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Vegetative Vigor of the Host as a Factor Influencing

Susceptibility and Resistance to Certain Rust

Diseases of the Higher Plants

BY

MORRIS ABEL RAINES

A DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIRE-
MENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY, IN THE FACULTY
OF PURE SCIENCE, COLUMBIA UNIVERSITY.

Reprinted from the

AMERICAN JOURNAL OF BOTANY, Vol. IX, No. 4, pp. 183-203,
April, 1922, and No. 5* pp. 215-238, May, 1922.

Vegetative Vigor of the Host as a Factor Influencing

Susceptibility and Resistance to Certain Rust

Diseases of the Higher Plants

BY

MORRIS ABEL RAINES

A DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIRE-
MENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY, IN THE FACULTY
OF PURE SCIENCE, COLUMBIA UNIVERSITY.

Reprinted from the

AMERICAN JOURNAL OF BOTANY, Vol. IX, No. 4, pp. 183-203,
April, 1922, and No. 5, pp. 215-238, May, 1922.

[Reprinted from the AMERICAN JOURNAL OF BOTANY 9: 183-203, April, 1922.]

VEGETATIVE VIGOR OF THE HOST AS A FACTOR INFLU-
ENCING SUSCEPTIBILITY AND RESISTANCE TO
CERTAIN RUST DISEASES OF THE HIGHER
PLANTS'

i

M. A. RAINES
(Received for publication July 13, 1921)

INTRODUCTION

Studies on the cereal rusts were made covering various phases of the
phenomena of rust epidemiology, including the effects of season, age of the
host plant, etc., on its susceptibility and on the virulence of the disease;
effects of varying dosage in securing inoculation; effects of the general
nutritional condition of the host, etc. In carrying out these studies I have
had the opportunity to convince myself of the frequently observed fact that
health and vigor of the host favor rather than hinder its inoculation by a
rust and the further development of the diseased condition. This observa-
tion has frequently been made and more or less casually reported in the
literature on the rusts and other fungous diseases of plants. The significance
of such observations in relation to general theories of immunity and resis-
tance to disease has, however, nowhere been adequately recognized, and
I have thought it worth while to bring together the available evidence
bearing on this point.

It is a commonplace of pathological theory that the health and vigor of
an organism and its susceptibility to disease are antithetic variables, that
as one increases or is increased the other diminishes or is diminished corre-
spondingly. Adami (1910, A i: 409), summarizing the subject of predis-
position to disease, lists the causes of acquired susceptibility as (i) social
and environmental conditions; (2) injury; (3) malnutrition; (4) previous
attack of the same disease or other infectious disease; and (5) exhaustion;
all of them factors diminishing the vitality of the host. Zinnser (1914,
p. 59), discussing the broader principles of infection and resistance, states:

A person suffering from functional impairment of any kind is more likely to permit the
invasion of a pathogenic microorganism than is a perfectly healthy well-nourished indi-
vidual of the same species.

Kolmer (1917, p. 101) says, similarly:

Acquired susceptibility . . . may be due to various factors, most of which lead to a
state of reduced vitality, normal physiologic processes being impaired to a greater or less
degree.

1 The list of literature cited will be found at the conclusion of the second paper of
this series.

1 84 AMERICAN JOURNAL OF BOTANY [Vol. 9

Among plant pathologists, Jones (1905, p. 23) writes:

Disease resistance and vegetative vigor are closely associated, although the factors
involved are not necessarily identical. ... So far as the evidence goes it seems to suggest
that high vegetative vigor enables the plant to ward off in some degree the fungus attack.

In direct contrast with this view it must be noted that workers in the
field of the rust diseases of higher plants have on several occasions been
prompted to generalize to directly the opposite effect — that they found host
vigor and susceptibility to disease not antithetic, and not independent, but
parallel variables. Arthur (1903, p. 13), in a presidential address before
the Botanical Society of America, stated from his long experience with
plant rusts that

So intimate is the association of parasite and host that as a rule the vigor of the parasite
is directly proportional to the vigor of the host. Every culturist soon learns that to have
success in his work he must employ strong, rapidly growing plants. Even if he succeeds in
infecting weak plants, the fungus will rarely come to satisfactory fruitage.

Sheldon (1903, p. 74), summarizing his illuminating studies on the
asparagus rust, concludes:

Lowered vitality does not favor infection. . . . Whatever affects the growth of the
asparagus has a like effect on the rust.

Stakman, in his extensive studies on the cereal rusts, on several occasions
expresses similar views. Thus (1914, p. 40) he concludes that

These experiments show that whatever is conducive to the vigorous development of
the host is ordinarily conducive to the vigorous development of the parasite also.

And in another place (Stakman and Levine, 1919, pp. 75 and 76):

Deficiency of soil moisture and sunlight and other ecological factors affecting the host
plant unfavorably appear to be equally unfavorable to the rust parasite. . . . Adverse
environmental conditions unfavorable to the host are also unfavorable for the parasite,
affecting the virulence and spore size of the latter.

While the authors make their point incidentally and in no instance dis-
cuss their findings from the point of view of the general question of the
relation between host vigor and susceptibility in -infectious disease, it is
evident that the question is suggested as to the possibly special and, from
the point of view of the relation observed in the larger number of infectious
diseases of plants and animals, peculiar relation between vegetative vigor
of the host and susceptibility to infection in the rust diseases of the higher
plants. The demonstration of such a peculiar relation would be of the-
oretical interest as limiting and qualifying the universality of the commonly
accepted dictum that host vigor and virulence of disease are in inverse
relation and would be of profound import in defining the practical problem
of the prevention and control of the diseases concerned.

Apr., 1922] RAINES— VEGETATIVE VIGOR OF THE HOST 185

REVIEW OF LITERATURE

Physiological studies on the rusts have been reported almost entirely
from the point of view of a direct relation between the environmental factor
' concerned and the rust fungus, the essential intermediary between the two,
the host, being kept more or less indistinctly in the background.- A marshal-
ing of the available data on the physiology of the rusts from the point of
view of the present study, the possible correlation between host vigor and
virulence of the parasite, reveals a very general agreement in favor of the
concept that in the rust diseases of the higher plants there is a tendency for
the parasite to exhibit a higher incidence of infection and greater virulence
on the host of greater vegetative vigor. Similar instances in other classes
of plant diseases are cited in the general discussion.

Host Nutrition : Nitrogen Nutrition and Mineral Nutrients

Field Studies

Butler (1918, p. 73) describes the coffee leaf disease (Hemileia vastatrix
B. & Br.) as having first appeared on some of the best coffee in Ceylon, and
states that it is, in the case of this disease, considered as established that
fungous infection and growth occur better in strong leaves, rich in nutriment,
than in those with less food supply.

The greater susceptibility to rust of wheat grown on highly fertile land
has been noted repeatedly. Little (1883, p. 634) states that high manuring,
especially with nitrogenous manures, predisposes wheat plants to rust.
And Bolley (1889, p. 17) writes that

It is a matter of common note that soils rich in organic plant foods, such as low-lying
loams, are quite liable to produce rusted crops; and in England, where great quantities of
nitrogenous fertilizers are used, much has been said as to the liability of the crop to rust
upon fields to which such manures have been applied. Such observations go to confirm
the belief that soils excessively rich in nitrogen, either natural or applied, produce wheat
easily attacked by rust.

Freeman and Johnson (1911, p. 69), in their general review of the cereal
rust problem in the United States, state:

... It is now well established that where there is an excess of nitrogen in the soil,
other things being equal, grains are more severely attacked by rust than crops on soil con-
taining less nitrogen. . . . Where barnyard manures have been applied heavily the result
is similar, and where grains are grown after a crop of clover, beans, or vetch, rusts may be
expected. In fact it may be generally stated that where soils are rich in nitrogen, pro-
ducing rank and succulent plant growth, rust attacks will, as a rule, be most severe on
account of increased succulence of the plants, increased rankness of growth, delay in drying
out after showers and dews, and slight delay in the ripening period. On the other hand
phosphate of lime tends to shorten the ripening period and thus acts as a rust preventive
to some extent. ... In general, a rust attack is most virulent on a healthy plant.

Peacock (1911) states that rust in wheat and oats is favored by pre-

1 86

AMERICAN JOURNAL OF BOTANY

[Vol. 9.

disposition due to a too vigorous growth in early life. Biffen (1912), in his
studies on the inheritance in wheat of rust resistance to Puccinia ghimarum,
found that the rust is most virulent when a complete fertilizer is used, and
that the virulence of the disease decreases with a decrease in the amount
of fertilizer. Comparing the two principal types of asparagus soils in
California, the sediment and the peat, Smith (1905, p. 56) notes that aspar-
agus growing in the latter soil is considerably more damaged by the same
amount of disease. He comments that on peat formations, composed
almost entirely of vegetable matter and water, a very luxuriant, quick-
growing, tender, and succulent asparagus is produced.

Zavitz (1913) reports some very interesting observations on the relative
susceptibility to rust of oats grown under conditions of varying thickness
of seeding. The experiment was conducted through each of four years,
using both large and small seed of heavy-stooling, medium-stooling, and
light-stooling varieties of oats, and planting the seed of each variety in
squares one, two, three, four, six, eight, and twelve inches apart. Table I
is adapted from the data presented by Zavitz, and presents the average
results of thirty-two tests made by planting oats at seven different distances
apart. The results are the averages for four years.

TABLE i

Inches

Number of

Height

5£

Days

Relative Yield

per Plant

Per-

between
Plants

Heads per
Plant

in
Inches

centage
Lodged

to
Mature

Straw

Grain

centage
Rusted

I

1.0

20.4

5-6

91

100

100

II. 8

2

I.I

27.8

11.9

93

361

457

15.0

3

1.3

32.6

12.8

94

782

1,227

17.8

4

2.0

33-i

29.9

95

1,179

2,031

20.9

6

4-2

35-3

35-8

97

2,823

4,402

254

8

6-5

34-9 34-7

99

4,389

6,645

27.7

12

II. 2

34-9

30.1

100

8,475

10,320

33-2

The greater amount of rust observed with the increased distance between
plants is best correlated with the increased luxuriance of growth exhibited
by these plants. The difference of a week in the time of maturing between
the most closely spaced and the most liberally spaced oat plants is hardly
sufficient to account for the difference in the amount of rust infection.
Observations were made at frequent intervals through the summer, and
a rust difference due only to difference in time of maturity would not have
shown up in this fashion in the data. A more logical explanation is the
increase in the amount of lodging which closely parallels the increase in
percentage of rust from the one-inch spacing to the six-inch spacing. But
from the six-inch spacing to the twelve-inch spacing the amount of lodging
decreases appreciably while the percentage of rust increases further, indicat-
ing that the increase in the amount of rust is independent of lodging. There

Apr., 1922] RAINES — VEGETATIVE VIGOR OF THE HOST 187

is the strong suggestion, therefore, in Zavitz's data that the increase noted
in the amount of rust present on oat plants grown at progressively greater
distances apart is correlated with the increased luxuriance of growth of the
host plants.

Water- Culture and Sand- Culture Studies .

Ward (19020) details two experiments on the susceptibility to rust in-
fection of host plants which had been starved of essential nutrients. In
the first experiment, 54 young seedlings of Bromus secalinus were used.
The plants were grown in sand in 14 glass beakers, four to seven plants to
a beaker, and watered with solutions -of varying nutritive value. The
plants in one beaker received only distilled water. The plants in another
beaker received a cold-water extract of fresh horse dung, as a solution of
high nutritive value. In a third beaker the plants received a full mineral
nutritive solution (described as a "normal nutritive mineral solution con-
taining nitrates, phosphates, and sulphates of potassium, calcium, and
magnesium"). The remaining eleven beakers received an incomplete
nutrient solution, the elements omitted being respectively K; N; Mg; Ca;
P; Fe; N and Fe; Mg and Fe; Ca and Fe; P and Fe. Inoculation was
effected by applying uredospores of Puccinia dispersa to the leaves by means
of a swab of cotton; at the time of inoculation the seedlings were 16 days
old, counting from the time of sowing.

Ward records detailed observations on the stature, robustness, color,
and number of leaves of the seedlings in each beaker; on the time of appear-
ance, number, and size of the pustules developed on them, and on the
relative number of spores produced. Comparing the twelve seedlings
which showed the most vigorous growth (6 which received the extract of
horse dung, 3 the full nutrient solution, and 3 the full nutrient solution
minus Fe, the plants averaging 20 cm. in height) with the ten poorest plants
(4 receiving distilled water, 3 the full nutrient solution minus N, and 3 the
nutrient solution minus N and Fe, the plants averaging II cm. in height),
the observations recorded by Ward indicate that in the plants suffering
from malnutrition (i) the incubation period of the rust was lengthened by
one and two days; (2) the rust pustules were much smaller and produced
fewer spores. In other words, a starved host meant a starved parasite.
There is also the suggestion in the data that the starved seedlings showed
a lower incidence of infection; but the small number of variables worked
with, together with the large irregularity in dosage inherent in the method of
inoculation used, compel reserve in making this deduction.

