File:Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania, vol. 14 (1934) (20067530653).jpg

Title: Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania, vol. 14
Identifier: contributionsfro14univ (find matches)
Year: 1934 (1930s)
Authors: University of Pennsylvania. Botanical Laboratory; University of Pennsylvania. Morris Arboretum
Subjects: Botany; Botany
Publisher: Philadelphia : (s. n. )
Contributing Library: Penn State University
Digitizing Sponsor: Lyrasis Members and Sloan Foundation

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troo with doprossi,,,, inn.UM a d> : /oVV if Vn^^^ ", ^'Z^'-^- '""'" "" ⢠-- .vc'nr old »J« -â ^ -^ â¢< r - 4 '⦠« - ⢠July, wlien 1 or 2, and in some eases as many as 4 lateral buds commence to o-row. The resultino- precocious shoots may attain a lenj^th of 3 to 4 inches, witli 1 or more winter buds at their apices, before becominj? dormant (Fig. 1, D). Needles develop on such shoots, but seldom attain more than half of their normal leno-th and fail to elonofate further at the initiation of g-rowth the followinj*' sprint-. The precocions shoots may continue to elon- gate until quite late in the current season, although, according to Gustafson (5), elongation in pine shoots has been ccmipleted by early Jnly in Michigan. Measurements of 10 precocious shoots in a planting of 8-year-old red pine were taken on August 15, 1937, and again on October 25. All but one of them showed an increase in length from ) to VI in. The formation of a bud cluter at the tip of the precocious shoot (Fig. 1, D) interfei-ed with normal subsequent growth, as it caused secondary branches to be formed within a few inches of the bole (Fig. 1, E). The termiiud bud of the cluster in which the extra-seasonal growth oc- curs seldom takes part in the abnormal development, and usually elongates at the normal time the following season. The laterals, however, during the course of their extra-seasonal growth, react as if the terminal bud had been injured or removed and grow in a more or less vertical direction. Thus the shoot, originating from the terminal bud the following season, grows in competition with one or more laterals that had commenced growth the preceding summer. This results in a bi- or trifurcated appearance of the tree, which will be referred to as ^'forking" (Fig. 1, A). This condition does not remain conspicuous for more than 2 or 3 seasons in most cases. Either the true leader or one of the precocious laterals will assume domi- nance and the other member, or members, of the foi-k will tend to the more or less horizontal position normally characteristic of red pine branches. Forking may occur repeatedly in a tree. One 22-year-old specimen, when dissected, showed this phen(mienon in at least 12 nodes (Fig. 2). An examination of nodes where forking had occurred at some previous time frequently showed a slight depression in the trunk immediately above the insertion of the branch (Fig. 1, C). There seems to be no relation between the age of a tree and its suscepti- bility to forking, in stands up to 25 years of age. No data have been obtained upon older trees because of the difficulty of making certain, without felling the tree, that a fork might have been induced by insect or mechanical injury. DAMAGE RESULTIXO FROM FORKIXG The structural injury that results from forking usually has its incep- tion during the season following the formation of the fork, and is caused by the failure of the forked members to completely unite as they increase in diameter. Because of the acute angle at which they stand in relation to each other, they are unable to slough off, or push aside, the bark that lies on the inside of the fork between their cambiums, in the manner that the growth of the trunk displaces the bark of a normal lateral branch. This

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