408 BOTANICAL GAZETTE [DECEMBER 
MITOSIS IN THE VEGETATIVE CELLS OF THE MALE, FEMALE, AND 
TETRASPORIC PLANTS. 
To make sure of the number of chromosomes contained within 
the nuclei throughout the life history, the mitoses in vegetative cells 
of the three forms of Polysiphonia plants—male, female, and tetra- 
sporic—were studied. The following is a very brief account of the 
essential features of these mitoses. 
The nuclei in the apical cells of any of the three forms of plants 
are somewhat larger in size than those in older region of the thallus; 
but although it is not difficult to obtain the successive stages of mitosis 
in older parts, the nucleus of the apical cell is somewhat more favor- 
able for study and will be used in this description. 
The cytoplasm in the apical cell shows very fine alveolar structure, 
the plastids lie near the wall, and the nucleus in the resting stage 
resembles that in the germinating carpospore and tetraspore (jigs. 26, 
45). The linin network becomes coarser (figs. 27, 46), and finally 
in the case of the male (figs. 28, 29) and female plants (fig. 36) 20 
chromosomes appear, whereas in the tetrasporic plant (fig. 47) 4° 
chromosomes are present. The chromosomes may be readily counted 
at metaphase in polar views of equatorial plates, when it is evident 
that the sexual plants have 20 (figs. 31, 38) and the tetrasporic plants 
40 (fig. 50). In spite of the small size of the nuclei, kinoplasmic 
accumulations at opposite poles of the nucleus are evident during 
prophase, and deeply staining centrosome-like bodies are conspicuous 
at the poles just before the spindle is formed (figs. 29, 36). Centro- 
sphere-like structures are very conspicuous at the poles of the spindle 
during metaphase (jigs. 30, 37, 48). These structures are more 
clearly shown in the mitosis in older regions of the thallus. Fig. 43 
illustrates such a mitosis from a female plant, those of the male and 
tetrasporic plants being omitted to avoid repetition. The smaller size 
of the nuclear cavity during metaphase is as constant a character of 
these mitoses as of those in the tetraspores and carpospores. After 
metaphase the two sets of daughter chromosomes remain included 
in the old nuclear membrane for a while (figs. 32, 39, 49)- During 
the anaphase the groups become further separated, the nuclear 
membrane disappears, and a large vacuole intrudes between them 
(figs. 33, 41, 51). When the daughter nuclei are completely formed, 
a cleavage furrow develops at the periphery"in the middle region © 
