ANIMALS AS PASSIVE MEMBERS (COACTEES) 137 



competition and ecesis, and hence in changing the composition. On 

 the other hand, the saprophytic forms, especially of bacteria, are in- 

 valuable in breaking down organic matter and converting it into 

 nutrient substances for green plants. Among the most important 

 fungous parasites of plants are the rusts, smuts, and mildews; the 

 other great groups, namely, black, cup, pore, and gill fungi, and the 

 molds, contain many parasitic species along with a much larger num- 

 ber saprophytic on dead leaves, wood, or humus material in the soil. 

 It is exceptional that even rusts and smuts kill their host plants, but 

 they sometimes handicap them sufficiently to lead to their partial 

 elimination through competition or unfavorable climatic conditions. 

 Many smuts, such as those of wheat and corn, destroy the seed and 

 thus have a significant effect upon numbers and through them upon 

 competition. Bacteria play a similar role, but one of relatively little 

 importance by comparison with that in animals and man. 



Animals as Passive Members (Coactees) 



Insectivorous Plants. These resemble partial parasites inasmuch 

 as they obtain a portion of their food from other organisms, but they 

 exemplify an entirely different physiological habit. The latter is 

 likewise more unique than socially significant, though it does denote 

 a minor coaction bond in the community, and some of the species are 

 more or less important serai dominants. Practically all the species 

 grow in wet or boggy situations where inorganic nitrogen is deficient, 

 but they differ much in the device for catching and digesting insects 

 and other invertebrates. The modifications concern the leaf and 

 range from ascidia or pitchers in Sarraceniaceae, Nepenthaceae, and 

 Cephalotus in Saxifragaceae to sensitive glandular hairs or leaves in 

 Drosera, Pinguicula, and Dionaea, and bladderlike traps in Utricu- 

 laria. The so-called catchflies, belonging to the genera Silene and 

 Viscaria of the Dianthaceae, entrap insects by means of a viscid 

 secretion on the stem, but it is doubtful that they digest them. Be- 

 cause of its submerged habit, Utricularia is the most important coactor 

 of the entire group; Forbes found 93 animals of 28 species in ten 

 bladders (cf. p. 165), a fact that justifies his contention that the 

 bladdcrwort is a formidable competitor of small fishes. 



Fungi and Bacteria. Fungi that parasitize animals and man are 

 found scattered through the algal fungi, sac fungi, yeasts, molds, and 

 dermaphytes, the last mostly confined to man. Two groups, Empu- 

 saceae and Laboulbeniales, are restricted to insects, and another, the 

 water molds or Saprolegniaceae, occur chiefly upon small aquatic ani- 



