32 MORPHOLOGY 



(gametophyte) is represented by the ordinary gamete-producing plant, 

 and the sexless generation (sporophyte) by the spore-producing body 

 developed by the oospore. In subjecting this life history to what 

 is regarded as a critical test of the two generations, it has been dis- 

 covered that this special spore-producing body is not a sporophyte. 

 The test has to do with the number of chromosomes in the nucleus, 

 a number which is definite for each plant species. The chromo- 



85 



FIGS. 85-89. Coleochaete: 85, development of antheridia, by the division of a 

 vegetative cell into four cells; 86, a sperm (after PRINGSHEIM); 87, an oogonium, con- 

 taining an egg showing nucleus and chloroplasts; 88, the heavy-walled oospore, invested 

 by a jacket of sterile cells, and producing a multi cellular body each of whose cells pro- 

 duces a zoospore (after OLTMANNS) ; 89, a zoospore (after PRINGSHEIM). 



somes are doubled in number by the fusion of the sperm and egg to 

 form the oospore; and this means that at some other point in the life 

 cycle the number must be reduced again. Accordingly the sporophyte, 

 which arises from the oospore, is characterized by the double or 2X 

 number of chromosomes in its nuclei ; and the gametophyte, which 

 gives rise to the gametes, is characterized by the reduced or x number 

 of chromosomes. Upon applying this test to Coleochaete, it was dis- 

 covered that the special spore-forming body produced by the oospore 

 contains the reduced number of chromosomes and is therefore not a 



