UNIVERSITY OF CALIFORNIA PUBLICATIONS
IN
AGRICULTURAL SCIENCES
Vol. 2, No. 7, pp. 217-242, plates 42-43, 3 figures in text June 8, 1923
INHERITANCE OF SOME MORPHOLOGICAL
CHARACTERS IN CREPIS CAPILLARIS*
BY
VENKATA KAU
CONTENTS
PAGE
Introduction 217
Objects and aims 218
Material and methods 219
Inheritance of length of leaf 221
Inheritance of number of lobes per leaf 223
Inheritance of size of capitulum 227
Influence of age of plant 228
Position of capitulum upon the plant as a factor 229
Environmental factors 230
A cross involving difference in head size 232
Discussion of results 233
Summar}' and conclusions 236
Literature cited 237
INTRODUCTION
Geneticists studying the inheritance of characters in plants have
been following with interest the monumental investigations on Droso-
phila by Morgai) and others, with especial attention to their studies
on the inheritance of both qualitative and quantitative characters.
The present paper reports the result of an investigation on the inheri-
tance of some quantitative characters in a wild plant, Crepis capillaris
(L) Wallr. The studies included characters in leaves and flowers,
and it will be shown that the inheritance of these characters is similar
to the inheritance of quantitative characters in other organisms.
*Submitted in partial fulfillment of the requirements for the degree of Doctor
of Philosophy at the University of California.
218 University of California Publications in Agricultural Sciences [Vol. 7
OBJECTS AND AIMS
The genus Crepis, comprising over 150 species, belongs to the
tribe Cichorieae of the natural order Compositae, and is closely related
to the genus Hieracium. The species, C. capillaris, so far as known,
has not been brought under cultivation, but grows as a wild plant
in widely separated parts of the world. This species can be easily
propagated and the plants are self-fertile so that investigations may
be carried on with inbred strains. Furthermore, the F1 and P2
generations from varietal crosses are fertile when crossed inter se,
and the species has a very low number of chromosomes. Hence as
Babcock (1920) pointed out, the advantages of the genus for genetic
investigation are many. Previous to that, some work had been done
on the cytological side, notably by Rosenberg (1909-1918), who de-
termined the number of chromosomes, Beer (1912), Miss Digby (1914)
and de Smet (1914). De Smet has given excellent illustrations of the
various stages of nuclear division. Other species of Crepis have been
studied by Rosenberg (1909-1918) and Juel (1905) ; interspecific
crosses between C. capillaris and C. tectorum have been reported by
Babcock and Collins (1920). The achenes of C. capillaris germinate
easily after a short period of rest and a very large percentage is
viable. The plant first develops a rosette and finally the central axis
elongates and terminates in an inflorescence; but under unfavorable
conditions it may remain indefinitely in the rosette stage. The plant
is strictly annual, however, and dies after once flowering. Plate 43
illustrates typical plants when the inflorescence has developed and
growth has practically ended.
The present investigation has to do specifically with differences in
the length of the radical leaves, in the number of lobes on the radical
leaves, and in the diameter of the flower heads. The aim was to deter-
mine whether these differences were inherited and to locate the factors
responsible for the genetic variations as distinct from modifications
due to the environment. In the case of the inheritance of morphologi-
cal characters in the leaf, the action of the environment had to be
taken into consideration, and in the case of the flowers, the action of
the environment in addition to the age of the plant and the position
of the capitulum upon the plant had to be evaluated before the true
genetic variations could be determined. The work has been carried on
1923] Eau: Morphological Characters in Crepis Capillaris 219
partly in the greenhouse and partly in the field and the results have
been found so consistent that the data have been combined. The
investigations herein reported were started in the fall of 1920 and
were carried on by the writer until July, 1922, but a great deal of
preliminary purification of material had been done before the material
was turned over to me.
The work was undertaken at the suggestion of Professor E. B.
Babcock, head of the Division of Genetics, University of California,
to whom my best thanks are due. My thanks are also due to Dr. K. E.
Clausen and Mr. J. L. Collins, of the Division of Genetics, for espe-
cially valuable help and suggestions during the progress of the in-
vestigations.
MATERIAL AND METHODS
The detailed work has been done on three inbred families. The
achenes were always germinated in seed pans in which the soil had
been sterilized, or which had been filled with soil near which no Crepis
plants had been grown within the last few years. The achenes were
lightly covered with soil and watered. The germination was fairly
rapid and the seedlings were ready for transplantation in about four
weeks from the date of sowing. They were transferred either to small
cardboard boxes about two inches square and planted out in the field
or to 4-inch or 6-inch pots directly. The size of the pot had very
little influence on the early development of the plant although, so
far as general vigor was concerned, the plants in the 6-inch pots gave
better results.
In measuring the length of the leaves and determining their lobe
number, the plants were allowed to develop as far as possible in the
rosette stage and data were secured before the central axis appeared
with the formation of the cauline leaves. The length of the leaf was
measured on a centimeter scale and the number of lobes counted on
one side of the leaf, usually the left side. Every lobe which was sup-
plied with a distinct vein was given a unit rank and in these calcula-
tions all scurs at the base of the leaf and the secondary lobes attached
to the main ones were not considered. Five leaves were indiscrimin-
ately chosen and counts made upon them.
