toward
it; the majority returned in the first 15 minutes, but they continued to
arrive for another quarter of an hour.
The experiments all served to show that the two species of wasps em-
ployed have no sense of direction in the form of a mysterious second sense
or of an ability to keep track of the turns and changes in a journey. In
spite of the fact that the wire cage permitted the use of sight, they fre-
quently started in a wrong direction as they flew out. In many instances,
however, these wasps returned to the nest and it seems probable that they
did this by rising higher and higher in the air and discovering some objects
that served them as landmarks.
Disturbance of memory in wasps. — In their study of the homing in
solitary wasps (1898:367), the Peckhams concluded that if these had an
innate sense of direction they would not need to make a study of the sur-
roundings of the nest in order to find the way back, but in the absence of
such a sense common prudence would require the careful inspection of the
location before the outward flight. After days spent in flying about the
garden, it would seem that further study of the precise locality might be
superfluous, but the wasps did not find it so. They made repeated and
detailed studies of the surroundings of the nests, and when their prey was
laid down for a moment on the return, they noted the place carefully before
leaving it. If the scrutiny of the objects about the nest makes no impres-
sion on the wasp, she should not be bothered or misled when weeds and
stones are removed and the ground smoothed, but this is just what happens.
Aporus fasciatus lost her way entirely when a leaf that covered the nest
was broken off, but found it readily when this was replaced. All the species
of Cerceris were extremely annoyed by new objects placed near the nests,
and Ammophila refused to make use of her burrow after deep lines were
drawn in the dust before it. The same annoyance was exhibited when
any change whatever was made near the spot where the prey was placed,
and experience showed how important it was not to disarrange the grass
or other plants on such occasions. Marchal (1900:1113) has given an
account of the errors made by Pompilus in the return to the nest and reaches
a similar conclusion to the effect that it is not guided by a special sense
of direction, but solely by vision and memory.
Observations on the homing of Bembex and Pompilus. — Stimu-
lated by the observations of Fabre on Bembex (1879:261), which led to the
conclusion that neither memory of place, sight, nor smell guided the insect,
Bouvier (1900:874) investigated the behavior of Bembex labiatus. His
first results were in agreement with those of Fabre to the effect that the
wasp always returned close to the entrance of its nest, regardless of the
substances used to mask this. However, when the objects have a consider-
able size, the insect is completely lost and sometimes spends hours seeking
here and there before relocating its burrow. When the latter was covered
with a flat stone about a decimeter in size, the wasp lighted on the stone,
scratched it, hunted beneath it, and found the entrance only after much
effort. The next day the stone was displaced about 2 dm. from the new
entrance that had been made, with the result that the insect flew at once
to the edge of the stone and began to dig as though at the right place. • He
222 PRINCIPLES AND CONCLUSIONS.
was twice driven away, only to return and start digging. Finally, the rock
was restored to its original position, and the wasp found the entrance
immediately. Clearing away the plants and smoothing the sand about a
burrow for a space of 7 or 8 square decimeters sufficed to mislead Bembex
entirely, and it was only after a long time spent in digging here and there
that the entrance was rediscovered. Bouvier concluded that memory of
place and vision play an essential if not exclusive role in the wonderful
facility with which Bembex returns to the entrance to its nest. Bouvier
has also given an admirable discussion of the faculty of orientation with
insects and other articulates (1922:230, 251).
Marchand (1900:248) found that when a plant growing about 5 cm.
from the burrow of Bembex was displaced about the same distance, the
insect was unable to relocate the entrance and hunted vainly in all directions
for several minutes. The plant was then restored to the original position,
and upon its return the wasp flew close to it and soon found the entrance
to his nest.
Memory of place in Osmia. — Ferton (1905:89) has made observations
on Osmia rufohirta which indicate that this solitary bee possesses the same
remarkable power of memory for place as the social bees and the wasps.
After closing its nest in a shell of Helix, an individual of this species moved
it to a new position a dozen centimeters away and then went to the plant
the leaves of which it was using to make a paste. On its return flights it
first flew to position A, slackened its speed without alighting, and then went
directly to position B, a path that it followed for a quarter of an hour or
more. The observer moved the shell to a new position at C, where the bee
found it after some trouble. On leaving, the latter made several vertical
flights of orientation above the nest before returning to the plant. On
coming back it took the path ABC, though when it went to another plant
growing near C, it returned directly to the latter. Soon afterward it
carried the shell back to A and again began to work on the original plant.
On its return it passed A and, making a slight turn toward B, reached the
point C, whence it returned to A, after determining the absence of the nest
at C. This experiment, with others that were repeated several times, dem-
onstrated that this species is guided by its memory of place. The results
obtained with Osmia ferruginea led to the same conclusion, but as this spe-
cies does not have the habit of moving its shell, it is less skillful in relocating
it and consequently has a poorer memory.
The manner in which Osmia searches for its nest when displaced indicates
that it is guided chiefly by vision. It lands upon all the shells found in its
exploration, which would not be the case if it were guided by smell alone.
However, the bees of this genus also employ the sense of smell, especially
that of contact. Moreover, they can make use of this sense at a distance,
as when it is used to guide them to their favorite flowers. It is unnecessary
to have recourse to the unlikely hypothesis of an unknown sense, since
vision, smell at a distance and in contact, and memory suffice to explain
all the observed facts (1906:29).
Ferton (1908:578) has also discussed Pieron's contention that the homing
of Osmia is due to muscular memory and rejects this except for movements
repeated a great many times.
HOMING FACULTY. 223
The field and nest flights of the bumble-hee.— Wagner (1907:51)
has considered the sense of direction of Bombus under the following cap-
tions: (1) observations on the return to the nest by running; (2) observations
on the field and the nest flight; (3) observations in cages; (4) homing in
nature. When the wings were cut off, Bombus was unable to return to the
nest, showing that it was not guided by a mysterious sense of direction.
Each flight of this bee consists of two separate acts, the field flight and the
return to the nest. These are impressed upon the memory and retained by
it in a different manner, though this holds much more fully for the nest
flight. The bumble-bee finds its way on the nest flight through the careful
inspection of a few objects in the proximity of the nest or with the aid of
the main points in memory. This inspection, as well as the correlated
impression on the memory, can result only from the position of the body
as taken on the return journey to the nest. The inspection of objects,
which leaves recollections of their features, demands a special behavior,
namely, a zig-zag flight near the object; objects not observed in this manner
are not impressed on the memory of the bee. Such a zig-zag flight continues
only so long as the bee can see the objects about the nest, which is within a
radius of a meter at most. Beyond this sphere of vision lies one of orien-
tation, which includes neither nest nor the small objects about it, but only
such large ones as can be distinguished vaguely at a distance greater than
10 meters. Beyond this the flight back and forth is guided by the sense of
direction. Even within the sphere of vision the sight of the bumble-bee
is incomplete in so far as it distinguishes only a few guide-points, which
are rather impressions of positions than of definite objects. As a conse-
quence, only a decreasingly small portion of the way to and from its nest
remains fixed in its memory, and hence the sense of direction plays an
important role in the field flight and the return to the nest.
The homing of the mud-dauber wasp. — In studying the homing
habits of the mud-dauber (1908:215), Turner noticed that the wasp never
flew directly to its nest, but always alighted on a certain crack. It ascended
this crack to the height of the nest and then turned and walked to the
latter, its behavior suggesting that the crack served as a landmark. The
method of experiment and the nature of the evidence may be obtained from
the account of the first experiment:
"The lower shade of window number one was raised halfway and the top shade as far
as it would go. While the wasp was out of the room all the blinds of windows number two
to six were closed, except the upper shade of window number four, which was raised as far
as possible.
"The wasp on entering through window number one flew obliquely upwards across the
beam of light from window number four to the upper third of upright C. (This line of
flight was convex towards the east.) It then flew vertically upwards almost to the ceiling,
then leftward about a foot (this is a little more than the distance of the nest from upright
B) and examined carefully the moulding. Not finding the nest, it began flying first to the
right and then to the left in constantly elongating ellipses with very short minor axes.
All this time it was carefully examining the moulding. Occasionally the mud-dauber
would fly downward into the beam of light and then resume its search. In its lateral
flights the wasp sometimes flew as far to the east as upright D and to the west almost as
far as upright B. At the end of three minutes it had not found the nest, although under
former conditions of illumination it required only half a minute to fly from window number
one to the nest.
224 PRINCIPLES AND CONCLUSIONS.
"While the wasp was still searching for the nest, the top shade of window number four
was lowered and the corresponding shade of window number three raised as far as possible.
This reproduced the conditions under which the wasp had originally worked. Almost
immediately the wasp found the nest!
"From these experiments it is evident that in finding its way back to its nest, the mud-
dauber is guided neither by what is known as a homing instinct nor by what Pieron has
called a kinesthetic reflex; for if either assumption were true, a manipulation of the light
should not have altered the wasp's behavior. Evidently light plays a prominent role in
the homing of wasps, yet the behavior of the mud-dauber is not a phototropism, for in no
case did the wasp so orient itself as to have the major axis of its body parallel to the rays
of light. Neither is the wasp's behavior merely a reflex response either to brightness or
to the direction of the rays of light; for if that were the case, in experiment six, when all
the shades of windows number two to four were lowered except the top shade of window
number two, the wasp should have flown, not to the wall to the west of window number
three, but to window number two. But brightness is not the only factor which influences
the movements of this wasp; else, when all the shades of windows number two to six
were lowered, it would have been impossible for it to rediscover the nest. This series of
experiments warrants the induction that, in the wasp's memory, the nest is located in a
certain direction and at about a definite distance from a bright patch which is situated
at a known elevation in a peculiar environment.
" The above statement predicates to wasps memory and an awareness of space relations.
As to the existence of memory, these experiments furnish unequivocal evidence, and they
warrant the conclusion that the flying mud-dauber, like the creeping ant, is guided by
certain landmarks, and that light plays a prominent role in furnishing such landmarks."
Experiments on the orientation of bees in homing. — Frisch (1914: 86)
has summarized the results of others as to the practical value of painting
hives in color and has contributed the details of some of his own experiments
in this field. All of these support the conclusion that honey-bees, when
their hive is set apart from the neighboring ones by means of color in a
striking manner, utilize this as the chief means of orientation in finding
their home. They further show that bees observe not only the color of
their own hive, but also the color and relative position of neighboring ones.
In consequence the bee-keeper can hardly devise a better and more certain
way of enabling bees to locate their own hive than that of painting it in
colors. For this, however, it is desirable to paint the entire outside and
not merely the landing-board or the entrance. Care should be taken not
to employ for neighboring hives colors that are distinct for our eyes but not
for those of the bee, such as blue and purple, or black and scarlet-red. As
a result, when hives are numerous, it is better to use color combinations for
each, such as one-half red and the other yellow, rather than too many
colors or shades which may merely be distinct to us.
Homing ability in Polistes. — The Raus (1918:273) have made a
number of experiments on the homing ability of the wasp, Polistes pallipes,
which they summarize as follows:
"Out of 33 queens which were taken for various distances from one-eighth mile
to 2.7 miles, 24 returned to the nest. Of the 22 taken out for the first time, 17 reached
home; of the 11 which had made previous test flights, 7 successfully returned. With
the workers, the results were quite different. Of 112 workers that were used, only
28 returned, and those that returned did so only in the short flights. The long dis-
tance tests always gave negative results. Out of the 17 new workers that were ex-
perimented upon, none returned; of the 33 old workers, 14 came back; of the 62
workers of unknown age, 14 returned. According to the law of chance, it is easily
possible that these 14 out of the 62 workers of unknown age may have been old ones.
SMELL. 225
Previous experience is not necessary to successful flights; 27 successful returns out
of 96 were made by wasps used for the first time, but only 1 out of 16 wasps that had
previous flights made a successful second trip. Not one of the 17 males returned
to their former nests, even though the distance for 16 of them was only one-eighth mile.
The function of the antenna? is not the sole factor in bringing them home, for out of
24 mutilated wasps, 18 successfully returned. Thus, by the elimination of other
faculties, the evidence grows stronger that vision is the sense whereby the insects
regain their homes."
SMELL.
Sense of smell in insects deprived of antennae. — Forel (1886:184) in-
sisted that the experiments of Graber (1885) with strong odors merely
proved whether these were irritating or not to the insects concerned and that
evidence of smell could be obtained only by causing the insect to recog-
nize a certain substance and especially to distinguish it from others in
a constant and indubitable manner. As an example, he cited the case of a
swarm of males of Saturnia carpini that besieged the window of his room
after some females had hatched out, which he regarded, together with many
previous observations of others, as demonstrating in insects a special
sense that corresponds to that in man. Further demonstration may be
furnished by the removal of the antennae whenever the loss of these or-
gans carries with it the loss of the sense of smell, as proved to be the case
in many of the experiments he carried out.
When the antennae were removed from individuals of four different
genera of ants, they mingled readily without harming each other, and they
recognized honey only when the mouth touched it by chance. If the an-
tennas were removed in Formica fusca and the ants placed in a globe with
their larvae, cocoons, and soil, they did not attempt the slightest digging
or give the larvae the least care. When ants of another species were added,
they did them no harm, but when the anterior tarsi were cut off above
the spine in the same species, they immediately killed other ants given
them, and made futile efforts to dig and to care for the larvae. A repetition
of these experiments eight years later gave similar results, except in the
case of Myrmica ruginodis, which killed other ants as well as its own kind.
In the case of Sarcophaga vivipara with both eyes excised, the female readily
found a dead mole on which it fed, but after the antennae were removed,
it paid no more attention to the mole, even when placed beside it. A blue
fly which also fed upon the mole and deposited eggs in it paid no attention
whatever to it after the antennae had been removed, in spite of the use of
its eyes. Two other individuals of Sarcophaga behaved in similar manner,
while a very active Lucilia caesar, though placed on the mole, ceased eating
and depositing eggs as soon as the antennae were gone. In like manner,
beetles of several genera were unable to rediscover putrid objects after the
removal of the antennae. Males of Bombyx mori, which perceived the fe-
males at a distance and ran to them directly, were no longer able to deter-
mine the direction of the female after the antennae had been removed.
In an experiment with a wasp, Polistes gallicus, three individuals were
employed, one having the antennae removed, the second the front of the
head with the sense-organs of the mouth, and the third was left intact.
In repose the latter was able to recognize honey at a distance of a centi-
226 PRINCIPLES AND CONCLUSIONS.
meter and followed it as the pin covered with it was withdrawn. The second
wasp behaved in identical fashion, though it was unable to sip the honey,
while the first was absolutely unable to perceive the honey until the latter
was put in contact with its mouth or to follow as it was moved away.
To determine how acute the sense of smell is in bees, Forel placed some
hungry honey-bees in a glass box with a drop of honey covered with a disk
of wire screen with large meshes, through which the honey could be read-
ily reached. In spite of this they walked back and forth over the screen,
passing a hundred times within 2 or 3 mm. of the honey, without stopping
or suspecting the presence of the food they sought. As soon as the screen
was removed, they found the honey by chance and sipped it with avidity.
In agreement with Lubbock, it was concluded that honey-bees guide
themselves almost exclusively by sight, their antenna? being very short,
without clubs, and having olfactory terminations only on the internal
dorsal face.
The following conclusions were deduced with reference to smell :
1. With many insects that guide themselves primarily by vision, as with dragon-
flies and cicadas, the antennae are rudimentary and the sense of smell likewise.
At night such insects are immobile and by day all their acts are guided by sight
(the cicadas also perhaps by hearing).
2. The sense of smell, notwithstanding the objections and the experiments of Graber,
resides in the antennae, especially in the swollen or perfoliate part in which
the antennal nerve ramifies.
3. With certain insects, especially the majority of the Diptera, the antennae are
stiff and probably serve solely or almost so as an organ of smell.
4. But with other insects they are mobile and serve at the same time to smell at a
distance and to feel near at hand. This is true of Hymenoptera in the highest
degree.
ForePs criticisms of Graber's results. — Emphasis was placed by
Forel upon the fact that we regard as odorous substances those that are
odorous for us, in spite of the fact that the study of animals shows enor-
mous differences between them in this respect, a substance extremely odor-
ous for one species being little or not at all for another. This general
fact was recognized by Graber, but his simple and uniform method of
experimentation failed to take account of it. Graber placed different
insects in the middle of a box divided into two compartments open below.
He put an odorous substance in the top of one of them and observed at
the end of a certain time the number of insects in each part. He employed
especially substances with strong and often corrosive emanations, and in
many cases found that insects deprived of their antennae behaved like
normal ones. But this was not always the case, Asphodius, for example,
ceasing to gather under cow-dung when the antennae were removed.
This was because Graber had made the proper choice, that of an substance
sought by this insect in nature. Moreover, he finally stated that a certain
degree of smell resided in the antennae.
In the case of Lucilia caesar, Graber found that 169 normal flies col-
lected under putrid meat, while 92 were found on the other side, but with
the antennae cut off the respective figures were 101 and 39, which he
thought proved irrefutably that they had smelled the meat without the aid
SMELL. 227
of antennae. Forel pointed out that the numbers were not sufficiently
different to prove much, and this is confirmed by the fact that the respective
percentages for meat were 64 and 72. In addition, the odor of putrid
meat in a box was regarded as sufficiently strong to provoke tactile or
gustatory reactions quite apart from smell, while flies inclosed in a box
are far from normal in their response. With Formica rufa, Graber found
that essence of rose was not liked, 515 ants collecting in the empty division,
and but 42 in that containing the essence, while with the antennas cut off
the respective numbers were 299 and 165, figures which Forel regarded
as insufficient to prove that ants have other organs of smell than antennas.
However this may be, he declared that Graber had absolutely not proved
that ants with or without antennas were in a state to recognize the essence
of rose as such, to distinguish it from another substance, or to find it when
hidden. Finally, in another place Graber seemed to be of the opinion
that these responses were rather of the nature of reaction to irritation
than smell. In the case of Silpha thoracica, while essence of rosemary
quickly produced a reaction in the absence of antennas, asafetida did not,
but with the antennas present the response to both was equally prompt.
In summarizing, Forel declared that the experiments of Graber ex-
hibited a very superficial knowledge of the habits of insects, often lacked
controls, and were too little varied, and that the means and the reagents
employed were frequently too strong and took no account of the habits
or needs of each species. Moreover, after seeking the location of the sense
of smell in various places in contradictory fashion, Graber finally stated
that "there are insects in which the antennas play a preponderant rdle
in the distinction of weaker odors, food, etc."
In a later paper (1887:13) Graber himself stated that the stronger
odors usually repel insects and that this response is not due to the sense
of smell, but to a generally very painful excitation of the sense of feel,
which is often extraordinarily developed. As a consequence of a number
of carefully controlled experiments, he reached the conclusion that Plat-
eau's results with the cockroach (1876) were untrustworthy, though he was
able to confirm the statement that the sense of smell is located in the
antennas.
Hauser's experiments. — Hauser (1880:367) determined the effect of
removing the antennas in a wide range of insects from beetles to bees.
The loss of the antennas caused many individuals to become sick and die,
though some lived for weeks afterward. Coating the antennas with paraf-
fin gave the same results as extirpation. Beetles made no response to
a clean glass-rod, but when this was dipped in carbolic acid, the effect
was noticed at 4 inches and the insect moved away quickly as the rod
was brought nearer. It reacted even more strongly to turpentine and
acetic acid. The experiments were repeated on the second day after the
removal of the antennas, but no response occurred. This was in spite of
the fact that the beetles ate more heartily after the operation and some
lived more than two months. Species of various genera gave similar re-
sults, but a few continued to respond slightly. Beetles of the genus Silpha
lost the power of finding putrid meat after the amputation of the antennas,
and the same result was obtained with different species of flies. Male and
228 PRINCIPLES AND CONCLUSIONS.
female beetles or butterflies that mated freely when normal did so only
occasionally after the antennae were lost.
Olfactory pores. — Hicks (1857-1860) was the first to discover the pores
now termed olfactory by Mclndoo, who summarizes the former's results
as follows (19142:38).
