THE SPERMAPHYTES. 



213 



8. Study Fig. 135, which is a cross section of the stem 

 of the White Pine, Pinus strobus, cut in July of the second 

 year of its growth. On the upper side of the picture is 

 the epidermis, J., which is smooth in the young branches, 

 but becomes covered, at a later period, with brown scales 

 that result from the dying of the earlier bark. Within 

 the epidermis is a broad band, E, which includes two 

 or three rows of rectangular (as seen in section) cells of 

 the cork la} r er, B ; 

 the cortical paren- 

 chyma, <?, which 

 makes up the 

 greater part of the 

 band ; and resin 

 ducts, jP, each sur- 

 rounded by layers 

 of epithelial or 

 glandular cells 

 whose function is 

 to secrete the resin 

 or pitch. On the 

 inner side, the cells 

 of the cortical layer 

 pass into the cells 

 of the irregular 

 layer, D, the true 



phloem. Again there is a gradual transition to the cells 

 of the cambium layer, Gr. All the tissues thus far men- 

 tioned up to and including the outer part of the cambium 

 layer make up the bark. Inside the cambium is a broad 

 layer, H, of the new wood formed during the second year's 

 growth ; inside of that is another broad layer, /, of wood 

 that was formed by the growth of the first year. The 

 two layers, H and J, and the inner part of the cambium 

 layer, constitute the xylem or wood. In the layer, Z are 



FIG. 135. White Pine, Pinus strobus. Trans- 

 verse section of a stem in the second year of 

 growth. A, epidermis; B, cork layer; C, cor- 

 tical parenchyma ; Z>, phloem ; F, resin ducts; 

 G, cambium layer ; H, wood in process of for- 

 mation in the second year; /, wood formed 

 during the first year. (X 35.) 



