I04 



GYMNOSPERMS 



6 cm., about the size of the largest seeds of Trigonocarpus. Most cy- 

 cads have seeds from 3 to 5 cm. in length. Zamia kickxii has very 

 small seeds, only a centimeter long, while Zamia pyi^maca, with seeds 

 from 5 to 7 mm. in length, has the smallest which have been meas- 

 ured. 



The principal features of the ovule are well illustrated by a longi- 

 tudinal section (lig. loi). Only the upper part of the nucellus is free 



Fig. 96. — Cycas circinalis: crown of sporophylls not yet expanded. The ape.\ of the 

 sporophyll has become merely serrate, there are no separate pinnae, as in Cycas revoluta. 



from the integument. After the ovule reaches its full size, as in the 

 illustration, the stony layer, with a fleshy layer on each side of it, is 

 very conspicuous. Later, as the female gametophyte grows, it ab- 

 sorbs most of the inner fleshy layer, so that it disappears, except as 

 a dry papery membrane closely applied to the megaspore membrane. 

 Usually two strong vascular strands enter the ovule. The outer 



