5°8 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
these divisions elongate and crowd by one another, thereby producing an 
increase in the girth of the cambium. 
3. In the latter type, in which the fusiform initials are relatively short, 
of nearly uniform length, and more or less symmetrically grouped in parallel, 
horizontal series, the bulk of the anticlinal divisions is radio-longitudinal, 
and the increase in the periphery of the cambium is due primarily to the 
lateral expansion of the products of these divisions. 
4. The transition from the non-stratified to the stratified arrangement 
closely parallels successive stages in the specialization of the vascular 
tissues, e.g., the differentiation of vessels, libriform fibers, etc., and appears 
to be due to a progressive reduction of cell size and of longitudinal sliding 
growth in the cambium. 
Acknowledgments 
The writer is much indebted to Doctor E. D. Merrill, Director of the 
Philippine Bureau of Science, and to Professor I. F. Lewis for their kindness 
in sending freshly killed material of a number of different plants. 
LITERATURE CITED 
Bailey, I. W. 1918. Size variation in tracheary cells I. A comparison between the 
secondary xylems of vascular cryptogams, gymnosperms and angiosperms. Proc. 
Amer. Acad. Arts Sci. 54: 149-204. 
-. 1920. The significance of the cambium in the study of certain physiological 
problems. Jour. Gen. Physiol. 2: 519-533. 
-. 1920a. The cambium and its derivative tissues II. Size variations of cambial 
initials in gymnosperms and angiosperms. Amer. Jour. Bot. 7: 355-367. 
-. 19205. The cambium and its derivative tissues III. A reconnaissance of cyto- 
logical phenomena in the cambium. Amer. Jour. Bot. 7: 417-434. 
Hartig, R. 1895. Ueber den Drehwuchs der Kiefer. Sitzungsber. Bayer. Akad. Wiss. 
Math.-Phys, Kl. 25: 199-217. 
Kleinmann, A. 1921. Uber Kern- und Zellteilungen im Kambium. Frankfurter Dis¬ 
sertation. Quoted from Neeff (1922). 
Klinken, J. 1914. Uber das gleitende Wachstum der Initialen im Kambium der Koniferen 
und den Markstrahlverlauf in ihrer sekundaren Rinde. Bibl. Bot. 19: 1-37. 
Nageli, C. 1864. Dickenwachsthum des Stengels und Anordnung der Gefassstrange 
bei den Sapindaceen. 66 pp. Miinchen. 
Neeff, F. 1920. fiber die Umlagerung der Kambiumzellen beim Dickenwachstum der 
Dikotylen. Zeitschr. Bot. 12: 225-252. 
-. 1922. fiber polares Wachstum von Pflanzenzellen. Jahrb. Wiss. Bot. 61: 205-283. 
EXPLANATION OF PLATE XXXVI 
Fig. 1. Pinus Strobus L. Tangential longitudinal section of non-stratified lateral 
meristem. The cells are so long that only a portion of each fusiform initial is shown in the 
photomicrograph. X no. 
Fig. 2. Myristica philippensis Lam. Tangential longitudinal section of non-strati¬ 
fied lateral meristem of less highly differentiated type of dicotyledon. X no. 
Fig. 3. Fraxinus americana L. Tangential longitudinal section of non-stratified 
lateral meristem of highly specialized type of dicotyledon. X no. 
