ii6 



MORPHOLOGY OF GYMNOSPERMS 





v^:^^^^^ 



The sporophylls are spirally arranged in a compact strobilus, and show 

 only slight traces of the pinnate character of the vegetative leaves. 

 At the apex and base of the cone the sporophylls are sterile, and the 

 remaining sporophylls bear abaxial sporangia in two more or less 

 distinct groups separated by a median sterile line (fig. 99). In the 

 median region of the cone the sporangia cover the entire abaxial sur- 

 face of the sporophylls and sometimes even their margins. In all 

 the genera the sporangia occur in soral groups of five, four, or three; 



but some sori may contain only two 

 sporangia, and in the more highly 

 specialized forms some of the spo- 

 rangia may occur singly. The sori are 

 surrounded by one-celled or two- celled 

 hairs, and such hairs appear even on 

 the lower portion of the sporangia 

 (figs. 100, in). 



The number of sporangia on a 

 sporophyll corresponds roughly to the 

 size of the sporophyll. The following 

 estimates have been made by Miss F. 

 Grace Smith (56) and by Cham- 

 berlain (63) : Dioon spinulosum 750, 

 Cycas circinalis 700, Encephalartos 

 Coffer 700, Macrozamia Miquelii 600, 

 Encephalartos villosus 500, Dioon edule 

 300, Ceratozamia mexicana 250-300, 

 Stangeria paradoxa 260, Microcycas 

 calocoma about 120, Bowevm spectabilis 

 67. A large number of sporangia on a sporophyll, and also the larger 

 number in a sorus, may be regarded as primitive features, while 

 fewer sporangia on a 'sporophyll and fewer in a sorus are probably 

 due to reduction. 



The first full account of the development of the microsporangium 

 was published by Treub (11) in 1881, who investigated especially 

 Zamia muricata. Lang's (22) work on Stangeria paradoxa confirmed 

 Treub's results in a general way and cleared up some doubtful points. 

 Later, Miss F. Grace Smith (56) studied abundant material of very 



Fig. 90. — Dioon edule: photo- 

 graph of two microsporophylls; 

 X^. — After Chamberlain (63). 



