378 MORPHOLOGY OF GYMNOSPERMS 



the sterile ovule of the staminate flower, and with a lacerate tip whose 

 lobes spread during pollination in Gnetmn. The three genera differ 

 so much in the details of the structure and development of the mega- 

 sporangium that they must be considered separately. 



In Ephedra trijiirca (Land i8, 23) the inner integument is free 

 from the nucellus for more than half its length, and the two integu- 

 ments are free from one another except at the base, and are multiple 

 in origin (fig. 423). The inner integument, never more than two 

 cells thick, appears first in two distinct parts, but the later develop- 

 ment is zonal, so that when this integument elongates rapidly just 

 before pollination and protrudes through the apex of the flower, the 

 exposed tip is wide open and is slit a short distance down one side. 

 It also contains two rudimentary vascular bundles, and there is every 

 evidence that it consists of two fused members. The outer integu- 

 ment, which becomes several cells thick and later hard, appears first 

 in four distinct parts, and contains as many rudimentary vascular 

 bundles. Such a multiple origin of integuments was described in 

 connection with the paleozoic Physostoma (p. 35), one of the Cycado- 

 filicales. 



Although the single hypodermal archesporial cell w^as not observed, 

 its existence was evident from the subsequent stages, a parietal cell 

 being cut off, which together with the overlying epidermal cells pro- 

 duces a large amount of sterile tissue above the mother cell. About 

 the time that archegonium initials appear, the tip of the nucellus 

 begins to be disorganized, and this disorganization gradually proceeds 

 downward, until when the ventral nucleus is cut off there is a broad 

 circular opening, narrowing below, from the tip of the nucellus to the 

 endosperm (fig. 423, p). This is the deepest pollen chamber known 

 among g}'mnosperms, for it permits the pollen grains to rest upon the 

 necks of the archegonia. The pollen chamber is finally closed by a 

 plug formed by the endosperm cells, preventing the escape of the 

 embryo into the chamber. The development of the megasporangium 

 of Ephedra campylopoda, as described by Strasburger (3), is essen- 

 tially the same, except that the archesporium is said to consist of a 

 group of hypodermal cells. 



In fruit the bracts of the strobilus become much modified in Ephe- 

 dra, becoming red and succulent, or much enlarged and chaffy, and 