"To summarize Hicks's three papers, he discovered these pores on the halteres and
on the bases of the wings of all Diptera examined; on the bases of all four wings
of the four- winged tribes; on the trochanter and femur of all insects, and occasionally
on the tibia. He examined many species representing various insect orders and found
the pores even on the lower insects, such as the earwig. In such wingless insects as
the worker and soldier ants, he infers that these pores are much more abundant on
the legs than they are on these appendages in the winged insects. Hicks suggested
an olfactory function for all of these pores, whether on the wings or legs, but he per-
formed no experiments of any kind. In regard to smell in insects and the function
of the pores on the legs, he says: 'The delicacy with which odors are perceived by
many insects argues an olfactory apparatus of considerable perfection; and it seems
to me not impossible that these latter-named organs (those on the legs) may be in
some way connected with the sense of smell, or perhaps with some sense not to be
found in the Vertebrata.'"
Mclndoo mentions the work of about a dozen other investigators on
these pores, two of whom regarded them as olfactory in function.
Mclndoo's own studies (1914) of the pores are much the most detailed
and comprehensive, and his experiments upon their function appear to
be the most extensive in the entire field of olfaction. The Hicks vesicles
or olfactory pores consist of inverted flasks in the chitin and of fusiform
sense-cells lying beneath the mouths of the flasks. The sense fiber pierces
the bottom of the cone and enters the pore aperture, thus coming in direct
contact with the air containing odorous particles, contrary to the condition
in the antennae, where the odors must pass through a hard membrane
in order to stimulate the sense-cells. In the case of the honey-bee the pores
are found on the bases of the wings, on the legs, and on the sting of worker
and queen. They also occur on the mouth-parts of all Hymenoptera, while
they are lacking on the antennae of the honey-bee and probably all other
Hymenoptera. For the legs of ants the number varies from 211 to 356
and for the winged ants the total number varies from 463 to 1,090. In the
honey-bee the queen has an average of 1,860, the worker 2,268, and the
drone 2,604; the averages for all four wings are 1,310, 1,510, and 1,998,
and for all six legs, 450, 658, and 606 respectively, the sting having an average
of 100. The total number for a bumble-bee was 1,627 and for a wasp 1,957;
the number of isolated pores is approximately one-half the number in groups,
except in the worker honey-bee, where it is somewhat less.
Experiments with antennae removed, mutilated, or coated. —
Mclndoo (1914 : 291) finds that worker bees with the left antennae
pulled off at the base reacted to the three essential oils, peppermint, thyme,
and wintergreen, in an average of 4.6 seconds in contrast to 2.3 seconds for
intact individuals. When 2 to 8 joints of the other antennae were removed,
the reaction-time rose proportionately from 15 seconds for the first case and
88 for the last. Bees with both antennae pulled off or covered with celloidin
failed entirely to respond to these oils. Drones with 4 or 5 joints of one
SMELL. 229
flagellum missing responded to 6 of the 10 odors used in an average re-
action-time of 3.16 seconds in contrast to 2.9 seconds for unmutilated ones.
When both antennae were removed from workers, none responded to oil
of peppermint held within a half inch or to smoke, while all the normal
bees reacted quickly and markedly. Similar experiments with other oils
yielded no reaction in the case of 50 mutilated bees, though the normal ones
never failed to react.
In the case of immature bees the results were quite different. When
both the antennae of workers were burned off, they responded readily to
the three essential oils by moving slightly and vibrating the stubs of the
antennae. Frequently, however, they did not react to odors or anything
else. When the antennae were covered with glue and the tarsi of the front
legs burned off to prevent the removal of the glue, most of the bees died
in a few days, but a score were fairly normal and responded to the oils
without failure.
Experiments with wings, legs, and stings mutilated. —
"To determine the function of these pores, the wings, legs, and stings of many worker
bees were mutilated (Mclndoo, 19143:47). The behavior of the mutilated bees was
carefully studied, and they were tested with odors in the same manner as were the
unmutilated ones. The stings of 100 workers were pulled out. These bees lived 30
hours on an average. Twenty of them were tested with odors. They responded only
slightly more slowly than unmutilated bees. The wings of 28 workers were pulled
off. When tested with odors, these bees responded one-eighth as rapidly as normal
bees. The bases of the wings of 20 workers were covered with liquid glue. When
tested, these bees also responded one-eighth as rapidly ao unmutilated ones. The
pores on the legs of 20 workers were covered with a mixture of beeswax and vaseline.
When tested, these bees responded two-fifths as rapidly as unmutilated workers.
The wings were pulled off and the pores on the legs of 20 workers were covered with
the beeswax-vaseline mixture. When tested with odors, these responded one-twelfth
as rapidly as unmutilated ones. All of the workers with mutilated wings and legs
lived just as long in the observation cages as did unmutilated workers, and they were
absolutely normal in all respects, except that they reacted to odors more slowly."
With the oils and other odors four dealated females of Formica gave
a reaction-time of 2.89 seconds in contrast to 2.45 seconds for winged
females of the same species. Pulling off the wings of 7 males removed
92 per cent of the pores and increased the reaction-time from 2.63 to 3.6
seconds. When the wing bases of female ants were covered with liquid
glue and the legs with beeswax-vaseline mixture, the reaction-time was
about doubled, and similar results were obtained with Camponotus. When
males of the latter had the wings pulled off, leaving but 12 per cent of the
pores, they gave a reaction-time of 3.49 seconds, which is one and a fourth
times that of the normal insects. Worker hornets similarly treated gave
nearly thrice the reaction-time for normal ones.
Mclndoo's criticisms of experiments with deantennate insects. —
"The following criticisms concerning the physiological experiments performed
with the antennae of the various insects may be offered (1914:342, 19143:54).
Most of the previous investigators have studied the behavior of the insects investigated
in captivity for only a short time, while the remainder have paid no attention at all
to the behavior of their unmutilated insects. They cut off either a few joints of both
230 PRINCIPLES AND CONCLUSIONS.
antennae, or these entire appendages, or varnished them with paraffin, rubber, and
so forth. When a few joints are severed, the sense of smell is apparently weakened.
This is true for bees also. When both antennae are amputated or varnished, the in-
sects as a rule fail to respond to substances which normally affect the olfactory sense.
They generally fail to respond to odors held near them and fail to find food in cap-
tivity, and do not return to putrid meat and dead bodies when removed from such
food. Males so mutilated as a rule do not seek females and show no responses when
females are placed near them. Such experiments were seriously criticised until Hauser
in 1880 presented his apparently conclusive results. Many of the insects on which he
experimented with the antennae amputated became sick and soon died. Most of
them failed to respond when the antennae were mutilated, although Carabus, Melo-
lontha, and Silpha responded slightly, while all the Hemiptera that he used responded
almost as well with their antennae off as they did with them intact. Only 40 per
cent of the ants from which Miss Fielde cut the antennae recovered from the effect
of the shock. Not one of these observers has studied the behavior of the species
under observation sufficiently to know exactly how long they live in captivity with
their antennae either intact or mutilated. No one, except Miss Fielde, has kept a
record of the death of the mutilated and normal insects so accurate that one might
know what percentage died from the operation. To cut off some other appendage
or even the lower part of the head, as Forel did, is not a fair test, because such oper-
ations seldom expose sense-cells and never any nerve equal in size to that of the an-
tennae, unless one pulls off the wings. When the wings are pulled off, the large nerve
is severed between the masses of sense-cells and the thorax, and the sense-cells are
not exposed to the air, as they are when antennae are removed. Even if the an-
tennae are cut through the scape, the large masses of sense cells belonging to John-
ston's organs are severed. When the lower part of the head or the tarsi are cut off,
as Forel did, no nerves are exposed to the air except ends of small nerves. From the
foregoing it is only reasonable to assume that when the antennae of any insect are
injured in the least degree, the insect is no longer normal and if it fails to respond
to odors placed near it, this negative response may be due to the shock of the injury."
Present status as to the seat of the olfactory sense. — In spite of
the obvious merits of Mclndoo's studies, it is evident that further in-
vestigations will be necessary to decide the respective claims of the an-
tennae and the olfactory pores as the organs of smell. The results of more
than a score of investigators, some of them, such as Forel, Graber, Hauser,
and Plateau, of the first rank, are in accord as to the olfactory function
of the antennae, and it is certain that their conclusions can not be rejected
without a repetition of their most decisive experiments. On the other hand,
many of Mclndoo's are similarly decisive, and at present it seems quite
possible that both antennae and pores have to do with smell. The burden
of proof rests upon the latter, however, since they lack the confirmation
given by successive investigators to the function of the antennae. Mcln-
doo has given a practically complete list of those who have based their
conclusion as to the olfactory function of the antennae upon experi-
mental evidence (19143:14). They are Dug6s (1838), Lefebvre (1838),
Ktister (1844), Perris (1850), Cornalia (1856), Donhoff (1861), Balbiani
(1866), Forel (1874, 1878, 1886, 1901), Trouvelot (1877), Layard (1878),
Slater (1878), Chatin (1880), Hauser (1880), Porter (1883), Graber (1885,
1887), Plateau (1886, 1902), Dubois (1895), Mayor (1900), Gorka (1900),
Fielde (1901, 1903), Barrows (1907), and Kellogg (1907). The most ex-
tensive and significant studies have been those of Forel, Hauser, Graber,
SMELL. 231
Plateau, and Mayor, since the extirpation of the antennae in most cases de-
stroyed the sense of smell without rendering the insects otherwise abnormal.
Graber's second series of experiments is especially important, since they
led him to abandon his former view that the antennae were not olfactory
organs. (See also Schenk, 1903 : 573.)
A scrutiny of Mclndoo's conclusions shows that they are not in entire
accord, though this may be due to a desire to avoid overstatement. The
statements concerned are as follows:
"These results indicate that the olfactory organs are located elsewhere. At most
it can be claimed only that the antennae may assist in the receiving of odor stimuli"
(1914: 297). "It may now be assumed that these pores constitute the olfactory organs
in the honey-bee, and perhaps in insects in general" (lb., 341). "Then it will be real-
ized that the antennas can no longer be regarded as the seat of the sense of smell
in insects" (lb. 345). "In conclusion, it seems that the organs called olfactory pores
by the author are the true olfactory apparatus in Hymenoptera and possibly in all
insects and that the antennae play no part in receiving odor stimuli" (19143:56).
The mature bees used in experiments with the antennae cut off gave either
greatly delayed reactions or none at all, but when these were burned off,
the reaction-time was but slightly increased. However, the latter lived
an average of 5% days, while the former in some cases lived an equal period,
indicating that both were equally abnormal and that the discrepancy must
be sought elsewhere. Forel long ago criticized Graber's results because of
the strong odors employed, insisting that natural odors to which the various
insects are accustomed should be used, and this objection may hold in some
measure for the essential oils. Moreover, it seems possible that reaction-
time experiments do not furnish such decisive tests as those made by Forel,
Hauser, Mayor, and others. Furthermore, the use of a stop-watch would
appear almost imperative, especially for short intervals.
Mclndoo frequently finds a relation between the number of pores and
the reaction-time. "If the reaction-time of each caste of the honey-bee
is compared with the total number of olfactory pores, a consistent ratio is
obtained. A drone has 2,600 pores and responds in 2.9 seconds; a worker
posesses 2,200 pores and responds in 3.4 seconds, and a queen has 1,800
pores and responds in 4.9 seconds." This, however, is only a qualitative
relation, since the worker with 400 pores less than the drone requires but
0.5 second longer, while the queen with 800 pores less takes 2 seconds
longer. The absence of a definite quantitative relation is further shown
by the fact that removing the wings of workers with 1,510 pores increased
the reaction-time 8 times, while coating the 658 pores of the legs increased
it but 2.5 times. Finally, although wasps are generally regarded as having
a keener sense of smell than bees, the one species studied possessed only
1,957 pores.
On theoretical grounds it is difficult to reconcile the large number of
pores and their distribution with the high development of the sense of
smell in insects. This is often much more highly developed than vision,
and one would expect a highly differentiated organ to correspond and one in
immediate connection with the "brain," as is the compound eye. On the
contrary, there are hundreds of pores, some of them as far away from the
central ganglion as possible and several times as far as others. Moreover,
232 PRINCIPLES AND CONCLUSIONS.
their position on the tarsi and the sting casts grave doubt upon their effec-
tiveness as olfactory pores. Their localization on the bases of the wings,
the legs, and the sting suggests that they have to do with the sense of touch
or feel in the wide sense and that their response to chemical stimuli is
somewhat similar to that of all exposed nerve-ends * However, it is idle to
speculate upon this until the results of new investigations, which take
into account the experiments of both Mclndoo and his predecessors, are
made available.
Turner (1916:385) states: "These experiments of Mclndoo are pains-
taking and his anatomical studies of what he calls olfactory pores are
excellent, but the serious student, who is acquainted with the experiments
of Forel and others who 'claim that the antennae are the organs of smell'
will not be convinced that the last word has been said on the subject.
They do not seem to have met the criticisms raised by Forel" (1878, 1886,
1908), as indicated above.
INTELLIGENCE.
Relation between the senses and mental faculties of insects. —
Forel (1886:233) considered that insects possess our five senses, with the
possible exception of hearing, in a well-differentiated degree and with a
special energy that we consider analogous to our own. The quality of their
vision is different from that of ours in certain respects, as certain of them
see the ultra-violet rays. Many insects have besides a kind of odor by
contact, which enables the ants in particular to distinguish their companions
from enemies. The development of each sense and of each of its kinds of
special energy (color, odor) varies enormously, not only for families and
genera, but even with related species and with the sexes of the same species.
Insects naturally combine their different senses in their acts, but in general
the principal sense is that of direction, just as sight is with man. Sight
assumes this role with the aerial insects, especially the dragon-flies and the
butterflies. With the workers among ants, it is in general smell, with the
spiders, touch, and with the beetles it is touch and taste combined.
It is evident that insects possess the faculty of the so-called voluntary
movements which are not merely reflex or simply automatic, but very
well coordinated and nearly all dictated by combinations of instinctive
reason with the aid of sensory impressions, and admirably adapted to their
end. They frequently have an excellent memory of places, of things, and
perhaps of persons. Thus, insects reason, and the most intelligent of them,
the social Hymenoptera, reason much more than one thinks when he ob-
serves the mechanism due to instinct, but to properly observe and compre-
hend these reasoning processes, it is necessary to put instinct out of com-
mission. Instinct is organized, systematized, and automatic reasoning,
that is, it has become unconscious. Instinct and reason are not in inverse
proportion to each other, as Pouchet has remarked, and the insects with the
most intelligence are generally those with the largest number of varied
instincts, though this is not always true. Finally, insects exhibit passions
that are more or less bound up with their instincts, and these vary enor-
* Since this was written, it has been found that Graber ascribed the sensitiveness of the
"afterborsten " and the legs to relatively strong odors to the sense of feel and not to that of
smell.
INTELLIGENCE. 233
mously with the species. Among the ants the traits of character recogniza-
ble are anger, hate, devotion, activity, perseverance, greediness, boldness,
discouragement, and fear. Thus, in studying the habits of insects it is
necessary to take into consideration their mental faculties as well as their
organs of sense.
Memory and general intelligence of wasps. — The Peckhams
(1887:121) concluded that wasps have a very good memory, remembering
for ten days the characteristics of the glass of a window through which
they were accustomed to fly. The memory varied greatly in different indi-
viduals; in the color experiments many wasps would fly into the false
entrance several times, while others would fly in but once, and still others
would only hover over it before turning to the true opening. When blades
of grass were placed across the entrance to the nest, not one of more than
300 wasps made any attempt to remove them, in spite of the fact that they
seriously hindered them and were less than a usual load in weight. Even
when going out without loads no endeavor was made to get rid of the ob-
stacle. They noted two classes of intelligent action among the Hymen-
optera, which are sufficiently distinct to be considered separately (1905:301).
The first includes those acts performed by large numbers in a similar
fashion under like conditions, while in the second each act is an individual
affair. The first is exemplified by Fabre's experiment with Osmia, in which
he took 2 dozen nests in shells from a quarry, where the bees had been
nesting for centuries, and placed them in his study along with some empty
shells and hollow stems. When the bees came out in the spring, nearly all
chose the stalks as better suited to build in than the shells, thus evidencing
an intelligent adaptation to new conditions. The second case is illustrated
by a wasp {Pompilus scelesius) which tried to drag its prey into the opening of
a nest that was too small. After several vain tugs, it was carried to a place
of safety up among some clover blossoms, and after some fifteen minutes
of walking and brushing herself, the wasp set about making the hole larger.
During this period she must have carried in mind the idea of doing a neces-
sary act outside of the ordinary routine, and it is also suggestive that the
hole when enlarged was exactly what was needed.
Memory of place in bees. — In an extended critique of Bethe's paper
(1898: 15) which endeavored to establish the hypothesis that bees are merely
reflex machines, Buttel-Reepen (1900:96, 1907) discussed the evidence
chiefly under three heads, namely, (1) the hive odor and the reactions
resulting from it, (2) the means of communication in bees, and (3) memory
of place in bees. The latter alone is directly connected with the present
inquiry and hence summarized here. Bethe assumed that —
"Bees are led back to the hive by a force entirely unknown to us. This force does
not adhere to the hive itself, and it does not lead bees back to the hive itself, but to
the place in space which the hive usually occupies. It does not act at boundless
distances. It is an old experience of bee-keepers that they can take a colony to another
stand without fearing that the bees will return to the old place, if the new spot is
only more than six kilometers from the old. It follows, then, that this force acts at
most at a distance of six kilometers, since the impulse to return to the hive is the strong-
est of all impulses in bees. But I believe that the zone of action of the force is not a
234 PRINCIPLES AND CONCLUSIONS.
circle with a radius of six kilometers, but of only three or four kilometers. If the cir-
cle had had a radius of six kilometers, then the bees of the transposed hive would
be back into the circle of action if they got more than half that distance near the old
position in foraging, and would have to return to the old place. But this only happens
if the old position is less than six kilometers away from the new. We must,, therefore,
accept something near three kilometers as the boundary for this circle of action for
this force."
When Bethe freed 8 marked bees at each of three distances from the hive,
namely, 350, 400, and 650 meters, they found their way back in 1.5 to 3.5,
5 to 10, and 4.75 to 10.5 minutes respectively. Buttel pointed out that at
the normal velocity for bees, doubled because they were carrying loads,
the unknown force should have led them all back in 1 minute 12 seconds,
1 minute 36 seconds, and 2 minutes 36 seconds, for the respective distances.
This discrepancy can only be explained on the assumption that the bees
had to orient themselves with their eyes and that they made errors in doing
so, and thus lost time. Since the unknown force does not bring bees back
to the hive but only to the place where it stands or usually stood, it must be
memory of location. When bees are stupefied with chloroform, ether,
saltpeter, etc., memory of location entirely disappears, and they no longer
recognize their home or the place where it stands. As soon as they become
normal, they again begin to orient themselves with regard to the home,
gathering new memory pictures of the sources of nectar and pollen as well as
of the new hive. This also shows their capacity for learning, a fact disputed
by Bethe. Buttel also emphasizes the discrepancy between Bethe 's as-
sumption that all the bees set free within the circle of action of the "un-
known force" must return to the place that "draws them like a magnet,"
and the actual results obtained by him in the box experiment. When the
bees were released from the box, most of them, after a few circles in the air,
went in the direction of the institute, but "two mounted to a height of
about 3 meters, made a few circles of 4 or 5 meters in diameter, and
then alighted on the box. I drove them away into the air again. They
flew in large circles about it, and then again alighted on the box. I then
took the box away and put it on another stone, having driven the bees into
the air once more. Both bees flew so high that I could no longer see them,
but a few seconds later they reappeared and slowly flew about the place
where the box had stood." Thus some bees were influenced by the "un-
known force" and others were not, a fact that Bethe did not attempt to
explain. Buttel carried out similar experiments with the same results and
all of them furnished evidence of memory for locality, though he regarded
the conditions as abnormal in comparison with those carried on at the
apiary. Although Bethe gave no explanation of why the "unknown force"
operates at a distance of but 3 or 4 km., it is really very simple, since
this supposedly mysterious force operates only within the space in which
the bees have made flights of orientation and stored up memory pictures.
