No. 575] RESPONSES OF PLANTS AND ANIMALS 



645 



(exclusive of roots) belong in this group. Single indi- 

 viduals as described here are the basis for determining 

 what shall be called individuals in colonial and compound 

 types. 



(b) Colonial or Multiple Individuated Plants and Animals 

 A number of animals and the vast majority of the 

 plants belong here. The group can be roughly divided 

 into two types, (a) those having a chain or plate arrange- 

 ment of incomplete individuals and (b) those having a 

 branching or tree-like arrangement. The groups of in- 

 complete individuals of type a occur among the Protozoa, 

 worms undergoing asexual reproduction, many of the 

 Bryozoa and some of the Tunicates; both sessile and 

 pelagic (plankton) forms occur. On the plant side type 

 a includes plate-like colonies of algae, filamentous algae, 

 some thallose plants and probably some of the fungi, 

 though the great multiplicity of forms makes the separa- 

 tion of this group from the branching tree-like types, 

 difficult. 



Type b includes some of the colonial Protozoa, the 

 majority of the sponges, hydroids, corals and the branch- 

 ing Bryozoa. The alga?, fungi, mosses, ferns and flower- 

 ing plants are all represented. The colonies are usually 

 attached to the substratum (sessile). 



i. Numbers of Individuals. — Among the animals the 

 number of so-called zooids is the number of incomplete 

 individuals. In the sponges there are as many zooids as 

 there are excurrent openings (oseula?) (Minchins, '00, 

 p. 91). Zooids usually possess a mouth opening and 

 organs for securing food, though in some cases they may 

 be specialized for reproduction, defence or locomotion as 

 in some of the Coelenterates. Among the colonial plants 

 there are as many incomplete individuals as there are 

 buds or growing points (vegetative regions). There are 

 no regularly occurring organs in animals, strictly com- 

 parable to leaves. However, any organs such as tentacles, 

 gills, etc., which secure or absorb nutriment may be re- 