The capitula were measured on the centimeter scale when they
were fully open. Flower heads in Crepis open centripetally, and a
220 University of California Publications in Agricultural Sciences [Vol. 7
flower head was considered fully open when all the disc florets had
opened and the stigmas were projecting. This stage is usually main-
tained for two or three days. Then the capitula widen and spread out,
and measurements taken at this stage always give results which are
about 3 mm. more than the actual diameter when the heads are fully
open. Moreover the flowers open at about 9 a.m. on bright days and
remain open till after 3 p.m. if the day is not hot. But on dull and
cloudy days they open about 10 a.m. or later, and occasionally they
fail to open altogether. The 25 flowers first formed were measured
in every case and their individual measurements noted. Inflorescence
in Crepis closely follows the type described by Gleason (1919) for
Vernonia mussurica. The main axis is the first to give off flowers,
and the few branches at the top are more or less leafless. The flowers
form a more or less flattened corymb at the top. The lower nodes
bear shorter and frequently less developed lateral branches which
usually appear so late in the season that none of the heads, or only
a part of them, open their flowers and set seed before the plant has
exhausted itself and dies down. In Vernonia three types of varia-
tions were investigated : ( 1 ) a variation between the heads of each
cyme, possibly correlated with their position whether terminal or
inferior; (2) a variation between different floriferous branches of the
same plant possibly correlated with the amount of available nourish-
ment ; (3) a general variation between different individuals, possibly
correlated with the size and vigor of the plant and therefore indirectly
with the habitat. Gleason finds that within a single cyme of from
two to six heads the terminal head is the largest. In larger cymes,
some of the secondary terminal heads are frequently larger than the
primary terminal head, the number of flowers is greatest for the
terminal head of each cyme, but it is relatively constant for each
individual plant. Two sets of factors, which may be environmental,
or hereditary, or both, are involved. One determines the number of
heads produced and the other the average number of flowers in each
head. These act upon the plant independently and thus give four
classes : many large heads, many small heads, few large heads, and
few small heads. This investigator based his measurements and con-
clusion on 25 flowers. Goodspeed and Clausen (1915) estimate 25 as
the minimum number on which to base any calculations for flower
size. Goodspeed and Clausen (1918) have' described a mechanical
apparatus by which measurement of flowers is made. East uses only
a millimeter scale ; I have followed East in this work.
1923] Bau: Morphological Characters in Crepis Capillaris 221
With regard to the method of cross-pollinating the plants, both
the methods suggested by Babcock and Collins (1920) were tried,
and depollination with a water jet has given results as good as emascu-
lation, although the latter method was employed in all cases of critical
investigation. The flowers were enclosed in translucent paper bags
to prevent insect pollination and the achenes gathered before they
were over-ripe and dropped to the ground or were taken off by the
wind. It is fairly easy to decide whether a cross-pollination has been
successful or not because the involucre assumes an ovoid form in the
successful crosses, whereas it remains more or less oblong in the unsuc-
cessful ones. The achenes, moreover, are plump and the ribs marked,
the seed coat itself being distinctly colored as compared with that of
the unfertilized achenes.
INHERITANCE OF LENGTH OF LEAF
In Crepis capillaris the first true leaves are small (about twice the
size of the cotyledons), and there is a continuous increase in leaf size
until the rosette is formed. Plate 42 shows stages of growth of the
leaves including the mature rosette when they are ready for measur-
ing. Even in the early stages the plants show different habits of
growth, some growing erect and others spreading horizontally. In
one family especially (20.6) there is a tendency for the leaf margins
to curl downward, thus rendering measurement difficult (plate 42y
fig. 4). In the earlier work, the leaves were clipped off with a pair of
fine scissors close to the stem and measured on a centimeter ruler.
But later on it was thought that injuring the plants thus might affect
the result, and the leaves were kept intact on the plant while the ruler
was thrust in as close to the stem as possible. Five mature leaves
were measured at random and the average of the readings has been
taken to represent the mean length of leaf in the plant. In table 1 it
will be seen that the length of leaf fluctuates widely from the mean
as compared with the breadth. The variation in length was 12.6 to
23.0 cm. in family 20.1, 11.8 to 18.4 cm. in family 20.6, 15.8 to 30.7 cm.
in family 20.11 and from 24.0 to 40.1 cm. in family 20.13. Crosses
were made between the 20.1 family with a range from 13 to 23 cm.,
and family 20.13 with a spread of 21.0 to 40.1 cm. with a view to
studying the way in which the factors for length segregated. Table
2 gives the usual biometrical data for the various families studied.
This table indicates that the factors for length show segregation in F2,
but owing to the fact that the environment plays such a great part in
222
University of California Publications in Agricultural Sciences [Vol. 7
determining the length, it is difficult to estimate the number of factors
involved. (See Hayes, 1912, p. 34.) Figure 1 shows the length
of leaves typical of the parent races, and typical leaves from the Fx
population. Figure 2 shows typical leaves from plants of the F2
generation. The drawings have been made from actual prints of
leaves on photographic paper and reduced equally in reproduction.
TABLE 1
Showing Measurements of Length and Width of Leaves
20
.1
20
.6
20
n
20
13
Length
Width
Length
Width
Length
Width
Length
Width
cm.
cm.
cm.
cm.
cm.
cm.
cm.
cm.
