EXPLANATION OF TERMS. 



XXI 



Ciliate : when provided with hairs that fringe the margins. 



Glaucous: when the surfaces are covered with a white powdery substance 

 called a bloom. 



The Midrib, or Midvein, of a leaf is the central one of its framework, 

 usually longer and more prominent than the others. The sub-divisions are 

 known as Veinlets and the finest ones as Veinulets. 



Not all veins and veinlets, however, are arranged in the same way. 

 Leaves, therefore, are divided into two classes, according to their venation, 

 the first being those that are Netted Veined and the second those that are 

 Parallel Veined. 



Under netted-veined leaves (FiG. 14), those in which the veins branch 

 and rebranch from the midrib and form a close mesh or network, we have 



FIGS. ID, II 



3, 14, i5» 16, 17, 



both Pinnately-Veined, or Feather- Veined, Leaves, and Palmately- Veined 

 Leaves. Of these. 



Pinnately, or Feather-Veined, Leaves are those wherein the veins, from 

 the base to the apex, all start out from the sides of the midrib, as in FiG. 25. 



Palmately-Veined Leaves differ from the former in having several veins 

 of nearly equal size which from a common point at the base branch at 

 various angles and extend to nearly the leaf's margin. (FiG. 18.) 



Under the second division of leaf venation we find those that are 

 Parallel Veined — their veins running side by side from the base to the apex 

 of the leaf without intermingling, and being only crossed by almost imper- 

 ceptible veinlets. (FiG. 23.) 



Leaves assume a great variety of forms, which, primarily, may be di- 

 vided into two large classes, Simple Leaves and Compound Leaves. 



Simple Leaves are those with the blade in one piece. 



Compound Leaves have their blades split into from three to many parts, 

 each part forming then a separate leaflet, which may or may not have a 

 little stalk of its owa. (Figs. 3, 4 and 5.) 



