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40 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
When P1 is sown with the reisolated H (see inoculation no. 1) 
the growth of both strains is about the same, and frequently 
fusion of hyphae takes place. Fusion was also frequent between 
two reisolated strains of P1 and P4, both of which were originally 
isolated from potato tuber (see inoculation no. 5). In no case 
was the fusion of hyphae observed when P7 was sown with one 
of these reisolated strains. 
These experiments establish the fact that fusion may occur 
either between hyphae of the same strain or between those of 
certain different strains. It is not to be inferred that this fusion 
phenomenon is analogous to that occurring in Mucor or other 
species of Zygomycetes. In the cases here reported the fusion 
took place only between the hyphae of strains which might 
possibly have originated rather recently from the same form or 
race, although modified by environmental conditions. The 
process by no means represents sexual union. This view is 
also confirmed by certain experiments with mixed cultures, in 
which the method described by Zeller and Schmitz (19) was 
employed, with slight modification. Petri dishes containing 
sugar beet agar were each inoculated with 3 of the strains in 
such a way as to have all possible combinations of each. P1, 
B1, and H grew much more rapidly than the remaining strains, 
frequently covering the latter. When hyphae of the same 
strain, but representing different isolations as P1 and H, came in 
contact, there was usually no influence of the one colony on the 
other; that is, the mycelium of the two colonies intermixed, show- 
ing a straight line at the margin of the two colonies, owing to 
the slight inhibition of growth. When B1 and any of the re- 
maining strains came in contact there was a slight stimulation 
of sclerotial formation on the side of B1 at the margin of the two 
colonies, shown by the heaping up of sclerotia, while P1 and H 
(or certain other strains) had rather a tendency to produce 
sclerotia at the opposite side of the contact line. 
The influence of one strain upon another was also studied by 
another method. After considerable growth of these strains 
on agar plates the agar-penetrated layer was cut into squares 
(about 8 mm. across) at the border of any two colonies in such 
manner that each square contained approximately the same 
amount of the two colonies. Freshly poured agar plates were 