The identity of this unknown force with memory of location is further
proved by the following facts: If young bees are let fly not far from the
apiary before they have had their flight of orientation, none of them find
their way back to the hive, but if old bees are released at a much greater
distance they all return. If a colony is brought from a place more than
INTELLIGENCE. 235
7 kilometers away and the old bees released only 30 or 40 meters from the
hive before they have been able to make their flight of orientation, none
find their way back in case trees or houses intervene. Memory of locality
may be lost through artificial swarming, by the influence of buckwheat
honey; by the effect of dark or cold; by throwing bees into water, and by
the lapse of time. Memories also disappear quickly by new impressions
obliterating the old. In their first flight from the hive, bees turn their
heads toward the latter and survey the hive, the neighboring hives, and
the general surroundings. After this short preliminary flight, small and
then larger orientation flights are taken and the landmarks impressed on
the memory. It is evident that bees also orient themselves in special ways.
If the height of a hive is changed so that the entrance is suddenly made
30 cm. higher or lower, the bees fly exactly to the level where the entrance
was before, and hours or even days pass before a smooth flight is made to
the new height. The ability to judge distances even goes so far that bees
normally fly in and out of the same corner of the hive-entrance. If the
entrance is closed to about the breadth of an inch, they will try to enter
at the usual spots and find the open part only after considerable search.
A bee flies to the point of entrance without being able to see it or the nearest
surroundings of the entrance, on the basis of its orientation in the neigh-
borhood. As it comes closer, it generally notices the surroundings of the
entrance, for it becomes aware of any changes in the outside of the hive.
Forel (1900, 1908:217) has dealt with Bethe's results and conclusions
in similar detail. He says :
"When writing the preceding, I was ignorant of the work of Buttel-Reepen. If
on the one hand I regret it, on the other it has the advantage of having rendered my
criticism of Bethe independent of his, and the reader of both will be astonished to
see to what extent our results agree.
"I am obliged to combat Bethe's conclusions as preconceived, one-sided, and of
an absolutism quite contrary to logic and the scientific spirit."
Memory of time and association of impressions. — Buttel-Reepen
stated that where colonies stand in fields of buckwheat the flight is lively
until about 10 o'clock, then becomes entirely quiet for the rest of the day,
to begin again vigorously the next morning. Buckwheat nectar is abun-
dant only in the early morning; as the nectaries dry up, the bees fly out
once or twice and then cease their vain flight. In spite of the sea of flowers
and the strong fragrance, few bees are found in the field after 10 o'clock.
Regardless of the constant attraction of color and scent and the habit of daily
flight to the fields, the processes of learning and remembering play the
directive role.
Association of impressions is illustrated by the behavior of bees that found
a honeycomb in a room, after flying through the open window. More and
more came, some of them being kept out at the second window, which was
closed. To prevent this the honeycomb was placed in the open window, and
a half-hour later the bees were driven away and the window closed. Twenty
minutes later the room above, the windows of which were open, was found
full of bees. In order to observe their behavior accurately, the bees were
driven out, the windows closed, and Buttel went into the garden. Here
the bees were seen trying to enter at the window from which they had been
236 PRINCIPLES AND CONCLUSIONS.
fed, then flying to the next window and afterward to the other windows until
they had tried them all. It was then assumed that the existence of an
actual association of honey with the form of a window would lead them to
extend the search to the neighboring house, which they did. He also cited
in confirmation the observation that, when a dish of honey is placed on the
trunk of a tree, bees afterward search for honey at the same place on all
the trees in the neighborhood.
Memory of time and memory association in honey-bees. — Forel
(1907:459) reported the behavior of bees which were led to visit an out-door
dining table, on which it was the habit to place preserves at breakfast,
from 7h30m to 9h30m a. m., and at tea, from 4 to 5 p. m. Drawn by the odor
of cooked cherries, one or two bees first found the preserves and in a day
or two a whole swarm came to feast on them. However, after having sought
for them at mid-day also and having found nothing, they entirely ceased
coming at this time and confined their visits to the hours of breakfast and
tea. After this habit had been confirmed, the table was set as for breakfast,
but no preserves were placed on it. A large number of bees came to it as
usual and searched everything in vain. They stopped coming at 10 o'clock
and only a single one appeared at noon and but one or two at 4 o'clock.
The next morning a much smaller number than usual was observed and
they did not stay long. More appeared at noon than before, as if driven to
make the search for the sweets at other hours. When they returned at
4 o'clock they were given some preserves, and this led others to come. The
next day the same behavior occurred at breakfast time, the bees flying
against an inverted glass containing preserves but paying no attention to
the edge where the odor could be perceived. At 10 o'clock all had again
disappeared. After several days a supply of sirup and preserves was made
constantly available, and the bees ceased to come at stated hours. These
facts were regarded as clearly proving that bees not only have place memory
but also that of time. In short, they returned to the same place and ex-
amined the same or similar objects only at the hours when they had found
them before, and, after several deceptions, but once at mid-day, the hour
at which they found nothing. Bees were found peculiarly adapted to the
experiment on account of their poor sense of smell, visual and gustatory
memory operating alone. The visual memory of colors and forms guided
them and also enabled them to distinguish the preserve container and
similar objects, the sense of smell coming into action at the very short
distance of 1 cm.
Intelligence of honey-bees. — In his conclusions (1907:44) Buttel-
Reepen stated:
"It is unquestionable to me that the senses of bees are similar to those of men, and
that especially the senses of sight, hearing, and smell play an important part. As
Wundt has already shown, we certainly are 'referred essentially to outer observations
in animals; what they teach us is not a total dissimilarity in the capacity of mind,
but the most essential conformity with the psychic processes that we observe in man,
and know chiefly from observation of ourselves.' The anthropomorphic apprehen-
sion relative to the question of consciousness has brought it about that there has been
ascribed to bees a consciousness similar to human consciousness, and accordingly
INTELLIGENCE. 237
the most varied human feelings. On the basis of my observations I am of the opinion
that bees possess either no consciousness at all, or one of only the lowest degree of
development. The question of consciousness is left to subjective estimates, but the
question whether an animal learns and can acquire experience or not may be deter-
mined objectively. We see that bees show signs of an admirable memory in their
orientation and also in other activities; further I believe I have shown that the
bee possesses a perception for color and form, and develops a rich capacity for com-
munication by means of its well-developed 'language'; that, further, it is able to
gather experiences, to learn and to form associations of impressions, etc. I can not
agree with Bethe, therefore, in his denial that the bee has capacity to gather expe-
rience and thereby to modify its action. The bee is evidently much more than a reflex
machine."
The psychic powers of insects. — Forel summed up his conclusions as
to the intelligence of insects as follows (1901:25; 1904:20; 1908):
"It ensues from the concordant observations of all the experts that sensation,
perception, association, inference, memory, and habit in the social insects follow the
same fundamental laws as in the vertebrates and ourselves. Moreover, attention
is strikingly developed in insects, often assuming the nature of an obsession that is
hard to divert. On the other hand, inherited automatism manifests an immense
preponderance, and the faculties mentioned are exhibited in but exceedingly feeble
form beyond the limits of the instinct-automatism fixed in the species.
"The senses of insects are our own. Only the sense of hearing remains doubtful
in so far as its location and interpretation are concerned. A sixth sense has not yet
been shown to exist, and a special sense of direction and orientation is certainly
lacking. Reflexes, instincts, and plastic individually adaptive central nervous activ-
ities pass over into one another by gradations. Without becoming antagonistic,
the central nervous activity in the different groups and species of animals becomes
complicated in two fashions: (1) through inheritance by natural selection, etc.,
of complex purposeful automatic responses, or instincts; (2) through the manifold
possibilities of plastic, individually adaptive activities, in combination with the faculty
of gradually developing secondary individual automatic responses, or habits. In social
insects the correlation of more developed psychic powers with the volume of the brain
may be directly observed. In these animals it is possible to demonstrate the existence
of memory, associations of sensory images, perception, attention, habits, simple
powers of inference from analogy, the utilization of individual experiences and hence
distinct, though feeble, plastic individual deliberations or adaptations.
"It is also possible to detect a corresponding, simpler form of volition, i. e., the
carrying out of individual decisions in a more or less protracted time sequence, through
different concatenations of instincts; furthermore different kinds of discomfort and
pleasure emotions, as well as interaction and antagonisms between these diverse
psychic powers. In insect behavior the activity of the attention is one-sided and
occupies a prominent place. It narrows the scope of behavior and renders the animal
temporarily unresponsive to other sense-impressions.
"Even to-day I am compelled to uphold the seventh thesis which I established in
1877 in my habilitation as privat-docent in the University of Munich: 'All the prop-
erties of the human mind may be derived from the properties of the animal mind.'
I would merely add to this: 'And all the mental attributes of higher animals may be
derived from those of lower animals.' In other words: The doctrine of evolution is
quite as valid in the province of psychology as it is in all the other provinces of organic
life. Notwithstanding all the differences presented by animal organisms and the
conditions of their existence, the psychic functions of the nerve-elements seem never-
theless to be everywhere in accord with certain fundamental laws, even where this
would be least expected on account of the magnitude of the differences."
238 PRINCIPLES AND CONCLUSIONS.
GENERAL RESUME.
TREATMENT.
Plateau focussed attention so exclusively upon attraction that it has
remained the chief theme of experimental pollination for 45 years. While the
present series of studies has endeavored to deal with the whole field in a
more comprehensive fashion, attraction is necessarily the central theme of
a resume that attempts to summarize all the experimental results in brief.
This is considered with respect to color, odor, form and size, distant and near
attraction, and competition. The first is discussed under the captions of
mutilation, artificial flowers, painted flowers, inclosing in glass, green and
showy nectarless flowers, color preference, and the second under those
of masking and concealing flowers, honey, perfumes and scents, and relative
values. The remaining major divisions are learning and habit, memory
and intelligence. For the treatment of these there is much less definite
and accurate experimental material, and an adequate exposition of them
must await extensive experimentation under the quantitative conditions
afforded by control and measurement.
ATTRACTION.
COLOR.
Mutilation. — Here it is necessary to take into account only those ex-
periments in which the corolla, perianth, ray-flowers, or bracts were removed
or reduced in expanse by shortening or otherwise. Covering the attractive
part produced essentially the same effect, but such cases are considered
under masking or artificial flowers in accordance with the device employed.
In Plateau's first experiments with decorollate flowers (1896), his results
in general failed to confirm his conclusion as to the insignificant role of the
corolla in attraction. In the case of several species of flowers and insects,
the mutilated flowers were visited less than the normal, for example,
24:44, 4: 10, 250:330, and 16 inspections to 29, and in others no comparison
was possible because the visits to normal flowers were not noted. More-
over, no account was taken of habit and the effect of removing the corolla
on the diffusion of the odor, especially of the nectar. In the studies of
decorollate poppies (19023), he obtained an average of 4.5 visits to the mu-
tilated flowers to 3.4 for the normal. These were wholly exceptional and
are negatived by the results of all other workers. They serve to illustrate
the variations in behavior that may be expected, but in this case they are
doubtless to be explained on the basis of habit and accessibility.
In working with decorollate poppies and geraniums (1904), Giltay
regularly obtained such ratios between normal and mutilated flowers as
96:9, and 38:1, while in the later studies of 1906, the intact flowers were
always much more visited likewise. On the second day of an installation,
the ability of the bees to learn changed such ratios as 15:0 and 12:0 to
18:13, but they were rarely if ever reversed. Similarly, Schroder (1901)
secured ratios of 37:0 and 21:4 with Syritta pipiens on the first day, but by
the second day experience increased the visits to the mutilated to almost
half, viz, 19 to 46. Andreae (1903) found decorollate flowers to be several
times less attractive than normal ones (3 : 24), and Errera (1904), about half as
GENERAL RESUME. 239
attractive (24:46). Wery (1904) regularly obtained more visits to the normal
flowers ; the difference was often small with a heterogeneous group of visitors,
such as 19 : 13, 27 : 24, 43 : 27, but when the honey-bees alone were counted the
ratios were 1 1 : 6, 29 : 10, and 20 : 6. The totals for one series was 138 normal
and 46 mutilated for all visitors, and 72 to 28 for the bees. Detto (1905)
observed that the removal of the corolla stopped visits completely, and
that replacing the petals caused them to be resumed. Lovell (1909) secured
decisive results as a rule by the removal of the corolla, as shown by the
following ratios for normal and mutilated, 15:0, 12:0, 7:0, and 12:1.
In Allard's experiments (1911) the loss of the corolla caused the inspections
to drop from 81 to 4, while a single petal received 16 inspections to 26 for
the normal. Placing a single petal on a decorollate flower yielded 8 inspec-
tions to 9 for such a petal pinned to a stem and 27 for the normal; replacing
the petals regularly brought the inspections back to the usual number.
In the present studies, the removal of the corolla has rarely eliminated
visitors entirely, but it has usually decreased them from three to ten times,
depending upon the flower and the habit of the visitors. Reducing the
size of the corolla was somewhat less effective as a rule, the decrease ranging
from a half to a tenth. With both lips removed in Monarda, visits were
reduced to a fortieth of the total for all mutilations and with the lower
lip gone, to a tenth. The most striking exception occurred in Chamae-
nerium, where the excision of all the flower parts but the ovary and nectar
ring resulted in nearly 5 times as many visitors and visits as to the normal.
This was apparently due to the marked effect of habit in responses to this
flower, as well as to the exposure of the nectar. This probably also explains
the discrepancy involved in Detto's results, in which the reduction of the
corolla was without effect. Experiments with newly hatched insects will
be required to evaluate the effect of habit, but practically all the existing
experimental results are in accord in demonstrating that the loss or re-
duction of the corolla has a significant and usually a decisive effect in de-
creasing visitors and visits. This applies with greatest force to the bees,
and is somewhat modified by the type of flower and especially its fragrance.
Artificial flowers. — Plateau devoted four papers to the attraction exerted
by artificial flowers, in which he insisted upon the perfection of his imitations
and ascribed the abundant visits obtained by other investigators to the
presence of materials attractive by their odor or to imperfections in the
method. Neither the presence of attractive substances nor the effect of
habit can explain the frequent initial visits obtained by the great majority
of workers, and the proper explanation seems to be that of the variation
to be expected in consequence of differences in time, place or installation.
In his preliminary studies (1877), Plateau obtained few visits to artificial
flowers and these were made chiefly by butterflies, but visits and inspections
were much more numerous in the experiments of 1897, though as a rule
far below those to normal flowers. Bombus gave 4 inspections out of 10
to imitations, Anthidium 11 out of 38, and Megachile 10 out of 17; in some
cases of those reported in the series of 1906, artificial flowers received as many
as 8 visits and 7 inspections to 15 visits to normal ones. Forel agreed with
Plateau's conclusions as to the ineffectiveness of artificial flowers, but
his results likewise were not at all in harmony with each other. Bees dis-
240 PRINCIPLES AND CONCLUSIONS.
dained imitations placed in the midst of dahlias, but visited artefacts
of Petunia and Hieracium. Moreover, it proved possible to train bees to
come to artificial flowers and ignore the dahlias.
Reeker (1898) found that artificial flowers were visited so regularly and
frequently when placed at 6 to 12 meters from the natural ones that he
found it undesirable to carry his experiments further, and Schroder (1901)
induced Syritta to visit them almost as abundantly as the normal by the
addition of honey. In an admirable series of experiments that rivaled those
of Plateau, Andreae (1903) obtained numerous visits to artificial flowers,
in one instance 81 visits being made to the latter and but 56 to the normal.
In the competition between color and odor as represented by artificial
flowers on one hand and masked natural ones on the other, the results were
uniformly in favor of the former, as shown by such ratios as 55 : 1, 41 : 0, 31 : 1,
and 28:3. Wery's results (1904) were equally conclusive, the artificial
flowers often equaling or exceeding the normal ones in attractiveness and
regularly surpassing honey in this respect. They attracted honey-bees
readily and to the same degree as normal flowers placed in a globe. Lovell
(1912) employed dry yellow immortelles in competition with honey, and
obtained three times as many visits to them as to the latter. Allard (1911)
found that the placing of cloth petals over the natural ones of cotton usually
decreased inspections, but a crepe-paper blossom of the proper color received
3 inspections to 8 for the normal. Detto (1905) also found that replacing
the corolla with one of yellow paper stopped visits, which began again as
soon as the petals were replaced. On the other hand, flowers with a ring
of colored paper were readily visited.
In the present experiments artificial flowers were visited about an eighth
as much as natural ones. In more than half the installations they were
completely ignored or visited but little. In several instances the total
number of visits to imitations was large, though the ratio rarely reached
one-half. The highest relative number of visits was in the case of a Frasera
supplied with Campanula petals, namely, 56:97, but this was doubtless
owing to the naturalness of the living tissue. The fact that Bombus went
readily to paper Mentzelias before the natural ones were open appears to
prove that the paper flowers were not repellent in themselves, but that the
habit response to the natural flowers was a very definite one, as would be
expected. While our results are more nearly in accord with those of Plateau
and Forel, there is sufficient variation in them with respect to the various
species of flowers and insects, as indeed there is in those of these two investi-
gators, to make it unnecessary to question the observations of Andreae,
Wery, and others. It has been repeatedly demonstrated that insects are not
repelled by paper or cloth flowers or by composite imitations, and it is no
longer possible to uphold Plateau's contention that insects do not go to arti-
ficial blossoms because odor is more powerful than color in attraction. In the
major number of investigations they have been found to visit such flowers
abundantly and repeatedly, and to prefer them all but exclusively to honey
or odor alone, as Andreae and Wery in particular have shown.
Painted flowers. — While painted flowers are artificial in a sense, this
is true to a much smaller degree than of paper or cloth ones, as is shown
by the relative number of visits. They have been modified as to color
GENERAL RESUME. 241
primarily, and perhaps slightly as to surface texture and odor. Their
greater naturalness is attested by the fact that they received about five
times as many visitors as the paper composites employed. With respect
to total response they were half as attractive as normal blossoms, though
in the case of particular species they were equally or even more attractive.
Thus, painted flowers of Rubus deliciosus were visited as readily as normal
ones, and in the installations of Aconitum and Chamaenerium they received
a larger number of visits absolutely. The greatest number of visits to such
flowers was made by Bombus juxtus, but in two experiments the honey-bee
made twice as many visits to them. The behavior of the latter was espe-
cially significant, since it ignored paper flowers altogether, but visited about
half as many painted as normal ones. On the whole, it seems clear that
changing the color of flowers as well as giving a wider range in color dis-
turbed the response of bees, but to a much smaller degree than artificial
flowers proper. The results secured by painting the white flowers of Rubus
suggest that making these more conspicuous overcomes the disturbance
arising from the addition of the water-colors, and indicate that white flowers
should be preferred for experiments of this kind.
Inclosing flowers in glass. — Glass containers, such as beakers, tubes, and
globes, have been employed by several investigators to eliminate odor and
determine the response to color alone. Andreae placed flowers under bell-
glasses or beneath inverted beakers and found that they received many visits,
in spite of the absence of odor. Wery also found out that cut flowers in a closed
globe exerted nearly normal attraction. The conical disk of three heads
of Rudbeckia was covered with a glass tube by Detto, with the consequence
that numerous bees flew against the glass. Allard made use of boxes with
a glass face and found that the inspections of the cotton blossoms were
reduced about half. These experiments show conclusively that color by
itself serves to attract insects in quantity, and to a degree equaling or
exceeding that of odor. This is confirmed by the experiments in masking
and covering discussed in the next section, the effect being to eliminate
color and to render odor the sole attractive force.
