C( «, ^^^^ " 



100 MR. r. DAKWTN O^ 'J HK KELATTOK BETWEEN ^* BLOOM 



ofF the bloom stops up tlie stouiata. There are certain facts 

 which go to show that atomata tend to be developed in parts 

 protected from rain. The well-known fact that in a large num- 

 ber of leaves the stomata are exclusively on the lower surface, 

 where they are not so likely to be wetted, is in accordance with 

 this statement. In vertical leaves, as is well known, the stomata 

 are equally distributed on the two surfaces*, and in most such 

 leaves .the surfaces would be equally wetted. An interesting 

 confirmation of this view may be found in the fact mentioned by 

 Haberlandt f that lenticels are " fairly equally distributed all 

 round vertical branches, w^hile on horizontal branches they are 

 much more numerous on the lower than on the upper side. We 

 might expect that the function of lenticels would be interfered 

 with by wetting in the same way as applies to stomata, and it is 

 therefore of interest to find that (at least in young branches, 

 according to Haberlandt) they tend to be developed chiefly on 

 the underside, where they are more or less protected. In 

 young leaves, which are often more nearly vertical than the 

 adult leaves of the same species, we may perhaps believe that 

 stomata are protected by not being open at first, but whether 

 tlie opening of the stomata corresponds with the assumption of 

 the horizontal position I cannot say. Von Hohnel has shown 

 that the cuticular transpiration of young leaves is very large, so 

 . that even with closed stomata they may transpire sufficiently. 

 The idea that the tendency to accumulation of stomata on 

 the under surface of leaves is an arrangement by which they 

 are protected against rain, is in accordance with Hohnfehit's 

 observations t- He found that in unde 

 mata show no marked tendency to accumulate on the under 

 surface; indeed the contrary is often the case. This is pre- 

 cisely what might be expected on the theory that they are deve- 

 loped on the under surface of aerial leaves as a protective against 

 rain, &c,, since the underground leaves are of course not ex- 

 posed to such dangers. Hohnfeldt quotes Camel's remarks on 



o 



* In the nearly vertical leaves of Lacfuca Scariofa I found the stomata on 

 the raorphologicallj lower side io be the most numerous— exceeding those on 



100, 



t Physiolog. rflanzenanatoniie, p. 317.— Haberlandt gives no explanation o 



f 



the fact. 



J As reported in tlie Botan. Ccntralblatt, 1880, p. IIGI. 



