SURFACE 177 



say where one begins and the other ends, we say they are Continuous 

 (Fig. 482). — 



Textiire. — As to their texture and consistency, the ordinary form of 

 leaf, in which it possesses active chlorophyll tissue, is denominated 

 Herbaceou s, in contradistinction to the Scarious or Scariose f orm, in 

 which it has a dry and papery texture. Herbaceous leaves are Mem- 

 branaceous in. their ordinary form, that is, not excessively thickened, 

 Coriaceous w hen tough and leathery. Fleshy or Succulent w hen largely 

 parenchymatous, thickened, and juicy. A leaf which exhibits trans- 

 lucent dots when held against a strong light, due to the presence of 

 oil-glands, is called Pellucid-punctate. 



Surface. — The surfaces of leaves may be classified in two ways: First, 

 as to the characteristics of the individual trichomes which they bear; 

 second, as to the general surface effects (Indumentum) which result from 

 the latter. The former method, although it cannot be taken up in this 

 part of the work, is of very great importance in the characterization 

 of medicinal herbs and leaves, especially as it constitutes one of the 

 greatest aids to the identification of powders. The latter method can 

 only be studied with advantage by the actual examination of typical 

 specimens, it being almost impossible to characterize the different forms 

 by definition. A surface is Opaque when it is not shining or lustrous. 

 It is Glabrous when it does not possess any trichomes in such forms as 

 to detract from the smoothness of the surface. It is Glaucous when 

 covered with a waxy exudation, imparting to it a peculiar whitish 

 appearance ("bloom"), such as characterizes the surface of an ordinary 

 black grape. It is Scurfy_w hen covered with more or less of an indumen- 

 tum in the form of granular or detached scaly masses. When the matter 

 of such masses is more thinly distributed, appearing in the form of a 

 powder rather than a scurf, the surface is calle d Pujv priilf^nt. 



A J'liVip'ipfnt surfa ce is a hairy surface which is not readily dis- 

 tinguished as pertaining to any one of the other specific classes. 



If the hairs of a pubescent surface are very short and fine, so that 

 the consequent roughness is reduced to a minimum, the surface is 

 called Puberulent. 



If a hairy indumentum is fine and of an ashy-gray color, the hairs not 

 arranged in any regular direction, the surface is Cinereous. 



If the hairs all he in one direction, are closely appressed, and have a 

 shiny or silky luster, the surface is called S ericeous. 



If this luster is intensified and of a strongly whitish color, whether 

 the trichomes be hairs or scales, the surface is denominated Argenteous. 

 12 