Green flowers and showy nectarless flowers. — Plateau contended
that green or dull-colored flowers which are visited by insects demonstrate
that color is unnecessary and hence ineffective in attraction. Andreae
showed that the color of inconspicuous flowers was often more attractive
than either odor or honey, and Lovell has proved that green leaves with
honey are much less attractive than yellow immortelles. When a head of
golden glow and a green spike of Amarantus were placed in competition,
the former obtained all told 51 visits to 16 for the latter. Plateau likewise
insisted that the failure of showy nectarless flowers to attract insects proved
that color was unimportant, and that it was necessary to supply them with
a sweet fragrant liquid to induce bees to come. Perez observed that bees
did go to showy flowers without nectar, but that they soon learned the futil-
ity of this and ignored such blossoms. They came readily to geranium
flowers supplied with honey, and not only returned to them after the honey
was exhausted, but also went to others that had received no honey. Giltay
found that bees trained to come to geranium flowers with honey went read-
242 PRINCIPLES AND CONCLUSIONS.
ily to flowers without it when these occupied the same place, although
they were unable to find honeyed leaves. Lovell noted visits to showy
nectarless flowers and was able to increase these by the addition of sugar
sirup with odor, thus negativing Plateau's assumption. In the case of
petunias, honey-bees continued to come for several days after the honey
was gone, while with geranium they not only behaved similarly, but also
went to a bed of Portulaca, which is regularly ignored, and inspected the
flowers repeatedly.
Thus, it is evident that the positive response to dull flowers with nectar
and the negative one to showy nectarless blossoms are largely matters of
experience and habit, in the case of adult insects. The nectar or pollen
reward being equal, bright flowers are visited more than green ones, and,
conversely, the size and color being equal or approximately so, flowers are
visited in proportion to the amount and accessibility of their nectar, the
nectarless ones, no matter how showy, receiving no visits after the bees
have determined the absence of nectar. Here, as elsewhere, it is desirable
to work with flowers of each sort that are entirely unknown to a particular
insect community, and with newly hatched bees, which are necessarily
without experience.
Color preference. — The view that bees do not discriminate between
colors has been advanced by Bonnier, Bulman, Plateau, Forel, MacLeod,
and others. Bulman stated that "it matters not one iota to a bee whether
the flower is blue, red, pink, yellow, white or green; so long as there is honey,
that is sufficient," a statement approved by both Plateau and Forel. They
have failed to reckon with intelligence and habit, however, as well as with
the fact that odor and form doubtless enable the bee to recognize that the
difference in color is immaterial to him. Darwin appreciated the significance
of this when he said, "humble and hive bees are good botanists, for they
know that varieties may differ widely in the color of their flowers and yet
belong to the same species" (1876:416), and Lovell in particular has con-
firmed the view of Lubbock and Mueller that bees easily distinguish colors
and go to some in preference to others. Mueller (1883:275) pointed out
that it is necessary to keep in mind certain characteristics of the honey-bee
in connection with its color preferences, if one is to avoid hasty conclu-
sions. Chief among these are their shyness and lack of cleverness in unac-
customed surroundings. However, their shyness and desire for freedom
are overruled by the all-powerful impulse for honey. The shyness and lack
of skill of bees in unaccustomed places are in marked contrast to their prompt
decisions and shrewdness at flowers. On flowers to which they are not
especially adapted, various individuals often behave very differently, and
they also show great individual differences in their color preferences.
Bonnier decided that bees exhibited no choice between red, yellow,
green and white, but his results were regarded as inconclusive by Lubbock,
since his squares were largely covered by the bees, and since he omitted blue
and used no uncolored checks. Lubbock made most extensive experiments,
which disclosed a decided choice for blue, with white and yellow usually
next. To avoid artificial colors, Mueller employed detached petals, but
obtained similar results. While there were marked individual differences,
there were but few cases in which one or more individuals reversed
GENERAL RESUME. 243
the preference (p. 139). The least attractive of all colors was glaring
yellow; white and yellowish-white were visited about as readily as many
shades of purple, but less readily than blue or violet. Violet excelled
all other flower colors except blue, a pure deep shade of the latter having
the advantage indicated by the ratios 81:37 and 50:35. Among the
brilliant flower colors, bright yellow was the most attractive. The green
of leaves was less than half as attractive as rose, but slightly more so than
scarlet or orange. Forel found that Bombus exhibited a distinct preference
for blue over red, though he appears to have forgotten the inability of the bee
to find honey on red or to have felt that this had no relation to the behavior
of bees at flowers. Plateau showed that insects made no choice between the
differently colored flowers of the same species or variety, but entirely over-
looked habit as an explanation of this. He did prove, however, that in
his experiments at least the so-called admiration of syrphids for bright
colors, mottling, etc., was little different from their behavior before color-
less or inanimate objects.
Contrary to the results of Lubbock and Forel with wasps, the Peckhams
found that wasps rely very greatly upon color for their guidance, a change
in the color of paper about the nest often causing all of them to hesitate
or go to the misplaced color. This is in harmony with the instances cited
by Theen, Buttel-Reepen, and Lovell of the effect of changing the color
of hives or their thresholds. Lovell corroborated the preference of bees
for blue, 15 going to this and but 1 or 2 to any other color. A bee trained
to red first gave a ratio of 8:2 for red and blue, but finally this shifted to
3 : 7. Turner showed that as a rule bees did not visit artefacts of the color
from which they had not been trained to forage when these were supplied
with honey and scattered among the others. Frisch found that bees paid
no attention to gray in competition with blue or yellow, but that they visited
red, dark gray, and black disks indifferently. He concluded that bees are
color-blind to red and a certain shade of blue-green, in agreement with the
views of Ladd-Franklin. Since there are many records of visits to both
these colors, which must have appeared in varying shades, and since several
shades of green have been much visited in the course of the present inves-
tigation, it is clear that further experimentation by means of colors of
known value is needed in this field (cf. Frisch, Knoll, Kiihn and Pohl, pp.
200 to 207).
While the different colors of the same variety or species may have no
significance for insects, it is evident that this is not true of the changes
in color shown by flowers in maturing or withering. Such colors are helpful
in guiding the insect and saving his time, and he regularly takes advantage of
them. Mueller (1883 : 81) observed that in a field of red and blue Pulmonaria
females of Anthophora pilipes visited almost exclusively the red blossoms
and those just beginning to change toward blue, but only rarely the blue ones.
F. Mueller (1877: 17) found that Lantana flowers were visited by butterflies
on the first and second day when they were yellow and orange-red, but
never on the third when they were purple; some species in fact visited the
yellow flowers alone. Here the perferences were naturally not for the colors
as such, but as indicators of the availability of nectar (cf. Ludwig, 1885,
1887). In conclusion, it may be affirmed that trained bees exhibit a
244 PRINCIPLES AND CONCLUSIONS.
marked and often persistent choice for the proper color, but that there is
a general preference for blue. In field and garden, differences in color are of
great importance in attraction, but the bee discriminates among them only
when it is to its advantage to do so, as between species, or between partly-
open buds or old flowers on the one hand and fresh ones on the other. When
the flowers differ in color alone, the bee has learned that this is unimportant
in comparison with odor and form. When a new factor is interjected, how-
ever, as in the case of flowers habitually visited which are changed by
painting them with water-colors, a preference is manifested until experience
again shows that it is undesirable or unnecessary.
ODOR.
Masking or covering flowers to conceal color. — Plateau thought to
have demonstrated by masking flowers and heads with paper or green leaves
that color is of little or no value in attraction and that odor alone is suf-
ficient. Most of his experiments lacked checks or controls, and were con-
tradicted by those of Forel, who found that flowers completely masked
received no visits. Wherever a slight gap permitted entrance, bees soon
found their way in and then returned regularly by the same route. More-
over, after the lapse of several hours they discovered the flowers and then
visited them normally. Andreae frequently employed beakers masked with
dark paper to determine the effect of odor alone; in three representative
cases the ratios for color and odor were 10:0, 31:1, and 35:3, indicating
that odor is much less effective than color as a rule. Wery noted 32 visitors
to normal flowers to 7 for similar ones hidden in foliage, and 19 to artificial
flowers fully exposed to but 4 for those concealed in leaves. Giltay repeatedly
masked flowers with pots so that no color was visible, but the odor
could regularly escape; such blossoms received no visits, but bees came
readily as soon as the pot was removed. When petals were placed in a dish
and covered with a pot so that they were invisible but the odor could escape
they were never visited, but after the pot was removed, bees alighted on
them, sometimes immediately. Allard concealed a cotton blossom so that
it was visible only from above; this obtained but 1 visit to 12 for the control.
When the disguise was taken away, the flower was inspected more than the
control.
These experiments leave no question that for the flowers concerned
at least the role of color in attraction is usually several times and often
many times greater than that of odor.
Odor of honey. — While honey has a strong attractive power, this is due
chiefly to its sweetness and but little to its odor, especially in the case of bees.
Even Plateau had remarked the fact that bees have a weak sense of smell
for honey, and this inability has been emphasized by Forel, Buttel-Reepen,
Giltay, Wery, Detto, Lovell, and others. Bombus and Apis have repeatedly
been observed to pass within a few millimeters of honey in both natural and
artificial flowers without perceiving it. In some cases they have even
become entangled in it and tried to clean it off without recognizing it.
Moreover, sugar sirups and other sweet liquids without odor have often been
found to be quite as attractive as honey. Once found, honey is a powerful
incentive to return until it is exhausted. In our experiments it never in-
GENERAL RESUME. 245
creased the number of visits to natural flowers and had practically no effect
upon those to artificial ones. In the majority of cases it actually decreased
the number of visits, often as much as ten times. Wery found that honey
remained practically untouched in competition with natural or artificial
flowers, obtaining such ratios as 49:0 and 25:0, and emphasized the fact
that honey attracts bees very little.
Effect of added odors. — In his first studies of the effect of adding odors
to flowers Plateau obtained no conclusive results. Thyme and sage appeared
to attract feebly, lavender not at all, and mint to repel. In his later studies,
he stated that it was indispensable for good results to avoid essences and
to employ substances known to attract. With these he had marked success
with but one or two, such as anisette, a sugar sirup flavored with anise.
On the other hand, our experiments showed a decrease of 50 per cent in
the number of visits when various perfumes and essences were added, even
in the presence of honey. With occasional exceptions, perfumes in them-
selves have no effect in increasing attraction, though they may serve as
indicators of the presence of honey or sirup and thus seem to be attractive,
as in Plateau's results. It is possible that positive results would be secured
by using perfume from flowers that bees had been visiting in other areas or
earlier in the season, and such experiments are now under way.
Relative value of color and odor. — Wery has endeavored to give
quantitative expression to the respective parts played by color, form, odor,
and food in the attraction of insects, and her values seem to be fair approx-
imations of the various roles. Her general conclusion in this respect was
formulated as follows :
"For the honey-bee the attraction exerted by the form and color of flowers is ap-
proximately four times greater than that of their pollen, perfume, and nectar taken
together. Thus, if the total attraction exerted by the most attractive flowers is taken
as 100, that of form and color will be represented by about 80 and that of the other
three factors by about 20."
In view of the faint sense of smell for honey and pollen exhibited by bees,
this seems a conservative figure except for flowers with a marked perfume,
which are still to be adequately investigated. It is these flowers that have
given rise to contradictory opinions as to the relative share of color and odor
in attraction from a distance and guidance near at hand.
FORM.
Distinction and role. — Following the views of Exner as to vision, both
Plateau and Forel were of the opinion that insects distinguish forms more
or less vaguely, except when in motion. When one recalls the incessant
activity of bees on flowers, this exception is nearly tantamount to the
admission that insects do distinguish forms and make use of them in deter-
mining their visits. Although Perez regarded form as less important than
color or odor, he pointed out the contradiction involved in Plateau's con-
tention that insects could not distinguish colors, but that they were guided
to buds, withered flowers, and fruits by their form. Moreover, Forel stated
that wasps readily recognize the forms and contours of objects, and he
demonstrated that wasps and bumble-bees could distinguish bands from
246 PRINCIPLES AND CONCLUSIONS.
disks. He also declared that his experiments with artefacts demonstrated
that honey-bees possess the perception of space, form, and color. Practi-
cally all other students of experimental pollination have agreed that insects
are guided in some degree by form, though Giltay thought that visits to
a single petal indicated that form could not be concerned. This does not
follow, however, since it is evident that color is often more potent than
form. Detto was also doubtful of the ability of bees to see forms, but he
explains certain of his results on the assumption that the bees were able to
recognize the stamens and pistil of a flower. The Peckhams, Dahl, Andreae,
Wery, Frisch, and Turner have shown that insects distinguish forms or
patterns, and some of Lovell and Allard's results permit no other conclusion.
Additional proof is furnished by the readiness with which they go from one
color to another of flowers of the same species or variety, whether fragrant
or not, and especially by their response to painted flowers. The minuteness
with which they can distinguish forms and structures is proved by the ease
with which they solve the problems presented by inverted and mutilated
flowers, as well as by the ingenious experiments of Detto on the relative
importance of vision and smell in enabling insects to locate the nectary open-
ings. Finally, it appears that insects can distinguish differences in surface
and texture sufficiently small to escape man. This conclusion seems un-
avoidable, when one recalls the readiness with which bees often distinguish
between the best of artificial or painted flowers and normal ones. In fact,
it is a curious paradox that Plateau, who thought insects distinguish neither
form nor color, and that Forel, who thought they had but a vague vision
of form, should have believed that they were able to discriminate between
artificial and natural flowers by means of other differences not visible to
the eyes of man.
ATTRACTION AT A DISTANCE AND NEAR AT HAND.
It is unfortunate that no definite experiments have been made as to the
distance at which various colors and odors as represented in flowers exert
attraction, but it is hoped that the experiments now contemplated will
yield accurate quantitative results. The general opinion has been that
odor attracts from a distance and color near at hand, and Plateau has defi-
nitely stated that insects do not perceive objects at a greater distance than
2 meters and many of them only when much nearer. On the other hand,
Wery believed that color could attract for a distance of 6 meters, since
insects were able to recognize artificial blossoms placed this far from natural
ones, and Andreae stated that honey-bees could see 8 to 10 meters at least,
basing this upon similar grounds.
The careful consideration of previous experiments confirms the evidence
derived from the present investigation. This indicates as the best working
hypothesis for further studies the conclusion that odor attracts for distances
beyond 10 meters, color in mass for the intermediate ones, and color and
form in detail within a meter or so, depending greatly upon the size and
color of the flower or cluster. For the majority of flowers without a marked
fragrance, odor can be effective only when near at hand and the effect is
probably small even then. It is hardly necessary to point out that this
must be true of color also in the case of green or dull flowers and especially
GENERAL RESUME. 247
those of small size. Since the senses of sight and smell differ greatly in the
various groups of insects, the relative importance of the three attractive
factors will be modified accordingly. In a group of plants or a floriferous
individual or even in the midst of a cluster of flowers, odor can have little
effect, except in the rare instances when very fragrant flowers or clusters
are widely separated in such groups. The odor is not only general, but it
is naturally most powerful at the flower or cluster on which the insect is
working. Such conditions would not permit it to go straightway and with-
out an instant's hesitation to the next flower or head, and guidance by
color and form alone can explain the assured and rapid flight of bees in the
midst of flowers. This is confirmed by their behavior when the wind is
blowing, for they fly most easily with the wind, though this carries the
fragrance of the next flower sought away from them. Moreover, the readi-
ness with which they often drop from the midst of a plant or bush to fallen
corollas on the ground a foot or more below further supports the view that
odor is rarely a guide among flowers. However, it must be kept in mind
that such studies have so far been incidental and concerned with bees al-
ready habituated to the flowers concerned, except in some of the competi-
tion studies already given in chapter 3.
LEARNING AND HABIT.
It is possible at present to deal with learning and habit only in
the general qualitative manner so admirably exemplified in the work
of Lubbock, Mueller, Forel, Peckham, Buttel-Reepen, Detto, Lovell, Turner,
Frisch, and Knoll. The time has come for a comprehensive quantitative
attack on the learning process and its relation to the fixation and modi-
fication of habit, and one of the primary objects of the present book is
to clear the way for such investigation, as indicated earlier. In view of
their generalized mental organization, the ability of insects, and especially
the bees, to learn by experience is remarkable. This has been widely recog-
nized by experimenters in this field, though it has been doubted by some
who failed to take into account the qualities emphasized by Mueller,
namely, the shyness and lack of cleverness in unusual surroundings and the
all-powerful obsession for honey. The ease and rapidity with which habits
of landing and securing nectar are modified under changed conditions
indicate a great power of learning and a corresponding plasticity of
habit that is surprising. These qualities will probably be found to be
even more marked in the case of newly hatched or young insects, and it is
possible that the training of these will disclose new possibilities of learn-
ing and adjustment. As the work of Giltay shows, the selection of marked
individuals on the basis of different types of response opens a new vista
in this field, and permits the extension and refinement of our knowledge
of the mental powers of the species and group by means of the psychology
of the individual.
MEMORY AND INTELLIGENCE.
The Peckhams concluded that wasps have a very good memory, and
Forel stated that bees not only have memory for place but also for time,
a statement in accord with the views of Buttel-Reepen. Probably the
248 PRINCIPLES AND CONCLUSIONS.
most remarkable instance of memory is that recorded by Hoffer (1886:11),
who found that bumble-bees remembered the place in which their nest
had been put, from the middle of October when they disappeared to the
beginning of April when they returned. It is evident also that wasps
in particular have a remarkable memory for forms and outlines along
the path of their flights, as shown by their ability to find their way back
for several miles, a faculty only less developed in the bees.
Both Buttel-Reepen and Forel have shown that bees are capable of
memory and other associations, and the former stated:
"We see that bees show signs of an admirable memory in their orientation and in
their other activities; further, I believe I have shown that the bee possesses a perception
for color and form, and develops a rich capacity for communication by means of its
well-developed 'language'; that, further, it is able to gather experiences, to learn
and to form associations of impressions, etc."
Forel independently declared that —
"It ensues from the concordant observations of all the experts that sensation,
perception, association, inference, memory, and habit in the social insects follow the
same fundamental laws as in the vertebrates and ourselves. In these animals it is
possible to demonstrate the existence of memory, associations of sensory images,
perception, attention, habits, simple powers of inference from analogy, the utilization
of individual experiences and hence distinct, though feeble, plastic individual de-
liberations or adaptations. It is also possible to detect a corresponding, simpler form
of volition, i. e., the carrying out of individual decisions in a more or less protracted
time sequence, through different concatenations of instincts; furthermore, different
kinds of discomfort and pleasure emotions, as well as interactions and antagonisms
between these diverse psychic powers."
As early as 1877, Forel said that all the properties of the human mind
may be derived from the properties of the animal mind and a quarter of
a century later he merely added the statement that all the mental attributes
of higher animals may be derived from those of lower animals.
With the development of more exact methods in comparative psychology
has gone a more critical spirit, which has discarded practically all the
observational and anecdotal material so long utilized. The same feeling
for accuracy and objectivity has led to the present endeavor to place the
study of the relations of flowers and insects upon a purely experimental
basis. In spite of this, however, the work of Forel, Lubbock, the Peckhams,
Buttel-Reepen, Ferton, and others was so largely experimental that their
general conclusions have remained true and still constitute much of the
essential foundation for the study of insect psychology, as is evident from
the recent and more exact researches of Frisch, Knoll, and Kuhn and Pohl
[see also Holmes (1911), Thorndike (1911), Smith (1915), and Bouvier
(1922)].
5. POLLINATORS AND FLOWERS VISITED.
Acmaeops longicornis :
Carduus hookerianus.
Mertensia sibirica.
Prunus demissa.
Rosa acicularis.
Rubus deliciosus.
Acmaeops pratensis:
Prunus demissa.
Rosa acicularis.
Rubus deliciosus.
Agapostemon color adensis:
Stanleya pinnatifida.
Taraxacum officinale.
Agapostemon splendens:
Malvastrum coccineum.
Pentstemon glaber.
Rosa acicularis.
Taraxacum officinale.
Agapostemon sp.:
Prunus demissa.
Stanleya pinnatifida.
Agathis vulgaris:
Achillea millefolium.
Ancistrocerus sp. :
Geranium caespitosum.
richardsoni.
Jamesia americana.
Mertensia sibirica.
Rubus deliciosus.
strigosus.
Andrena apacheorum:
Erigeron macranthus.
Geranium caespitosum.
Andrena braccata:
Geranium caespitosum.
Andrena canadensis:
Prunus demissa.
Rubus deliciosus.
Andrena crataegi:
Carduus hookerianus.
Frasera speciosa.
Holodiscus dumosus.
