NOTES ON THE ERYSIPHACEAE 5 
ment of haustoria. The intercellular hyphae have thicker walls, 
and the intercellular appressoria are conspicuous, flattened, sucker- 
like structures pressed tightly against the cells of the leaf. So far 
as could be ascertained, these appressoria never give rise to the 
normal haustoria as in other examples of Phyl/actinia, the only 
penetrating organs observed being minute tubes, bearing a vesicle 
apparently without protoplasmic contents. These latter Smith 
considers to be modified or stunted haustoria. 
Neger’s paper is entitled ‘“ Beitrage zur Biologie der Ery- 
sipheen’’ (52), and is a valuable contribution to our scanty knowl- 
edge of the subject. Some points in this paper I shall here criti- 
cise in detail, and at the same time record some observations I have 
made on the same subject. 
Neger, by means of microtome radial sections, has carefully 
investigated the structure of the perithecial wall in many species o1 
the Erysiphaceae. Summarized briefly, the following modifications 
of structure were found. 
In Lrysiphe polygon, E. cichoracearum and E: galeopsidis no 
marked difference in the cellular structure of the lower and upper 
halves of the perithecium occurs. In £. graminis, and more 
markedly in Z. saurica, the perithecial wall consists towards the 
exterior of several layers of very strongly thickened cells with an 
almost obliterated lumen. These layers of thick-walled cells are 
more numerous on the under than on the upper side. In conse- 
quence of this structure the perithecium becomes in a dry condition 
(on loss of turgescence) slightly concave on the upper surface, but 
never on the under surface. It may be noted here that Neger is 
incorrect in stating (on p. 365) that the genus Erysiphe (excluding 
£. graminis) is characterized by “ Perithecien nicht dorsiventral,”’ 
as in &. taurica and in many forms of £. cichoracearum (e. g. 
the large form on Arctium) the perithecium becomes in the dry 
state very strongly concavo-convex. 
In the species of Sphaerotheca examined, no difference in the 
cellular structure of the wall in the lower and upper halves of the 
perithecium was found to exist; consequently the perithecium in 
drying contracts equally on all sides. 
In the genus Microsphaera (M. alni, M. euonymi, M. grossu- 
lariae, M. berberidis, and M. euphorbiae were examined) a well- 
