136 Dr. F. Darwin and Miss D. F. M. Pertz. [June 15, 



in the latter, a supply would be provided owing to the breaking down of the 

 former. 



Our present methods need elaboration before this question can be settled. 



Summary of Conclusions. 



1. Eed blood corpuscles are heemolysed by the action of a-rays, and oxy- 

 hemoglobin is converted into met-haemoglobin. 



2. Leucocytes undergo marked degenerative changes when subjected to 

 a-rays. During the process of clotting, leucocytes appear to move away from 

 an a-radiated region. This movement has been attributed to changes found 

 to occur in the surface tension of blood serum when radiated. 



3. The specific properties of opsonin and haemolytic complement are lost 

 when serum is exposed to a-rays. The progressive changes caused by these 

 rays indicate the separate identity of opsonin and complement. 



4. The ft- and 7-rays have yielded negative results in analogous experi- 

 ments. 



On a Neiv Method of Estimating the Aperture of Stomata. 

 By Francis Darwin, F.E.S., and D. F. M. Pertz. 

 (Eeceived June 15, — Read June 29, 1911.) 

 CONTENTS. 



§ 1. Method 136 



§ 2. Difficulties 139 



§ 3. Comparison with other Methods 139 



§ 4. Stomatal Aperture and Transpiration 141 



§ 5. Light and Darkness 143 



§ 6. Withering 149 



§ 7. Conclusion 153 



§1. Method, 



It is usually assumed that transpiration is regulated by two principal 

 factors : (1) the relative humidity of the air, and (2) the degree of aperture 

 of the stomata. Neither of these assumptions has been experimentally 

 proved, though both of them are necessarily true, but it must be remembered 

 that the factors referred to are not necessarily the only ones that govern the 

 phenomena. 



The experiments hitherto made on (1) the effect of relative humidity are 



