Nov. 1, 1924 
A Mycorrhizal Fungus in the Roots of Legumes 
469 
SIGNIFICANCE OF THE MYCOR¬ 
RHIZAL FUNGUS IN LEGUMES 
The relation between the fungus and 
its host plants described in these pages 
appears to be a long-standing case of 
mutual adaptation to which the term 
“ symbiosis’’ may appropriately be ap¬ 
plied; but here there is no apparent 
benefit accruing to the plant invaded. 
The discoloration and eventual disin¬ 
tegration of the cortex of the roots and 
the slow growth of the plants at the 
time when root invasion reaches its 
maximum suggest that the plant is 
retarded and injured, at least in so far 
as vegetative growth is concerned. 
This may not be determined until the 
fungus is secured in pure culture. But 
some evidence of apparent value has 
already been obtained. This fungus can 
be destroyed with others in the soil by 
sterilizing agents, and legumes grown in 
soil so treated seem to thrive better than 
in untreated soil. In the spring of 
1922, alfalfa, sweet peas, and red, 
white, and alsike clovers were grown 
in a small plat which had been treated 
with formaldehyde the previous au¬ 
tumn, and had been kept covered 
during the winter to prevent reinfes¬ 
tation. A similar plat was soaked 
with water to which no formaldehyde 
had been added. At examinations 
made during the season, root growth 
appeared to be about equal for all 
plants in both plats. But the roots in 
the treated soil remained white and 
clean until late in the summer, when a 
little mycorrhizal infestation began to 
appear. No other root parasite was 
detected on plants in either plat. On 
July 16 the sweet-pea plants in treated 
soil were twice as tall as in the un¬ 
treated soil, and had twice as many 
blossoms. Unfortunately, mosaic ap¬ 
peared in all plants at this time, where¬ 
upon blossoming ceased; but the 
plants in the treated plat remained 
green throughout the season, while 
those in untreated soil died and shriv¬ 
eled. The clovers and alfalfa showed 
little difference until July 30, when the 
plants in the treated plat stood 1 to 2 
inches taller, a superiority which was 
maintained throughout the autumn. 
These results agree with Demeter’s ( 1) 
work with Vinca minor , but like his are 
open to the objections that other un¬ 
recognized soil parasites may also have 
been excluded by treatment, and that 
soil changes favorable to the plant 
may have resulted from the treatment. 
Work is now in progress which may 
furnish more adequate evidence of 
effect of this fungus on its host plants. 
99186—25f-4 
MYCORRHIZA OF HERBACEOUS 
PLANTS OTHER THAN LEGUMES 
In order to determine whether roots 
of plants other than Leguminosae are 
subject to this type of mycorrhizal 
invasion, a number of cultivated 
plants and weeds growing at Madison, 
Wis., have been examined. A similar 
condition has been found in the follow¬ 
ing plants: 
Allium cepa L. 
Asparagus officinalis L. 
Aster spp. 
Bidens vulgata Greene. 
Eupatorium perfoliatum L. 
Frageria virginiana Duch. 
Ipomoea purpurea (L.) Roth. 
Panicun capillare L. 
Leontodon taraxacum L. ( Taraxa¬ 
cum officinale Web.) 
Verbascum thapsus L. 
Viola sp. 
Zea mays L. 
A mycorrhizal fungus was not found 
in a considerable number of other 
species which are not listed here since 
the number of plants examined was 
usually small. It is of interest to 
record that with the exception of an 
intensive invasion of rootlets of Sola - 
num tuberosum growing in sandy soil 
in a greenhouse, the author failed to 
find any mycorrhizal fungus of this 
type in such solanaceous plants as he 
has had occasion to examine, this 
failure being in general agreement 
with the findings of Magrou (J) in 
France. 
None of the plants listed above have 
been examined in sufficient numbers to 
indicate clearly whether the fungus is 
constantly associated with their roots 
or not. In Panicum and Viola espe¬ 
cially, its comparative scarcity in the 
plants examined suggests that it is 
not a constant associate. Some varie¬ 
ties of sweet corn seemed more thor¬ 
oughly infested than other varieties 
of Zea mays , half the small roots in 
one field being invaded, whereas on 
the same date (Sept. 1) not more han 
a quarter of the roots of a dent variety 
growing close by were found invaded. 
Roots of strawberry plants from several 
gardens showed wide differences in 
extent of invasion. Plants of very 
vigorous growth from one garden had 
nearly all rootlets filled almost to the 
end, while those from a neighboring 
garden had but few infected rootlets. 
Whether the fungus in this wide 
range of plants belongs to the same 
or to several species, or to specialized 
races can not be determined readily 
until the fungus has been obtained in 
