THE FORMATION OF HYPHAL FUSIONS 



55 



the mycelium displays the greatest tendency to convert itself into 

 a close-meshed network. 



Pleurage anserina. — Spores of this fungus were sown in a hanging 

 drop of cleared dung-agar, and next day hyphal fusions were 

 observed forming in the mycelium. 



Three hypha-to-peg fusions were observed. In two of them the 

 pegs were prominent and distinctly peg-like, but in the third the 

 peg never became as long as it was broad and had the form of a 

 blunt convex process scarcely protruding from the older hypha of 

 which it was an outgrowth. Six stages in the formation of a hypha- 



Fig. 29. — Pleurage anserina. The formation of a hypha-to-peg fusion. That part 

 of a mycelium shown in A was watched continuously. At first there were 

 present only the hyphae a and c. Then the branch-hypha b came into existence 

 and, in the course of about an hour, attained the length shown in A. The end 

 of b is now about 10 /u from the side of c and is stimulating c morphogenically. 

 B, two minutes after A ; c has produced a peg opposite to the end of b. C, two 

 minutes after B ; the peg and the branch-hypha b are growing toward one 

 another. D, one minute after C ; the peg and the branch-hypha are rapidly 

 approaching one another. E, one minute after D ; the ends of the peg and the 

 branch-hypha have met. F, three minutes after E ; the peg and the branch- 

 hypha have completely fused with one another. Magnification, 434. 



to-peg fusion, passed through in succession in the course of about 

 ten minutes, are shown in Fig. 29. 



Two peg-to-peg fusions were witnessed. In the one illustrated 

 in Fig. 30, A and B, the more or less parallel older hyphae which 

 stimulated one another were 26 \x apart at the place where they sent 

 out their pegs. 



Hypha-to-hypha fusions doubtless occur in the mycelium of 

 P. anserina, but they were not actually observed taking place. 



In places in the mycelium were found instances of : (1) one peg 

 growing toward one of two opposing pegs (Fig. 30, C) ; (2) one peg 

 which had fused with one only of two opposing pegs (Fig. 31, A) ; 

 (3) one peg which had fused with both of two opposing pegs (Figs. 30, 

 D, and 31, B), and (4) a hypha-to-peg fusion in which evidently the 

 approaching hypba had induced the formation of two opposing pegs 



