64 BOTANY. 



rows of cells which border the rather large canals. The 

 function of these canals and their secretion has not yet 

 been made out with certainty. The recent suggestion that 

 the turpentine may be for the coating over of wounds is by 

 no means satisfactory. 



Practical Studies. — (a) Make extremely tWn cross- sections of the 

 stem of Indian corn, using a very sharp scalpel (or razor). Note the 

 small triangular intercellular spaces. 



(6) Make thin cross-sections of an apple-leaf and note the intercel- 

 lular spaces of the lower half of the section. Remember that in this 

 leaf there are nearly 250 breathing-pores to every square millimetre 

 of lower surface, while there are none at all upon the upper. 



(c) Study in cross-section the intercellular spaces in the stem of the 

 Rush (Juncus), and the leaf-stalks of water-lilies, water plantains 

 (Alisma), and arrowheads (Sagittaria). 



(d) Study turpentine-canals in very thin cross- sections of leaves of 

 pines and spruces. The larger-leaved species, as Scotch, Austrian, 

 or Scrub pine, and the Balsam-fir, are the most satisfactory. 



(e) Make cross-sections of the twigs of White pine and study tur- 

 pentine canals in bark and wood. 



(/) Study the oil-receptacles in the fresh rind of the orange and 

 lemon by thin cross-sections. These are not strictly intercellular, 

 but are formed by the breaking away of the secreting cells, thus 

 leaving a cavity. 



{g) The similarly -formed oil-receptacles of the mints and the gar- 

 den Fraxinella may be studied by making very thin cross-sections of 

 the leaves. 



