STRUCTURE OF THE STEM. 53 
(b) The narrow lines running in very young stems pretty straight from 
pith to bark, in older wood extending only a little of the way from centre 
to bark, the medullary rays, shown in Fig. 40.1 ~ 
(c) The wedge-shaped masses of wood between these. 
(a) The holes which are so grouped as to mark the divisions between 
successive rings. These holes indicate the cross-sections of vessels or 
ducts (§ 82). Note the distribution of the vessels in the rings to which 
they belong, compare this with Figs. 40, 41, and decide at what season 
of the year the largest ducts are mainly produced. Cut off a grapevine 
several years old and notice the great size of the vessels. Examine the 
smoothly planed surface of a billet of red oak that has been split through 
the middle of the tree 
(quartered oak), and note 
the large shining plates 
formed by the medullary 
rays. 
Look at another stick 
that has been planed away 
from the outside until a 
good-sized flat surface is 
shown, and see how the 
medullary rays are here jg, 40, — Cross-Section of Oak Wood as seen with 
represented only by their the Magnifying Glass. 
edges. J, J, the annual rings.? 
Hi. 
76. Details of Structure; Cross-Section. —Cut from shoots of the 
apple tree, ranging in age from one to five years, a number of sections. 
These should be as thin as they can be made without breaking up. It 
will save time to make at one time a good many sections of any woody 
part of the plant that is to be examined.# 
For examination with the lowest powers, cylinders + to 4 inch long 
cut smoothly from the twig to be examined, and viewed as opaque objects, 
will answer well. 
1 These and many other important things are admirably shown in the thin wood- 
sections furnished for $4 per set of 24 by R. B. Hough, Lowville, N. Y. 
2 The shading in fine lines at J would be rendered more naturally by dots. 
3 Tf time allows, the students should cut their own sections : frequently this will 
be impracticable. Sections not needed for the current lesson may be put in 50 per 
cent alcohol or other preservative fluid in wide-mouthed bottles carefully labeled and 
kept for future use. For a list of sections see Appendix C. 
