4 68 SCIENCE PROGRESS 



continuous at the back wall and it stretches over the lateral 

 ones somewhat like the fingers of a hand. Steinbrinck and 

 others see in the fibrous layer the mechanism for opening and 

 rolling back of the anther walls and they attribute its operation 

 to the cohesion of the water contained in the individual cells of 

 the fibrous tissue. As the anther ripens, more water is lost 

 from this layer than can be made good from the adjacent tissues 

 and the result is that the cell contents are in a state of stress 

 and the cells themselves tend to become smaller. But inasmuch 

 as the inner walls, as already explained, are practically rigid, 

 owing to the extensive thickening present there, the reduction 

 in size can only be effected by a collapsing inwards of the outer 

 sub-epidermal wall and of the membranous parts of the lateral 

 walls lying between the bars of thickening. These lateral walls, 

 owing to the bars, are springy ; they can converge as a whole 

 towards the anterior end (though as soon as the internal stress 

 is removed they might spring back to their former position). 

 Such a convergence at the sub-epidermal end of the lateral walls 

 would obviously bring about a stressed condition in the anther 

 wall as a whole. The external surface would occupy a smaller 

 area and equilibrium could only be restored by a curvature of 

 the wall as a whole, whereby the originally outer surface would 

 occupy the inner side of the curve, the outer being formed by 

 the unaltered back walls of the fibrous layer. And this is just 

 what actually happens. 



It is thus highly probable that a correct explanation of the 

 effective mechanism has been reached in many instances. The 

 anther wall is held in a rolled-back position owing to the con- 

 ditions imposed, by the cohesion of water in the fibrous cells of 

 the wall which have been compelled to assume a new and 

 appropriate form by the force in question. If water is supplied 

 to them they again become relaxed and the anther more or less 

 closes again. 



Nevertheless, there are difficulties in extending this "cohesion" 

 explanation to meet every case. In the anthers of the Torch 

 Plant (Kniphophia), for example, an arrangement of the fibrous 

 tissue is encountered which is at first sight difficult to reconcile 

 with it. Beneath the well-developed epidermis is a fibrous layer 

 composed of rather irregularly shaped spindle - formed cells 

 whose long axes run transversely round the cavity of the anther. 

 The cells are provided with annular rings of thickening which 



