88 INTRODUCTION TO CYTOLOGY 



becomes transformed into the cilia-bearing thread after the manner of 

 the blepharoplast of Equisetum, described below. 



Spermatogenesis in Pellia, Atrichum, and Mnium has been described 

 by M. Wilson (1911). In Mnium and Atrichum the spermatogenous 

 divisions show no centrosomes, whereas in Pellia centrospheres, and 

 probably centrosomes, are present during the later mitoses. The origin 

 of the blepharoplast as here described is very peculiar. In the spermatid 

 of Mnium a number of bodies are said to separate from the nucleolus and 

 pass out into the cytoplasm where they coalesce to form a limosphere, 

 The nucleolus then divides into two masses, both of which pass into the 

 cj'toplasm; one functions as the blepharoplast and the other gives rise 

 to an accessory body. In Atrichum the first body separated from the 

 nucleolus becomes the blepharoplast, a second forms the limosphere, and 

 a third the accessory body. In all three plants the blepharoplast goes 

 to the periphery of the cell and grows out into a thread-like structure 

 along the plasma membrane. The nucleus then moves against this 

 ( hread and the two grow together to form the spirally coiled spermatozoid. 

 Two cilia grow out from the anterior end of the blepharoplast. 



The most detailed and critical of all researches on the motile cells 

 of bryophytes are those of C. E. Allen (1912, 1917) on Polytrichum 

 (Fig. 29). The first of these papers contains a description of the cyto- 

 logical phenomena accompanying the multiplication of the spermato- 

 genous cells (androgones} up through the last mitosis, which differentiates 

 the spermatids (androcytes) . In the cytoplasm of all the androgones 

 there is a deeply staining kinoplasmic mass; in the early androgones this 

 has the form of a flat plate, while in the later ones it consists of a group 

 of granules (kinetosomes). Prior to each mitosis the plate or group 

 divides to daughter plates or groups which pass to the daugher cells. 

 In the cells of the penultimate generation (androcyte mother-cells) there 

 are no kinetosomes, but instead a spherical "central body" with radia- 

 tions. This body divides into two which move apart and occupy the 

 spindle poles during the last mitosis. Each resulting androcyte therefore 

 has one such body, which functions as the blepharoplast. Allen does not 

 regard the kinetosomes as definite morphological entities, but rather as 

 masses of reserve kinoplasm. The blepharoplast, however, is a definite 

 cell organ, and although Allen inclines toward the view that it is the 

 homologue of a centrosome he regards the question as an open one. 

 Sapehin (1913) looks upon these bodies as plastids. 



Allen's second paper deals with the transformation of the androcyte 

 (spermatid) into the spermatozoid. The blepharoplast elongates to 

 form a uniform rod and develops two cilia from near its anterior end. 

 The nucleus moves against the middle portion of the blepharoplast and 

 the two elongate together in close union to form the body of the sperma- 

 tozoid, the blepharoplast projecting beyond the anterior end of the 



