IV.—The Occurrence of Cell Division in the Endodermis

Abstract

Summary1. Endodermal cells frequently show considerable increase in tangential dimension at a late stage in their existence, as a result of which the continuity of the endodermis may be maintained, despite the rapid expansion of the intra-endodermal cylinder following secondary growth.2. This tangential increase in size of the endodermal cells is usually accompanied by their division. The divisions may actually cause the increase in size of the cells, that is, there is active growth of the cells. Or they may follow a passive stretching. In either case the new walls fulfil a mechanical function, lending added strength to the stretched walls of the original cell.3. Two types of division are distinguishable:(a) Those occurring in primary endodermal cells. The new walls soon develop Caspary strips, linking up with those of the parent cells.(b) Divisions in tertiary endodermal cells. The new walls here show neither Caspary strip nor suberin lamella.4. It is pointed out that in neither case does the development of new walls interfere with the impermeability of the endodermis.5. The occurrence of the divisions is considered in relation to the supposed impermeability of the suberin lamella of the secondary endodermal cell, and to the conditions resulting in the deposition of the Caspary strip.