. Our native ferns and their allies [microform] : with synoptical descriptions of the American pteridophyta north of Mexico. Ferns; Fougères. FERN STRUCTURE, 25 71. Tissue Systems.—The earliest tendency to differen- tiation of cells is seen in the arrangement of the outer row of cells to form a boundary wall. In higher forms of growth the interior cells tend to form one or more series of string-like rows surrounded by the normal cellular tissue. We thus reach the basis of the classification of vegetable tissues into three groups: (a) Epidermal (b) Fibro-vascular System, (c) Fun- damen
. Our native ferns and their allies [microform] : with synoptical descriptions of the American pteridophyta north of Mexico. Ferns; Fougères. FERN STRUCTURE, 25 71. Tissue Systems.—The earliest tendency to differen- tiation of cells is seen in the arrangement of the outer row of cells to form a boundary wall. In higher forms of growth the interior cells tend to form one or more series of string-like rows surrounded by the normal cellular tissue. We thus reach the basis of the classification of vegetable tissues into three groups: (a) Epidermal (b) Fibro-vascular System, (c) Fun- damental System (Fig. 17). The first and third are common to both ferns and mosses. The second is first seen in the ferns and their allies, where it is a character so constant that it serves as the basis for separating the so-called " vascular" cryptogams from other flowerless plants. These three forms of tissue may be seen by examining a thin cross-section of the stipe of a living fern with the microscope. Longitudinal sections will show still further the character of the tissues composing the fibro-vascular bundle. 72. Roots.—Roots are constantly produced as the root- stock advances, and consist for the most part of little fibrils which are naked for a short distance from the apex in order that they may freely absorb moisture from the earth. The epi- dermis is also thin, and usually consists of a single layer of small cells. It differs from that of the rest of the plant in having no stomata i^i). As the apex continues to grow, the epidermis of the part behind becomes harder, and frequently develops hairs, or more frequently irregular scales. 73. Stipe.—The stipe is made up of the three forms of tissue (Fig. 17), and usually con- tains several bundles of vascular tissue. In the dried stipe these can be easily seen, by scraping off the external covering of the stem. These bundles of fibres give sta- bility to the fern, and are con- tinued through the rachises and ve
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