144 
XXII, XXIII). The occurrence of clumps of mycelium upon the surface 
of the cultures has been stressed by Rayn (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 (Pl. 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 C1-1, 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 (Pl. 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 (Pl. XXX, below; XX XI), 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 
