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 Syste.n. (b) Fibro-vasctilar 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 (77). 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 

 veins, thus forming the frame- 



. FIG. 17. Cross-section of stipe of 



Work for the Softer portions of Cystopteris fragilis Bernh., showing 

 , c j TI two bundles of fibro-vascular tissue. 



the frond. The stipes are some- 

 times smooth and polished, sometimes hairy or beset with 

 stalked glands, and sometimes densely clothed, especially near 

 the base, with chaffy scales. 



