58 BOTANY. 
my or resinous secretions. Such ones are surrounded by 
secreting cells which 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. 
(6) Make thin cross-sections of an apple-leaf and note the intercel- 
lular spaces of the ower 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. 
(¢) Make cross-sections of the twigs of White pine and study tur- 
pentine-canals in bark and wood. 
(f) 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 ate secreting cells, thus lesiy: 
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, 
