THALLOPHYTES: ALG.E 
and becomes more complex in the higher forms, so repro- 
duction begins in very simple fashion and gradually be- 
comes more complex. Two general types of reproduction 
are employed by the Algae, and all other plants. They are 
as follows : 
(1) Vegetative multiplication. This is the only type of 
reproduction employed by the lowest Algae, but it persists 
in all higher groups even when the other method has been 
introduced. In this type no special reproductive bodies are 
formed, but the ordinary vegetative body is used for the 
purpose. For example, if the body consists of one cell, that 
cell cuts itself into two, each half grows and rounds off as 
a distinct cell, and two new bodies appear where there was 
one before (Fig. 204), This process of cell division is very 
complicated and important, involving a division of nucleus 
and cytoplasm so that the new cells may be organized just 
as was the old one. Wherever ordinary nutritive cells are 
used directly to produce new plant bodies the process is 
vegetative multiplication. This method of reproduction may 
be indicated by a formula as follows : P P P P P, in 
which P stands for the plant, the formula indicating that 
a succession of plants may arise directly from one another 
without the interposition of any special structure. 
(2) Spores. Spores are cells which are specially organ- 
ized to reproduce, and are not at all concerned in the nutri- 
tive work of the plant. Spores are all alike in their power 
of reproduction, but they are formed in two very distinct 
ways. It must be remembered that these two types of 
spores are alike in power but different in origin. 
Asexual spores. These cells are formed by cell divi- 
sion. A cell of the plant body is selected for the purpose, 
and usually its contents divide and form a variable number 
of new cells within the old one (Fig. 205, B). These new 
cells are asexual spores, and the cell which has formed them 
within itself is known as the mother cell. This peculiar 
kind of cell division, which does not involve the wall of the 
