FERN STRUCTURE. 2$ 



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 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 tlie 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 ijl^. 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. T7. — Cross-section of stipe 01 



work for the softer portions of Cystofterls /nigiUs ^fixn\\..%\\ovi\n% 



, . , T^, • two bundles of fibro-vascular tissue. 



the frond. 1 he 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. 



