LEAVES 



623 



P 



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. 



n 



FIG. 915. A capi- 

 tate, multicellular 

 glandular hair from a 

 geranium leaf (Pelar- 

 gonium), showing the 

 accumulation of an oil 

 drop (0) just beneath 

 the cuticle (c); highly 

 magnified. 



FIG. 914. Hairs 

 from a vervain leaf 

 (Verbena stricta); con- 

 trast the pointed, thick- 

 walled, unicellular 

 "protective" hair (/>) 

 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 (k); n, 

 nucleus; highly mag- 

 nified. 



plants (as Brasenia and 

 Nymphaea, fig. 916; algo 

 fig. 805) possess, slimg 

 glands, which secrete 

 copiously. In the gold- 

 back and silverback ferns 

 (Gymnogramme) there is 

 a glandular waxy secre- 

 tion copious enough to 

 give the leaves their char- 

 acteristic color. 



Internal elands. Many plants possess in- 

 ternal glands, which of^n flpp par a 



Y T 



FIG. 916. Multicellular 

 slime glands of the water 

 shield (Brasenia Schreberi) ; 

 note the stalk cells (/), the 

 slime-secreting cells (c), and 

 the superficial slime layer, 



Jucent dots, as in the leaves of Citrus and whose outer limit is indi- 

 ~EucalyJtus. In most cases the glands are cated b ? the do " e ^ Une 



**-: r^-T i L u i i t (*): highly magnified. 



spherical, there being a penpheral layer ot 



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



Often this structure is surrounded by a relatively impermeable pro- 



