CEDOGONIUM. 



IOI 



opening through which the spermatozoid entered to fecundate 

 the egg. 



238. Dwarf male plants. — In some species there will also be 

 seen peculiar club-shaped dwarf plants attached to the side of the 

 oogonium, or near it, and in many cases the end of this dwarf 

 plant has an open lid on the end. 



239. Antheridium. — The end cell of the dwarf male in such 

 species is the antheridium. In other species the spermatozoid s 

 are developed in different cells (antheridia) of the same thread 

 which bears the oogonium, or on a different thread. 



240. Zoospore stage of cedogonium. — The egg after a period of rest starts 

 into active life again. In doing so it does not develop the thread-like plant 

 directly as in the case of vaucheria and spirogyra. It first divides into four 

 zoospores which are exactly like the zoogonidia in form. (See fig. 103.) 

 These germinate and develop the thread form again. This is a quite re- 

 markable peculiarity of cedogonium when compared with either Vaucheria 

 or spirogyra. It is the introduction of an intermediate stage between the 

 fertilized egg and that form of the plant which bears the sexual organs, and 

 should be kept well in mind. 



241. Asexual reproduction. — Material for the study of this stage of cedo- 

 gonium is not readily obtainable just when we wish it for study. But fresh 

 plants brought in and placed in a 

 quantity of fresh water may yield 

 suitable material, and it should be 

 examined at intervals for several 

 days. This kind of reproduction 

 takes place by the formation of 

 zoogonidia. The entire contents 

 of a cell round off into an oval 

 body, the wall of the cell breaks, 

 and the zoogonidium escapes. It 

 has a clear space at the small 

 end, and around this clear space 

 is a row or crown of cilia as shown in fig. 97. By the vibration of these cilia 

 the zoogonidium swims around for a time, then settles down on some object of 

 support, and several slender holdfasts grow out in the form of short rhizoids 

 which attach the young plant. 



242. Sexual reproduction. Antheridia. — The antheridia are short cells 

 which are formed by one of the ordinary cells dividing into a number of 

 disk-shaped ones as shown in fig. 98. The protoplasm in each antheridium 



Fig. 97. 

 Zoogonidia of cedogonium escaping. 

 At the right one is germinating and 

 forming the holdfasts, by means of which 

 these algae attach themselves to objects 

 for support. (After Pringsheim.) 



