MOVEMENTS OF PLANTS. 655 



paralyze the latter, but have no effect on the spontaneous movements. 

 There is no special contractile tissue in these plants. 



Petals. The movements of opening and closing have been alluded to. 

 Other induced movements occur in connexion with fertilization, one of 

 the most striking of which is that of Pterostylis, an Australian Orchid, 

 where the lip has a tongue-shaped extremity covered with hairs and a 

 hinge-joint in the middle. If an insect alight on the tongue, the tip 

 bends upwards in such a manner as to imprison the insect, and fix 

 it up against the anther till he has removed the pollen. See also Drakea, 

 fig. 462, p. 372. 



Stamens curving towards or away from the stigma and dehiscing 

 when touched : Herberts vulgaris and other species, Parietaria judaica, 

 Sparmannia africana, Cereus grandijlorus, Helianthemum vulgare and 

 other species, and various plants of the tribe Cynarece. Other curious 

 movements of the stamens and pistils, and also of the staminodes, are 

 alluded to under the head of Fertilization. Heckel attributes the move- 

 ments of the stamens of Berber is to the alternate changes of form, now 

 long, now short, in the constituent cells of the stamens. In order to 

 verify this, M. Heckel availed himself of anaesthetics. The necessity for 

 doing this arises from the fact that immediately the stamens are cut, in 

 order to take from them a slice to examine under the microscope, con- 

 traction is caused ; but by, so to speak, paralyzing the cells, a section may 

 be taken, and the normal unirritated condition of the cells ascertained. 

 So treated, longitudinal slices of the irritable part of the stamen (the 

 concave inner surface in this instance) are seen, according to M. Heckel, 

 to be arranged in parallel rows, and each cell to be longer than it is wide, 

 its yellow contents being diffused throughout the cavity and applied to 

 the walls. An examination of the same cells in the excited or irritable 

 state shows that they become shortened, contracted, and gathered together 

 till they only occupy two thirds of their original space ; the contents of 

 each individual cell are collected together in the centre of the cavity, and 

 the outer cell-wall or envelope is thrown into transverse ridges. So, then, 

 in the one case the cell is at rest, in the other it is tense and contracted, 

 the seat of contraction being in the protoplasm lining the interior of the 

 cell- walls, rather than in the cell-wall itself. 



The opposite convex surface of the same stamen, with which an insect 

 visiting the flower does not come in contact, is not sensitive to external 

 impressions of this character, though it also shows contractile power 

 arising from internal causes. This contraction is exercised in a manner 

 directly contrary to that manifested by the cells on the inner surface 

 that is to say, that when in a state of rest, under the influence of the 

 chloroform, they are contracted, while after irritation they are distended. 

 They would thus have the effect of pulling the stamen back into its old 

 position after irritation. 



The peculiar movements of the pollen-masses of Orchids have already been 

 alluded to (p. 373) . Another illustration from Orchis pyramidcdis may here 

 be given. In this plant the two caudicles of the pollen-masses are connected 

 together by a saddle-shaped disk, the pollen-masses when in the anther 

 being nearly vertical in direction and parallel one to the other. When 

 removed from the anther by the proboscis of an insect or the point of a 

 needle (fig. 618, ) the saddle-like disk contracts so as to attach the 



