INTRODUCTION. 



end proposed is as efficiently attained by the simplest agency as by the most com- 

 plex ; as if the Creator had designed to show us plainly how it is the same to 

 Him to act by many or by few, by the most elaborate arrangement when He wills 

 it, and by the simplest when that is His pleasure. 



In all the cases of Avhich we have as yet spoken, seeds are the result of the vege- 

 table cycle ; a seed being a compound body, containing an embryo or miniature 

 plant, having stem, root, and leaf already organized, and enclosed with proper 

 coverings or seed coats. But some plants do not produce such seeds. At least 

 one-sixth of the vegetable kingdom, perhaps more, are propagated by isolated cells 

 (or spores) cast loose from the structure of which they had formed a portion, and 

 endowed thenceforth with independent powers of growth and development. Such 

 are the reproductive bodies of the Ferns, the Mosses, and all plants below them in 

 the vegetable scale, concluding with the large class to which our attention will now 

 be confined — the Algas — which of all are the lowest and simplest in organization. 



The framework of every vegetable is built up of cells, little membranous sacs of 

 various forms, with walls of varying tenacity, empty, or containing fluid or 

 granular, organized matter, from which new cells may be developed. Among 

 more perfect plants there is, in difi'erent parts of the same individual, consi- 

 derable variety in the form and substance of the cells ; those of the wood and 

 of the veins of the leaves being different from those of the soft part of the 

 leaves, and these again different from those of the skin which is spread over 

 the whole. But as we descend in the scale of organization, greater and greater 

 uniformity is found. Below the Ferns, no vascular tissue and no proper wood- 

 cells occur ; and at last in the Algas, no cells exist difi'ering from those of ordinary 

 parenchyma or soft cells, such as compose the pulp of a leaf Algse, then, together 

 with Mosses, Lichens and Fungi, are termed cellular plants, in contradistinction to 

 Ferns and Flowering plants, which are denominated vascular. Among the most 

 perfect of the Algse, however, though the cells are all of the same substance and 

 nature, all parenchymatic, they are of various forms and arrangement in difi'erent 

 portions of the vegetable, often keeping up a very perfect analogy with the double 

 system of arrangement — the vertical and horizontal, or woody and cellular sys- 

 tems — of higher plants. Thus the cells of the axis of the compound cylindrical 

 Algee are arranged longitudinally, like the wood-cells of stems, while those of the 

 periphery or outer coating of the same Algae have a horizontal direction. 



In the most perfect of such Algte the frame still consists of root, stem, and 

 leaves, developed in an order analogous to that of higher plants. Passing from 

 such, Ave meet with others gradually less and less perfect, until the whole vegetable 

 is reduced either to a root-like body, or a branching naked stem, or an expanded 

 leaf ; as if Nature had first formed the types of the compound vegetable organs 

 so named and exhibited them as separate vegetables ; and then, by combining 

 them in a single framework, had built up her perfect idea of a fully organized 

 l^lant. But among the Algfe, we may go still lower in vegetable organization, and 

 arrive at plants where the whole body is composed of a few cells strung together ; 

 and finally at others — the simplest of known vegetables — whose Avhole framework is 

 a single cell. These are the true vegetable monads : with these we commence the 



