180 JOURNAL OF FORESTRY 



inception is observed to be always in a state of confusion and the cells 

 to be distorted as are also the adjacent wood fibers, a phenomenon 

 never observed in connection with normally produced tissue." 



The author's hypothesis, as summarized above, is discussed by him 

 in the light of the views expressed in the older text books by T. Hartig, 

 Sachs, and later by Strasburger and others, with special reference to 

 the relation of interfascicular cambium and rays. He considers the 

 radial division of the cambium and cambial activity in ray formation 

 inadequate to account for the circumferential expansion of the tree. 

 The author also uses his hypothesis to explain the presence of multi- 

 seriate rays associated with leaf traces, the increasing number of rays 

 as the stem increases in age, the formation of pith flecks (which he 

 considers healing structures of the same type as rays), ray conditions 

 in all cases of wounds, bird's eye in maple, the diiterences between 

 "exogenous" and "endogenous" woods, intercellular spaces in rays, 

 and further concludes that rays are valueless for classification or phylo- 

 genetic purposes, although possibly useful as a generic or subgeneric 

 character in oaks. He advocates that the term "medullary rays" be 

 strictly confined to the partitions of the pith in the early portion of the 

 first year, before the cambium has commenced to produce wood. The 

 observations of Erich Schmidt on the "proximal end-cells" of the rays 

 are discussed in support of the author's views. 



With reference to the function of the rays it is stated that "the rays 

 as channels for the conveyance of sap in a horizontal direction are as 

 much inferior to an open unoccupied slit as an intercellular canal, as is 

 a vessel obstructed by tyloses." That they may aid in rupturing the 

 bark in spring is also postulated. The radial shearing which has been 

 seen to take place when a dry disk of wood is placed in water is cited 

 in support of this. 



The chief difficulty with the views cited appears to be that, as the 

 author himself states, he has not seen nor has he found references to 

 investigators who have seen the ray mother cells at the cambium. 

 Consequently on theoretical grounds he contends that the cambium 

 (he appears to consider all cambial cells alike) cannot produce daughter 

 cells "that are not in their own likeness." The recent work of I. W. 

 Bailey, especially that published in the Journal of General Physiology, 

 Vol. 2, page 519, May 20, 1920, and also in the American Journal of 

 Botanv and elsewhere, on the nature and activities of the cambium, 

 is verv illuminating in this connection. E. G. 



