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ANATOMY, AND LTFE-HISTOHT OF THE COTOPEB^. 



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uniform and 4-seriate. The branching on the main leader- 

 shoots takes place, according to Meehan, pretty regularly 



at the fourth node, sometimes from the second, rarely from the 

 fifth. ' 



Thuyopsis dolabrata has very flat branch-systems, the leaves 

 are decussate, and branching takes place from one or both of the 

 third or fourth lateral pairs of leaves above the one taken as a 

 starting-point, 



Thuyopsis borealis is, in the young state, a shrub of pyramidal 

 habit, with pendulous flattened branch-systems. The leaves are 

 uniform, in four rows. Branching occurs pretty regularly from 

 one of each of the lateral pair of leaves, now to the right, now to 

 the left, rarely from both sides at the same level. On the main 

 quick-growing shoots, the order of branching, 

 Meehan, is the same as in Thuya occidentals and gigantea. 



according 



to 



Sometimes in very stout shoots of this plant," says Meehan, 

 "the leaves will be in whorls of three, and then the branching is 

 on the odd numbers 3, 5, 7, but not in a regular graded series as in 

 rts normal condition. I have counted as many as fifteen nodes 

 without a branch ; and this absence of order in branchiug exists 

 also in Junipers. In these the leaves are mostly in threes, though 

 still decussate, and the branching takes place at the odd numbers 

 and ig irregular. Oallitris quadrivalvis has four leaves in a 

 whorl, and here again we have the irregular branching of the 

 Junipers. 



u The result of these observations is that in a large number of 

 cases the frequency or degree of branching is seen to be asso- 

 ciated with declining vigour; that presence of leaves in an 

 opposite pair is favourable to a regularity of branching on even 

 numbers ; and that whorls of three or more are associated with 

 "•regular branching on odd numbers." Probably the phenomena 

 noted by Mr- Meehan are not so much the result of declining 

 vigour as of alteration in the direction and locality in which the 

 energy i 8 manifested. The long quick-growing extension-shoots 

 ha ve, as their function, the formation of the trunk and principal 

 branches ; the multitude of branchlets is adapted to sustain an 

 even greater number of leaves on whose due action the life of the 

 whole tree depends. Vigour, or the amount of work done, may 

 be as great in the one case as in the other, though exerted in a 

 different direction. It is probable that some of the irregularities 

















































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