1 74 ANGIOSPERMS. 



with that one of the axial row which develops into the embryo-sac. 

 The view held by the author is that the hypodermal cells in both cases 

 are macrospore mother-cells. In Lilium this macrospore mother-cell 

 becomes at once the macrospore, while in Helleborus it gives rise to 

 four spores. In both cases the reduoed number of chromosomes is 

 present, and the egg-cell of Lilium is hereditarily the equivalent of 

 the egg-cell in Helleborus. The number of cell-divisions elapsing 

 between that period in which the reduced number of chromosomes 

 appears and the differentiation of the sexual cells is of no importance, 

 since in many ferns, for example, thousands of cell-divisions occur 

 between these points in ontogeny. It seems, therefore, that the view 

 held here not only does no violence to either the facts of morphology 

 or cytology, or to the most widely accepted theory concerning the 

 significance of the reduction of the number of chromosomes, but it is 

 also in complete harmony with these facts. 



THE MALE GAMETOPHYTE. 



As in the case of the embryo-sac, the development of the male 

 gametes in the microspore or in the pollen tube, the male gameto- 

 phyte, is so well known that only the briefest mention of it is necessary. 



In the microspore of Lilium, in which the cytological details are 

 probably best understood, the antheridial or generative cell is clearly 

 differentiated from the remaining cytoplasm of the spore by a plasma 

 membrane. The generative cell is moon- shaped or crescentic in Lilium 

 candidum and L. martagon, and its cytoplasm behaves somewhat 

 differently toward certain stains, 1 so that the contrast between the gen 

 erative cell and the cytoplasm of the tube cell is often very striking. 

 Strasburger ('98), who attributes a fibrillar structure to the cytoplasm 

 of the generative cell, regards it as kinoplasm, and since some cyto- 

 plasm accompanies the male nucleus into the embryo-sac, the theory 

 may not be without significance. In Lilium and in many other 

 Angiosperms the generative or antheridial cell divides in the pollen 

 tube to give rise to the two male gametes, but in some instances this 

 division takes place in the spore. Each male gamete consists, there- 

 fore, of a nucleus surrounded by a small portion of cytoplasm derived 

 from the generative cell. 



Nothing need be added here concerning the growth of the pollen 

 tube toward the egg-cell of the embryo-sac. The result is the same 

 whether the tube enters through the micropyle or chalaza. The end 

 of the tube may enter the sac at one side of one of the synergidae, in 



1 . f., Flemming's triple stain. 



