LEAVES 



623 



n 



FIG. 915. A capi- 

 tate, multicellular 

 glandular hair from a 

 geranium leaf (Pelar- 

 gonium), showing the 

 accumulation of an oil 

 drop (o) just beneath 

 the cuticle (c); highly 

 magnified. 



with a head and with a more or less evident stalk; the cells, both in 

 the head and in the stalk, vary in number from one to several and are 

 rich in cytoplasm (figs. 914, 915; also fig. 632). In the mints the 

 glandular hairs occur in leaf depressions and are relatively stalkless. 

 In some plants (as in Silene) there is a region of palisade-like secretory 



cells instead of glandular 



hairs, while in many plants 



ordinary epidermal cells ex- 



crete wax, varnish, etc., as 



previously noted (p. 570). In 



oil glands the secretions gather 



within the walls of the head 



cells, where they press the 



cuticle away from the other 



layers of the wall, ultimately 



bursting it and discharging to 



the exterior. The cuticle may or may not regen- 



erate, but in any event old glands lose the power 



of excretion, the oil ac- ,.. 



cumulating in the cell 



lumen. Many water 



plants (as Brasenia and 



NympJiaea, fig. 916; also 



fig. 805) possess slime 



glands, which secrete 



copiously. In the gold- 



back and silverback ferns 



(Gymno gramme) there is 



a glandular waxy secre- 



tion copious enough to 



give the leaves their char- 



acteristic color. 



Internal glands. Many plants possess in- 

 ternal glands, which often appear as trans- 

 lucent dots, as in the leaves of Citrus and 

 Eucalyptus. In most cases the glands are 

 spherical, there being a peripheral layer of 



FiG. 914. Hairs 

 from a vervain leaf 

 (Verbena stricta); con- 

 trast the pointed, thick- 

 walled, unicellular 

 "protective" hair (p) 

 with the capitate, thin- 

 walled, multicellular 

 glandular hair (6), the 

 latter being much the 

 richer in protoplasm 

 both in the stalk and 

 in the head (h); n, 

 nucleus ; highly mag- 

 nified. 



FIG. 916. Multicellular 

 slime glands of the water 

 shield (Brasenia Schreberj) ; 

 note the stalk cells (<), the 

 slime-secreting cells (c), and 

 the superficial slime layer, 

 whose outer limit is indi- 

 cated by the dotted line 

 (s); highly magnified. 



glandular cells which secrete into a common central reservoir (fig. 917). 

 Often this structure is surrounded by a relatively impermeable pro- 



