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 



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 



Fi(!. Ti.i. — Intcrnalstructureof a pine 

 stem, showing transverse section of a tra- 

 cheid : 7, cell walls; //), intermediate layer 

 between walls of adjoining cells ; m', inter- 

 cellular space here occupied by substance 

 of intermediate layer; b, bordered pit in 

 section at right angles to the surface ; t, 

 membrane for closing the pit canal. 



