GINKGOALES 41 



most identical with that in the Cycads. According to Pax,® 

 a many-celled archesporium is differentiated. The single thick 

 integument with a long and narrow micropyle, the large mass of 

 sterile nucellar tissue above the single megaspore, the conspicu- 

 ous and resistant nvicellar beak projecting into the micropyle 

 and containing a pollen chamber, the comparatively loose nu- 

 cellar tissue between the beak and the megaspore, are all as in 

 the Cycads (Fig. 31). Hirase ^^ says that the pollen chamber is 

 organized early in May, soon after the maturing of the pollen, 

 and that near the time of pollination it is fiiU of liquid. He 

 also observes that the chamber results from the exclusive devel- 

 opment of the external tissue of the beak, the inner tissue thus 

 becoming ruptured and disorganized. The changes which occur 

 in the nucellus in connection with tlie development of the pollen 

 tubes will be described under fertilization. 



III. THE GAMETOPHYTES 



THE FEMALE GAMETOPHYTE 



The development of the endosperm seems to proceed in the 

 same way as in the Cycads, although such full details are 

 not on record. However, the following sequence of events 

 is the same: free nuclear division, parietal placing of free 

 nuclei imbedded in a cytoplasmic layer, appearance of walls 

 resulting in the organization of a tissue, and gradual growth of 

 the parietal tissue toward the center of the sac, which it finally 

 completely fills. During this development the sac encroaches 

 upon the adjacent nucellar tissue, practically obliterating all of 

 it except that which caps the sac. Hirase has made the inter- 

 esting observation that about 256 free nuclei have been organ- 

 ized when walls begin to appear, representing eight successive 

 nuclear divisions. 



There are usually two archegonia, but sometimes a greater 

 number has been observed. They are exactly as in the Cyeads, 

 with two neck cells, and a central cell which develops remark- 

 ably in size and nutrient material (Fig. 34, A-C). As in Cy- 

 cads, also, the adjacent cells of the endosperm organize a layer 

 of jacket cells about the central cell, and a heavy wall is de- 

 veloped. It seems very probable that the central cell in this 

 case receives nutritive supplies from the jacket cells through 



