STROBILI 



447 



rangia are produced. The name, however, suggests the Ukeness 

 of the microsporophylls to the stamens of ^lowering Plants. 

 The ovulate strobiU are strobili in which only megasporophylls 

 and megasporangia occur. The term ovulate suggests the like- 

 ness of the megasporangium to the ovule of Flowering Plants. 

 The megasporangia are now called ovules because they remain 

 closed, so that the female gametophyte is at no time exposed. 



It is obvious that the Cycads have carried the differentiation 

 of structures farther than the Selaginellas have. In Cycads, not 



Fig. 397. — Staminate strobilus and microsporophylls in Cycads. At the 

 left, a staminate strobilus of a Cycad (Dioon); at the right, microsporo- 

 phylls from two different Cycads, showing difference in shape, and the way 

 the sporangia are borne. After Chamberlain and Richa;^. 



only spores, sporangia, and sporophylls are differentiated, but 

 there is also a differeritiatioii of strobili. 



The strobili of Cycads are much larger than those of Selaginella 

 or Lycopodium, and the sporophylls are usually very different 

 from the foliage leaves. In some Cycads the strobili are a foot or 

 more in length and several inches in diameter. 



In the staminate strobili, the sporophylls are closely crowded 

 and practically have no resemblance to foliage leaves. They 

 vary considerably in shape in different Cycads, but have an 

 outer, expanded, sterile portion and bear the microsporangia, 

 usually grouped in sori, on their under surface {Fig. 397). 



The ovulate strobili are often much larger than the staminate 

 strobili. The megasporophylls are usually closely crowded, and 



