1897.] Mr Darwin, Observations on Stomata, etc. 303 



Monday, 10 May, 1897. 

 Professor Liveing, Vice-President, in the Chair. 



The following Communications were made to the Society : — 



(1) Observations on Stomata by a new method. By Francis 

 Darwin, M.A. 



I. 



Our knowledge of the behaviour of stomata is defective 

 principally for want of good methods. The earlier workers simply 

 stripped off the epidermis and examined the stomata microscopi- 

 cally. This plan is obviously untrustworthy and has been replaced 

 by a better method, i.e. cutting surface sections. This is less 

 inaccurate but is still open to the objection that it does not give 

 evidence of the condition of the stomata in the uninjured leaf. 

 Where the stomata are large it is possible with a microscope to 

 see whether they are open or shut in the uninjured leaf; this is 

 the method followed by Kohl*. The chief objection to this plan 

 is that it can only be used in certain selected plants, e.g. Trianea, 

 Caltha, and that it is laborious and requires considerable practice. 

 Lastly, there is the method of N. Mullerf, in which the condition 

 of the stomata is estimated by the rate of flow through them of a 

 stream of air. 



Another set of methods are indirect in character and depend 

 on the fact that in aerial leaves the loss of watery vapour takes 

 place almost entirely by the stomata and not by the cuticle. 

 In a leaf with stomata on the lower surface only, transpiration 

 is all but confined to that surface. Such a leaf placed between 

 two glass plates will bedew the lower but not the upper plate. 

 Various methods have been founded on this basis. 



MergetJ used paper soaked in mixture of certain salts of 

 palladium and mercury, the paper is applied to the surface of 

 the leaf and becomes black or brown owing to the moisture 

 coming off from the stomatal side. 



* Botanisches Bciblatt zur Leopoldina, 1895. 

 t Pri7igsheim's Jahrbiicher, Vol. viii. 

 J Comptcs rendus, 1878. 