Monarda fistulosa.
Opulaster opulifolius.
Prunus demissa.
virginiana.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Andrena edwiniae:
Jamesia americana.
Prunus demissa.
Andrena gardineri:
Astragalus drummondi.
Andrena imitatrix:
Astragalus drummondi.
Andrena lewisi :
Rubus strigosus.
Andrena madronitens:
Frasera speciosa.
Geranium caespitosum.
richardsoni.
Holodiscus dumosus.
Andrena madronitens — Con.
Mertensia sibirica.
Onagra biennis.
Opulaster opulifolius.
Pentstemon glaber.
secundiflorus.
Prunus demissa.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Sedum stenopetalum.
Andrena placida:
Rubus deliciosus.
Andrena prunorum:
Pentstemon glaber.
Prunus demissa.
virginiana.
Rubus deliciosus.
Andrena vicina:
Astragalus drummondi.
Geranium caespitosum.
Pentstemon glaber.
Potentilla arguta.
Prunus demissa.
virginiana.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Stanleya pinnatifida.
Andrena washingtoni :
Pentstemon gracilis.
Rosa acicularis.
Andrena sp. :
Prunus demissa.
virginiana.
Rosa acicularis.
Andronicus sp. :
Carduus hookerianus.
Geranium caespitosum.
Pentstemon gracilis.
Rubus deliciosus.
Anthidium tenuiflorae:
Sedum stenopetalum.
Anthophora bomboides:
Pentstemon glaber.
Anthophora occidentalis :
Chamaenerium angusti-
folium.
Anthophora neomexicana:
Pentstemon gracilis.
Anthophora simillima:
Aragalus lamberti.
Capnoides aureum.
Dodocatheon meadia.
Lithospermum canescens.
Pentstemon glaber.
gracilis,
halli.
secundiflorus.
unilateralis.
Rosa acicularis.
Rubus strigosus.
249
Anthophora smithi :
Campanula rotundifolia.
Chamaenerium angusti-
folium.
Monarda fistulosa.
Anthrax alternata:
Holodiscus dumosus.
Anthrax fulviana:
Erigeron macranthus.
Anthrax halcyon:
Solidago missouriensis.
Anthrax hypomelas:
Heracleum lanatum.
Potentilla gracilis.
Anthrax lateralis:
Rosa acicularis.
Anthrax nigra:
Rosa acicularis.
Anthrax sinuosa:
Sedum stenopetalum.
Tradescantia virginiana.
Anthrax tegminipennis:
Erigeron macranthus.
Anthomyia sp. :
Clementsia rhodantha.
Apanteles sp. :
Geranium caespitosum.
Apis mellifica:
Arctostaphylus uva-ursi.
Asclepias halli.
speciosa.
Chamaenerium angusti-
folium.
Frasera speciosa.
Geranium caespitosum.
richardsoni.
Holodiscus dumosus.
Jamesia americana.
Linaria vulgaris.
Mentzelia multiflora.
Opulaster opulifolius.
Pentstemon glaber.
unilateralis.
Petalostemon candidus.
purpureus.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Solidago missouriensis.
Stanleya pinnatifida.
Taraxacum officinale.
Thalictrum fendleri.
Tradescantia virginiana.
Archytas sp.:
Geum rivale.
Arctophila flagrans:
Rosa acicularis.
Argynnis atlantis:
Chamaenerium angusti-
folium.
Erigeron macranthus.
Monarda fistulosa.
Pentstemon secundiflorus.
250
EXPERIMENTAL POLLINATION.
Argynnis eurynome:
Geranium caespitosum.
Helianthus petiolaris.
Rydbergia grandiflora.
Sedum stenopetalum.
Atrytone taxiles:
Capnoides aureum.
Chamaenerium angusti-
folium.
Monarda fistulosa.
Pentstemon glaber.
Basilarchia weidemeyeri:
Linaria vulgaris.
Bembex spinolae:
Asclepias halli.
Bombomelecta fulvida:
Capnoides aureum.
Mertensia sibirica.
Pentstemon glaber.
gracilis.
Bombus americanorum:
Pentstemon unilateralis.
Rubus deliciosus.
Thermopsis montana.
Bombus appositus:
Aconitum columbianum.
Carduus hookerianus.
Chamaenerium angusti-
folium.
Delphinium occidentale.
Gentiana parryi.
Geranium caespitosum.
Ibidium strictum.
Monarda fistulosa.
Pentstemon glaber.
gracilis.
Petalostemon candidus.
purpureus.
Rubus deliciosus.
Rydbergia grandiflora.
Rosa acicularis.
Bombus bifarius:
Aconitum columbianum.
Carduus hookerianus.
Chamaenerium angusti-
folium.
Delphinium scopulorum.
Dodocatheon meadia.
Elephantella groenlandica.
Erigeron macranthus.
Geranium caespitosum.
richardsoni.
Holodiscus dumosus.
Jamesia americana.
Mentzelia multiflora.
Mertensia sibirica.
Monarda fistulosa.
Pentstemon glaber.
glaucus.
gracilis,
secundiflorus.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Stanleya pinnatifida.
Bombus centralis:
Chamaenerium angusti-
folium.
Delphinium scopulorum.
Monarda fistulosa.
Pentstemon glaber.
gracilis.
Bombus dorsalis:
Capnoides aureum.
Bombus edwardsi:
Aconitum columbianum.
Allium recurvatum.
Arctostaphylus uva ursi.
Aster foliaceus.
Astragalus drummondi.
Calochortus gunnisoni.
Campanula rotundifolia.
Carduus hookerianus.
Chamaenerium angusti-
folium.
Chrysopsis villosa.
Cleome serrulata.
Delphinium scopulorum.
Dodocatheon meadia.
Drymocallis fissa.
Erigeron macranthus.
Fragaria vesca.
Frasera speciosa.
Geranium caespitosum.
Holodiscus dumosus.
Jamesia americana.
Lathyrus ornatus.
Mertensia sibirica.
Opulaster opulifolius.
Pedicularis racemosa.
Pentstemon glaber.
glaucus.
gracilis,
secundiflorus.
Petalostemon candidus.
purpureus.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Rydbergia grandiflora.
Sedum stenopetalum.
Sieversia ciliata.
Solidago missouriensia.
Bombus fervidus:
Astragalus drummondi.
Monarda fistulosa.
Pentstemon unilateralis.
Petalostemon candidus.
purpureus.
Rubus deliciosus.
Bombus flavifrons:
Aconitum columbianum.
Aster foliaceus.
Calochortus gunnisoni.
Chamaenerium angusti-
folium.
Dasyphora fruticosa.
Delphinium scopulorum.
Dodocatheon meadia.
speciosa.
Mertensia sibirica.
Monarda fistulosa.
Bombus flavifrons — Con.
Prunus demissa.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Rydbergia grandiflora.
Solidago missouriensis.
Bombus fulvida:
Mertensia sibirica.
Bombus hunti:
Aquilegia brevistyla.
coerulea.
Astragalus drummondi.
Campanula rotundifolia.
Carduus hookerianus.
Castilleia miniata.
Chamaenerium angusti-
folium.
Erigeron macranthus.
uniflorus.
Frasera speciosa.
Geranium caespitosum.
richardsoni.
Helianthus petiolaris.
Holodiscus dumosus.
Jamesia americana.
Monarda fistulosa.
Pedicularis parryi.
Pentstemon glaber.
gracilis.
Petalostemon candidus.
purpureus.
Potentilla gracilis.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Rydbergia grandiflora.
Sedum stenopetalum.
Solidago missouriensis.
Stanleya pinnatifida.
Thermopsis montana.
Trifolium dasyphyllum.
Bombus juxtus:
Aconitum columbianum.
Astragalus drummondi.
Campanula rotundifolia.
Capnoides aureum.
Carduus hookerianus.
Chamaenerium angusti-
folium.
Chrysopsis villosa.
Delphinium scopulorum.
Frasera speciosa.
Gentiana parryi.
Geranium caespitosum.
Holodiscus dumosus.
Jamesia americana.
Mentzelia multiflora.
Mertensia sibirica.
Monarda fistulosa.
Onagra biennis.
Pentstemon glaber.
glaucus.
gracilis.
secundiflorus.
unilateralis.
Potentilla arguta.
POLLINATORS AND FLOWERS.
251
Bombus juxtus — Con.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Thermopsis montana.
Bombua kirbyellus:
Castilleia miniata.
Pedicularis parryi.
Pentstemon glaber.
Potentilla arguta.
pulcherrima.
Rubus deliciosus.
Trifolium dasyphyllum.
Bombus morrisoni:
Astragalus drummondi.
Delphinium scopulorum.
Ibidium strictum.
Monarda fistulosa.
Pentstemon glaber.
glaucus.
gracilis.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Scutellaria resinosa.
Stanleya pinnatifida.
Bombus nevadensis :
Carduus hookerianus.
Chamaenerium angusti-
folium.
Gentiana parryi.
Opulaster opulifolius.
Bombus occiden talis:
Aconitum columbianum.
Allium recurvatum.
Aquilegia coerulea.
Calochortus gunnisoni.
Capnoides aureum.
Carduus hookerianus.
Castilleia miniata.
Chamaenerium angusti-
folium.
Delphinium scopulorum.
Erysimum asperum.
Erigeron uniflorus.
Geranium caespitosum.
richardsoni.
Heracleum lanatum.
Holodiscus dumosus.
Jamesia americana.
Linaria vulgaris.
Mentzelia multiflora.
Mertensia sibirica.
Monarda fistulosa.
Opulaster opulifolius.
Pedicularis racemosa.
Pentstemon glaber.
glaucus.
secundiflorus.
Petalostemon purpureus.
Potentilla pulcherrima.
Prunus demissa.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Sieversia ciliata.
Solidago missouriensis.
Bombus pennsylvanicus:
Monarda fistulosa.
Bombus ruf ocinctus :
Aconitum columbianum.
Calochortus gunnisoni.
Chamaenerium angusti-
folium.
Geranium caespitosum.
Pentstemon glaber.
gracilis.
Petalostemon candidus.
purpureus.
Rosa acicularis.
Rubus deliciosus.
Solidago missouriensis.
Stanleya pinnatifida.
Bombylius atriceps:
Rosa acicularis.
Brachyopa notata:
Prunus demissa.
Rubus deliciosus.
Bracon helena:
Erigeron macranthus.
Bracon vulgaris:
Stanleya pinnatifida.
Brenthis triclaris:
Dasyphora fruticosa.
Prunus demissa.
Calliphora vomitoria :
Prunus demissa.
Celerio lineata:
Pachylophus caespitosus.
Pentstemon glaber.
Cenis uhleri:
Geranium caespitosum.
Cerastomia lignaria:
Pentstemon gracilis.
Ceratina sp. :
Mertensia sibirica.
Pentstemon gracilis.
Stanleya pinnatifida.
Chilosia petulca:
Prunus demissa.
Chilosia tristis:
Prunus demissa.
Chionobis macouni:
Draba aurea.
Iris missouriensis.
Potentilla pulcherrima.
Chrysogaster parva:
Rubus deliciosus.
Chrysophanus helloides:
Achillea millefolium.
Erigeron macranthus.
Oreochrysum parryi.
Chrysophanus rubidus.
Campanula rotundifolia.
Carduus hookerianus.
Phacelia heterophylla.
Chrysophanus sirius:
Monarda fistulosa.
Chrysotoxum integrum:
Holodiscus dumosus.
Rosa acicularis.
Chrysotoxum upsilon:
Polygonum bistorts.
Chrysotoxum ventricosum :
Potentilla pulcherrima.
Clisodon terminalis:
Aquilegia coerulea.
Carduus hookerianus.
Chamaenerium angusti-
folium.
Frasera speciosa.
Geranium caespitosum.
Holodiscus dumosus.
Mertensia pratensis.
Monarda fistulosa.
Pentstemon glaber.
glaucus.
gracilis,
secundiflorus.
Petalostemon purpureus.
Rosa acicularis.
Rubus strigosus.
Clisodon sp.:
Carduus hookerianus.
Mertensia sibirica.
Pentstemon glaber.
gracilis.
Coelioxys moesta:
Chamaenerium angusti-
folium.
Geranium caespitosum.
Coenonympha pamphiloides :
Dasyphora fruticosa.
Erigeron macranthus.
Prunus demissa.
Colias alexandra:
Potentilla pulcherrima.
Colias edwardsi:
Carduus hookerianus.
Colias keewaydina:
Castilleia miniata.
Colias scudderi:
Carduus hookerianus.
Colletes americanus:
Rosa acicularis.
Solidago missouriensis.
Colletes kincaidi:
Geranium caespitosum.
Pentstemon gracilis.
Petalostemon purpureus.
Prunus demissa.
Colletes oromontis:
Capnoides aureum.
Geranium caespitosum.
Holodiscus dumosus.
Mertensia pratensis.
sibirica.
Monarda fistulosa.
Rubus deliciosus.
strigosus.
Solidago missouriensis.
Colletes sieverti:
Geranium caespitosum.
Ctenucha sp.:
Chamaenerium angusti-
folium.
Monarda fistulosa.
Curtipogon leucozona:
Calochortus gunnisoni.
252
EXPERIMENTAL POLLINATION.
Dasyllis fernaldi:
Calochortus gunnisoni.
Chamaenerium angusti-
folium.
Dejeania vexatrix:
Chamaenerium angusti-
folium.
Mertensia sibirica.
Opulaster opulifolius.
Dolichovespula arctica:
Chamaenerium angusti-
fohum.
Delphinium scopulorum.
Dolichovespula diabolica:
Chamaenerium angusti-
folium.
Echinomyia algens:
Chamaenerium angusti-
folium.
Chrysopsis villosa.
Heracleum lanatum.
Echinomyia decias:
Asclepias speciosa.
Ectemius montanus:
Geranium richardsoni.
Ectemius muricatus:
Heracleum lanatum.
Eliphilus latifrons:
Cleome serrulata.
Epalpus bicolor:
Carduus hookerianus.
Polygonum bistorta.
Solidago missouriensis.
Epalpus rufus:
Carduus hookerianus.
Valeriana edulis.
Epeolus helianthi:
Geranium caespitosum.
Erebia epipsodea:
Dasyphora fruticosa.
Geranium caespitosum.
Potentilla pulcherrima.
Prunus demissa.
Eristalis arbustorum:
Prunus demissa.
Rubus strigosus.
Eristalis dimidiatus:
Prunus demissa.
Eristalis flavipes:
Rubus deliciosus.
Eristalis latifrons:
Opulaster opulifolius.
Rosa acicularis.
Rubus deliciosus.
Eristalis meigeni:
Potentilla gracilis.
Eristalis temporalis:
Prunus demissa.
Rubus deliciosus.
Rydbergia grandiflora.
Eristalis tenax :
Jamesia americana.
Erynnis leonardus snowi:
Chamaenerium angusti-
folium.
Monarda fistulosa.
Erizoa olivahs:
Carduus hookerianus.
Exoprosopa caliptera:
Rubus deliciosus.
Exoprosopa divisa:
Sedum stenopetalum.
Exoprosopa volucris:
Silene acaulis.
Foenus perplexus:
Geranium caespitosum.
Geocoris bullatus:
Potentilla pulcherrima.
Glypta sp. :
Geranium caespitosum.
Gnophaela vermiculata:
Achillea millefolium.
Polygonum bistorta.
Potentilla pulcherrima.
Rubus strigosus.
Solidago missouriensis.
Gonochrysis densa:
Pentstemon glaber.
Grapta hylas:
Carduus hookerianus.
Halictus (Chloralictus) sp.:
Asclepias halli.
Castilleia miniata.
Geranium caespitosum.
Gilia aggregata.
Mertensia sibirica.
Monarda fistulosa.
Opulaster opulifolius.
Pentstemon glaber.
gracilis.
Prunus demissa.
Halictus (Evylaeus) sp.:
Apocynum androsaemi-
folium.
Astragalus drummondi.
Castilleia miniata.
Chamaenerium angusti-
folium.
Mertensia sibirica.
Pentstemon gracilis.
Prunus demissa.
Rosa acicularis.
Tradescantia virginiana.
Halictus fendleri:
Thalictrum fendleri.
Halictus (Lasioglossum) sp. :
Asclepias speciosa.
Castilleia miniata.
Chamaenerium angusti-
folium.
Geranium caespitosum.
Monarda fistulosa.
Opulaster opulifolius.
Prunus demissa.
Rubus deliciosus.
strigosus.
Halictus lerouxi :
Halictus medionitens:
Geranium caespitosum.
Holodiscus dumosus.
Halictus medionitens — Con.
Potentilla pulcherrima.
Rosa acicularis.
Rubus deliciosus.
Halictus manitonellus :
Monarda fistulosa.
Rosa acicularis.
Halictus pulzenua:
Castilleia miniata.
Chamaenerium angusti-
folium.
Frasera speciosa.
Geranium caespitosum.
richardsoni.
Gilia aggregata.
Mertensia sibirica.
Monarda fistulosa.
Opulaster opulifolius.
Pentstemon glaber.
gracilis,
halli.
secundiflorus.
Prunus demissa.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Halicyoides mamus:
Achillea millefolium.
Hammerschmidtia ferruginea:
Geranium caespitosum.
Heracleum lanatum.
Holodiscus dumosus.
Heriades gracilior:
Fragaria vesca.
Pentstemon glaber.
gracilis.
Heringia salix :
Rubus deliciosus.
Hyloicus separatus :
Pachylophus caespitosus.
Irbisia brachycerus:
Caltha leptosepala.
Drymocallis fissa.
Geranium caespitosum.
Jamesia americana.
Malvastrum cocineum.
Lemonias nubigena wheeleri :
Geranium caespitosum.
Helianthus petiolaris.
Rydbergia grandiflora.
Leptura chrysocoma:
Sambucus racemosa.
Lithargus apicalis opuntiae:
Stanleya pinnatifida.
Lycaena glaucon:
Galium borealis.
Lycaena pseudargiolus:
Geranium caespitosum.
Lygus pratensis:
Ibidium strictum.
Mallota flavoterminata:
Rosa acicularis.
Megachile gemula albula:
Chamaenerium angusti-
folium.
Megachile pugnata:
Carduus hookerianus.
POLLINATORS AND FLOWERS.
253
Megachile pugnata — Con.
Chamaenerium angusti-
folium.
Erigeron macranthus.
Geranium caespitosum.
Petalostemon purpureus.
Megachile relativa:
Chamaenerium angusti-
folium.
Geranium caespitosum.
richardsoni.
Rosa acicularis.
Megachile texana:
Chamaenerium angusti-
folium.
Rosa acicularis.
Megachile vidua:
Chamaenerium angusti-
folium.
Megachile wootoni:
Astragalus drummondi.
Campanula rotundifolia.
Carduus hookerianus.
Chamaenerium angusti-
folium.
Monarda fistulosa.
Opulaster opulifolius.
Pentstemon glaber.
glaucus.
gracilis.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Thermopsis montana.
Megachile wootoni calogaster:
Chamaenerium angusti-
folium.
Pentstemon glaber.
Rosa acicularis.
Rubus deliciosus.
Melitaea whitneyi :
Rydbergia grandiflora.
Melitaea sp. :
Rubus deliciosus.
Melissodes aurigenia:
Chamaenerium angusti-
folium.
Melissodes fremonti:
Monarda fistulosa.
Pentstemon glaber.
Melissodes sp. :
Carduus hookerianus.
Geranium caespitosum.
Mesogramma marginata :
Potentilla gracilis.
Microdon cothurnatus:
Prunus demissa.
Monumetha albifrons:
Apocynum androsaemi-
folium.
Astragalus drummondi.
Carduus hookerianus.
Chamaenerium angusti-
folium.
Frasera speciosa.
Geranium caespitosum.
Mertensia sibirica.
Monumetha albifrons — Con.
Pentstemon glaber.
glaucus.
gracilis,
halli.
Rosa acicularis.
Rubus deliciosus.
Monumetha argentif rons :
Chamaenerium angusti-
folium.
Mordella melaena:
Solidago missouriensis.
Myopa clausa:
Rubus deliciosus.
Nathalis iole:
Potentilla pulcherrima.
