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1431

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EXCHANGE

BIOLOGY

LIBRARY

G

BXORAIK

THE RESULTS OF SELECTION WITHIN

PURE LINES OF PESTALOZZIA

GUEPINI DESM.

BY

CARL DOWNEY LA RUE

A DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT OF THE

REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

AT THE UNIVERSITY OF MICHIGAN

MAY, 1921

Reprinted from GENETICS 7: 142-201, March, 1922

GENETICS

A Periodical Record of Investigations Bearing on
Heredity and Variation

EDITORIAL BOARD

GEORGE H. SHULL, Managing Editor
Princeton University

WILLIAM E. CASTLE EDWARD JV1. EAST

Harvard University Harvard University

EDWIN G. CONKLIN ROLLINS A. EMERSON

Princeton University Cornell University

CHARLES B. DAVENPORT HERBERT S. JENNINGS

Carnegie Institution of Washington Johns Hopkins University

BRADLEY M. DAVIS THOMAS H. MORGAN

University of Michigan Columbia University

RAYMOND PEARL

Johns Hopkins University

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THE RESULTS OF SELECTION WITHIN PURE LINES OF
PESTALOZZIA GUEPINI DESM.1

CARL DOWNEY LA RUE

University of Michigan, Ann Arbor, Michigan

Received June 30, 1921

TABLE OF CONTENTS

INTRODUCTION 1*2

Reason for the choice of Pestalozzia 145

Experiments 1*0

Methods and conditions 150

Selection of spores according to their progeny

Experiment 1. Selection for length of spores 158

Experiment 2. Selection for length of spore appendages 162

Selection of spores according to visible characters 167

Experiment 3 168

Experiment 4 172

DISCUSSION 174

CONCLUSIONS 182

LITERATURE CITED • 182

APPENDIX — TABLES 184

INTRODUCTION

Since JOHANNSEN'S classic experiments on beans led him to formulate
his theory of the multilinear composition of species and the inefficacy
of selection within any of the lines, several workers have studied the effect
of selection within pure lines of various other organisms. No apology need
be offered, however, for this extension of the work to one of the asexually
reproducing Fungi Imperfecti, for the peculiarities of the material make
possible a quite different experimental attack. Inasmuch as the literature
of the selection problem has recently been thoroughly reviewed by
JENNINGS (1916, 1920). and others, only those papers will be considered
here which have special bearing on the present investigation.

One of the most noteworthy of such contributions is that of JENNINGS
(1908) on Paramecium. In a carefully planned and executed series of
experiments in which numerous selections were made, JENNINGS was unable

1 Papers from the Department of Botany of the UNIVERSITY OF MICHIGAN, No. 186. A
portion of this investigation was carried out at Kisaran, Asahan, Sumatra; the remainder in
the Botanical Laboratory of the UNIVERSITY OF MICHIGAN.

CiEN-ETics 7: 142 Mr 1922

oA BIOLOGY
oX^ y- LIBRARY

-*^> iC^ £*•> G

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SELECTION WITHIN PURE LINES OF PESTALOZZIA 143

to detect any effect of selection. This was among the first of the consider-
able series of investigations which appeared to bear out the JOHANNSEN
theory.

The work of EWING (1914 a, 1914 b, 1916) is of particular interest be-
cause of the large number of generations during which he practiced selec-
tion. He studied an aphid, Aphis avenae, and found that selection, even
for eighty-seven generations, was totally without effect.

The work of HANEL (1908) has received much attention and adverse
comment. HANEL concluded that selection was without effect on Hydra,
but it is doubtful whether the experimental results justified the conclusion.
More recently the status of HANEL'S work has been discussed and the ex-
periments have been repeated by L ASHLEY (1915, 1916). The latter
worker took account of the sources of error in HANEL'S experiments and
carried out so excellent an investigation as to leave no doubt that selec-
tion within the genus Hydra is ineffective.

A number of other investigators have secured results which substantiate
the work of JOHANNSEN. Some of them have made careful investigations
which are of considerable value. In other cases the results of loosely
planned and brief experiments have been recorded. For one to- believe,
because selection for one generation within a line has had no effect, that
selection is therefore in all cases ineffective, requires a very sanguine tem-
perament. There was ground for the protests of PEARSON (1910) and
HARRIS (1911) that the pure-line theory had been too readily accepted
before adequate evidence had been presented. However, all in all, a
considerable body of data supporting JOHANNSEN has been secured, some
of it exceedingly hard to refute. Until recently the results of all investi-
gations seemed only to add more evidence in support of the theory.

Within the last few years, however, more and more conflicting evidence
has been amassed, partly through critical analysis of the older data, and
partly by new experimentation. JOHANNSEN'S experiments have been
criticized because they were not carried on for a sufficiently large number
of generations. By statistical analysis PEARSON (1910) found that there
was some evidence that JOHANNSEN'S results really showed inheritance
of somatic variations within pure lines. ROOT (1918) has discounted
EWING'S results because the organism concerned is one which in nature
is highly stable, its lack of variability affording at the start little ground
for hope that new strains could be produced.

Several objections have been offered to the conclusions of JENNINGS
from his work on Paramecium. One is that he studied size characters
which are highly variable under different environmental conditions. These

GENETICS 7: Mr 1922 5 0 7 «J 7 9

144 CARL DOWNEY LA RUE

characters also vary with different stages of maturity of the individuals
and it is admitted by JENNINGS himself that one cannot be certain that
only mature specimens are being measured.

Turning now from reinterpretation of old work to the newer experimen-
tal data, we find that several studies have been interpreted as showing
positive selection effects. Thus STOCKING (1915) found that it was pos-
sible to produce distinct groups by selection within certain lines of abnor-
mal Paramecia. MIDDLETON (1915) was able to produce strains of
Stylonychia, distinct in regard to rate of fission, and this almost at will.
JENNINGS (1916), with much greater difficulty, detected small changes
in DifHugia, which he attributed to selection. ROOT (1918) and HEGNER
(1919), working with Centropyxis and Arcella, respectively, secured data
in conformity with those of JENNINGS with DifHugia.

To this later work, however, certain objections have been made. STOCK-
ING'S results were obtained with abnormal forms and it seems to have been
generally concluded that normal variations might not necessarily behave in
the same way. MAST (1917) secured two groups distinct for rate of
fission in Didynium nasutum, without selection, presumably by a mutation
in one group. This has some bearing on MIDDLETON'S results, and if it
be argued that very frequent mutations would be needed to account for
the rapid changes produced by MIDDLETON'S selections, it may be pointed
out that great instability must obtain in an organism to allow of such
changes even by selection.

MORGAN (1916) suggests that the selection results with DifHugia may
be due to random distribution of discrete particles of nuclear material
(chromidia) to the pairs of offspring. If such were the case, and if the
bearers of particular hereditary characters were contained in the chromi-
dia, one would not expect the effects of selection to be indefinitely cumula-
tive. Moreover, the variations would necessarily be of a discontinuous
type, and perhaps remotely comparable to non-disjunctional mutations
or somatic mutations. The same suggestion would also apply to the
res'ults of selection in Centropyxis and Arcella. In all three cases it is
likely that the variations dealt with are not of the usual continuous type.

LASHLEY (1915, 1916) has produced evidence that PEARSON'S criticism
of JOHANNSEN'S work is not well founded, and that the parent-offspring
correlation is not reliable as a criterion in selection work.

It must be obvious that the question as to whether variations occurring
within a pure line are purely somatic and non-heritable or not, is one that
is far from a definite answer. Further investigations on forms suitable
for the study of the problem, wherever they may occur, are greatly needed.

SELECTION WITHIN PURE LINES OF PESTALOZZIA 145

Thus far Protozoa have been used in most of the critical and extensive
investigations, and these organisms are not only subject to great environ-
mental effects, but give rise to only two offspring at a time, — a serious dis-
qualification for the most accurate results. JOHANNSEN'S original material,
the garden bean, was ideal from the standpoint of number of offspring,
but, reproducing sexually, it offered a possibility of Mendelian segregation
obscuring the true fluctuation which it was desired to study. The Fungi
Imperfecti seemed to afford an ideal material, combining the advantages
of numerous progeny with uniparental, non-sexual reproduction.

REASON FOR THE CHOICE OF PESTALOZZIA

P estalozzia Guepini Desm., one of the Fungi Imperfecti, was chosen by
the writer as a species unusually well suited for use in the study of the
selection problem. The species is polymorphic, containing a number of
different strains, so that it is not unlikely that new strains are being formed
at the present time. It is very easily grown in culture in the laboratory
and does not require tedious, special methods. Sporulation occurs readily
in culture, and development from the spore to the fruiting stage requires
only a few days, so that generations can be grown in rapid succession.
Spores are produced in enormous numbers so that more than enough are
always available for observation. They possess two characters that are
capable of accurate measurement, and a change in color at maturity en-
ables one to tell with certainty which spores are mature and which imma-
ture. Size characters may therefore be studied without fear that forms
apparently small are only immature. In addition to these advantages the
spores are produced, as in all Fungi Imperfecti, entirely asexually, so that
there is no possibility that the results are influenced by sexual phenomena.

P estalozzia Guepini Desm. is widely distributed in the eastern tropics,
where it causes the gray-blight disease of tea, and leaf-spot diseases of
cocoanut, betel nut palm, African oil palm, Para rubber, and doubtless
many other wild and cultivated plants of those regions. The species con-
tains a number of forms which differ more or less markedly from one anoth-
er in morphological characters. Some of them are likewise supposed to
be restricted to particular hosts. Strains occurring in regions far removed
from areas known to contain Pestalozzia Guepini, and on hosts not previ-
ously reported for this fungus, have been described as new species. This
is only natural, for the species was originally not closely defined. The
new species however, are even less perfectly described than P. Guepini, so
that one gains nothing by using their names. For the purposes of this

GENETICS 7: Mr 1922

146 CARL DOWNEY LA RUE

study the concept of P. Guepini employed is that given in a preliminary
study of the strains of the species by LARus and BARTLETT (1922).

In this investigation the authors found that from thirty-five isolations
of Pestalozzia from the Para rubber tree, the cocoanut palm, the African
oil palm, the betel palm, and the tea plant, at least fourteen strains,
distinct in regard to morphological characters, could be distinguished.
More minute morphological studies would in all probability have resulted
in the division of some of these strains into smaller distinct groups. Cross
inoculations might possibly have revealed variations in regard to hosts
infected, and physiological studies would almost certainly have shown that
some isolations differ physiologically from others in the same morpho-
logical group. The large number of forms found within the comparatively
limited territory on the East Coast of Sumatra, from which the cultures
were secured suggests that an equally large number of strains might be
found in other regions, many of them doubtless distinguishable from those
already studied. The formation of at least one new strain by mutation
during the period covered by the present investigation of the effect of
selection leads to the belief that other strains are now being formed in
nature and that P. Guepini is a species in what may be called a plastic
condition. In this respect it is comparable to the organisms studied by
other recent workers who have sought to find a clue to the process by
which evolution proceeds.

Only the spores' of the fungus were studied minutely by LARUE and
BARTLETT (1922) in the investigation of variability in P. Guepini men-
tioned above. The vegetative characters and growth habits also show
considerable variation but these are much more limited in range and more
difficult to measure than the quantitative characters of the spores, and
therefore were not utilized. For selection studies also, the spore characters
were chosen as most suitable though other characters might* have given
equally satisfactory results had they been more easily measured.

The spindle-shaped spores of Pestalozzia Guepini are composed of five
cells of which the three central ones are smoky or black at maturity, while
the other two are hyaline. The distal hyaline conical cell normally bears
at its tip three slender, unjointed, hyaline appendages which diverge so
that their tips are widely separated. Spores are occasionally found which
contain three or four cells, and others which bear two appendages or
even only one, but these are apparently aberrant forms. Thus far no
strain has been found which is constant for any of these peculiarities,
and in the cases where the aberrant spores have been tested, they have
produced normal progeny.

SELECTION WITHIN PURE LINES OF PESTALOZZIA

147

The total range of mean length of spores for all the strains of P. Guepini
isolated by LARUE and BARTLETT (1922) was from 19.9ju to 28.3/z. Figure
1 shows the polygons of variation in spore length for a few representative
strains. Mean appendage lengths of the strains ranged from 10.9jit to
30.0/i. The polygons for variation in appendage length are shown for
six representative isolations in figure 2. More complete data, which can-
not be reproduced here, are given in the paper already cited. In view of
the large number of strains which exist within the species, this fungus is a
very favorable organism for use in making an attempt to develop still
other strains by the selection of variant spores.

