ZOOLOGY AND BOTANY, MIGBOSCOPY, ETC. 803 



they meet with living leaves of Potamogeton lucens, which they pene- 

 trate in the same manner as Chlorochytrium Lemnce, forming resting- 

 cells within the tissue. These appear always to hibernate before 

 again developing into zoospores. 



Phyllobium dimorplium is another hitherto midescribed form, endo- 

 phytic in the leaves of Lysimachia nummularia, and occasionally in 

 Ajuga reptans, Chlora serotina, and Erythrcea Centaurium. The resting- 

 cells are very large, causing wart-like protuberances in the leaves of 

 the host. They are of two kinds ; the larger ones have a very thick 

 cell-wall, and peculiar tubular appendages at one or both ends ; the 

 smaller ones have no such appendages. The cell-wall of the larger 

 cells is as much as • 018 mm. in thickness, and is evidently composed 

 of two layers. It encloses a green protoplasm with a large roundish 

 nucleus, and a great quantity of starch, and a yellow or red oil of 

 peculiar properties, called by Cohn hcematochrome. Under certain 

 circumstances they contain peculiar, roundish, flat corpuscles, the 

 function of which is obscure. For the production of zoospores, small 

 masses of protoplasm 'ne first formed within the resting-cells, from 

 each of which is developed a small number of zoospores. At the 

 period of ripeness a particular point of the cell-wall of the resting- 

 cell gelatinizes, and through this opening the masses of protoplasm 

 force their way with beautiful regularity, the zoospores thus becoming 

 free. They are biciliated and of two kinds, alike except in size ; the 

 smaller ones being about 6 • 8 /x long and 5 • 7 yu, broad, the larger ones 

 8' 2 /A long and 7'0 //, broad.. These always perish unless they conju- 

 gate. They appear only to arrive at a conjugating condition after 

 moving about for a time. This always takes place between one 

 of each kind, the larger one remaining passive during the process, 

 the smaller one moving rapidly roimd it, then bringing its apex into 

 contact with the colourless apex of the other, and finally entirely 

 coalescing with it. The resulting zygozoospore has, as a rule, only two 

 cilia. The author never observed conjugation between two zoospores 

 of the same kind, nor between two from the same sporangium. Zygo- 

 zoospores with four cilia were occasionally seen, which may be the 

 result of the conjugation of two macrozoospores ; they are about 

 11*8 /A long and 8-8 /a broad. As soon as they come to rest they 

 become invested with a cell-wall, and then begin to put out a germi- 

 nating tube, which sometimes branches and assumes a great vai'iety 

 of forms. By means of these tubes they penetrate the tissue of the 

 host, especially in the neighbourhood of the veins of the leaves, 

 developing among the spiral vessels by apical growth, sometimes to a 

 length of several centimetres. To form a resting-cell, the tube swells 

 up at a particular spot, where the protoplasm congregates from the 

 various branches, this portion of the tube finally becoming separated 

 and rounded off. Whether more than one resting-cell is ever deve- 

 loped from the same tube was not clearly determined. The smaller 

 resting-cells are found beneath the epidermis, in the neighbourhood 

 of the stomata, either singly or in numbers ; they are much smaller 

 than the large ones, and appear to produce macrozoospores only, 

 between which conjugation was never observed. In some cases they 



