70 A. H. Graves, 



fig. 36). In the case of the stem, however, the natural arrangement 

 often remains apparent (PL I, fig. 2; PI. II, fig. 6). 



On account of this distichous system, it is possible to cut a 

 longitudinal section through all of the branches and the stem at 

 the same time, especially if the region of the growing point is 

 selected, as is represented in PL I, fig. 1 (cf. PL VI, fig. 25). 



A study of this figure of a vigorously developing stem apex will 

 show clearly the order of development and the orientation of the 

 branches. Since the origin of the branches is inseparably connected 

 with the leaf development, it will be necessary to include in a 

 description of the figure some reference to leaf development. 



The apical growing point G P has given off" in alternate succession 

 the primary leaves L^, L^^, L^^^. L^^, &c. A secondary growing 

 point arises in the axil of each of these leaves, which develops 

 leaves in the same manner. The first leaf, however, is a scale leaf, 

 which will be discussed at length later. (See p. 99.) 



Since L^, L ^^, L ^^^, L ^^, &c. are developed in acropetal suc- 

 cession and hence show equal gradations in age, a study of their 

 successive axillary structures presents a clear idea of the manner 

 of development of the branch. The youngest leaves, L ^^^^ and 

 L ^^^ are hardly more than protuberances from opposite sides of 

 the growing point, and as yet reveal no structures in their axils. 

 At L ^^ we first see a small axillary growing point — the beginning 

 of a branch. In the axil of L ^^ the rudimentary scale leaf, v s /, 

 appears on the left of the growing point gp^^^- At the base of 

 L^^^ we find the scale leaf (vsl) in its normal position, and also 

 on the left df'the growing point point the first vegetative leaf of 

 the branch, li^^^l The axils of L^^^ and L^^ show successively 

 advanced stages until in L^ appear four leaves of the branch besides 

 the scale leaf;— /jW, ^t^', is^^'' and l^^^l Moreover in the axils 

 of /i*^) and /2^^) appear young growing points to form branches of 

 a second order. 



Such a growing point under ordinary conditions will develop in 

 a regular way for some time, the leaves and axillary shoots appear- 

 ing in acropetal succession and the nodes of increasing length 

 basipetally, according to their age. This stage is represented in 

 PL I, fig. 2, a sketch from a living specimen. 



Sooner or later, however, in the course of the development of 

 the system, its regularity becomes more and more modified to suit 

 environmental relations, a condition which is of course true of any 

 branch system. PL II, fig. 6 is a drawing from nature of the upper 

 portion of a plant whose vegetative branch system has undergone 



