k^D THK mSTBlBVTlON OF THE STOMATA. 103 



i 



Between leaves such as these and thoHe which are completely 



wetted, a number of gradations occur. We find more or leas 



perfect developments of a certain character of the surface 



which may be called greasiness. The water coating the surface 



shrinks into patches or drops, leaving large areas dry. The leaf, 



in fact, behaves towards water like certain metallic or greaae- 



coated surfaces. The degree of greasiness varies a good deal, 



some leaves exhibiting it in great perfection, w^hile others do so 



only w^hen the leaf is shaken. The stomata of many of this kind 



of leaf must, no doubt, be protected against wet ; but as they 



graduate into those which are easily wetted, I have placed them 



(except those mentioned on p. 108) in the class having no 



bloom. I am inclined to think that immersion in water is 



not a thoroughly satisfactory test of the leafs capacity of 



resisting natural sources of wet, since some of the "greasy" 



or "metallic" class of leaf seem to be much more completely 



wetted by rain than by a single immersion in water. This is a 



further reason for keeping the best protected leaves, those which 



have a true bloom, in a separate class. Leaves such as Hydrangea 



quercifolia and the Easpberry have their lower surfaces almost 



perfectly protected against wetting, but this is due to a fine 



coating of hairs. As such cases do not bear on the function of 



bloom proper, but oidy on the general question of the protection 



of stomata, they are excluded from my tables. 



It must be remembered that bloom is in many cases easily 

 injured, and that in old leaves it is sometimes washed off by rain 



or removed by rubbing against other leaves, <fec. It is tlierefore 

 possible that some leaves noted as having no bloom may show 

 this coating under other circumstances ; I can only say that I 

 have been aware of, and tried to avoid, this error. 



In dealing with the results I have been obliged to use a few 

 simple symbols. The number of the stomata on a leaf is ex- 

 pressed as a fraction, of which the numerator expresses the 

 number of stomata on the upper surface and the denominator 



the number on the lower. Thus |-^ would mean that the upper 



stomata are to the lower as 100 to 150. My figures being taken 

 from different sources cannot be taken to represent any absolute 

 number of stomata per square millimetre, but merely the 

 proportion belAcen the stomata on the upper and lower 

 surfaces. 



