456 GYMNOSPERMS LESS. 



The comparison of the reproductive organs of the pine 

 and larch with those of Vascular Cryptogams and of 

 Angiosperms will be facilitated by a consideration of two 

 exotic genera of palm-like Gymnosperms. In Zamia both 

 male (Fig. 122, A) and female (B) cones bear a close 

 external resemblance to those of Equisetum, the sporophylls 

 (sp. ph. $ , sp. ph. 9 ) being stalked hexagonal scales on the 

 inner surfaces of which the pollen-sacs (B, mi. spg) or ovules 

 (D, mg. spg} are borne. In the female Cycas the carpels 

 (E, sp. ph. $ ) are not arranged in a cone, but form a whorl 



FIG. I2i. A single carpel or female sporophyll of pine, with pla- 

 cental scale bearing two megasporangia or ovules. 



of leaf-like bodies obviously homologous with foliage leaves. 

 Each carpel is, in fact, a leaf 20-30 cm. long, and deeply 

 lobed at its edge : in the distal portion the lobes are long 

 and slender, but proximally they take the form of ovoidal 

 bodies (mg. spg), about the size of plums, the ovules or 

 megasporangia. 



The ovules differ strikingly in structure from the megaspor- 

 angia of Cryptogams. Each consists of a solid mass of small 

 cells called the nucellus (Fig. 119, D, net), attached by its 

 proximal end to the sporophyll, and surrounded by a wall 

 or integument (/) also formed of a small-celled tissue. The 



