83 ELEMENTARY BIOLOGY, [CHAP. 



d. The leaves. 



1 . Their form and composition. 



a. Each leaf consists of a number of different 



parts, viz. : 

 a. The stalk or petiole. 

 /8. The four to six oval leaflets attached laterally 



to the stalk, 

 y. The pair of small leaf-like expansions (stipules) 



at the base of the petiole. 



8. The rudimentary tendril terminating the pe- 

 tiole. 



2. The histological structure of a leaflet. 



a. Imbed a leaflet in paraffin or hold it between 

 two bits of carrot or turnip and cut a thin sec- 

 tion from it, perpendicular to its surfaces. Let 

 the section lie in water a few minutes to drive 

 the air out of its intercellular spaces, and then 

 mount it in water, and examine with i inch 

 objective. 



b. Begin at the upper surface (marked out by its 

 more closely packed cells), and work through to 

 the lower. Note 



a. The colourless epidermic layer consisting 

 of a single row of cells; the openings here 

 and there in it (stomata). 



(3. Beneath the upper epidermis come elongated 

 chlorophyll-containing cells, set on perpendi- 

 cularly to the surface. 



y. Then come irregularly branched (stellate} cells 

 forming the lower half of the leaf-substance ; 

 these also contain chlorophyll. 



