28 PRACTICAL BOTANY. 



will be seen, which are the terminations of canals like 

 those seen in the sections of the longitudinal walls. 



Pits can be readily seen, without making sections, in the leaves 

 of some species of Trichomanes. 



Cystoliths may be included here, since they are 

 developed from the cell- wall. 



Cut a transverse section of a leaf of Ficus elastica : 

 mount in water; examine with a high power. 



Observe the layer of large clear cells underlying the 

 superficial layer of the epidermis of the upper surface 

 of the leaf : here and there one of these cells is seen 

 to contain a botryoidal body suspended by a stalk from 

 the top of the cell ; this is a Cystolith : it consists of 

 a mass of cellulose developed as an outgrowth from the 

 cell-wall, encrusted with calcium carbonate. 



Run in a drop of acetic acid : observe that the 

 cystolith becomes gradually transparent, and that an 

 evolution of bubbles of gas is taking place from it. 



When the calcium carbonate is all dissolved, a mass 

 of cellulose will be seen to remain, presenting both 

 striation (from above downwards) and stratification 

 (parallel with its margin). Apply tests for cellulose 

 (p. 29). 



1. Starch-grains. Scrape lightly with the blade of 

 a knife the freshly cut surface of a piece of a potato ; 

 mount the scrapings in a drop of water ; examine with 

 a high power. 



A number of somewhat ovoid bodies of various sizes 

 will be seen ; these are Starch-grains. 



Near the pointed end of a well-developed grain will 

 be seen a small, round, clear spot, the hilum. 



