2 
INTRODUCTION. 
IV. 
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 which 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 Algae — 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 different 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 A lgse, no cells exist differing from those of ordinary 
parenchyma or soft cells, such as compose the pulp of a leaf. Algae, 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 Algae, however, though the cells are all of the same substance and 
nature, all parencliymatic , they are of various forms and arrangement in different 
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 
Algae 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 Algae the frame still consists of root, stem , and 
leaves , developed in an order analogous to that of higher plants. Passing from 
such, we 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 
plant. But among the Algae, 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 whole framework is 
a single cell. These are the true vegetable monads : with these_^e commence the 
