Fecundation in Orchidece and Asclepiadece. 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 Satyrinae or Ophrydeae, and Arethuseae, 

 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 Brongniartt. 



In Orchideae 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 l-2000th of an inch, and they acquire a great 

 length, even while adhering to the grains producing them. 

 From these, however, they separate generalh'^ 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. I 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 delta Soc. Ital. xix. par. 2. p. 254. Annal. des Sc. Nat. ii. p. 66. 

 f Jnnal. des Sc. Nat, xii. p. 34. 



4x2 power 