Nomada sp. :
Prunus virginiana.
Rubus deliciosus.
Odynerus annulatus:
Campanula rotundifolia.
Stanleya pinnatifida.
Omalus sp. :
Pentstemon glaber.
Ophion sp.:
Caltha leptosepala.
Osmia abnormis :
Iris missouriensis.
Osmia albolateralis :
Mertensia pratensis.
Osmia bella:
Iris missouriensis.
Osmia brevij:
Mertensia pratensis.
Osmia bruneri:
ElephanteUa groenlandica.
Geranium caespitosum.
Opulaster opulifolius.
Pentstemon glaber.
gracilis,
secundiflorus.
Rosa acicularis.
Osmia coloradella:
Mertensia sibirica.
Pentstemon glaber.
Osmia densa. :
Capnoides aureum.
Geranium caespitosum.
Mertensia pratensis.
sibirica.
Opulaster opulifolius.
Pentstemon glaber.
gracilis,
halli.
Rosa acicularis.
Osmia fulgida:
Fragaria vesca.
Geranium richardsoni.
Rosa acicularis.
Rubus deliciosus.
Osmia hypoleuca:
Mertensia pratensis.
Pentstemon gracilis.
Silene halli.
Osmia megacephala :
Rydbergia grandiflora.
Osmia melanotricha:
Mertensia pratensis.
Pentstemon glaber.
glaucus.
gracilis,
halli.
Rosa acicularis.
Osmia nigrif rons :
Mertensia pratensis.
sibirica.
Osmia pentstemonis :
Mertensia sibirica.
Pentstemon glaucus.
gracilis,
secundiflorus.
Osmia phaceliae :
Geranium caespitosum.
Mertensia sibirica.
Pentstemon glaber.
gracilis,
halli.
Osmia propinqua:
Geranium caespitosum.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Taraxacum officinale.
Osmia pusilla:
Mertensia pratensis.
Osmia rohweri :
Mertensia pratensis.
Osmia wardiana:
Chamaenerium angusti-
folium.
Osmia sp. :
Geranium caespitosum.
Monarda fistulosa.
Thermopsis montana.
Oxybelus sp. :
Pentstemon glaber.
Panurginus cressoniellus:
Erigeron macranthus.
Geranium caespitosum.
Ibidium strictum.
Rosa acicularis.
Rubus deliciosus.
Panzeria radicum :
Achillea millefolium.
Erigeron macranthus.
Papilio rutulus:
Pentstemon glaber.
Paragus bicolor:
Sieversia turbinata.
Parnassius clodius:
Carduus hookerianus.
Erigeron macranthus.
Parnassius smintheus:
Allium recurvatum.
Drymocallis fissa.
Geranium caespitosum.
Iris missouriensis.
Pentstemon secundiflorus.
Potentilla pulcherrima.
Peleteria robusta:
Erigeron macranthus.
Phorbia fusciceps:
Erigeron macranthus.
254
EXPERIMENTAL POLLINATION.
Phorbia fusciceps — Con.
Holodiscus dumosus.
Potentilla pulcherrima.
Phormia regina:
Pentstemon gracilis.
Tradescantia virginiana.
Phyciodes camillus:
Rubus deliciosus.
Sedum stenoptetalum.
Pieris protodice:
Sedum stenopetalum.
Pieris sisymbri :
Carduus hookerianua.
Pipiza vanduzeei:
Rubus deliciosus.
Pipiza sp. :
Rosa acicularis.
Rubus deliciosus.
Pompiloides sp. :
Pentstemon glaber.
Stanleya pinnatifida.
Prosopis basalis:
Chamaenerion angusti-
folium.
Geranium caespitosum.
Pentstemon gracilis,
halli.
secundiflorus.
Rosa acicularis.
Rubus deliciosus.
Prosopis coloradensis:
Rosa acicularis.
Prosopis cressoni:
Rubus deliciosus.
Prosopis elliptica:
Apocynum androsaemi-
folium.
Chamaenerium angusti-
folium.
Dasyphora fruticosa.
Erigeron macranthus.
Geranium caespitosum.
richardsoni.
Monarda fistulosa.
Pentstemon glaber.
glaucus.
gracilis,
secundiflorus
Rosa acicularis.
Rubus deliciosus.
Prosopis episcopalis :
Galium boreale.
Pentstemon glaber.
Rubus strigosus.
Prosopis tridentula:
Geranium caespitosum.
Prosopis varifrons:
Apocynum androsaemi-
folium.
Geranium caespitosum.
richardsoni.
Holodiscus dumosus.
Opulaster opulifolius.
Pentstemon glaber.
gracilis,
unilateralis.
Rubus deliciosus.
Prosopis varifrons — Con.
Rubus strigosus.
Rosa acicularis.
Prosopis wootoni:
Geranium caespitosum.
Pentstemon glaber.
Rosa acicularis.
Rubus deliciosus.
Prosopis sp. :
Solidago missouriensis.
Protoparce quinquemaculatus
Pachylophus caespitosus.
Protothyreopus dilectus:
Geranium caespitosum.
Psammophila violacepennis:
Geranium caespitosum.
Pseudomasaris vespoides :
Calochortus gunnisoni.
Geranium caespitosum.
Mertensia sibirica.
Monarda fistulosa.
Opulaster opulifolius.
Prunus demissa.
Pentstemon glaber.
glaucus.
gracilis.
Rubus deliciosus.
strigosus.
Pseudomelecta californica
miranda:
Asclepias halli.
Psithyrus ashtoni:
Chamaenerium angusti-
folium.
Geranium caespitosum.
Psithyrus consultus:
Delphinium scopulorum.
Monarda fistulosa.
Solidago missouriensis.
Psithyrus f ernaldae :
Carduus hookerianus.
Psithyrus insularis:
Aquilegia coerulea.
Carduus hookerianus.
Chamaenerium angusti-
folium.
Dasyphora fruticosa.
Gentiana parryi.
Geranium caespitosum.
Ptilodexia harpasa:
Prunus demissa.
Pyrameis atlanta:
Carduus hookerianus.
Linaria vulgaris.
Satyrus charon:
Carduus hookerianus.
Erigeron macranthus.
Sedum stenopetalum.
Scaba opinator:
Mertensia sibirica.
Selasphorus platycercus:
Castilleia miniata.
Iris missouriensis.
Mertensia sibirica.
Monarda fistulosa.
Pentstemon gracilis.
secundiflorus
Solenius sp. :
Chamaenerium angusti-
folium.
Specomyia vittata:
Prunus demissa.
Spegina infuscata:
Prunus demissa.
Sphaerophoria cylindrica:
Rosa acicularis.
Sphecodes sophiae:
Chamaenerium angusti-
folium.
Lappula floribunda.
Potentilla arguta.
gracilis.
Prunus pennsylvanica.
virginiana.
Valeriana edulis.
Sphex vulgaris:
Geranium caespitosum.
Sterictophora sp. :
Petalostemon candidus.
Synanthedon albicornis:
Achillea millefolium.
Rubus strigosus.
Syritta pipiens:
Prunus demissa.
Syrphus amalopis:
Geranium caespitosum.
Syrphus americanus:
Asclepias halli.
Chamaenerium angusti-
folium.
Frasera speciosa.
Geranium caespitosum.
Pentstemon gracilis.
Rosa acicularis.
Rubus deliciosus.
strigosus.
Tradescantia virginiana.
Syrphus disgregus:
Prunus demissa.
Syrphus nitens:
Rubus deliciosus.
Syrphus opinator:
Gentiana parryi.
Geranium caespitosum.
Pentstemon gracilis.
secundiflorus.
Rosa acicularis.
Systoechus vulgaris:
Pentstemon gracilis.
Rosa acicularis.
Rubus deliciosus.
Tabanus rhombicus:
Geranium caespitosum.
Temnostoma aequale:
Rubus deliciosus.
Tenthredella unicincta :
Erigeron macranthus.
Pentstemon glaber.
Tenthredella flavomarginis:
Heracleum lanatum.
Tetrachrysis lauta :
Pentstemon glaber.
POLLINATORS AND FLOWERS.
255
Tetraopee sp.:
Asclepias halli.
Thanaos martialis:
Chamaenerium angusti-
folium.
Delphinium scopulorum.
Erigeron macranthus.
Geranium caespitosum.
richardsoni.
Mertensia sibirica.
Monarda nstulosa.
Pentstemon glaber.
Thanaos propertius:
Capnoides aureum.
Theventimtia muricatus:
Prunus demissa.
Thyreocoriaanthracina :
Frasera speciosa.
Physaria didymocarpa.
Titusella pronitens:
Pentstemon glaber.
gracilis.
Trichius affinis:
Calochortus gunnisoni.
Trichodes ornatus:
Rubus deliciosus.
Trichopticus septentrionalis :
Rubus deliciosus.
Triepeolus helianthi grandior:
Asclepias halli.
Trypeta occidentalis :
Achillea millefolium.
Vespa germanica:
Chamaenerium angusti-
folium.
Jamesia americana.
Mertensia sibirica.
Monarda nstulosa.
Opulaster opulifolius.
Pentstemon glaber.
unilateralis.
Vespa occidentalis:
Erigeron macranthus.
Linaria vulgaris.
Volucella rufomaculata:
Castilleia miniata.
Rubus deliciosus.
strigosus.
Volucella satur:
Rubus deliciosus.
Stanleya pinnatifida.
Xylota angustiventris:
Heracleum lanatum.
Xylota flavitibia:
Holodiscus dumosus.
Rosa acicularis.
Rubus deliciosus.
Xylota nigra:
Rosa acicularis.
Zodion pygmaeum:
Prunus demissa.
6. FLOWERS AND THEIR VISITORS.
Achillea millefolium:
Agathis vulgaris.
Chrysophanus helloides.
Gnophaela vermiculata.
Halicyoides mamus.
Panzeria radicum.
Synanthedon albicornis.
Trypeta occidentalis.
Aconitum columbianum:
Bombus appositus.
bifarius.
edwardsi.
flavifrons.
juxtu3.
occidentalis.
rufocinctus.
Allium recurvatum:
Bombus edwardsi.
occidentalis.
Parnassius smintheus.
Apocynum androsaemifolium :
Halictus (Evylaeus) sp.
Monumetha albifrons.
Prosopis elliptica.
varifrons.
Aquilegia brevistyla:
Bombus hunti.
Aquilegia coerulea:
Bombus hunti.
occidentalis.
Clisodon terminalis.
Psithyrus insularis.
Aragalus lamberti:
Anthophora simillima.
Arctostaphylus uva-ursi :
Apis mellifica.
Bombus edwardsi.
Asclepias halli:
Apis mellifica.
Bembex spinolae.
Halictus (Chloralictus) sp.
Pseudomelecta miranda.
Syrphus americanus.
Tetraopes sp.
Triepeolus helianthi
grandior.
Asclepias speciosa:
Apis mellifica.
Echinomyia decisa.
Halictus (Lasioglossum)sp.
Astragalus drummondi:
Andrena gardineri.
imitatrix.
vicina.
Bombus edwardsi.
fervidus.
hunti.
juxtus.
morrisoni.
Halictus (Evylaeus) sp.
Megachile wootoni.
Monumetha albifrons.
Aster f oliaceus :
Bombus edwardsi.
flavifrons.
Calochortus gunnisoni:
Bombus edwardsi.
flavifrons.
occidentalis.
rufocinctus.
Curtipogon leucozona.
Dasyllis fernaldi.
Panurginus sp.
Pseudomasaris vespoides.
Trichius affinis.
Caltha leptosepala:
Irbisia brachycerus.
Ophion sp.
Campanula rotundifolia:
Anthophora smithi.
Bombus edwardsi.
hunti.
juxtus.
Chrysophanus rubidus.
Megachile wootoni.
Odynerus annulatus.
Capnoides aureum:
Anthophora simillima.
Atrytone taxiles.
Bombomelecta fulvida.
Bombus dorsalis.
juxtus.
occidentalis.
Colletes oromontis.
Osmia densa.
Thanaos propertius.
Carduus hookerianus:
Acmaeops longicornis.
Andrena crataegi.
Andronicus sp.
Bombus appositus.
bifarius.
edwardsi.
hunti.
juxtus.
nevadensis.
occidentalis.
Chrysophanus rubidus.
Clisodon terminalis.
sp.
Colias edwardsi.
scudderi.
Epalpus bicolor.
rufus.
Erizoa olivalis.
Grapta hylas.
Megachile pugnata.
wootoni.
sp.
Melissodes sp.
Monumetha albifrons.
Parnassius clodius.
Pieris sisymbri.
Psithyrus fernaldae.
insularis.
256
Carduus hookerianus — Con.
Pyrameis atlanta.
Satyrus charon.
Castilleia miniata:
Bombus hunti.
kirbyellus.
occidentalis.
Colias keewaydinus.
Halictus ^Chloralictus) sp.
(Evylaeus) sp.
(Lasioglossum)
sp.
pulzenus.
Selasphorus platycercus.
Volucella rufomaculata.
Chamaenerium angustifolium:
Anthophora occidentalis.
smithi.
Apis mellifica.
Argynnis atlantis.
Atrytone taxiles.
Bombus appositus.
bifarius.
centralis,
edwardsi.
flavifrons.
hunti.
juxtus.
nevadensis.
occidentalis.
rufocinctus.
Clisodon terminalis.
Coelioxys moesta.
Ctenucha sp.
Dasyllis fernaldi.
Dejeania vexatrix.
Dolichovespula arctica.
diabolica.
Echinomyia algens.
Erynnis leonardus snowi.
Halictus (Evylaeus) sp.
(Lasioglossum)
sp.
pulzenus.
Megachile gemula albula.
pugnata.
relativa.
texana.
vidua,
wootoni.
wootoni calo-
gaster.
Melissodes aurigenia.
Monumetha albifrons.
argentifrons.
Osmia wardiana.
Prosopis basalis.
elliptica.
Psithyrus ashtoni.
insularis.
Solenius sp.
Sphecodes sophiae.
Syrphus americanus.
FLOWERS AND VISITORS.
257
hamaenerium angustifolium
—Con.
Thanaos martialis.
Vespa germanica.
Chrysopais villosa:
Bombus edwardsi.
juxtus.
Echinomyia algens.
Cleome serrulata:
Bombus edwardsi.
Eliphilus latifrons.
Clementsia rhodantha:
Anthomyia sp.
Daeyphora fruticosa:
Bombus flavifrons.
Brenthis triclaris.
Coenonympha pamphi-
loides.
Erebia epipsodea.
Prosopis elliptica.
Psithyrus insularis.
Delphinium scopulorum:
Bombus appositus.
bifarius.
centralis,
edwardsi.
flavifrons.
juxtus.
morrisoni.
occidentalis.
Dolichovespula arctica.
Psithyrus consultus.
Thanaos martialis.
Dodocatheon meadia:
Anthophora simillima.
Bombus bifarius.
edwardsi.
flavifrons.
Draba aurea:
Chionobis macouni.
Drymocallis fissa:
Bombus edwardsi.
Irbisia brachycerus.
Parnassius smintheus.
Elephantella groenlandica:
Bombus bifarius.
Osmia bruneri.
Erigeron macranthus:
Andrena apacheorum.
Anthrax fulviana.
tegminipennis.
Argynnis atlantis.
Bombus bifarius.
edwardsi.
hunti.
Bracon helena.
Brenthis helena.
Chrysophanus helloides.
Coenonympha pamphi-
loides.
Megachile pugnata.
Parnassius clodius.
Panurginus cressoniellus.
Panzeria radicum.
Peleteria robusta.
Prosopis elliptica.
Erigeron macranthus — Con.
Satyrus charon.
Tenthredella unicincta.
Thanaos martialis.
Vespa occidentalis.
Erigeron uniflorus:
Bombus hunti.
occidentalis.
Erysimum asperum:
Bombus occidentalis.
Fragaria vesca:
Bombus edwardsi.
Heriades gracilior.
Osmia fulgida.
Frasera speciosa:
Apis mellifica.
Andrena crataegi.
madronitens.
Bombus edwardsi.
flavifrons.
hunti.
juxtus.
Clisodon terminalis.
Halictus lerouxi.
pulzenus.
sp.
Monumetha albifrons.
Syrphus americanus.
Thyreocoris anthracina.
Galium boreale:
Lycaena glaucon.
Prosopis episcopalis.
Geum rivale:
Archytas sp.
Gentiana parryi:
Bombus appositus.
juxtus.
nevadensis.
Psithyrus insularis.
Syrphus opinator.
Geranium caespitosum:
Ancistrocerus sp.
Andrena apacheorum.
braccata.
madronitens.
vicina.
Andronicus sp.
Apanteles sp.
Apis mellifica.
Argynnis eurynome.
Bombus appositus.
bifarius.
edwardsi.
hunti.
juxtus.
occidentalis.
rufocinctus.
Cenis uhleri.
Clisodon terminalis.
Coelioxys moesta.
Colletes kincaidi.
oromontis.
sieverti.
Epeolus helianthi.
Erebia epipsodea.
Foenus perplexus.
Geranium caespitosum — Con.
Glypta sp.
Halictus (Chloralictus) sp.
(Lasioglossum)
sp.
medionitens.
pulzenus.
Hammerschmidtia ferru-
ginea.
Irbisia brachycerus.
Lemonias nubigena
wheeleri.
Lycaena pseudargiolus.
Megachile pugnata.
relativa.
Melissodes sp.
Monumetha albifrons.
Osmia bruneri.
phaceliae.
propinqua.
sp.
Panurginus cressoniellus.
Parnassius smintheus.
Protothyreopus dilectus.
Prosopis basalis.
elliptica.
tridentula.
varifrons.
wootoni.
Psammophila violace-
pennis.
Pseudomasaris vespoides.
Psithyrus insularis.
Sphex vulgaris.
Syrphus amalopis.
americanus.
opinator.
Tabanus rhombicus.
Thanaos martialis.
Geranium richardsoni:
Ancistrocerus sp.
Andrena madronitens.
Apis mellifica.
Bombus bifarius.
hunti.
occidentalis.
Ectemius montanus.
Halictus pulzenus.
Megachile relativa.
Osmia fulgida.
Prosopis elliptica.
varifrons.
Thanaos martialis.
Gilia aggregata:
Halictus (Chloralictus) sp.
pulzenus.
Helianthus petiolaris :
Argynnis eurynome.
Bombus hunti.
Lemonias nubigena
wheeleri.
Heracleum lanatum :
Anthrax hypomelas.
258
EXPERIMENTAL POLLINATION.
Heracleum lanatum — Con.
Bombus occidentalia.
Echinomyia algena.
Eclimus muricatus.
Hammerschmidtia ferru-
ginea.
Tenthredella flavomar-
ginis.
Xylota angustiventris.
Holodiscus dumosus:
Andrena crataegi.
madronitena.
Anthrax alternata.
Apis mellifica.
Bombus bifarius.
edwardsi.
hunti.
juxtus.
occidentalis.
Chrysotoxum integrum.
Clisodon terminalis.
Colletes oromontis.
Halictus medionitens.
Hammerschmidtia ferru-
ginea.
Phorbia fusciceps.
Prosopis varifrons.
Xylota flavitibia.
Ibidium strictum:
Bombus appositus.
morrisoni.
Halictus sp.
Lygus pratensis.
Panurginus cressoniellus.
Iris missouriensis:
Chionobis macouni.
Osmia abnormis.
bella.
Parnassius smintheus.
Selasphorus platycercus.
Jamesia americana:
Andrena edwiniae.
Ancistrocerus sp.
Apis mellifica.
Bombus bifarius.
edwardsi.
hunti.
juxtus.
occidentalis.
Eristalis tenax.
Irbisia brachycerus.
Vespa germanica.
Lappula floribunda:
Sphecodes sophiae.
Lathyrus ornatus:
Bombus edwardsi.
Linaria vulgaris:
Apis mellifica.
Basilarchia weidemeyeri.
Bombus occidentalis.
Pyrameis atlanta.
Vespa occidentalis.
Lithospermum canescens:
Anthophora simillima.
Malvastrum coccineum:
Agapostemon splendens.
Irbisia brachycerus.
