106 PRACTICAL COURSE IN BOTANY 
Fig. 122.— Internal structure of a pine stem, showing longitudinal section of a 
fibrovascular bundle through «a medullary ray, sm, sm‘: s, tracheids; t, bordered 
pits, surface view; c, cambium; v, sieve tubes; vt, sieve pits, analogous to the 
sieve plates in dicotyl stems. 
stem as it appears under the microscope, labeling correctly 
all the parts observed. Show the shape and relative size of 
Fic. 123. — Internal structure of a pine 
stem, showing transverse section of a tra- 
cheid : 7, cell walls; m, intermediate layer 
between walls of adjoining cells; m’, inter- 
cellular space here occupied by substance 
of intermediate layer; 6, bordered pit in 
section at right angles to the surface; ¢, 
membrane for closing the pit canal. 
the different cells. Com- 
pare your drawings with 
those made in your study 
of monocotyl stems, and 
write in your notebook the 
essential points of difference 
between the two. 
117. The stems of coni- 
fers, the group of Gymno- 
sperms to which the pine 
belongs, do not differ greatly 
from those of dicotyls, the 
chief difference being that 
the vascular bundles contain 
tracheids only, correspond- 
ing to the smaller vessels of 
