PROPERTIES OF PROTOPLASM 



13 



certain limit of size is reached, every animal and every plant 

 having such a limit to size, and to form as well, and when this 

 limit is reached many of the physiological activities are directed 

 toward reproduction of the race or of kind. Such a stage is 

 spoken of as the period of maturity, and it varies according to 

 the total length of life of the organism. This period of maturity 

 is preceded by a period of active growth when constructive 

 processes are far in excess of the destructive, and is called the 

 period of youth. Succeeding this comes 

 a period, adolescence, of greater equilib- 

 rium between constructive and de- 

 structive processes, and with this comes 

 a period of maturity with the power to 

 reproduce the species. This power 

 marks a fourth property of protoplasm : 



4. REPRODUCTION 



Reproduction of kind is a phenom- 

 enon exclusively confined to living 

 things but the manner of reproduction 

 varies in different cases. In some cases 

 the living organisms divide through the 



middle to form two similar halves, each ,, 



, FIG. 4. Division of Eu- 



of which forms a new organism. This, plotes patella. Photograph 

 the most simple method of reproduc- from a P re P aration - 

 tion, is called simple division or binary fission (Fig. 4) . Again, 

 minute bits of the organism may be pinched off the periphery 

 of the parent, and these grow into organisms similar to the par- 

 ent (Fig. 5). This method is termed budding or gemmation, 

 and the buds thus formed may be single or multiple in number, 

 as in Hydra. Sometimes the entire substance of the parent 

 organism breaks into minute reproductive bodies to which 

 the term spores is applied, the process being known as repro- 

 duction by spore-formation or sporulation (Fig. 6). All of 

 the above methods of reproduction are limited to the lower 

 types of organisms, while the higher types reproduce by proc- 



