LARCH MISTLETOE. 



15 



infected area (fig. 13), but large brooms are almost invariably 

 produced. 



In mistletoe regions no trees of any age are safe from infection. 

 A great many trees surrounded by other species not attacked by the 



! INCHES ( . 



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I ! ii i ! 1 1 ( 1 1 n I. i n ii ; i i i ii 1 1 i 1 1 i 1 1 1 1 n ! ii 1 1 1 1 1 1 u 1 1 



Fig. 11. — The main stem of a young larch, showing two separate infections, one at the 

 whorl of branches and the other on the internode. Both infections are of the same 

 age, as indicated by the large primary sinkers, which terminate at the same annual 

 ring. Note the rough bark on the swellings, the beginning of typical trunk burls. 

 The branches of the mistletoe have fallen, but the sinkers are still living and will 

 remain alive for an indefinite period, stimulating the host tissues to a greater devel- 

 opment. The central areas of the burl soon die, leaving an open wound. 



same mistletoe escape early infection and grow to a fair size, with 

 normal, healthy crowns. Such uninfected trees are always conspicu- 

 ous among their more heavily infected neighbors. These trees are 

 eventually attacked, 

 but owing to the ad- 

 vantage of a some- 

 what isolated posi- 

 tion, they may not 

 become badly in- 

 fected, since the 

 seeds must be 

 brought from a dis- 

 tance greater than 

 the natural expelling 

 force of the seed 

 capsule is capable of 

 exerting. Undoubt- 

 edly this force is 

 aided by the wind. 

 The final result is the infection of the terminal twigs, and 

 in nio-f cases those of the lower branches. The infection 

 gradually spreads upward; the bmnches either become broomed 



Fio. 12. — A larch twig, showing the abnormal size of the 

 foliar spurs when stimulated by the parasite. These spins 

 are nearly four times the size of the normal spurs on the 

 : ame bra nch, 



