CHAP. II. 
POLLEN. 
183 
membrane, acquires a pale yellow colour, and is now the per- 
fect grain of pollen.” {On Orchid, and Asclep. p. 21.) 
In 1832, Mirbel examined the developement of pollen in the 
anther of a Gourd. He states that ‘‘ when the flower-bud of 
this plant is about a line in length, each lobe of the anther is 
entirely composed of cellular tissue, the bladders of which 
present in general a pentagonal or hexagonal figure more or 
less regular when cut across. In every cell, without excepting 
even those which constitute the superficial layer of the lobe, 
are certain loose particles, of such extreme minuteness that a 
magnifying power of 500 or 600 diameters is required to exa- 
mine them satisfactorily. I cannot compare them to anything 
better than to little transparent bladders, nearly colourless, 
more or less rounded, and of an equal size. I examined the 
cells of the lobe of the anther one by one ; and I affirm that, 
at this early period, there is no trace of either the cells of the 
anther or of the grains of pollen. The whole of the tissue is 
perfectly uniform. In a flower-bud, but little larger than the 
first, I remarked on each side of the medial line of the slice a 
group, consisting of a few bladders, which were rather larger 
than the others, but otherwise like them. These larger bladders 
I propose to call pollen-cells, seeing that it is in their inside that 
the pollen is organised. In flower-buds, from I|- to 2 lines 
in length, some remarkable changes were observable. The 
pollen-cells had become larger ; their granules were so much 
multiplied that they were grouped and packed in opaque 
masses, and wholly filled the cells. These cells and granules 
together constituted a greyish body, joined to the rest of the 
tissue by the intervention of a cellular membrane, — a sort of 
integument which, notwithstanding its organic continuity with 
the surrounding parts, was readily distinguishable ; for while 
the bladders of the surrounding parts lengthened parallel to 
the plane of the surface, and to the plane of the base of the 
anther, those of the integument lengthened from the centre 
to the circumference. In anthers a little further advanced, 
the sides of the pollen-cells, instead of being thin and dry as 
they had previously been, acquired a notable thickness, and 
their substance, gorged with fluid, resembled a colourless 
jelly. The cellular integument continued to adhere by its 
N 4 
