154 
are also distinct.’’ (See Pl. IX, No. 20.) Conidial length is given in 
Fig. U, Graph 100; breadth, in Fig. V, Graph 102; septation, in Fig. T, 
Graph 88. (See also photomicrographs of conidia in Pl. XXVI, d.) 
By comparing these graphs and data with those of H. No. 3 and H. No. 1 
it will be seen that the conidia are quite short and a trifle thick. The 
coefficient of cylindricity—78 for subcylindrical conidia, 74 for the more 
elliptical ones—is the highest coefficient shown in any of my strains (cf. 
with page 119). It seems very probable,therefore, that either the culture 
was contaminated in Dr. Westerdijk’s laboratory or the other culture in 
Dr. Bakke’s hands; or that Dr. Bakke’s description was erroneous or that 
one of the cultures was contaminated by me; or that the facts represent 
a real hereditary change in morphology during a long series of transfers— 
and I incline strongly to the last of these alternatives. 
H. No. 23 showed what appears to be a modification rather than a 
saltation, in that in the original culture received from Miss Weniger there 
were many abnormal tri-pointed conidia (see page 101). It is suggested 
that a change somewhat like this, if permanent, may have given rise to 
the forms with unequal central cell, for example, to H. No. 29. 
All of the above-mentioned examples appear to represent clear-cut 
cases of change in morphological character in test-tube culture. The 
only essential difference between these changes in test-tube culture and 
the saltation reported in Petri dishes is that in the cases of the Petri dish 
selection of the saltant was voluntary, while in making transfers from 
tube to tube the selection was accidental. 
= 
SALTATIONS IN NATURE 
That changes do occur under my culture conditions renders it highly 
probable that they also occur in nature—in the fields. Thus a saltant 
strain may become established on one wheat plant, form large numbers 
of conidia, gain foothold in a region, and then enlarge this foothold, per- 
haps to cover large areas. That one strain may thus outgrow another 
has been shown by Crabill (36) and is evident in my own work (PI. XXX, 
XXXI, lower figs.). The fact that so many strains of Helminthosporium 
differing slightly but distinctly from each other, yet agreeing closely in gen- 
eral, can readily be isolated from cereals, indicates that probably this also 
has naturally happened, and that in the fields we have today large numbers 
of races or strains of closely related forms derived more or less recently from 
acommon parent stock. To test this hypothesis experimentally, in field or 
greenhouse, by inoculation with pure cultures, and later isolating organ- 
