910 TRANSACTIONS OF SECTION K. 



of the upper and lower epidermis of leaves of many species of plants. Among 

 these are portraits from life which are clearly recognisable, reproductions of 

 photographs of various kinds, flowers, and other objects direct, and it has even 

 been found possible to photograph trees, houses, and landscapes, and to reproduce 

 simple diagrams in colour on the autochrone plates of Messrs. Lumiere. 



Haberlandt put forward the hypothesis that the convergence of the light 

 rays causes a differential illumination of the protoplasmic layer on the basal 

 walls of the epidermal cells, and in some way sets up a stimulus which results 

 in the orientation of the leaf into the position in which it can obtain the most 

 suitable illumination. The alternative hypotheses (1) that the orientation of the 

 leaf may be bound up with the absorption of light by the chlorophyll grains, and 

 (2) that the convergence of the light rays may bring about a more efficient 

 illumination of the chlorophyll grains have not, in my opinion, been sufficiently 

 considered. A further possibility that the phenomenon is a purely incidental one, 

 due to the curvature of the cell-walls by turgescence, and not of any utility to 

 the plant, is also deserving of attention. 



Observations which have been made upon Schistosteffa osmundacea seem to 

 indicate a clear case of chlorophyll illumination, and in some Selaginellas and 

 Ilepaticffi a similar explanation is possible. So also in the case of Botrydimn 

 (jranulatum, the spherical form of the cell brings about a total internal reflection 

 of some part of the light rays which fall upon it and causes a very efficient 

 illumination of the chlorophyll grains which form a lining over the whole of the 

 inside of the wall of the cell. 



Haberlandt has described cases in which special cells or cell-wall thickenings 

 appear to be developed with a lens function. These appear to be only on the 

 upper epidermis. It is interesting to note that in a species of Mesembryauthemum 

 I have found these special lens cells equally abundant and well developed on 

 both sides of the leaf, and that in Garrya elliptica special lens thickenings of 

 the cuticle occur also equally well on both sides. In this last case they are 

 more or less regularly arranged over the whole surface, and appear to be inde- 

 pendent of the position of the epidermal cells. 



The elongate cells of such leaves as those of Hyacinth and Iris bring the 

 light rays to a focus in the form of an elongate bar of light. The epidermal 

 cells of Aspidistra lurida do not cause a convergence, but there is very distinct 

 and transparent nucleus in some of the cells through which an image was photo- 

 graphed. The epidermal cells of the petals of some flowers also form good 

 images through their curved walls, and in the case of a fungus, Russula emetica, 

 the spherical cells found in the pileus also bring about a convergence of the light. 



2. The Contractile Boots of the Avoid Sauromatum guttatum. 

 By Mrs. D. H. Scott, F.L.S. 



Contractile roots, which have the power of pulling bulbs and tubers down into 

 the ground, have been known for some centuries. Nehemiah Grew, in his work 

 on the anatomy of plants, published in 1682, writes of the descent of ' bulbous 

 roots ' being already known to * botanicks.' He goes on to describe the process 

 in the crocus, &c. ; and, in speaking of the cause of the descent, says : ' The 

 immediate visible one are the String-roots, which this kind of trunks frequently 

 put forth, which, descending themselves directly into the ground like so many 

 ropes, lug the trunk after them.' 



This mechanism has been worked out in more detail in the present day. 



In Sauromatum guttatum, a member of the Arum family, the bulb, if placed 

 on an inverted flower-pot, flowers without any water being given it. If then 

 planted on the surface of the soil it throws out leaves. When these begin to 

 wither the tuber gradually disappears from sight, and when dug up in about two 

 months' time was found 6 inches below the surface of the soil. It had thrown 

 out thick, fleshy roots from its upper surface, the tips of which had firmly attached 

 themselves by their root-hairs to pieces of broken tile, bracken, rhizomes, &c. 



