474 
Journal of Agricultural Research 
Vol. XXVI, No. io 
species described in the body of this paper. There are, however, a 
number of species that enter the vascular bundles of peas when they have 
been exposed by other agencies of decay, and once within may hasten 
greatly the destruction of the plant. These species are not to be regarded 
as parasites, inasmuch as they do not penetrate and destroy living cells. 
SUMMARY 
1. A very destructive stem and rootrot of peas is known in almost all 
regions where peas have been grown for a long time. Investigators who 
have studied this disease have usually found a species of Fusarium to be 
the cause of decay, but in different parts of Europe and of the United 
States different species have been described as the parasites. The pres¬ 
ent investigation, which has extended over four years, has discovered 
but a single species of Fusarium parasitic upon peas in the United States. 
This species is that previously reported by Bisby in Minnesota, and it is 
here described as Fusarium martii var. pisi. Other species of Fusarium 
are sometimes found, sometimes consistently during a season in a locality, 
in the vascular bundles of peas, but they are found to have gained entrance 
not by traversing or destroying the living cells surrounding the vascular 
system, but through cells which have been killed by some other invader. 
A few other species of Fusarium are found able to enter and destroy a 
limited amount of parenchyma in a susceptible region at the base of the 
stem under very favorable conditions of temperature; but they are not 
regarded as important parasites under field conditions. 
2. The species of Fusarium described here is found widely distributed 
in pea-growing districts of the United States; but the injury which it 
causes is far less important than that caused by Aphanomyces sp. 
3. Several species of Pisum are susceptible to the disease. 
4. The most susceptible portion of the plant is the base of the stem just 
above the attachment of the seed. The fungus entering here in seedlings 
may invade the vascular system and produce a wilt, but older plants are 
rarely so affected. Small rootlets are invaded, especially at the growing 
points and killed. 
5. A comparatively high soil temperature, above 18 0 C., favors rapid 
development of the disease; but variations in soil moisture within the 
limits favorable for plant growth do not appear to affect its development. 
6. Soils containing much organic matter appear to favor the persist- 
ance of the fungus in the field. 
7. No evidence of dissemination of the fungus by seed has been ob¬ 
tained. Its wide distribution and the variability in the pathogenicity of 
cultures indicate that it is a widely disseminated soil organism having 
physiological varieties capable of varying degrees of pathogenicity. 
8. A number of selected varieties of peas have been grown in infested 
soil which has been held under uniform controlled conditipns to determine 
possible differences in resistance to disease. No marked differences in 
the resistance of the susceptible cortex at the base of the stem has been 
found. However, the vascular tissue beneath the parenchyma seems 
more resistant to invasion in certain varieties. There is an apparent 
difference in the resistance of the small rootlets to injury, and varieties 
capable of rapid extension of the root system possess an apparent resist¬ 
ance. However, a greater degree of resistance than has been indicated 
by this work must be found in desirable varieties before it can be regarded 
as of commercial importance, unless such resistance can be combined 
