300 The American Naturalist [April, 



times capable, it has been observed, of being fertilized as egg 

 cells and developing embryos (in cases of polyembiyony). 

 The lower cell (fig. 35, b) is the egg cell proper. The three 

 basal cells become partitioned off by walls also and are known 

 as antipodal cells; they appear to have no function in fertiliza- 

 tion (fig. 35, d). 



Development of Pollen: — The pollen or male germ cells are 

 produced in great quantities in the pollen sacs of the anthers. 

 They are formed in mother cells by two successive divisions of 

 the nucleus, thus there are four pollen grains produced in each 

 pollen mother cell (figs. 49 to 55). Later the nucleus of the 

 pollen grains thus formed divides again (fig. 39) forming two 

 cells in the grain, a small and a large one, the so-called 

 generative and vegetative cells. The generative nucleus 

 (fig. 40, b) of the small cell is the one important in fecunda- 

 tion. The vegetative nucleus (fig. 40, a) remains in the pollen 

 grain having no further role in fecundation, or according to 

 Guignard, sometimes passes into the pollen tube in advance of 

 the generative nucleus and follows down the tube as it 

 lengthens, until the micropyle is reached, when it gradually 

 disorganizes and before fertilization takes place has disap- 

 peared. At first these two nuclei are separated by a cell 

 wall but sooner or later the wall is broken down allowing the 

 two nuclei to float free in the protoplasm of the pollen grain. 

 Reduction of the Number of Chromatin Elements in Sexual 

 Nuclei. — Guignard 1 in a late article has emphasized the fact 

 that in sexual cells there is a reduction in the number of the 

 chromatin segments. In somatic cells he finds usually 24 

 segments, in the sexual cells the number is reduced to 12. In 

 the formation of the young tissue of the anther 24 bands are 

 uniformly present as far as the mother cells, the nucleus of 

 which receives, as have the others so far 24 segments. After 

 the complete differentiation of the mother cell it relapses for a 

 time into a state of repose before the two divisions which are 

 to form the pollen grain. When now the nucleus of the 

 mother cell begins to manifest division it shows all the normal 



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