SURFACE 177 



say wliere one Ix^^ins aiul the other cinls, we say they arc Continuous 



(Fis- 4S2)- 



Texture. — As to their texture and consistency', the or(Hnai-y form of 

 leaf, in which it ])ossesses active chlorophyll tissue, is denominated 

 Ilerhaceous, in contradistinction to the Scarious or Scariose form, in 

 which it has a (hy and papery texture. Herbaceous leaves are ]\Iem- 

 l)ranacet)us in their ordinary form, that is, not excessively thickened, 

 Coriaceous when tough and leathery. Fleshy or Succulent when 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 cainiot be taken uj) 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 when 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 called Pulverulent. 



A Pubescent surface 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 ])ubescent 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 lie in one direction, are closely appressed, and ha\e a 

 shiny or silky luster, the surface is called Sericeous. 



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

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

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