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AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
two short halves which in turn elongate and divide (text figure 2, A). 
Owing to the fact that the cells do not divide and elongate in unison, there 
is a very considerable variability in the length of adjacent initials. In 
addition, owing to the fact that the frequency of the anticlinal divisions and 
the elongation of the fusiform elements are not constant, the size of the 
initials tends to fluctuate more or less in different parts of a given individual; 
e.g., they tend to be considerably shorter in slender shoots than in robust 
stems (text figure i). Thus, the non-stratified arrangement and the 
variability in size of the fusiform cells are both due primarily to elongation 
Text Fig. 2. Diagrams illustrating modus opercmdi of the increase in girth of cambium 
in non-stratified and stratified lateral meristems. A, Fusiform initial from non-stratified 
cambium, dividing pseudo-transversely; a, a , products of this division which elongate and 
slide by one another. B , Fusiform initial from stratified cambium; b, b, products of the 
radio-longitudinal division of this initial, which expand laterally but not longitudinally. 
Text Fig. 3. Types of anticlinal divisions in fusiform initials. A, Typical fusiform 
initial of a conifer. B, Fusiform initial of a dicotyledon, having non-stratified cambium. 
C, Fusiform initial of a dicotyledon, having a stratified cambium. 
following pseudo-transverse, anticlinal divisions. In meristems of the latter 
type, on the contrary, the initials divide radio-longitudinally and the 
products of such divisions expand laterally, but they do not elongate to any 
considerable extent (text figure 2, B). The structure of the secondary 
