470 PROCEEDINGS OF THE ACADEMY OF [May, 



winds following ou warm days which have started the root action — 

 for we must bear in mind that the roots are more easily awakened 

 after our warmer winters than is safe for the tree. It amounts to 

 this, therefore, that iu the plains the long-coutiuued period of folia- 

 tion allows insects, frost, Avinds, etc., some six weeks or two months 

 in which to injure the slowly sprouting tender shoots, whereas in 

 the mountain heights they have only a fortnight or so in which to 

 do such damage. ' ' 



May we not have a parallel case in the retarding influence of the 

 conditions which surround the white cedar in its boggy home, and 

 which influence is reflected iu the structure of the annual rings of 

 wood already alluded to and the development of the disease about 

 to be described ? 



Additional Facts Con'cerning the Normal Structure 

 OF White Cedar Stems. 



Before beginning the pathological description, it may be well to 

 say a few more words concerning the normal structure of the stem. 

 The woody tracheids are elongated and marked with bordered pits 

 in their radial walls. The bordered pits are large and well defined, 

 both in the radial longitudinal section and in the transverse section. 

 Eesin canals (fig. 11) are entirely absent from the wood, and in 

 this the general resemblance of the xylem of the white cedar to 

 that of the pine ceases. The absence of a well-defined pith in 

 Cupressus thyoides is also noteworthy. The phloem or bast region of 

 a twenty-one-year-old stem consists of alternate concentric rings of 

 hard and soft bast. The hard bast consists of bast fibres with thick 

 chromophobic'" walls and obsolete lumen. The bast fibres are 

 arranged in a single layer of cells in each of the annual rings of 

 bast fclements. Alternating with these are the soft bast layers, the 

 layer latest formed being found next to the wood cambium. 

 Numerous large circular and elliptical resin canals are found in the 

 phloem region, breaking the continuity of the rings of hard and 

 soft bast (fig. 11). 



A stem forty-one years old shows essentially the same structure 

 with some differences in the cortical i-egion. The same uniformity 

 in the size of all the tracheids is noticeable, there being no sharp 



I'A term proposed by ^loutgomery to describe the walls and proto- 

 plasm of cells that are refractory to stains. 



