166 BOTANICAL GAZETTE [MARCH. 
sharp boundary separates the proximal from the distal end, 
The granular character of the latter gradually lessens toward the 
dense proximal end, which stains very slightly with safranin. 
The still slender penetrating tube is to be seen piercing this 
basal portion and extending into the now disintegrating distal 
extremity. It is to be observed that the plasmic membrane of 
the cell, by means of which the ingrowth has been formed, 
passes up the side and over the end of that structure. The 
gradual disintegration of this ingrowth of cellulose thus 
forms the early stages from which the true structure of the 
haustorium sheath can be understood. 
The growth of the haustorium now continues with accelerated 
speed. It will be seen in fig. 5 that the penetrating tube has 
taken a straight course through the cell wall and the basal por- 
tion of the papilla, for a distance approximately equal to the 
length of the collar in a mature haustorium. From that point 
on to the point where its growth was checked by the fixing fluid, 
the tube has pursued a rather tortuous way or else the distal sur- 
face of ingrowth has offered some resistance to the progress of 
the tube. The end of the tube has begun to enlarge into the 
vesicle which forms the body of the mature haustorium. The 
nucleus has not yet started in. The whole distal portion of 
the cellulose surrounding the end of the tube is now distinctly 
granular and takes a deep orange stain. The staining of the 
wall on the line of its original inner surface is no longer visible. 
The hypha from which this tube originated is sufficiently 
enlarged and flattened to fall within De Bary’s class of haustoria 
appendiculata, peculiar to forms of this genus possessing two- 
spored asci. Erysiphe communis, however, would be a species 
without appressoria, according to this classification. 