4-0

1

35
30
25
20
15
10

13

\

14 16 18 20 ^^ 24 26 28 30 32 34 36 3G

FIGURE 1. — Polygons of variation in spore length for six strains of Pestalozzia Guepini.
The ordinates are percentages; the abscissae, lengths in p.

It is essential that any organism which is to be employed in the study
of the selection problem be easy to cultivate and in this respect P. Guepini
is admirable. It will grow readily and rapidly on almost any common
nutrient agar and can also be grown on sterilized leaves, twigs and fruits
of its common hosts. In Sumatra usually only about four days time was
needed to develop the fungus from spore to the fruiting condition. In
Michigan a slightly longer time was needed to secure spores even when
the fungus was kept at a temperature approximately the same as that of
Sumatra. Strong light appears to inhibit the growth of the young myceli-
um, but exposure to light after the mycelium is about three days old seems
to hasten the production of spores.

GENETICS 7: Mr 1922

148

CARL DOWNEY LA RUE

When speculation begins the spores are developed very rapidly and in
enormous numbers. This is a characteristic exceedingly valuable in
biometrical studies, since the variates are produced under as nearly identi-
cal conditions as may be found anywhere. By measuring a sufficient
number of such spores one can get the whole range of variability induced
by the reaction of a given set of environmental conditions with the heredi-
tary characters of the organism. In an organism which produces offspring
slowly a number of fluctuations in environment must necessarily take place

> 10 \l 14 16 16 ?0 II 24 26 28 30 32 54 36 40

FIGURE 2. — Polygons of variation in length of spore appendages for six strains of Pestalozzia
Guepini. The ordinates are percentages; the abscissae, lengths of appendages in M.

before a number of individuals sufficient to give a reliable mean is produced.
This complicates the situation greatly and the means of two groups of
organisms so produced are less readily comparable than those developed
in an organism such as Pestalozzia.

Mention has already been made of the dark color of the three central
cells of mature spores of P. Guepini. This color is a valuable index of the
age of the spores because it does not fully develop until the spores have
reached their full size and the appendages have been fully formed. One
can always recognize mature spores at a glance and is thus able to reject

SELECTION WITHIN PURE LINES OF PESTALOZZIA 149

all immature stages of development. This completely obviates one great
difficulty usually found in the study of size characters, that of determining
.which individuals are really small, which only immature. This difficulty
seems insurmountable in such forms as Paramecium, but in Pestalozzia,
as in Difflugia, the nature of the organism allows size characters to be
observed without fear of complications from this source.

A further word of explanation may be desirable with regard to the
assumed absence of sexual reproduction in Pestalozzia. As has been stated,
it belongs to the group of Fungi Imperfecti. Many of the species in this
miscellaneous assemblage have been found to have other stages in their
life-history which have enabled them to be classified under other groups.
With few exceptions these other stages of Fungi Imperfecti have shown
them to be degenerate members of the Ascomycetes. Many Ascomycetes
have both the ascus stage, which follows a sexual fusion, and an asexual,
conidial stage. It is commonly assumed that the conidial forms, which
make up the Fungi Imperfecti, either have, or have had at some time, a
stage with a higher spore form. Whether Pestalozzia now has an unknown
ascus stage is not so important, as is the probability that if it had a sexual
stage at all, it would be indicated by the appearance of a readily recogniz-
able ascus stage. No such form has ever been observed in the hundreds
of cultures grown in this series of experiments and it is reasonably certain
that it never appeared. From the data gained from the study of analogous
forms we can safely assume, (1) that the conidia of Pestalozzia are entirely
asexual, (2) that if a sexual stage appears it will result in the production
of an ascus form and therefore will be easily detected, and (3) that we
have no need to fear that obscure nuclear recombinations are complicating
the results secured.

The unique combination of characters possessed by Pestalozzia and
discussed above renders the organism an unusually suitable one for use in
study of the results of selection within vegetative lines. Because the
fungus was so well adapted for this use and because no similar material
had ever been used for this purpose the author was led to undertake the
investigation here described. Presented in review, the characters which
make Pestalozzia specially desirable for such use are: (1) The presence of
numerous distinct strains within the species; (2) the ease with which it
is grown in culture; (3) the rapidity with which consecutive generations
may be produced; (4) the availability of at least two easily measurable
independent characters; (5) the rapidity with which spores are produced
and the enormous numbers of spores produced, which enable one to secure
significant statistical constants for each generation; (6) the dark colora-

GENETICS 7: Mr 1922

150 CARL DOWNEY LA RUE

tion of the three central cells of the spore which appears only at maturity,
and serves as a criterion for the elimination of mere growth stages; (7) the
total absence of any sexual form of reproduction.

EXPERIMENTS

Methods and conditions

Since the aim of the investigation was to study variations of genetical
significance, every reasonable attempt was made either to remove varia-
tions in environment or to provide controls for them. All the cultures
used were grown on agar in tubes, and under ordinary laboratory condi-
tions. Aside from the fact that it would be extremely inconvenient, if not
impossible, to control a selection experiment in which the organism was
grown as a parasite on its usual host, such a procedure would doubtless
offer more variations as to food supply, etc., than would growth on culture
media. WOLLENWEBER (1914) has shown that organisms which are
facultative parasites show as normal development in culture as on their
usual hosts.

That fungi, especially Saprolegnias, may be exceedingly sensitive to
variation in food supply has been shown by KAUFFMAN (1908) and PIET-
ERS (1915). However it is not believed that Pestalozzia is so exquisitely
sensitive to such variations as are some other fungi. In any event the
variations thus introduced into this work are doubtless much smaller than
those which of necessity apply to any other organism which has been used
in the study of selection up to the present time.

The nutrient solution was all made up before the experiment was begun.
Tender twig tips and young leaves of Hevea brasiliensis were boiled in
water and a quantity of brown sugar made from the sugar palm (Arenga
saccharifera) was added. The decoction was strained, concentrated by
boiling, and after thorough mixing to secure uniformity, was poured into
flasks which were plugged with cotton stoppers and sterilized.

The single lot of medium thus prepared was stored and used throughout
the experiments until the writer's return to the United States. (A supply
of the medium was brought to America but was lost in transit, so that it
was necessary to supply a substitute, as will be noted later.) For growing
the cultures nutrient agar was made up according to the following formula:
Hevea decoction, 250 cc
Water, 3750 cc

Agar-agar, 120 gm

SELECTION WITHIN PURE LINES OF PESTALOZZIA 151

The medium was very thoroughly mixed before being put into tubes, and
the same amount was placed in each tube. In making cultures care was
taken that all the tubes of a given generation were poured from agar of
the same lot.

The cultures were not kept in a constant-temperature chamber but the
range of variation in temperature and humidity is not great in the east
coast region of Sumatra. For the greater part of the year the daily change
in temperature is from about 23° C to about 32° C. The total range of
fluctuation for one five-month period of the selection experiment was from
19.4° to 33.9° C. During the same period the moisture content of the air
varied from 52 percent to 100 percent with a usual daily range of approxi-
mately from 60 percent to 100 percent. In general the climate of Asahan
varies so little from day to day, or from month to month, that it would
be hard to find any place more uniform. This uniformity allows cultures
to be carried on indefinitely without danger of extremes of heat or cold
such as have ended various experiments of other investigators.

The selection experiments were made according to two plans. In the
major part of the work the line of descent was determined wholly by
divergence in progeny means without regard to the visible characters of
the spores chosen as generation parents. In other words, the direction of
selection in the chief experiments was guided by the performance of particu-
lar spores, rather than by their appearance, but the method was checked
by parallel experiments in which the usual basis of selection, namely,
selection of visibly divergent individual spores, was employed.

The characters concerned were length of spore and length of spore
appendage. That these characters are heritable to a very considerable
degree is shown by the fact that strains, distinct for either spore length or
for length of spore appendages, have been isolated, and that these strains
remain distinct from generation to generation in spite of fluctuations in
environmental conditions. The heritable differences between the different
strains are very considerable as may be seen from figures 1 and 2, and these
differences make them especially promising for use in a study of the results
of selection.

The number of cells in the spore and the number of appendages per
spore might appear to be characters suited for study but this was soon
found not to be the case. The number of cells in the spore shows little
variation; the smallest number found in observing hundreds of thousands
of spores was three, and the largest number seen was nine. In two cases
where spores having one more than the normal number of cells were

GENETICS 7: Mr 1922

152 CARL DOWNEY LA RUE

selected it was found that the spores produced by the mycelia from these
spores were entirely normal in regard to cell number.

The range of variation in number of spore appendages is even less than
that in cells. The greatest number recorded from all observations made
was four and the smallest number, one. Three different spores were iso-
lated which bore only one appendage each. However, when these spores
germinated and the mycelia from them produced spores, the latter were
found to have the normal three appendages. Another spore bearing two
appendages was isolated with the same result, and still another bearing
four appendages gave progeny which showed no sign of this abnormality.
Apparently variation in cell number and spore appendage number are not
greatly different in behavior from sundry other abnormalities which appear
from time to time in Pestalozzia, none of which appears to be hereditary.

Selection of spores according to their progeny

The method of procedure in selecting spores according to their progeny
was as follows : A single spore culture was made from a given strain. When
this culture produced mature spores agar plates were poured with various
dilution^ of these spores. A mass of spores was taken from the culture
with a platinum wire and mixed with about 10 ~cc of sterile water in a
sterile tube. From this water suspension of spores two loops were put into
a tube of melted agar and thoroughly mixed. Two loops of this agar were
then mixed in the next tube; and again two loops were used to inoculate
the third tube. The agar from each tube was then poured into a sterile
petri dish, and the dish was covered with a bell jar. When the spores
germinated the agar plates were examined and spores were cut out from
the most suitable ones and put into separate tubes of Hevea agar. Micro-
scopic examination was made in each case to make sure that only one
spore was used in inoculating each tube. On this account it was found
more convenient to use a 1 -percent beef-extract agar instead of Hevea
agar for pouring the plates. It was not always possible throughout the
experiments to regulate the number of spores in the poured plates. The
third dilution plate was the one from which the spores were usually taken,
but whenever this contained too few spores to make a full set of cultures
for a given generation, the second dilution plate was used instead.

All the tubes contained agar made in one lot, tubed and sterilized at the
same time, and stored under the same conditions. The transfers of the
twenty single spores were made one immediately after the other, so that
the time of transfer of each was so nearly the same as to admit of no
reasonable assumption that this variation could be of effect. The twenty

SELECTION WITHIN PURE LINES OF PESTALOZZIA

153

tubes were put into one rack so that all might be subject to the same
general environmental conditions.

When the mycelia had all grown and the spores were mature, 100 spores
of each culture were measured and the mean spore length, or mean append-
age length, as the case might be, was computed. By trial it was found
that 100 measurements were sufficient to secure a smooth distribution

TABLE 1

Typical frequency distribution of measurements of spores and spore appendages from different
cultures of Pestalozzia Guepini. Measurements in (JL.

SPORE LENGTHS

SPORE APPENDAGE LENGTHS

Experi-

Experiment 1

Experiment 1

Experiment 1

Experiment 1

Experiment 2

ment 2

Length

Plus group

Plus group

Minus group

Length

Minus group

Plus group

Plus

Generation 3

Generation 3

Generation 4

Generation 6

Generation 1

group

Culture 3

Culture 8

Culture 3

Culture 1

Culture 1

Gen. 1

Cul. 15

19.8

1

2

3

10.8

2

20.7

1

2

3

12.6

2

2

21.6

4

5

8

14.4

3

3

1

22.5

8

9

11

16.2

8

. 5

7

23.4

11

17

15

18.0

15

11

12

24.3

12

19

17

19.8

17

12

15

25.2

19

14

15

21.6

16

15

18

26.1

14

12

12

23.4

13

17

14

27.0

8

9

6

25.2

10

14

10

27.9

8

4

3

27.0

7

14

8

28.8

8

4

2

28.8

5

5

6

29.7

2

1

2

30.6

2

3

3

30.6

2

2

2

32.4

1

3

31.5

1

1

34.2

1

Means

25.54±.15

24.79±.15

24.53+. 16

21.22±.21

22.81±.27

22.42
±.31

Standard

devia-

2.18

. 2.18

2.38

4.61

3.96

4.57

tions

curve and a mean with a satisfactorily small probable error, so with some
exceptions, where a few more spores were taken, one hundred from each
culture were measured. Typical distributions are shown in table 1.