A second experiment with 64 seedlings, duplicating the first, gave
similar results. Regarding the spores produced on well nourished and on
starved seedlings, Ward states that microscopic examination revealed no
differences. Spores from starved seedlings could produce infection on
other seedlings, similarly starved.

1 88 AMERICAN JOURNAL OF BOTANY [Vol. 9,

In 1905, Ward reports experiments indicating that starving the host
tissue after infection has taken place has an adverse effect on the growth
of the fungous mycelium. He cut off infected leaves of cereals on the third
day after artificial inoculation and floated them on water. Histological
examinations of the leaves indicated that the rust fungus in the tissues
continued to grow for a time, but soon showed signs of starvation.

Spinks (1913, p. 238) describes an experiment on the susceptibility to
Puccinia glumarum of wheat plants grown in water cultures. He used six
plants grown in each of three solutions: a standard nutrient solution (Det-
mer's) ; a nutrient solution containing four times the quantity of ammonium
phosphate; and a nutrient solution containing four times the quantity of
potassium chloride. The cultures were inoculated by applying uredospores
to the leaves; they were then set outdoors, so that further spread of the
rust occurred naturally. Spinks gives no data on the condition of the
plants, and this can only be inferred from the mode of treatment they re-
ceived. The data presented indicate that the plants growing in the nutrient
solutions containing a four-fold concentration of nitrogen were more sus-
ceptible than those in the standard solution. Excess concentration of
KC1 gave an apparent slight depression of susceptibility.

Stakman (1914, p. 39) reports some experiments with Puccinia graminis
tritici on wheat seedlings grown in water cultures. In an experiment in
which nitrogen and phosphorus were omitted from the culture solutions,
the check plants were more severely attacked than the experimental plants.
Summarizing his results, Stakman says (p. 48) :

It was found that in general the absence or presence in excessive amounts of various
nutrient substances, such as nitrogen and phosphorus salts, did not directly affect the
immunity or susceptibility of wheats. Conditions favoring a normal development of the
host were conducive to a vigorous development of the rust. The action of fertilizers, either
natural or artificial, is probably indirect.

Soil-Culture Experiments

Sheldon (1905, p. 226) remarks on the low susceptibility shown by
poorly growing carnations to artificial infection with Puccinia Caryophylli:

The results show that the plants that were making a vigorous growth were more sus-
ceptible to artificial infection than those that were making little or no apparent growth.
A few slowly growing plants were repeatedly inoculated without success until the plants
were given extra care and stimulated so that they began to grow more vigorously. Some
carnations, grown in small pots, were each inoculated five or six times at intervals of about
twenty days without any of the inoculations being effective. These plants grew very
slowly, were slender, and produced only one, or at most two, small blossoms.

In the same paper (p. 228) Sheldon reports an experiment on the length
of the incubation period of the carnation rust in which he inoculated simulta-
neously 170 pinks growing in soils of varying nutritive values. The plants
had been derived by taking sets of cuttings from the same stock plant, a

Apr., 1922] RAINES— VEGETATIVE VIGOR OF THE HOST 189

green-leaved pink known to be very susceptible to carnation rust, and they
were grown in five different soils ranging in composition from one that was
principally sand to one containing chiefly organic matter. Sheldon's ob-
servations indicated that the growth of the host varied directly with the
amount of organic matter, nitrogen, and silt in the different-soils ; and that
with increasec} vigor and growth of the host the incubation period of the
fungus decreased in length, from 21 days in the poorest plants to 16 days
in the most vigorous individuals.

Miss Gibson (1904, p. 188) describes an experiment on the effects of
nutritional treatment on the susceptibility ol certain varieties of chrysan-
themum to rust.

The young plants were then divided into four groups. A were fed as if for exhibition ;
B were grown normally; C were starved by being grown in small pots; and D were grown in
a warm greenhouse.

The rust developed on all the plants, but a luxuriant state of growth of
the host favored the greater development of the fungous mycelium.

Spinks (1913, p. 240) conducted an experiment on the susceptibility
to rust of wheat plants grown in pots receiving different nutritive solutions.
The data indicate somewhat higher susceptibility on the part of the plants
richly fed with nitrogen. Stakman (1914, p. 16) finds that high fertilization
of the soil increased the susceptibility to infection by Puccinia graminis
tritici of resistant varieties of wheat, and so concludes that high fertilization
is conducive to increased severity of rust attack on very resistant varieties
as well as on susceptible forms.

Indicating that the effect of specific nutrient substances is indirect,
secondary to their effect on the vigor of the host, is the observation by
Stakman and Levine (1919, p. 72) that an application of sodium nitrate,
excessive to the point of inhibiting the growth of the host, also inhibits the
development of the rust and diminishes very perceptibly the size of the
urediniospores. Ward (i9O2a) states that the size of the uredospores was
not affected by starving the host. Stakman and Levine arrived at their
observation that the size of the spores is affected by biometrical methods,
which would cause to stand out distinctly size differences not apparent on
gross examination. Ward does not give any spore measurements.

Host Nutrition: Carbon Metabolism

Intimate relation between the progress of a rust infection and the
carbon metabolism of the host tissue has been demonstrated by Ward
(1905), Fromme (1913), and Mains (1917). Sheldon (1903) studied the
effect of light and temperature on rust development, and Stakman and his
co-workers (1917, 1919) have studied quantitatively the effects of light on
the cereal rusts.

Ward (1905, p. 40) refers to experiments on cereal rusts indicating that

AMERICAN JOURNAL OF BOTANY [Vol. 9,

when, shortly after inoculation, the host is placed under conditions where
it cannot manufacture carbohydrates, as by keeping it in the dark or in
light from which the red-orange end of the spectrum is filtered off or in air
deprived of carbon dioxide, the development of the rust is inhibited.

Fromme (1913, p. 516) found that placing oat plants recently inoculated
with Puccinia coronifera in the dark for a period of several days increased
the length of the incubation peiiod of the rust by a corresponding interval.
Fromme interprets the observation to indicate that the fungus is dependent
for its nutrition on some intermediate product of photosynthesis.

Mains (1917, p. 191) confirms Fromme's observation that the develop-
ment of the crown rust of oats is retarded in the absence of light, and adds
that if the infected plant is left in the dark too long (which would greatly
impair the vitality and vigor of the host tissue) the rust is killed. Mains
also independently repeated Ward's observation that growing the host
plants in an atmosphere free from carbon dioxide inhibits the development
of the rust. Similar experiments with Puccinia Sorglii on seedling plants of
Zea Mays, however, failed to arrest the development of the rust. Further
experiments showed that if the host leaf is supplied with carbohydrates,
either from the reserve stores of the endosperm or by being floated under
aseptic conditions on a sugar solution, then the rust develops successfully,
even if, because of the absence of light or of carbon dioxide, the host tissue
cannot manufacture its own carbohydrates. Mains is therefore prompted
to qualify Fromme's inference that the rust is dependent upon intermediate
products of photosynthesis into the statement that the rust is dependent
upon transitory carbohydrates.

It does not necessarily follow from an observation that the development
of the rust is inhibited upon a plant starved of an essential nutrient—
whether carbon, or nitrogen, or potassium, etc. — that the rust fungus is
dependent for its nutrition upon compounds of that substance. As long
as the host plant is at all alive, or, even if it is dead, before disintegration
of its substance has set in, it contains carbon, nitrogen, etc., compounds,
and we cannot say that the rust could not develop because of the absence of
such compounds. Such observations are best interpreted on the basis of
the physiological condition of the host when it is starved of an essential
nutrient substance. We can not say that a host plant starved of an essential
nutrient is a host plant deficient in that particular class of substances; but
we can say that a host plant starved of an essential nutrient is a host plant
that is not assimilating, that is not growing, a plant in which anabolic proc-
esses are at a standstill and katabolic processes predominate. And we
are justified in inferring from the observed behavior of rust fungi on host
plants starved of essential nutrients that a plant which is not assimilating,
which is not growing, in which anabolic processes are at a standstill and
katabolic processes predominate*, does not make a congenial host for the
rust fungus. The suggestion that the rust is dependent for nutrition upon

Apr., 1922] RAINES — VEGETATIVE VIGOR OF THE HOST 19!

some particular class of substances within the host is strongest in the case
of the carbon compounds, because of the relatively large amounts of carbon
needed by the growing plant and because of the facility and exactness with
which the growth and vitality of the host plant can be experimentally con-
trolled through this phase of its metabolism.

Stakman and his co-workers have studied the light relations of Puccinia
graminis tritici inoculated on seedling plants of wheat. Stakman and
Piemeisel (1917, p. 487) state that a considerable amount of sunlight is
necessary for the best development of the rust. They found that during
periods of cloudy weather the incubation period may be lengthened a week
or more, and that the rust does not develop so abundantly as during bright
weather. Shaded plants invariably were more weakly infected than the
others. Partially etiolated plants were infected with difficulty, and 'the
rust developed very weakly on them. No rust developed on etiolated
plants. Stakman and Levine (1919, p. 71) found that the rust developed
considerably better in fairly high intensities of light than under conditions
of less favorable illumination. The size of the urediniospores responded in
a similar manner. They summarize their observations on the light relations
of the rust as indicating that

... In as much as the photosynthetic activities of the host plant are affected by the
light intensity, in so much does the structure and function of the rust depend on the same
factor.

Water Relations

While many observations have been made on the relation of moisture
conditions of soil and air to rust virulence on plants in the field, they are
subject to criticism in that they do not distinguish between the effect of the
moisture conditions on uredospore germination and penetration, and the
effect on the vigor of the host and the progress of the rust infection in its
tissues. Abundant moisture is always favorable to uredospore germination
and infection, but the effect on the physiology of the host is specific for the
plant. Abundance of moisture will favor the growth of a mesophyte, but
it will have a depressing effect on the vigor of a plant of xerophytic tend-
encies. Limiting ourselves, therefore, to observations when inoculation
was artificially effected under conditions of maximum atmospheric humidity,
the evidence permits the inference that the moisture conditions of at-
mosphere and soil most favorable for the growth of the host plant are
likewise optimum for the growth and sporulation of the rust.

The most complete and suggestive experiment is reported by Stakman
(1914, p. 35). Wheat plants of both drought-resisting varieties and or-
dinary mesophytic types were employed, and they were grown in two series.
The soil in one series was kept very wet, while that in the other series was
kept as dry as possible without endangering the life of the plants. On
inoculation with rust, the drought-resisting forms exhibited better infection

IQ2 AMERICAN JOURNAL OF BOTANY [Vol. 9.

in the dry soil', while the mesophytic types showed slightly greater virulence
of disease in the moist soils. Repeated trials were made with substantially
the same result. Stakman concludes:

It is probable then that, conditions having been favorable for a rust infection, the water
relation in the soil which is most favorable for the host plant's development is also the most
favorable for the development of the rust.

Mains (1917, p. 189) found that the development of P. Sorghi on corn,
as shown by the number of pustules produced, is favored by a humid at-
mosphere and by a wet soil — conditions favorable to the growth of the
corn plant. The length of the incubation period was not appreciably
influenced.

Stakman and Levine (1919, p. 45), in experiments to determine the
length of time that wheat seedlings inoculated with P. graminis tritici
should be kept in a saturated atmosphere in order to obtain maximum in-
fection, found that keeping the plants under a bell jar for more than 48
hours reduced the amount of infection obtained and appreciably lengthened
the incubation period. In other experiments (p. 70) they noted a tendency
for excessively high or excessively low humidity during the incubation
period to cause a decrease in the size of the urediniospores. In another
experiment on soil moisture (p. 71) in which three series of plants were
employed, one of which was heavily watered, the second moderately, and
the third received only enough water to prevent the plants from wilting,
Stakman and Levine found that the plants in the wet soil were more severely
attacked and that the urediniospores developed on them were larger than
those in the other two series. The plants that suffered from drought pro-
duced the smallest spores. The authors conclude as a result of their study
on the effect of environmental factors on the morphology of the uredinio-
spore of Puccinia graminis tritici that deficiency of soil moisture and of sun-
light and other ecological factors affecting the host plant unfavorably ap-
pear to be equally unfavorable to the rust parasite.

Temperature Relations

There is abundant evidence of a tendency towards physiological par-
allelism of host and rust in their temperature relations.

Sheldon (1903, p. 33) studied the relation between greenhouse tempera-
ture and hours of sunshine per day, and the length of the incubation period
in the asparagus rust. His experiments extended over a period of five
months, from December, 1900, to May, 1901, and yielded data on 132
asparagus plants. The results indicate an inverse relation between the
temperature and light conditions under which the host was growing and the
incubation period of the rust. During December and January the length
of the incubation period was regularly 14 to 17 days. During April and
May, when the day was longer, the light better, and the temperature
higher, the length of the incubation period was only 8 to 10 days.

Apr., 1922] RAINES — VEGETATIVE VIGOR OF THE HOST 193

Similar experiments with the carnation rust (Puccinia Caryophylli on
Dianthus sinensis) gave opposite results. The incubation period increased,
from 15 days in January to 21 days in May. In explanation, Sheldon
suggests the possibility that the temperature and light in the greenhouse
were better suited to the asparagus than to the pinks. In Bailey^s Cyclopedia
of Horticulture (1914, p. 670) the. carnation is characterized as a cool-tem-
perature plant.

