174 



MORPHOLOGY OF GYMNOSPERMS 



regarded as a unique feature among gymnosperms until the terminal 

 and erect microsporangia of Cycadofilicales were discovered. The 

 Calymmatotheca type of stamen bears a terminal and erect synangium, 

 in which the sporangia occur in various degrees of "coalescence." 

 If such sporangia should fail to organize a 

 synangium and should remain separate, 

 such a stamen as that of Cordaitales would 

 be the result. 



THE MEGASPORANGIUM 



The young ovulate strobilus can scarcely 

 be distinguished from the staminate, the 

 ovules at that stage being completely hidden 

 by the overlapping bracts. Renault's 

 description (3) of Cordaianthus Williamsonii 

 will illustrate the structure of the strobilus 

 (fig. 207). Upon a thick conical axis con- 

 spicuous bracts are inserted in spiral 

 succession, and in some of their axils there 

 arises a very short dwarf branch which bears 

 some small bractlets and a terminal ovule. 



The ovule (fig. 208) has two integuments, 

 the outer one being described as thick and 

 fleshy, the inner one delicate but later be- 

 coming hard. The two integuments are free 

 from one another below, but are more or less 

 united above. They may correspond to the 

 outer fleshy and stony layers of the single 

 integument of cycads and Ginkgo. There is nothing to indicate 

 the presence of an inner fleshy layer. The nucellus is nearly 

 distinct from the integument, and develops a prominent beak 

 which contains a large pollen chamber. A single vascular strand 

 enters the chalaza and sends out two systems of branches, one 

 into the outer integument, and the other into the peripheral region 

 of the nucellus. The freedom of integument and nucellus, and 

 the occurrence of the inner set of vascular strands in the nucellus, 

 are the striking features of the Stephanospermum type of seed, as 



Fig. 206. — Cordaianthus 

 Penjonii: section showing 

 three stamens with their 

 sporangia; the stamen in 

 the middle bears four spo- 

 rangia, the one farthest to 

 the right having dehisced; 

 X23. — After Renault (3). 



