OF CAMPANULA. 93 
cell, by virtue (as I suppose) of some action of exosmosis, operating 
in conjunction with an opposite action of endosmosis on the part 
of the stigmatic tissue, the effect of both which actions is to pro- 
duce the revolution of the branches of the stigma (which until then 
are erect and in mutual contact and cohesion), and to remove every 
obstacle which would prevent the revolute stigma from coming 
into contact with the mass of pollen lodged upon the style. The 
withdrawal of fluid from the interior of the pollen-collector will 
necessarily cause the fine inner membrane to shrink : it is thereby 
shortened, and acting with tension on the external membrane of 
the hair, which is elastic and somewhat horny, the latter is drawn 
inwards, as the sliding tubes of a telescope are made to retire into 
each other, until the whole of the exserted hair is retracted into its 
base, which forms an embedded cavity in the substance of the 
style. An interval of at least a day, perhaps two days, may exist — — 
between the moment of dislodgement of the pollen from the anthers _ 
and its ultimate deposition on the stigmatic papilla. The pollen — — 
is emitted from the anthers when the flower is just opening: at —— 
this moment the anthers form a tube around the style and stigma, — 
the latter being scarcely protruded above the tube. As the flower — 
advances, the style is elongated to nearly twice its original length, 
or more, before the branches of the stigma begin to roll backwards: _ 
this elongation causes the pollen to be brushed out of the anthers, 
and the pollen then adheres very copiously to the style and back of 
the stigma; but as yet not a single grain can touch the stigmatic 
papillæ : this can happen only after the branches of the stigma are 
separated from mutual contact. Previous to the revolution of the 
stigma the pollen-collectors are retracted, those at the back of the 
stigma somewhat sooner than the rest ; and by means of the revo- 
lution the surface of the stigma is brought into close contact with 
the pollen-grains, a sufficient number of which are thus made to 
adhere to the stigmatic papillæ, and to produce pollen-tubes. The 
pollinic tubes penetrate between the papille, and between the 
stratum which they form and a layer of vascular tissue, into the- 
tubular central cavity of the style, which forms a channel of com- - 
‘munication with the placentæ. The course of the pollen-tubes 
