Fecundation in Orchidee and Asclepiadea. 705 
Believing, therefore, this to be the only mode in which im- 
pregnation is effected, I proceeded to examine the immediate 
changes produced by the application of the pollen masses to 
the stigma. 
From numerous observations and experiments made with 
this view, chiefly in Satyrine or Ophrydez, and Arethusez, 
not however confined to these tribes, it was ascertained that the 
grains of pollen, soon after being applied to the stigma, either 
in the entire mass or separately, produce tubes or boyaux ana- 
logous to those first observed in one case by Professor Amici*, 
and afterwards in numerous others, and in many families, by 
M. Adolphe Brongniart*t. 
In Orchidez one tube only is emitted from the absolutely 
simple grain, while the number of tubes generally corresponds 
with that of the divisions or cells of the compound grain. 
These tubes are of extreme tenuity, their diameter being gene- 
rally less than 1-2000th of an inch, and they acquire a great 
length, even while adhering to the grains producing them. 
From these, however, they separate generally while still in- 
volved in the secretion and mixed with the utriculi of the 
stigma ; and I have never observed an instance of a tube with 
its grain attached to it lower than the tissue of the stigma. In 
form they are perfectly cylindrical, or of equal diameter, neither 
dilated at the apex nor sensibly contracted in any part of their 
course. J have never found them either branched or jointed ; 
but have frequently observed apparent interruptions in the 
tube, probably caused by partial coagulations of the contained 
fluid. Even in their earliest stage, while in length hardly equal 
to the diameter of the grain, I have not been able to observe 
them to contain distinct granules in employing a magnifying 
* Atti della Soc. Ital. xix. par. 2. p. 254. Annal. des Sc. Nat. ii. p. 66. 
+ Annal. des Sc. Nat. xii, p. 34. 
4x2 power 
