SPERMATOPHYTA 389 



Fritillaria. In Fritillana, Tulipa, Ltlium, and certain other Liliaceae, 

 as well as members of other families, a characteristic development occurs 

 (Fig. 333). The four megaspore nuclei, arranged in a linear row, are not 

 separated by walls. As the embryo sac enlarges, the three lower mega- 

 spore nuclei migrate to the chalazal end. All four nuclei now begin to 

 divide, but before the division is complete, the three lower nuclei fuse. 

 As a result, a second four-nucleate stage appears, the two micropylar 

 nuclei being separated from the two chalazal ones by a large vacuole. 

 The micropylar nuclei are haploid, the chalazal ones triploid. After 

 another free-nuclear division occurs, the upper group of four nuclei give 

 rise to the egg, two synergids, and a haploid polar nucleus, the lower group 

 to three antipodals and a triploid polar nucleus. Sometimes only two 

 antipodals are formed. 



Plumhagella. The embryo sac of Plumbagella, one of the Plumbagina- 

 ceae, closely resembles that of Fritillaria. Four megaspore nuclei arise 

 without any wall formation. The three lower nuclei pass to the chalazal 

 end of the embryo sac, a large vacuole appearing between them and the 

 micropylar nucleus. The three chalazal nuclei fuse. Both nuclei now 

 divide and the embryo sac usually remains four-nucleate. The egg is 

 organized from one of the two haploid nuclei, an antipodal cell from one 

 of the two triploid nuclei. The fusion nucleus is formed by the union of 

 the two remaining nuclei, one of which is haploid and the other triploid. 



Plumbago. In Plumbago and several other genera of the Plumbagina- 

 ceae, a unique type of embryo sac is seen. The four megaspore nuclei, 

 formed without the appearance of walls and arranged in a cross-like man- 

 ner, undergo one more division. One of each pair of nuclei becomes a 

 polar nucleus, the second member of the micropylar pair is organized into 

 the egg, while the three other nuclei degenerate. The mature embryo 

 sac has only two nuclei — that of the egg and a fusion nucleus formed by 

 the union of the four polar nuclei. 



Adoxa. The type of development seen in this genus and in Sambucus, 

 both members of the Caprifoliaceae, has been reported in members of 

 many other families, but some of these {e.g., Lilium) have been shown to 

 belong to other types, while many others are doubtful. In Adoxa no 

 cell-wall formation accompanies the two divisions of the megaspore 

 mother cell, the four nuclei dividing again to form an eight-nucleate game- 

 tophyte. Thus the egg is separated from the megaspore mother cell by 

 only three free-nuclear divisions and all four megaspore nuclei participate 

 in the formation of the embryo sac. This has the ordinary type of 

 mature organization. 



Male Gametophyte. In angiosperms the male gametophyte is reduced 

 even more than in gymnosperms. No prothallial cells are produced. 

 Before the anther dehisces, the microspore nucleus divides to form the 



