56 THE ANATOMY OF WOODY PLANTS 



as contrasted with the sapwood. In this connection it will be well 

 to begin with a conifer. Fig. 42 represents side by side the micro- 

 scopic aspects of heart and sap tissues in the case of the white pine 

 (Pinus strobus). Beginning with the sapwood, which appears on 

 the right of the illustration, it is clear that both its rays and the 

 cells surrounding a resin space or canal are possessed of nuclei and 

 likewise contain a somewhat granular living substance or proto- 

 plasm. Imbedded in the protoplasm are usually found oval bodies, 



FIG. 42. Sap- and heartwood of the pine. Explanation in the text 



the grains of starch, which are lacking, indeed, only in the cells 

 immediately surrounding the resin canal or space. By examination 

 of the bordered pits of the tracheids it becomes evident that in the 

 wood of the sap the membranes of the pits are central in position. 

 Turning to the left side of the figure, we find represented the corre- 

 sponding organization of the wood in the case of the heart. The 

 elements distinguished by simple pits hi the delineation on the 

 right in other words, the living cells here have lost their living 

 contents and are quite empty. Moreover, in the water-conducting 

 cells, or tracheids, distinguished by the presence of bordered pits, 

 we discover that the membranes of the pores with their thickened 

 central region, or torus, are no longer median in position, but in 

 general have become adherent to one side or the other. Further, 

 the resin space has been stopped by an ingrowth known as tylosis. 



