1882.] the Pollinium in Asclepias. 297 



tapetal membrane and the upper portion of the inner epidermis 

 which is never cuticularized becoming broken down ; an external 

 wall of several layers, and also in the lower two-thirds of the 

 loculus an internal, alone persisting, while in the upper third 

 the pollinium is freely exposed on that side which is directed 

 internally, a large oval longitudinal but slightly obliquely directed 

 aperture in the anther-wall being formed opposite each. This 

 disintegration appears to take place first at the apex of the loculus 

 and gradually to proceed downwards. The apices of the pollinia 

 are thus exposed first, and each pollinium immediately on its 

 exposure becomes attached to the free end of one of the 

 "appendages" of a corpusculum which directly impinges upon it, 

 and the end of which is still in a semifluid highly viscid condi- 

 tion. The attachment takes place just below the apex of the 

 pollinium, which is pear-shaped, the narrow end of the pear 

 being directed upwards and slightly obliquely away from the 

 median line of the anther, since the loculus in its superior portion 

 comes actually to abut by one end upon the extreme external wall 

 of the anther itself. It has the form of a minute adhesive surface 

 formed by the flattening of the viscid end of the "appendage" 

 against the external coat of the pollinium. The two parts though 

 externally united are however never confounded. The pollinia 

 being thus firmly held from above, the rest of the parenchymatous 

 tissue disintegrates, and the pollinia are left hanging freely sus- 

 pended in the two open pouches of the anther, and in no way 

 adherent to any portion of its substance ; the pair are separated 

 only by the median vertical dissepiment of the anther which 

 persists connecting the inner and outer sides of the anther 

 between the two cavities. 



Jacquin 1 , who examined the anthers only in their adult con- 

 dition when they had already dehisced in this introrse fashion, 

 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 Kolreuter and many 

 others, and when Schreber 2 in 1789 insisted that these sacs of 

 Jacquin were really anthers, he was instantly denounced by an 

 indignant host of authorities, although his opinion has been since 

 most amply confirmed and borne out. The comparatively late 

 period to which the tapetal membrane persists in Asclepias is a 

 noteworthy point : in other Dicotyledons it usually breaks down 

 in consequence of the growth of the pollen-grains after the 

 absorption of the walls of their special-mother-cells ; while in the 

 group of the Monocotyledons it becomes either diffluent or ab- 



1 Selectae Stirjjcs Amcricanae, 1763, p. 82. 

 a Genera Plantarum, p. 166 et seq. 



