LEAVES 



623 



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 

 Nymphaea, fig. 916; also 

 % 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 (/>) 

 with the capitate, thin- 

 walled, multicellular 

 glandular hair (&), the 

 latter being much the 

 richer in protoplasm 

 both in the stalk and 

 in the head (h); n, 

 nucleus; highly mag- 

 nified. 



FIG. 9 1 6. Multicellular 

 slime glands of the water 

 shield (Brasenia Schreberi) ; 

 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- 



