ANATOMICAL STRUCTUKE AND VITALITY. 65 



the apex, as may readily be seen in the Lily, Iris, and 

 Grass families* (fig. 11, a, b, c, d) ; or they diverge 

 from each other or from a midrib, as in palms, banana, 

 cycad, screw pine, travellers' tree, strelitzia, dragons- 

 blood tree, aloes, yuccas, Australian grass trees, and 

 several arborescent species of the pineapple, all having 

 firm tree-like stems. 



Besides this characteristic tree structure of endogens, 

 a considerable number of plants of the same division are 

 stemless, their leaves being developed from a bud or 

 crown, which never rises more than a few inches, or 

 scarce a foot above the surface of the ground. This kind 

 of crown or stem varies much in its nature, in many 

 grasses being quite undefined or rudimentary only. 



In the bulbous section of the Lily family, it consists 

 of a small thin disc which is the base of the bulb, and 

 produces roots from its under side, the body of the bulb 

 being formed of the broad bases (j)etioles) of the leaves 

 which overlap each other, forming what is called a tuni- 

 cate, or coated bulb, through the centre of which the 

 flower stem rises ; the onion and hyacinth are good ex- 

 amples. 



From the oni(m we pass to the leek, the bases of the 

 leaves of which being long, overlap by their lengthened 

 edges, and thus form an apparent stem. This mode of 

 structure is also characteristic of the Banana {Musa) ; 

 and although M. Ensete has a stem seven to eight feet 

 in girth, and as much in height, it cannot be viewed 

 otherwise than a gigantic leek {Phyllacorm) . 



From what has been stated regarding the structure of 

 exogens and endogens, it may be ascertained by examin- 



* The Sarsaparilla, Yam, and Arum Families are exceptions* 

 P 



