It is in accordance with the same natural law which governs sprout 

 growth after a basal burn, and the production of adventitious shoots 

 after an injury on the stems or branches of certain broadleaf trees. 



Yellow pine marked by fire scars shows a germination 15 per cent 

 above that of healthy yellow pine. Fire scars are confined almost 

 entirely to the base of the tree. They begin as a small burn in the 

 bark and cambium, but increase in size and depth with recurring 

 fires, until finally they sometimes extend 5 feet or more up, and one- 

 half or two-thirds through the stem. Trees thus affected generally 

 bear no marked signs of reduced vitality except in advanced stages, 

 although possibly measurements might show a diminution in growth. 

 The direct effects of the burn are a reduction of the water supply of 

 the crown of the tree because of the destruction of more or less of 

 the water-transporting elements, and at the same time a reduction 

 of the food supply of the roots through the destruction of some of 

 the elements bringing elaborated food material from the crown to 

 the roots. It is evident that the food supply of the roots will suffer 

 more than the water supply of the crown, because the elements 

 bringing down the food, being nearer the surface, are more readily 

 destroyed by the fire. The eventual result will be a reduction of the 

 food supply of the entire tree, due to a reduction of the amount of 

 water which the tree is able to absorb. In spite of this fact, burns 

 appear to stimulate seed production, as does the injury causing 

 spike top. 



Mistletoe-infected blackjack shows a germination 17 per cent below 

 that of unaffected blackjack. Although mistletoe stimulates growth 

 in the immediate region of the parasite, causing the abnormal devel- 

 opment of certain branches, the excess of carbohydrates produced 

 by the additional foliage of the mistletoe-stimulated branches is used 

 by the parasite itself, so that the final result is a drain upon the tree. 

 It seems highly improbable that mistletoe would ever act as a stimulus 

 upon seed production, because its action is insidious, slowly sapping 

 the vitality of the tree instead of causing injuries in the nature of 

 a shock, as is the case with burns or other mechanical injuries. 



The effect of suppression is not clearly demonstrated. Of . the two 

 yellow pine included in our data, one has a germination per cent of 

 92 and the other only 14.5, the average of the two being 53, or 11 

 per cent below that of normal yellow pine. The only blackjack 

 tested shows a germination of 90.5 per cent, or 12.5 above that of 

 the average healthy blackjack. On account of the great variation 

 between the individual trees cited above, it is impossible to predict 

 the result of averaging a large number of trees. One would naturally 

 expect to find an inferior quality of seed on a suppressed tree, but 

 this would vary with the degree and period of suppression. It will 

 also be counterbalanced to a certain extent by those factors which 



[Cir. 196] 



