66 MOEPHOLOGY, OR COMPARATIVE AKATOMY. 



hard rigid hair-like processes, called bristles or seta, make the surface 

 setose ; and similar structures still more developed (occurring mostly at 

 the apex and the points of the teeth of leaves), called spines, sometimes 

 occur and produce a spinous surface. Modified, usually compound hairs, 

 containing oily or resinous secretions, are called glandular hairs, rendering 

 a surface viscous or glutinous, which conditions, however, are sometimes 

 produced by glands sunk in the epidermis. The glands are sometimes 

 superficial productions from the epidermis or skin of the leaf, at other 

 times they are outgrowths from the tissue of the leaf itself, as will he 

 described more fully when their structure is considered. Stings are long 

 stiffish hairs containing an irritating fluid. Scaly (lepidotus) surfaces are 

 produced by the occurrence of minute stalked flat scales, analogous in 

 their nature to hairs. Sometimes the cuticular layer of the leaf separates 

 in minute scale-like fragments, giving a scurfy appearance to the surface, 

 which is termed furfuraceous (as in the leaves of the Pine-apple and its 

 allies). The pruinose condition is that which results from the conversion 

 of the cuticle into a thin detachable film of waxy matter, of which the 

 "bloom" of plums, grapes, &c. affords an example. These structures 

 will be more fully described under the head of Minute Anatomy. 



Characters afforded by Leaves and their Modifications. In 

 Descriptive Botany attention is specially paid to the situation, 

 attachment, duration, direction, arrangement, form (general and of 

 base, apex, margins, surfaces), nervation, colour, texture, &c., as above 

 described and as further illustrated in the section on the mode 

 of describing plants. With the necessary modifications, the same 

 directions apply to the parts of the flower, &c. 



Special Modifications of the Leaf and its Parts. 



Under the head of the petiole we have spoken of pliyllodia as 

 blade-like forms of the petiole (figs. 57 & 58). Not only does 

 the leaf-stalk exhibit this and other modifications, disguising its 

 real nature, but the blade also and the stipules are subject to 

 similar modifications, in which the organ or region is only re- 

 cognizable by its position and relations. 



As these metamorphic structures fall under certain types, which are 

 represented in different cases by all the different regions of the leaf, it is 

 most convenient to describe them under special names. 



Pitchers (ascidia) are structures of the form indicated by their 

 name, produced by peculiar modes of development of the petiole, 

 the blade, or of both together. 



One of the best-known examples is found in the Nepenthes, or Pitcher- 

 plants, in which a portion of the leaves exhibit a very long stalk, winged 

 at the base, supporting at the extremity a pitcher-like'sac of ordinary leafy 

 texture, furnished at its mouth with a little flat plate resembling a lid 

 (fig. 111). The pitcher is commonly explained as a kind of phyllode, or 



