Nov. 1, 1924 
A Mycorrhizal Fungus in the Roots of Legumes 
467 
There was great variation in the 
extent to which the root s} stems were 
invaded. Roots with a relatively thick 
cortex, as of peas and clover, generally 
showed more abundant development 
of the fungus and a more extensive 
invasion than beans which have a 
thinner cortex. There appears to be 
a difference in infestation between 
-closely related species, the roots of 
which can hardly be distinguished 
morphologically. Thus red clover ap¬ 
pears to be more thoroughly infested 
than alsike or white clover. 
The fungus was not found in roots 
of Oxytropis sp., Cicer arietinum L., 
or Lupinus perennis L. There is no 
apparent explanation for the complete 
absence of the fungus from these three 
species. 
DISTRIBUTION OF THE FUNGUS IN 
AGRICULTURAL LAND 
The territory in which the mycor¬ 
rhizal fungus was first found in native 
as well as in introduced legumes is com¬ 
paratively old agricultural land, on the 
greater part of which leguminous crops 
have been grown repeatedly. In these 
older districts many growers believe, 
not without some good evidence, that 
certain legumes, especially clover, do 
not flourish as when first introduced. 
This opinion is supported by the fact 
that clover, at least, is at present more 
successful in newly cleared land. 
Alfalfa also is not generally so success¬ 
ful in the humid eastern States as in 
regions of lesser rainfall or under 
irrigation. These facts suggest the 
question whether there is any correla¬ 
tion between the abundance of this 
mycorrhizal fungus and the vigor of 
these plants. Perhaps newly cleared 
forest land in which leguminous plants 
were not numerous and semiarid land 
with a small plant population of any 
kind are when first cultivated less 
thoroughly infested or are free from 
this fungus. 
These questions were in mind when 
in the summer of 1923 an opportunity 
was afforded to examine alfalfa and 
peas in Utah, Idaho, and Montana 
and also on newly cleared land in 
Michigan and Wisconsin. It would 
serve no useful purpose to list here 
the localities from which specimen 
plants were taken, or to describe the 
different cultural conditions under 
which the plants were grown. It 
suffices to state that no field however 
recently reclaimed in arid regions was 
found free from infestation, and but 
few mature plants were uninvaded. 
On newly cleared land in one locality 
in northern Wisconsin where peas were 
the first crop, the fungus was found 
only in plants growing in a few low 
spots, though at the time examination 
was made the plants were so young that 
invasion to a conspicuous degree might 
not yet have occurred even if the fungus 
were present. In Montana the fungus 
was found in the roots of native species 
on a mountain side far above culti¬ 
vated fields. Plants in reclaimed 
swamps in Wisconsin have whiter roots 
than those in surrounding fields, and 
indeed in the spring clover has been 
found in such locations in which no root 
infestation was discovered. However, 
a later search in the summer usually 
disclosed some invasion, though not 
with accompanying discoloration. It 
thus appears that not many leguminous 
plants which are potential hosts reach 
maturity anywhere in the United States 
without becoming invaded; and con¬ 
spicuous vigor in these plants in any 
locality can hardly be ascribed to the 
absence of this fungus. On the other 
hand, it is not easy to determine quan¬ 
titative differences in invasion in dif¬ 
ferent soils, and much work must be 
done before such differences will be 
demonstrated, if they exist, and their 
effect upon the development of the 
plants determined. 
RELATION OF THE SEASONAL DEVELOP¬ 
MENT OF THE PLANT TO THE FUNGUS 
INVASION OF THE ROOTS 
During the autumn of 1922 and the 
entire following year roots of clover 
and alfalfa were examined from time 
to time at Madison, Wis., to determine 
approximately the time at which 
smaller roots of these plants are devel¬ 
oped and when they are invaded by 
the mycorrhizal fungus. Agronomic 
and botanical literature appears to 
contain little information regarding the 
relation of top growth to root growth 
in our perennial and biennial legumes, 
and no information regarding the lon¬ 
gevity of the smaller roots. About the 
middle of April, 1923, as soon as the 
ground was free from frost, many 
clover rootlets washed from the soil 
were found yellow in color. Although 
the discoloration at this time was 
largely in the cell walls and had no 
relation to the presence of the fungus, 
many of the small roots from all plants 
in established clover fields contained 
the fungus, though it was sometimes 
absent from volunteer plants in fertile 
gardens. By May 22 the new growth 
of alfalfa and sweet-clover roots, though 
varying greatly in different locations, 
usually amounted to between 1 and 2 
inches. In the basal part of this new 
