File:Bulletins on forest pathology - from Bulletin U.S.D.A., Washington, D.C., 1913-1925 (1913) (19883992913).jpg

Title: (Bulletins on forest pathology : from Bulletin U.S.D.A., Washington, D.C., 1913-1925)
Identifier: bulletinsonfores00unit (find matches)
Year: 1913 (1910s)
Authors: United States. Dept. of Agriculture
Subjects: Trees; Plant diseases
Publisher: (Washington : U. S. Dept. of Agriculture)
Contributing Library: Robarts - University of Toronto
Digitizing Sponsor: University of Toronto

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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 shown 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 necessarj^, 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
Text Appearing After Image:
Fig. 16.—Abnormal foliar spurs of the western larch caused by Razoumofskya laricis. Note their size as compared with normal spurs.

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