28 
WALTER SPURGEON BEACH 
Effect of the mass of inoculum. The effect of varying the concentration 
of the spore suspension was tested. One hundred areas upon Erigeron 
annuus were inoculated with loop-drops containing approximately lOO 
spores, and an equal number of areas with loop-drops averaging 1-3 spores. 
In the former case there were 35 areas infected, and in the latter 15, but 
in the 35 areas over 80 points of infection were noted, while in the 15 areas 
only 18 were present. Infections were obtained upon Lactuca scariola 
with loop-drops containing only 1-3 spores in 1 1 percent of the inoculations. 
Effect of wounding. Certain leaves of young potted plants of Malva 
rotundifolia were perforated with a fine needle in numerous places. All the 
leaves of each plant were inoculated over the entire upper surface, and 
bagged for four days. Only the perforated leaves became infected. Either 
the wounding had the effect of overcoming the resistance that may have 
been present in the cell contents of the young foliage, or the pierced epi- 
dermis afforded an easy entrance for the germ tubes of the spores. 
Variations in the morphology of the fungus. The more detailed studies 
of morphological variations were made with Septoria tritici and S. verbas- 
cicola, and the chief results obtained are shown in graph i by curves which 
represent the ranges of spore length in these fungi under a number of dif- 
ferent conditions. No investigation was made of the factors causing 
these variations, but apparently they are due to differences in humidity. 
An increase in spore length when infected leaves were kept in a moist 
chamber for a period was apparent in many other species of Septoria. 
There was no alteration in spore length when 5. verbascicola was trans- 
ferred from Verbascum blattaria to Scrophularia marilandica under com- 
parable conditions, as E and F of graph i show. Norton (22) reports that 
the spores of the tomato Septoria become longer upon the potato and 
Solanum carolinense, but shorter upon Datura tatu>la than they were upon 
the original host, when the inoculations were made within humid inclosures. 
It is not stated whether he took account of environmental relations other 
than the change of host, but the lesser spore length upon Datura tatula 
makes it appear that the host has a definite effect on morphology. Still, 
in the numerous crosses recorded in the tables of the present paper, no 
changes of spore length were observed for which environmental factors 
such as humidity might not account, at least in all cases in which the fungus 
and host were in compatible relations. 
If all the species of Septoria have a corresponding relation to the en- 
vironment, and if all have a broad range between the maximum and mini- 
mum spore length, as in 5. tritici and S. verbascicola, it is obvious that many 
of the measurements now given in specific descriptions are far from ac- 
curate. The range of 19 to 62 microns reported for S. sisymbrii is not of 
greater width than that shown for the fungi in graph i , and indicates care 
in measurement. It is not proper to compare dry herbarium specimens 
with material freshly collected, especially if it has been allowed to form 
