ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 229 



direct division is the original and simplest mode of division of the 

 nucleus, from which the more complicated modes of indirect division 

 have sprung. In addition to some nuclei, direct division still prevails 

 in chlorophyll-grains. The division of many cells by constriction 

 may also be regarded as an analogous process. All stages of transi- 

 tion between the two modes of division may be conceived, and are in 

 fact presented, in the most various modifications, in the lower organ- 

 isms. The final development of indirect division depends mainly on 

 the close association of the processes of division of the cell and of the 

 nucleus. When the processes are commenced but not completed, we 

 get multinucleated cells. A peculiar and abnormal case occurs in 

 Anthoceros and Isoetes, where the processes of cell-division are adapted 

 to division of a chromatophore and not of the nucleus. Indirect division 

 of the nucleus is initiated by the cytoplasm, as is shown by the simul- 

 taneous division of the nuclei in some multinucleated cells, and in the 

 frequent accumulation of cytoplasm around the nucleus which is 

 about to divide. An instructive case occurs in the endosperm of 

 Galanthus, where the nucleus which is about to divide is surrounded 

 by an accumulation of protoplasm of fusiform shape and with longi- 

 tudinal striation, the direction of which corresponds to that of the 

 future nuclear spindle. In direct division he is of opinion that the 

 cytoplasm has no influence whatever. 



In the first stage of division of the pollen-mother-cells of Hemero- 

 callis fulva it often happens that more than two (from three to seven) 

 daughter-cells are formed. This results from the separate elements, 

 instead of approaching the pole when the halves of the nuclear plate 

 separate from one another, remaining in the equator of the spindle. 

 When the mass of uniting-threads increases, these are subsequently 

 pushed towards the periphery, and there form small independent 

 nuclei, eventually developing into small secondary cells, themselves 

 capable of further division, and thus giving birth to small but other- 

 wise normal pollen-grains. 



The first stage of division of pollen- and spore-mother-cells is 

 also characterized by the formation of a " secreting corpuscle." When 

 the nucleoli have just disappeared in the formation of the knots in 

 the filament, a homogeneous, strongly refractive substance usually 

 collects at one, or less often more than one spot at the surface of the 

 nucleus. Its shape is at first lenticular, afterwards spherical, and it 

 lies on the inside of the nuclear membrane. It becomes more and 

 more sharply differentiated from the network of the nucleoplasm, and 

 from the first takes a moderately intense colour from safranin and 

 methyl-green. In its interior are seen small vacuoles. Subsequently 

 it loses its capacity for receiving colour, and decreases gradually in 

 size, until finally it disappears in the cytoplasm when the nuclear 

 plate is formed. It is of uniform occurrence in the pollen-mother- 

 cells of all angiosperms and gymnosperms examined, and in the 

 spore-mother-cells of Equisetum limosum and Psilotum triquetrum. 

 The secreting corpuscles are possibly analogous structures to the 

 secondary nuclei observed by la Valette St. George and Grobben in 

 the spermatocytes of animals. 



