653 
THE PRINCIPLES OF BOTANY. 
By Professor James Buckman, F.L.S., F.G.S., &c. &c. 
{Continued from p. 580.) 
- Class I .— Thallogens. 
Plants belonging to this class may be distinguished by 
their extreme simplicity of structure; they have no wood, pro¬ 
perly so called, though in some of the older sea-weeds there 
is an apparent hard woody structure, nor is there any 
approach to those leafy organs so conspicuous in higher 
classes, and consequently stomata or breathing pores are also 
absent. The want of leaves necessitates an absence of floral 
envelopes; these and sexual organs then are scarcely, if at 
all, even represented, and reproduction is not by pollen and 
ovules, or ordinary seed, but by a separable cell, which is 
very variously prepared. It is true,” as remarked by Pro¬ 
fessor Lindley, that such names as Antberidia and Pistil- 
lidia are met with in the writings of Cryptogamic botanists, 
from which it might be inferred that something analogous at 
least to sexes was observable among such plants; but these 
are theoretical expressions, and unconnected with any proof 
of the facts to which they are applied, performing the office 
of anthers and pistils. If it should be assumed, as it has 
been by some, that they do represent sexual organs, it is to 
be remembered that it is a mere assumption unsupported by 
sufficient evidence.” 
Dr. Balfour says that “ in the Confervte and Diatomacege 
there is a union of the cells of the plant by conjugation, so as to 
produce germinating bodies. In these cases the contents of 
one cell pass, by tbe formation of a tube, into the other.” 
But whatever may be the nature of the reproductive ele¬ 
ment, we may view it simply as a separable cell, as in the spores 
of the mushroom and other agarics, in 'which, by placing the 
fungi on pieces of writing paper a different coloured dust, 
according to tbe species, will in a short time be found to cover 
their surfaces. These are perfectly cellular grains, but after 
all it is doubtful whether they alone can reproduce the plant 
from which they spring, and if we admit such separate cells 
to be the true seed 'vve shall find that many and peculiar con¬ 
ditions are required for its development—so many, indeed, 
that almost every decaying substance becomes tbe nidus, and 
probably, to some extent, the parent of one or more species 