After the twenty cultures were measured the one with the greatest mean
spore length was chosen as the starting point for plus selection. Similarly
the culture with the smallest mean spore length was taken as the beginning

GENETICS 7: Mr 1922

154

CARL DOWNEY LA RUE

of the minus selection. Another culture, which had a mean spore length
as nearly midway between the other two as could be found, was chosen as
the origin of an intermediate line to be carried on from generation to
generation without selection.

From each of the chosen cultures plates were now poured. When the
spores had germinated, ten single spores were cut out from the plates
made from the plus-selection culture and the same number from the minus-
selection culture. From the intermediate culture only one single-spore
culture was made. See figure 3.

FIGURE 3.— Plan of method of selection used in experiments 1 and 2. A represents the
parent culture; B, the agar plate poured with a dilution of spores from A; C, the daughter cul-
tures grown from spores from B, of which L has the highest mean value for the selected character
and is chosen as parent of a plus-selected line; S has the lowest mean value for the selected char-
acter and is selected as parent of a minus-selected line; and I, with a mean as nearly intermediate
between those of L and S as possible, is used as parent of an unselected intermediate line; D,
the plates poured from cultures L, S, and I; and E, the daughter cultures grown from spores
isolated from the plates in D. L and S are again selected as parents of the plus and minus
lines, respectively, and I is carried on without selection.

SELECTION WITHIN PURE LINES OF PESTALOZZIA

155

All the plates from the three different cultures were poured on the same
day, and from agar of the same lot. All the spore transfers were made
on the same day and all were kept in the same rack under the same
environmental conditions. Whatever the influences of environment were
they would act on all the cultures in the same way, and such variations
as might occur between cultures would therefore be ascribed to heredity.

Some variation in time of sporulation was always found but no definite
correlation was noted between the characters studied and the relative
rapidity of development. It was found that the difference in size between

TABLE 2

Comparison of spore appendage lengths of early and late spores from the same culture. (Strain
29, experiment 2, generation 17, plus-selected group, culture 3.} Lengths in ju.

LENGTHS

EARLY SPORES

LATE SPORES

9.0

1

2

10.8

1

9

12.6

4

13

14.4

16

14

16.2

16

18

18.0

28

23

19.8

20

12

21.6

8

6

23.4

2

3

25.2

2

27.0

2

Total

100

100

Means

18.16±.216

18. 03 +.234

Standard deviations

3.15+0.15

3.36±0.16

Difference of means

0.13+0.32

the spores first developed in a culture and those developed several days
later was not significant when compared with the differences which were
usually found between different cultures.

This fact is shown in table 2 where distributions of measurements of
early and late spores from the same culture are given. The early spores
were taken when only a few had been formed, the late spores were the last
of which the time of formation was definitely known. It should be noted
that all the spores measured here, as in all other parts of this investiga-
tion, were mature normal spores, being fully septate and having three

GENETICS 7: Mr 1922

156 CARL DOWNEY LA RUE

dark central cells. The difference between the mean appendage length of
early and late spores is 0.13±0.32ju. From SHEPPARD'S tables (PEARSON
1914) it may be found that the chances are fifteen to one that this difference
is due to random sampling. Accordingly it may be assumed that the two
sets of measurements are parts of the same frequency distribution. Thus it
appears that one may safely measure either early or late spores of a culture
without fear of introducing serious errors. In practice the cultures were
not measured until a vast number of spores had been produced and the
sample was then taken by drawing a sterile platinum wire over the fruiting
surface of the culture from the bottom of the agar slant to its top. In this
way a random sample was doubtless secured.

The sample was now mounted on a clean slide on which a drop of a
weak solution of magenta-red in 40 percent alcohol had been placed. The
spores were mixed in the solution by stirring with the platinum wire,
covered, and the excess of solution removed with blotting paper after
which the spores and appendages were clearly defined in the remaining
solution. The appendages and the hyaline cells at either end of the spores
were stained deeply by the magenta-red, so that both spore length and
length of appendage could be measured accurately. The solution did
not cause plasmolysis or shrinking of either the spores or the appendages.

Duplicate measurements were avoided by measuring all spores encoun-
tered in a path across the slide just below the upper edge of the cover-
glass and in another such path just above the lower edge of the glass.
The chances that any spore was encountered twice were thus rendered
exceedingly small.

When the means of the ten cultures of the plus group and those of the
minus group had been measured in the manner described above, the
cultures with the longest and shortest means were selected to continue the
plus and minus selections respectively.

As contrasted with the selection methods of other investigators, it will
be seen that only the range of variation happening to occur in a random
sample of ten variates is made available by this method. It may sometimes
happen that ten variates chosen at random will all fall near the modal
condition, but ten is a large enough number so that in general a random
sample of this size is likely to spread over a fair proportion of the range of
variation. To have made more than ten cultures in each line of descent in
each generation would have required an impossible amount of labor in
measuring. A larger number, as 100, for instance, would have insured the
detection of a greater number of extreme variates, but would also have
vastly increased the likelihood of selecting sporadic mutations rather than

SELECTION WITHIN PURE LINES OF PESTALOZZIA 157

extreme plus and minus variates in the range of continuous variation.
From one point of view the method might be looked upon as an inefficient
one, in that it surely failed to take advantage of the total range of variation
in each generation.

However, when it is considered that not only is the culture from which
the spore came known to possess the quality for which selection is being
made, but the culture derived from each spore in the line of descent is
known to possess this quality before that spore is selected as a parent, it
is clear that each selection is much more significant than is usual in cases
where many individuals are selected in each generation. For example,
in the line selected for plus spore length, each spore chosen as a parent
was known to be descended from a series of ancestral spores, each of which
had the potentiality for producing a longer-spored progeny than nine
other spores of its own generation, chosen at random. Similar plans of
selection have been used in one or two previous investigations but not
extensively nor with so full a knowledge of the behavior of both the
ancestors and the progeny of the parent individuals as in the present work.

So far as the writer knows no other investigator of the selection problem
has been able to establish the mean of the offspring of each selected indi-
vidual as was done in this experiment. Most of the organisms which have
been used in selection experiments are of such a nature as to prevent the
possibility of securing a sufficiently large number of offspring, all of one
age and all developed under the same environmental conditions, to estab-
lish such means. Obviously to secure as many as a hundred direct off-
spring from one parent DifHugia, (JENNINGS uses the term parent as
applying to the individual of a dividing pair which retains the old shell),
one would have to wait for just that many divisions of the parent, which
would demand considerable time. The progeny being formed at different
times, might be subjected to different environmental influences, so that the
range of variation might be greatly increased. It is therefore not possible
to know, in such forms as Difflugia, what the mean of the offspring would
be were they all produced under the same conditions. When too small a
progeny is secured, one does not know whether these approximate the
mean value for the generation or lie at one or the other extreme of the
range. Pestalozzia is especially favorable in that one can attain a full
knowledge of each generation, which is not the case for most forms.
Though such data are obtained only by the expenditure of a vast amount
of labor it is believed they are well worth while in a serious study of so
complicated a problem as that with which we are here concerned.

GENETICS 7: Mr 1922

158

CARL DOWNEY LA RUE

Experiment 1. Selection for length of spores

In this experiment the character studied was the length of the spore
from the tip of the proximal cell to that of the distal cell. In figure 1,
frequency polygons for this character are presented for six strains, of which
No. 29 was the one used in this experiment. Strain No. 29 was secured
from an isolation of fungi from the wood of a sapling of the Para rubber
tree, Hevea brasiliensis. Previous to its use in this experiment it had
been observed for eight consecutive generations in pure culture on Hevea
agar. The data concerning these generations are shown in table 3.

The experiment lasted from January 1919 to June 1919 and included
ten selections, all of which were made exactly according to the method
described above. Through some unfavorable circumstance, one of the
selections for the eleventh generation failed to grow and the experiment
was thus brought to an end. The entire experiment was done in Sumatra,
and Hevea agar was used for growing all the cultures.

TABLES

Mean spore lengths of cultures of strain 29, grown prior to the initiation of experiment 1. Mea-
surements in //.

GENERATION

SPORE LENGTH

RANGE OF MEA-

SUREMENTS

1

23.6

21-29

2

21.7

16-27

3

25.6

21-30

4

22.2

17-26

5

25.1

21-29

6

25.9

23-30

7

25.5

21-30

8

24.8

21-29

9

25.95

25-40

Mean

24.5

Figure 4 shows the greatest mean spore length in each generation for the
plus selections and the least mean spore length in each generation for the
minus selection; the so-called intermediate line carried on without selection
is shown also. The figure thus shows the range of difference between the
plus and minus selections. In case an effect of selection were present,
this range should become greater. In this experiment, this is obviously
not the case, since the range does not become greater. It is true that it
increases at different times for a number of generations, but this increase
is followed by a corresponding decrease, so that in the end no permanent

SELECTION WITHIN PURE LINES OF PESTALOZZIA

159

change is effected. The intermediate line shows continual fluctuation
from generation to generation. Similar fluctuation has been found by
all workers who have made careful studies of variation in pure lines of
organisms. It is presumably due to environmental influences, although
the writer was unable to correlate very considerable fluctuations in the

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FIGURE 4. — Graph of the mean spore lengths of parent cultures of experiment 1. P repre-
sents the parents of the plus-selected line, M those of the minus-selected line, and I, those of the
unselected intermediate line. The ordinates are lengths in n; the abscissae, the generations of
the experiment.

spore length of Pestalozzia with any significant fluctuations in any of the
environmental factors which are easily measured. The fluctuations in
the plus and minus selections appear to be due, not to selection, but to
such influences as cause the variations in the unselected intermediate line.
In most cases the fluctuations of the plus and the minus selections in a

GENETICS 7: Mr 1922

160

CARL DOWNEY LA RUE

given generation parallel each other. When this is the case the deviation
between the two selections is small. When the fluctuations, for any reason,
do not parallel each other the deviations between the two selections may
be considerably increased or considerably decreased.

From an inspection of figure 4 lit is difficult to tell whether or not the
parent cultures of the plus and minus strains are really different. It is
absolutely essential in selection studies that all selections be significant,
that is, the plus selection must be greater than the minus selection, not
only apparently, but statistically. It is by no means certain that this
has always been the case in previous investigations, and in many cases

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selected line is designated by P; the minus-selected line by M. The ordinates are lengths in /u;
the abscissae, the generations of the experiment.

it is difficult if not impossible to know whether or not the differences are
significant, especially where individuals are selected without knowledge of
the mean of the generation.

Pestalozzia is a very favorable organism in this respect since one can
employ the mean spore length of the selected cultures and know at the
same time the means of all the other cultures of that generation, as well
as the mean of those means. In this experiment it was found by computing
the errors of the differences between the plus and the minus selections that
these differences were significant in all cases. The smallest difference found
in the course of the experiment, .900 + .206^ in the ninth selection, is more
than four times its probable error and may be considered significant.

SELECTION WITHIN PURE LINES OF PESTALOZZIA

161

The means of the different generations of the plus and minus lines are
plotted in figure 5 and show variations comparable to those shown in
figure 2. If an effect of selection had been secured the means must neces-
sarily have shown increasing deviation one from another throughout the
experiment. Such increases as they have shown have been compensated
by corresponding decreases so that it becomes evident as the experiment
is carried on for a considerable period that these increases and decreases
of the deviation between the two selections are only the result of the chance
fluctuations which take place within the two lines. It is probable that such

TABLE 4

Mean spore lengths of generations of experiment 1. Each mean was computed from the means
of the cultures in its group for that generation. Each mean, except in the intermediate group is
accordingly based on approximately 1000 individual measurements. Values are given in fi.

GENERATIONS

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

1 (unselected)

24.91

24.91

24.91

2

25.54

25.38

24.12

3

25.25

24.61

26.59

4

24.41

24.28

24.38

5

24.51

24.82

25.25

6

24.75

24.70

23.94

7

24.71

24.64

23.83

8

24.50

24.21

24.23

9

24.19

24.43

23.92

10

24.41

23.67

24.03

Means of generation

means based on means

24.727 + 0.0559

24.622 + 0.0407

24.552±0.126

of all cultures in each

line

Difference between plus-selected line and minus-selected line = 0.105 + 0.068.
Difference between plus-selected line and intermediate line = 0.18 + 0.104.
Difference between minus-selected line and intermediate line =0.07 +0.097.

differences would occur between any two separate lines, descended from
the same parent but cultivated separately.