Several observers comment on the lengthening of the incubation period
in cold weather, and the difficulty of obtaining infection in very warm
weather. Christman (1905, p. 106) found that in the cooler weather of
spring in Wisconsin the incubation period of cereal rusts is usually lengthened
to between three and four weeks. Ward (1902^, p. 233) remarks that, in
working with the brown rust of the bromes, he found infection difficult to
carry out in hot weather; and in a succeeding paper (1905, p. 41) he re-
peats and emphasizes the significance of the observation. In this paper
(P- 39) » Ward also refers to experiments in which the normal development
of the rust was interfered with by warming and chilling the root system of
the host plant. Butler and Hayman (1906) describe unsuccessful efforts to
produce artificial rust infection on plants growing in the open in the hot
weather in India, and express doubts whether the uredospores have power
to infect when exposed to temperatures exceeding 100° F. Fromme (1913)
found that temperatures below 20° C. increased the incubation period of
Puccinia cor on if era on oats.

Stakman (1914, p. 30), in his culture work with cereal rusts, observed
the incubation period to vary with temperature conditions, both high and
low temperatures lengthening the period very perceptibly. Mains (1917,
p. 187) observed that low temperatures retarded the development of P.
coronata and P. Sorghi in the host. Stakman and Levine (1919, p. 68)
report the optimum temperature for P. graminis tritici to be between 66.5°
and 70° F., this giving the shortest incubation period, the most vigorous
infection, and the largest urediniospores, for the host employed. At a
higher temperature than 70° F. the development of the uredinia was re-
tarded at the rate of one day for every 10 degrees' rise in temperature, but
rust developed at as high a temperature as the host endured although the
size of the urediniospores produced was considerably decreased. At low
temperatures the development of the uredinia was retarded at the rate of
one day for every 5 degrees' fall in temperature. Infection resulted at as
low temperatures as the host could stand. The spores at the lower tem-
peratures were rather small, but the difference was not as great as in the
case of the high temperatures, with moderate temperatures as the basis for
comparison.

Lauritzen (1919, p. 19) reports experiments indicating that 42° F. is
below the minimal temperature at which P. graminis tritici is able to infect
wheat. Above this temperature the amount of infection rises rapidly until

194 AMERICAN JOURNAL OF BOTANY [Vol. 9,

at 53° F. it approaches the average for the higher temperatures. The
highest temperature at which the rust will produce infection in wheat was
found to be 80° F. under the conditions of the experiments. The figures ob-
tained by Johnson (1912) are cited in evidence that it is not failure of the
spores to germinate which determines the infection limits observed in the
experiments. Johnson (p. 48) found the optimum temperatures for the
germination of the uredospores of the common cereal grain rusts to be low
—12° to 17° C. — helping to explain such observations as the difficulty of
keeping rust in culture in the greenhouse in the summer, when the incubation
period of the rust is shorter than at any other time of the year but it is re-
markably difficult to obtain infection ; the difficulty of finding viable uredo-
spore material in the spring, the larger number of the spores having already
germinated; and the favoring of rust development and epidemics by sub-
normal temperatures at the critical infection periods in the life of the host
plants.

Stimulants and Depressants ; Toxic Agents

Observations on chemical and physical agents stimulating or depressing
the vitality of the host plant indicate that susceptibility to rust infection
is affected in like manner.

Sheldon (1903, p. 44) found that in the case of the asparagus rust and
the cai nation rust complete immunity to infection can be produced by
lowering the vitality of the host — an end the failure to achieve which in
the case of the brown rust of the bromes caused disappointment to Ward.
Concerning the asparagus rust, Sheldon states (p. 44) :

Attempts have been made repeatedly not only on asparagus but on several species of
pinks, to inoculate them when they are not growing well. It was tried on repotted plants,
those attacked by insects, and young seedlings. A failure was the result in nearly every
case; while with vigorous, growing plants which had become established there were few
failures — thirty-seven out of forty-two inoculations made at one time being successful in
one instance — approximately 90 percent.

In his experiments with the carnation rust Sheldon (p. 83) found attacks
by thrips a very disturbing factor, as it was almost an impossibility to
secure infection where the thrips had worked to any extent either before or
after inoculation, while vigorously growing plants which were free from
thrips were readily inoculated.

Spinks (1913, p. 243) and Voelcker (1912, p. 319) have made observa-
tions on the susceptibility to rust of the wheat plants grown in the pot-
culture experiments on the fertilizing effects of small quantities of the salts
of the heavy metals conducted at Woburn, England. They found that
the lithium salts of the 1911 experiments depressed susceptibility, with the
exception of lithium nitrate which gave increased susceptibility to rust.
The experiments of 1912 were with zinc salts, and they were all found to
produce increased susceptibility to rust, zinc nitrate seeming particularly
notable in this respect.

Apr., 1922] RAINES- — VEGETATIVE VIGOR OF THE HOST IQ5

Stakman (1914, p. 15) increased the susceptibility of cereals to rusts
to which they are ordinarily highly resistant by slight anaesthetization with
ether and chloroform. Jost (1907, p. 195) states that weak etherization
accelerates respiration, and such treatment is usually considered as stimulat-
ing the metabolism of the plant. Stakman (1914, p. 39) also describes an
experiment in which it was sought to influence the susceptibility of wheat
plants grown in water cultures by introducing various salts into the culture
solution. Copper sulphate, copper carbonate, and iron sulphate were
added in varying amounts. The results showed that none of the salts ex-
perimented with appreciably decreased the amount of rust when used in
such concentration as to permit the normal development of the host plant.
Infection was secured on all the plants, even those which were stunted to
one sixth their normal size.

Eriksson and Hammarlund (1914) report partial success in delaying
and inhibiting the development of Puccinia malvacearum on Althea rosea
by treating the soil with a 3 to 5 percent solution of copper sulphate. They
give no data on the vigor of the plants.

Bailey (1920, p. 76) found that hollyhock plants stunted by red spider
showed comparative immunity to rust.

Trauma

There are only two recorded experiments on the effect of trauma on
susceptibility to rust; they do not agree in their findings. Trauma usually
has an immediately stimulating effect on the metabolism of a plant tissue
and might be expected to increase susceptibility to rust. Hecke (1915)
mentions that Barfuss working in his laboratory has demonstrated that
wheat rust, which ordinarily does not go to rye or barley, readily infects
rye and barley leaves if they have previously been injured. After cultivat-
ing the rust for seven generations on wounded leaves, Barfuss succeeded in
definitely obtaining infections on uninjured leaves; but these did not mature
spores. The rust did not lose its power to go back to wheat. This is much
after the manner of Salmon's work in increasing the susceptibility of re-
sistant host plants to Erysiphaceous parasites.

Similar efforts to these by Stakman, also working with cereal rusts,
gave negative results. Stakman (1914, p. 16) found leaf injury to have no
effect on susceptibility to rust.

In one experiment 16 leaves were pricked full of holes in an area of one centimeter or
more. They were then inoculated and 4 became flecked, but no pustules developed.
Histological examination showed that the spores had sent out germ tubes in large numbers.
These grew among the host cells, but true infection did not take place. Sections of these
plants were made and examined. It was clearly evident that leaf injury did not increase
the chances for infection.

196 AMERICAN JOURNAL OF BOTANY '[Vol 9.

Age and Maturity of Host Tissue

In his experiments with the asparagus rust Sheldon (1903, p. 47) found
a great difference in susceptibility in favor of young and vigorously growing
shoots as against older shoots of the same plant. His observations indicated
that

The incubation period of the rust on plants of the same age and growing in the same
pot so that conditions were practically identical, was very uniform. When the plants were
of the same age and growing in the same kind of soil in different pots, there was still a uni-
formity. But when there was a difference in maturity, as of two shoots from the same
root, or several plants growing in the same pot, there was a difference in the time — of four
days in one instance, the young growing shoots showing sori first. The sori showed first
on the young growing shoots, and developed faster and to larger size. The more robust
the shoot, the larger the sori were and the more spores they produced.

Sheldon found practically no difference between young shoots of young
and old plants. A few shoots from three-year-old plants growing in the
same pots showed rust the same day that the seedlings did. Sheldon made
similar observations on the carnation rust.

An age factor of a different kind is reported by Sheldon (1905, p. 227)
in the susceptibility of onions to Puccinia Asparagi. Complete immunity
was found when seedling onions were inoculated with the rust. The inocu-
lations were begun as soon as the seedlings appeared above ground, and
were repeated at intervals until the seedlings were two months old, when
almost every inoculation was successful.

Galloway (1903, p. 208) reports a maturity factor as seemingly affecting
the susceptibility of wheat to rust. In his extensive experiments on the
possibility of controlling cereal rusts by means of spraying or soil treatment,
Galloway found that the rust, while abundant on the primary experimental
plots, was absent from nearly all the duplicate plots. The latter had been
planted a week to ten days later than the oiiginal plots, and in point of
growth were at least as much behind them at the time of observation. As
the experiments were with a winter wheat, planted the preceding fall, it
cannot have been that the plants of the duplicate plots had missed a wave
of inoculating material.

Miss Gibson (1904, p. 188) reports the presence of a seasonal factor in
the susceptibility of certain varieties of chrysanthemum to the chrysan-
themum rust. She noticed that certain varieties do not take the rust in
summer, although growing in the midst of plants thickly covered with it.
As the rust spores germinate well in summer and the germ tubes penetrate
readily, it is a problem not in the physiology of the parasite but rather in
that of the host.

Stakman and Piemeisel (1917, p. 486), in their extensive inoculation
work with cereal and grass rusts, found the cereals and Dactylis glomerata
apparently equally susceptible at all ages up to ripening time. Agropyron
and Elymus were extremely susceptible when young and much less so when

Apr., 1922] RAINES VEGETATIVE VIGOR OF THE HOST 197

older. On the other hand, Phletim pratense and Agrostis alba were more
susceptible when older.

Stakman and Levine (1919, p. 73) observed an age difference in the
progress of an infection of P. graminis avenae on oats. Plants that were
one week old at the time of inoculation were somewhat more heavily in-
fected at first than plants one, two, and four weeks older; but at the end of
ten days the infection was heavier on the older plants, especially so on the
plants that were three weeks old at the time of inoculation. The size of
the urediniospores was uniform regardless of the age of the host, nor was
any difference observed in the shape and color of the spores. They also
state that

. . . the junior author has obtained very successful infection on mature plants of more
than a hundred different varieties of wheat, grown in the greenhouse and artificially inocu-
lated with P. graminis tritici.

Giddings (1918, p. 33) found susceptibility in apple leaves to infection by
Gymno sporangium juniperi-mrginiana to be limited to young leaves, not
more than fifteen to twenty- four days old after unrolling from the bud,
older leaves being almost completely resistant. H. H. York (personal
communication) has found that the very young leaves of Ribes are resistant
to infection by Cronartium ribicola, susceptibility not appearing until some
time after the unfolding of the leaf.

The factor of age and maturity of host tissue is reviewed here briefly
because of its close association in thought with vegetative vigor. There is
no necessary physiological connection between the two factors, and their
significance in susceptibility and resistance to rust infection is probably of
a different nature. The age factor in disease resistance is probably to be
classed rather with varietal and constitutional differences than with physi-
ological condition.

FIELD STUDIES AND EXPERIMENTS

A series of studies was made to determine the general facts as to the
occurrence and epidemiology of the rusts on the cereal grains in the so called
local-flora region of New York, and especially for the New York Botanical
Garden and vicinity. Data as to the points involved were found to be
very meager, and these preliminary studies were made as a contribution to
the general problem of rust epidemiology in the Atlantic States, a field so
far little studied because of the relative unimportance of grain growing in
these regions. More especially also it was desired to lay a foundation for
future studies of rust problems which presuppose a knowledge of the general
behavior of the rusts under the climatic and other conditions of the region.

The Rusts of the Cereal Grains and Related Grasses
in the Vicinity of New York

The time of first appearance, period of greatest virulence, and even the
identity of the rusts on the cereal grains and related grasses which have been

198 AMERICAN JOURNAL OF BOTANY [Vol. 9,

suspected of harboring cereal rusts in the vicinity of New York City cannot
be regarded as accurately determined.

The herbarium of the New York Botanical Garden contains 17 col-
lections of four different species of rusts on cereal grains and grasses which
might bear related rusts from the region about New York City, the so called
local-flora region, as follows:

Puccinia rubigo-vera DC. (Puccinia dispersa Eriks. & Henn. ex parte):
On wheat, at Cedarville, N. J., June 3, 1880. Ellis collection (II).
On rye, at Flatbush, L. I., May 25, 1889, by Zabriskie (II).
Puccinia poculiformis (Jacq.) Kuntz (Puccinia graminis Pers.):

On wheat, at Greencastle, Putnam Co., N. Y., September, 1893, by L. M. Underwood

(II, HI).
On oats, at Greencastle, Putnam Co., N. Y., September, 1893, by L. M. Underwood

(II, HI).
On oats, at the New York Botanical Garden, October, 1900, by the class in mycology

(II, HI).

