258 leaf-anatomy op sc^vola crassifolia, 



Summary. 

 i. Sccevola crassifolia is characterised by the development of 

 peltate, glandular hairs, which secrete resin in great quantity. 

 The-^e hairs reach tlieir maximum activity in the buds and young 

 leaves. 



ii. As the leaves become older, the glands become less active, 

 the secretion loses its mobility, dries-up, and gives the surface 

 of the leaf a lacquered appearance. 



iii. The mature leaves of .S'. crassifolia are thick and succulent. 

 The glands are sunken, and no longer functional on the blade of 

 the leaf. They retain their activity only in the region of the 

 leaf-base, protecting the axillary buds. Si^ecial xerophilous 

 adaptations are found in : 



[a). The secondary increase in size of the epidermal cells. 



(6). The massive development of palisade-tissue. 



(c). The development of special water-storage cells, such as 

 mucilage-cells, water-storage tracheides, and ordinary, thin- 

 walled, water-storage cells. 



EXPLANATION OF PLATES XX VII. -XXVIII. 



All tigiues were made at table-level, with the aid of Zeiss* camera lucida, 

 with mirror at its j^reatest inclination, and with tube at 160 mm. Leitz 

 objectives 3 and (J, and oculars 2 and 4 were used. 



Plate xxvii. 



Firf. 1. — A slit^htly oblique section throu^fli a bud, to show development of 

 •glandular hairs : a, stem-apex; h, rudimentary- leaf; c, leaf-base; r/, 

 petiole of slighth' older leaf; c, glandular hair; ( > 160). 



Fig. 'J. —Section across sheathing base of a mature leaf, to show develo})- 

 ment of glandular and clothing hairs; ( x 1(50). 



Plate xxviii. 



Fig.o. — -Part of .section through young leaf, to sliow depth of secretion and 

 outline of glandular hairs; ( x o30). 



Fig.4, — Section of a lacquered leaf, to show patch of secretion blocking 

 mature stoma; ( x 300). 



Fig. 5. — Section of a mature leaf : p, palisade-tissue: c, central water- 

 storage tissue; m, mucilage-cell; f, water-storage tracheides; ( x 100). 



