424 H. MAESHALL WAED. 



granular protoplasm. In the preparation drawn the hyphse 

 are particularly luxuriant and thick, the diameter varying, 

 however, in different parts of their course. Several interesting 

 questions here suggest themselves. How are these hyphse 

 nourished in the '' middle lamella " ? Is any protoplasmic sub- 

 stance present ? Processes are very rarely sent into the cells 

 of the cortex ; the branches in the upper part of the drawing 

 are running over the cells and in the middle lamella, between 

 the cell which is drawn and one that would have lain nearer 

 the observer. The longitudinal hyphse often run for some 

 distance in the line of junction between three cells. The cells 

 contain pale chlorophyll-corpuscles ; a nucleus is present in 

 the one to the left, and a few crystals lie iii the large cell to 

 the right of it. 



Fig. 11. — A potato-tuber was sliced across, and the mycelium 

 ofPhytophthora, from a diseased potato planted on the clean 

 cut. The preparation was then put aside, and was not kept 

 particularly damp. On examining the sections cut vertically 

 to the cut surface, some time later, the mycelium was seen 

 attacking the tuber, as in the drawing. The cut surface of the 

 wound (at the top in the drawing) had undergone partial heal- 

 ing by means of tangential divisions of the exposed cells (the 

 rotten remnants of the cut cells were destroyed), and the two 

 or three tiers of cells thus cut off had become cork-like. The 

 contents of the cells were removed to a large extent in making 

 the preparation. The protoplasm or its remains turns coarsely 

 granular, and eventually rusty brown ; the starch-grains are 

 dissolving, remains of the nuclei are found as opaque, coarsely 

 granular masses, and here and there a crystal is noticed. The 

 mycelium is strictly intercellular, the branches running between 

 the cells in the narrow lacunae, or in the substance of the walls. 

 Eventually the cell walls soften and swell, and split apart, and 

 finally turn rusty red and decay. 



Figs. 12 and 13. — Cells of a diseased potato in a somewhat 

 more advanced condition. In addition to the changes above 

 referred to the cell walls are now swelling, and the cells sepa- 

 rating from one another at the middle lamella. In the pre- 