22.2
3.9
18.1
4.5
15.8
3.1
29.4
4.0
17.3
3.6
15.5
4.3
23.3
4.4
34.0
5.0
17.2
3.5
14.6
3.7
25.5
6.8
35.0
6.0
15.0
2.5
16.3
3.5
30.7
6.8
30.0
3.6
18.4
2.8
11.8
2.0
20.0
4.5
40.1
5.8
15.5
3.4
16.1
3.7
29.5
7.3
26.1
5.1
15.6
3.4
16.0
3.7
32.2
5.6
37.7
6.5
15.6
3.4
14.7
3.2
28.6
6.0
26.0
3.5
20.0
3.4
18.4
4.5
18.5
5.0
24.0
3.0
23.0
4.4
13.2
2.5
28.6
6.0
28.0
6.0
19.8
2.9
14.9
3.6
33.0
4.5
12.6
2.0
15.8
3.1
34.0
24.0
34.0
29.0
31.0
31.5
23.0
31.0
21.0
21.6
29.5
6.0
3.5
5.6
5.0
4.0
3.8
3.0
5.0
2.5
3.0
4.3
Total:
212.2
35.8
185.4
42.3
252.7
55.5
652.9
98.7
Average :
17.7
3.0
15.45
3.5
25.3
5.5
29.7
4.5
It should be stated that the plants of the F2 population were grown
in 4-inch pots while those of the parent races and Fx population
were in 6-inch pots. However, the F2 plants were all grown under
uniform conditions so that the evidence of segregation in both leaf
length and number of lobes may be referred to genetic differences
among the F2 plants.
1923]
Ban: Morphological Characters in Crcpis Capillaris
223
INHERITANCE OF THE NUMBER OF LOBES
The problem of the number of lobes on the leaves resolves itself
into four distinct subheads. The first of these involves the question
whether the leaf shall be considered lobed at all. There are families
in which the lobing, if present, is so shallow that the leaves would be
described as entire or merely dentate. This type is designated as
TABLE 2
Showing the Eesults of Crossing for Inheritance of Leaf Length
Nature of Cross
Generation
Mean
Stand, deviation
Coef. of Var.
20.1x20.13
Pi
Pi
Fl
F2
17.9 ± .588
29.7 ± .699
29.0 db .282
14.9 ± .137
2.89 db .468
4.97 ± .495
2.33 ± .188
5.28 ± .097
16.1
16.7
8.0
35.4
Applying Castle's formula
(29.7 - 17.9)2 139.24
8(5.282 - 2.332) 179.2
Factors responsible for length = 1 factor.
This result is very improbable, but the results can be interpreted on a modified
dihybrid ratio of 9:6:1 where the two single homozygous genotypes give identical,
effects. On this ratio and from a study of the data, the result may be stated thus:
A B = 9, leaf length from 6 — 18 cm.
A b = 3, leaf length from 19 — 25 cm.
a B = 3, leaf length from 19 — 25 cm.
a b =1, leaf length from 26 — 34 cm.
Where factors A and B stand for two independent factors in the absence of both
of which the double recessive a b is obtained:
Observed numbers: 491 : 158 : 27
Calculated numbers: 378 : 252 : 42.
simplex in the accompanying account. There is another type where
the lobes are distinct and simple and look like the steps on a ladder.
This is designated as the scalaris type. A third type has a complex
type of lobes where the scalaris type of lobing is surmounted by
smaller secondary lobules or wings. The second subhead refers to
the incision or depth of lobing. In the families studied the lobing
extended halfway from the margin to the mid-rib or completely to
the mid-rib. The third subhead concerns number of lobes on the leaf
and the fourth refers to the character which is shown when the "second-
ary lobules instead of remaining attached to the main lobes are
224
University of California Publications in Agricultural Sciences [Vol. 7
separated and form independent lobes attached to the mid-ribs. The
first of these is the major character because, without a tendency to
form the lobes, the rest of the factors could not express themselves.
But the remaining three subheads behave as separate groups of factors,
the depth of incision having an independent action on the leaf as do
the other two characters mentioned above. One thing, however, was
clear from the studies made, and that was the complex way in which
Fig. la. A typical leaf of the race with long leaves and many lobes, g. A
typical leaf of the race with short leaves and few lobes, o-f. Typical leaves from
different plants of the Fx generation, c. X %.
each of these characters was inherited. That these groups of charac-
ters are inherited in a Mendelian fashion cannot be doubted, but the
work has not advanced enough to estimate with certainty the number
of factors involved in these cases, except in the number of lobes, which
has been more extensively studied.
The same families that furnished material for studying the inheri-
tance of length have been used for studying the lobe numbers. Table
3 shows the lobe numbers of the various families handled in this work.
The same illustrations, figures 1 and 2, show the nature of lobing and
the number of lobes.
1923]
Emi: Morphological Characters in Crepis Capillaris
225
TABLE 3
Showing the Kesults of Crossing for Inheritance of Number of Lobes
Nature of Cross
Generation
Mean
Stand, deviation
Coef. of Var.
