1. The adjacent, undifferentiated, uninucleated cells of the lateral meristem or cambium are of two distinct shapes and sizes: (1) small, more or less isodiametric initials which are of the same general order of magnitude as the cells of the terminal meristem and embryo; and (2) large, elongated initials which in certain cases may attain a length of more than 10,000 micra and a volume of 10,000,000 cubic micra. The large initials may be induced to divide to form small initials, and the latter to regenerate elongated cells of normal dimensions. Thus, the cambium affords an unusually favorable medium for the study of a number of fundamental physiological and cytological problems.
2. A study of the cambium reveals the fact that there is a very-much greater variability in the size of meristematic cells in plants than was suspected by Sachs or Strasburger, and that the working sphere of the nucleus is by no means so restricted as assumed by these investigators.
3. Although the larger cambial initials of Pinus strobus tend to have larger nuclei, the nucleocytoplasmic-relation varies within wide limits and the diploid number of chromosomes is constant. The conditions in the cambium do not support Winkler's view that there is a close correlation between chromosomal number (chromosomal mass) and cell size in the somatic tissue of plants, and that giant cells are hyperchromatic.
4. The process of cell plate formation in the cambium is a remarkable phenomenon, and one which is significant in discussing the relative merits of various theories concerning the dynamics of karyokinesis and cytokinesis.
5. The newly formed partition membranes in the cambial initials frequently intersect the side walls at angles of varying degrees of acuteness, which is in contradiction to Errera's (Plateau's) Law of Minimal Area.