1900] THE HAUSTORIA OF THE ERYSIPHELE 167 
In fig. 6 the absorbing organ is in a thick-walled epidermal 
cell in the region of the midrib of the leaf. The vesicle has 
continued to enlarge until it has reached the form, but not the 
size of amature haustorium. It would never have possessed the 
usual sheath, because by pressure or fermentative action, or 
by both, it has escaped from its enclosing cellulose, which has 
approximately the same structure as the disintegrating papilla 
shown in fig. 5. The collar at its base, therefore, consists of the 
entire ingrowth and not of its basal portion only, as is common 
in most mature haustoria. It does not as yet contain a nucleus. 
Outside of the cell is shown a piece of mycelium containing 
numerous safranin-staining bodies which are probably food 
material of some sort. 
In fig. 7 is shown a nucleus making what appears to be an 
unsuccessful attempt to enter the haustorium. The hypha has 
been broken away so far that none of the pieces lying above the 
cell could be identified surely as belonging to the haustorium. 
The nucleus seems to find some difficulty in entering, either 
because of its size or, possibly, because the darkly staining 
material lying in front of it offers some resistance to its progress, 
The passage of the nuclei into the haustoria is naturally most 
difficult to see. This unsatisfactory example is the only case 
observed. The haustorium must attain nearly its full size, there- 
fore, before it is provided with a nucleus. Up to this time it 
contains only highly vacuolated protoplasm. It is difficult to 
find cases which show nuclei in position to pass down the pene- 
trating tubes into the haustoria. The few cases observed have 
been figured, but it cannot be said conclusively that these are 
the nuclei which were ultimately to find their way into the haus- 
toria. The nuclei of the hyphe are sometimes greatly elon- 
gated and narrowed (fig. rg). It must be in such a form that 
they make their way into the tube.‘ Fig. 7 is instructive in 
another respect. The sheath of the haustorium contained, when 
the material was fixed, nothing but fluid. The contents have 
been entirely consumed. But the bounding membrane is 
‘See also figures by Harper, 17, p. 663. 
