1882.] the Pollinium in Asclepias. 291 



two smaller segments of oblong form and equal size 1 . The con- 

 spicuous nucleus of each of these oblong cells then becomes further 

 subdivided by vertical division at right angles to the length of the 

 cell. This division is followed by division of the protoplasm and 

 formation of a cellulose septum running in the same plane. The 

 walls formed by the two last series of divisions are of course only 

 visible in transverse sections. In the upper narrower part of the 

 anther lobe the number of longitudinal divisions which the pri- 

 mary-mother-cell undergoes is very small, and in consequence of 

 this, fewer long narrow prismatic cells are visible in a transverse 

 section through this part. Further, in this portion sometimes 

 only one of the two oblong cells formed by vertical division of the 

 narrow prism divides again vertically, so that in transverse section 

 three cells only are apparent in an oblique row, viz. one larger 

 and two slightly smaller. The cells formed by these successive 

 vertical divisions of the narrow prisms, each with a conspicuous 

 nucleus, are at first cubical, and in longitudinal section they are seen 

 to be disposed in numerous rows more or less horizontally arranged 

 one above another. Soon, however, they become spherical in form, 

 owing to the rounding off of their walls on all sides, though they 

 still remain firmly adherent together, and at the points where they 

 touch adjoining cells there still exists only a common partition 

 wall. They are the special-mother-cells of the pollen. At this 

 period the mass of granular protoplasm contained in each of them 

 cannot be discovered to have any special cellulose coat or wall 

 deposited on it, but is surrounded only by the wall of the special- 

 mother-cell. Thus none of the cell-walls so far produced in the 

 whole course of the development of the pollen undergo absorption 

 as is commonly the case, and as Reichenbach has shewn to be the 

 case in the waxy pollinia of the Orchids (where the mother-cells are 

 broken down and form a viscid pulp in which the tetrads lie) 2 , but 

 persist ; the cells which they bound, though now become rounded, 

 adhering, as has just been mentioned, closely to one another. 

 Their contents also never become now or subsequently set free 

 except on the rupture and bursting of the pollinium. By the 

 unequal extension of the whole loculus the special-mother-cells 

 contained in it now become polyhedral. They are formed by 

 division of the single primitive-mother-cell in three planes at right 

 angles to each other, but the rhythm of the divisions is quite unique 

 and is not that usually characteristic of Dicotyledons. 



1 The effect of all these divisions in the primary-mother-cell is merely to in- 

 crease the number of mother-cells from which the special -mother-cells are subse- 

 quently to be derived. 



2 Schleiden (loc. cit.) states that the walls of the primary-mother-cells in 

 Asclepias are absorbed, and that at a very early period. Such, however, is not the 

 case. In Naias, according to Hofmeister, they are resolved, along with those 

 of the special-mother-cells. 