On Anthoxanthum odoratum, at Newfield, N. J., May 4, 1890. Ellis collection (III).
On Ammophila brevipile Torr., at Egg Harbor, N. J., 188-, by S. M. Tracy (III).
On Agrostis vulgaris L., at Plainville, Conn., August 23, 1883, by A. B. Seymour

(II, HI).
On Poa pratensis L., at Greencastle, Putnam Co., N. Y., September, 1893, by L. M.

Underwood (III).

On Berberis vulgaris L., at Newfield, N. J., May 24, 1875. Ellis collection (I).
On J). vulgaris, at Newfield, N. J., May, 1881. Ellis collection (I).
On B. vulgaris, at Richmond Hill, L. I., May 22, 1889, by S. E. Jelliffe (I).
Puccinia andropogonis Schw. :

On Aureolaria villosa (Muhl.) Raf. (Gerardia villosa Muhl.), at Newfield, N. J., June,

1874, by Gerard (I).

On Gerardia quercifolia Pursh., at Westville, Conn., June, 1890, by R. Thaxter (I).
Puccinia Ellisiana Thum.:

On Andropogon sp., at Newfield, N. J., September, 1897. Ellis collection (III).

On Andropogon Scoparius Michx., at New Haven, Conn., October 4, 1913, by J. M.

Bates (III).
On Viola pedata L., at New Haven, Conn., May 31, 1841, by Manlius Smith (I).

I have also found the following notes on the occurrence of these forms
in the local-flora region. Peck (1871, p. 121), in his list of the Pucciniae of
New York State, lists P. coronata Cord, as common on the leaves of grasses
and cereals in August and September, and P. graminis Pers. as common on
the leaves and sheaths of grasses and cereals in autumn and spring. Thaxter
(1890, p. 98) notes the abundant occurrence of P. rubigo-vera DC. (probably
P. dispersa Eriks. and Henn.) on rye in Connecticut in the year 1890,
describing it as covering the leaves with its rust-covered uredo form and
doing considerable damage.

Humphrey (1891, p. 228) remarks on the occurrence of rust (Puccinia
sp.) on rye in Massachusetts in 1891. He records some interesting obser-
vations on the mode of wintering over of the fungus. The rust, he notes,
appeared on rye in June so abundantly that the spores rose in clouds when
the plants were touched. In July this stage of the fungus had largely

Apr., 1922] RAINES — VEGETATIVE VIGOR OF THE HOST

disappeared, and the winter pustules were mainly in evidence. Observa-
tions seemed to indicate that the rust does not survive the winter in its
host plant but depends upon fresh infection in the spring on the plots of the
Massachusetts Agricultural Experiment Station. In this connection Hum-
phrey notes that uredosori on rye seedlings survived the early frosts and
seemed vigorous until the heavy frosts and snowfalls. The plots were then
covered with snow until spring. When they were again exposed, the dis-
colored spots where the pustules had been could be readily observed, and
examination showed mycelium to be present in the spots; but it was appar-
ently dead, for repeated examination of the plot failed to detect new spores
breaking out from any of the old spots. The fungus was not observed after
growth was resumed until early in June.

Jelliffe (1889, p. 35) reports Puccinia graminis Pers. on the barberry
and on wheat as of frequent occurrence throughout Long Island. Clinton
(1903) reports the occurrence in Connecticut of P. rubigo-vera DC. (probably
P. dispersa Eriks. & Henn.) on rye and barley, of P. graminis Pers. on rye,
barley, oats, red-top, and timothy, and of P. coronata Cord, on the leaves of
Rhamnus cathartica, Notoholcus lanatus, and Avena saliva. The outbreaks
of the last, Clinton notes, are not nearly so prolonged or prominent as those
of P. graminis. Burnham and Latham (1914) report finding P. coronata
Cord, on the leaves of Rhamnus cathartica, Notoholcus lanatus, and Avena
sativa at Sothold, L. I. They also report the occurrence there of P.
graminis Pers. on Berberis vulgaris and on the leaves of various grasses, and
of P. triticina Eriks. on various species of Triticum.

During the summer and fall of 1916 the writer collected the following
cereal and grass rusts in the so called "local-flora region," i.e., the region
within one hundred miles of New York.

Puccinia dispersa Eriks. & Henn.:

On wheat, five collections: at Lakehurst, N. J., June 6 (II) and August 23 (II, III);
at Yonkers, N. Y., July 16 (II); at New Brunswick, N. J., July 24 (II); at Williams-
bridge, N. Y., July 19 to September (II, III); at the New York Botanical Garden,
July 17 to October (II, III).

On rye, eight collections: at Tom's River, N. J., June 3 (II, III); at Lakehurst, N. J.,
June 20 (II, III); at Yonkers, N. Y., July 16 (II); at Queens, L. I., June 15 (II);
at New Brunswick, N. J., July 24 (II); at Williamsbridge, N. Y., July 19 (II);
at the New York Botanical Garden, July 17 to October; at Nyack, N. Y., July 8
(II).

On barley, two collections: at Williamsbridge, N. Y., September 13 (II); at the New
York Botanical Garden, September 15 (II).

On Agropyron repens, three collections: at Tom's River, N. J., July 4 (II); at Williams-
bridge, N. Y., July 19 (II); at the New York Botanical Garden, July 8 to October
(II, HI).

These rusts correspond closely with Eriksson and Henning's Puccinia
dispersa (Puccinia rubigo-vera DC. pro parte). The uredo of the above-
listed collections is amphigenous. The number of pustules on the upper
surface is somewhat in excess of that on the lower surface, counts on pieces

2OO AMERICAN JOURNAL OF BOTANY [Vol. 9.

of leaf I cm. in length giving the numbers 174 to 158, and 217 to 195 re-
spectively. The sori on the upper surface are more pulverulent.

The uredos on the wheat, rye, and Agropyron were certainly not dis-
tinguishable by morphological characters. The pustules on the barley
show very little pulverulence. Measurements of the pustules on the barley
(measurements being made on the size of the rupture in the epidermis)
show them to be of the same size as the pustules on the other hosts of P.
disperse, . The spores of the barley rust are narrower than those on the
other cereals. Twenty-five spores gave an average ratio of length to width
of 1. 218. Seven such measurements on wheat gave ratios ranging from
1.083 to 1.163.

Puccinia graminis Pers. :

On Phleum pratense, at Tom's River, N. J., August 23. Only II was found on this
host, as others have noted.

On oats, at Tom's River, N. J., August 23 (II, III); at Williamsbridge, N. Y., August
16 (II, III); at the New York Botanical Garden, August 26 (II, III). The rust
was never abundant, occurring as a thin sprinkling on the leaves and sheaths
among the crown-rust sori, and on the culms. The long, rectangular, erumpent
teleutosori are very conspicuous scattered among the mass of smaller, covered sori
of the crown rust.
Puccinia coronifera Kleb. :

On oats, at Williamsbridge, N. Y., August 2 to September (II, III); at the New York
Botanical Garden, August 12 to October (II, III); at Tom's River, N. J., August 23
(II, HI)-

The crown rust of the present collections differs in some minor particulars
from the published descriptions I found it somewhat later in its appear-
ance on the sheath, but both uredo and teleuto in the end are as abundant
on the sheath as on the leaf blade. Eriksson and Henning (p. 240) found it
" rarely on the sheath." Both the uredo and the teleuto occur in abundance
on the lower and the upper surfaces of the leaves, but the uredo is always
in excess on the upper surface while the teleuto first appears and is always
in advance in its development on the under surface. Grove (p. 256) and
Fischer (p. 375) describe the teleuto as hypophyllous. The most con-
siderable discrepancy between the descriptions of Grove and Plowright and
the rust here described is in the number of the germ pores. Five spores of
which the germ pores were counted showed respectively 9, 9, 9, n, and 8
pores. The germ pores as well as the spines are inconspicuous until brought
out by treatment with lactic acid. Grove (p. 256) and Plowright (p. 164)
describe the germ pores as 3 to 4 in number. Fischer (p. 275) simply icfers
to them as inconspicuous, and Eriksson and Henning (p. 240) do not men-
tion them in their description of the crown rust.

Puccinia impatientis (Schw.) Arth.:

On Elymus virginicus L., at Valley Stream, L. I., August 12 (II); at Hackensack, N. J.,
September 18 (III); at the New York Botanical Garden, June to October (II, III).

At the last-named station Impatiens aurea Muhl. near by was infected

Apr., 1922] RAINES — VEGETATIVE VIGOR OF THE HOST 2OI

with an aecidium. The uredospores of this form are markedly less rounded
and the teleutosori are much longer than in the case of the wheat and rye
rusts as I have found them. The rust on Elymus has, however, been classed
with P. rubigo-vera DC.

Puccinia poculiformis:

On Cinna arundinacea, at Jerome Avenue, New York City, September 15 (III).

An Experiment to Determine the Time and Method of First Appearance of

the Rust, in which the Source and Condition of the Seed

as Possible Factors are also Tested

In investigations of a physiological nature on the cereal rusts it is de-
sirable that the probability be established that, for the variables being
compared, the source of the fungus being worked with is constant. This
point in experimental method assumes particular importance, in investiga-
tions such as are the subject of the present paper, from the recent demon-
stration of the variation in physiological properties of strains of rust from
different localities. Assuming that the rust endemic in any locality is
fairly constant in its behavior (whether the constancy is due to actual
genetic purity, or to an admixture of strains in constant proportions), a
possible source of error would be the seed transmission of the rust, making
the source and condition of the seed a factor in determining the nature of
the rust. Critical evidence on the question of the role played by the seed
in the first appearance of rust on cereals in early summer is still lacking.
As against the feeling of necessity, almost, in the minds of some investi-
gators, of the assumption of seed transmission of the rusts in explaining
certain phenomena in the epidemiology of these diseases, must be counted
the inability to demonstrate with certainty a means of transmission, or to
observe seed transmission of cereal rusts under controlled experimental
conditions.

To test the possible role played by the seed in determining the first
appearance of rust under field conditions in the vicinity of New York, 25
patches of wheat, 8 patches of barley, one patch of rye, and one patch of
oats were planted with seed from widely different sources, and of varying
age and condition on a plot of ground near the New York Botanical Garden.
The plantings were made on high, well drained land which had not been
cultivated since 1912, when it had been put to corn. The nearest plot of
cereal was a field of oats about one quarter mile away, and there were no
other grain fields within a distance of one mile at least. It is not thought
that this single experiment is of very great significance as to the general
question of possible seed transmission of rust. It is of interest, however,
to include such inferior seed as that planted in the first three plots in a test
as to the time of appearance of the rust.

The varieties planted, the source of the seed, and the date the rust first
appeared on the plants are shown in table 2.

;

202

AMERICAN JOURNAL OF BOTANY

[Vol. 9,

TABLE 2
(The designations "screening wheat," "smutted wheat," etc., are the millers' terms)

Plot
No.

Cereal
Planted

Variety

Source of Seed

Date Rust First
Appeared

I

Wheat

"Rusted wheat"

Fargo Milling Co., Fargo, N. D.,

1915

July 19

2

11

"Smutted wheat"

Washburn-Crosby Co., Minneapolis,

Minn., 1915

t I

3....

ii

"Screening wheat"

Fargo Milling Co., Fargo, N. D.,

I9I5

4....

ii

Haynes Bluestem

Arlington Station, 1912

5....

"

Minnesota no. 163

Akron Substation, 1912

6....

«

no. 163

Arlington, 1912

7....

n

no. 188

Minn. Exp. Station, 1912

8....

«

no. 181

Minn. Exp. Station, 1912

9....

«

no. 169

Minn. Exp. Station, 1912

10

"

Rural New Yorker

Arlington Station, 1912

ii

4<

Early Genesee Giant

Akron Substation, 1912

12

11

Dawson's Golden

Chaff

Arlington Station, 1912

13....

ii

Early Red Chief

Arlington Station, 1912

14....

"

Seneca Chief

Wis. Exp. Station, 1912

IS----

11

Fish-head

Minn. Exp. Station, 1912

16....

11

Red Russian

Akron Substation, 1912

17

"

Amantka

Akron Substation, 1912

18....

"

Galgalos

Akron Substation, 1914

19....

i

Little Club

Arlington Station, 1913

20

<

Wasnani

Akron Substation, 1913

21

<

Erivan

Akron Substation, 1913

22

<

Ghanooka

Wis. Exp. Station, 1912

23

1

Beloturka

Akron Substation, 1912

24....

'

Macaroni

Wis. Exp. Station, 1914

25

1

Rupert's Giant

Thorburn Co., 1916

26

Rye

Spring

Thorburn Co., 1916

27....

Oats

Tartar King

Thorburn Co., 1916

August 2

28....

Barley

White Smyrna

Akron Substation, 1912

Sept 13

29....

«

Chevalier

Minn. Exp. Station, 1912

30. ...

ii

Black Hulless

Hays Exp. Station, 1913

SI.--

a

White Hulless

Hays Exp. Station, 1913

32....

