AGE CYCLE IN PLANTS AXD LOWER AMMALS 



249 



viduals. Various investigators, prominent among whom is Klebs,' 

 have investigated and analyzed the external conditions which 

 determine spore formation in the algae and fungi, and the results of 

 their work agree well with this idea. 



PI 



'^ "1.-'. ■:. 



mm 



hi-, m 



10? 



A 



101 g 



© 



?rt Qi 



'& 



107 C 



Figs. 106-108. — Formation of spores in lower fungi: Fig. 106, a terminal cell of 

 Saprolcgnia producing zoospores; Fig. 107, A-C, three stages in the development of 

 the sporangium in Mucor; Fig. 108, branches of the sporophore of PcnidUium, pro- 

 ducing series of conidia. From Coulter, etc., '10. 



While these forms in nature usually go through a more or less 

 definite life history in which vegetative growth or growth with 

 reproduction of new vegetative phytoids occurs for a time, and is 

 followed by the formation of spores and in many cases still later 



' See Klebs, '93, '96a, '96^, '98, '99, 00(2, 'oo/>, '03, '04. 