The means of each of the generations in the plus-selected line, the minus-
selected line, and the unselected intermediate group, and also the mean
of means of all cultures in each of these lines for the whole experiment are
shown in table 4, while table 12 (in the appendix) gives the means of all
cultures measured in this experiment. The differences between the lines
are in themselves very small and when compared with their probable
errors they are seen to be insignificant. However, had the experiment

GENETICS 7: Mr 1922

162 CARL DOWNEY LA RUE

been discontinued after three selections it would have appeared that a
small, but possibly significant, result had been produced by the selections.
The difference between the two lines at that time was 0.267/1, which is
probably more than three times its probable error which has not been
computed. It is at any rate, more than three times the error of the differ-
ence between the plus- and minus-selected lines for the whole experiment.

When selection is continued for a longer time the apparent effect of
selection is soon lost and the minus-selected line at times produces longer
spores than the plus-selected one. The intermediate form, which is entire-
ly unselected, shows greater fluctuations than either of the other groups,
and its mean for the whole experiment is less than that of the minus-
selected line. If we assume that the upward and downward swings, so
prominent in this experiment, are merely chance fluctuations due to
environmental influences we can understand why the intermediate line
shows more fluctuation than the others, since it is represented by only one
culture in each generation and its generation means are computed from
only 100 measurements instead of 1000 as in the case of the other two lines.

Since the two selected lines cannot be shown to differ from one another,
or from the unselected line, we can only conclude that selection has been
of no avail in producing lines of Pestalozzia Guepini distinct for length of
spore.

Experiment 2. Selection for length of spore appendages

In this experiment the same strain was used as in experiment 1 , namely,
No. 29. Table 5 presents the means and ranges of appendage length for
the eight generations during which the fungus had been studied prior to
the initiation of this experiment, and a frequency polygon of this strain
is shown in figure 2.

The plan of the experiment was that explained earlier in this paper
and used in experiment 1, and was rigidly followed throughout the whole
series of selections which were continued for more than a year. All of the
cultures were grown on Hevea agar, made according to the formula already
given, from the original lot of Hevea decoction, and used with all the
precautions previously mentioned. This work, like that of experiment 1,
was all done in Sumatra within a few hundred yards of the place where
line No. 29 was originally found.

In this experiment twenty-five selections were made for length of spore
appendages, and twenty-five successive generations were grown of an
unselected intermediate line also. The appendage lengths of all the parent
spores are shown in figure 6. The extreme cultures of the plus and minus

SELECTION WITHIN PURE LINES OF PESTALOZZIA

163

lines parallel each other in a remarkable manner but the differences
between them are not great. In one case (generation 11) the two lines are
so nearly coincident that parent cultures certainly different for appendage
length, could not be secured from the plus and minus lines. The range
of variation in appendage lengths did not consistently increase from gen-
eration to generation as they should if selection were effective but under-
went successive increases and decreases as the two lines drew nearer to-
gether or deviated more widely. The differences between the plus-selected
parent and the minus-selected parent vary from generation to generation,
but are large enough to be of significance except in the one case mentioned.
Figure 7 shows the means of the generations for the whole experiment
and from this figure it is at once apparent that the two lines of descent did

TABLE 5

Mean lengths of spore appendages of cultures of strain 29, grown prior to beginning experiment 2.

Measurements in fi.

GENERATIONS

LENGTHS OF
APPENDAGES

RANGE OF MEA-
SUREMENTS

1

24.5

20-30

2

21.7

10-27

3

23.1

16-30

4

26.7

20-36

5

25.1

20-39

6

22.4

14-39

7

24.0

16-33

8

24.1

19-31

9

21.8

16-40

Mean

23.71

not become more widely divergent as the number of selections increased.
Instead the same upward and downward swings appear as were seen in
experiment 1, but in this experiment the two lines parallel each other in
these fluctuations in a surprising way.

The means of the generations of each line and the mean of means of
each line for the whole experiment are presented in table 6, while table 13
(in the appendix) gives the data for all the cultures grown during the course
of the experiment. After examining figure 7 one is not surprised to find
that the differences between the three different experimental lines are of no
significance. In one case the difference is less than its probable error. Each
case where the plus line has grown longer and the minus line shorter has

GENETICS 7: Mr 1922

164

CARL DOWNEY LA RUE

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SELECTION WITHIN PURE LINES OF PESTALOZZIA

165

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GENETICS 7: Mr 1922

166

CARL DOWNEY LA RUE

apparently been so nicely balanced by one where the minus line has grown
longer and the plus line shorter, that the result has been an almost absolute
identity of the two lines as regards length of spore appendages.

TABLE 6

Mean appendage lengths of generations of experiment 2. Each mean was computed from the
means of the cultures in its group for that generation. Each mean, except in the intermediate group,
is based on approximately 1000 measurements. Measurements are given in JJL.

GENERATIONS

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

1

23.94

23.94

23.94

2

21.22

20.54

23.04

3

19.06

18.74

20.78

4

19.66

20.74

20.93

5

21.78

19.73

20.78

6

20.77

21.0)8

22.63

7

21.32

21.99

22.41

8

20.88

21.22

20.98

9

18.61

18.23

18.83

10

17.33

17.87

17.05

11

19.71

21.37

21.39

12

19.42

19.28

20.14

13

18.99

18.74

18.67

14

20.66

21.42

18.59

15

20.90

20.63

21.24

16

20.61

19.26

20.47

17

18.56

18.34

18.62

18

17.98

18.70

19.44

19

20.68

20.83

20.47

20

19.62

19.62

19.42

21

20.03

19.53

18.65

22

20.20

20.65

19.04

23

20.34

20.29

21.83

24

20.74

20.02

21.06

25

19.31

19.22

19.62

Means of generation

means based on means of

20.394+0.0844

20.223 + 0.0774

20.502±0.227

all cultures in each line

Standard deviations

1.908±0.0598

1.746±0/050

1.681+0.160

Difference between plus-selected line and minus-selected line =0.171 +0.1 15.
Difference between plus-selected line and unselected intermediate line = 0.108 ±0.242.
Difference between minus-selected line and unselected intermediate line =0.279 +0.239.

The minute scrutiny of each generation in the course of this experiment
and of experiment 1 made it possible to detect at once the appearance of
any aberrant form by mutation. It is desirable that such control be kept

SELECTION WITHIN PURE LINES OF PESTALOZZIA 167

in all selection studies since it is not improbable that in some cases small
mutations have arisen in the course of selection experiments, which have
not been detected and have produced effects attributed to selection. In
this experiment in the minus line of generation 14, culture 5, a distinct
mutation appeared which had a greater length of spore appendages
than any other culture encountered in the whole experiment. The spores
themselves were also longer, much more slender, and lighter in color than
those of any other culture seen during the whole range of my experience
with Pestalozzia. This form has since remained distinct through several
generations and will be studied further at a later date. It is mentioned
here merely to show the possibility that such mutations may account for
some of the results which are apparently due to selection. In the present
instance the mutation occurred in a plus direction but in the minus line
and so could hardly have escaped attention, but had it occurred in the
plus line, had it been somewhat less striking, and had it occurred in a less
carefully controlled experiment it might have escaped detection, and have
greatly confused the results of that experiment.

That the new form was not a contamination from outside instead of a
mutation, was made practically certain because no such form had ever
been isolated from the surrounding country; because all culture work
was carefully done and the usual contaminating organisms were rarely
found in the cultures; because Pestalozzia is not a fungus which is likely
to be found as an air-borne contamination in cultures; and finally, because
blank plates were poured in many generations without ever securing any
growth of any organism.

Experiment 2, carried on for more than one year, through twenty-five
generations, involving nearly 500 different cultures, and 50,000 spore
measurements, should have been a sufficiently thorough and long-con-
tinued study to demonstrate any effect of selection which might have ap-
peared. Since no such effect has been demonstrated we can only conclude
that the result of this experiment agrees entirely with that of experiment 1
and that it is not possible to produce lines distinct for lengths of spore
appendages by even long-continued selection.

Selection of spores according to visible characters

The selection of spores according to their appearance was now under-
taken as a check on the results of the previous selections. On account of
the small size of the spores of Pestalozzia considerable difficulty was ex-
perienced in finding a method by which the measured spores could be

GENETICS 7: Mr 1922

168 CARL DOWNEY LA RUE

isolated. Finally a special method was devised which has been described
in the Botanical Gazette (LARuE 1920).

In this method a selecting device was used which consisted of a brass
cone threaded at one end, and turned into a small tube at the other, the
end of the wall of the tube being made thin so as to form a sharp cutting
edge. The device was screwed into the nosepiece of a microscope in place
of one of the objectives. The spores to be examined were mixed in a
sufficient dilution in a tube of 1 -per cent LIEBIG'S beef -extract agar and
sterile slides were spread with a thin layer of this agar. When the agar
cooled the spores were firmly fixed in a thin transparent agar matrix and
could easily be located and measured under the microscope. When a
spore of the desired size was located it was carefully centered in the field
of vision and the nose-piece of the microscope was turned so as to place
the selecting device, of which the tip had just been sterilized by flaming
with a gas or alcohol flame, immediately above the spore. In a good
microscope, made so that the objectives center properly, this is an entirely
mechanical process requiring no skill on the part of the operator. The
microscope tube was now lowered until the sharp tube entered the agar
and cut a ring completely around the spore. The agar disk containing the
spore was now examined to see that only the chosen spore was contained
in it, and then lifted with a flattened platinum wire and transferred to a
tube of nutrient agar.

The agar used for imbedding the spores on the slides was filtered very
carefully to render it as transparent as possible so that it might not inter-
fere with a clear view of the spores. After selection the spores were grown
in Hevea agar of the same composition as that used in the former experi-
ments. However, after five selections had been made the cultures were
transferred from Sumatra to Michigan, and the supply of Hevea decoction
taken with them having been lost in transit, prune-juice agar was used
for the remaining cultures of the experiment. The prune agar, which
gave satisfactory results, was made by adding 2 percent of agar-agar to a
decoction of prunes. Since only one lot was made, and used for all the
cultures the exact proportions are of no special significance in the experi-
ment, and are therefore omitted. Care was taken, however, to see that the
medium was as uniform as possible for all the cultures.

Experiment 3

The line used for this experiment was No. 17, an isolation made from a
leaf-spot of a seedling of Hevea brasiliensis, which had been grown in
culture and measured for nine generations prior to the initiation of the

SELECTION WITHIN PURE LINES OF PESTALOZZIA

169

experiment. The variation of the strain during these generations may be
seen in table 7.

The character selected in this study was length of spore. Spores of the
last culture shown in table 7 were mounted in agar on slides and measured.
The longest spore found was selected as the parent of a plus-selected line,
* and the shortest spore encountered was chosen as the parent of a minus-
selected line. When sporulation took place in the resultant cultures
the spores were measured and the mean spore lengths of the cultures
determined precisely as in experiments 1 and 2. Spores from each culture
were now mounted and measured, the longest found in the plus cul-

TABLE 7

Mean spore lengths of cultures of strain 17, grown prior to the selections in experiment 3. Mea-
surements in (JL.

GENERATIONS

SPORE LENGTHS

RANGE OF MEA-

SUREMENTS

1

22.0

17-24

2

21,1

17-23

3

21.2

19-24

4

23.4

20-29

5

22.3

19-29

6

22.5

17-26

7

23.3

19-27

8

23.5

20-28

9

23.9

20-28

Means

22.58

ture being selected to continue the plus line, and the shortest found in the
minus culture being taken as parent of the next generation of the minus
line.

The selections thus begun were continued until ten had been made
when the experiment was discontinued. No attempt was made to make
the selections in the two lines at the same time. Thus the cultures in the
two groups usually developed under somewhat variable environmental
conditions so that a given selection is not precisely comparable with the
selection of the same number in the other line. However, in the long run
this variation is probably not significant since the fluctuations in environ-
ment should be about the same in summation for one line as for the other.

GENETICS 7: Mr 1922

170

CARL DOWNEY LA RUE

From the nature of the method of selection, spores near the extremes
of the range of variation were chosen, and accordingly the difference
between the selected spore of the minus line, and that for the plus line in a
given generation, was always large. The lengths of the selected spores
for the experiments are shown in figure 8. The differences between the
parent spores of the two groups does not increase significantly during the
experiment, nor does it decrease. At the time the cultures were transferred
to America the lengths of the parent spores decreased considerably but the
deviations between them were unchanged. To what extent the decrease
in spore length was due to change of culture medium, and to what extent
due to change of climate, is unknown.

30

p

/

•— — ^

^^

2t

V

x,

/

\

/•

?k

\s.

/

?4

??.

?0

1ft

\
\

M

16

x

N
\

^**

»**.

