CASPARY, ON THE ZOOSPORES OF CHROOLEPUS. 161 



observed in the middle of July, 1856, and in May, 1857 ; but 

 after the dry and hot spring of 1858, were sought for in vain. 

 They have never been found in the autumn, or late in the 

 summer. In order to find them, it is a good plan to leave a 

 piece of the bark covered with the plant in a damp vasculum 

 for a night. Chroolepus umbrinum usually forms solitary 

 globular cells, frequently, however, exhibiting two or three 

 together (figs. 18 and 19), and rarely as many as from four 

 to seven. The gobular or sub-globular cells are 0-0071 to 

 0*0098 mm. in diameter. The membrane is thick, and con- 

 sists of cellulose ; it is not coloured, however, by iodine, but 

 it becomes of a beautiful blue under iodine and sulphuric 

 acid. (Fig. 20.) The contents consist of small granules, 

 coloured reddish brown by the colouring matter adherent to 

 them ; they are turned to a dirty blue by iodine, and con- 

 sist of starch and of large, reddish-brown, highly refractive 

 oil-drops. Strange to say, the oil-drops are coloured a deep 

 dirty blue by iodine. The zoospores are not so numerous 

 as in C. aureum. The mother-cells of the zoospores are some- 

 what larger than the vegetative cells, but not otherwise dis- 

 tinguishable. The spores are larger than in C. aureum (figs. 

 21 and 22), and 0-0042 to 0-0043 in length. They are oval 

 on one side (fig. 21), but quite flat on the other (fig. 22), and 

 rotate perpetually in swimming. They have a clear border 

 (figs. 21 and 22, s) (? substantial or an optical appearance), 

 which remains after treatment with iodine, or with iodine 

 and diluted sulphuric acid. The apex of the zoospores is 

 colourless, the expanded hinder portion being filled with red- 

 dish-brown granular matter. They have two cilia at the apex, 

 which are two or three times as long as the cell. When treated 

 with iodine, the apex remains colourless and hyaline; the upper 

 part, however, becomes of a dirty blue colour. (Figs. 25 and 

 26.) If diluted sulphuric acid is employed after iodine, the 

 whole cell, including the apex and cilia, becomes of a deep 

 brown colour, but a tinge of dirty blue is still visible in the 

 middle of the cell. (Fig. 27.) 



The zoospores, therefore, of Chroolepus umbrinum, are acted 

 upon by reagents very similarly to those of C. aureum, the 

 difference being that the reddish-brown granular contents of 

 C. umbrinum are somewhat firmer, whilst the contents of 

 C. aureum consist of a substance not coloured blue by iodine. 

 It is particularly worthy of notice, that the hyaline apex of 

 the zoospores of both plants is not rendered brown, but re- 

 mains colourless under iodine, proving, it would seem, the 

 absence of nitrogenous matter in the covering of the zoospores 

 of Chroolepus, or at least in the apical portion of it. The 

 author was unable to separate the covering from the cell- 