11

Swankali

Minn. Exp. Station, 1912

33----

"

Telli

Arlington Station, 1912

34....

a

Gaitami

Arlington Station, 1912

35--.-

ii

Wis. Fed. no. 5

Minn. Exp. Station, 1913

As the table shows, the rust appeared simultaneously on all the plots of
wheat and barley respectively. It appeared at the same time on a resistant
variety such as the Macaroni wheat and on a susceptible variety such as
Rupert's Giant; on plants grown from seed coming from North Dakota
and on plants grown from seed coming from Maryland; on plants from
good, plump seed and on plants grown from seed rejected by the miller,
such as the "rusted wheat" and the "screening wheat" seed. Evidently
the nature and first appearance of the rust were determined by local environ-
mental conditions, and variety, age, source, and condition of the seed played
a subordinate role at least in this particular case. It is also to be noted
that the rust appeared at different times on the different cereals except in

Apr., 1922! RAINES VEGETATIVE VIGOR OF THE HOST 2O3

the case of wheat and rye. This may be regarded as further evidence, if
any be required, of the physiological distinction of the rubigo-vera forms
growing on wheat and rye on the one hand, and on barley and oats on
the other.

Hungerford (1920, p. 270) reports an experiment testing the time of
first appearance of rust on wheat plants grown from rust-infected and from
clean seed, similarly indicating that the condition of the seed does not
affect the time of first appearance of the rust.

VEGETATIVE VIGOR OF THE HOST AS A FACTOR INFLUENCING

SUSCEPTIBILITY AND RESISTANCE TO CERTAIN

RUST DISEASES OF THE HIGHER PLANTS

II

M. A. RAINES
(Received for publication July 13, 1921)

FURTHER FIELD STUDIES AND EXPERIMENTS

The Rust History of Plots of Cereals Sown at Successive Intervals
through the Summer

To test the susceptibility to rust of plants of different ages at each period
of the summer and of young plants at different times in the summer, and
1o follow the subsequent history of the disease on plantings of cereals
started at successive intervals through the season, plots of wheat, rye,
oats, and barley were started in the breeding plot of the New York Botanical
Garden on June 10, June 23, July 6, July 20, August 5, and August 25, 1916.
Observations were made at intervals on the height of the plants, the time of
first appearance of the rust, the amount of infection, and the proportion
of the rust in the teleuto stage.

The results for the different cereals are shown in table 3 and are discussed
below. In the table, the days on which the observations were made are
£:iven at the top. The height of the plants is given in inches ("). When
the plants have headed, it is indicated by an "H." The degree of rust
infection is indicated by a numeral, and was estimated on a scale of 10,
ihe values of the numbers in the scale being: i = an occasional pustule
here and there; most of the leaves not affected. 2 = most of the leaves
with from one to five sori. 3 = about ten pustules on each leaf. 4 =
leaves heavily infected. 5 = leaves bearing the maximum possible amount
of rust. 6 = leaf sheaths infected as well as the leaf blades. 7 = a
sprinkling of rust sori on the stem and leaf sheaths; blades heavily infected.
<S = infection on sheath and stem well developed. 9 = heavy infection
on the stem. 10 = heaviest possible infection on the whole plant. The
leleuto stage is indicated by its Roman numeral, "III." A fraction pre-
ceding the "III " gives the proportion of the rust in the teleuto form.

As is indicated in table 3, the plots of wheat planted on June 10 and
June 23 headed out in 77 and 64 days respectively. Those planted July 6,
July 20, August 5, and August 25 never headed and never exceeded a
height of 20 inches. The rust invariably appeared on the young plot as a
thin, evenly distributed infection when the host plant was putting out its

215

216

AMERICAN JOURNAL OF BOTANY

[Vol. 9

TABLE 3
Wheat

Observations

Date
Sown

JulyS

July 17

July 24

Aug. 12

Aug. 26

Sept. 15

Oct. i

Oct. 23

No. of Days
to Head

June 10. . .

8"-2

I2"-4

l8"-4

24"~5

H-6

7

7

77

slight

III

June 23...

2"

9"-2

I2"-4

2O"~4

H-5

6

7

6

64

slight

slight

slight

July 6....
July 20. ..

5"

8"-l

i5;;-5

io"-3

i8"-5
i2"-5

i8"-5
i5"-4

20"-5

2o"-5

20"-4
20"-3

Aug. 5-...

9"-3

10-4

i5"-5

15-4

Aug. 25...

5"~2

9-4

i5"-3

Rye

Observations

Date

jNo. ot Days

Sown

JulyS

July 17

July 24

Aug. 12 1 Aug. 26

Sept. 15

Oct. i

Oct. 23

to Head

j

June 10. . .

de-

stroyed

June 23...
July 6....
July 20. . .

3"

r

20"-2

8"-i

H-3

'i-:?

3-5

I2"-4

6
i8"-6

7
H-7

7 •
I

33
51
73

Aug. 5----

4"-i

io"-5

i5"-6

H-5

79

Aug. 25...

8"-2

io"-5

20-4

Oats

Date
Sown

Observations

No. of Days
to Head

JulyS

July 17

July 24

Aug. 12

Aug. 26

Sept. 15

Oct. i

Oct. 23

June 10. . .

10"

I4"

18"

H-2

6

8

9

77

slight
III

slight
III

KHI

all III

June 23...

5"

10"

18"

24"-2

slight

H-7
1AUI

8
Kill

alHII

Q

all III

63

III

July 6....

4"

8"

I5"-2

slight
III

20"~6

slight
III

H-8
%lll

8
KHI

o

all III

70

July 20. ..

IO"-I

1 2 "-3

slight

i8"-5
^III

24"-6

Mill

H-8
K HI

91

III

Aug. 5....

9"-i

i5"-5
slight

i8"-5
^IH

20"-7

Kin

III

Aug. 25...

6"-i

IO"-2

3ti

May, 1922]

RAINES — VEGETATIVE VIGOR OF THE HOST
Barley

217

Observations

Date
Sown

July 8

July 17

July 24

Aug. 12

Aug. 26

Sept. 15

Oct. i

Oct. 23

No. of Days
to Head

June 10. . .

8"

15"

H

2

I

44

June 23. . .

4"

15" ! 18"

H

I

3

50

July 6. . . .

3"

8"

15"

H

i

I

50

July 20. ..

9"

15"

20"

H

70

Aug. 5....

6"

10"

15"

15"

Aug. 25...

6"

10"

12"

third leaf. The rust increased steadily in abundance on the leaf blade
until it reached the maximum, and only then began to appear on the leaf
sheaths. On the stem there were never more than a few scattered pustules.
Teleutosori did not appear until the middle of September. They were to
be found only on plants of the two oldest plots, and then not without care-
ful search. The observations of October 23 showed a distinct drop in the
amount of rust on all the plots of wheat. The new leaf growth of October
tended to show but little rust. In view of Johnson's (1912) findings that
low temperatures promote uredospore germination, these observations
may be interpreted as indicating greater resistance to rust infection on the
part of the host tissue due to the decreased rate of metabolic activity con-
sequent on the onset of cooler weather.

All of the plots of rye except that sown August 25 headed out, but the
rate of growth varied as is indicated by the successively greater intervals
required by the younger stands to head out. The behavior of the rust on
the plots of rye was much the same as on the wheat. In the younger
plantings it was somewhat less marked and less severe than on the wheat
plants of the same age, but the development of the rust was more severe
on the rye than on the wheat. It seemed, too, to go more readily to the
leaf sheaths and stems in the case of the rye. No teleuto was found on
the rye.

Of the oats, the first three plots headed out in 77, 65, and 70 days
respectively; the fourth plot produced only one head, 91 days after planting.
The plots planted August 5 and August 25 never headed out. No rust
appeared on the oats until August 12 when four plots were up, ranging in
age from seedlings in the four-leaf stage to plants in bloom. The rust
appeared on all four of the plots at the same time and in relatively the
same abundance. However, once the rust had appeared, its subsequent
history on the various plots differed decidedly. The older the plant, the
greater the abundance of rust on it, and the larger proportion of the rust
in the teleuto stage.

In the series of barleys, the three older plots headed in 42, 50, and 50
days respectively. The fourth put out a few heads 70 days after planting.

218 AMERICAN JOURNAL OF BOTANY [Vol. 9

The last two sowings, of August 5 and August 25, never reached the heading-
out stage. The barleys were rust-free until the middle of September,
when a few uredo pustules were to be discovered on the leaves and sheaths
of the three older plots. No teleuto was found.

As has been noted for the plots of wheat and rye, even more strikingly
in the case of the oats, the rate of development of the parasite differs with
the host. It is much more rapid in the case of the oats than in that of the
other cereals. For example, in the seedling stage the amount of rust on
the plants may appear less on the oats than on the rye and wheat, although
at the time of heading out the same plants will show the reverse condition,
the oats being much more severely infected.

The rust history of plots of cereals sown at successive intervals through
the summer may be taken as indicating that the age and maturity of the
host is a factor in the progress of the disease, and that the action of this
factor differs with the identity of the host plant.

LABORATORY AND GREENHOUSE STUDIES
Culture Methods

Four cereal rusts — Puccinia coronifera Kleb., P. secalina Grove, P. triti-
cina Eriks., and P. Sorghi Schw. — were successfully grown for periods of
time on the host in pots on greenhouse benches as described by Melhus
(1912) and Fromme (1913), and under aseptic conditions on host seedlings
growing in test tubes as described by Ward (19020) and Mains (1917).
Variations were introduced in both methods.

Fromme (1913) reviews the problem of growing cereal rusts in the green-
house. The method recommended by him includes sowing rust spores on
new host plants every few weeks by applying them with a scalpel or camel's
hair brush, or spraying on in suspension in water with an atomizer, and
then putting the host plants into a moist chamber for from 24 to 48 hours
to provide the conditions of high humidity necessary for spore germination
and infection. Tests, however, indicated that the first part of the method
recommended by Fromme, artificially sowing rust spores on the new host,
was not necessary under the conditions obtaining in the Columbia green-
house. It was found that when new host plants are grown beside infected
plants in the greenhouse, rust spores will be sown on them by natural
agencies, such as convection and other atmospheric currents, sufficient to
produce abundant infection if conditions of high humidity are provided
occasionally to render possible the germination of the spores.

Accordingly, the method adopted for maintaining stock cultures of the
cereal rusts in the greenhouse was to introduce new host plants alongside
the infected plants every third week and to cover the cultures with a moist
chamber every second or third night. The fungus maintained itself self-
sown in this manner, and no artificial inoculations were needed. The

May, 1922] RAINES — VEGETATIVE VIGOR OF THE HOST 219

advantage of such a method of maintaining stock cultures of cereal rusts
is that it eliminates the most technical operation, that of sowing or applying
the fungous spores to the new host, and reduces the problem of maintaining
cereal rusts in culture in the greenhouse to a non-technical routine such as
can be entrusted to the average gardener or greenhouse marh —

In growing the rust under aseptic conditions on seedlings in test tubes,
the method developed was to treat the seed with chlorine water (cf. Wilson,
1915), put the seed to germinate on filter paper in Petri dishes, and transfer
the germinated seed to a test tube plugged with cotton. Half an inch of
sterile water was put into the test tube with the plant. The reserve food
materials of the endosperm are capable of bringing the seedling to the third
leaf stage, which is sufficient to raise a generation of the rust on it. P.
coronifera was cultivated for 10 generations in this manner, transfers being
made once a month ; P. Sorghi for 8 generations ; P. triticina for 8 generations ;
and P. secalina for 6 generations. A small platinum spatula was employed
for making transfers; spores were applied to the upper surface of the first
leaf in each case, and material for inoculum was taken from the under
surface. That a cereal rust can thus be grown under conditions free from
accidental contamination was indicated by the total absence of organic
growth, bacterial or fungous, when a rust-infected seedling was deposited
on sterile beef-peptone agar.

Studies on the Incidence of Infection by Measured Doses of Uredospores
of Puccinia Sorghi on Zea Mays

An effort was made to determine the minimal dose of uredospores of
P. Sorghi that (i) can possibly, and (2) will certainly produce infection in
Zea Mays. 191 tests were made on corn seedlings growing under aseptic
conditions in twelve-inch test tubes.

The method employed to determine the dose and to inoculate was as
follows: A dilute suspension of uredospores was made in a vial of sterile
water. A small drop from this suspension was put on a piece of sterile
cover slip, and the number of uredospores in the drop was counted under
the microscope. The piece of cover glass was then inverted and deposited
on the upper surface of the first leaf of the young corn seedling in the test
tube, about one half inch below the tip, bringing the drop of water con-
taining the known number of uredospores in contact with the host tissue.
The work was done in the winter in the laboratory, with no rust growing
free anywhere in the building, so that the danger of accidental contamina-
tion was negligible. No infection ever developed on the seedlings except
on the spot where the plant had been inoculated.

The inoculated seedlings were kept under observation for 21 days.
If the inoculated leaf yellowed or withered before 15 days, the plant
was discarded. The data on 191 tests are shown in table 4.