—

^^v

X.

M

1

)

\

I

t

«M

>

6

)

r

i

c

%

10

FIGURE 8. — Graphs of the lengths of individual spores selected as parents of the plus and
minus line of experiment 3. P, the plus selections; M, the minus selections. The ordinates are
lengths in /*; the abscissae, the successive generations.

The mean spore lengths of the generations of this experiment are shown
in table 8. The removal of the cultures to America resulted in a decrease
in mean spore length which is clearly shown in figure 9. The plus and
minus lines did not parallel each other so closely as in experiments 1 and 2.
This is to be expected because the selections in the two lines were not
usually made at the same time. The two lines were consequently not in
harmony in regard to the conditions under which they were developed and
their fluctuations were not parallel. In five of the ten generations the
minus line has a greater spore length than the plus-selected one. That
this result is due to selection is unthinkable. It serves as a warning that
small changes, apparently in the direction of a selection effect, should not
too readily be considered as due to selection, though they have usually
been so interpreted.

SELECTION WITHIN PURE LINES OF PESTALOZZIA

171

The means of means of all the cultures in the two lines when compared
are found not to be significantly different. The upward and downward
swings have had the same total effect in one line as in the other though the
different lines have scarcely paralleled each other at all during these swings.
Experiment 3, then, entirely substantiates the results gained in experi-
ments 1 and 2, and shows that the selection of visible characters within a
pure line is no more effective in producing distinct groups than selection
on the basis of progeny.

In the course of experiment 3 an aberrant form appeared, which seems
to be a mutation. This arose in the plus line in the seventeenth generation.

25
24
23
22
21
20

M

\,"

-£

/
/

f^

V
\
\

,'*\.

/

\\

1

— —

""/

*s*

\

^

Ss

\

/

\

/

X

>

f

2345 67 69 10

FIGURE 9. — Graphs of the spore lengths of cultures grown in experiment 3. P shows the
cultures of the plus line; M those of the minus line. The ordinates are lengths in n; the abscissae,
the generations of the experiment.

In regard to length of spores and of spore appendages it is identical with
strain 17 from which it arose. However, it has vegetative characters
quite distinct from those of strain 1 7 and this makes it appear very different
to the naked eye. Strain 17 produces a very small amount of mycelium
on the surface of the agar substratum, which becomes almost completely
covered with a black, slimy mass of spores. The new form produces a
thick felt of mycelium all over the surface of the agar, and sporulation is
much more tardy than in strain 17. The spores are produced in small
black masses which are rather sparsely scattered over the surface of the

GENETICS 7: Mr 1922

172

CARL DOWNEY LA RUE

mycelium. Thus far the form has remained distinct for two generations,
and will be studied further in the near future. If it continues to show
distinctive characters it will have to be considered as a mutation, though
one which affected fewer characters than the one encountered in experi-
ment 1. More detailed statements concerning both these mutations will
be presented in another publication.

TABLE 8

Mean spore lengths of cultures grown in experiment 3. One culture was grown in each line
in each generation. Each mean is based on 100 measurements. Measurements in fj,.

GENERATIONS

PLUS SELECTIONS

MINUS SELEC-

TIONS

1

24.37

23.65

2

23.53

24.30

3

24.34

24.16

4

24.01

25.04

5

22.09

22.30

6

20.78

22.40

7

22.56

22.46

, 8

21.43

22.98

9

22.58

22.51

10

21.97

21.76

Means of

generation

22. 766 +.251

23.16+. 212

means

Standard

deviations

1.18+.17

1.01 + .15

Difference between plus-selected line and minus-selected line =0. 390 +0.328/-1.

Experiment 4

It was originally intended that this experiment should be carried on for
an extended period of time. In order to lessen the labor required, some
changes were made in the method which had been used in experiment 3.
The spores were selected and grown in the same manner as in experiment 3
but the cultures of each generation were not measured. Instead it was
planned to measure them only from time to time to determine whether
or not the plus and minus lines were diverging one from another. Un-
fortunately only a few selections had been made before the writer left
Sumatra. The strain used, No. 5, which was isolated from a leaf spot of
cocoanut palm and had been successfully grown for nine generations in

SELECTION WITHIN PURE LINES OF PESTALOZZIA

173

culture with the results shown in figures 1 and 2, and in table 9, did not
thrive well in Michigan, even when kept in a constant-temperature room,
so after six selections the experiment was discontinued. While the experi-
ment included fewer selections than is desirable, a large number, perhaps
the majority, of selection experiments have been carried no farther, and
no apology need be made for presenting the results. These are shown in
table 10 and the measurements of the selected parent spores are presented
in figure 10.

The spores selected, on the basis of spore length, as parents of the plus
and the minus lines, were significantly different from each other in every
generation, so that there can be no doubt that real selections were made.

TABLE 9

Mean spore lengths of cultures of strain 5, grown prior to the initiation of experiment 4. Measure-
ments in p.

GENERATIONS

SPORE LENGTHS

RANGE OF MEA-

SUREMENTS

1

24.4

20-29

2

21.1

17-26

3

22.3

17-24

4

20.2

17-24

5

22.2

19-26

6

22.4

19-29

7

20.6

17-24

8

23.2

19-29

9

21.9

18-25

10

21.5

17-27

Mean

21.98

The cultures were removed from Sumatra after three minus selections
and two plus selections had been made. The fourth, fifth, and sixth selec-
tions of the plus line show no decrease in spore size following this change
of climate, since they are all at least equal in size to the third selection,
and the sixth selected spore equals the size of the first and second parent
spores of the line. In the minus line, however, the third, fourth, and fifth
selections show a decided decrease in spore size. The sixth selected
spore is equal in size to the second, but it should be noted that another
chosen spore of precisely the same size as the fifth selected spore failed
to grow. It is rather uncertain whether any of these changes may be
attributed to climatic changes.

GENETICS 7: Mr 1922

174

CARL DOWNEY LA RUE

Only the cultures of the fifth and sixth generations were measured.
In the fifth generation the culture of the plus line had a greater mean spore
length than that of the minus line, but in the next generation the result
was reversed, and the culture of the minus line had the higher mean. The
summation of the two generations shows that the two lines are not dis-
tinct, the difference between them being barely larger than its probable
error. The result of this experiment is the same as that for the three
preceding experiments, namely, that selection has no appreciable result.

22

20

18

16

14

M

123456

FIGURE 10. — Graphs showing the lengths of the individual spores selected as parents of
the plus and minus lines of experiment 4. P indicates the plus selections; M, the minus selec-
tions. Lengths in n are given as ordinates; the successive generations as abscissae.

The evidence gained from two experiments, in which visible characters
were selected, is in entire agreement with that secured from the more
extensive experiments in selection according to progeny, and all the experi-
ments, whatever the method and strain used, consistently show that
selection within pure lines of Pestalozzia is entirely ineffective, but that
rarely mutations occur which are significantly different from the parent
line.

DISCUSSION

JENNINGS (1916, 1920) considers that if the experiments which have
been supposed to demonstrate the negative result of selection had dealt with
characters which were less likely to be influenced by degree of maturity
and environmental influences, had been more carefully conducted, and
had involved a larger number of selections, they would likely have shown a

SELECTION WITHIN PURE LINES OF PESTALOZZIA 175

positive result. The Pestalozzia investigation has greater evidential
value. It was carried on for 10, 25, 10, and 6 generations, respectively,
in the several experiments. The characters studied were such as to admit
of certainty as to maturity of the observed individuals, and they were not
more subject to environmental influence than those considered in investi-
gations which have seemed to give evidence of an effect of selection. In
certain respects, which have already been pointed out, the different genera-
tions have been more fully known, and a larger number of variates have
been considered, than in any other investigation yet reported. Neverthe-
less, the different experiments consistently fail to show any effect of selec-
tion. The evidence secured in this study then is a direct confirmation of
the results of JOHANNSEN and the other early workers on the pure-line
problem. In attempting an explanation of the discrepancy between
these results and those which contradict them, it is necessary to attempt
to evaluate the experiments that have shown a positive selection effect.

TABLE 10
Means of generations measured in experiment 4. Measurements in JJL.

GENERATION

PLUS-SELECTED

LINE

MINUS-SELECTED
LINE

5

6

21. 142 ±.110
20.428±.114

20. 802 +.117
. 21.500±.112

Means

20. 785 +.241

21.151±.236

Difference between plus-selected line and minus-selected line = 0.366 + 0.337/J.

The results of STOCKING (1915), while sufficiently striking and credible,
can be given little weight in a general consideration since the abnormal
characters dealt with so strongly suggest a pathological condition of the
organism. To be given weight in a discussion of selection as a factor in
evolution, the supposed modification produced by selection must affect a
normal character in a direction shown by existing forms in nature to have
been actually traversed by these other forms in the course of their evolu-
tion.

MIDDLETON (1915) found selection for fission rate in Stylonychia effec-
tive to a degree which must have been surprising, even to believers in the
possibility of modification by selection. The great readiness with which
organisms could be altered in MIDDLE-TON'S experiments indicates that the
response of Stylonychia to selection is to some degree exceptional. ROOT
(1918) suggests that "the inheritance of variations in fission rate in Sty-

GENETICS 7: Mr 1922

176 CARL DOWNEY LA RUE

lonychia might be due to the accumulation of waste products in the cyto-
plasm of the slowly-dividing, large-sized group." The fact that MAST
(1917) secured two lines with different fission rates mDidynium nasutum
without selection is suggestive that mutation may offer an alternate
explanation of MIDDLETON'S results.

ROOT (1918) working on Centropyxis has secured data worthy of consid-
eration. In one experiment, using mass selection, he found a decided
effect of selection on the number of spines after only four selections.
However, the number of individuals studied was very small, — 88 in the high
series and 77 in the low series. In another mass selection the results were
exactly opposed to those of the first; that is, the parents with a low spine
number produced offspring with more spines than those from parents with
a large number of spines. The latter result obviously cannot be due to
selection, though had it stood alone it might have been so interpreted.
The two experiments show the danger of drawing conclusions from a small
number of individuals and a few selections.

In a third experiment in which individuals were selected according to the
character of their progeny no considerable effect was gained until the
fourth selection. From the fourth selection a large effect was secured.
One selected individual gave offspring all of which had a high spine number.
This individual (5ala of ROOT'S series), the offspring of which are respon-
sible for a decided increase in the number of spines in the plus series, may
have been a mutation. The number of spines in the low series did not
appreciably decrease during the selection period. The whole experiment
included only a small number of individuals, 56 in the plus series and 51
in the minus, and only four selections were made.

In the fourth experiment in which mass selection for number of spines
was practiced, two populations were segregated which varied in respect to
spine number. The difference between the two populations was small and
fluctuated from generation to generation. In the second selection period
the difference was less than in the preceding period. The number of
individuals observed was larger than in the other experiments but still
relatively small. It would have been interesting to see what the result
of a continuation of the cultures would have been. As it is, one suspects
the separation to have been only a temporary one, such as is shown for
Pestalozzia in table 4 of this paper.

HEGNER (1919) carried on extensive selection experiments on Arcella
and finds that it is possible to separate by selection within families groups
which are distinct in regard to the selected character. In his principal
experiment, however, the effects of selection on number of spines are by no

SELECTION WITHIN PURE LINES OF PESTALOZZIA 177

means consistent. The first set of selections produced a higher number of
spines in the group selected for low spine number than in the group selected
for high spine number. It is unfortunate that at this point a change was
made in the method of selection. The author attributes the effect secured
in further selections to the use of a better criterion for the selection. The
effect may have been due to independent chance fluctuations within the
two groups and not to selection at all but the change in procedure prevents
this being detected. It would have been very interesting to know whether
or not such divergences would have occurred had the original method been
continued. Five further selection periods showed an increase in spine
number in the group selected for high spine number and a decrease in the
group selected for low number. The difference between the high and the
low series, however, does not show a steady increase, but fluctuates from one
selection period to the next. When the divergence between the two groups
was at a maximum, selection was stopped, so that we do not know whether
the divergence would have decreased or not had selection been continued.

On the cessation of selection the divergence between the groups de-
creases very little for one period. In the next period the divergence falls
to almost nothing while in the next following period it again rises to nearly
half that secured at the end of the six selection periods. It is approximate-
ly equal to that found in the second selection period. In the second selec-
tion period the increase in divergence is attributed to selection. To what
is it due in this non-selection period? It seems logical to assume that it
is due to the same cause in both cases, probably to the independent
chance fluctuations of the two groups.

