GNETALES— EPHEDRA 



373 



Fig. 355. — Ephedra trifurca: longitudinal section of 

 ovule, showing nucellus with deep pollen chamber 

 (/»), inner (i) and outer (0) integuments, and female 

 gametophyte with reproductive storage (5) and hausto- 

 rial (h) regions; X48. — After Land."* 



tip, and the sporangiophore {a in fig. 353) soon appears in its axil. 

 The two scales {p, in the figure) appear at 

 the base of the sporangiophore, and the hy- 

 podermal archesporial cells become recog- 

 nizable, not at the center of the top, but in a 

 circle around it. 



From this point up to the microspore, the 

 development is about as in any eusporangi- 

 ate microsporangium. The wall of the ma- 

 ture microsporangium in Ephedra trifur- 

 ^^338, 339 is very thin, with usually one layer 

 of crushed wall cells between the epidermis 

 and tapetum. The tapetal cells are very 

 large, several times the diameter of the epi- 

 dermis and wall cells together. In the vicin- 

 ity of Mesilla Park, New Mexico, the locality 

 of most of Land's material, the reduction 

 division, by which the microspore mother- 

 cell gives rise to four microspores, takes ^ 

 place about March 12. At the first division 

 in the spore mother-cell, a wall begins to 

 form, as if the bilateral type, characteristic p 

 of monocots, would result; but the incipi- 

 ent membrane disappears and spores of the 

 tetrahedral type are formed. 



The ovulate strohilus. — The ovulate stro- 

 bilus can be distinguished from the stami- 

 nate, even in the early stages, because it is 

 elongated and pointed, while the staminate 

 is globular (fig. 354). The ovulate strobili, 

 like the staminate, are in whorls of 2, 3, or 

 4, at the nodes of the small green branches. 



h- 



