4 Miyake; The development of the gametophytes etc. 



the poles, they appear as two thick and bent double rods (figs. 10, 

 11). Fig-. 12 Shows the chromosomes as they accumulate in both 

 poles of the spindle; the daughter-nuclei are then organized as 

 shown in fig. 13. 



The daughter-nuclei, between which no wall is formed, soon 

 become ready for the next division. The two spindles of the second 

 division, are eith er ^parallel or perpendicular to each other. Various 

 stages of the division are shown in figs. 14 — 18. After the four 

 grand- daughter-nuclei are completely formed, walls appear between 

 them and thus four poUen-cells or microspores are organized. Ultima- 

 tely a fresh wall is formed around each cell, and the microspores then 

 separate from each other by the dissolution of the original walls 

 (fig. 19). After the microspores are separated from each other, 

 they undergo a rapid growth and the walls become considerably 

 thickened (fig. 20). The fully-formed microspore is a more or less 

 spherical cell with a prominent nucleus ; the nucleus usually contains 

 a uucleolus. The wall of the microspore seems to consist of a thin 

 exine and a thick intine (figs. 20, 21). 



Development of the Male Gametophyte. 



Pollination begins, as a rule, in the first few days of April, 

 though the date differs somewhat by season as well as by locality. 

 In Kyoto one tree has begun to shed the poUen on April 4 in 1906. 

 In Tokyo pollination began in two different trees on April 1 in 

 1908. It usually lasts about ten days or two weeks. The pollen- 

 grain, at the time of pollination, contains two nuclei unequal in 

 size. The larger one represents the vegetative or tube-nucleus, 

 and the smaller one corresponds to the generative nucleus. The 

 two nuclei are separated from each other by a delicate plasmic 

 membrane (fig. 26). The division in the formation of these two 

 nuclei or cells seems to take place a few days before pollination. 

 Various stages of the division are shown in figs. 22 — 25. The 

 absence of the sterile prothallial cells seems to be the rule among 

 the Taxodieae and the Ciqjressineae. The same thing is also found 

 in the Taxeae^). In other groups of the Coniferae, one or two 

 prothallial cells are usually formed. 



A few days after poUination, the poUen found at the apex 

 of the nucellus begins to send out tube. The pollen-tube, pene- 

 trating the tissue of the nucellus, grows graduaUy downward. The 

 generative cell now divides into two, i. e., the so-called stalk- and 

 body-cells. The process of the division itself has not been observed. 

 The body-ceU then assumes a more or less spherical shape, while 

 the nucleus of the stalk-ceU soon looses its own cytoi»lasm and lies 

 free in the cytoplasm of the tube (fig. 27). Both the body-ceU 

 and the stalk-nucleus now enter into the pollen-tube, and move 



1) The genus Phyllucladus which was Ibrmally placed in the Taxeaf, 

 having two or three prothallial cells in the polleu, seems to have more affinity 

 to the Podocarpeae, and should better be excluded from the former (Pilger, 

 1905j Robertson, 1906; Kildahl, 1908). 



