188 VANDE^. Chap. VII 



(7. saccafum a gentle touch from a fine needle was 

 necessary ; but in four other specimens a slight blow 

 was requisite. In G. tridentatum a stream of air and 

 of cold water from a small pipe did not suffice ; nor 

 in any case did a touch from a human hair ; so that 

 the antennae are less sensitive than the rostellum of 

 Listera. Such extreme sensitiveness would indeed 

 have been useless to the plant, for, as is now known, 

 the flowers are visited by powerful insects. 



That the disc does not separate owing to the simple 

 mechanical movement of the antennae is certain; for 

 they adhere firmly for a considerable space to the 

 sides of the stigmatic chamber, and are thus im- 

 movably fixed near their bases. If a vibration is 

 conveyed along them, it must be of some special 

 nature, for ordinary jars of manifold greater strength 

 do not excite the act of rupture. The flowers in some 

 cases, when they first arrived, were not sensitive, but 

 after the cut-off spikes had stood for a day or two in 

 water they became sensitive. Whether this was owing 

 to fuller maturity or to the absorption of water, I know 

 not. Two flowers of C. caUosum, which were completely 

 torpid, were immersed in tepid water for an hour ; 

 and then the antennae became highly sensitive ; this 

 indicates either that the cellular tissue of the antennae 

 must be turgid in order to receive and convey the 

 effects of a touch, or, as is more probable, heat in- 

 creases their sensitiveness. Two other flowers placed 

 in hot water, but not so hot as to scald my fingers, 

 spontaneously ejected their pollinia. A plant of C. 

 tridentatum had been kept for some days in a rather 

 cool house, and tiie antennae were consequently in a 

 torpid condition ; f. flower was cut off and placed in 

 water at a temperature of 100'' F. (37-7° C), and no 

 effect w*:s immsd lately produced ; but when it was 



