483 Prof. H. Karsten on the Formation, 



by the different size of these cells in different mother cells, even 

 in the same anther. By the agency of diosmotic fluids, the 

 secondary pollen-cell detaches itself from the primary cell, and 

 contracts into an irregularly shaped or lobed body upon the 

 granularly cellular contents. 



It is at a somewhat later stage of development that these 

 large mother cells of the pollen-cells detach themselves singly 

 from their compartment (fig. 9). The central nucleus is then 

 still recognizable ; but its nuclear corpuscle is seen no longer^ 

 or with difficulty. The nucleus is situated between four deli- 

 cate-walled cells, the peripheral portions of the membranes of 

 which are closely applied to the mother cell. 



The membrane of the mother cell is more thickened, rather 

 unequally and in laminae ; at that part above the septal wall of 

 the two endogenous cells it is rather thicker, and at a later" 

 period its thickness becomes still more decidedly pronounced. 



By means of solutions of salts, of sugar, &c., it is possible, 

 even at this stage of development, to separate the contents of 

 the daughter cells fi*om the still delicate primary membrane. 

 The contents of each cell separately form a more or less spherical 

 and smooth mass, whilst the four together constitute a lobed 

 body seen within the centre of the mother-cell, which is divided 

 into compartments by very delicate membranes. These four 

 daughter cells behave, when treated with reagents, in an appa- 

 rently similar or identical manner with those of Cladophora 

 already described. Here also the four daughter cells coherent 

 in the centre may be isolated by the partial solution of their 

 primary cell-walls by reagents ; and if the mother cells were in- 

 jured by cutting, they are, although but rarely, pressed out 

 from it, nearly in the form in which Mohl represented this 

 'Vegetable CelP (taf. i. fig. 10). 



The granular contents of the secondary pollen mother cells 

 external to the daughter cells either vanish entirely, or a mu- 

 cilaginous-looking material appears in their stead around these 

 cells, in which case the delicate envelopes of the daughter cells 

 look like the inner contour of a thick-walled cell. In conse- 

 quence of these changes the pollen mother cell acquires a great 

 similarity to the next phase of development, in which, instead of 

 the central nucleus, a gelatinous mass occupies the centre of the 

 cell betwixt the four daughter cells (fig. 11). This breaking-up 

 of the regenerating nucleus of the cell (nuclear cell) is a sign of 

 the termination of the individual development of the mother 

 cell. The contiguous walls interposed between the four endo- 

 genous and much-distended cells form between them apparently 

 simple and very delicate laminae, which appear to subdivide the 

 cavity of the mother cell then filled with opalescent mucous fluid. 



