Embryo of Cryptomeria Japonic a. 427 
extend all the way to the centre of the prothallium. Now these delicate 
membranes take no part whatever in the formation of the cell-walls of the 
permanent prothallial tissue. As we shall proceed to demonstrate, these 
permanent cell-walls originate in quite another way. 
By the time the central vacuole has been completely closed by the 
ingrowing primary cells, the nuclei continue to divide without the formation 
of walls between them. As the membranes of the primary cells do not 
extend all the way across, the median region of the prothallium consists 
merely of numerous nuclei lying freely in the cytoplasm. These free 
nuclei, as well as those in the primary cells, now undergo a peculiar division, 
which results in the formation of permanent cell-walls. The manner in 
which these walls are formed is extremely interesting, and unlike anything 
that has so far been reported for the Gymnosperms. Sections of the 
prothallium at this time showed hundreds of the free nuclei in all stages 
of mitosis. The early stages in the development of the spindle clearly 
showed the multipolar character, indicating that they follow the same 
general method that prevails in the Angiosperms. As shown in Fig. 24, 
the mature spindle is quite narrow and sharply pointed at the ends. When 
the chromosomes reach the poles, numerous kinoplasmic fibrils stretch 
between them (Fig. 25), and by the time the daughter-nuclei are organized, 
these fibrils increase in number and curve outward on all sides. This 
condition is shown in Figs. 26, 27, 28. Ordinarily we should expect to find 
the cell-plate formed from these fibrils midway between the two daughter- 
nuclei, but this does not occur. The fibrils continue to increase in number 
and curve outward still further as shown in Figs. 29, 30. This process 
continues until both daughter-nuclei are completely surrounded by a sheath 
of fibrils. Of the somewhat spherical structure thus formed, the fibrils are 
all at the periphery and the nuclei are within, one at each end and 
surrounded by ordinary cytoplasm. Fig. 31 shows the appearance of one 
of these structures in cross-section — that is at right angles to the long axis 
of the spindle. The fibrils in section appear as small dots closely packed 
together, and arranged in a dense zone which completely encircles the two 
nuclei (Fig. 32). From this view the two nuclei cannot be seen at the 
same focus. The fibrils which compose these peculiar kinoplasmic structures 
fuse laterally with one another and are gradually converted into a permanent 
cell-membrane, which completely encloses the two nuclei. As these divisions 
of the free nuclei occur almost simultaneously, the prothallium at this time 
presents a most extraordinary appearance. The process goes on throughout 
the whole of the prothallium except in the region of the archegonial 
initials. All stages in the process could be observed in a single section. 
Fig. 24 represents a portion of the prothallium at this time. Although this 
division brings about the formation of the first permanent cell-membranes 
in the endosperm, no cell-plate is developed between the daughter-nuclei as 
