(Vor. 8 
54 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
Concerning the relationship between P1 and P4 there are 
marked differences in morphological and physiological charac- 
teristics, as shown by dimensions and color of sclerotia, by dias- 
tase and invertase activities, by temperature requirement, by 
cultural characters, and by pathogenicity. Nevertheless, these 
differences may not perhaps be considered sufficient to dis- 
tinguish these permanently as different species, especially since 
these characteristics are more or less modified by environment, 
particularly by a change of host plants. Some important 
indications obtained by a study of reisolated cultures of these 
two strains, made from sclerotia appearing on potato tubers 
artificially inoculated (see inoculation experiment no. 5), are 
shown below. 
REISOLATED STRAIN P1 
(1) Selerotia: cells 16-23 x24- 
48 u, dark brown in color. 
(2) Hyphae: diameter 8-14 y, 
turning dark brown when old. 
(3) Pathogenicity: not so viru- 
lent as the original P1. 
(4) Cultural characters: black- 
ening of potato agar is not so 
striking as that of original strain. 
(5) Diastatic efficiency: 92 
(original strain averages 45). 
REISOLATED STRAIN P4 
(1) Sclerotia: cells 16-22 x23- 
48 u, dark brown in color. 
(2) Hyphae: diameter 8-14 y, 
turning dark brown when old. 
(3) Pathogenicity: about the 
same as the original P4 or re- 
isolated P1. 
(4) Cultural characters: black- 
ening of agar is about the same 
as in the original strain P4. 
(5) Diastatie efficiency: 100. 
The evidence presented above makes it safe to assume that 
these two strains P1 and P4 may be properly regarded as a single 
species modified more or less by environment. In general, the 
strain P4, as Duggar (16) says, in itself scarcely merits consider- 
ation as a causal fungus of disease and I find it less virulent than 
the strain Pl. As a matter of fact, in no case may the strain 
P4 be so changed as to resemble the form P1, either by changing 
the eulture media or host plants, while P1 may be easily trans- 
formed into P4 as has been shown. 
The strain B1 is notably distinguished from the remaining 
strains by its characteristic sclerotia, by its cultural characters, 
and by having a higher temperature requirement for mycelial 
