LEAVES 



617 



insect further incites an incurving of the leaf margins and of the glan- 

 dular hairs not originally touched, so that most of or even all the hairs may 

 take part in secretion and digestion. The latter phenomenon is facili- 

 tated, especially if the insect alights at the leaf center, by the fact that the 

 hairs are progressively longer from the center outward. The hair struc- 

 ture is somewhat complicated, there being two peripheral layers of 



Figs. 906, 907. — The absorptive and digestive glandular hairs of a sundew (Drosera 

 rotundifolia) : 906, a leaf, showing the conspicuous glandular hairs (g) covering the upper 

 surface; the hairs at the right are inflected toward an entangled insect; note that the 

 hairs are tipped by a drop of secreted liquid (d), which attracts insects to the leaf and 

 also entangles them; 907, the terminal capitate portion of a glandular hair, as seen in a 

 median longitudinal section; the conductive bundle (v) entering the hair from the leaf 

 is much enlarged at its terminal portion, where it is composed of tracheids (t) ; the ter- 

 minal tracheids are inclosed by the protective sheath or endodermis (e), outside of which 

 are two epidermal layers of secretory cells (s s') ; note the palisade-like nature of the cells 

 in the outer secretory layer ; w, a drop secreted by these layers ; go6, somewhat magnified ; 

 907, highly magnified. — go6 after Keener, 907 after DeBary. 



secretory cells containing the wine-red pigment, underneath which is the 

 endodermis and a branch of the leaf conductive system; the latter con- 

 sists chiefly of a row of tracheids, which diverge in the terminal part of 

 the hair, thus presenting an enlarged surface (fig. 907). After the 

 digestible portions have been absorbed, the secretions cease, and the 

 glandular hairs assume their original position. It is said that inorganic 

 bodies, such as dirt particles, excite no enzym secretions or leaf move- 

 ments. 



