LARCH MISTLETOE. 



positively phototropic. The possible influence of the low absolute 

 humidity and rapid evaporation on the entrance of host, reproduc- 

 tion, etc., is counteracted by the parasite by means of special struc- 

 tures enabling it to withstand long periods of drought. 



Probably no factor of the region so greatly aids the destructive 

 effects of the mistletoe on the larch as the high, strong winds so 

 prevalent in these mountains. The velocity of the winds is sometimes 

 very great. During 1913 hundreds of 

 reserved yellow pines on the sales area of 

 the Whitman National Forest were up- 

 rooted. The wind in this case was mate- 

 rially aided hy the insecure rooting of the 

 trees on the surface of a hard stratum 

 of rocks and gravel, together with a cer- 

 tain amount of decay in the brace roots. 

 This is a condition often found in cases 

 of this kind. 



Strong winds probably do greater injury 

 to the larch than to any other conifer. An 

 examination of the branching or crown of 

 a mature or middle-aged healthy larch will 

 show that in most cases, especially in 

 windy regions, the tree has been able to 

 reach the standard size only through the 

 production of several generations of 

 branches replacing those broken off by the 

 wind and by other causes (fig. 2). The 

 loss of branches through crowding or 

 natural priming is not here considered. 

 Trees standing under open conditions from 

 the beginning will show this interesting 

 phenomenon of regeneration. Increasing 

 age, within a certain limit, on the part of 

 the main trunk doe£ not interfere with the 

 anatomical and physiological connections 

 of old branches. Consequently, branches 

 forming at any age sufficient^ high on the 

 trunk to escape the influence of suppression should and would remain 

 intact, barring all deteriorating influences, during the natural life of 

 the tree. 



Trees with wood exhibiting a natural brittleness, which is always 

 very pronounced at the bases of branches, suffer greatly from break- 

 age by the wind. The western larch is especially subject to this 

 form of injury. The brittleness of its branches at their point of 

 attachment with the main trunk is so pronounced that it is not un- 



Fig. 3. — A larch tree of greatly 

 reduced vigor caused by the 

 formation of great witches'- 

 brooms and the accumulation 

 of dead leaves and lichens in 

 them. Note that the tips of 

 the branches, also the witches'- 

 brooms in the upper portion 

 of the crown, are dying. 



