NATURAL SCIENCES OF PHILADELPHIA. 35 



the branchlet pushes front the main branch, the first series of two 

 or sometimes three are one above another, and on the upper side. 

 The flattened frondose form is the result of this plan of develop- 

 ment. Rarely two branchlets will proceed from each node, one 

 from the axil of each opposite leaf. 



In some species each succeeding pair of cohering leaves are 

 of equal length and strength. In the Thujas and in Ghamse- 

 cyparis Lamsoniana this is characteristic; but in Libocedrus 

 decurrens, and Chamascyparis obtusa, and allies, every first pair 

 succeeding a branchlet, and which on the flattened conditions 

 constitute the dorsal pair, are very much abbreviated and 

 shortened, so much indeed as to scarcely proceed beyond the line 

 of the lower pair, and tbus some writers have been led to describe 

 these plants as having 4-verticillate leaves. 



The seedling or first year's growth of Biota orientalis exhibits 

 this subverticillate character. The first pair of leaves succeeding 

 the cotyledons is so near as to appear almost two of a series of 

 four cot3 T ledon lobes. For many successive nodes the leaves 

 appear to be 4-verticillate. 



In regard to the early leaves of coniferous plants, those which 

 follow the cotyledons are nearly free, having little cohesion with 

 the stem or " decurrence," as botanists sa} r . As the axis becomes 

 thicker, or, as I have termed it in the paper referred to, endowed 

 with more vitality, there is less of the free portion and more of 

 the adnated or cohering, until in Pinus there is nothing left but 

 a thickened bed or pulvinus ; and the axial bud which generally 

 marks th f o diverging place of the proper leaf has to push and in 

 a difficult way perform the function of leaves. If any thing tend 

 to check the vitality of the tree, so that the axial buds do not 

 develop, the adnating power is weakened, and the true leaves 

 again become free from the stem. This is seen in Pinus edulis, 

 Engl. At any time through its existence, where the branches are 

 weak by being shaded or starved by other branches, the pulvini 

 develop into true leaves, and the axial bud, usually producing 

 two "needles," does not push. Street trees and osier willows when 

 annually trimmed, though the subsequent growth is vigorous, 

 increase their trunks slowly in girth, and die much earlier than 

 uncut ones. Thus their vitality is impaired. Some pine trees 

 when cut down push up strong sprouts, and these will often have 

 the pulvini developed into true leaves as in the weakened Pinus 

 1872.1 