Mentzelia multiflora:
Apis mellifica.
Bombus bifarius.
juxtus.
occidentalis.
Mertensia pratensis:
Clisodon terminalis.
Colletes oromontis.
Osmia albolateralis.
brevis.
densa.
hypoleuca.
melanotricha.
nigrifrons.
pentstemonis.
pusilla.
rohweri.
Mertensia sibirica:
Acmaeops longicornis.
Ancistrocerus sp.
Andrena madronitens.
Bombus bifarius.
edwardsi.
flavifrons.
ftflvida.
juxtus.
occidentalis.
Bombomelecta fulvida.
Ceratina sp.
Clisodon sp.
Colletes oromontis.
sp.
Dejeania vexatrix.
Halictus (Chloralictus) sp.
(Evylaeus) sp.
pulzenus.
Monumetha albifrona.
Osmia coloradella.
densa.
nigrifrons.
pentstemonis.
phaceliae.
Pseudomasaris vespoidea.
Scaba opinator.
Selasphorus platycercus.
Thanaos martialis.
Vespa germanica.
Monarda fistulosa:
Andrena crataegi.
Anthophora smithi.
Argynnis atlantis.
Atrytone taxiles.
Bombus appositus.
bifarius.
centralis,
fervidus.
flavifrona.
hunti.
morrisoni.
occidentalis.
pennsylvanica.
Chrysophanus sirius.
Clisodon termininalis.
Colletes oromontis.
Ctenucha sp.
Erynnia leonardus snowi.
Monarda fistulosa — Con.
Halictus (Chloralictus) sp.
(Lasioglossum)
sp.
manitonellus.
pulzenus.
Megachile wootoni.
Melissodes fremonti.
Osmia sp.
Prosopis elliptica.
Pseudomasaris vespoidea.
Psithyrus consultua.
Selasphorus platycercua.
Thanaos martialis.
Vespa germanica.
Onagra biennis :
Andrena madronitena.
Bombus juxtus.
Megachile sp.
Opulaster opulifolius :
Andrena crataegi.
madronitens.
Apis mellifica.
Bombus edwardsi.
nevadensia.
occidentalis.
Dejeania vexatrix.
Eristalis latifrons.
Halictus (Chloralictus) sp.
(Lasioglossum)
sp.
pulzenus.
Megachile wootoni.
Osmia bruneri.
densa.
Prosopis varifrons.
Pseudomasaris vespoides.
Vespa germanica.
Oreochrysum parryi :
Chrysophanus helloides.
Pachylophus caespitosus:
Celerio lineata.
Hyloicus separatua.
Protoparce quinquemac-
ulatus.
Pedicularis parryi :
Bombus hunti.
kirbyellus.
Pedicularis racemosa :
Bombus edwardsi.
occidentalia.
Pentstemon glaber:
Agapostemon splendena.
Andrena madronitena.
prunorum.
vicina.
Anthophora bomboidea.
simillima.
Apis mellifica.
Atrytone taxiles.
Bombus appositus.
bifarius.
centralis,
edwardsi.
hunti.
juxtus.
kirbyellus.
FLOWERS AND VISITORS.
259
Pentstemon glaber — Con.
Bombus morrisoni.
occidentalis.
rufocinctus.
Bombomelecta fulvida.
Celerio lineata.
Clisodon terminalis.
sp.
Gonochrysis densa.
Halictus (Chloralictus) sp.
pulzenus.
Heriades gracilior.
Megachile wootoni.
wootoni calo-
gaster.
Melissodes fremonti.
Monumetha albifrons.
Omalus sp.
Osmia bruneri.
coloradella.
densa.
melanotricha.
phaceliae.
Oxybelus sp.
Panurginus sp.
Papilio rutulus.
Pompiloides sp.
Prosopis elliptica.
episcopalis.
varifrons.
wootoni.
Pseudomasaris vespoidea.
Tetrachrysis lauta.
Tenthredella unicincta.
Thanaos martialis.
Titusella pronitens.
Vespa germanica.
Xylota angustiventris.
Pentstemon glaucus:
Bombus bifarius.
edwardsi.
juxtus.
morrisoni.
occidentalis.
Clisodon terminalis.
Megachile wootoni.
Monumetha albifrons.
Osmia melanotricha.
pentstemonis.
Prosopis elliptica.
Pseudomasaris vespoides.
Pentstemon gracilis:
Andrena washingtoni.
Andronicus sp.
Anthophora neomexi-
cana.
Anthophora simillima.
Bombus appositus.
bifarius.
centralis.
edwardsi.
hunti.
juxtus.
morrisoni.
rufocinctus.
Bombomelecta fulvida.
Pentstemon gracilis — Con.
Ceratina sp.
Cerastomia lignaria.
Clisodon terminalis.
sp.
Colletes kincaidi.
Halictus (Chloralictus) sp.
(Evylaeus) sp.
pulzenus.
Heriades gracilior.
Megachile wootoni calo-
gaster.
Monumetha albifrons.
Osmia bruneri.
hypoleuca.
melanotricha.
pentstemonis.
phaceliae.
Phormia regina.
Prosopis basalis.
elliptica.
varifrons.
Pseudomasaris vespoides.
Selasphorus platycercus.
Syrphus americanus.
opinator.
Systoechus vulgaris.
Titusella pronitens.
Penstemon halli:
Anthophora simillima.
Halictus pulzenus.
Osmia densa.
melanotricha.
phaceliae.
Monumetha albifrons.
Prosopis basalis.
Penstemon secundifiorus :
Andrena madronitens.
Anthophora simillima.
Argynnis atlantis.
Bombus bifarius.
edwardsi.
juxtus.
occidentalis.
Clisodon terminalis.
Halictus pulzenus.
Osmia bruneri.
pentstemonis.
Parnassius smintheus.
Prosopis basalis.
elliptica.
Selasphorus platycercus.
Syrphus opinator.
Pentstemon unilateralis:
Anthophora simillima.
Apis mellihca.
Bombus americanorum.
fervidus.
juxtus.
Prosopis varifrons.
Vespa germanica.
Petalostemon candidus:
Apis mellifica.
Bombus appositus.
edwardsi.
fervidus.
Petalostemon candidus — Con.
Bombus hunti.
rufocinctus.
Sterictophora sp.
Petalostemon purpureus:
Apis mellifica.
Bombus appositus.
edwardsi.
fervidus.
hunti.
occidentalis.
rufocinctus.
Clisodon terminalis.
Colletes kincaidi.
Megachile pugnata.
sp.
Phacelia heterophylla :
Chrysophanus rubidus.
Physaria didymocarpa:
Halictus sp.
Thyreocoris anthracina.
Polygonum bistorta:
Chrysotoxum upsilon.
Epalpus bicolor.
Gnophaela vermiculata.
Potentilla arguta:
Andrena vicina.
Bombus juxtus.
kirbyellus.
Sphecodes sophiae.
Potentilla gracilis:
Anthrax hypomelas.
Bombus hunti.
Eristalis meigeni.
Mesogramma marginata.
Sphecodes sophiae.
Potentilla pulcherrima :
Bombus kirbyellus.
occidentalis.
Chionobis macouni.
Chrysotoxum ventri-
cosum.
Colias alexandra.
Erebia epipsodea.
Geocoris bullatus.
Gnophaela vermiculata.
Halictus medionitens.
sp.
Nathalis iole.
Parnassius smintheus.
Prunus demissa:
Acmaeops longicornis.
pratensis.
Agapostemon sp.
Andrena canadensis.
crataegi.
edwiniae.
madronitens.
prunorum.
vicina.
sp.
Bombus fiavifrons.
occidentalis.
Brachyopa notata.
Brenthis triclarius.
Calliphora vomitoria.
260
EXPERIMENTAL POLLINATION.
Prunus demissa — Con.
Chilosia petulca.
tristis.
Coenonympha pamphi-
loides.
Colletes kincaidi.
oromontis.
Erebia epipsodea.
Eristalis arbustorum.
dimidiatus.
temporalis.
Halictus (Chloralictus) sp.
(Evylaeus) sp.
(Lasioglossum)
sp.
pulzenus.
sp.
Microdon cothurnatus.
Pseudomasaris vespoides.
Ptilodexia harpasa.
Specomyia vittata.
Spegina infuscata.
Syrphus disgregus.
Syritta pipiens.
Thevenetimyia muricatus.
Zodion pygmaeum.
Prunus pennsylvanica:
Sphecodes sophiae.
Prunus virginiana:
Andrena crataegi.
prunorum.
vicina.
sp.
Nomada sp.
Sphecodes sophiae.
Rosa acicularis:
Acmaeops longicornis.
pratensis.
Agapostemon splendens.
Andrena crataegi.
madronitens.
vicina.
washingtoni.
sp.
Anthrax lateralis.
nigra.
Anthophora simillima.
Apis mellifica.
Arctophila flagrans.
Bombus appositus.
bifarius.
edwardsi.
flavifrons.
hunti.
juxtus.
morrisoni.
occidentalis.
rufocinctus.
Bombylius atriceps.
Chrysotoxum integrum.
Clisodon terminalis.
Colletes americanus.
Eristalis latifrons.
Halictus (Evylaeus) sp.
manitonellus.
medionitens.
pulzenus.
Mallota flavoterminata.
Rosa acicularis — Con.
Megachile relativa.
texana.
wootoni.
wootoni calo-
gaster.
Monumetha albifrons.
Osmia bruneri.
densa.
fulgida.
melanotricha.
propinqua.
Panurginus cressionellus.
Pipiza sp.
Prosopis basalis.
coloradensis.
elliptica.
varifrons.
wootoni.
Sphaerophoria cylindrica.
Syrphus americanus.
opinator.
Systoechus vulgaris.
Xylota flavitibia.
nigra.
Rubus deliciosus:
Acmaeops longicornis.
pratensis.
Ancistrocerus sp.
Andrena canadensis,
crataegi.
madronitens.
placida.
prunorum.
vicina.
Andronicus sp.
Apis mellifica.
Bombus americanorum.
appositus.
bifarius.
edwardsi.
fervidus.
flavifrons.
hunti.
juxtus.
kirbyellus.
morrisoni.
occidentalis.
rufocinctus.
Brachyopa notata.
Chrysogaster parva.
Colletes oromontis.
Eristalis flavipes.
latifrons.
temporalis.
Exoprosopa caliptera.
Halictus (Lasioglossum)
sp.
medionitens.
pulzenus.
sp.
Heringia salix.
Megachile wootoni.
wootoni calo-
gaster.
Melitaea sp.
Monumetha albifrons.
Myopa clausa.
Rubus deliciosus — Con.
Nomada sp.
Osmia fulgida.
propinqua.
Panurginus cressionellus.
sp.
Phyciodes camillus.
Pipiza vanduzeei.
sp.
Prosopis basalis.
cressoni.
elliptica.
varifrons.
wootoni.
Pseudomasaris vespoides.
Systoechus vulgaris.
Syrphus americanus.
nitens.
Temnostoma aequale.
Tricopticus septen-
trionalis.
Trichodes ornatus.
Volucella rufomaculata.
satur.
Xylota flavitibia.
Rubus strigosus:
Ancistrocerus sp.
Andrena crataegi.
lewisi.
madronitens.
vicina.
Anthophora simillima.
Apis mellifica.
Bombus bifarius.
edwardsi.
flavifrons.
hunti.
juxtus.
morrisoni.
occidentalis.
Clisodon terminalis.
Colletes oromontis.
Eristalis arbustorum.
Gnophaela vermiculata.
Halictus (Lasioglossum)
sp.
pulzenus.
sp.
Megachile wootoni.
Osmia propinqua.
Prosopis episcopalis.
varifrons.
Pseudomasaris vespoides.
Synthedon albicornis.
Syrphus americanus.
Volucella rufomaculata.
Rydbergia grandiflora:
Argynnis eurynome.
Bombus appositus.
edwardsi.
flavifrons.
hunti.
Eristalis temporalis.
Lemonias nubigena
wheeleri.
Melitaea whitneyi.
Osmia megacephala.
FLOWERS AND VISITORS.
261
Sambucus racemosa:
Leptura chrysocoma.
Scutellaria resinosa:
Bombus morrisoni.
Sedum stenopetalum:
Andrena madronitens.
Anthidium tenuiflorae.
Anthrax sinuosa.
Argynnis eurynome.
Bombus edwardsi.
hunti.
Exoprosopa divisa.
Phyciodes camillus.
Pieris protodice.
Satyrus charon.
Sieversia ciliata:
Bombus edwardsi.
occidentalis.
Halictus sp.
Sieversia turbinata:
Paragus bicolor.
Silene acaulis:
Exoprosopa volucris.
Silene halli:
Osmia hypoleuca.
Solidago missouriensis:
Anthrax halcyon.
Apis mellifica.
Bombus edwardsi.
Solidago missouriensis — Con.
Bombus flavifrons.
hunti.
occidentalis.
rufocinctus.
Colletes americanus.
oromontis.
Epalpus bicolor.
Gnophaela vermiculata.
Halictus sp.
Mordella melaena.
Prosopis sp.
Psithyrus consultus.
Stanleya pinnatifida:
Agapostemon coloraden-
sis.
sp.
Andrena vicina.
Apis mellifica.
Bombus bifarius.
hunti.
morrisoni.
rufocinctus.
Bracon vulgaris.
Ceratina sp.
Lithargus apicalis opun-
tiae.
Odynerus annulata.
Pompiloides sp.
Volucella satur.
Taraxacum officinale:
Agapostemon coloradensis.
splendens.
Apis mellifica.
Osmia propinqua.
Thermopsis montana:
Bombus americanorum.
hunti.
juxtus.
Megachile wootoni.
Osmia sp.
Thalictrum fendleri:
Apis mellifica.
Halictus fendleri.
sp.
Tradescantia virginiana:
Anthrax sinuosa.
Apis mellifica.
Halictus (Evylaeus) sp.
Panurginus sp.
Phormia regina.
Syrphus americanus.
Trifolium dasyphyllum :
Bombus hunti.
kirbyellus.
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INDEX.
Acer pseudoplatanus, 151
Achillea millefolium, 115
Acmaeops longicornis, 63
Aconitum, 18, 90, 91, 93, 241
columbianum, 15, 18, 111
lycoctonum, 16
napellus, 16
Agrostis, 150
Ajuga, 131
Allium recurvatum, 106, 137
Althea rosea, 137, 161, 188
Amarantus, 196, 241
Ammophila, 221
Ampelopsis, 146, 168
Anchusa, 162, 164, 193
Andrena, 101, 104, 134, 181
crataegi, 27, 28, 30, 31, 37, 79, 97, 105, 106,
109
madronitens, 33, 35, 39, 46, 62, 65, 105
vetula, 175
vicina, 29, 33, 65, 69, 70, 71
Anemone, 130
japonica, 149
Angelica, 165
Anoda triloba, 187
Anthidium, 131, 147, 151, 153, 154, 157, 181
manicatum, 155, 239
Anthophora acervorum, 176
pilipes, 243
simillima, 34, 40, 68, 74, 77, 106, 109, 136,
155, 181
Anthoxanthum, 150
Antirrhinum, 131
majus, 147, 148, 170, 184
Apis mellifica, 27, 28, 30, 31, 32, 33, 39, 40, 46,
52, 57, 58, 60, 61, 62, 69, 74, 75, 78, 89,
93, 97, 104, 106, 109, 114, 131, 134, 136,
148, 149, 150, 153, 155, 157, 160, 161, 162,
164, 165, 179, 180, 181, 183, 244
Aporus fasciatus, 221
Aquilegia coerulea, 100, 101, 105, 106, 111
Arabis, 136
Argemone platyceras, 217
Argynnis atlantis, 46, 79, 80, 89, 91, 119, 181
Asparagus, 138
Asphodius, 226
Aster, 80, 109, 185
bigelovi, 85, 106, 115
Aucuba, 137
Bembex labia tus, 221, 222
mori, 225
Bombus, 62
appositus, 88, 89, 91, 119
bifarius, 15, 16, 17, 18, 20, 21, 22, 33, 35, 39,
41, 44, 46, 49, 58, 66, 73, 74, 79, 90, 92,
116, 119, 134
californicus, 40
edwardsi, 19, 22, 23, 24, 25, 33, 62, 76
flavifrons, 33
hortorum, 158
hunti, 119
hypnorum, 158
Bombus — Continued.
juxtus, 15, 16, 17, 19, 20, 21, 22, 23, 24, 25,
26, 29, 30, 34, 36, 37, 38, 39, 41, 43, 44, 45,
46, 48, 49, 51, 52, 53, 58, 59, 61, 62, 63,
66, 70, 73, 75, 76, 77, 78, 79, 88, 89, 90,
91, 92, 93, 101, 105, 110, 116, 119, 134,
241
lapidarius, 132, 158
morrisoni, 23, 29, 76, 77, SO, 91
muscorum, 132, 147, 158
occidentalis, 30, 57, 91, 105, 119
pennsylvanicus, 79
pratorum, 141
proximus, 24, 25, 26, 31, 33, 35, 36, 37, 39,
46, 76, 77, 79, 80, 134
silvarum, 132
terrestris, 132, 141, 147, 149, 158
terricola, 194
Bombylius fimbriatus, 175, 182
fuliginosus, 205, 206
Borrago, 159, 175
officinalis, 175
Brachypodium, 150
Brassica, 173
Bromus, 150
Bryonia dioeca, 138, 187
Calceolaria, 131
Calliphora, 156
Callosamia promethea, 159
Calluna, 131
Calochortus gunnisoni, 115
Caltha, 131
Campanula, 61, 62, 92, 106, 115, 240
Camponotus, 229
Carabus, 230
Carex, 150
Castilleia, 64
affinis, 64
linarifolia, 64
niiniata, 106, 109
Celerio lineata, 55
Centaurea, 130, 133, 169
cyanus, 148, 162, 170, 171, 184
Cerceris, 221
Chalicodoma, 218, 219, 220
Chamaenerium, 46, 48, 54, 57, 58, 78, 81, 85,
89, 93, 98, 99, 101, 105, 110, 111, 114, 115,
116, 119, 239, 241
Chenopodium album, 150
Chrysanthemum, 176, 186
leueanthemum, 178
Cirsium oleraceum, 133
palustre, 133
Cistus, 176
Clematis jackmanni, 165, 196
Cleome serrulata, 95, 98, 99, 101, 104
Clisodon terminalis, 36, 38, 58, 68, 69, 70, 71,
72, 75, 81, 88, 89, 91, 119, 134
Coelioxys, 40
Convolvulus, 136
sepium, 149, 165
Corylus avellana, 150
269
270
INDEX.
