248 
AMERICAN JOURNAL OF BOTANY 
[Vol. 10, 
dissolves the epidermal cells, thereby permitting the germ tube to enter; 
and fifth, by means of wounds. Blackman and Welsford (2) found that 
the germ tubes of spores of Botrytis cinerea Pers. in turnip juice on the 
leaves of Vida faba L. penetrated mechanically the unbroken epidermis. 
Initial infections were never found to occur through the stomata. However, 
after the penetration of germ tubes through the epidermis had reduced their 
resistance to infection, the hyphae were seen to enter through the stomata. 
Dey (10) and Weimer (35) showed that Colletotrichum lindemuthianum 
(Sacc. and Wagn.) Scribner and the basidiospores of Gymnosporangium 
Juniperi-virginiani Schwein. penetrated mechanically the unbroken epi¬ 
dermis of the bean and of the leaves of healthy apples respectively. From 
the results of these investigations there appears to be little doubt that 
certain fungi have the power to penetrate the epidermis mechanically 
independently of an apparent enzymic action. Other fungi have been 
found to gain an entrance through the stomata. Jones, Giddings, and 
Lutman (23) picture the entrance into the leaf of the potato by Phytophthora 
infestans (Mont.) De Bary both by way of the stomata and by the penetra¬ 
tion of the epidermis. Harter (15) observed the germ tube of Diaporthe 
phaseolorum (C. & E.) Sacc. entering the leaf of Phaseolus lunatus L. only 
by means of the stomata, and Gardner and Kendrick (12) found that 
Bacterium exitiosum Gardner & Kendrick entered the leaf through the 
stomata, although entrance of the fruit was accomplished only through 
a wound. 
That wounding plays an important role in the infection of many crops 
by various fungi is well recognized. There are in fact organisms often 
regarded as weak parasites which can infect only through a wound. Even 
those organisms which are able to penetrate the epidermis or those which 
usually enter through the stomata frequently gain an entrance to the host 
through a wound. Hurd (21) found that an unbroken seed coat of wheat 
or barley ordinarily affords absolute protection against attacks on living 
seeds by Penicillium or Rhizopus in damp storage, in the soil, or in blotter 
germinators. Infection of such seeds was obtained, however, by retarding 
germination of the seed by means of low temperatures. Orton (30) found 
that infection of the Irish potato by Rhizopus nigricans was accomplished 
only through some abrasion in the skin. 
The part played by enzyms in infection of the host has been a subject 
of study and investigation for a long time, and some of the earlier investi¬ 
gators noted what they believed to be cases of the entrance of a fungus 
only after the epidermis had been softened or weakened by means of an 
enzym. Busgen (7) and Ward (34) believed that the germ tube of Botrytis 
cinerea accomplishes its entrance into the tissue of the host with the aid 
of an enzym which dissolves the epidermal walls of the host. Voges (33) 
and Miyoshi (27), working with Fusicladium and Botrytis cinerea respec¬ 
tively, are of the opinion that softening of the cuticle by an enzym or some 
