FIBRO-VASCULAR BUNDLES. 51 



certain cells of the epidermis give origin to structures known 

 as epider?nal appendages, such as hairs or glands, which are 

 outgrowths originating from one or several epidermal cells. 

 Amongst the most highly differentiated of such structures 

 may be mentioned the sporangia or spore-producing organs 

 of ferns. 



The Fibro-vascular System is present in the higher 

 Cryptogams and Phanerogams under the form of one, or 

 usually several, strands called fibro-vascular bundles. As 

 examples of such bundles may be mentioned the veins of 

 leaves, and the wood and bast of stems. Owing to the 

 thickening of the cell-walls of most elements constituting 

 a fibro-vascular bundle, these structures remain after the 

 parenchymatous portions of the structure have decayed, as ' 

 illustrated by a " skeleton leaf," which consists entirely of 

 fibro-vascular tissue, the parenchyma having been removed 

 along with the epidermis. In aquatic plants as a rule, 

 however, the fibro-vascular bundles are softer than the 

 surrounding parenchyma or fundamental tissues. The 

 structure and arrangement of the fibro-vascular bundles is 

 constant in the same species, and in addition, depend- 

 ing on its origin, increase, and detailed structure, is 

 of great value in classification. In leaf-stalks or petioles, 

 and stems, and all organs that grow especially in length, 

 the fibro-vascular bundles run longitudinally, or in the 

 direction of the long axis of growth ; and as a rule the 

 bundles of the leaves are continuous with those of the 

 stem, in other words the bundles from the leaves pass 

 continuously into the stem and coalesce with older bundles ; 

 such are termed leaf-traces or common bundles, in the sense 

 of being common to leaf and stem. In rare instances 

 in flowering plants certain bundles, called cauline bundles, 