Further selection for one period in the high line resulted in a slightly
larger number of spines in the group selected for low spine number than
in that selected for high spine number. That this is due to selection is,
of course, impossible.

Three selection periods were effective in that they developed two diver-
gent lines within the low line established by the early selection. Here
again the divergence fluctuates from period to period. After selection
ceases the divergence becomes greater than it was during the selections.
This again indicates that the divergence may be totally unrelated to the
selection. In experiment 1 of this paper may be found similar divergences,
which were only temporary.

In another experiment HEGNER practiced selection for diameter and
spine number for a period of nine days. During this time distinct high
and low lines were produced. In a non-selection period of thirteen days
following the selections the divergence between the high and low series

GENETICS?: Mr 1922

178 CARL DOWNEY LA RUE

continued to increase to a marked degree. Obviously this continued
increase was not due to selection; on the contrary one would expect a
lessened divergence between the high and low series following the cessation
of selection. The increased divergence during the non-selection period
was almost entirely due to increase in size and spine number in the high
series. That this series later produced some very large forms, and that
great difficulty was experienced in securing offspring from this group are
facts that may be indicative of abnormality in the group. As in HEGNER'S
other experiments, relatively few individuals were studied.

The extensive and painstaking studies of JENNINGS (1916) on Difflugia
present what appears to be the least questionable evidence of the effective-
ness of selection yet published. In one experiment he made selections for
seven periods, each of which, except the first, included one generation.
Selection was made for number of spines, individuals with from 1 to 3 spines
being chosen as parents for a "low" set, and those with from 5 to 8 spines
being retained as parents of a "high" set.

The selection was apparently effective and is so interpreted by JEN-
NINGS. Two lines were formed by the selection which differ in mean spine
length. However, a closer examination shows that the divergence of the
two lines varied from generation to generation. In the second period the
divergence is equal to nearly a whole spine (.95 spines), but in the third
period the divergence falls to .03 spines, which means the lines are really
identical statistically. From the third period on the divergence continu-
ally rises and falls but never again reaches so high a point as in the second
period. If the divergence is due to selection why is the effect so great in
the second period, and why do further selections result in a decreased
divergence?

The individual measurements are not published, but if we compute the
error of the difference between the means of the two groups, using the
generation means, we find it to be . 103. The difference between the means
of the two groups is .22 ± .103 spines. The divergence is barely more than
twice its probable error and so is not statistically significant.

During the selection periods the two groups showed fluctuations in
regard to diameter of shell and length of spine which are similar to those
already noted for number of spines. Table 11 shows the divergence of the
two groups for each of the three characters.

It may be seen at a glance that the differences do not steadily increase
with an increased number of selections but rise and fall as if by chance.
The difference in spine number is greatest in the second period, that of
shell diameter is greatest in the fourth period; and that for spine length

SELECTION WITHIN PURE LINES OF PESTALOZZIA

179

is greatest in the fifth period, falling to a minus value in the sixth period.
The mean for shell diameter is the only one which is equal to three times
its probable error. Apparently the two lines are not demonstrably dis-
tinct.

In family 314 also, JENNINGS attempted to isolate lines distinct for spine
number. Selection was continued for seven periods in the same way as
within family 304. The means of the "high"-selected line and of the
"low"-selected line were separately computed for each generation. The
differences between the two lines varies from generation to generation as
in family 304. It is noteworthy that the greatest divergence (1.24 spines)
appears in the first selection period; the lowest deviation in the sixth period.
The difference between the mean numbers of spines for the two groups is

TABLE 11

Differences between "low" and "high" selected groups of family
303 of Difflugia.

SELECTION

DIFFERENCES IN

DIFFERENCES IN

DIFFERENCES IN

PERIODS

NUMBER OF

SHELL DIAMETER IN

LENGTH OF LONGEST

SPINES

UNITS OF SCALE

SPINES IN SCALE

UNITS

1

.41

.52

.48

2

.95

.63

.57

3

.03

1.16

.39

4

.35

2.88

.02

• 5

.25

.61

.67

6

.34

.95

.29

7

.60

.94

.13

Mean

.22+. 103

.93+. 26

.76+. 299

.42 ±.2 5 spines. Since the divergence is less than twice its probable
error, we can only conclude that the lines are not distinct and that the
apparent difference is due to the independent fluctuation of the two groups.

In another and more extensive experiment, JENNINGS sought to isolate
distinct lines by selection within family 326. Again spine number was the
character selected, and selection was continued for twelve periods. For
the first six periods selection was ineffective and both plus and minus diver-
gences between the "low" and the "high" groups appeared.

As in one of HEGNER'S experiments, a change in the method of selection,
made at this time, prevents us from knowing what would have resulted
from further selections in which large numbers of individuals were used.
Following the change in method two series distinct for spine number were

GENETICS 7: Mr 1922

180 CARL DOWNEY LA RUE

isolated by selection during six periods.' The difference between the means
is 0.51 ±0.109 spines or less than five times its probable error.

During the six selection periods following the change in the method of
selection (periods 11 to 16) the divergence between the two groups did
not constantly increase but fluctuated from period to period. In the
eleventh period it was .52 spines, in the twelfth it fell to .49 spines, in the
thirteenth it rose to .84, the highest point reached. In the fourteenth
period the difference fell to .28 spines, in the fifteenth to .23 spines, which
is probably not significant, and in the sixteenth or last period it again
rose to .66 spines. If the divergence in period thirteen is due to selection,
it is difficult to see why further selection for the same number of periods
that caused this divergence, should cause a decrease in the difference of
the two groups.

After selection was discontinued the two groups were kept under obser-
vation during five different periods which varied from eight to twenty- two
days in length. The mean spine number of the individuals in the low-
selected group was 5.19 while that of the high-selected group was 5.58.
The error of the difference between the means of the two lines is 0.178
spines while the difference is only 0.39 spines, or slightly more than twice its
probable error. The difference would not be considered significant if it
were not for the fact that the variations in the various lines, though great,
are insufficient to bridge the gap between oppositely selected lines. Is it
a fair criticism that Difflugia is insufficiently plastic to show rapid changes
from a certain condition of the shell after that condition is once attained?
The results suggest that the shell itself plays a part in determining the
character of the new individual formed by division of the old one. This shell
effect may be regarded as superposed upon the other factors determining
the form of the new shell. Such an effect might be expected upon physical
grounds. Naked protoplasm protruded from a large orifice is under dif-
ferent surface conditions than if the orifice were smaller; the extruded
protoplasm would be expected to assume a different form and size in the
two cases, and the newly secreted shell would therefore be different. In
other words, any accidental size modification might be maintained through
several generations, not through any protoplasmic modification, but
merely because the nature of the shell imposes certain physical conditions
upon the development of the new individuals. A modification having
once occurred in the shell through any cause, becomes comparable to an
environmental factor which is maintained for several successive genera-
tions. The nature of new individuals is largely determined by the environ-
ment, and of the environmental factors the shell is one of the chief. If this

SELECTION WITHIN PURE LINES OF PESTALOZZIA 181

suggestion has any validity, it follows that the two groups, while apparently
different, were not significantly different, even while selection was being
practiced.

If two lines are isolated within a strain and cultivated separately these
lines will be independently subjected to the environmental influences
which cause variation for the character studied. The lines will tend to
coincide if they are subjected to these influences at the same time and to
the same degree. This is the case with the strain of Festal ozzia studied in
the author's experiment 2 and is shown in figure 7. It is apparent that
there is a certain rhythm, either in the organism itself or in the environ-
mental factors, which causes upward and downward swings of the organism
in respect to the character under observation. Since great care was taken
to have the two groups subject to identical conditions at all times the two
groups follow one another very closely in these swings. In experiment 1
the swings follow each other less closely but with some exceptions there is a
strong similarity of behavior in the two lines as is shown in figure 5. In
MAST'S work with Didynium, where two groups have been separated,
apparently by a mutation, these groups fluctuate in the same direction
at the same time, with remarkable unison.

If two lines are isolated and cultivated separately, but the offspring are
produced in such a way that those of the two lines are subjected to the
environmental factors causing variation for a given character, at a different
time, or in a different degree, each of the lines will fluctuate in a different
way, and this will cause divergence between the two. However if the
lines are continued the fluctuations will compensate one another so that
in the end the two lines will be found to give practically the same mean
value for the character studied.

To the writer it appears that JENNINGS'S results with Difflugia, ROOT'S
with Centropyxis, and HEGNER'S with Arcella, are explained by the above
assumption quite as well as are his own with Pestalozzia. If this be true
they tend rather to demonstrate the ineffectiveness of selection within
pure lines than the opposite.

It is warranted to express the belief that the "pure-line" hypothesis is
still valid. The writer does not wish to express an opinion that ultimately
the effectiveness of selection may not be shown, but he feels that the bur-
den of proof lies with those who question the results of JOHANNSEN and
his followers. At the present time incontestable evidence of an effect of
selection is wanting. From, the recent investigations made in this field
it is obvious that the situation is vastly more complicated than was
formerly supposed. The truth or falsity of the "pure-line" hypothesis

GENETICS 7: Mr 1922

182 CARL DOWNEY LA RUE

will be finally determined by numerous investigations with various or-
ganisms, involving infinite care and toil. There is need of more investiga-
tions of the type which JENNINGS has made on Paramecium and Difflugia,
but carried for longer periods, with organisms more favorable for study,
if they may be found.

Nothing has been said in this paper, of the bearing of the "pure-line"
hypothesis on theories of evolution. Almost every worker who has made
careful biometric studies of highly variable groups has recorded the occur-
rence of mutations or "something like mutations." JENNINGS, ROOT,
MAST, and HEGNER have all recorded them for the lower animals. BAR-
BER (1907) noted the occurrence of mutation in yeasts; STEVENS (1920)
has reported a number of mutations in Helminthosporium ; and the writer
has found mutations in Pestalozzia. It is unnecessary to catalogue the
numerous cases of mutation recorded in various groups of higher plants
and animals. Further careful study will doubtless reveal many more.
When more is known of their occurrence, frequency, and reaction to
environment, to other existing organisms, and to one another, may we not
be able to conceive of evolution, even without cumulative growth of char-
acters by the selection of fluctuating variations?

CONCLUSIONS

Selections according to progeny within pure strains of Pestalozzia were
made for length of spores for ten generations, and for length of spore
appendages for twenty-five generations, without result. Selections ac-
cording to visible characters were made for spore length for ten genera-
tions in one experiment and for six generations in another, without
establishing differences between the plus-selected and minus-selected lines.
Whatever method and strain may be employed, selection is totally in-
effective in establishing distinct lines within pure strains of Pestalozzia
Guepini.

Mutations which give rise to lines significantly different from the parent
lines, infrequently occur.

LITERATURE CITED

BARBER, M.A., 1907 On heredity in certain micro-organisms. Kansas Univ. Sci. Bull. 4, 48 pp.
EWING, H. E. 1914 a Pure line inheritance and parthenogenesis, Biol. Bull. 26: 25-35.
1914 b Notes on regression in a pure line of plant lice. Biol. Bull. 27: 164-168.
1916 Eighty-seven generations in a parthenogenetic pure line of Aphis avenae Fab. Biol.

Bull. 31:53-112.

HANEL, ELISE, 1908 Vererbung bei ungeschlectlicher Fortpflanzung von Hydra grisea. Jenaische
Zeitschr. 43:221-372.

SELECTION WITHIN PURE LINES OF PESTALOZZIA 183

HARRIS, J. A., 1911 The biometric proof of the pure line theory. Amer. Nat. 45:346-363.
HEGNER, R. W., 1919 Heredity, variation, and the appearance of diversities during the vege-
tative reproduction of Arcella dentata. Genetics 4: 95-150.
JENNINGS, H. S., 1908 Heredity, variation and evolution in Protozoa. II. Heredity and

variation in size and form in Paramecium with studies of growth, environmental action

and selection. Proc. Amer. Philos. Soc. 47:393-546.
1916 Heredity, variation and the results of selection in the uniparental reproduction of

Difflugia corona. Genetics 1 : 407-534.
1920 Life and death, heredity and evolution in unicellular organisms. 233 pp. Boston:

Richard G. Badger.
JOHANNSEN, W., 1913 Elemente der exakten Erblichkeitslehre. Zweite Ausgabe, xi-f-723 pp.

