90 MORPHOLOGY OF SPERMATOPHYTES 



The microsporangium passes the winter in the mother-cell 

 stage. About the 1st of May the mother cells are found in vari- 

 ous stages of the reduction division. The divisions do not 

 appear to be so simultaneous as in the Angiosperms, for in the 

 same sporangium some mother cells are preparing for the first 

 division, others contain completed tetrads, and others represent 

 every stage between (Fig. 68). In the same sporangium, also, 

 the division may be simultaneous or successive, although the 

 former seems to be the prevailing method; and they may be 

 tetrahedral or bilateral. As was stated in connection with the 

 female gametophyte, the reduction number of chromosomes 

 in Pinus silvestris and Pinus Laricio has been found to be 

 twelve. In 1892 Strasburger 31 counted twelve chromosomes in 

 the endosperm of Pinus silvestris. Recently Blackman 37 has 

 counted the same number in the oosphere, the jacket cells, the 

 ordinary endosperm, and the pollen mother cells ; while in the 

 first division of the oospore, and in the embryo, twenty-four were 

 counted. Chamberlain 39 obtained the same results from Pinus 

 Laricio, counting twelve chromosomes in the jacket cells, the 

 ordinary endosperm, and the pollen mother cells. The wings of 

 the spores begin to develop while they are within the mother cell. 



About May 20th the nucleus of the spore enlarges for its 

 first division (Fig. 69, D\ a spindle is formed rapidly (Fig. 

 69, E), and an equal division follows, so far as the mass of 

 chromatin is concerned. Before the cell plate is organized, 

 however, the nucleus nearer to the wall of the spore begins to 

 disorganize, and the other begins to enlarge (Fig. 69, F). In 

 this way a lenticular and disorganizing cell is cut off against 

 the wall of the spore (Fig. 69, G). A second division immedi- 

 ately follows, the spindle being observed about May 25th (Fig. 

 69, H). This division is a repetition of the first in details, and 

 the two lenticular cells disorganize rapidly (Fig. 69, I\ become 

 flattened against the spore wall, and very soon appear merely 

 as two thin and darkly staining disks (Fig. 69, J). 



It seems reasonable to suppose that these two evanescent 

 cells represent a vestige of the vegetative tissue of the gameto- 

 phyte, and they may be called properly vegetative cells. It will 

 be remembered that in the Cycads only one such cell is said to 

 appear, and that it persists; while in Ginkgo two appear and 

 the second one persists. 



