FILICINE.E. 



475 



central vascular body, and continually producing new layers of parenchyma on 

 the outside. This takes place especially in two or three directions, so that two or 

 three corresponding masses of tissue are formed, slowly dying off on the outside 

 between which lie as many deep furrows meeting on the under surface of the stem. 

 From these a large number of roots are produced in rows in acropetal succession. 



In the Selaginelleae the stem remains slender, but lengthens rapidly, branching 

 profusely, and forms distinct internodes. The end of the stem rises above the 

 youngest leaves as a slender cone. In Selaginella a tendency prevails to sympodial 

 scorpioid development of the branches which not unfrequently leads to the system of 

 abundantly branched shoots developed bilaterally in one plane attaining a definite 

 outline, and a corresponding resemblance to a compoundly pinnate leaf. In con- 

 sequence of the small size of the leaves in this 

 genus, the general habit is mainly dependent on 

 the development of the systems of branches. 

 The main shoots which result from the sympo- 

 dial development of the branches may creep like 

 rhizomes, may grow obliquely upwards, may 

 climb, or may form the stems of arborescent 

 and fruticose plants. In all cases the repeated 

 branchings take place in one plane, for the 

 bilateral symmetry which is so marked in the 

 position of the branches and in the phyllotaxis 

 already exists in the growing point. 



The Leaves are always simple, unbranched, 

 penetrated by only a single fibro^ vascular bundle, 

 terminating in a simple point, and ending, in 

 Selaginella^ in a fine awn. The largest leaves 

 occur in Isoeles, where they attain a length of 

 from 4 to 60 cm. They are in this case divided 

 into a basal part or sheath, and an upper part 

 or lamina. The sheath does not entirely em- 

 brace the stem, but rises in a somewhat trian- 

 gular form from a very broad insertion, and is 

 acuminate ; it is convex behind and concave in 

 front, where there is a large depression, the Fovea, 



containing the sporangium ; the margin of this depression rises in the form of a thin 

 membranous outgrowth, which in many species lies above the sporangium and 

 envelopes it, the Velum. Above the fovea and separated from it by the * saddle,' 

 lies a smaller depression, the Foveola, the lower margin of which forms a lip, the 

 Labium, while from its bottom an apiculate membranous structure, the Ligule (or 

 Lingula), with a cordate base, is prolonged beyond the foveola (Fig. 334, A). The 

 lamina of the leaf, confaining chlorophyll, into which the sheath passes above, is 

 narrow and thick, almost cylindrical, but flattened in front, and penetrated by four 

 wide air-canals, which are divided by septa. This form is exhibited by the fertile 

 leaves of all the species of Isoeles ; a rosette of such leaves is produced annually ; 

 but between each pair of annual whorls is formed a whorl of imperfect leaves, which 



Fig. 334. — A longitudinal section through the base 

 of a leaf of Iso'ites lacustris with its microsporangium 

 ■)ni still unripe ; B longitudinal section of the lower 

 part of a young sporangium (X 300) (after Hofmeister). 