Jena: Gustav Fischer.
KAUITMAN, C. H., 1908 A contribution to the physiology of the Saprolegniaceae, with special

reference to the variations of the sexual organs. Annals of Bot. 87: 361-386.
LA RUE, CARL D., 1920 Isolating single spores. Bot. Gaz. 70: 317-318.
LA RUE, CARL D., and BARTLETT, H. H., 1922 A demonstration of numerous distinct strains

within the nominal species Pestalozzia Guepini Desm. Amer. Jour. Bot. 9:79-92.
LASHLEY, K. S., 1915 Inheritance in the asexual reproduction of Hydra. Jour. Exper. Zool.

19: 157-210.

1916 Inheritance in the asexual reproduction of Hydra. Jour. Exp. Zool. 20: 19-26.
MAST, S. O., 1917 Mutation in Didynium nasutum. Amer. Nat. 51: 351-360.
MIDDLETON, A. R. 1915 Heritable variations and the results of selection in the fission rate of

Stylonychia pustulata. Jour. Exper. Zool. 19:451-503.
MORGAN, T. H., 1916 A critique of the theory of evolution, x-f 197 pp. Princeton: Princeton

University Press.
PEARSON, KARL, 1910 Darwinism, biometry and some recent biology. I. Biometrika 7:

368-385.
1914 Tables for statisticians and biometricians. Ixxxiii + 143 pp. Cambridge: Cambridge

University Press.

PIETERS, A. J., 1915 New species of Achlya and of Saprolegnia. Bot. Gaz. 60: 483-490.
ROOT, F. M., 1918 Inheritance in the asexual reproduction of Centropyxis aculeata. Genetics

3: 173-206.
STEVENS, F. L., 1920 Heterogenetic saltation in the genus Helminthosporium, with comments

on morphology and culture characters. Paper read before the Bot. Soc. Amer., Myco-

logical Section, Chicago, Dec. 1920.
STOCKING, RUTH J., 1915 Variation and inheritance of abnormalities occurring after conjugation

in Paramecium caudatum. Jour. Exper. Zool. 19 : 387-449.
WOLLENWEBER, H. W., 1914 Identification of species of Fusarium occurring on the sweet

potato, Ipomoea Batatas. Jour. Agric. Res. 2: 251-285.

GENETICS 7: Mr 1922

184

CARL DOWNEY LA RUE

APPENDIX

Tables of constants of experiments 1 and 2

TABLE 12

Means and standard deviations of spore lengths of cultures grown in experiment 1. The mean of
each culture was calculated from at least 100 measurements. Values are given in units of the scale of
the eye-piece micrometer used. 1 unit = 1.8 microns. Single spore culture of parent strain (No. 29} .
Mean = 13.80, ff = 1.58.

Generation 1 of experiment

CULTURE

MEAN

a

CULTURE

MEAN

9

1

14.46

1.55

11

14.16

1.43

2

13.90

1.76

12

13.72

1.82

3

13.61

1.85

13

13.64

1.43

4

13.97

1.63

14

13.62

1.54

5

13.51

1.79

15

14.18

1.84

6

14.02

1.90

16

13.58

1.67

7

13.71

1.80

17

13.85

1.87

8

13.57

1.71

18

13.79

1.82

9

13.95

1.47

19

13.95

1.65

10

13.71

1.71

20

13.89

1.52

Mean of generation 13.84.

Generation 2

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

a

Mean

<T

Mean

0-

1

14.03

1.41

14.23

1.66

13.40

1.10

2

14.29

1.44

13.99

1.38

3

14.94

1.52

14.19

.39

4

13.95

1.43

14.00

.29

5

14.33

1.49

13.82

.39

6

14.35

1.52

14.00

.27

7

14.94

1.55

14.31

.43

8

13.43

1.33

14.12

.52

9

13.72

1.54

14.17

1.62

10

13.94

1.93

14.15

1.33

Generation

means

14.19

14.10

13.40

SELECTION WITHIN PURE LINES OF PESTALOZZIA

185

TABLE 12 (continued)
Generation 3

PLUS SEL

ECTIONS

MINUS SE]

.ECTIONS

INTERMEDIA!

'E GROUP

Mean

a

Mean

<r

Mean

<r

1

14.46

1.26

13.55

.24

14.77

1.38

2

13.88

1.28

13.92

.22

3

14.19

1.21

13.60

.38

4

14.11

1.09

13.61

.29

5

14.34

1.25

13.60

.96

6

13.75

1.18

13.54

.18

7

13.75

1.16

13.79

.33

8

14.22

1.33

13.77

.21

9

13.74

1.07

13.59

.33

10

13.88

1.15

13.70

.31

Generation

means

14.03

13.67

14.77

Generation 4

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

<r

Mean

<r

1

13.50

1.17

13.27

1.13

13.55

1.14

• 2

13.62

1.22

13.68

1.24

3

13.87

1.04

13.63

1.32

4

13.11

1.12

13.79

1.13

5

13.37

1.11

13.32

0.99

6

13.93

1.33

13.09

1.29

7

13.78

1.12

13.64

1.07

8

13.53

1.37

13.44

1.29

9

13.27

1.01

13.55

0.95

10

13.59

1.21

13.52

1.07

Generation

means

13.56

13.49

13.55

GENETICS 7: Mr 1922

186

CARL DOWNEY LA RUE

TABLE 12 (continued)
Generation 5

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

a

Mean

a

1

13.92

1.17

13.93

1.12

14.03

1.32

2

13.55

1.04

14.19

1.26

3

14.07

1.31

13.43

.29

4

13.60

1.24

13.75

.13

5

13.77

1.02

13.41

.21

6

13.88

1.10

13.71

.42

7

13.40

1.19

13.81

.10

8

13.47

1.37

14.14

.27

9

14.05

1.02

13.53

.12

10

13.63

1.10

14.04

.19

Generation

means

13.73

13.79

14.03

Generation 6

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

a

Mean

a

Mean

a

1

13.73

1.17

13.75

1.18

13.31

1.12

2

13.74

.18

13.65

1.19

.

3

13.91

.12

13.75

1.33

4

14.14

.01

13.60

0.88

5

13.62

.05

13.23

1.08

6

13.65

.00

13.87

1.06

7

13.64

.11

13.68

1.18

8

13.69

.10

14.10

1.13

9

13.84

.20

13.66

1.36

10

13.50

1.15

13.91

1.24

Generation

means

13.75

13.72

13.31

SELECTION WITHIN PURE LINES OF PESTALOZZIA

187

TABLE 12 (continued)
Generation 7

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

a

Mean

<r

Mean

<r

1

13.84

1.28

13.26

1.06

2

13.76

1.21

3

13.59

1.13

14.17

1.40

4

13.78

1.09

5

13.33

1.33

6

14.08

0.98

7

13.86

1.12

13.76

1.33

8

13.45

0.97

13.67

1.37

9

13.87

1.22

13.17

1.66

10

13.75

1.22

Generation

means

13.73

13.69

13.26

Generation 8

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

a

Mean

<r

1

13.46

0.95

13.47

0.98

2

13.65

1.11

3

13.79

1.17

13.03

1.01

4

13.93

1.06

13.79

1.05

5

13.89

1.07

13.49

0.98

6

13.18

1.11

13.60

1.15

7

13.42

1.05

13.59

1.13

8

13.80

1.14

13.17

1.08

9

13.47

1.08

10

13.49

1.15

Generation

'

means

13.61

13.45

13.47

GENETICS 7: Mr 1922

188

CARL DOWNEY LA RUE

TABLE 12 (continued)
Generation 9

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

<r

Mean

<r

1

13.46

.23

13.43

1.07

13.29

1.03

2

13.50

.17

13.56

1.21

3

13.28

.08

13.92

1.03

4

13.71

.13

13.84

1.02

5

13.26

.06

13.57

0.99

6

13.53

.09

13.21

1.34

7

13.55

.31

13.47

1.11

8

13.45

1.04

13.68

1.05

9

13.38

1.17

13.25

0.98

10

13.31

1.08

13.75

1.08

Generation

means

13.44

13.57

13.29

Generation 10

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

a

Mean

<r

1

13.45

1.22

13.05

1.03

13.35

1.03

2

13.31

1.15

13.13

1.38

3

13.89

1.33

13.14

1.00

4

13.03

0.95

12.96

1.02

5

13.71

0.94

13.27

0.91

6

13.86

0.96

13.26

0.88

7

13.67

0.99

13.19

1.18

8

13.12

1.08

9

13.57

1.11

12.92

1.17

10

13.54

1.04

13.44

1.07

Generation

means

13.56

13.15

13.35

Means of all cultures in experiment 1

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

13.736+0.0311
<r=0.435±0.0219

13. 679 ±0.0226
<r=0.331±0.0159

13.640 + 0.070
o-=0.326±0.0492

Difference between plus selections and minus selections =0.05 7 + 0.03 8
Difference between plus selections and intermediate group =0.10 + 0.058
Difference between minus selections and intermediate group =0.039 + 0.054.

SELECTION WITHIN PURE LINES OF PESTALOZZIA

189

TABLE 13

Means and standard deviations of appendage lengths of cultures studied in experiment 2. The
mean of each culture was calculated from 100 or more measurements. Values are given in units of
micrometer scale: 1 unit = 1.8 microns. Single-spore culture of parent strain (No. 29). Mean —
12.42, a =2. 08.

Generation 1 of experiment

CULTURE

MEAN

a

CULTURE

MEAN

0-

1

12.67

2.20

11

13.62

2.21

2

12.50

2.22

12

13.52

3.07

3

13.58

2.30

13 .

13.69

2.96

4

13.57

2.40

14

13.48

2.55

5

13.85

2.43

15

12.48

2.54

6

13.46

2.26

16

14.01

2.52

7

13.64

2.52

17

12.01

2.81

8

13.10

2.30

18

13.08

2.42

9

13.66

2.34

19

13.74

2.72

10

13.81

2.29

20

12.46

2.33

Mean of generation 13.30

Generation 2

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

<r

Mean

<r

1

11.70

2.00

11.59

2.17

12.80

2.28

2

12.16

1.08

11.42

2.24

3

12.09

1.95

11.60

2.31

4

12.03

1.88

11.44

2.07

5

11.92

2.26

11.40

2.06

6

11.44

2.19

10.63

1.91

7

11.49

2.03

11.36

2.22

8

11.92

2.71

11.60

2.13

9

11.14

2.16

11.68

2.29

10

11.97

1.98

11.42

2.03

Generation

means

11.79

11.41

12.80

GENETICS 7: Mr 1922

190

CARL DOWNEY LA RUE

TABLE 13 (continued)
Generation 3

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

CULTURE

Mean

<r

Mean

a

Mean

a

1

10.05

1.77

10.31

2.34

11.55

2.33

2

9.99

2.20

10.41

1.67

3

9.84

2.07

10.44

2.20

4

11.29

2.17

11.01

2.09

5

10.64

2.16

10.78

2.19

6

10.85

2.08

10.17

1.60

7

10.48

2.12

10.01

2.04

8

10.53

2.07

10.11

1.76

9

10.75

1.96

10.49

2.27

10

11.52

1.99

10.41

2.10

Generation

means

10.59

10.41

11.55

Generation 4

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

<T

Mean

o-

1

10.60

1.88

12.42

2.08

11.60

2.08

2

9.99

2.16

11.69

2.60

3

11.04

1.83

10.97

1.98

4

10.61

2.18

11.32

1.83

5

10.18

1.94

11.78

2.36

6

11.48

2.18

11.23

2.43

7

12.14

2.17

10.99

2.03

8

11.40

2.20

11.72

2.27

9

11.18

1.77

11.82

2.36

10

10.55

1.93

11.22

2.17

Generation

means

10.92

11.52

11.60

SELECTION WITHIN PURE LINES OF PESTALOZZIA

191

TABLE 13 (continued)
Generation 5

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

a

Mean

a

Mean

<T

1

11.82

2.46

11.93

1.96

11.55

2.43

2

12.22

2.08

10.95

2.44

3

11.60

1/98

10.51

2.31

4

12.42

2.38

11.13

2.67

5

11.64

2.17

10.54

1.96

6

12.33

2.12

11.52

2.14

7

12.39

2.22

11.17

2.35

8

12.19

2.30

10.26

2.46

9

12.04

2.43

11.15

2.28

10

12.33

2.63

10.45

2.37

Generation

means

12.10

10.96

11.55

Generation 6

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

a

Mean

a

Mean

a

1

10.96

2.57

11.79

2.36

12.57

2.34

2

11.92

2.36

11.47

2.31

3

11.91

2.13

11.39

2.30

4

11.04

2.31

12.40

2.21

5

11.60

2.16

12.00

2.37

6

11.50

1.90

11.08

2.18

7

11.80

2.60

11.88

2.41

8

11.58

1.86

11.82

2.47

9

11.19

2.61

11.20

2.31

10

11.93

2.61

12.02

2.84

Generation

means

11.54

11.71

12.57

GENETICS 7: Mr 1922

192

CARL DOWNEY LA RUE

TABLE 13 (continued)
Generation 7

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

CULTURE

Mean

<r

Mean

r

Mean

o-

1

12.11

2.16

11.86

2.34

12.45

2.30

2

12.34

1.98

3

12.08

2.25

12.29

2.58

4

12.10

2.27

12.36

2.22

5

12.49

2.74

6

12.16

2.35

12.14

2.15

7

11.87

2.31

11.94

2.25

8

12.38

1.86

12.35

2.44

9

12.25

2.13

12.25

2.10

10

12.30

1.65

11.82

2.20

Generation

means

12.18

12.16

12.45

Generation 8

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

tr

Mean

<r

1

11.58

1.99

11.84

2.09

11.65

2.18

2

11.72

1.96

11.91

2.20

3

12.47

1.94

10.68

1.74

4

11.41

2.26

11.92

2.05

5

11.42

2.12

12.08

2.14

6

11.71

2.17

12.03

2.09

7

11.51

2.22

12.34

2.02

8

11.39

2.24

11.23

2.19

9

11.95

2.15

12.04

2.33

10

10.81

2.18

11.87

2.30

Generation

means

11.60

11.79

11.65

SELECTION WITHIN PURE LINES OF PESTALOZZIA

193

TABLE 13 (continued)
Generation 9

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

CULTURE

Mean.