220

AMERICAN JOURNAL OF BOTANY

[Vol. 9

TABLE 4

No. of
Spores

No. of
Inoculations

No. of
Infections

No. of
Spores

No. of
Inoculations

No. of
Infections

I

58

2

52

O

2

18

o

53

4

O

3

6

I

55

0

4

4

0

56

o

i

10
4

0
0

57
58

I

0

7

3

o

59

I

8

5

I

61

0

9

3

I

62

0

10

6

I

63

o

ii

2

0

64

0

12

2

0

65

o

J3

2

I

67

0

14

2

0

68

I

16

2

I

69

o

19

I

0

72

I

22

I

o

74

o

23

I

o

77

2

25

2

2

79

o

27

I

0

86

0

28

3

I

98

o

31

I

o

IOO

32

I

0

103

35

I

0

104

o

36

2

I

119

40

3

0

142

42

3

0

135

44

2

0

425

47

I

0

700

48

3

0

800

'

50

i

o

1000

The results cannot be considered as entirely convincing in view of the
many factors involved in a successful inoculation. The evidence indicates,
however, that, as to the minimal number of uredospores which can possibly
produce infection, it is possible for a single uredospore to produce infection.
In each of the two cases in which infection was produced after inoculation
with a single uredospore, the rust appeared after the usual incubation period
as a very small pustule at the point of inoculation. In one case the in-
fected leaf withered shortly after the appearance of the pustule; in the other
instance the mycelium showed normal growth, and about a week later
seven new uredosori were produced in a ring around the first pustule.

As regards the second question, the minimal dose of uredospores which
will certainly produce infection, the data indicate this to be, for the con-
ditions under which the work was done, between 100 and 125. This is
high. In view of the varying viability of spores taken at one time from the
same pustule, and of their further variation with the age of the pustule,
it was not considered possible actually to test the germination for each
sample used. However, the spores were always taken from the surface of
a large and pulverulent sorus, and, considering that the index of germination

May, 1922] RAINES — VEGETATIVE VIGOR OF THE HOST 221

of the uredospores under the conditions of inoculation was from 75-90
percent, and that it is possible for a single spore to produce infection, we
can say that (taking the conservative germination figure of 50 percent) of
more than fifty spores germinating on the surface of the leaf, only one
produced successful infection. Evidently, successful infection~by a uredo-
spore involves other factors besides that of germination on the leaf surface
of the host plant.

The Constitution of the Fungous Mycelium as a Factor in Teleutospore
Production by Puccinia coronifera

Our knowledge of the conditions governing teleutospore production in
the cereal rusts is summarized and extended by Gassner (1915), who con-
siders that the determining factor is the physiological aging of the host
tivssue, teleutospore production being particularly coincident with the
mobilization of the food resources of the plant for flower and fruit produc-
tion. The picture of teleutospore production presented by the plants of
the experimental field plots described above closely parallels Gassner's
observations in similar experiments and is consistent, with his views.

Consideration of the behavior of Puccinia coronifera as regards teleuto-
spore production, when grown in the greenhouse, leads to the suggestion
that the protoplasmic constitution of the fungous mycelium may be a factor.
Greenhouse cultures of the rust from material brought in from the field in
the vicinity of New York exhibited moderate teleutospore production. A
series of cultures from material sent the writer by J.I. Durrell from Ames,
Iowa, on the other hand, grown at the same time on similar host material
and under similar conditions, showed very abundant teleutospore produc-
tion, the difference in this respect between the two series of cultures being
readily noticeable. While such teleutospore production on potted oat
seedlings in the greenhouse is more commonly on the older infected leaves,
which are yellowing at the tip, it is not unusual to observe the production of
teleutospores by rust pustules on young and vigorous leaves shortly after
first infection.

Experiment showed that it is readily possible to secure variation in the
tendency of the rust towards teleutospore production by selection. The
rust was grown in test tubes under aseptic conditions. Large variation in
the tendency towards teleutospore production was noted in cultures of the
third generation, some rust cultures showing no teleutosori at all; in others
as much as 75 percent of the pustules were teleutosori. Two series of
cultures were therefore propagated. In one of the series, transfers were
made from cultures showing no teleutospores. Of 36 cultures in this series,
20 showed complete absence of teleutosori ; only 2 of the cultures developed
more than 50 percent of the winter stage.

In the second series, transfers were made from cultures showing 75
percent teleutosori. Of 35 cultures in this series, 30 showed more than

222

AMERICAN JOURNAL OF BOTANY

[Vol. 9

50 percent teleutosori, and only 5 less than that. Two of the cultures in
this series never produced any uredospores whatever, teleutosori only being
developed. It was obviously impossible to make transfers from such
cultures.

Figure 3, Plate XII, shows a rust mycelium in which only the first
pustule produced uredospores, succeeding pustules bearing only teleuto-
spores.

Apparently there may be wide differences in the tendency towards the
production of teleutospores in different cultures of a rust fungus, and the
factor of fungous constitution should be given consideration in work on
the conditions of teleutospore production.

Nutrition and Growth Studies

Water Cultures

Six experiments were performed with Puccinia Sorghi on corn to test
the effect on rust development of growing the host plants in culture solu-
tions of varying nutritive value. A sugar corn was used, as being more
susceptible to rust than a flint or dent corn. The seedlings were grown in
water culture in 25o-cc. Erlenmeyer flasks. Knop's nutrient solution was
used as a base. Except as otherwise noted, the endosperm was removed
about the time that the first leaf was breaking through the coleoptile, so
that the plant was entirely dependent for sustenance on the mineral salts
it could obtain from the nutrient solution and on the carbohydrates it
could manufacture in its leaf tissue. Inoculation was effected by spraying
with a suspension of uredospores and covering with a bell jar for 24 hours.
Observations were made on the incubation period and on the progress of
the disease on the plants. The dry weight of the top of the plant at the
conclusion of the experiment was taken as an index of the relative vigor of
growth of the plant.

TABLE 5
Exp. i. Effect of Renewing Solution. Plants Inoculated February 28, 1919.

No. of

Treat-

Dry Weight
of Top

Observations

Plant

ment

of Plant
inMg.

March 9

March n

March 13

I
2

3

Solution
changed once
a week

Solution not
changed

Solution not
changed

340
310
280

3 pustules on
third leaf

No infection
No infection

I pustule on
second leaf;
3 pustules on
third leaf
i pustule on
second leaf

No infection

2 pustules on second
leaf; 3 pustules on
third leaf

i pustule on first leaf;
4 pustules on second
leaf; i pustule on
fourth leaf
i pustule on first leaf;
I pustule on third
leaf

May, 1922]

RAINES — VEGETATIVE VIGOR OF THE HOST

223

Exp. 2. Effect of Removing Endosperm. Plants Inoculated February 2$,

No. of
Plant

Treat-
ment

Dry Weight
of Top
of Plant
inMg.

Observations

March 9

March n

March 13

March 15

I

Endosperm not
removed

Endosperm re-
moved

Endosperm re-
moved; solution
rendered highly
toxic by large
excess of Fe2Cl6

150
80
40

3 pustules
on first
leaf
No infec-
tion

No infec-
tion

4 pustules
on first
leaf
i pustule
on second
leaf
No infec-
tion

4 pustules"
on first
leaf
i pustule
on second
leaf
No infec-
tion

5 pustules
on first
leaf
3 pustules
on second
leaf
No infec-
tion

2 . .

3

Exp. j. Effect of Culture Solutions of Varying Nutritive Value. Plants Inoculated March 19,

IQIQ.

No. of
Plant

Treat-
ment

Dry Weight
of Top
of Plant
in Mg.

Observations

March 25

March 26

March 27

March 29

I

Full nutrient solu-

1 60 Infection

Infection

13 pustules

2pustuleson

tion ; endosperm

on second

on second

on second

first leaf; i

not removed

and third

and third

leaf; 4

pustule on

leaves

leaves

pustules

second

on third

leaf; 7 pus-

leaf

tules on-

third leaf

2

Full nutrient solu-

80

No infec-

No infec-

3 pustules

5 pustules

tion

tion

tion

on first

on first

leaf; 4

leaf; 5

pustules

pust ules

on second

on second

leaf

leaf

3

Full nutrient solu-

80

No infec-

No infec-

i pustule

3 pustules

tion

tion

tion

on first

on first

leaf; 2

leaf; 4

pustules

pustules

on second

on second

leaf; i

leaf; 2

pustule

pust ules

on third

on third

leaf

leaf

4.... .

Nutrient solution

50

No infec-

No infec-

2 pustules

2 pustules

rendered toxic

tion

tion

on second on second

with excess of

leaf

leaf; I

Fe2Cl6

pustule on

third leaf

5

Tap water

40

No infec-

No infec-

i pustule

2 pustules

tion

tion

on first

on first

leaf; 2

leaf; 2

pustules

pustules

on third

on second

leaf

leaf; i

pustule on

third leaf

6

Distilled water

2O

No infec-

No infec-

No infec-

2 pustules

tion

tion

tion

on second

leaf

7

Highly toxic nu-

2O

No infec-

No infec-

No infec-

i pustule on

trient solution

tion

tion

tion

first leaf

224

AMERICAN JOURNAL OF BOTANY

[Vol. 9

Exp. 4. Effect of Varying Concentration of Nutrient Solution.

1919

Plants Inoculated April 2,

No. of
Plant

Concen-
tration of
Nutrient
Solution

Dry Weight
of Top
of Plant
in Mg.

Observations

April 8

April 9

April 14

I.

0.012
O.OO9

O.OO6
0.003

0.0015

Distilled
water

2O
140

no

110
100

(d

No infection
Rust showing
on second leaf

No infection

Rust showing
on third leaf

No infection
jst roved)

No infection
12 pustules on
second leaf

3 pustules on
second leaf
19 pustules on
second leaf;
10 pustules
on third leaf
No infection

No infection; plant dying
Large number of pustules
on first, second, and
third leaves
5 pustules on second leaf;
plant dying
5 pustules on first leaf; 20
pustules on second leaf;
10 pustules on third leaf

17 pustules on first leaf;
8 pustules on second leaf

2

3
4

K .

6

In all the water-culture experiments (table 5) an increase in the incuba-
tion period of the rust with depression in the vigor and rate of growth of the
host plant was apparent. Coincident with the increased incubation period
of the rust on host plants of poor growth and little vigor went always a
marked depression in the luxuriance of the fungus. The pustules were
appreciably smaller, and produced decidedly fewer spores.

Comparing the incubation period of the rust on the leaves of the same
plant, it is found to be shorter on the younger leaves. Comparing the
first and second leaves, we find :

Infection noted on the first leaf before it appeared on second leaf. . . . o

Infection noted simultaneously on first and second leaves 5

Infection noted on second leaf before first 7

Infection on first leaf; none on second 2

Infection noted on second leaf; none on first 7

The older host tissue, it would seem, provided a less congenial environ-
ment for the development of the rust.

Incidental to the above-described water-culture experiments was the
demonstration of the ability of the rust to develop on chlorotic tissue.
Some corn seedlings were grown in iron-free nutrient solution, and the
fourth and fifth leaves produced by the plants were completely blanched.
The plants were sprayed with a spore suspension to test the susceptibility
of these leaves to the rust. Nine days after inoculation the chlorotic leaves
showed abundant rust infection. Giddings (personal communication)
has obtained infection with Gymno sporangium juniperi-virginianae on apple
leaves blanched by being kept in the dark room while unfolding from the
bud. It may be concluded that the presence of chlorophyll is not a neces-
sary condition for rust development.

May, 1922] RAINES — VEGETATIVE VIGOR OF THE HOST 225

Soil Cultures

From the studies of Sheldon, Ward, and Stakman, as also from the
experiments described above, it may be considered as established that,
within the range of forms worked with, conditions unfavorable to the
growth of the host cause an increase in the incubation period of the rust and
depress the luxuriance of growth of the fungous mycelium as indicated by
the size of the pustules and the number and size of the spores produced
in them.

Concerning the effect of conditions unfavorable to the growth of the
host on the incidence of rust infection — the number of successful infections
produced on a unit area of host tissue by a given dose of inoculum — our
knowledge must be regarded as not so definite. The data extant are sub-
ject to criticism because of the relatively small number of variables studied
and because of the irregularity of dosage inherent in the method of inocula-
tion employed. Ward (1902) applied spores to the leaf by means of a
swab of cotton, and Stakman (1914, p. n) employed a flat inoculating
needle for this purpose.

Studies on the relation between host vigor and incidence of infection,
to be of critical value, must be made with numbers of variables sufficient
to preclude undue distortion of the results by fluctuations in condition of
host and fungus, and by errors in the taking and studying of data; the
method of inoculation employed must stand criticism as to the uniformity
of dosage for the variables compared; and, if any but the grossest relations
between the variables studied are to be made apparent, a more exact basis
than visual observation and judgment must be employed for determining
vigor of growth of host plant and degree of rust infection on it.

In the experiments described below on the relation between host vigor
in the oat plant and its susceptibility to crown rust, data were obtained on
1450 individual plants receiving different nutritive treatment and exhibiting
wide variation in vigor of growth. The plants were grown in pots in
the greenhouse. Inoculation was effected under natural field conditions
by placing the pots containing the experimental plants out of doors near a
stand of oats heavily infected with crown rust. Analysis of the data indi-
cates that the dosage for the variables compared was uniform. The experi-
ments were concluded and the readings taken before the rust on any of the
plants approached the maximum that the leaf tissue could support, so
that the infection present at the time may be considered an index of the
response of the host tissue to the conditions of inoculation to which it was
subjected, and variation in this response between host tissues receiving
similar doses of inoculum was presumably due to differences in the condi-
tion of the tissues compared.

