1908] YAMANOUCHI—APOGAMY IN NEPHRODIUM 297 



ture seems to become influenced by the artificial conditions. The 

 growth becomes very slow, and the cells show a tendency to increase 

 greatly in size, while under normal conditions mitosis would occur 

 before such a size had been reached. Probably for this reason mitotic 

 figures are less frequently met during the growth of such prothallia. 

 As the cell increases in size, its nucleus grows large and the mitotic 

 figure is generally larger than in normal prothallia of this species. 



It was not difficult to find stages of mitosis in the vegetative cells, 

 and their comparatively large size facilitated the accurate counting 

 of chromosomes. The resting nucleus contains a delicate reticular 

 structure consisting of a mixture of ragged clumps and slender threads 

 of chromatin. Nucleoli with conspicuous peculiarities of form are 

 always present; sometimes there are two to several isolated round 

 nucleoli scattered irregularly within the nucleus, and sometimes part 

 of them are arranged into a group or groups. They are likely to be 

 mistaken for chromatin nucleoli, but after a close examination of 

 serial stages in the development of the chromosome it is clear that 

 they lie entirely free from the chromatin network and do not seem 

 to contribute any material to the chromosomes by direct transforma- 

 tion. Cell contents beside the nucleus and cytoplasm are not so 

 abundant as in normal cases, the cell cavity consisting largely of 

 vacuoles. 



In prophase, the spirem is developed from the chromatin reticulum 

 {■fig. 4) as described for normal prothallia. The metaphase {fig. 5) 

 and anaphase {figs. 6, f) show no peculiar deviation from the typi- 

 cal mitosis. The number of chromosomes is 64 {fig. 8) or 66. When 

 two daughter nuclei are reconstructed, a cell plate is laid down 

 between them which finally divides the mother cell into two cells. 

 In this material the binucleate condition was seldom observed, so 

 that it may be claimed that the telophase of mitosis in the vegetative 

 cell is always followed by cell division, and that there is no migra- 

 tion of the nucleus of one cell to an adjacent one. 



As stated before, mitosis in the vegetative cells of the normal 

 prothallia and in those reproducing apogamously agree except as 

 to the axis of the spindle, which does not hold any regular relation 

 to the surface of the prothallia, the cell walls being laid down in 

 various directions. This is quite contrary to the condition in normal 



