400 BOTANICAL GAZETTE [November 



their predecessors had yet attained their maximum size and 



strength. 



rings 



These 



miscalculation as to age. The phenomenon 



double ring formation has often been observed, especially in broad- 



leaved trees. Here 



plete defoliation, at others to favorable or unfavorable external 

 factors. The first assumption would not hold in Pinus rigida in 

 this case or in general, since defoliation rarely occurs. The cause 

 must be ascribed to external growth conditions, but what these are 



difficult 



most 



this 



manner correlated with inhibit 



since the effects of this are most marked on older less vigorous 



individuals. 



Secondary thickening in the roots 



Little stress was put on the study of secondary root thickening 

 in the present investigation. Only one cutting was taken, on 

 April 27, 1 9 10, for purposes of comparison, so that no reliable 

 deductions can be made. At this time cambial activity was not 

 manifest, although it must have been in process throughout the 

 aerial portion with the possible exception of the apical shoot. 

 T. Hartig (8) claimed that cambial awakening in the roots is 



much lal 

 the time 

 Whether 



He 



can decide. Suffice it to say, however, that the growth in thickness 

 of roots must not be confused with growth in length. The latter 



manifest often as early as March 



season. 



Summary 



1. The histological cha 

 iation from the normal 



wide 



thickening in the root is similar 



the stem, but differs (a) in less sharp demarcation between the 

 annual rings, (b) in the biseriate character of tracheids, and if) m 

 less density. 



