THE DEVELOPMENT OF ROOT HAIRS BY ELODEA CANADENSIS

Abstract

IT is characteristic of a number of water plants that they produce roots which are hairless in water but develop hairs when they penetrate the mud. Although this phenomenon has given rise to much speculation in the past no satisfactory reason has as yet been advanced to explain the hairless condition of the roots in water. In the present investigation an experimental and microchemical attack on this problem has been undertaken. Elodea canadensis was chosen as the experimental material not only because it has been studied to some extent in the past but because it is of common occurrence and produces abundant roots under normal conditions. Preliminary studies established the fact that the roots are perfectly hairless in water but that once they penetrate the mud hairs are abundantly produced. Figs. I-3 represent strips of epidermis removed from various roots after warming with dilute ammonia, and illustrate the occurrence of special preformed hair-producing cells scattered haphazardly over the surface of the root. They are shorter than the neighbouring epidermal cells, and are distinguishable also by the greater density of their protoplasm. Fig. i, from the meristematic region of a root growing in the soil, illustrates clearly the difference between the two types of cell. Fig. 2 is from the mature region of the same root, the circles representing the bases of root hairs. Fig. 3 is from the mature region of a root growing free in water. Such roots were always hairless, and their short cells are generally much longer than the haired cells of the soil roots. Though hairless they are clearly distinguishable from neighbouring long cells in the same region. In the older regions of the root they are not so easily recognized. Such cells were first reported on Elodea roots by Schwarz (I883) and Sauvageau (I889). The former failed to produce root hairs by