OF THE LOWER GRADE. 67 



division, into two, four, and sixteen such plants, and so on. But if 

 these cells had merely remained in connection as they multiplied, 

 they would have composed one plant, consisting of a stratum of cells. 

 This is just what we have in the Dulse or Laver (Ulva, &c.) and 

 some other simple leaf-like Algje of various kinds, such, for example, 

 as that illustrated in Fig. 95 - 97. "WTien the whole body of a plant 

 is thus expanded and leaf-like, it forms Avhat is called a Froxd. 



108 ". Not only Sea-weeds, but many Liverworts and Lichens, 

 grow in 'this way. (In Lichens, &c., the expanded body usually 

 takes the name of Thallus.) In most cases, however, such plants 

 are composed of more than one layer of cells, or of a considerable 

 number of layers. And those of thread-like forms, resembling naked 

 stems and branches, in all the coarser and in some very delicate 

 kinds, are made up, like the parts of ordinary vegetables, of several 

 thicknesses of cells ; that is, they are 



109. Plants of a Solid Tissue of Cells, formed by cell-multiplication 

 through division taking place in more than two directions. Sea- 

 weeds, Lichens, and other plants of the lowest ordcrs,^ forming in 

 this Avay {i tissue of cells, generally exhibit either leaf-hke or stem- 

 like shapes, but seldom if ever do they present both in the same 

 plant. They may resemble leaves, or they may resemble stem and 

 branches, or display a variety of forms intermediate between stem 

 and leaf. But it is only when we come to the highest tribe of 

 Liverworts, and to the true Mosses, that the famihar ti/pe of ordinary 

 vegetation is realized in 



110. Plants witli a Distinct Axis and Foliage; that is, with a stem 



which shoots upward from the soil, or whatever it is fixed to, or 

 creeps on its surface; which grows onward from its apex, and is 

 symmetrically clothed with distinct leaves as it advances. All these 

 lower vegetables, of whatever form, imbibe their food through any 

 or every part of their surface, at least of the freshly formed parts. 

 Their roots, when they have any, are usually intended to fix the 

 plant to the rock or soil, rather than to draAv nourishment from it. 

 The strong roots of the Oar-weed, Devil's Apron (Laminaria), and 

 other large Sea-weeds of our coast, are merely hold-fasts, or cords 

 expanding into a disc-like surface at the extremit}% which by their 

 adhesion bind these large marine vegetables firmly to the rock on 

 which they grow. Mosses also take in their nourishment through 

 their whole expanded surface, principally therefore by their leaves ; 

 but the stems also shoot forth from time to time delicate rootlets, 