20.1 x20.13
Pi
8.9 ± .352
1 . 73 ± . 248
19.4
Pi
11.3 ± .171
1.21 ± .134
10.7
Ft
11.17 ± .156
1.37 ± .110
12.2
F2
8.1 ± .087
3.36 ± .061
41.5
Applying Castle's formula the number of factors would be
(11.3 -8.9)2 5.76
8(3.362 - 1.372) 75.2
an obvious impossibility
Fig. 2. — Typical leaves from different plants of the F2 generation, c. X %•
The data can be interpreted on a four factor hypothesis where
each factor in a homozygous condition contributes two lobes and, in a
heterozygous condition
formula would be,
, one lobe. On
this 1
a a b b c c d
d
5
a a b B c c d
d
6
a a B B c c d
d
7
a A B B c c d
d
8
A A B B c c d
d
9
A A B B C c d
d
10
A A B B C C d
d
11
A A B B C C D
d
12
A A B B C C D
D
13
and the data on this hypothesis would give a curve which simulates
the normal curve of error with the mode at 8.
226 University of California Publications in Agricultural Sciences [Vol. 7
From the data presented in table 3, it is fair to conclude that
there is segregation with respect to mean lobe number in F2. Both
the F1 and F2 are intermediate between the two grandparent types
and in the latter there is no transgressive segregation on the side of
the higher number of lobes. The number of lobes ranges from 6 to 13
in the F2 family 21.141 and arranging the plants in class groups their
distribution is as follows, the mean being at 9.
6
31
7
42
8
54
9
35
0
47
1
37
2
9
3
1
256
This tabulation shows that the inheritance of lobe number is compli-
cated ; and, while more of the plants show the lobe number of the lower
numbered parent, the majority of them are intermediate as required
by the hypothesis of multiple factors. The same remarks apply to the
other F2 populations studied, and there must be at least four factors
responsible for number of lobes in the leaves.
The length of the leaf has little or no influence upon the number of
lobes in the leaves. The accompanying correlation chart, table 4,
TABLE 4
Correlation Table for Number of Lobes (x) and Length of Leaf in cm. (y)
Family 21.140
4
5
6
7
2y
8-11
10
4
14
11-14
1
15
25
41
14-17
11
17
1
29
17-20
8
46
6
60
20-23
9
54
4
67
23-26
9
38
1
48
26-29
4
8
0
12
2X
1
66
192
12
rxv = 0.2302 ± 0.0388
1923] Rau: Morphological Characters in Crepis Capillaris 227
constructed for family 21.140, shows that the correlation between the
two is very low. For purposes of calculation, length of lobe is ex-
pressed in round numbers of centimeters, the fraction being treated
as one when more than half and ignored when less than that amount.
The absence of influence of length of leaf on number of lobes is
also illustrated by a comparison of the leaf outlines which show practi-
cally the same number of lobes on leaves of different lengths and in
other cases different numbers of lobes on leaves of practically the same
length. From an extended study of the data as well as from observa-
tions in the field and green house on various races of Crepis capillaris,
I am led to conclude that number of lobes is a definitely heritable
character and is not influenced by length of leaf, by soil or by any
other environmental conditions under which the plant is grown.
INHERITANCE OF SIZE OF CAPITULUM
Goodspeed and Clausen (1915) have determined a number of fac-
tors which influence flower size in Nicotiana. Under the heading,
"age of plant," they have considered the difference in size of flowers
borne early in the season as compared with those borne late in the
season on the same plants as well as the difference in size of flowers
during the first blooming season of the plant compared with that of
flowers produced the next year and on the same plants cut back and
sprouting from the roots. Under the heading "age of flower," they
include, first, a consideration of the difference in the size of flowers
borne on the terminal inflorescences first coming out of the stem and
those borne at the same time on laterals and seconds, and (2), the
influence of age on the individual flower by comparing measurements
of flowers fully opened before and after shedding pollen. Other factors
such as influence of removal of flowers and developing seed capsules,
the behavior of cuttings under various conditions, and the influence of
soil fertility were also studied. They find that the flowers produced
later in the season have usually been of smaller size. By removing all
flowers as fast as they are produced, they find it possible to keep
the flower size nearly equal to that of the first flowers produced and
were able in some cases to double the length of a plant 's life. During
the period which elapses from the time a flower is fully opened to the
time when pollen is shed, there is a considerable increase in corolla
spread, and associated with it, little or no increase in corolla
228 University of California Publications in Agricultural Sciences [Vol. 7
length. Soil also had a great influence in their experiments in deter-
mining the size of the flowers. ' ' The conclusion seems irresistible that
flower size in Nicotiana is not so constant as it has been assumed to be,
but that it is affected by a number of conditions and that at least
some of these may not affect the length and spread in the same
Influence of Age of Plant
In Crepis capillaris, the 25 capitula first formed are usually very
uniform and show a very narrow range of variation. The terminal
flower is usually the largest, although the next two flowers below it
are of the same size in many instances; but usually there is a signifi-
cant difference of 1 mm. when a large number of flowers are measured.
