I 



THALLOPHYTES: ALGJE 229 



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 Algse, 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 mult ij^licat ion. 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 



