58 BOTANY. 



my or resinous secretions. Such ones are surrounded by- 

 secreting cells wliicli manufacture the gummy or resinous 

 matter and then exude it into the cavity. The Turpentine- 

 canals of the pines and spruces are of this nature, the well- 

 known turpentine being secreted by one or more rows of 

 cells which border the rather large canals. The function 

 of these canals with their secretion has not yet been made 

 out with certainty. The recent suggestion that the tur- 

 pentine may be for the coating over of wounds is by no 

 means satisfactory. 



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

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

 small triangular intercellular spaces. 



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

 lular spaces of the lower half of the section. Eemember 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 

 Bush (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 sat|isfactory. 



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

 pentine canals in bark and wood. 



(/) Study the oil receptacles in llie 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 leav- 

 ing 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. 