The flowers were pulled off and measured in every instance, which
eliminated to a large extent the possibility of the flowers' growing
slightly smaller. As a rule the 25 flowers required were measured in
about a week's time, although the plant normally continues to flower
for about four to five weeks. Flowers measured at the end of a season
are about 15 to 20 per cent smaller than those measured at the begin-
ning and, owing to the setting of seed and senility of the plant, all
the buds formed do not open. In an experiment which was carried
on to measure the entire lot of flowers that were produced on 6 plants
of a strain, the plants started flowering on the tenth of February and
continued till the end of April. Comparing the early flowers with
those formed later, the size of the latter is smaller. But this reduction
is not so great as in the case of plants from which no flowers are
removed. Two things can be noted, however, in the flowers formed
later. The number of flower heads that open on any given day is less
than before and the number of florets per head is significantly smaller,
the capitulum showing a more open center. The actual size of the
floret is not perceptibly reduced and this accounts for, the fact that
the size of the flowers remains fairly constant. Another character
that can be seen in the flower heads formed later is the slender elon-
gated stalks on which they are borne as compared with the robust stalks
of the earlier formed flower heads, while in many cases the internodes
between the flower stalks are longer in the later formed flowers.
1923]
Ban: Morphological Characters in Crcpis Capillaris
229
Position of Capitulum upon the Plant as a Factor
The position of the capitulum cannot always be categorically sep-
arated from the influence of age of plant. Two distinct facts, however,
are involved in this group. The first is the position of the capitulum
with reference to its origin, which may be in the axils of the lower
or the upper leaves or in the terminal cyme. The second is the
position of the capitulum with reference to the cyme itself of which
it forms a part. Figure 3 shows a diagrammatic representation of
Fig. 3. — Diagrammatic representation of the inflorescence in Crepis capillaris.
Numbers indicate diameter of capitula of a single plant measured in centimeters.
230 University of California Publications in Agricultural Sciences [Vol. 7
the inflorescence and furnishes the measurements of the diameters
of individual capitula of a single plant. Comparing the individual
cymose clusters, the terminal cluster has the largest central flowers
closely followed by the next few lower clusters. As the measure-
ments are followed farther down, the central capitulum becomes
slightly smaller. The lateral capitula are generally smaller thai
the central capitulum in each cluster, but at times they may attain
to the same size, especially in the uppermost cymes. Very rarely
they are larger than the central capitulum of the cyme of which
they are laterals. The central capitula of the lower cymes may
be larger than the lateral capitula of the upper cymes. In com-
paring flower heads as to size, however, the facts that all the capitula
do not ripen at the same time and that the age of the plant is a
factor causing variation should be kept in mind. Moreover, in this
group of measurements, the flowers were pulled off for measuring,
and this has a tendency to keep the inflorescence active for a longer
time and to maintain the flower size, as has been noted by Goodspeed
and Clausen. The facts as to variation of size in the flowers, due to
the age and position of the flower, may be summarized by saying
that, in plants allowed to flower normally, the terminal flower head
is usually the largest, closely followed by the second and third flower
heads, after which the size becomes slightly smaller. The relative
size of the flowers on the lower branches is similar, but the terminal
flowers on the lower branches are smaller than the terminal flower of
the whole plant or than those terminal flowers which arise from
branches in the axils of the uppermost leaves.
Environmental Factors
Light. — With regard to the effect of light on the flowering of
plants, some interesting results have been obtained. Klebs (1918)
in his work on Sempervivum divided the process of flower formation
into three distinct stages : (1) production of the condition of ripeness
to flower, (2) formation of flower primordia, and (3) development
of flower clusters and elongation of the axis. He found that light is
the dominant factor in determining all three stages. More recently
Garner and Allard (1920) have published their opinion that the three
primary factors that enter into the action of light upon plants are (1)
intensity of the light, (2) quality, that is, the wave length of the
1923] Bau: Morphological Characters in Crepis Capillaris 231
radiation, and (3) duration of exposure. They conclude that the
relative length of day is a factor of prime importance in the growth
and development of plants, particularly with respect to sexual repro-
duction, and in 1922 they confirmed and amplified their work. I
have been able to confirm this work to a certain extent. A culture
of plants growing in the greenhouse was close to an electric lamp
used to maintain a constant temperature in a chamber close by, and
the plants that were closest to this lamp flowered first, the arc of
flowering spreading out centrifugally. After some time all the plants
that were near the lamp had flowered, although the rest of the cultures
took nearly two months longer to produce flowers. Moreover, the
plants that bloomed first were in a comparatively disadvantageous
position during the day, so that the effect of the artificial illumination
on the flowering of the plants is all the more striking. This observa-
tion was repeated in an attempt to hasten the process of flower forma-
tion. Two strains of plants, 0215 and 0217, which were both Fx
progeny of crosses made by me, were growing very slowly and were
still in the rosette stage by the end of March of this year due to the
cold winter. In order to hasten their growth and obtain seed for
growing an F2 population, a few of them were placed three feet below
a 300 Watt electric lamp surrounded by a reflector every day from
6 p.m. to 8 a.m. the next day. Some of them shot out flower buds in
about three weeks from the time the experiment was started. The
rest of the plants in the same families which were not subjected to
artificial light had in many cases not started to send up the central
floriferous axils. The heat from the lamp may also have had a slight
effect.
