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 IN ORCniDE.E AND ASCLEPIADEiE. 507

Believing, tliercforc, this is to ho the only mode in [705 which impregnation is effected, I proceeded to examine the immediate clianges produced by the application of the pollen masses to the stigma.

From mnnei'ous observations and experiments made with this view, chiefly in Satyrina) or Ophrydea:*, and Are- thuseac, not however confined to these tribes, it was ascer- tained that the grains of pollen, soon after being applied to the stigma, either in the entire mass or separately, .produce tubes or hoyaux analogons to those first observed in one case by Professor Amici,^ and afterwards in numerous others, and in many families, by M. Adolphe Bronguiai't."

In Orchidese one tube only is emitted from the abso- lutely simple grain, while the number of tubes generally corresponds with that of the divisions or cells of the com- pound grain. These tubes are of extreme tenuity, their diameter being generally less than l-200th of an inch, and they acquire a great length, even ^vhile adhering to the grains producing them. From these, however, they separate generally while still involved 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 interrup- tions 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 power of 150. With a ctoc power of 300 or 400 indeed, extremely minute and very transparent granular matter may be detected; but such granules are very different from those which havi^ been supposed to belong to the grains of pollen.

As an entire pollen mass is usually applied to the surfjice

Atti della Sor. Hal. xix, par. 2, p. 25!•. Aminl, de.9 Sc. Xat. ii, p. 00. Annul, lies iSr. Nat. xii, p. '.\\.

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