26 ANATOMY OF THE GYMNOSPERMS 



A concrete illustration of the conditions which would be likely 

 to produce such a result is presented in a late frost which seri- 

 ously affected vegetation in the neighborhood of Montreal in the 

 spring of 1902. On the 9th and loth of May of that year a cold 

 wave passed over Montreal, and inflicted such serious losses upon 

 early crops and effected so much damage to trees and shrubs 

 as to excite much comment. At that time nearly all trees and 

 shrubs were in tender leaf. Many were either in bloom or the 

 flower buds --as in the horse-chestnut -- were well formed 

 but not open. In such cases the new branches had already 

 attained a considerable length, but in many of the later species, 

 such as Catalpa, the English maple (Acer campestre), sumac 

 (Rhus typhina), and the ash, the leaf buds were not opened and 

 no material injury resulted. In all of the earlier forms, however, 

 the leaves and young branches were killed, and in the horse- 

 chestnut and elder (Sambucus racemosa) recovery involved the 

 formation of an entirely new set of organs from latent or adven- 

 titious buds. In such cases it is altogether likely that an exami- 

 nation of the wood for that year would show two rings of growth, 

 between which the distinction might be expected to be less 

 clearly defined than between those of successive years. 



Variations in the width and prominence of growth rings of 

 successive years are in some cases so marked that, were pieces 

 of wood from the same stem to be examined without any knowl- 

 edge of their previous relations, they might be regarded as 

 representing wholly different species. This is notably the case 

 in the hard pines, such as P. palustris, P. cubensis, P. echinata, 

 etc., while it is also true of Pseudotsuga Douglasii, in which this 

 feature has been critically studied. In a large cross section of 

 this wood, embracing five hundred and thirty-eight growth rings, 

 the latter were found to be disposed in well-defined zones, which 

 vary greatly in width, while the component rings of contiguous 

 zones show well-marked differences in radial volume. An in- 

 structive example of such growth is given by Hartig (22, 40) in 

 the case of the Tyrolean larch, taken from a height of a thou- 

 sand meters and having an age of one hundred and ninety years 



