OF THE POLLINIUM IN ASCLEPIAS CORNUTI. 79 
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 (Pl. XVI. 
fig. 9). They are formed by division of the single primitive mother cell in three planes, 
at right angles to each other; but the succession of the divisions is quite unique, and is 
not that usually characteristic of Dicotyledons. 
That vertical wall of each of the limiting tapetal cells which is adjacent to the special 
mother cells now undergoes, at least in part, conversion into сит, and іп so doing 
increases considerably in volume; the chemical change is likewise accompanied by a 
change in colour from colourless to pale yellow. This change is followed successively 
by a like conversion of all the walls surrounding the special mother cells, which assume 
the same tint. On treating these walls with concentrated sulphuric acid a pale ruby-red 
colour is produced in all alike. 
In this manner the pollinium is produced; and it can at this period be extracted from 
the anther-loculus in the form of a single, definite, compact, solid, coherent mass, of con- 
siderable size, with a deep golden-yellow colour and a waxy look externally. Its surface, 
which is perfectly smooth, and not in the least viscid, as it is stated to be by Thomé, pre- 
sents the appearance of being divided in a reticulate manner into areole or hexagonal 
meshes, the apparent bulging of each areola being caused by the shape of the under- 
lying cell filled with protoplasm (Pl. XVI. fig. 10). 
Each pollinium contains all the adherent or firmly united special mother cells pro- 
duced in one anther-loculus or pollen-sac. In transverse section it exhibits a cellular 
appearance and structure, consisting of three series ог rows of cells * parallel to its sides, 
the middle series being more or less interrupted. These cells are enclosed by thick 
pale yellow-coloured semitransparent cell-walls, the cell-walls of those belonging to the 
two outer rows being continuous at certain points with, and surrounded by, a deep- 
_ golden-yellow, pellucid, cuticularized membrane, which has a resistant horny texture, 
cuts with great ease, and is derived from the change of those portions ofthe surfaces of 
the tapetal cell-membranes immediately adjacent to the special mother-cells. This mem- 
brane, forming an unbroken sheet, encloses and envelops completely every part of the 
entire, compact, solid, concrete mass of coherent special mother cells filling the anther- 
loculi, thus forming a general coat of considerable thickness. Brongniart (loc. cit. 
р. 267) and Schleiden (* Principles of Scientific Botany,’ ed. 3, 1849, p. 356) both 
Нате that this yellow investing membrane, which I have shown to be formed from the 
tapetum, was itself really of a cellular nature, і. е. composed of cells; for the former 
observer tells us that the areolate appearance is due “ not to the underlying cellular 
mass, but to the cells themselves which constitute the membrane, and which are 
disposed after the fashion of epidermal сейз;” while the latter regards it as formed “ of 
the outermost layer of the special mother cells in which no pollen-grains are developed.” 
* In the oblique planes of the original prismatic mother cells, each row consists of four cells, not three. The 
relation of the descriptions framed from the two points of view, viz. m and oblique, is Pound scen, 
however, on reference to the figures. 
