Chap. VII. CATASETUM. 189 



looked at after an interval of 1^ 30™ tlie pollinium was 

 found ejected. Another flower was placed in water at 

 90" F. (32-2" C), and after 25™- the pollininm was found 

 ejected : two other flowers left for 20™- in water at 

 87° F. (30*5° C.) did not explode, though they were after- 

 wards proved to be sensitive to a slight touch. Lastly, 

 four flowers were placed in water at 83° F. (28-3° C.j ; 

 two of these did not eject their pollinia in 45™, and 

 were then found to be sensitive ; whereas the other two, 

 when looked at after 1^ 15™-, had spontaneously ejected 

 their pollinia. These cases show that immersion in 

 water raised to a temperature only a little higher than 

 that to which the plant had been exposed, causes the 

 membrane by which the discs are attached to rupture. 

 A thin stream of almost boiling water was allowed to 

 fall through a fine pipe on the antenna3 of some flowers 

 on the above plant ; these were softened and killed 

 but the pollinia were not ejected. Nor did sulphuric 

 acid, dropped on the tips of the antennae, cause any 

 action ; though their upper parts which had not 

 been injured by the acid were afterwards found to bo 

 sensitive to a touch. In these two latter cases, I 

 presume that the shock was so sudden and violent 

 that the tissue was instantly killed. Considering 

 the above several facts, we may infer that it must 

 be some molecular change which is conveyed along 

 the antennae, causing the membrane round the discs to 

 rupture. In G, tridentatum the antenna? were one inch 

 and a tenth in length, and a gentle touch from a bristle 

 on the extreme tip was conveyed, as far as I could 

 perceive, instantaneously throughout this length. I 

 measured several cells in the tissue composing the 

 antennae of this species, and on a rough average it 

 appeared that the stimulus must travel through no less 

 than from seventy to eighty cells. 



