Page:Popular Science Monthly Volume 33.djvu/498

482 a felting of hairs encompassing the stem, in which water rises as in a piece of filtering paper. Dicramim, undulatum, Climacium dendroides, and Hylocomium splendens are among the species thus furnished. These hair formations commonly resemble the root hairs, and might eventually he designated as of that class; but in single cases, as in Thuidium iamariscinum, they exhibit a peculiar construction. The hairs are undoubtedly adapted to taking up the water with which they come in contact.

With the phanerogams, the plenteous absorption of water by organs above ground is a rare phenomenon of adaptation, and is limited to a number of epiphytes (Bromelaciæ) and desert-plants. In these, again, different forms of hair-growth assist the reception of water. Volkens has recently shown that many of those desert species whose leaves are furnished with a hair-felting absorb rain and dew in this manner. But he has never observed the reception of the water going on over the whole surface of the hair, but only in specific cells at the base of the hair which act as the absorbing element; while the dead cells composing the felt fulfill the purpose of retaining the water, covering the surface of the leaf, and in that way facilitating absorption.

The capillary apparatus of the peat-mosses is peculiar and without any analogies with the more highly developed plants. The leaves of the Sphagnaceæ consist of two kinds of elements; of long-drawn, chlorophyll-bearing cells woven into a net-work, and of dead, colorless capillary cells, which form the meshes of the net. The walls of the capillary cells are furnished with large, usually round pores, the points at which the water is admitted, the situation and arrangement of which in many species materially facilitate the passage of the water from one cell to another. The edges of the pores are usually hemmed with a thicker fibrous ring, the office of which is evidently mechanical, or to prevent tearing. The walls of the cells are also stiffened with spirally arranged fibrous structures, like the duct-walls of the more highly developed plants. The stems of the peat-mosses have also a "bark-envelope" from two to four cells thick, which serves as a reservoir and a medium for the circulation of water.

The stems, fruit-stalks, and leaves of numerous mosses possess a water-bearing tissue-cord occupying an axillary position. This cord, which consists of narrow, thin-walled, and elongated cells, has been described by W. Ph. Schimper and Fr. Unger, to whom we owe some excellent researches on the anatomy of the mosses. Its precise physiological function has until very recently not been made clear. While it was not doubted that it had some connection with the circulation, it was not certain whether or not it presented any analogies with the vascular system of the higher