LABORATORY STUDIES 283 



spring and note the primary leaves with the growth of twiglets 

 in tlieir 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. JMake 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. 



(0 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 raj^s are seen split lengthwise. 



(k) Make very thin cross-sections of the stem through bark 

 and wood, and note the layers of ver}^ soft thin-walled tissue 

 (cambium) between wood and bark. This may be made more 

 evident bj' soaking the section for some time in eosin, by which 

 the cambium will be stained. 



(l) Compare the cones of Pinus, Picea, Abies, Taxodium, 

 Sequoia, Cupressus, Thuya, and Juniperus. 



(7/1) Compare the leaves of Pinus, Picea, Abies, Thuya, and 

 Juniperus. 



LITERATURE OF STROBILOPHYTA. 



J. AI. Coulter and C. J. Chamberlain, Morphology of 



Gijmnoa perms, Chicago, 1910. 

 C. S. Sargent, Manual of the Forest Trees of Xorth Amei'ica, 



Boston, 1905. 



