162 BOTANICAL GAZETTE [MARCH 
effect. Harper (17, p. 664), disagreeing with De Bary, thinks 
that among the Erysiphez this peculiar sheath is, as in Puccinia, 
the disorganizing nucleus of host-cell. The delicate bounding 
membrane would, therefore, be the nuclear membrane. 
I have not found evidence of such a relation between haus- 
torium and host nucleus in the Erysiphee. In the examina- 
_ tion of many sections in searching for stages in the development 
of the haustoria, it becomes more and more clear that the host- 
nuclei and haustoria are indifferent to each other. The sheaths 
are present around the haustoria even if there are several infest- 
ing one cell, as frequently happens. In such cases, if the cell is 
not so full of haustoria as to obscure the cell contents or crowd 
the nucleus, that body can be seen ina more or less normal con- 
dition. In the cells of hairs which are large enough to contain 
several haustoria easily, the sheath of each can be seen. while 
the host-nuclei occupy distant positions in the cells. The 
sheaths are to be accounted for in another way, as will be shown 
subsequently. 
In most of the figures the host-nuclei lie at a greater or less 
distance from the haustoria. When, as in fig. 76, the connection 
between the two is close, the nuclei are more or less disorgan- 
ized. But the cases figured make the proportion seem much too 
large to be in accordance with the facts. The sheath is not 
usually bounded by a tensely stretched membrane (jig. 7 repre- 
sents a special case), but by a membrane having a more or less 
irregular outline in section, beginning where the cellulose collar 
Stops. The orange-staining contents are usually present in more 
or less abundance, except in Evysiphe graminis on Poa, where. 
only the sheath is present and is sometimes inconspicuous. 
The outer walls of the epidermal cells have an affinity for be 
Safranin stain, but the collar about the haustorium neck stains 
much more delicately with it. In fig. 10, shown because the 
cell was plasmolyzed, the collar is distinct from other parts and 
appears under the microscope very slightly stained with safranin. 
Again (as in jigs. 16, 21, and frequently in other figures), the 
reaction is such that the neck of the penetrating organ 
