[Vor. 8 
48 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
substance, which was not of the nature of oxalic acid nor an 
oxalate, as Smith and others claimed. 
Concerning the penetration of epidermal cells by the fungus 
last mentioned, Blackman and Welsford (16) showed very clearly 
that this fungus bores through the cuticle in a purely mechanical 
way. In his second paper Brown (716) is convinced that, ‘‘the 
infecting germ tubes of Botrytis cinerea are unable to affect 
chemically the cuticle of the host, nor do they secrete any toxic 
substance which can pass through the cuticle and bring about 
the death of the underlying cells." When the cuticular obstacle 
has been penetrated in a purely mechanical way, the underlying 
tissues are entered. 
Büsgen (’18) published a further study on Botrytis cinerea, and 
from an abstract of this paper it appears that he found no cuti- 
cular lesions; the cell walls of invaded cells were more or less 
dissolved, nucleus and chlorophyl bodies were mostly intact, 
and the fungus produced a poison not of the nature of an enzyme. 
More recently Hawkins and Harvey (19), in a physiological 
study of Pythium, conclude that the fungus secretes a toxin 
which kills the cells of the potato, likewise an enzyme by which 
the organism breaks down the middle lamellae of the host cell, 
but mechanical pressure exerted by the fungous hyphae seems to 
be the most important factor in cell wall penetration. 
METHODS IN THE Stupy oF Host PENETRATION 
In the studies on penetration, most of the investigators men- 
tioned above made use of sections of different parts of the host 
plants obtained as nearly sterile as possible and then incubated 
with the fungus. This method of study, however, did not 
seem applicable in my investigation, because under such condi- 
tions penetration would take place much more easily than under 
natural conditions, and the degree of the parasitism of the diff- 
erent strains would not be ascertainable. The study was there- 
fore undertaken under conditions as near natural as possible. 
The method employed in the present experiment was as fol- 
lows: Seed disinfection for pure culture work was carried out 
after the method of Duggar and Davis (19). About 30 seeds 
of the garden pea were placed in a small cheese-cloth bag, and 
these immersed in a covered vessel containing 10 per cent Javelle 
