80 ELEMENTAEY BIOLOGY. [VIII. 



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 section 

 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 1 inch objective. 



h 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 {stomatd). 



13. Beneath the upper epidermis come elongated 

 chlorophyll-containing cells, set on perpendicu- 

 larly to the surface. 



<y. Then come irregularly branched (stellate) cells 

 forming the lower half of the leaf-substance; 

 these also contain chlorophyll. 



S. The epidermic , layer of the lower surface ; 

 like a. 



€. The intercellular spaces, through the whole 

 thickness of the leaf: the direct communication 

 of some of them with stomata. 



^. Here and there sections of ribs or veins : make 



out in them the same elements as in c. 2.f. 

 Draw. 



c. Treat with iodine : make out the sac, proto- 

 plasm {primordial utricle), nucleus and vacuole 

 of the cells : the starch-granules. 