Values for the vigor of the host plant and for the amount of rust in-
fection present on it were obtained as follows: At the conclusion of the
experiment the plant was cut off at the base and observations were taken

226

AMERICAN JOURNAL OF BOTANY

[Vol. 9

of the number of rust pustules on the upper surface of each leaf, of the
length of each leaf in inches, of the extreme length of the entire plant, and
of the number of stools it had produced. The plant was then dried, and
its dry weight was obtained. The dry weight of the plant was adopted
as the index of its relative vigor of growth, because it makes possible more
accurate seriation of the variables on this value than an index such as the
height of the plant or the total leaf length.

As an index of the degree of infection of the plant the value adopted
was the number of pustules on an average unit area of the most severely
infected leaf — calculated by dividing the number of rust pustules on the
leaf by the length of the leaf in inches, and by its width at the base in six-
teenths of an inch. This value was found to have a positive correlation
(r = .7803 =b .0167 for the 250 variables of experiments I, II, and III)
with the value that at first thought would seem most desirable: namely,
the total number of rust pustules counted on the leaves of the plant, divided
by the total leaf length in inches, and by the largest leaf width in sixteenths
of an inch — and is preferable for adoption in work of this kind not only
because it is easier to obtain, but also because it avoids the error introduced
by the development of new leaf surface during the incubation period. The
most highly infected leaf on the plant was usually the lowest leaf in good
condition. In tables 6-10 both values are given.

Experiment I

66 oat plants were grown in soil in 2-inch pots, divided into three groups
on the basis of the number of plants grown to a pot. The soil was a rich
garden loam. The seed was sown July 6, 1920, three grains being put
into the soil for every plant desired, and the seedlings were later thinned out
to the number of plants desired. The pots were kept on a bench in the
greenhouse until August n, when they were taken out of doors and set
near a patch of rusty oats, subjecting the plants to natural conditions of
inoculation and infection. The experiment was concluded on August 24.
The data on this experiment are given in table 6.

TABLE 6

Mean

Mean No. of

Mean No. of

No. of

No. of

Dry Weight

Pustules

Pustules

Group

Variables

Plants to a
2-inch Pot

of Top of
Plant

per Ave. Unit
Area of Total

per Ave. Unit
Area of most Severely

in Mg.

Leaf Surface

Infected Leaf

a

23*

5

6l

I.I

4.2

b

18

2

135

2.1

6.0

c

25

I

183

2-3

6.1

Experiment II

70 plants were grown in 3-inch pots, divided into three groups on the basis
of the number of plants grown to a pot. Soil, method of seeding, and dates
* Plus 2 destroyed.

May, 1922]

RAINES — VEGETATIVE VIGOR OF THE HOST

227

of sowing, setting out of doors to be inoculated, and of concluding the experi-
ment were the same as in experiment I described above. The results are
shown in table 7.

TABLE 7

Mean

Mean No. of

Mean No. of

No. of

No. of

Dry Weight

Pustules

Pustules

Group

Variables

Plants to a
3-inch Pot

of Top of
Plant

per Ave. Unit
Area of Total

per Ave. Unit
Area of most Severely

in Mg.

Leaf Surface

Infected Leaf

a

25

5

96

1.6

4.1

b

20

2

264

i-7

4.8

c

25

I

407

2.O

5-2

Experiment III

12 o plants were grown in 4^-inch pots, divided into four groups on the
basis of the number of plants grown to a pot. Soil, method of seeding, and
dates of sowing, of setting out-doors to be inoculated, and of concluding the
experiment were the same as in experiment I. Results are given in table 8.

TABLE 8

Mean

Mean No. of

Mean No. of

No. of

No. of

Dry Weight

Pustules

Pustules

Group

Variables

Plants to a
4^-inch Pot

of Top
of Plant

per Ave. Unit
Area of Total

per Ave. Unit
Area of most Severely

in Mg.

Leaf Surface

Infected Leaf

a

50

IO

161

1-5

3-6

b

25

5

352

2.4

6.4

c

2O

2

66 1

2.7

6-5

d

25

I

976

2-5

6.2

i

Experiment IV

600 oat plants were grown in 4^-inch pots, 5 plants to a pot; 15 grains
being planted in each pot in the first place, and the young seedlings thinned
out to the desired number. The plants were divided into six groups of
100 individuals each on the basis of soil composition and treatment, as
follows :

Group A : Soil composed of sand only.

Group B: Soil a mixture of i sand and 3- garden loam.

Group C: Soil a mixture of i sand and ^ garden loam.

Group D: Soil the same mixture as in Group C. In addition, KC1 at the rate of 350
pounds to the 6-inch acre of 2,000,000 pounds was intimately mixed with the soil.

Group E: Soil the same mixture as in Group C. In addition, acid phosphate at the
rate of 750 pounds to the acre was intimately mixed with the soil.

Group F: Soil the same mixture as in Group C. In addition, sodium nitrate at the
rate of 500 pounds to the acre was intimately mixed with the soil.

Seed was sown July n, 1920. On July 24, July 31, and August 7 the
plants of groups Z), £, and F had additional quantities of fertilizer applied

228

AMERICAN JOURNAL OF BOTANY

[Vol. 9

in water solution at the rate of 100 pounds to the acre. On August 9 the
plants were placed out of doors to be inoculated. The experiment was con-
cluded on August 27. Figures I and 2, Plate XI, illustrate the growth
differences obtained between the plants of the different groups in these
experiments.

In table 9, the groups are arranged in order of the vigor of growth ex-
hibited by the plants.

TABLE 9

Mean

Mean No. of

Mean No. of

No. of

Soil

Dry Weight

Pustules

Pustules

Group

Variables

Treatment

of Top
of Plant

per Ave. Unit
Area of Total

per Ave. Unit
Area of most Severely

in Mg.

Leaf Surface

Infected Leaf

A

100

sand

120

.6

2.0

E

100

acid

155

.8

2.7

phosphate

B

100

$ sand

20O

•7

2-3

D

IOO

KC1

2O2

I.O

3-2

C
F

IOO
IOO

\ sand
NaNO3

341

564

•9

1.2

3-i

4-5

Experiment V

This was a duplicate of Experiment IV, started a week later. The seed
was sown July 17, the plants were placed out of doors to be inoculated
August 10, and the experiment was concluded August 31. The results are
shown in table 10.

TABLE 10

Mean

Mean No. of

Mean No. of

No. of

Soil

Dry Weight

Pustules

Pustules

Group

Variables

Treatment

of Top

per Ave. Unit

per Ave. Unit

of Plant Area of Total

Area of most Severely-

in Mg. Leaf Surface

Infected Leaf

A

IOO

sand

47

5-1

11.6

B

IOO

£ sand 53

5-1

11.8

E

IOO

acid 93

5-2

H-3

phosphate

C

IOO

£ sand

93

4.5

9-5

D

IOO

KC1

96

4.4

10.2

F

IOO

NaNO3 359

3-i

7.6

Relation between Host Vigor and Pustule Size

In all five of the soil-culture experiments there was evident a marked
decrease in the size of the rust pustules on the host plants the growth rate
of which was depressed. The lengths of 100 contiguous pustules on plants
from groups a and c of experiment I; groups a and c of experiment II;
groups a and d of experiment III; groups A and F of experiment IV; and
groups A and F of experiment V were found to fall into the following
classes ;

May, 1922] RAINES — VEGETATIVE VIGOR OF THE HOST

TABLE n

229

Experiment

I

II

III

IV V

\

Group

Group

Group

Group

Group

a

c

a

c

a

d

A

F

A

F

No. of pustules | mm. long
i mm

94
6

20
20

34
24

2

72
28

H

>!

4

2

82
18

22
30
30
12

4

2

96

4

12
30
46
8

4

70
25
3

2

8
24
24
34

7
3

i£ mm.
2 mm

2\ mm.
3 mm.

Sum of lengths of 100 pustules in mm.

53

134

64

130

59

126

52

131

68

169

Figures 4 and 5 of Plate XII illustrate the relative size of the pustules
on leaves of semi-starved and of vigorously growing plants.

Pustules attained a larger size on the more rapidly growing host plants,
indicating that a more luxuriant host tissue means a more luxuriant parasitic
mycelium.

DISCUSSION
Relation between Host Vigor and Incidence of Infection

On their face the figures obtained in the soil-culture experiments indicate
that in experiments I, II, III, and IV there occurred a decreased incidence
of infection with depression in growth vigor of the host; but in experiment V
the figures indicate quite as definitely precisely the opposite relation —
namely, increased incidence of infection with depression in the growth
rate of the host.

The dosage for all six groups of variables in soil-culture experiments
IV and V was probably essentially the same. The plants were arranged in
order of alphabetical designation of the groups: A, B, C, D, E, F. The
possibility might be suggested that in experiment IV inoculation proceeded
from the direction of F and that the plants from F to A were subjected to
progressively diminishing doses of inoculum; and, conversely, that in
experiment V inoculation was from the direction of A and that the plants
from A to F received progressively diminishing doses of uredospores. This
would. make the amount of infection observed on the plants of the different
groups a function of their positions relative to each other. But actually
the amount of infection observed is correlated not with the position of the
group but with its relative growth vigor as indicated by the mean dry
weight of the plants. Thus, in both experiments IV and V, group E exhibits
an amount of infection not like group F, next to which it was placed, but
like group B which it resembles in vigor of growth. We may conclude that

230

AMERICAN JOURNAL OF BOTANY

[Vol. 9

the dosage for the variables compared in any experiment was uniform and
that the variation in the amount of rust observed on the different groups
of plants in the experiment is due to differences in the reactions of the plant
tissue to the infection to which they were subject.

The explanation of the apparent reversal of the result in soil-culture
experiment V as compared with the others is probably to be found in the
age of the plants and in the length of time they were exposed to infection.
The experiments are compared in table 12.

TABLE 12

Experiment

I

II

in

IV

v

Age of plants at conclusion of experiment (days)
Age of plants when set out of doors to be in-
oculated

49

^5

49

35

49

T.SL

47
*l

45
24

Number of days out of doors and exposed to
infection

15

15

15

16

21

Number of variables

66

7O

I2O

600

6OO

Average dry weight of top of plants (mg )

127

278

518

26/L

123

Average infection (total leaf surface)
Average infection (most severely infected leaf) . .

1.8
54

1.8
4-7

2.3
5-7

•9
3-0

4.6
10.4

Experiment V differs from the other four experiments in that (i) when
set out of doors to be inoculated the plants were from 7 to 1 1 days younger.
Even at the conclusion of the experiment these plants had only half the
dry weight of the plants of experiment IV and were evidently much less
mature. (2) When the experiment was concluded the plants had been
out of doors and subject to infection 6 days longer. If we allow an incuba-
tion period of 10 days for the rust, then the rust present on the plants of
experiment V at the conclusion of the experiment represents inoculation
through a period of time twice as long as in the case of the other experiments.
(3) The amount of rust on the plants at the conclusion of the experiment was
several times greater in experiment V than in any of the other experiments.

The last-mentioned fact immediately brings into view an aspect of the
method of experimentation used tending to limit the value of the pustule
count as a criterion of the frequency of penetration and infection by the
uredospore germ tube. It is probable that only in cases of very sparse
infection is there a pustule for every focus of infection, and that only in
cases of very sparse infection is the number of pustules counted an accurate
index of the number of infections which have taken place. With abundance
of infection there appears a tendency for the coalescence of foci of infection,
for two or more mycelia the result of contiguous infections to coalesce and
produce only one pustule; and this tendency would be highly accentuated
on the more vigorously growing host plants where the parasite finds a
favorable nidus and develops more luxuriantly. In experiment V the
error introduced by the coalescence of mycelia may well have masked a

May, 1922]

RAINES VEGETATIVE VIGOR OF THE HOST

231

higher incidence of infection in the vigorously growing plants of group F
and have converted it into an apparently lower susceptibility. It is notice-
able that the pustules were larger in experiment V than in the other four
experiments.

Variation in the Incidence of Rust Infection with Variation in the Growth
Vigor of the Host Plant, due to Constitutional or Racial Differences

In soil-culture experiments IV and V, when the 100 variables of each
group were arranged in order of dry weight, the series divided into five
equal parts of 20 variables each, and the average weights and degrees of
infection of these sub-groups determined, a certain relation was apparent
between the relative weight attained by a plant and the incidence of rust
infection on it. The figures obtained in this analysis of the data are pre-
sented in table 13.

TABLE 13

Experiment I V

Mean Dry Weight of Tops of

Mean Infection per Unit Area of most

Plants in Mg.

Severely Infected Leaf of Plant

Group

Sub-groups

First

Second

Third Fourth

Fifth

First

Second

Third

Fourth

Fifth

A....

40

65

110

148 239

2.3

2.4

1.8

2.O

1.6

E... .

