MOTILE MECHANISMS IN HIGHER PLANTS 469 



run completely round the thin walls. It would seem then that 

 the effect of any diminution of the water content in this tissue 

 would lead to a closer approximation of the rings as a whole, 

 accompanied by a sinking in of the intervening unthickened 

 parts of the membrane. And the effect of this over the whole 

 tissue would be to produce not a rolling back but an inrolling of 

 the flap. Such an inrolling of the edges just near the line of 

 dehiscence may, as a matter of fact, be observed but still the flaps 

 as a whole diverge and so open the pollen chambers. The 

 explanation is to be sought in the fact that the thickened ring is 

 more strongly developed at the back (towards the pollen cavity) 

 than at the front (next the epidermis) of the cell. Furthermore, 

 two adjacent rings are sometimes connected, others nearly so, by 

 an extension of the thickening over the intervening part of the 

 membrane at the back of the cell. 



In such cases the spindle or maggot-like cells of which the 

 fibrous tissue, in this plant, is composed would naturally tend to 

 curve in such a way as to produce precisely the curvature of the 

 anther wall as a whole which is actually observed. A further 

 extension of the mechanism in this particular instance is seen 

 in an increase, at the bases of the flaps, in the number of 

 rows of annularly thickened cells. 



That this is not a case of hygroscopic mechanism is proved 

 by the fact that when the cohesion of the water is destroyed, 

 e.g. by soaking in alcohol, the anther flaps curl inwards again 

 and cannot afterwards be induced to open either by drying or by 

 immersion in water. 



One specially interesting example of an anther mechanism 

 which acts like the fern sporangium may be adduced. The 

 Castor Oil Plant was observed by Steinbrinck to jerk out its 

 pollen forcibly. Opening of the pollen chamber is produced in 

 much the same way as has already been described for other 

 anthers but presently the elasticity of the walls overcomes the 

 cohesion of the water in the cells. The result is a sudden break 

 in the cohesion of the contained water; this is accompanied by 

 an instantaneous reversal of the curvature of the anther wall and 

 consequently the pollen is propelled from its surface. 



No attempt has been made here to deal at all exhaustively 

 with the recent work on the motile organs of plants but perhaps 

 enough has been said to justify the statement in the earlier part 

 of this article to the effect that the various mechanisms are con- 



