144 



XXII, XXIII). The occurrence of clumps of mycelium upon the surface 

 of the cultures has been stressed by Ravn (91) as of taxonomic importance 

 (cf. also with PL XI, XIII, XXIII (below), XXVIII). H. No. 13, in one 

 small sector, showed eight white clumps; the balance of the plate, none. In 

 transfer M71 the clumping character seemed lost, but the following transfers 

 were pale in type. In other cases the clumping habit seemed to be fixed 

 and characteristic (PI. XXVIII). 



Variability in colony color. The color is mainly due to abundance or 

 scarcity of conidia or to abundance or lack of aerial mycelium, or to both. 

 The white aerial mycelium is practically without conidia. Transfers 

 from sectors with much white, sterile aerial mycelium were not always 

 constant in these characters, but in many instances they were so; for 

 example, M72, derived from single conidium Cl-1, and M78, derived from 

 M26. Differences quite comparable with these were noted by Crabill (36) . 



Zonation was well marked in some saltants and almost entirely lacking 

 in others (PI. IX, 3, 4, 5, 20). Some saltants formed sclerotia abundantly 

 though the originals did not do so. Density of colony also differed, some 

 saltants producing colonies of much denser growth than others. 



Variability. -Variability itself was a distinctive character in certain 

 instances. Thus, while the original of any given saltant is usually fairly 

 constant in its characters and only occasionally gives rise to saltants, one 

 saltant, M26 (PI. XXX, below; XXXI), was definitely characterized by 

 the fact of its inconstancy (see page 143). 



Many saltants were tested as to their infecting power and their rotting 

 power, but no real difference in these respects was noticeable between the 

 different saltants, or between the saltants and H. No. 1 . Since many species 

 of Helminthosporium can infect many cereals this power may be rather 

 fundamental in the genus and thus not be so readily subject to saltation as 

 are less fundamental characters. I have no means as yet to measure slight 

 differences in either virulence or rotting power. It may be mentioned here 

 that Ravn (91) states that culture upon dead substrata diminishes the vir- 

 ulence of Helminthosporium. Whether such diminution was permanent 

 or merely a temporary modification he did not determine. Edgerton (51) 

 reports that different races of Glomerella differ in virulence. 



Correlation of characters in saltation. Certain correlations of characters 

 are noticeable; thus, colonies of slow linear growth were usually high in 



