150 



Thus, it will be seen that single conidium 3 gave rise to sixteen clearly 

 denned saltants; C5, to one; Cl, to two; and C2, to seven demonstrating 

 absolutely that these saltants were not due to impurity of cultures. Evi- 

 dently the saltant sectors do not result from contaminations. 



FREQUENCY OF SALTATION 



It is impossible to give any mathematically accurate statement as to 

 the frequency of saltation in Helminthosporium. One hundred and 

 twenty-six variant sectors were selected, transferred, and more or less 

 studied; and this number could easily have been doubled or trebled. It 

 is not probable that all the forms in these sectors were truly saltants; 

 doubtless some of them were mere modifications, but the number that were 

 permanent in character is large. How many of these saltants agreed with 

 each other in observable characters it is also impossible to say, but since 

 they arose independently it may be that they do not often agree absolutely. 

 The percentage of saltants, based on those theoretically possible, is, how- 

 ever, small even in races that are most actively saltating. Thus in a colony 

 6 cm. in diameter there are probably more than 5,000,000 cells, and theo- 

 retically it appears probable that saltation occurs in a single mycelial cell, 

 or perhaps by the union of two cells, yet saltations occur with even less 

 frequency than one to each 6-cm. colony, therefore less than once out of 

 5,000,000 possibilities. In this connection, though no direct comparison 

 is possible, it may be noted that East (47) considers the occurrence of twelve 

 inherent variations in observations made on 100,000 hills of more than 700 

 varieties of potatoes, that is, about 1:10,000, as an unexpectedly high rate 



