12 BOTANY AND PHARMACOGNOSY. 



is said to be ccenocytic, i.e., like a syphon. But it should be borne 

 in mind that the plant contains a great many nuclei, and as we 

 have seen (page 2) a nucleus with its associated cytoplasm 

 constitutes a unit of work. Hence such a plant as Vaucheria is in 

 a certain sense equivalent to a plant having as many uninucleate 

 cells as it has nuclei. It would probably be better to call such a 

 plant multinucleate rather than unicellular. 



Reproduction by means of asexual spores is brought about as 

 follows (Fig. S>, A) : A cross wall is formed near the end of one 

 of the branches, the end portion constituting a sporangium. The 

 contents, including numerous nuclei group themselves into one 

 large zoospore, which escapes through an opening in the sporan- 

 gial wall, and after swimming about for a time comes to rest 

 and germinates, giving rise to a new plant (Fig. 8, C, D). This 

 large zoospore is multinucleate and multiciliate. there being two 

 cilia for each nucleus, and by some botanists is considered to be 

 an aggregation of numerous biciliate zoospores. It is also of 

 interest to note that the zoospores of Vaucheria appear to arise by 

 a grouping of the cytoplasm and the nuclei already existing in the 

 sporangium rather than by repeated divisions of a single nucleus. 



Another method of reproduction in Vaucheria (Fig. 8, F) 

 is that by means of oospores, or spores formed by the union of 

 tgg and sperm cells. Two special branches are formed on the 

 thallus as sliort side shoots. One of these branches, known as 

 the oogonium (Fig. 8, og), is somewhat egg-shaped and sepa- 

 rated from the thallus by means of a cross wall. It contains a 

 great many chromatophores and considerable oil, and has a com- 

 paratively thick wall. The apex is somewhat beaked and con- 

 tains colorless protoplasm. The second branch, which is known 

 as an antheridium (Fig. 8, h). is smaller, somewhat cylindrical 

 and curved towards the oogonium. It is also cut ofif from the 

 thallus by means of a cross wall. The antheridium contains very 

 little chlorophyll, but a great many sperm cells. These are oval 

 or egg-shaped and have two cilia, one at each end. The sperms 

 escape from the apex of the antheridium and enter an opening 

 at the apex of the oogonium, one of them uniting with the egg 

 cell, which then develops a thick membrane, the resulting oospore 

 being a resting spore. 