Moisture. — The plants as they grow in pots in the greenhouse are
not subject to much variation in soil moisture because they are
watered regularly and the minimum soil moisture necessary for proper
growth is usually maintained. The case of the plants grown in the
field, however, was different because irrigation water was applied
periodically, and owing to the variation in temperature of the days
intervening between two successive irrigations, the soil moisture was
neither constant, nor was it always above the minimum water require-
ments of the plants. Consequently, the flowers gradually got smaller
as time elapsed after irrigation until, during the hottest part of
the day, the plants would show signs of withering. Measurements
were taken at this period and showed comparatively the smallest size
in the diameter of the capitula. This difference went up usually
232
University of California Publications in Agricultural Sciences [Vol. 7
to a maximum of 4 mm., but usually it ranged between 2 mm. and
3 mm., and more often reached the lower limit. If at this stage
the land was irrigated, the measurements taken the next day in-
variably showed a rise. The following data taken on plants of the
same population both before and after irrigation illustrate this point.
-Culture Hsu 20.1-
Before Irrigation
After Irrigation
Number of plant
Number of flowers
measured
Average diameter
in cm.
Number of flowers
measured
Average diameter
in cm.
3
9
27
38
49
59
77
99
4
4
4
3
3
5
4
3
1.87
1.97
1.90
2.00
1.96
1.98
2.05
2.00
5
5
6
5
4
4
5
5
2.16
2.22
2.10
2.22
2.25
2.05
2.16
2.16
Total
30
1.95
39
2.16
There is an average difference of 0.21 cm. or approximately 2 mm.
A Cross Involving Difference in Head Size
This particular work was started in the summer of 1921 and was
carried only to the F1 stage. Two strains were chosen, one having a
diameter ranging from 17 to 25 mm., and the other from 21 to 36 mm.
These races had undergone a preliminary purification for size of flower
head. The F± was intermediate and the mean of the Fx population
was closer to the mean of the smaller parent than that of the larger
parent. The data that have been secured on this work are given in
table 5. Other crosses have given similar results, but as the parent
strains did not differ in any marked degree, the Fx obtained shows
about the same size of head diameter.
1923]
Rau: Morphological Characters in Crepis Capillaris
233
TABLE 5
Showing Results of Crossing for Diameter of Capitulum
Frequencies
Diam. of heads in mm.
H21.1
B21.13
Fi hybrids
17
8
18
74
19
266
17
20
444
42
21
343
19
85
22
368
53
98
23
278
60
142
24
149
33
103
25
71
36
94
23
24
16
32
27
29
12
28
25
29
7
30
10
31
12
32
11
33
13
34
2
35
36
1
Mean
21.27 ± .027
25.37 ± .131
22.96 ± .048
Stand. Dev.
1.84 ± .019
3.52 ± .093
1.81 ± .036
Coef. Var.
8.6
13.87
7.8
DISCUSSION OF RESULTS
1. The leaves of Crepis capillaris vary in outline from a simplex
through a scalaris to a bipinnate type of lobing. In the first ease, as
evidenced by one of the parents used in the cross (fig. 1) the outline
is more or less entire, while the other parent in this cross represents
the scalaris type. The Fx progeny obtained exhibited considerable
variation but were always intermediate between the two extreme types.
In the F2 there was decided segregation and since only one plant out
of over 250 showed characters almost similar to one grandparent,
there must be more than one factor responsible for the occurrence of
lobes as well as for the number of lobes. The cross 20.1 X 20.13 has
234
University of California Publications in Agricultural Sciences [Vol. 7
given an intermediate number of lobes in Fx generation and in F2
the progeny ranged from one parent type to the other. Out of the
250 F2 plants studied not one fully represented the grandparent types,
and on mathematical considerations there must be at least four factors
responsible for this condition. Shull (1918) in his work on the leaf
forms of the Shepherd 's Purse has formulated a two factor hypothesis,
the double dominant homozygote, the two single dominant homozygotes
and the double recessive, giving the four classes which he obtained.
With regard to the work on the length of the leaf, it has been found
that, as compared to the length, the breadth of a leaf is a much more
constant character as shown by table 6. The data for this table were
TABLE 6
Showing Average Length and Width of Leaves in 100 Plants of Family 20.140
Length in cm.
17
18
19
20
21
22
23
24
25
26
27
28
Number of plants
2
6
10
6
6
10
15
13
11
13
6
2
Width in cm.
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
Number of plants
13
11
26
27
8
9
0
5
1
obtained from a family of plants selected at random. This observation
is in accordance with the reports of some other investigators. More-
over, the length of a leaf is more markedly susceptible to environ-
mental influences and fluctuations due to modifications will profoundly
interfere with estimating the effects of recombinations. It is therefore
believed that races should be purified for the breadth factor rather
than for the length factors for facilitating studies in this direction.
During the progress of the work, several crosses were made between
strains of Crepis, and some of the strains were inbred. The result in
many cases was comparable to the results of inbreeding in corn. As
Collins (1920) has noted, plants of inbred strains may not put out
flowers at all, or if they do, very few of the heads set seed. Some of
these are viable and give rise to seedlings which may not thrive very
well unless they are given special care. They are not as strong as those
obtained from hybrid plants. When they have grown beyond the
seedling stage, they sometimes stay in the rosette stage much longer
than is usual and the vegetative period is consequently prolonged. One
strain remained in the rosette stage and produced no flowers although
it had been growing for over a year and a half. Other abnormalities
have also been noted, such as vegetative proliferation and fasciation
of stems and peduncles. Often the flower heads are fasciated and
1923] Rau: Morphological Characters in Crepis Capillaris 235
flattened on two sides assuming the shape of an oval as opposed to
the normal round shape and at times, owing to a shortening of the
pedicels, two or three flowers appear to be joined together. All these
malformations have been noted in one or another of the cultures, and
emphasize strongly the effects of inbreeding in bringing to light
undesirable recessive characters which are disadvantageous to the
growth of the individual plant.
