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A TEXT-BOOK OF BOTANY. 



vary in form and are very characteristic in a great many plants. 

 The terms used to describe the various types of hairs are in a 

 few instances rather simple, but there are so many modifications 

 that nothing short of an illustration will suffice to define them. 

 The simple hairs may be divided into a number of sub-divisions: 

 (a) Papillose hairs, being short outgrowths of the epidermal cells, 

 somewhat resembling the papillae found on the ventral surfaces of 

 petals. This form is found in a relatively few families, (b) 

 Unicellular hairs, being outgrowths considerably longer than 

 papillae and occur in a large number of plants. This is also true 

 of a third type (c), known as uniseriate hairs and in which there 



Fig. 152. Forms of non-glandular hairs: A, twisted hairs from under surface of 

 leaf of eriodictyon; B, lignified hairs from the epidermis of nux vomica; C, branching 

 hairs from the leaf of mullein (I'crbasciitn Tliaj^sus). 



are two or more cells connected as in a chain. Among special 

 terms frequently used the following may be mentioned: (of) 

 Hooked hairs (Fig. 154, A, B), in which the summit is bent in the 

 form of a hook, {e) Two-armed hairs (Fig. 153, D), in which 

 the summit consists of two cells which diverge from each other 

 and spread out horizontally or parallel to the surface of the leaf. 

 (/) Stellate hairs (Fig. 151, B) consist of a group of cells ar- 

 ranged around a simple point, as in the Cruciferae and Saxifra- 

 gaceae. {g) Peltate hairs (Fig. 153, E) consist of a group of 

 radially arranged cells, of which all or only some reach the centre 

 of the shield, as in the Solanaceae, Malvaceae, Loganiaceae, and 



