kind of brick, called a cell, modified in form and function; when we see
the smallest and simplest equally with the largest and most complicated
plant increasing in size subject to the laws of growth by
intussusception and cell division, which are universal in the organic
world; we should not be surprised if all the methods by which plants are
reproduced can be reduced to a very small number of types.

The first great generalization is into--

1. The vegetative type of reproduction, in which one or more ordinary
cells separate from the parent plant and become an independent plant;
and--

2. The special-cell type of reproduction, in which either one special
cell reproduces the plant, or two special cells by their union form the
origin of the new plant; these two modifications of the process are
known respectively as asexual and sexual.

The third modification is a combination of the two others, namely, the
asexual special cell does not directly reproduce its parent form, but
gives rise to a structure in which sexual special cells are developed,
from whose coalescence springs again the likeness of the original plant.
This is termed alternation of generations.

The sexual special cell is termed the _spore_.

The sexual special cells are of one kind or of two kinds.

Those which are of one kind may be termed, from their habit of yoking
themselves together, _zygoblasts_, or conjugating cells.

Those which are of two kinds are, first, a generally aggressive and
motile fertilizing or so-called "male cell," called in its typical form
an _antherozoid_; and, second, a passive and motionless receptive or
so-called "female cell," called an _oosphere_.

The product of the union of two zygoblasts is termed a _zygospore_.

The product of the union of an antherozoid and an oosphere is termed an
_oospore_.

In many cases the differentiation of the sexual cells does not proceed
so far as the formation of antherozoids or of distinct oospheres; these
cases I shall investigate with the others in detail presently.

First, then, I will point out some of the modes of vegetative
reproduction.

The commonest of these is cell division, as seen in unicellular plants,
such as protococcus, where the one cell which composes the plant simply
divides into two, and each newly formed cell is then a complete plant.

The particular kind of cell division termed "budding" here deserves
mention. It is well seen in the yeast-plant, where the c