18 Miyake, The development of the gametophytes etc. 



prothallial tissue in the center of the archegonial comjjlex of 

 Cimninghamia is certainly a primitive character. So far as Cunning- 

 Mmia is concerned, I can agree with Arno Uli in considering it 

 as more primitive than other memhers of the Cwpressinem so far 

 investigated. 



From the presence of a steril prothallial tissue in the arche- 

 g-onial complex, I consider Cunninghmiia as the most ])rimitive 

 of the three genera. Otherwise, Ounninghamia ag-rees with Taxo- 

 dium in the esseutial characters of the g'ametophytes. Cryptomeria 

 is considered as of more modern origin than the other two, as the 

 tapetum of the female gametophyte seems to be less developed 

 than the others. Lawson (1904) was not able to detect any ta- 

 petum in Cryptomeria, but Thomson (1905) has found a poorly 

 developed tapetum around the young female prothallium. 



Summary. 



The staminate cones begin to develop in the autumn of the 

 year preceding poUination. The pollen mother-cells are formed 

 before the end of the year. 



The division of the pollen mother-cell takes place about the 

 end of February or the beginning of March. The division shows 

 clearly the stages characteristic of the reduction-division, the reduced 

 number of chromosomes being twelve. 



The mature pollen-grain contains two cells, the larger tube- 

 cell and smaller generative cell. PoUination takes place during the 

 first half of April. 



As the pollen begins to send out tube, shortly after poUination, 

 the generative cell divides into the body- and stalk-cells, and these 

 move down toward the tube-nucleus which has previously found 

 in the tube. 



The stalk-cell soon looses its own cytoplasm and its nucleus 

 then passes the body-cell and lies near the tube-nucleus. 



The downward growth of the pollen-tube is at first relatively 

 slow and at the later stage it is much accelerated. The pollen- 

 tube reaches the female prothallium about the end of June and 

 penetrates into the depressiou just above the archegonial complex. 



The body-cell Avhich is very much enlarged and almost 

 spherical, now lies at the enlarged tip of the pollen-tube. It then 

 divides to form two sperm-cells which are equal in size. The 

 sperm-cell contains numerous starch-granules in its cytoplasm, and 

 is ready to fertilize soon after its formation. 



The pistillate cones begin their development in the autumn, 

 and a Single megaspore mother-cell is formed in each ovule shortly 

 before poUination, in the following spring. 



The megas])ore mother-cell divides about the time of i)oIli- 

 nation. The division commences with the synapsis stage and is 

 evidently the reduction-division. 



The usual number of the potential megaspores is probably 

 three. One of the megaspores, the lowest of the row, develops 

 into the female gametophyte. 



