PRELIMINARY REMARKS. 3 
these, mingling together, form a magma, soon charged with pollen-tubes, all pervading 
the central space and confined within it: this magma now flowing over the stigmata, the 
pollen-tubes penetrate their papillee, and pass down the stigmatic channels of the style, 
eventually impinging upon the ovules; and thus the work of fertilization is effected 
without the aid, or even the possibility of insect agency. This mechanism, tending 
to the exact apposition of the several parts towards one another, and their appliance to 
functional purposes, appears so wonderful, and so very like the most ingenious design, 
that it cannot fail to excite our admiration. 
There is a considerable degree of analogy in the development and fertilization of the 
Apocynacee and Asclepiadacee, more so than is generally supposed. In the latter 
family the prevailing floral structure is different. The corolla is much smaller, its tube 
very short, its segments equilateral and expanded: within these segments is a corona of 
five, ten, or fifteen petaloid lobes, in one, two, or three series; but their use is not manifest. 
The five conspicuous stamens, alternate with the border segments of the corolla, are 
peculiar in their construction: they are fixed to the short tube of the corolla by broad 
filaments united into a short funnel, each continued into a free broad connective, and 
terminated by an expanded membrane, all connivent in the centre over the stigma, thus 
forming what may be called a stegium. Each connective bears inside two adnate anther- 
cells, sometimes divided into four; each cell consists of two distinct laminze, the outer 
one (exothecium) being part of the soft connective, the inner one (endothecium) being 
separable, forming a polliniferous lobule of an oblong form, terminating at one end in a 
thread. Here we find a singular arrangement: the thread of one of the lobules of one 
anther is conjoined at its apex with the thread of one of the lobules of the adjacent 
anther, and geminately united to a small corpuscle (retinaculum) which is agglutinated 
to one of the angles of the clavuncle, leaving them generally pendulous, but sometimes 
erect. Each endothecium is thick in substance, and is pitted all over with numerous 
minute hexagonal recesses, severally containing a granule of pollen, according to the 
analyses of Bauer and Brown *. The style is short, and surmounted in most of the genera 
by a very large, flattened, peltate, pentagonal clavuncle, its angles being furnished with 
nectarial glands, somewhat as in the Apocynacee, exhibiting in the centre, at the 
summit, two distinctly developed stigmata, often very short, which are studded all over 
with the usual papillee. The nectarial juice of the glands is now conveyed by the agency 
of capillary attraction along the threads of the lobules, and is diffused over their pollini- 
ferous surface; and under this stimulus the pollen granules expand into long tubes or 
boyaux, which spread in all directions, a sufficient number reaching and penetrating the 
papillee of the stigmata, thence passing down the ordinary stigmatic channels to arrive 
at the ovules. As the stegium is contrived so that nothing can enter that hollow space, 
it follows that the work of fertilization (as in the 4pocynacee) is here effected without 
the aid of insect agency. 3 
The apparent similarity in the mode of suspension of the pollen-masses in ico 
has suggested an affinity between that family and Asclepiadacee; but such an approxi- 
* Linn. Trans. xvi. p. 734, tab. 34. figs. 4-6, tab. 35. figs. 7-11. 
B 2 
