754 



ECOLOGY 



furthermore, the commensalistic ants (as Asteca) usually are without effective weap- 

 ons of offense and are not disposed to attack intruders. The domatial chambers 

 develop quite independently of ant stimulation. 



A remarkable case of symbiosis is found among certain South American leaf- 

 cutting ants. The fungus, Rozites gongylophora, is said to furnish the sole food of 



certain ants, which cultivate it in their 

 " fungus gardens.'' The ants cut off 

 leaves and take them to the "gardens," 

 where they serve as food for the fungi. 

 Similarly, the termites or white ants 

 have " fungus gardens," and even are 

 supposed to weed out undesirable fungi. 



Saproph3^sni. — General con- 

 siderations. — Saprophytes are 

 defined as plants that obtain their 

 food from dead organic matter, 

 appearing to contrast sharply on 

 the one hand with autophytes or 

 independent plants, and on the 

 other hand with parasites, which 

 derive their food from living or- 

 ganisms. However, careful study 

 has shown that all gradations 

 occur between saprophytes and 

 autophytes and between sapro- 

 phytes and parasites, making it 

 often a matter of extreme diffi- 

 culty to determine how certain 

 plants should be classified; indeed, in many cases a particular plant 

 may vary in its nutritive relations, belonging sometimes to one group 

 and sometimes to another. Those plants which obtain all their food 

 from dead organic matter may be termed holosaprophytes, while those 

 plants that are partially saprophytic and partially autophytic may 

 be termed partial saprophytes. The more facultative or plastic forms, 

 which may live as autophytes, as saprophytes, or as partial saprophytes, 

 may be termed mixophytes. 



Saprophytism in the fungi and bacteria. — The most representative 

 holosaprophytes occur among the fungi and bacteria. Among the com- 

 mon saprophytic bacteria are the nitrifying organisms of soil and water, 

 the organisms causing the putrefaction of meat and the decomposition of 



Figs. 1076, 1077. — A myrmecophyte, 

 Acacia sphacrocephala : 1076, a portion of a 

 shoot, showing part of a doubly pinnate 

 leaf (/), whose pinnae terminate in "food- 

 bodies"; note the hollow paired thorns (/) 

 which are punctured by ants that live within 

 the thorns; 1077, a single pinna with its 

 terminal "food-body" (/), somewhat en- 

 larged. 



