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SCIENCE 



[N. S. Vol. XXVII. No. 6S7 



present strikingly different characters at 

 different stages in the development of the 

 individual. 



A Unicellular Marine Broivn Alga: Dr. G. 

 T. Moore, Marine Biological Laboratory. 

 (By title.) 



The Cytology of the Male Gametophyte of 



Polytrichum juniperinum: Professor C. 



B. Allen, University of Wisconsin. 



The chromosome number in somatic and 

 spermatogenous cells is six. In vegetative 

 divisions an aggregation of cytoplasmic 

 materials, but no definite body of kino- 

 plasmic or centrosomal nature, appears in 

 the region of the spindle poles. 



In the early spermatogenous divisions, a 

 dark-staining plate appears at each pole; 

 fibers connect the two plates, forming a 

 broad-poled spindle. These plates persist 

 during the division. 



In later divisions appears a group of 

 bodies similar to the "chromidial fila- 

 ments ' ' of animal cells. The group divides 

 into two, which separate from one another 

 and pass to the poles of the future spindle. 



In one or more of the latest spermato- 

 genous divisions, probably only in the last, 

 a dark-staining granule, surrounded by as- 

 tral radiations, appears in the cytoplasm 

 near the nucleus. This divides into two 

 granules, which separate and, each with its 

 aster, pass to opposite sides of the cell. A 

 spindle is formed between the two granules, 

 the nuclear membrane disappears, and 

 nuclear and cell division completed. 

 After "the formation of the spindle, the 

 polar radiations disappear; the polar gran- 

 ules become less distinct, but are sometimes 

 seen as late as the telophases. Cell division 

 is in all cases by means of a cell-plate. 



After the last division, the cell walls are 

 dissolved and the cells round up. Each 

 now contains, besides the nucleus, a long 

 rod (the blepharoplast) lying just inside 

 the plasma membrane, and a large dark- 



staining body, which becomes constricted 

 into two (bodies a and b). The nucleus 

 becomes applied closely to the blepharo- 

 plast, pushes out a beak toward one end of 

 the latter (the anterior end), and elongates 

 gradually into a slender spiral of about one 

 and one half turns. After the early stages 

 the blepharoplast can not be distinguished, 

 except that its anterior end seems to extend 

 a short distance beyond the nucleus. The 

 two cilia grow out from this portion of the 

 blepharoplast. Body a becomes applied 

 closely to the anterior end of the blepharo- 

 plast, persisting to a very late stage. It 

 may give rise to a slight swelling at the 

 anterior end of the mature antherozoid. 

 Body b becomes attached to the posterior 

 portion of the nucleus and persists, form- 

 ing the "vesicle" which is for a time at- 

 tached to the mature antherozoid. 



Apogamy in Nephrodium: Dr. S. Yaman- 

 oucHi, University of Chicago. (By in- 

 vitation.) 

 The nuclear condition in Nephrodium 



molle may be summarized as follows: 



1. The nuclei of the prothallia contain 

 64 or 66 chromosomes, the x number, and 

 the nuclei of the gametes contain the same 

 number. The fusion nucleus in the fertil- 

 ized egg presents 128 or 132 chromosomes, 

 the 2x number, Avhich remains unchanged 

 until it is reduced during sporogenesis. 

 Consequently, in the normal life history of 

 Nephrodium the gametophyte generation 

 contains the x number of chromosomes and 

 the sporophyte generation the 2x number. 



2. The nucleus of a prothallial cell with 

 the X number of chromosomes (64 or 66) 

 sometimes become directly the nucleus of a 

 sporophyte, apogamously produced ; so that 

 the X number of chromosomes continues 

 through the whole life history of the apog- 

 amous sporophyte. This fact does not 

 seem necessarily to affect the fundamental 

 idea that the alternation of generations is 

 marked by the difference in the number of 