The outcome of this portion of the work has given results in no way
contradictory to the conclusions arrived at by other investigators who
have relied upon multiple factors as an explanation of inheritance of
quantitative characters. As the experiment has not been carried to
the F3 stage, it is not possible to state whether this material will yield
results entirely consistent with the requirements (East, 1916) of the
multiple factor hypothesis. But as far as the results go, they are in
agreement with the explanation suggested that inheritance of the
number of lobes in Crepis capillaris is a Mendelizing quantitative
character and that it is controlled by many factors which affect
occurrence of lobes, depth of the incisions, number of lobes, and shape
of the lobes.
It may be here noted, in passing, that in a work of this nature a
certain amount of discretion is necessary in determining the class to
which a given individual belongs. Classification of the shape of a
leaf and the exact number of its lobes are, to a certain extent, decided
by the investigator, who can handle them quickly as he gains practice.
Moreover, the exact times when the measurements are to be taken
are more or less fixed by the investigator himself, who should try to
secure as uniform material as possible in the several generations.
East (1921) has raised a similar point in his work as regards the
personality of the investigator. He says, ' ' I believe that in such work
as this, the investigator who lives with his plants in the field, who
uses all the quantitative data at his command, but who, nevertheless,
brings to his aid all the somewhat intangible facts that intimate experi-
ence gives him is able to come to a better realization of the truth than
one who works on cold data obtained by others. ' '
2. Size of capitulum is a character which is controlled by genetic
factors, and it is fairly constant for a given family. It is practically
independent of the size of the plant and it cannot fall below a certain
minimum. It is also independent of the number of capitula on the
entire plant or the number of florets per flower head. It is similarly
uninfluenced by the shape of the plant. The tall, erect, vertical type
of plants, and the bushy spreading type of plants (pi. 43) have given
236 University of California Publications in Agricultural Sciences [Vol. 7
sizes of flowers which are practically identical (see East, 1921, p. 329)
and while casual observation leads me to believe that the number of
flowers per plant and the number of florets per head vary directly
with the size and shape of the plant, the diameter of the flower heacL
is not subject to influence by any one of these three factors and is
relatively stable. (See Stout, 1918.) The only factor that has been
found to influence the size of the flower heads is the moisture content
of the soil. The drier the soil the smaller the heads become. Here
the plants in pots have an advantage because the soil is never allowed
to become dry and the slight variations of moisture to which the plants
in pots are subject do not affect the diameter of the flower heads to
any appreciable extent. The results obtained from field plants are
strictly comparable among themselves, however, since all the strains
are subject to the same unfavorable environmental influences and as
such give results strictly comparable.
SUMMARY AND CONCLUSIONS
1. Crepis capillaris has been found to be a valuable species for
genetic investigations because it is a wild plant which has not been
subjected to conscious selection by human agency.
2. It can be cross-fertilized and the progeny derived from such
cross-fertilization is fertile inter se and gives viable seed.
3. Several characters in the plant are constant and breed true when
the material has been purified to bring it into a homozygous condition
for the character in question.
4. Continual selfing of the plant is followed by the usual symptoms
of such treatment in naturally cross-fertilized species, resulting in
reduced vitality, arrested development at the rosette stage, formation
of many sterile flowers, few viable achenes, vegetative proliferation
and fasciation of the capitula and the stem.
5. Three quantitative characters were studied in this plant: the
length of the leaf, the number of lobes in the leaves, and the diameter
of the flower heads.
6. Length of leaf is a heritable character, but the environment
has a very great influence. The resulting fluctuating variability is
so great that although crosses have been made for studying the type
of inheritance, it is difficult to classify and segregate the F2 progeny.
7. In inheritance studies, width of leaf is a better index of leaf
size than length.
1923] Eau: Morphological Characters in Crepis Capillaris 237
8. Number of lobes per leaf is constant for any given race of plants
and the character is determined by four sets of factors :
(a) The group of factors for presence of lobes.
(b) The group of factors for depth of the. incisions.
(c) The group of factors for number of lobes.
(d) The group of factors for extension by which the secondary
lobules are developed into lobes.
9. Of these the group of factors for number of lobes consists of
at least four interacting factors. The Fx in these crosses was found
to be intermediate and F2 showed segregation.
10. Races of Crepis capillaris with different diameters of capitula
were isolated and when crosses were made between such races the
diameter of the capitula of Fx was found to be intermediate between
the two parents. The work has not progressed far enough to study the
F2 plants and determine the type of segregation.
11. As far as studied, environment, except moisture, has very little
influence on the size of capitula,
LITERATURE CITED
Babcock, E. B.
1920. Crepis, a promising genus for genetic investigations. Am. Naturalist,
vol. 54, pp. 270-276.
Babcock, E. B. and Collins, J. L.
1920. Interspecific hybrids in Crepis. I. C. capillaris (L) Wallr. X C.
tectorum L. Univ. of Calif. Publ. in Agr. Sci., vol. 2, pp. 191-204.
Beer, Eudolf
1912. Studies in spore development, 2. Annals of Botany, vol. 26, pp.
705-726.
