42 MARGARET C. FERGUSON 



As soon as the microspore has reached maturity, there arises 

 within its nucleus one of the most beautiful, homogeneous, 

 loosely-looped and coiled spireme-bands that I have ever seen 

 in any dividing nucleus (fig. 54). The material studied showed 

 every stage in the first division, and all succeeding mitoses 

 which occur within the microspore, but they offer nothing 

 especially instructive from a cytological point of view, since 

 they conform to the typic method of division. I shall, there- 

 fore, describe and figure only such phases as are of interest in 

 tracing the development of the pollen-grain. It is interesting 

 to note that in the late prophase of all the mitoses which occur 

 in the development of the male gametophyte the achromatic 

 figure presents a very characteristic appearance, being sharply 

 monopolar at its outer or lower extremity and broadly multi- 

 polar at the opposite end. It thus forms a fan-shaped body 

 rather than one resembling a spindle. During the telophase it 

 usually becomes bluntly bipolar, though the upper pole often 

 remains to the last somewhat broader than the lower pole (figs. 

 55, 56 and 60, and plate V. A similar method of karyokinesis 

 has been noted by Wiegand ('99) in the development of the 

 pollen-grain in Potamogeton, by Duggar ('oo) in Symplocarpus, 

 and by Coker ('02) in Podocarpus. This mode of division will 

 be referred to again in connection with certain phases in the 

 development of the female gametophyte. 



In all the divisions which occur within the wall of the micro- 

 spore the nuclear substance is divided equally, the cytoplasm 

 unequally. The nucleus of the first prothallial cell, however, 

 never equals in size that of the apical cell and always stains 

 more or less diffusely, thus showing signs of disintegration from 

 the time of its organization (fig. 57). Fig. 58 shows one of the 

 very largest and most nearly normal of all the prothallial cells 

 observed. The nucleus of the apical cell enters the complete 

 resting stage, instituting a definite network within the meshes of 

 which one or more faintly staining nucleoli become apparent, 

 but this reticulum at once resolves itself into a homogeneous, 

 spireme exactly similar to the one first formed. When the 

 nucleus of the apical cell has reached the spireme-stage of the 

 second division, the first prothallial cell is invariably found 