a

Mean

a

Mean

a

1

10.45

1.98

10.40

1.92

10.46

2.13

2

10.88

2.16

10.83

1.94

3

10.66

2.12

9.47

2.04

4

10.21

2.03

9.37

1.86

5

10.27

1.94

9.75

1.84>

6

10.05

2.00

10.30

2.06

7

10.59

2.23

9.85

2.15

8

9.70

2.02

10.13

2.17

9

9.95

1.74

10.32

2.02

10

10.63

2.16

10.81

1.93

Generation

means

10.34

10.12

10.46

Generation 10

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<T

Mean

<r

Mean

<T

1

9.07-

1.86

10.19

2.07

9.47

1.55

2

9.49

1.79

9.64

2.20

3

9.27

1.98

10.03

2.14

4

10.20

1.80

9.82

1.84

5

9.13

1.69

10.00

1.60

6

9.88

2.07

9.87

2.03

7

9.54

1.68

9.98

1.93

8

10.22

1.92

9.79

1.69

9

9.84

1.99

10

9.88

1.94

10.18

1.97

Generation

means

9.63

9.93

9.47

GENETICS 7: Mr 1922

194

CARL DOWNEY LA RUE

TABLE 13 (continued)
Generation 11

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

a

Mean

9

Mean

0-

1

10.82

2.09

12.60

1.93

2

12.30

2.25

3

12.07

2.20

4

11.32

2.14

5

11.33

2.17

6

12.23

2.19

7

11.99

2.07

8

11.75

2.10

9

11.46

2.02

10

10.95

1.83

11.87

2.13

Generation

means

11.62

11.87

12.60

Generation 12

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

a

Mean

<r

1

11.22

2.09

11.40

2.08

11.19

1.95

2

11.07

1.96

10.33

2.11

3

4

10.43

2.05

10.94

2.27

5

10.76

2.12

10.24

1.78

6

10.63

2.09

10.92

2.22

7

8

10.77

2.17

10.91

2.14

9

10

10.69

1.94

10.22

2.01

Generation

means

10.79

10.71

11.19

SELECTION WITHIN PURE LINES OF PESTALOZZIA

195

TABLE 13 (continued)
Generation 13

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

CULTURE

Mean

a

Mean

<r

Mean

<r

1

10.53

2.04

9.77

1.76

10.37

2.05

2

10.07

1.87

10.49

2.16

3

11.22

2.08

10.75

2.38

4

10.61

2.33

10.65

1.69

5

9.76

2.09

10.72

2.32

6

10.52

2.20

10.04

1.99

7

10.94

2.33

10.87

2.18

8

10.66

1.93

10.94

2.19

9

10.35

2.31

10.19

2.26

10

10.83

2.25

9.63

2.32

Generation

means

10.55

10.41

10.37

Generation 14

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

a

Mean

<r

Mean

a

1

11.48

1.92

10.58

2.15

10.33

2.10

2

10.47

1.76

12.16

2.17

3

10.64

1.82

4

10.74

1.83

10.33

2.13

5

11.98

2.55

14.85*

2.70

6

12.52

2.33

7

11.71

2.11

11.24

2.35

8

12.29

2.16

9

11.29

2.10

12.30

1.98

10

11.68

2.22

11.76

2.22

Generation

means

11.48

11.90

10.33

*Mutant.

GENETICS 7: Mr 1922

196

CARL DOWNEY LA RUE

TABLE 13 (continued)
Generation 15

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

<r

Mean

a

1

11.67

2.11

11.78

2.08

11.80

2.46

2

11.78

2.07

11.47

1.76

3

11.90

1.87

12.12

2.11

4

11.34

2.34

11.65

1.91

5

11.75

2.04

11.36

2.02

6

11.33

2.33

11.07

1.79

7

11.35

2.28

11.20

1.98

8

12.50

2.24

11.71

2.06

9

11.27

2.21

11.77

2.04

10

11.22

1.85

10.47

2.19

Generation

means

11.61

11.46

11.80

Generation 16

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

a

Mean

ff

1

11.37

2.08

10.86

2.05

11.00

2.45

2

11.52

2.10

10.41

2.09

3

10.50

2.07

10.79

2.21

4

11.57

2.01

10.82

2.26

5

11.27

2.07

10.55

1.97

6

11.49

1.98

7

11.17

2.33

11.25

1.96

8

11.76

2.25

10.73

1.73

9

12.09

1.78

10.22

1.65

10

11.77

2.04

Generation

means

11.45

10.70

11.00

SELECTION WITHIN PURE LINES OF PESTALOZZIA

197

TABLE 13 (continued)
Generation 17

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<T

Mean

<r

Mean

ff

1

10.70

1.98

9.97

1.63

10.34

1.81

2

9.83

1.82

10.60

1.93

3

10.36

1.77

9.92

1.87

4

10.46

2.01

10.09

1.75

5

10.61

1.92

9.88

1.80

6

10.32

2.16

10.37

1.87

7

10.17

1.72

10.01

1.73

.

8

10.87

1.67

10.17

2.00

9

10.01

1.83

10.60

2.21

10

9.80

1.96

10.29

1.86

Generation

means

10.31

10.19

10.34

Generation 18

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

CULTURE

Mean

<r

Mean

<r

Mean

<r

1

9.56

1.97

10.80

1.95

2

9.94

2.43

10.66

2.02

3

10.47

1.82

9.92

1.54

4

10.36

2.01

5

10.00

1.78

6

9.72

2.08

10.45

1.74

7

10.46

1.93

8

9

10.02

2.16

10.26

1.74

10

9.85

2.04

10.62

1.79

Generation

means

9.99

10.39

10.80

GENETICS 7: Mr 1922

198

CARL DOWNEY LA RUE

TABLE 13 (continued)

Generation 19

PLUS SELECTIONS

MINUS SELECTIONS.

INTERMEDIATE GROUP

Mean

<7

Mean

9

Mean

<r

1

11.60

1.74

11.37

1.89

2

11.49

2.08

11.41

1.97

3

11.12

2.02

11.22

1.97

4

11.14

2.16

10.85

1.99

5

11.12

2.18

10.72

1.69

6

11.49

2.07

11.71

2.11

7

11.69

1.96

11.91

2.28

8

11.61

1.98

12.30

2.04

9

11.44

1.99

12.15

1.98

10

11.79

2.18

Generation

means

11.49

11.57

11.37

Generation 20

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

a

Mean

<r

1

11.59

2.05

11.35

1.91

10.79

1.81

2

10.89

2.05

11.11

1.86

3

11.00

2.11

11.05

1.93

4

10.55

1.93

11.14

1.94

5

10.69

2.00

10.68

2.18

6

11.22

1.90

11.41

1.96

7

10.68

1.91

10.88

1.78

8

10.98

2.14

10.95

1.81

9

10.53

2.02

10.02

2.03

10

10.86

2.07

10.49

2.10

Generation

means

10.90

10.90

10.79

SELECTION WITHIN PURE LINES OF PESTALOZZIA

199

TABLE 13 (continued)
Generation 21

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

a

Mean

a

1

11.70

2.26

11.43

2.01

10.36

2.01

2

11.47

1.96

11.01

1.87

3

10.49

1.92

9.64

1.70

4

10.74

1.69

5

10.80

2.09

10.86

2.00

6

11.37

1.94

7

10.78

1.98

10.88

2.10

8

8.99

1.87

11.44

1.99

9

11.95

2.09

10.46

2.02

10

12.21

2.04

10.59

1.84

Generation

means

11.13

10.85

10.36

Generation 22

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

a

Mean

o-

1

11.76

2.07

11.96

2.00

10.58

1.94

2

11.22

2.10

10.85

1.99

3

11.14

2.00

11.39

2.33

4

11.06

1.74

10.75

2.26

5

10.66

1.74

11.21

1.74

6

11.11

1.95

11.76

2.32

7

11.37

2.15

12.16

2.20

8

11.42

2.14

11.56

1.67

9

11.38

2.14

11.30

1.87

10

11.04

1.83

11.80

2.30

Generation

means

11.22

11.47

10.58

GENETICS 7: Mr 1922

200

CARL DOWNEY LA RUE

TABLE 13 (continued)
Generation 23

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

(7

Mean

(T

1

11.37

2.02

10.89

1.95

12.13

2.28

2

10.80

.92

11.29

1.84

3

11.29

.77

10.96-

1.80

4

11.50

.80

10.82

1.81

5

10.94

.95

11.50

1.96

6

11.30

.83

11.53

1.77

7

11.44

2.05

8

10.98

1.90

11.28

1.86

9

10.98

1.91

11.56

1.88

10

10.87

1.82

11.46

1.99

Generation

means

11.11

11.27

12.13

Generation 24

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<T

Mean

cr

Mean

a

1

11.48

2.26

11.48

1.92

11.70

2.52

2

11.56

2.23

10.88

2.25

3

10.40

1.89

4

11.35

1.98

5

10.63

2.02

6

11.26

2.22

7

11.11

2.00

8

11.22

1.93

9

11.37

2.14

10

11.46

2.17

Generation

means

11.52

11.12

11.70

SELECTION WITHIN PURE LINES OF PESTALOZZIA

201

TABLE 13 (continued)
Generation 25

CULTURE

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

Mean

<r

Mean

a

Mean

a

1

2

10.33
10.45

1.62
2.00

10.90

1.91

3

11.45

2.23

4

10.44

1.91

5

10.58

2.17

10.46

1.96

6

10.91

1.87

7

10.72

1.85

8

10.87

2.31

9

10

Generation

means

10.73

10.68

10.90

Means of all cultures in experiment 2

PLUS SELECTIONS

MINUS SELECTIONS

INTERMEDIATE GROUP

11.330 + 0.469
<r = l. 06 + 0. 033

11.235 + 0.043
<7=0.97±0.030

11.39 + 0.126
<r=0. 034 + 0. 089

Difference between plus and minus selections =0.095 + 0.064

Difference between plus selection and intermediate group =0.060+0.134

Difference between minus selections and intermediate group =0.155 ±0.133.

GENETICS 7: Mr 1922

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GENETICS, MARCH 1922

TABLE OF CONTENTS

PAGE

MACDOWELL, E. C., The influence of alcohol on the fertility of white

rats

117

LA RUE, CARL DOWNEY, The results of selection within pure lines of

PestalozziaGuefini Desm 142

THE GALTON AND MENDEL CENTENARY

The year 1922 is notable as the centenary of the births of both FRANCIS
GALTON and GREGOR MENDEL. An international celebration of the centenary
of the birth of MENDEL is to be held in Briinn, Czechoslovakia, iu September,
and a portion of the scientific programs at the corning Convocation- Week
meetings in Boston, U. S. A., will be arranged as a memorial to GALTON and
MENDEL.

The coincidence of these two centenaries deserves to be signalized by the
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In asking all subscribers to contribute liberally to this FUND, the two fol-
lowing considerations may be pointed out: (a) GENETICS is not published to
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La Rue, C.D,

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