No. 575] RESPONSES OF PLANTS AND ANIMALS 647 



most complex types the stolon (stem) gives rise to new 

 individuals and possesses all the layers of cells which 

 take part in forming them. The connection between 

 different individuals differs in different groups and is 

 determined by the particular mode of asexual reproduc- 

 tion. As the individuals are quite independent of one 

 another in function, these connections do not have the 

 same significance as in plants. Even where there is a 

 common blood circulation, as for example in the Clavel- 

 linidce (Harmer, '04, p. 71), there is no noteworthy divi- 

 sion of labor. 



iii. Metabolic and Reproductive Relations of Individ- 

 uals. — The flat worms at certain times consist of chains 

 of zooids at various stages of development and with 

 various degrees of independence. Child ('13) has found 

 that these chains of zooids present a series of gradients 

 in rate of metabolic reaction. The rate is highest at the 

 anterior end of the whole chain and decreases toward the 

 posterior end, not uniformly, however, for the rate is 

 lower immediately in front of each head region than it 

 is in the head region itself. A gradient is present in the 

 axis of each zooid. The most anterior head dominates so 

 long as the chain remains intact. In the corals certain 

 zooids dominate (Wood- Jones, '11) over the others. 

 Some types have a single dominant zooid and some more, 

 while in other cases all are equal. 



Among plants whose form is that of a chain or a plate 

 the individuals are less closely bound together and domi- 

 nant vegetative regions are probably less well developed. 

 In the branching tvpes, dominant vegetative regions occur 

 (Cowles, "11, p. 747; Goebel, '00, Vol. I, p. 206). In the 

 conifers, for example, there is a leader, a dominant grow- 

 ing region at the tip of the main stem just as in certain 

 madrepore corals (Wood- Jones, p. 83). Other plants like 

 the elm have several vegetative regions which dominate 

 over others, as they do in the branching madrepores. 



Growth form or colony form varies according to cer- 

 tain laws dependent, in part at least, upon the metabolic 



