LINNEA.N SOCIETr OF LONDOX. 3 



Mr. William Booth Waterfall was proposed as a Fellow. 



Miss Eleanor Pearse, B.Sc. (Lond.), and Mr. James Moore 

 Williams were severally balloted for and elected Fellows. 



Mr. Harold AVageii,F.E.S.,F.L.S., gave a lantern demonstra- 

 tion on " The Optical Behaviour of the Epidermal Cells of Leaves." 

 He stated that Professor Haberlandt had suggested that the 

 epidermal cells of certain leaves are functional as ocelli or primi- 

 tive eyes and are capable of the perception of light. The structure 

 of these cells is such that the rays of light which fall upon them 

 are refracted and brought to a focus, and in one case Haberlandt 

 was able to obtain a photograph of a microscope the image of 

 which was focussed upon the basal walls of the epidermal cells. 

 This image, as figured in his book, is not very clear, and it has 

 since been found possible to obtain much clearer images of a 

 variety of subjects through the cells both of the upper and lower 

 epidermis of many leaves, including portraits from life, flowers, 

 houses and landscapes, reproductions of photographs and pictures, 

 and simple diagrams in colour on the autochrome plates of 

 Messrs. Lumifere. 



In order to explain this lens-function, Haberlandt has put 

 forward the extremely interesting hypothesis that the convergence 

 of the light rays causes a differential illumination of the proto- 

 plasmic layer on the basal walls of the epidermal cells and sets up 

 a stimulus which results in the orientation of the leaf into that 

 position in which it can obtain the most suitable illumination. 



There is no doubt a good deal of evidence in favour of Haber- 

 landt's view, but there are many facts to be explained before a 

 definite conclusion can be arrived at. For example — convergence 

 takes place in the lower as well as in the upper epidermal cells, as 

 shown by Albrecht for Viscum and by the exhibitor in many other 

 plants. In a species of Mesembryanthemum there are special lens- 

 cells equally well developed on the lower surface as on the upper 

 surface. In Garrya elliptica also there are special lens-shaped 

 thickenings of the cuticle equally well developed on both surfaces. 

 The papillate cells of many petals show a very clear convergence. 



It is not impossible that the convergence may bring about a 

 more efficient illumination of the chlorophyll grains. Haberlandt 

 himself suggested something of this kind many years ago, and the 

 numerous observations which have been made upon ScMsiostega, 

 Osmundaceoe, some Selaginellas and Hepatics, and other plants, 

 and some observations by the exhibitor upon Botrydium granu- 

 latum, all clearly indicate that this hypothesis must be taken into 

 account. It is significant, also, that epidermal cells v^■ith long 

 focus appear to be associated with long palisade-cells, whilst the 

 cells with short focus are associated with short palisade-cells. 



The President and Dr. S. E. Chandler commented on the exhi- 

 bition, and the Author replied. 



62 



