504 



General Botany 



C.J. Chamberlain 



Fig. 312. South African cycads (Encephalartos), showing characteristic leaning trunks. 

 These specimens are probably 500 years old. 



The root system consists of a long tap root and usually some 

 basal adventitious roots. This root system is a distinct advance 

 over that of the ferns. The stem is surmounted by a crown of 

 leaves that is renewed by the growth of the terminal bud at 

 intervals of from i to 3 years. The pinnate leaves, like those 

 of the ferns, uncoil during their development. 



Cycads produce the two kinds of spores on separate plants. 

 The sporangia are borne on spirally arranged sporophylls that 

 are aggregated into cones. The microspores or, as we are accus- 

 tomed to call them in the seed plants, pollen grains are produced 

 in large numbers, in sporangia scattered over the under surface 

 of the microsporophylls or stamens. We may therefore call 

 this aggregate of microsporophylls the staminate cone. 



The ovulate cones consist of aggregates of megasporophylls, 

 each of which bears from two to eight megasporangia (ovules) 

 on its lower margins. In the more primitive species {Cycas) 



