MISTLETOE INJURY TO CONIFERS. 



19 



ceases to grow in length and instead forms abnormally abundant 

 lateral branches. The terminal buds of these are likewise overtaken 

 by the parasite, resulting in additional lateral branches, and so on, 

 until a type of dichotomous branching results. This is more notice- 

 able in the compact type of broom than in the long, trailing type, but 

 is quite common in both, especially on exposed and wind-swept areas. 



A very interesting hypertrophy of the foliage spurs is often 

 shoAvn by the brooms 

 of the larch. The 

 spurs are frequently 

 abnormally large 

 and may be four or 

 five times as long as 

 those of normal 

 branches (fig. 16). 

 On such spurs the 

 needles are usually 

 shorter and spar- 

 ingly clustered. 

 Eventually the para- 

 site enters the spur 

 and kills it. Not in- 

 frequently a mistle- 

 toe plant is found 

 growing out at the 

 apex of the spur or 

 from its side, caus- 

 ing great distortion 

 and the total disap- 

 pearance of the nee- 

 dles, and eventually 

 the death of the spur. 

 The reduction of 

 foliage by the thin- 

 ning and shortening 

 of the needles of the trees as a whole, and of the brooms sooner or 

 later, is characteristic of mistletoe infection on all hosts. 



The food material, which undoubtedly is accumulated in the 

 brooms, seems to be entirely appropriated at these points and does 

 not serve the host as a whole. The support of the excessive number 

 of branches is necessary, but the parasite itself undoubtedly appro- 

 priates a large share at the expense of the healthy branches. The 

 yellow-pine mistletoe has been observed to become more luxuriant 

 and to develop abnormally long stems on swellings which had been 

 lacerated or gnawed by rodents. Evidently the accumulation of 



FIG. 16. Abnormal foliar spurs of the western larch caused 

 by Razoumofskya laricis. Note their size as compared 

 with normal spurs. 



