504 BOTANICAL GAZETTE [JUNE 
‘host penetration by the sporidial germ tube of the cereal stem rust fungus. 
Although Eriksson studied sporidial infection in the mallow rust, concluding 
that penetration is directly through the epidermal cell wall and never through 
stomata, no careful study of the mechanism of entry of the sporidial germ 
tube has previously been made. In the present account penetration is shown 
to result from mechanical action alone, the structures concerned in the process 
being a mucilaginous investment of the germ tube and a fine style-like infection 
hypha, originating either from the germ tube or the sporidium directly. The 
entry of the parasite at first causes no visible alteration of the host cell contents. 
This manner of parasitic entry, that is, in the absence of visible chemical 
softening processes of the cuticle, is similar to that previously reported for the 
infection hypha of Botrytis and Colletotrichum, and for the zoospore of Synchy- 
irium (CURTIS). A new interest is thereby given to studies of disease resistant 
or disease escaping plants directed toward the mechanical properties of the 
cuticle and cell wall. Evidence that resistance to infection of potato by 
Pythium debaryanum is of this type has already been presented (HAWKINS and 
Harvey); similarly for resistance in the tomato to infection by Macrosporium 
tomato (SANDO and RosENBAUM 
The question is pertinent whinhes the resistance or immunity shown by 
different species of Berberis to infection by Puccinia graminis is due to mechani- 
cal exclusion of the germ tube by a heavy cuticle. There is some evidence 
that this may be true for the evergreen thick leaved species of Berberis generally 
referred to Mahonia or Odostemon. Greenhouse inoculations with several 
forms of Puccinia graminis have resulted in infection of very young leaves of 
Berberis trifoliolata, B. Fremontii, and the tall form of B. Aquifolium=Odos- 
temon Nutkanus (DC) Rydb., although on the last named host only abortive 
pycnia and no aecia developed. Some other factor appears to be concerned 
in the immunity of Berberis Thunbergii to cereal stem rust, since this plant 
has soft, thin leaves which Jack a well developed: cuticle —FREEMAN WEISS. 
Further studies on Tmesipteris—The life history of the Psilotales is 
becoming as well known as that of more accessible lycopods through the 
continued researches of Hottoway,” who has published a second paper on 
the prothallus of Tmesipteris, containing additional observations made possible 
by the finding of more than 200 additional prothallia. Tmesipieris and 
Psilotum both have sporelings which resemble their gametophytes. This 
similarity is not considered by Hottoway as being sufficient evidence for the 
primitiveness of the Psilotaceae; but he points out that this close corres espond- 
ence is not found in the life history of other modern Pteridophytes. This 
resemblance between the two generations, the superficial position of the sex 
organs, the persistent single apical cell of the prothallus, the dichotomous 
» Hottoway, J. E., Further studies on the prothallus, embryo, and young 
sporophyte of Tmesipteris. Trans. New Zealand Inst. 53:386-422. 1921. 
