Fecundation in Orchidee and Asclepiadea. 133 
of fecundation ; the tubes being merely the channels conveying 
them to the organ or surface on which they are destined to act. 
The arguments which might be adduced in favour of this, the 
generally received, opinion, would probably be the variety in the 
formi and size of the granules in different plants, with their great 
uniformity in these respects in the same species; added to the 
difficulty of conceiving in what manner the tubes themselves can 
operate. On the other hand, their great diminution in number, 
or even total disappearance, in Asclepiadez and Orchidez, long 
before the tubes have finished their growth, would afford an ar- 
gument of some weight at least against their essential import- 
ance in any case; and it may be added, that in Asclepiadex 
there appears to be no other source of nourishment for the tube 
until it has penetrated into the style, than these granules. Nor 
is it necessary to suppose that the tubes themselves act directly, 
it being even probable that they also contain a fluid or granular 
matter much more minute than that originally filling the cavity 
of the grain *. 
Our knowledge indeed appears to me not yet suflicient to 
warrant even conjectures as to the form of the immediate agent 
derived from the male organ, or the manner of its application to 
the ovulum in the production of that series of changes consti- 
tuting fecundation. I may however be allowed to observe, that 
. at present, with respect to this function, we are at least as far 
advanced in these two families, hitherto considered so obscure, 
as we are in any other tribe of Phanogamous plants: and I 
even venture to add, that in investigating the obscure subject 
of generation, additional light is perhaps more likely to be de- 
rived from a further minute and patient examination of the 
structure and action of the sexual organs in Asclepiadec and 
Orchidez, than from that of any other department either of the 
vegetable or animal kingdom. 
* See Additional Observations. 
ExPLANATION 