99

129

I48

172 231

2.8

2.1

2.9

3-5

2.1

B....

99

140

179

231 345

2.3

2.9

2-5

2.1

1.8

D....

90

144

182

231 363

3-6

3-0

2-5

3-9

2.9

c....

141

233

336

430

596

4.0

3-0

2-3

44

1.7

F....

305

450

555

653

812

4-7

57

5-2

3-8

3-3

129

193

252

3ii

431

3-3

3-2

2-9

3-3

2.2

Experiment V

Mean Dry Weight of Tops of

Mean Infection per Unit Area of most

Plants in Mg.

Severely Infected Leaf of Plant

Group

Sub-groups

First

Second

Third

Fourth

Fifth

First

Second

Third

Fourth

Fifth

A..

21

34

43

54

83

n.8

13-6

H.5

1 1. 6

9-3

B....

22

36

50

65

92

12.3

14.0

11.7

12.2

8.6

E....

42

67

85

1 08

159

15-9

12.2

11.9

8.6

7.8

C....

53

71

88

106

148

IO.2

IO.O

II. O

8.6

74

D....

47

72

90

107

162

12. 0

13.2

10.5

8.0

7.2

F. . . .

190

283

349

416

558

9-9

6.8

7-2

7-7

6.2

63

94

118

.

143

200

12.0

n.6

10.6

9-5

7-8

The figures show that there was considerable variation in the growth

232 AMERICAN JOURNAL OF BOTANY [Vol. 9

attained by plants receiving the same treatment, and that the larger plants
were less susceptible to rust infection — increased resistance being par-
ticularly marked in the sub-group including the largest of the plants.

The seed employed was a commercial " Swedish Select" oats in which
we should expect a mixture of strains as regards rate of growth, speed of
maturity, and susceptibility to rust. In view of the uncertainty as to
the varietal purity of the seed employed, the differences in incidence of
rust infection on plants receiving the same treatment and showing differences
in vigor of growth are probably indicative of constitutional differences in
susceptibility to rust which may be correlated with similar constitutional
differences in speed of growth; and so may be considered as not necessarily
bearing on the main problem I am considering, which is concerned with
the effect on rust susceptibility of externally induced variations in the
vegetative vigor of the host. The establishment of an inverse relation
between susceptibility to rust and speed of growth in oat varieties would
lend, however, new significance to the practical injunction of the agrono-
mists to plant early-maturing varieties of oats in order to escape loss from
rust, indicating that selection of rapidly growing and early-maturing strains
of oats automatically implies selection for rust resistance as well.

The Possibility of a Direct Relation between Environmental
Conditions and Rust Resistance

Groups D, E, and F in experiments IV and V were intended as tests for
a possible direct effect on rust susceptibility of specific nutrient substances —
that is, an effect independent of variations in the health and vigor of the
host plant. A potash fertilizer was applied to the plants of group D\ a
phosphate fertilizer to those of group E\ and the plants of group F were
richly fed with a nitrogen salt.

The infection observed in these groups is in no instance so far different
from that on plants of similar weight in the groups not treated with any
special fertilizer as to justify the inference that the fertilizing chemicals
were exerting any influence on the rust resistance of the host other than is
implied in their effect on the general condition and vigor of the plant.

In experiment IV the potash and phosphate applications proved ex-
cessive, and the growth of the plants was appreciably retarded as compared
with the plants of group C\ in experiment V the potash and phosphate
fertilizers had no effect on the growth of the plants. In both experiments
the potash- and phosphate-fertilized plants show a somewhat higher in-
cidence of infection than plants of similar weight not treated with special
fertilizers; a tendency at variance with the statements of Bolley (1889, p. 18)
and Spinks (1913. P- 247) that these fertilizers give increased rust resistance.
In group F the stimulating action of the nitrate fertilizers on the growth of
the host was so marked that there can be no hesitation in referring the
increased susceptibility observed to this effect rather than to any direct

May, 1922] RAINES — VEGETATIVE VIGOR OF THE HOST 233

action of the chemical. This aspect of the soil-culture experiments may
be considered as in agreement with the suggestion arrived at in the biblio-
graphical review that it is questionable whether a direct relation between
any environmental factor, either physical or chemical, of the nature of a
nutrient or a stimulus, and susceptibility to rust, has been established in the
case of the cereal grains.

Vegetative Vigor of the Host as a Susceptibility- and Resistance-factor

in Infectious Diseases

Increased susceptibility with increased vigor of the host, in plant
diseases, is not confined to the rusts. Marchal (1902) found that infection
of lettuce by Bremia lactucae was favored by nitrogen and phosphates and
retarded by an excess of potash. Jones (1905, p. 38) mentions that high
fertilization, especially with nitrogenous manures, lowers the powers of
the potato plant to resist blight and rot. McCue (1913, p. 18) observed
that tomato plants treated with phosphatic fertilizers developed less leaf
blight than control plants, while plants on nitrogen and potash plots which
at the same time gave the highest yields, indicating greatest vigor of growth,
were more heavily infected than the controls. Peltier (1918) has observed
with the citrus canker, and Fromme and Murray (1919, p. 227) with the
angular leaf spot of tobacco ("the development of the organism within the
tobacco leaf is apparently dependent to a marked degree on those pre-
disposing factors which promote a rapid, vigorous growth of the host"),
that infection is heavier under conditions which favor the growth of the
host. Thomas (1921) obtained evidence of increased resistance to leaf
spot (Septoria Apii) of celery plants the vitality of which was depressed
as a result of infestation of the root system by nematodes ; and of decreased
resistance in plants richly fed. And Levine (1921) has observed that crown
gall on beets developed more rapidly and to larger size on roots grown in a
highly manured soil.

While the claim that increased vigor of the host means greater sus-
ceptibility to an infection may appear somewhat anomalous from the point
of view of current theories regarding the infectious diseases, observations
such as form the subject of the present paper are readily understood when
we consider the infectious diseases in the light of the larger class of biological
phenomena of which they are an artificially selected group — namely,
parasitism, commensalism, and symbiosis, the class of biological phenomena
in which one organism lives within, and derives its sustenance from, the
tissues of another living organism. In each of the four main groups of
parasitic organisms — the bacteria, the protozoa, the worms, and the fungi—
a series of intergradations are to be observed in the physiological interrela-
tions of host and parasite, from the unceasing and violent struggle that
continues until the destruction of one or other of the principals, to a relation
of a more benign type characterized by great subordination and even tend-

234 AMERICAN JOURNAL OF BOTANY [Vol. 9

ency to usefulness on the part of the parasitic organism, and by the utmost
tolerance on the part of the host. In many instances the nature of the
reaction is not constant, but varies with the progress of the host-parasite
relation. In this intergrading series of possible host-parasite relations, the
inverse relation between host vigor and parasite virulence obtains only in
the instances and phases where the reaction of the host to the parasite is
one of active antagonism; here a more vigorous host means a host of greater
physiological capacity to combat the progress of the invader. But when
the relation between host and parasite is of a symbiotic type, a more vigorous
host means a host in which more food is available for the development of
the parasite. Because, of the general class of parasitological phenomena,
the instances mainly in the field of pathological interest (the diseases
ordinarily so called) are an artificially selected group in which relations of
violent antagonism between host and invading organism are most promi-
nently in evidence, thought in the field of pathology has developed with the
physiological antagonism of host and parasite as its basal concept; and the
theories of immunity extant are largely concerned with the nature of the
antagonistic reactions.

In the group of the fungi the transition from violent and destructive
parasitism to parasitism of^the symbiotic type is accompanied by a transi-
tion from facultative to obligate parasitism, as if the physiological corollary
of parasitism of the latter type is extreme specialization in food preferences.
The series in the fungi grades from violent and destructive parasites like
Botrytis, on the one hand, to, on the other hand, so benign an infestation as
the seed fungus of Lolium temulentum (described by Freeman, 1903) in
which the relation is so intimate and devoid of any untoward effect on the
host, and the life history of the cohabiting organism is so parallel with that
of the grass that its distinct individuality is almost open to question.

The mutualistic nature of the relation between host elements and
fungus in rusts of the type of the cereal rusts is commented on by Tubeuf
(1897, p. 91) who very aptly compares the mass of chlorophyll-bearing
leaf cells infested with the rust mycelium to a lichen structure, especially
to those lichens whose algae obtain water and inorganic materials direct,
rather than through the fungous hyphae. Certainly, during the greater
part of the relation, there is here no evidence of any deleterious effects on
the host cells. While the contribution of the affected elements to the
.growth and fruiting economy of the host plant as a whole may be diminished,
the infected protoplasts continue essentially unimpaired in structure and
function. The parasite does not attack the living substance of the host
protoplast, but confines itself to establishing such a relation with the latter
that it shares the available food resources of the cell ; and the rust haustorium
is not an implement for mechanical disruption, but a structure more in the
nature of the placenta of the mammalian foetus for establishing physiological
communication with the food resources of the host.

May, 1922] RAINES — VEGETATIVE VIGOR OF THE HOST 235

The data presented by Thomas (1921) on the parallel relation between
health of the host and infection in the case of the leaf blight of celery, and
observations of similar occurrences in other diseases caused by non-obligate
parasites like the late blight of the potato (Jones, 1905) and the crown gall
of the beet (Levine, 1921) indicate that phases in which a symbiotic tend-
ency comes to the fore may occur in diseases of a predominantly destruc-
tive type caused by facultative parasites, and suggests the generalization
that the host-parasite relation in any given instance is not constant but
may vary with the state and condition of the organisms and with the prog-
ress of the relation. It is important to recognize that there may occur
mutualistic phases and stages in host-parasite relations of a violent and
destructive type, just as there are destructive phases in parasitisms of a
predominantly symbiotic tendency such as those of the mildews, the rusts,
and the smuts.

CONCLUSION

The inquiry initiated by the occurrence in rust literature of statements
of a relation between host vigor and susceptibility other than the inverse
relation commonly conceived as existing between these variables can be
considered as having brought forward evidence indicating that through
most of the course of certain infectious diseases such as the rust diseases
of the cereal grains, and in certain phases of other diseases like the leaf
spot of celery and the crown gall of the beet, the vegetative vigor of the
host and the virulence of the disease may be in direct relation. The demon-
stration of such a relation in diseases of large importance suggests, in turn,
emendation of current pathological concepts of the relation between host
vigor and pathogen activity into a form more in accord with our knowledge
of parasitological phenomena in general. A more catholic point of view
in pathologic thought, recognizing that, for longer or shorter phases in the
course of a disease, the relation between host and parasite may be highly
mutualistic, would be of material value as a working concept in the study
of disease and in defining the practical problem of disease prevention and
control.

The work presented in this paper was done in the Botanical Laboratory
of Columbia University, under Professor R. A. Harper, to whom the writer
is greatly indebted for pointing out the problem and for constant con-
sultation and advice during the progress of the investigations. Acknowl-
edgment is also made of indebtedness to Dr. Michael Levine for taking the
photographs of the soil-culture experiments, and to Dr. H. E. Thomas for
helpful advice in devising the method used in the dosage studies on the
corn rust.

LITERATURE CITED

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238 AMERICAN JOURNAL OF BOTANY [Vol. 9

DESCRIPTION OF PLATES
PLATE XI

FIG. I . View of one of the four series of pots of experiment V of the soil-culture studies,
illustrating the difference in vigor of growth between plants receiving different nutritive
treatment.

FIG. 2. On the left, a pot containing 5 plants of group A (grown in sand) ; and on the
right a pot containing 5 plants of group F (soil highly fertilized with NaNO3) ; experiment
V of the soil-culture studies.

PLATE XII

FIG. 3. Crown rust of oats. A rust mycelium exhibiting a very marked tendency
towards teleutospore production. The first sorus produced by the mycelium (in the center)
is a uredosorus. The others are teleutosori. Photographed with Zeiss 3.5 cm. microplanar.
X24.

FIG. 4. View of infected leaves of a semi-starved plant and of a richly fed plant of
soil-culture experiment V, showing larger size of pustules on more luxuriant host plant.
Photographed with Zeiss microplanar. X 15.

FIG. 5. Same as figure 4. X 10.

AMERICAN JOURNAL OF BOTANY.

IX, PLATE xii.

'\J

RAINES: VEGETATIVE VIGOR OF THE HOST

VITA

MORRIS ABEL RAINES. Born 1894. Elementary and high school
education in the public schools of New York City. Entered Columbia Col-
lege in 1912. Received degree of Bachelor of Science "with high honors in
botany and zoology," 1915; degree of Master of Arts in 1917. Pulitzer
Scholar in Columbia University, 1912-1916. Research Assistant in Botany
in Columbia University, 1916-1917. Appointed Gottsberger Fellow in Col-
umbia University for 1917-1918, but resigned to enter National Service.
Flying Cadet, and later Lieutenant (airplane pilot, rated "Reserve Military
Aviator") in the United States Army Air Service, 1917-1918. Instructor
in Botany in Columbia University Summer Session, 1919. Gottsberger
Fellow in Columbia University, 1919-1920. Instructor in botany in West
Virginia University, 1920-1922.

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