432 BOTANICAL SURVEY OF DISMAL SWAMP REGION. 



of wax. Waxy incrustations prevent such transpiration from the 

 general surface of the leaf as normally takes place in addition to that 

 from thestomatal pores, and which, while relatively slight, amounts 

 in the total to a considerable quantity. Moreover wax, even more 

 effectually than a covering of hairs, prevents rain water from stand- 

 ing upon the leaf surface. A glaucous leaf, in other words, "sheds 

 water/" ' 



4. Strong secondary thickening of the cuticle and outer walls of the 

 epidermis cells. — The leaves of almost all the woody plants of this for- 

 mation which were examined exhibit such thickening, especially upon 

 the more exposed upper (ventral) surface. This is particularly evi- 

 dent in the rather numerous species with thick, coriaceous, persistent 

 leaves, e. g., Pieris nitida, Leucothoc axillaris, Ilex opaca, I. lueida, 

 I. glabra, Gelsemium semper v ire ns, Magnolia virginiana, Smilax 

 laurifolia. The possible advantages of the polished, shining upper 

 surface of these leaves were discussed in relation to certain species of 

 the Sand Strand. Wiesner has advanced the theory that they serve 

 to reflect, some of the incident light. 



In a number of species the cuticle is roughened; wrinkled in Smilax 

 laurifolia, Lt ucolhoi' oxilhiris, Pieris nitida, Xplisma foliosiflora, and 

 Chionanthus virgmica; granular in Berchemia scandens. In the first 

 three of the species with wrinkled cuticle the ridges are stronger on 

 the lower (dorsal) surface; in the last, two, on the upper (ventral) sur- 

 face. As the leaves of all these species are plagiotropic with ventral 

 surface upward, this difference seems unaccountable. T1, has already 

 been mentioned that such unevennesses on the surface of the cuticle 

 are believed to refract part of the light, and hence to diminish the 

 intensity of its action upon the tissues below. 



5. Mucilage in flu cells of the epidermis. — This occurs in Berchemia 

 scandens, and may aid in preventing the loo rapid escape of water 

 from the leaf. 2 



('.. Hypodenn. — A continuous hypoderm, of one layer of colls, lies 

 lieneath the ventral epidermis in the leaves of Pieris nitida. Its func- 



1 Equally effective in preventing the accumulation of water on the surface of 

 the leaf is a dense covering of papillae, such as occurs on the upper surface of the 

 floating leaves of some aquatics and is not rarely present in ombrophobia, shade- 

 loving plants, especially in the tropics. Oinbrophobic leaves are injured by long- 

 continued exposure to rains or immersion in water, while this is not the case with 

 foliage that is ombrophilous. Oinbrophobic leaves are almost always possessed by 

 xerophilous plants, while of plants that are hygrophilous some have ombrophilous, 

 others oinbrophobic foliage. " Largely speaking one can regard the ' unwetable- 

 ness ' of the leaf as a sign that it is ombrophobie: ' wetableness ' as an indication 

 that it is ombrophilous." Wiesner, Sitzuugsber. der K. Acad, zu Wien, Math.- 

 Naturw. Classe, vol. 10'J, Abth. 1. pp. 503to521 (1893); and vol. 103, Abth. 1, pp. 

 169 to 191 (1894). 



s Volkens, Flora der iigypt. arab. Wiiste, pp. 43-45, discusses this question at 

 some length, and suggests the above-mentioned as the probable advantage of 

 mucilage in the epidermis cells. 



