THE CAMBIUM AND ITS DERIVATIVE TISSUES IV. 
THE INCREASE IN GIRTH OF THE CAMBIUM 
I. W. Bailey 
(Received for publication December 19, 1922) 
Introduction 
Since the publication of Nageli’s (1864) “ Dickenwachsthum des 
Stengels,” most botanists, if we may judge from statements in standard 
textbooks, have assumed that the increase in girth of the lateral meristem, 
during successive stages in the enlargement of a stem or root, is due to 
“radial,” anticlinal divisions of the cambial initials. Not all investigators, 
however, have accepted Nageli’s generalization. Robert Hartig (1895) 
inferred from the structure of the secondary xylem of Finns silvestris L. 
that the increase in the periphery of the cambium in conifers is due primarily 
to the elongation of transversely dividing fusiform initials. Klinken (1914) 
reached a similar inference from the study of serial sections of the phloem 
of Taxus baccata L. He concluded that there are two fundamental types 
of meristematic activity, one characteristic of the conifers and the other of 
the dicotyledons. Neeff (1920) subsequently found evidences of Hartig’s 
and Klinken’s type of cambial activity in the xylem and phloem of Tilia 
tomentosa which led him to believe that there is no such fundamental dis¬ 
tinction between the lateral meristems of gymnosperms and dicotyledons. 
There is, of course, a considerable element of uncertainty in ascribing a 
particular type of meristematic activity to large groups of the vascular 
plants, either upon the basis of a priori deductions or upon that of indirect 
evidence obtained from the study of the xylem or phloem of one or two 
supposedly representative species. 
In 1917, the writer perfected methods for sectioning the cambium and 
for investigating its histological and cytological details. As stated in the 
third paper (1920 b) of this series, he did not succeed in finding evidences of 
the hypothetical radial, anticlinal divisions which are described and even 
figured in botanical textbooks. The normal, anticlinal divisions of the 
fusiform initials, in all of the gymnosperms and less highly specialized 
dicotyledons examined, were transverse or more or less oblique. That 
radial longitudinal divisions do occur, at least in certain cases, is suggested 
however by Kleinmann (1921), upon the basis of the orientation of karyoki¬ 
netic figures in the cambium of Raphanus. In view of these facts, it is 
evident, on the one hand, that the increase in girth of the lateral meristem 
is not the simple phenomenon that Nageli hypothesized, and, on the other 
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