5^4 



hiuls and iheir appearance can he traced hack primarily to a local increase 

 in growth. It cannot he denied that this is the most pertinent explanation, 

 but the condition of the wound in many cases also indicates some frost 

 action. 



It is finally possihle. in artificial frost experiments, to produce such 

 frost tears and thereby ])ut an end to such douhts. Fig. 131 gives the 



ig-. 131. Cross- sect i 



throush th(> Inui cushii 

 aitiflcial frost. 



larch bi-anch, injured l)y 



anatomical appearance of such a v^ound which had l)een produced by the 

 action of artificial cold on a larch branch a year and a half old. The 

 branch was cut through a bud cushion; the wood (h), which otherwise 

 would have formed an uniform ring about the pith (m), appears inter- 

 rupted by the broad parenchymatous medullary bridges (m-mtr). 



