LABORATORY STUDIES 283 
spring and note the primary leaves with the growth of twiglets 
in their axils bearing young secondary leaves. 
(h) Make cross-sections of mature leaves, and note the 
turpentine-canals, one near each angle, with others symmetric- 
ally arranged between. Make cross-sections of the young 
twigs, and note the canals in the rind or bark. Make similar 
sections of the wood of the trunk, and note similar canals at 
intervals. 
(¢) Make very thin cross-sections of the mature wood of the 
stem and note shape and size of the cells; note also the gradual 
decrease in their size in passing from the inner to the outer side 
of a growth ring. Now make a very thin longitudinal-radial 
section, and observe the bordered pits. A longitudinal section 
at right angles to the last (longitudinal-tangential) will show 
no bordered pits. In all these sections note that the wood is 
made up of but one kind of cells, viz. tracheids. 
(j) In a cross-section of a stem note the thin radiating plates 
of tissue (medullary rays), in many cases extending from pith 
to bark. In longitudinal-tangential section of the stem these 
rays are seen in cross-section to be made of thick-walled cells. 
In longitudinal-radial sections the rays are seen split lengthwise. 
(k) Make very thin cross-sections of the stem through bark 
and wood, and note the layers of very soft thin-walled tissue 
(cambium) between wood and bark. This may be made more 
evident by soaking the section for some time in eosin, by which 
the cambium will be stained. 
(1) Compare the cones of Pinus, Picea, Abies, Taxodium, 
Sequoia, Cupressus, Thuya, and Juniperus. 
(m) Compare the leaves of Pinus, Picea, Abies, Thuya, and 
Juniperus. 
LITERATURE OF STROBILOPHYTA 
J. M. Courter and C. J. Cuamperzarn, Morphology of 
Gymnosperms, Chicago, 1910. 
C. S. Sarcent, Manual of the Forest Trees of North America, 
Boston, 1905. 
