470 
Journal of Agricultural Research 
Vol. XXIX, No. 9 
pure culture. It may be of interest to 
add, however, that when onion sets 
were planted with the legumes in the 
soil temperature series described pre¬ 
viously, their roots became about 
equally (though more slowly) invaded 
except in soil at 9° C. This fact may 
indicate that the same fungus entered 
both plants, since the soil used was 
taken from a locality where no species 
of Allium has been found. 
SUMMARY 
1. During a study of the fungus 
parasites of the roots of peas and other 
legumes it has been found that the roots 
of nearly all our common leguminous 
crops, wherever grown, are extensively 
invaded by a characteristic fungus 
which has previously been known in a 
considerable number of plants as a 
mvcorrhizal fungus. 
2. The term mvcorrhizal fungus 
as used here does not carry with it any 
implication that the association of the 
fungus with the higher plant is of 
benefit to the latter plant. In fact, 
there is some evidence which indicates 
that it is more or less injurious. 
3. So abundant is this mvcorrhizal 
fungus that it appears unlikely that 
many plants of alfalfa, clover, peas, 
and other legumes ever reach maturity 
without having their roots more or less 
invaded. 
4. The fungus is found only in the 
primary cortex. 
5. The mycelium is coarse, non- 
septate in the roots, and though it passes 
through the outer cells when entering 
the root is chiefly intercellular in the 
deeper cells, advancing in long strands 
toward the growing end. It sends into 
the deeper cells haustoria which are 
often of complicated structure, filling 
more than half the lumen of the cell. 
The contents of many of the cells con¬ 
taining haustoria become greenish yel¬ 
low, thus imparting a characteristic 
discoloration to the entire root. The 
taxonomic position of the fungus has 
not been determined, but it appears to 
belong among the Phycomycetes. 
6. No culture medium has yet been 
found which appears to be capable of 
supporting the growth of this fungus 
independently of host tissue. 
7. The new growth of perennial 
clover and alfalfa roots in early spring 
contains but little of this fungus, inva¬ 
sion occurring at least in part from the 
growth of the previous season. When 
root growth is retarded in midsummer, 
the rootlets become invaded almost to 
their tips. In autumn, when root 
growth is again rapid, the fungus is 
unable to keep pace with it and the 
new growth is largely free from inva¬ 
sion. 
8. The fungus has been found able 
to invade roots of peas and sweet peas 
which are grown in a constant soil 
temperature as high as 33° and as 
low as 9° C. These temperatures 
approach closely the extreme limits at 
which these plants are able to grow. 
9. In a single plat experiment clover, 
alfalfa, and sweet peas were found to 
grow more vigorously in soil in which 
this fungus had been killed by for¬ 
maldehyde, but it is not certain that 
the absence of this parasite is the only 
factor which was responsible for the 
benefit. 
10. A list of plants other than le¬ 
gumes in which this same type of 
mvcorrhizal invasion has been found is 
given. 
LITERATURE CITED 
(1) Demeter, K. 
1923. UEBER “PLASMOTYSEN ” —MYRKOR- 
rhiza. Flora 116: 405-456, illus. 
(2) Janse, J. M. 
1897. LES ENDOPHYTES RADICAUX DE QUEL- 
ques plantes javanaises. Ann. Jard. 
Bot. Buitenzorg 14: 53-201, illus. 
(3) Jones, F. R. 
1923. MYCORRHIZAL FUNGI IN THE ROOTS OF 
legumes. Rpt. Internat. Conf. Phytopath, 
and Econ. Ent. Holland 1923: 204-205. 
(4) Magrou, J. 
1921. SYMBIOSE ET TUBERISATION. Ann. Sd. 
Nat. Bot. (X) 3: 181-296, illus. 
(5) Peyronel, B. 
1923. FRUCTIFICATION DE L’ENDOPHYTE A 
ARBUSCULES ET A VESICULES DES MYCOR- 
HIZES ENTOTROPHES. Bui. SOC. MyCOl. 
France 39:1 19-126, illus. 
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