The composition of the cell-wall at the apical meristem of stem and root

Abstract

It is a striking feature of the growth of any highly organised plant body that the construction of new protoplasm and consequent formation of new cells is usually strictly localised to certain definite regions, known generally, as the meristematic tissues. In the normal flowering plant, the main meristematic regions of the axis are found at the apices of stem and root as the apical or polar meristems and distributed in the intercalary region as two thin cylinders of cambial meristem, one between xylem and phloem, the vascular cambium, the other the cork phellogen, situated near the periphery. No tissues are more important in plant development than these meristematic regions, but so far their study has mainly been carried out by cytological methods, which have supplied much information as to the structural organisation of the protoplast, and especially of the nucleus. In the present paper, two of these meristematic regions, namely, the polar meristems of shoots and roots, are studied with reference only to the biochemical changes that proceed within the wall separating the protoplasts. Originally these walls are extremely thin, and from general considerations, as well as from cytological observations upon the phenomena at the completion of anaphase, it would appear that these walls, commencing as interfaces in a protein-containing medium, may be regarded as composed at first mainly of protein. The original wall may be homogeneous in physical structure, but will be of extremely complex chemical nature. From the observations that follow it would appear that its subsequent history represents chemically a progressive simplification; the constituent substances segregate into special lamellæ as they are released, so that the change is accompanied by an increasing complexity of organisation, of which the distinction between middle lamella and inner wall is the first visible indication.