Castle, W. E.
1921a. On a method of estimating the number of genetic factors in cases
of blending inheritance. Science, n.s., vol. 54, pp. 93-96.
Castle, W. E.
19216. An improved method of estimating the number of genetic factors
concerned in cases of blended inheritance. Science, n.s., vol.
54, p. 225.
Clausen, E. E. and Goodspeed, T. H.
1921. Inheritance in Nicotiana taoacum II. . On the existence of genetically
distinct red-flowering varieties. Am. Naturalist, vol. 55, pp.
328-334.
Collins, J. L.
1920. Inbreeding and crossbreeding in Crepis capillaris (L) Wallr. Univ.
Calif. Publ. Agr. Sci., vol. 2, pp. 205-216.
Digby, L.
1914. A critical study of the cytology of Crepis virens. Archiv f. Zell-
forsch., Bd. 12, pp. 97-146.
East, E. M.
1916. Studies on size inheritance in Nicotiana. Genetics, vol. 1, pp.
164-176.
238 University of California Publications in Agricultural Sciences [Vol. 7
East, E. M.
1921. A study of partial sterility in certain hybrids. Genetics, vol. 6,
pp. 311-365.
Garner, W. W. and Allard, H. A.
1920. Effect of the relative length of day and night and other factors of
the environment on growth and reproduction in plants. Jour.
Agr. Kes., vol. 18, pp. 553-606.
Garner, W. W. and Allard, H. A.
1922. Photoperiodism, the response of the plant to relative length of day
and night. Science, n.s., vol. 55, pp. 582-583.
Gleason, H. A.
1919. Variability in flower number in Vernonia mussurica Eaf. Am. Natur-
alist, vol. 53, pp. 526-534.
Goodspeed, T. H. and Clausen, R. E.
1915. Factors influencing flower size in Nicotiana with special reference
to questions of inheritance. Am. Jour. Bot., vol. 2, pp. 332-374.
Goodspeed, T. H. and Clausen, R. E.
1918. An apparatus for flower measurement. Univ. Calif. Publ. Bot.,
vol. 5, pp. 435-438.
Hayes, H. K.
1912. Correlation and inheritance in Nicotiana tabacum. Conn. Agr. Exp.
Sta. Bull. No. 171.
Juel, H. O.
1905. Die Tetradteilungen bei Taraxacum und anderen Cichorieen. K.
Svenska Vetenskapsakad. Handl., Bd. 39, no. 4, pp. 1-21.
Klebs, George
1918. tiber die Blutenbildung von Sempervivum. Jena. Festschrift zum
Ernst Stahl, pp. 128-151. (Abstract in Bot. Gaz., vol. 67, p. 445.)
Rosenberg, O.
1909. Zur Kentniss von den Tetradteilungen der Compositen. Svensk
Botanisk Tidskrift, Bd. 3, pp. 64-77.
Rosenberg, O.
1918. Chromosomenzahlen und chromosomendimensionen in der Gattung
Crepis. Arkiv for Botanik, Bd. 15, no. 11, pp. 1-16.
Schmidt, Jos.
1918. Investigations on Hops: XL Can different clones be characterized
by the number of marginal teeth in leaves'? C. R. des Travaux
de Laboratoire de Carlsberg, Kj0benhavn, vol. 14, pp. 1-22.
Shull, G. H.
1914. Duplicate genes for capsule form in Bursa bursa-pastoris. Ztschr. induk-
tive Abstamm. u. Vererbungslehre, vol. 12, pp. 97-149.
Shull, G. H.
1918. Duplication of leaf-lobe factor in the Shepherd's Purse. Mem.
Brooklyn Bot. Garden, vol. 1, pp. 427-443.
de Smet, Edmond
1914. Chromosomes, prochromosomes, et nucleole dans quelques dicotylees.
La Cellule, vol. 29, pp. 335-377.
Stout, A. B. and Boas, Helene M.
1918. Statistical studies of flower number per head in Cichorium intybus:
kinds of variability, heredity, and effects of selection. Mem.
Torrey Bot. Club, vol. 17, pp. 334-458.
PLATE 42
Fig. 1. Very young stage; cotyledons still persist.
Fig. 2. Early rosette stage.
Fig. 3. Later rosette stage.
Fig. 4. Nearly mature resette in a family showing a characteristic retrorse
rolling of the leaf margins.
Fig. 5. Fully developed rosette, the stage in which measurements of length
of radical leaves were taken.
[240]
UNIV. CALIF. PUBL. AGRI. SCI. VOL. 2
[ RAU ] PLATE 42
¥
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
PLATE 43
Fig. 1. Fully developed plant of spreading habit, i.e., having many divari-
cate branches arising from the base of the axis. Fully open capitula shown.
Fig. 2. Nearly mature plant similar to that shown in fig. 1, but of erect
habit.
Fig. 3. Mature plant of distinct habit, having no secondary branches arising
from the base of the axis.
Fig. 4. Mature plant of spreading habit, but a dwarf in stature.
Fig. 5. Fully open capitula such as were used in taking measurements
of diameter.
[242J
UNIV, CALIF, PUBL. AGRI. SCI. VOL. 2
[ RAU | PLATE 43
Fig. 1
Pig. 3
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:
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if tJ
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Fig. 5
Fig. 4
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