68 
PLAN! MORPHOLOGY. 
I. Simple leaves (axillary bud at the base). 
(1) Parallel veined. 
(2) Keticulately veined. 
(а) Pinnately veined. 
(б) Palmately veined. 
II. Compound (leaflets without axillary bud). 
(1) Pinnately compound. 
(2) Palmately compound. 
(/) STRUCTURE OF THE LEAF. 
The leaf usually consists of three kinds of tissues : 
(1) epidermal, (2) parenchymatous, and (3) fibrovascu- 
lar; in some cases there may also be a development of 
collenchyma. 
The Epidermis forms the surface of the leaf and may 
consist of one or more layers of cells. The outer walls 
are cutinized, and when nearly smooth the leaf is 
said to be glabrous. They may contain wax in addi- 
tion, as in senna, when the leaves are spoken of as 
glaucous. 
In other cases the outer walls of the epidermal cells 
are modified to hairs. When the hairs are unicellular 
and lie over one another in one direction, they give the 
leaf a sericeous or silky appearance ; when they are very 
short and straight, the surface is described as puberulent; 
or when they are still longer, as pubescent; or when long 
and straight, as pilose ; when the hairs are long and 
matted togther, as tomentose, or woolly; when they are 
hard and prickle-like, the leaf is spoken of as hispid, 
or strigose; when modified to spines, as spinose, and echi- 
nate, when they are hooked. 
In still other cases the epidermal cells are uneven, 
forming depressions and protuberances which, if slight, 
the surface is described as rugose ; or if wart-like, as 
varicose. Furthermore, the veins may be quite promi- 
nent, particularly on the lower surface, and if they are 
