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Full text of "Inheritance of some morphological characters in Crepis capillaris"

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 F 1 and P 2 
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 42 y 
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 F 2 , 
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 F x 
population. Figure 2 shows typical leaves from plants of the F 2 
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 F 2 population were grown 
in 4-inch pots while those of the parent races and F x population 
were in 6-inch pots. However, the F 2 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 F 2 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 

F 2 


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(5.28 2 - 2.33 2 ) 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 F x 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 




F 2 


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(3.36 2 - 1.37 2 ) 75.2 



an obvious impossibility 




Fig. 2. — Typical leaves from different plants of the F 2 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 F 2 . Both 
the F 1 and F 2 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 F 2 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 





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 F 2 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 





12 


2X 


1 


66 


192 


12 





r xv = 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 F x 
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 F 2 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 F 1 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 F x 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 F x 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 F x progeny obtained exhibited considerable 
variation but were always intermediate between the two extreme types. 
In the F 2 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 F x generation and in F 2 
the progeny ranged from one parent type to the other. Out of the 
250 F 2 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 





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 F 3 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 F 2 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 F x in these crosses was found 
to be intermediate and F 2 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 F x was found to be intermediate between 
the two parents. The work has not progressed far enough to study the 
F 2 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 







* •». 





: 





v- 



if tJ 



t„«{V 







*••♦ - 



Fig. 5 



Fig. 4