MR. T. H. CORRY ON ASCLEPIAS CORNUTI. 183 
against the external covering of the side of the attenuated end of the pollinium, imme- 
diately below its apex, forming a slightly expanded adhesive surface, and so the two parts 
become firmly attached to each other (fig. 19). The pollinium being thus firmly held from 
above, the rest of the parenchymatous tissue disintegrates, an internal wall several layers 
thick, and in the lower two thirds of each cell an internal wall also, persisting. The ро! 
linia are thus left hanging freely suspended in the 2 open cavities of the anther, and 
in no way adherent to it, the pair being separated only by the median dissepiment. This 
latter persists. The pairs of contiguous pollinia belonging to adjacent anthers are, by 
the intervention of the corpuscular appendages and their corpuscula, attached to the 
upper part of the style-table below its margin. It is then possible, by inserting a fine 
needle between the contiguous anther-al: near the base of the alar fissure, and carrying 
it upwards along the line of the fissure, to lift away the corpusculum with its appendages 
and the two pollinia which are attached to them (fig. 19). 
Jacquin * , who examined the anthers only in their adult condition, when they had 
already dehisced, naturally regarded the anthers in which the pollinia lay freely immersed 
as * antheriferous sacs," and the pollinia themselves as the true anthers: in this he was 
followed by Kólreuter t, Rottboell $, and a host of others; and when Schreber $, in 1789, 
insisted that these sacs of Jacquin were really anthers, he was instantly denounced by 
an indignant host of authorities, although his view as to the true nature of these parts 
has been since most amply confirmed and borne out. 
It is an important feature that in the anther of Asclepias no special provision which 
shall determine its dehiscence exists, such as takes place in other plants by the reticulate 
thickening of the walls in a layer of cells immediately internal to the epidermis, i. e. the 
so-called * endothecium " of Purkinje |. Schleiden є states that the inner wall of the 
anther is torn away from the connective in the median line, and *that the wall of the 
cells which thus becomes disengaged is dry and elastic, and is termed the valve (valvula)."' 
This observation is certainly inaccurate ; for in every case dehiscence of the anther occurs 
solely by absorption of the tissue, and not by any portion becoming disengaged. 
The nearest instance which I have been able at present to discover to this type exhi- 
bited by Asclepias occurs in a case described by Hofmeister, where the anther-lobes open 
at the apex by a pore which results from the destruction of a small portion of tissue 
at this spot; but, in all probability, other instances of the same phenomenon will not be 
wanting when a more extensive and exact knowledge is attained of the various modes 
in which the dehiscence of anthers can take place. 
II. Море or FERTILIZATION. 
1. POLLINATION. 
A. Historical Sketch. 
That the Asclepiades are pollinated by the agency of insects has long been known. 
+ «Select: Stirpes Ашепсапе, 1763, p. 82. 
t ‘Anthera Contortum. Actorum Academiz electoralis Theodoro-Palatine V. vol. iii. Physic., 1775, рр. 41 et seq. 
$ ‹ Botanikens udstrakte Nytte,’ pp. 27 et seq. $ ‘Genera Plantarum,’ pp. 166 et seq. 
|| ‘De Cellulis Antherarum fibrosis.’ © Loc. cit. p. 359. 
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