INTRODUCTION TO CEYPTOGAMIC BOTANY. 



89 



impossible to assert that the two were only distantly related. 

 We have here, then, indications of two distinct stages of ex- 

 istence, the first, animal, and the second, vegetable. But fur- 

 ther experience shows us that the organism which produces 

 these active cells, is no doubtful being, a mere Polypidom, as 

 it were, but a real vegetable, for in other Algae, we find two sorts 

 of organisms, the one of which produces from its bosom ordi- 

 nary spores, the other bodies precisely like the zoospores of 

 the Ulothrix. "We might expect, from the perfect resemblance 

 and identity of origin of these zoospores and spermatozoids, 

 for both arise from the protoplasm of the cells, that these 

 also would, after moving about, subside, and reproduce the 

 species. But this is not the fact; like spermatozoa, their 

 activity is of short duration, and capable of being destroyed 

 at once by iodine and other chemical bodies; when this 

 activity has ceased without the presence of any such injurious 

 substance, the bodies acquire no attachment, and do not 

 grow into a thread, but gradually decay. The spores, on 

 the other hand, make no progress, and retain their vitality but 

 a short time if kept alone, but if the two bodies are mixed 



Fig. 25. 



a. Portion of a thread of Vaucheria sessilis, Lyngb., shewing a spore 

 cell and an antheridium. The protoplasm of the spore cell is collected 

 towards the centre of the cell, which is filled with jelly, the apex has 

 ruptured, as also that of the antheridium, and the spermatozoids are 

 entering through the aperture. 



b. A spore perfectly formed, which, since impregnation, has acquired 

 a membrane. 



c. Spermatozoids. All more or less magnified. From Pringsheim's 

 memoir. 



