1900 ] THE HAUSTORIA OF THE ERYSIPHEE hy Oy § 
at the sides of the hyphz exclusively, as Palla observed (24, p. 
70), but frequently from the end, as in figs. 29, 37. In all of 
the hosts mentioned, excepting Xanthoxylum, the haustoria 
agree in structure with those of &. communis. Fig. 31 shows the 
haustorium in one of the big parenchyma cells which form a 
sheath for the bundle. It also arises from the end of a hypha 
and contains a crystal which is so large as to distort the absorb- 
ing organ. 
The haustoria of Phyllactinia on Xanthoxylum Americanum 
offer some striking differences in comparison with the ones just 
described. The intercellular hyphe have thicker walls and the 
- intercellular appressoria are conspicuous, flattened, sucker-like 
structures appressed tightly to the cells of the leaf (jig. 28). 
The leaves of Xanthoxylum have a thin layer of loose paren- 
chyma. The bundles are near the lower epidermis. These facts 
of structure seem to influence the parasite. Its intercellular 
hyphe, as a rule, are short and the cells are thick. They are 
more vigorous in appearance, the walls are less delicate, and they 
stain more readily than the surface hyphe. Since the leaves of 
the host are thin the intercellular hyphe are shorter than in 
those hosts where the haustoria are developed far from the sto- 
mata. No appressoria were observed on the surface hyphe, 
though no special effort was made to find them. The appresso- 
ria of the intercellular hyphe are numerous and conspicuous. 
Even beyond the point where the haustorium is produced, the 
hypha may adhere to the cell (fig. 27). The chief point of inter- 
est, however, is the absence of typical haustoria. In a long 
search through many sections I was unable to identify surely a 
single absorbing organ having the typical structure for haustoria 
of the Erysiphee. There are numerous absorbing organs such 
as are represented by figs. 27 and 29. The penetrating tubes 
which pierce the host-cells are as minute as in Erysiphe, but the 
vesicles within the cells appear to have no protoplasmic contents, 
They have thick shining walls which, in exactly longitudinal sec- 
tions, appear to be continuous with the walls of the host-cells. 
It was supposed at first that they were young haustoria differing 
