FOREST PROTECTION 149 



Farming can be carried on remuneratively in closer proximity of 

 the smelters than forestry. Obviously, in the case of annual 

 plants, there is no cumulative influence of SO 2 due to many 

 a year's exposure. 



The fact that farm crops are more resistant to smoke than forest 

 crops may be explained ,also, by the higher reproductive power 

 of the former and by the greater height of the latter, the leaves 

 of which are exposed to more concentrated gases of S0 2 . 



In case of fruit trees, mulberries seem to be least sensitive; then 

 follow apples, pears, peaches, plums, with cherries as the most 

 sensitive fruit trees at the rear end. 



Wherever fruit trees are well attended by cultivation and by fer- 

 tilizing, the damage by sulphur fumes is minimized. 



The "floral organs' ' of the fruit trees seem to be less affected by 

 smoke than the "pulmonary organs/' which means to say 

 the fruiting of the trees is not badly interfered with by S0 2 

 and SO 8 . 



H. Damage to Forests. 



The forest trees, according to species and individuality, exhibit 

 a very varying degree of sensitiveness to the influence of sul- 

 phur fumes. The degree of liability to damage is in no way 

 proportioned to the readiness with which the trees inhale sul- 

 phuric fumes. For instance, the conifers are more affected 

 by sulphur fumes than are the hardwoods. Still, exposed to 

 the same atmosphere charged with sulphuric fumes, the coni- 

 fers will inhale smaller quantities of toxic gages than the hard- 

 woods. 



The power of resistence which the various species show to the in- 

 fluence of sulphur fumes is, on the other hand, directly pro- 

 portioned to the power of reproduction (power of recovery) 

 which the various species show. It is obvious that this power 

 of recovery is particularly good in hardwoods, which must 

 recover, every spring, from the natural loss of foliage sustained 

 in the preceding fall. 



In the case of broad-leaved species, any loss of vital organs is readily 

 made up, whilst in the case of conifers the reproductive power 

 is comparatively low. 



Amongst the conifers, those which retain their needles for a num- 

 ber of years are more apt to suffer from sulphuric fumes than 

 those which retain their needles for one or two years only. 



Inasmuch as the resistence which the trees offer to injury by sul- 

 phurfumes is proprotioned to their power of reproduction, 

 and inasmuch as this power of reproduction largely depends 

 on the fertility of the soil, it is obvious that all species suc- 

 cumb on impoverished soil more rapidly than on good soil. 



