66 



Spalding : Mechanical adjustment of suaharo 



This very incomplete evidence indicates, as far as it goes, that 

 temperature is an altogether subordinate factor, the effect of which, 

 however, may increase or diminish that of water-supply. 



Recurring again to the relation of the mechanical system to 

 the processes of expansion and contraction, it would be difficult to 

 imagine a more perfect arrangement for prompt and safe accom- 

 modation to variation in the large quantities of water held by these 

 great columnar reservoirs. The strong central cylinder of fibro- 

 vascular bundles necessarily retains the relative position of its ele- 

 ments through all such variations ; and the peripheral band of 

 mechanical tissue is so disposed as to promptly adjust itself, by 

 the simple change of position that has been described, to changes 



Jan. 



February 



March 



April 





o 



Figure 8. Six curves from as many different plants, each representing the varia- 

 tions of the furrow which faced nearest north. Rain, February 6 (0.54 in.). 



in the bulk of the tissue which it surrounds. The circumference 

 of the stem can therefore be increased or diminished without inter- 

 fering in the slightest degree, as far as the present observations 

 indicate, wnth the strength or efficient distribution of either the 

 central or peripheral mechanical elements. That the change in 

 girth may be considerable in a relatively short period is shown by 

 the fact that some furrows of number 9, which was watered 

 about two months, actually increased 35 per cent, of their origi- 

 nal width, and that one furrow on a plant not watered expanded 



