AGENCIES, HABITAT, AND GROWTH 101 



communion of social life, that this phase of growth 

 stands out with unmistakable clearness. Nevertheless 

 this merging of life with life through connecting sys- 

 tems of conveyance and mutual service is one of nature's 

 most common and effective methods of growth. 



There are a great many different ways of bringing 

 this about; but the creative value of the mergers al- 

 ways depends more on the duration and cooperative 

 efficiency of the system than on the duration of the 

 cooperating individuals, or the intimacy of their union. 



8. Profitable, Cooperative Mergers. In the com- 

 mensal merger, for example, different kinds of animals, 

 such as a jelly-fish and a worm, a vertebrate and an 

 invertebrate, may be united in life-long companionship 

 under a common menage. 



In the symbiotic merger, widely different kinds of 

 plants, such as algae and fungi, are so interwoven in a 

 life-long physical contact as to form one inseparable 

 organic body (lichens). 



There is also the merging of all the offspring from 

 the same parents into a single vital system. In such 

 cases many sister cells, or polyps, or zoids, form com- 

 pound organic units, or colonies, held together, under 

 a common system of self-insulation, in life-long unity 

 by common physical bonds, and sustained by living 

 channels of communication and exchange. 



Then there are innumerable cases where different 

 kinds of life are partly blended into one through do- 

 mestication. Although there may be no physical con- 

 tact, or intimate communication with one another, yet 

 the life of one has become largely dependent on the life 

 of the other, as in the man-dog, man-wheat, and man- 

 horse association. 



