428 



THE VASCULAR PLANTS 



The sporangia which produce megaspores are called 

 megasporangia, and the sporophylls which bear them are 



called megasporo- 

 phylls. Similarly we 

 speak of the micro- 

 sporangia and micro- 

 sporophylls. All 

 these facts are also 

 true of seed plants 

 and the same terms 

 are used to describe 

 them. 



This matter is 

 made easier to un- 

 derstand by studying 

 the pictures. In 

 Figure 220 you see 

 the two kinds of 



FIG. 220. The two kinds of sporophylls of Sela- sporophylls, the two 

 ginella. The one at the left bears a sporangium T^J- n f cnnranm'a 



... ,, , . v ., .KJliUS (JL bLHJId.Ilt!Jil 



containing many small spores (microspores) ; the 

 one at the right bears a sporangium containing 

 just four large spores (megaspores). The mega- 

 spores and microspores are shown below the 

 sporophylls which bear them; note the differ- 



ence in size. 



which they bear, 

 and the two kinds of 

 spores which are pro- 

 duced. The mega- 

 sporangium contains only four megaspores. 



The life history of Selaginella may be indicated by the 

 following formula in which S stands for the sporophyte 

 generation and G for the gametophyte generation. 



,-, /megasporophylls megasporangia m 



S strobilussf . u 11 



\microsporophylls microsporangia mi 



megaspores 

 microspores 



- female G - egg \ 



^oospore - C 



male 



-sperm/ 



