222 PRACTICAL BOTANY 



4. The rapid movement of the large zoogonidium when free, 

 which may be followed with the naked eye, and under the 

 microscope is seen to be rotatory. The motile period lasts but 

 a short time, and varies in different species. 



Treat a zoogonidium, which has just escaped and is in rapid 

 motion, with a solution of iodine : put on a cover-slip, and 

 examine under a higher power : no cell-wall will be visible, 

 though the solution will in some measure plasmolyse the cell. 

 Turning more especially to the ectoplasm, there will be seen 

 numerous cilia, arranged in pairs, projecting from the surface 

 of the zoogonidium, while in the transparent ectoplasm will be 

 seen numerous highly refractive bodies, which stain with iodine : 

 these are nuclei, and a careful observation will show that their 

 position is exactly opposite the insertion of the pairs of 

 cilia. 



Treat a zoogonidium, which has come to rest, with a plasmo- 

 lysing agent such as 2 per cent, solution of common salt, 

 watching it meanwhile under a high power : the protoplasm 

 will contract, and a fine cell-wall will be seen. This result may 

 also be obtained by pressure on the cover-slip. 



Mount and examine zoogonidia which have already come to 

 rest, and by a comparison of them the process of germination 

 of the zoogonidia, and the development of new plants from 

 them may be deduced. 



