594 SUMMARY OF CURRENT RESEARCHES RELATING TO 



identify the last division of the spermatogenous tissue until it is com- 

 pleted. 6. The first indications that this division is completed, and that 

 the androcytes have been formed, is found in the separation and rounding 

 off from each other of the cells. Next, the blepharoplast appears La the 

 cytoplasm apparently as a cytoplasmic differentiation in the androcyte 

 in which it functions. 7. The blepharoplast develops as a more or less 

 radially flattened band in a course closely applied to the plasma mem- 

 brane. The nucleus becomes closely applied to the blepharoplast, loses 

 its coarse network and stains homogeneously, and lengthens parallel with 

 and very closely applied to the blepharoplast. The development of the 

 blepharoplast precedes that of the nucleus. The nucleus and cytoplasm 

 during this process may not be kept entirely separate, but there are 

 indications of a certain amount of diffusion from one to the other. 

 8. As the blepharoplast and nucleus lengthen to form the mature sperm, 

 they fuse more closely and eventually become indistinguishable, forming 

 a homogeneous band or cord which in cross-section may be elliptical 

 and densely granular, or more nearly circular and hollow, showing the 

 structure to be, at certain stages of its development, tubular throughout 

 part of its length. 9. A vesicle, enclosed within the coiled body of the 

 sperm and containing cytoplasm and probably some nuclear material, 

 disappears as the sperm approaches maturity. The granular substance 

 of the vesicle is apparently used up in the process of development, 

 possibly being directly absorbed through the inner surface of the main 

 portion of the sperm. 10. The mature sperm is long and slender, 

 almost filiform, pointed at both ends, with two cilia attached at the 

 forward extremity of the blepharoplast. 



Sex Determination in Mnium hornum.* — M. Wilson discusses the 

 question of sex determination in Mnium hornum. He describes an axis 

 of this species which bears normal antheridia, bisexual organs, and 

 modified archegonia. The structure of these is figured. The sperma- 

 togenetic cells of the normal antheridia possess six chromosomes, and 

 since this is the normal gametophytic number, the plant in question 

 cannot have been produced aposporously. The author discusses the 

 results obtained by El. and Em. Marchal, and suggests that sex de- 

 termination is not bound up with meiosis, but is brought about by 

 metabolic processes which operate in the organism over a considerable 

 part of its life-history. 



Flattened Protonema of Tetraphis.f— AY. J. Hodgetts discusses 

 the vegetative production of a flattened protonema in Tetraphis pellucida. 

 Thalloid or flattened protonemata occur in Sphagnum, Andresea, Tetra- 

 phis, Tetrodontium, Buxbaumia, Diphyscium. But none of these mosses 

 (except Sphagnum) have been recorded as producing a protonema 

 vegetatively as many other mosses do. The author has, however, in 

 the case of Tetraphis growing under natural conditions, observed the 

 vegetative production of large flattened protonemata. They were found 

 in the leaf axils of stems which, being decapitated, were precluded from 



* Arm. Bot., xxix. (1915) pp. 433-40 (1 pi.). 

 t New Phytologist, xiv. (1915) pp. 43-9 (fig.). 



