Contributions to the Knowledge of the Diaphragms of Water Plants. I. Scirpus validus

Abstract

1. Diaphragms, although present in many monocotyledons, are not restricted to that group. The present state of our knowledge, however, does not allow us to make definite statements as to their distribution. 2. Diaphragms are especially characteristic of leaves, but have been reported for all parts of plants except flowers and fruits. 3. Diaphragms have been found in immersed and in aerial parts of plants. 4. Diaphragms appear to be characteristic of plants growing in water or very wet places. 5. The structure of diaphragms varies: (a) they may be one to several layers thick; (b) the cells vary from polygonal to stellate; in the "scirpus type" the cells are in groups (usually of four) and are long and narrow, with short arms; (c) the presence of cross-bundles appears to vary with the form studied. In Scirpus validus nearly all the diaphragms have bundles in them. 6. The cross-bundle is made up of xylem and phloem. At first the connection with the longitudinal bundles is with the phloem, but later a secondary connection is made with the xylem. 7. The stellate cells originate from ordinary parenchyma cells by the differential growth of the cells from the inside outward. 8. Diaphragms in Scirpus validus arise by a division of the parenchyma into layers, some of which retain their meristematic character, while the remaining cells gradually cease growing and become the slender stellate cells of the air spaces. 9. Each group of four cells of the diaphragm of Scirpus spp. arises from a mother cell. The formation of dividing walls parallel to the long axes of the cells is probably determined by the current of food materials passing from the cross-bundle to the partition walls of the space. 10. Diaphragms have the following functions: (a) to resist strains and keep the spaces open; (b) to support cross-bundles; (c) to prevent entrance of water by the small size of the perforation; (d) perforations permit air to circulate; (e) while young and green, to manufacture carbohydrates; (f) to store food: (i) this is possibly in the form of some tannin compound containing the phloroglucin radical, and may or may not be associated with glucose; (ii) this substance is stored in special cells which are distinct from the starch-bearing cells; (g) to conduct food materials from the cross-bundle to the partition walls of the space.