468 BOTANICAL GAZETTE [December 



they are present very sparsely, but are readily recalled under 

 traumatic stimulus. In this genus, according to Miss Holden, 

 ray tracheids usually occur as very irregularly walled cells, thickly 

 pitted on the tangential walls, usually constituting a ray one cell 

 high. According to Penhallow there are no ray tracheids in 

 Libocedrus, but Miss Holden reports them sparsely located under 

 traumatic stimulus in wounded material from L. decurrens. 



It is to be noted that while ray tracheid structure is an essential 

 feature of the Conifer ales, it is only constantly and normally 

 present in the older genera. In the younger genera this structure 

 may or may not be present, yet is invariably recalled under trau- 

 matic stimulus. This is in reality the general conclusion arrived 

 at by Thompson (8) for Abies. 



The foregoing resume of the work already done in this subject 

 is presented in an introduction to a description of a peculiar adapta- 

 tion in ray tracheid structure noted in second growth wood tissue of 

 Sequoia washingtoniana from the Sequoia National Forest in Cali- 

 fornia. The sections were taken from the main trunk of the tree, 

 which shows a phenomenally rapid growth not usually associated 

 with Sequoia, attaining in 30 years a diameter of 19 inches at the 

 point of section. Growth was kept up fairly regularly and con- 

 sistently during the entire period. 



The wood was very light in weight and very soft, was very 

 easily cut with a knife, and capable of successful sectioning with no 

 further treatment other than boiling. In texture the wood was 

 harsh and coarse and somewhat inclined to be cross-grained. 

 Sapwood was very prominent, comprising more than 90 per cent 

 of the cross-sectional area. The growth rings were wide spaced, 

 varying from o . 2 to o . 7 inches for a single season's growth. Micro- 

 scopically the cell structure was large and thin-walled, with a very 

 gradual transition from spring to summer wood. 



As has already been stated, ray tracheid structure normally 

 occurs in both of the present members of the genus Sequoia. In 

 the mature wood of S. washingtoniana, two kinds of ray tracheids 

 are to be found. First, the single, isolated, detached, radially 

 elongated tracheary cell found on the upper and lower margins of 

 primary rays, as is shown in fig. i. The extent of the radial 