Crataegus, 187
Crocus, 136, 161, 178, 179, 182
luteus, 161
sativus, 185
vernus, 161
Cucurbita maxima, 194
Cytisus, 131
Dahlia, 145, 147, 148, 149, 152, 157, 168, 172,
180, 183, 184, 185, 186
variabilis, 161, 181
Deiliphila, 159
elpenor, 175, 192
Dejeania vexatrix, 62
Delphinium ajacis, 147, 164
consolida, 23, 147
elatum, 23
scopulorum, 22, 93, 111, 115
tricorne, 23
Deutzia, 187, 188
Dianthus barbatus, 153, 175, 192
carthusianorum, 132, 151, 164, 175
Digitalis purpurea, 147, 148, 151, 169, 194
Dodecatheon meadia, 112
Doronicum caucasicum, 180
Echinacea purpurea, 187
Elephantella groenlandica, 112, 114
Epilobium spicatum, 131, 184
Eranthis nivalis, 178
Erigeron macranthus, 115
Eristalis tenax, 130, 147, 156, 157, 181, 182,
183, 191
Erynnis leonardus snowi, 79, 80, 89, 91
Eschscholtzia, 184, 185
Eupatorium, 131
Festuca, 150
Ficaria, 131
Fragaria, 62
Frasera carolinensis, 59
speciosa, 61, 92, 93, 95, 98, 99, 111, 240
Fritillaria, 136
Formica fusca, 225
rufa, 227, 229
Fumaria officinalis, 165
Galium, 206
Gentiana parryi, 115
Geum intermedium, 131
rivale, 131
urbanum, 131
Geranium, 28, 39, 41, 57, 58, 80, 82, 92, 95,
99, 104, 115, 119
caespitosum, 85, 89, 101, 105, 106, 110, 114,
115, 134
carolinianum, 40
maculatum, 40
richardsoni, 40, 98, 105, 106, 110, 116, 134
Gerardia purpurea, 195
Gilia aggregata, 82, 85, 110, 115, 119
Glycine, 167
Halictus, 27, 28, 39, 41, 63, 113, 160, 165
(Evylaeus) sp., 62, 63
(Lasioglossum) sp., 46
pulzenus, 31, 36, 39, 44, 62, 64, 65, 66, 70,
73, 75, 78, 79, 92
Helianthus annuus, 162, 185
Heliopsis levis, 187, 188
Helix, 222
Heracleum lanatum, 106, 133, 148, 169
Hesperis, 186
Hieracium, 176, 240
Hyacinthus, 136
Hydrangea, 153
Hyloicus separatus, 55
Ipomoea purpurea, 147
Jamesia americana, 97
Laciniaria punctata, 217
Lamium album, 129, 132
Lantana, 243
Lathyrus, 133
latifolius, 151
Lavandula, 131
Leucanthemum vulgare, 162
Leycesteria, 131
Lilium candidum, 165
Linum perenne, 165
Linaria vulgaris, 207
Listera, 169
Lobelia erinus, 147, 169
Lucilia, 157, 161
caesar, 225, 226
Lycaena, 16
Macroglossa, 16, 153, 164, 165, 205, 206
stellatarum, 136, 164, 190, 191, 192, 193
Malva, 159, 175
silvestris, 184
Megachile pugnata, 46
wootoni, 34, 105, 106, 109, 145, 146, 148,
149, 151, 154, 155, 156, 161, 165, 239
Melampyrum nemorosum, 132
Melandrium, 162
Melanostoma, 154
Melissodes fremonti, 71, 198
Melolontha, 230
Mentzelia, 57, 58, 92
Mercurialis, 131
Mertensia alpina, 100, 101, 105, 106
sibirica, 62, 63, 95, 98, 105
Monarda fistulosa, 79, 80, 81, 82, 85, 88, 89,
91, 110, 115, 116, 117, 134, 239
Monumetha albifrons, 27, 34, 36, 39, 66
Musca, 151, 156, 179
Muscari comosum, 175, 205
Myosotis alpestris, 151, 161
Myrmica ruginodis, 225
Nicotiana, 148
Odynerus, 150, 151
Oenothera biennis, 55, 131, 147, 210, 212, 217
fruticosa, 55
missouriensis, 55
pinnatifida, 55
speciosa, 165
Osmia, 28, 30, 31, 40, 92, 113, 161, 181
bruneri, 33, 34, 39, 70, 71, 73, 76
californica, 48
coloradella, 65
INDEX.
271
Oamia — Continued.
densa, 65, 68
ferruginea, 222
melanotricha, 65, 69, 70, 71, 72, 73
phacelia, 65, 68, 69, 70, 71, 73, 75, 76, 105
pentstemonis, 62, 65, 69, 70, 72, 73, 75, 76
rufohirta, 222
tricornis, 176
Opulaster opulifolius, 95, 97, 101, 104, 134
Oxybelus, 151
Paeonia, 181
Papaver orientalis, 159, 160, 161, 174, 18a
rhoeas, 160, 171, 172, 184
Papilio, 164
Passiflora, 165
Pedicularis canadensis, 129
Pelargonium zonale, 149, 165, 166, 174, 196
Pentstemon, 134
barbatus, 100, 101, 106, 109, 112, 113, 114,
115
barbatus labrosus, 68
bridgesi, 68
glaber, 78, 89, 111, 112, 113, 114
glaucus, 111, 112, 114
gracilis, 78, 111, 112, 113, 114, 115
halli, 111, 112, 113, 114
palmeri, 68
secundiflorus, 78, 100, 101, 106, 109, 113, 115
unilateralis, 112, 113, 114
Perdita, 133
Petunia, 147, 176, 240
hybrida, 165
Phlox drummondi, 175
paniculata, 149, 159, 164, 175, 192
Pieris, 136. 137, 145, 146, 149, 153, 156, 161,
163, 171, 181
brassicae, 154, 191
Pirus communis, 194
Pisum sativum, 165
Poa, 150
Polistes pallipes, 224
gallicus, 141, 225
Polygonum convolvulus, 165
Pompilus, 221
scelestus, 233
Portulaca grandiflora, 196, 242
Primula, 131, 136, 181
Prosopis, 28, 37, 41, 92, 101, 105, 106, 113,
161, 163, 165, 181
elliptica, 34, 39, 73, 79
episcopalis, 32, 33
varifrons, 41, 66, 75
Protoparce quinquemaculata, 55
Prunus demissa, 28, 101, 134
pennsylvanica, 28
Pseudomasaris vespoides, 39, 67, 68, 70, 71,
77, 90, 101, 109
Pulmonaria, 136, 243
Pyrethrum leucanthemum, 184
Ranunculus, 130, 136
acris, 171
Ratibida, 217
Reseda, 180
Rheum tataricum, 150
Rhodocera, 153
rhamni, 192
Rhododendron ciliatum, 179, 186
Ribes, 138
sanguineum, 150
rubrum, 151
Rosa, 18, 33, 34, 92, 95, 104, 105, 106, 109, 134
acicularis, 101, 102, 134
canina, 34
rubiginosa, 34
Rubus deliciosus, 24, 28, 32, 33, 81, 89, 92,
93, 95, 101, 134, 241
strigosus, 32, 33, 62, 95, 97, 99, 101, 102,
106, 134
Rudbeckia, 157, 188, 241
laciniata, 187, 217
Rumex obtusifolius, 150
Salix, 131, 138
Salvia horminum, 153, 154, 155, 165, 181, 183,
193
splendens, 166
Sarcophaga vivipara, 225
Saturnia carpini, 225
Saxifraga umbrosa, 151
Scabiosa, 130, 132, 149, 154
atropurpurea, 161
Scrophularia nodosa, 100, 101, 106, 109, 115
Secale, 150
Selasphorus platycercus, 63, 64, 74, 79
Silpha thoracica, 227, 230
Solanum rostratum, 217
Solidago, 217
Sphecodes sp., 64
Sphex vulgaris, 39
Sphinx convoluta, 189
Stelis, 163
Symphoricarpus racemosus, 151, 167
Symphytum officinale, 184
Syritta pipiens, 178, 238, 240
Systoechus vulgaris, 74, 77
Syrphus americanus, 35, 129, 130, 137, 154.
156, 191
opinator, 38
Tagetes, 147, 151
Teucrium chamaedrys, 137
scorodonia, 137
Thanaos martialis, 23, 26, 76
Tilia, 131
Titusella pronitens, 66, 74
Tragopogon, 130
Tremandra, 131
Trichius, 136
Trifolium, 132
Tropaeolum, 131
majus, 191
Vanessa, 136, 145, 146, 161, 181
Verbena, 192
Veronica, 141
Vespa germanica, 27, 46, 62, 65, 69, 70, 71, 72,
73, 76, 77, 141, 149, 150, 164, 165
Vicia americana, 129
sepium, 132
Viola, 136
odorata, 161
Volucella, 182
Zinnia, 130, 154, 183
elegans, 161, 181
Descriptions of Plates.
Plate 1. Painted flowers of Aconitum and Delphinium, showing experimental method.
Plate 2. Life-history of flowers: Aconitum columbianum: (1) bud opening; (2) 4
anthers open; (3) 8 anthers open; (4) 16 anthers open; (5) 4 anthers whole;
(6) all anthers shed, styles visible; (7) carpels enlarging, stamens shrunken;
(8) petals falling. Delphinium scopulorum: (9) flower just open; (10) 4
anthers shed; (11) 8 anthers shed; (12) 16 anthers shed; (13) 4 anthers whole;
(14) all anthers shed, styles visible; (15) carpels enlarging, stamens shrunken;
(16) sepals falling.
Plate 3. Life-history of flowers: Rubus strigosus: (1) bud in section; (2) bud partly
open; (3) flower open, upper anthers shedding; (4) sepals flat, petals converg-
ing, all erect anthers shedding; (5) petals erect, stamens mostly shed, con-
verging; (6) petals flat, stamens brown; (7) petals falling; (8) sepals erect.
Potentilla arguta : (9) bud cut, stamens converging; (10) flower hah open,
stamens erect, stigmas receptive; (11) petals flat, stamens spreading; (12)
petals ascending, inner stamens erect; (13) all stamens shedding and con-
verging; (14) petals fallen, sepals erect, anthers shrunken; (15) sepals closed.
Plate 4. Life-history of flowers: Heracleum lanatum, X6: (1) bud; (2) 1 stamen out;
(3) 2 stamens out; (4) 3 stamens out; (5) 4 stamens out; (6) all stamens out,
erect, mostly shedding; (7) stamens deflexed, stigma tips visible; (8) stamens
fallen, styles lengthened; (9) petals falling, styles and stylopodium full-grown.
Sedum stenopetalum, X6: (10) bud in section; (11) flower half open; (12) flower
open, inner anthers shedding; (13) inner anthers shed, outer shedding carpels
separating; (14) all anthers shed, stigmas receptive; (15) stamens recurving,
carpels converging; (16) anthers fallen, filaments ascending; (17) petals
ascending, drying.
Plate 5. Life-history of flowers: Galium boreale, X10: (1) bud in section; (2) flower
open, stamens erect, shedding; (3) stamens spreading, anthers shed; (4) sta-
mens flat, styles receptive, spreading; (5) stamens deflexed, stigmas enlarged;
(6) corolla withering, style elongated. Saxifraga bronchialis, X4: (7) bud
hanging; (8) bud horizontal, enlarged; (9) flower open; (10) inner row of
anthers shedding; (11) inner shed, outer shedding, style tips recurved, recep-
tive; (12) petals and anthers fallen, carpels enlarging.
Plate 6. Life-history of flowers: Campanula rotundifolia, Xl.5: (1) bud in section,
erect; (2) bud horizontal; (3) bud hanging; (4) flower half open, anthers
shedding on style; (5) flower open, stamens curling downward, style dusted
with pollen; (6) anthers separating, stigmas starting to recurve; (7) stigmas
recurved, receptive; (8) corolla shriveling and drying. Erysimum asperum,
X2: (9) bud in section; (10) stigma protruding, receptive, petals incurled;
(11) flower opening, 4 upper anthers shedding; (12) flower open, upper anthers
recurving, 2 lower shedding; (13) upper anthers shrunken, lower shed; (14)
lower' anthers shrinking, petals falling.
Plate 7. Life-history of flowers: Geranium caespitosum, Xl.5: (1) bud horizontal,
corolla tip appearing; (2) bud erect, petals separating; (3) flower open; (4)
upper anthers shedding; (5) upper shed, lower shedding; (6) anthers mostly
fallen; (7) styles spread, receptive; (8) petals fallen, pistil enlarged. Dode-
catheon meadia, Xl.5: (9) bud upright; (10) bud hanging, in section; (11)
flower half open, stigma receptive, anthers swollen; (12) flower fully open,
petals reflexed, anthers shrinking; (13) flower horizontal, anthers separating;
(14) flower erect, anthers spread; (15) petals shrunken and dried; (16) young
pod with stigma still fresh.
272
DESCBIPTIONS OF PLATES. 273
Plate 8. Life-history of flowers: Chamaenerium angustifolium, X2: (1) bud hanging;
(2) bud rising; (3) bud in section, horizontal, beginning to open; (4) flower
open, style reflexed, stamens whole; (5) 2 longer stamens shedding; (6) 4
longer stamens shedding, style hanging; (7) 4 anthers shrunken and 4 shed-
ding, stigma lobes spreading; (8) all anthers shrunken, hanging, stigma lobes
recurved, receptive; (9) petals closed, stigma projecting; (10) flower withering.
Plate 9. Life-history of flowers: Pachylophus caespitosus, XI: (1) bud in section, an-
thers shedding; (2) bud opening, stigma lobes protruding; (3) stigma lobes
separating; (4) stigma lobes horizontal; (5) flower fully open, anthers shed;
(6) petals erect, corolla closing; (7) petals withering, bringing anthers against
stigma lobes; (8) corolla wilted.
Plate 10. Life-history of flowers: Pirola ellipiica, X2: (1) bud in section, pores
directed inward; (2) flower opening, style appearing, straight, pores still
closed but directed downward; (3) pores open, downward, style curved,
bringing stigma under pores; (4) style full length, curved forward, carpels
enlarged, petals fallen. Frasera speciosa, Xl.5: (5) bud in section; (6) flower
half open, anthers vertical, introrse; (7) flower open, anthers horizontal; (8)
anthers extrorse; (9) 1 anther shedding; (10) 2 opposite anthers shedding;
(11) 3 anthers shedding; (12) 2 anthers shedding and 2 shed; (13) petals erect,
flower half closed; (14) flower tightly closed, stamens projecting. Gentiana
amarella, X2: (15) bud in section, stamens introrse, short; (16) bud in sec-
tion, anthers horizontal, level with style; (17) anthers extrorse, shedding;
(18) anthers shed, stigmas recurved; (19) flower closed, stigmas closed, pistil
enlarged, corolla withering.
Plate 11. Life-history of flowers: Gilia aggregata, Xl.5: (1) bud, anthers whole;
(2) bud, anthers shedding; (3) corolla lobes erect, anthers mostly shed; (4)
lobes spread, style elongated; (5) lobes reflexed, anthers all shed, style longer,
stigmas opening; (6) stigma lobes fully spread, receptive; (7) corolla fallen,
style still turgid. Gilia pinnatifida, X3: (8) flower half open, 1 stamen out;
(9) flower open, 2 stamens out; (10) 3 stamens out; (11) first anther shed; (12)
2 anthers shed, style one-half length; (13) 3 anthers shed, style two-thirds
length; (14) all anthers shed, style full length; (15) stamens shrunken, stig-
mas turgid. Mertensia sibirica, X2: (16) bud in section; (17) bud partly
open, style protruding, receptive; (18) anthers shedding, style elongating;
(19) style as long as corolla; (20) anthers shed; (21) corolla wilting and clos-
ing, style bent. Lithospermum multiftorum, X2: (22) bud in section, about
two-thirds grown; (23) flower just open, anthers shedding; (24) corolla lobes
spreading; (25) anthers shed; (26) style lengthening, stigma lobes separating;
(27) corolla fallen.
Plate 12. Life-history of flowers: Pentstemon glaber, X2: (1) flower just open, an-
thers whole; (2) upper pair of anthers shedding; (3) upper pair shed, lower
shedding; (4) anthers all shed, style elongated; (5) stigma curved down-
ward; (6) corolla fallen, stigma turgid; (7) longisection of stage 2; (8) longi-
section of stage 5.
Plate 13. Life-history of flowers: Castilleia miniata, X2: (1) corolla in calyx, 7 mm.
long; (2) corolla 10 mm. beginning to open; (3) corolla 15 mm., stigma
protruding, receptive; (4) outside view of full-grown calyx with stigma ex-
serted; (5) section of preceding; (6) style 3 mm. long, erect; (7) section of
preceding, showing the pollen mass; (8) corolla full length, style 5 mm. long;
(9) style withering at tip; (10) style reflexed, corolla withering. Monarda
fistulosa, X2: (11) bud in section, anthers cracking; (12) flower open, anthers
shedding; (13) stigma projecting; (14) stamens withering, style elongated,
stigma lobes spread; (15) lower lip withering; (16) corolla and style withering.
274 EXPERIMENTAL POLLINATION.
Plate 14. Life-history of flowers: Allium cernuum, X3: (1) Bud hanging, cracking;
(2) bud starting to ascend, 1 stamen out; (3) bud at 45 degrees, perianth
lobes opening, 2 stamens out, 1 anther shedding; (4) 3 stamens out, 1 anther
shedding, and 1 shed; (5) 5 stamens out, 2 shed and 1 shedding; (6) flower hor-
izontal, 5 anthers shed; (7) flower ascending, style elongating; (8) anthers
falling, style exserted, receptive; (9) anthers fallen, corolla withering; (10)
style shrunken, corolla withered. Zygadenus elegans, X2: (11) flower half
open; (12) flower open, anthers contiguous; (13) outer row of anthers spread
and shedding; (14) inner row of anthers spread and shedding; (15) anthers
shed, converging, stigmas beginning to spread; (16) anthers fallen, stigmas
separated, receptive; (17) petals ascending, pistil enlarged; (18) petals
erect, keeled.
Plate 15. Mutilated and inverted flowers of Aconitum, XI.
Plate 16. Mutilated flowers: Aconitum columbianum, X1.5: (1) lower sepals re-
moved; (2) hood removed; (3) perianth removed; (4) hood split and spread;
(5) hood and nectaries removed; (6) side petals removed. Delphinium
scopidorum, Xl.5: (7) normal flower; (8) petals removed; (9) side sepals
removed, (10) lower sepals removed; (11) spur cut off. Monarda fistulosa,
X2: (12) lower lip cut off; (13) upper lip cut off; (14) both lips cut off; (15)
lower lip split; (16) corolla shortened; (17) upper lip, stamens and style cut
away.
Plate 17. Mutilated flowers: Geranium caespitosum, Xl.5: (1) petals shortened half;
(2) petals trifid; (3) petals removed. Chamaenerium angustifolium, X2:
(4) petals shortened half; (5) petals removed; (6) all parts removed except
pistil and nectary; (7) petals and sepals removed; (8) flower reduced to ovary
and nectary. Pentstemon glaber, X2: (9) lower lip removed; (10) upper lip
removed; (11) both lips removed; (12) corolla lobes split.
CLEMENTS AND LONG
' 11
F.<iith S. Clements 'hi.
Life-history of the flowers of Aconitum columbianum and Delphinium
scopulorwn.
CLEMENTS AND LONG
"4
^asm
"<^ L^ *
i
l'7
*
r^^k^i^l
S /< ^ , ,s
w
%
Edith S. Clements del.
Life-history of the flowers of Rubus strigosus and Potentilla gracilis
CLEMENTS AND LONG
Edith S. Clements del.
Life-history of the flowers of Heracleum lanatum and Sedum stenopetalum.
CLEMENTS AND LONG
s~77
7A 10
'dith S. Clements del.
Life-history of the flowers of Galium boreale and Saxifraga bronchialii
CLEMENTS AND LONG
Edith S. Clements del.
Life-history of the flowers of Campanula rotundifolia and Erysimum asperum.
CLEMENTS AND LONG
Edith S. Clements del.
Life-history of the flowers of Geranium caespitosum and Dodecatheon meadia.
CLEMENTS AND LONG
Edith S. Clements del.
Life-history of the flower of Chamaenerium angustifolium.
CLEMENTS AND LONG
Edith S. Clements del.
Life-history of the flower of Pachylophus caespitosus
CLLMLNTS AND LONG
15 II 16
Edith S. Clements del.
Life-history of the flowers of Pirola elliptica, Frasera speciosa, and
Gentiana amarella.
CLEMLNFS AND LONG
r ,
Edith S. Clements del.
Life-history of the flowers of Cilia aggregata and pinnatifida, Mertensia
sibirica, and Lithospermum multiflorum.
Cl.f'.MENTS AND LONG
,l,U, S. Clements del.
Life-history of the flower of Pentstemon glaber,
CLEMENTS AND LONG
. J '- 113 J 14
Edith S. Clements del.
Life-history of the flowers of Castilleia miniata and Monarda fistulosa.
CLEMENTS AND LONG
Edith S. Clements del.
Life-history of the flowers of Alii inn cernuum and Zygadenus elegans.
CLEMENTS AND LONG
I
Edith S. Clements del.
Mutilated and inverted flowers of Aconitum.
CLEMENTS AND LONG
13 \JU j\:, yi6
Edith S. Clements del.
Mutilated flowers of Aconitum, Delphinium, and Monarda.
CLEMENTS AND LONG
11
Mutilated flowers of Geranium, Chamaenerium, and Pentstemon glaber.
Edith S. Clements del.
florth Carolina State Library
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