Mar. 25, 1914 



Tyloses in American Woods 



461 



TABLE III. Occurrence of true tyloses in native conifers Continued. 

 OTHER CONIFERS Continued. 



TYLOSEUKK CELLS 



The tyloselike epithelial cells which surround the resin canals were 

 also carefully studied in Pinus, Larix, Picea, and Pseudotsuga. In these 

 woods both the horizontal and vertical resin canals often contained dis- 

 tended cells which partly or sometimes completely filled the canal 

 openings. (PI. LVII, fig. 2; and PI. LVIII, figs. 2, 5, and 6.) This 

 closed condition of the vertical canals is particularly noticeable near the 

 medullary rays. (PI. LVI, fig. i; and PI. LVII, fig. 2.) The distended 

 closing cells correspond to the plasma-containing cells described on page 

 446. (PI. LVIII, figs. 2 and 5.) A large number of the canals were, 

 however, entirely open. 



In pines where many of the epithelial cells remain capable of growth, 

 three types of conditions may be found in the canals. 



(1) The canals of the sapwood, especially of the outermost ring, may 

 not have yet opened that is, the space which the canal will occupy may 

 still be filled by the parenchyma cells which later form the epithelium. 

 (PI. LVI, fig. i.) 



(2) Many canals may be partly open. (PI. LVII, fig. i.) Frequently 

 the cells surrounding the opening are somewhat contracted and col- 

 lapsed; or, again, individual cells containing plasma may become dis- 

 tended, bow out into the open lumen of the canal, and thus assist in 

 partially closing it. 



(3) Canals in the heartwood as well as in the outer rings of the sap- 

 wood may be completely closed. 1 This may come about in two ways: 

 First, the groups of parenchyma cells observed in the sapwood may 



1 Compare Thomson, R. B. 



28736 14- 



