Tliere arc many intimate relations between plants 

 and animals (Buchner 1953). Mutualism is sus- 

 pected in the ]>resence of photosyntlietic algal cells 

 in the protective ectoderm of green hydra, and those 

 associated with turbellarians. mollusks, aimelids, 

 bryozoans, rotifers, protozoans, and the egg capsules 

 of salamanders. The algae give off o.xygen, bene- 

 titing the animals, which in turn supply carbon di- 

 o.xide and nitrogen to the plants. The thick growth 

 of algae often found on the carapace of the aquatic 

 turtles is important mostly as camouflage for the 

 turtles (Xeill and Allen 1954). Certain beetles, ants 

 ( Hailey 1920, Weber 1957), and termites cultivate 

 fungi for food. Bacteria in the caeca and intestine of 

 iierbivorous birds and mammals aid in the digestion 

 of cellulose. The cross-pollination of flowers by the 

 agency of insects and birds seeking nectar and pollen 

 is of such great importance that many structural 

 adaptations in both plant and animal fit the one to the 

 other to insure the success of the function (Robert- 

 son 1927, Dorst 1946). 



Animals, especially birds and mammals, arc of 

 great importance as agents of plant distribution ( Mc- 

 Atee 1947). Seeds, fruits, even entire plants become 

 attached to feathers or fur, or ingested seeds are eaten 

 and eliminated unharmed with the feces. When bare 

 seeds are eaten they are usually macerated, digested, 

 and entirely destroyed unless they have very hard 

 coats. But fruits are fed upon primarily for pulp, 

 and most of the seeds pass through the alimentary 

 tract unharmed. Animal transportation of ingested 

 seeds is perhaps the most important means by 

 which fruit species are dispersed (Taylor 1936). 

 Furthermore, germination of the seeds is frequently 

 improved by mechanical abrasion in the stomach 

 and thinning of the seed coat by digestice juices, 

 making it more permeable to water and oxygen 

 (Krefting and Roe 1949). Germination of acorns 

 and nuts is improved if they are buried in the 

 ground rather than left lying on the ground sur- 

 face. Squirrels, chipmunks, wood rats, and some 

 birds, particularly jays ( Chettleburgh 1952) and 

 woodpeckers, cache acorns and nuts as a winter food 

 supply, hiding them in cavities and nooks or burying 

 them in the soil. Perhaps most are recovered and 

 eaten ; Cahalane ( 1942) found that 99 per cent of the 

 acorns buried by the fox squirrel in a locality where 

 the animals were numerous were recovered by the 

 animals, largely through the sense of smell. One per 

 cent of the thousands of nuts produced by it during 

 the lifetime of a tree that are buried but not recovered 

 would be adequate to insure the continuance of the 

 forest. Invasion of oak and hickory trees into sandy 

 areas is greatly accelerated by, and is sometimes de- 

 pendent on, this coaction of squirrels (Olmsted 

 1937), and the dispersal of forests up the slopes of 

 mountains against gravity may also depend in large 



part on trans|)ortation oi tiic heavy seed by animals 

 (Grinnell 1936). The interesting concept involved 

 here is that plants have evolved fruits and nuts that 

 are highly attractive to animals as food substances. 

 However, the production of prodigious numbers of 

 fruits and nuts during their lifetimes insures that 

 at least some will escape consumption and will be 

 more widely and effectively disi^ersed. 



Large populations of such herbivores as rabbits 

 and deer sometimes do considerable damage to new 

 propagation of herbs and trees, but the effects of over- 

 browsing cannot be dismissed as all bad (Webb 

 1957). Removal of the lower branches of established 

 trees by deer may not seriously affect the vigor of the 

 trees ; indeed, such pruning may actually increase 

 their value as liuuber. Deer pawing the leaf-litter 

 may thereby plant, so to speak, some seeds that would 

 not otherwise become established. Thinning dense 

 stands of young trees may allow residuals to grow 

 more rapidly ; much of new growth is doomed any- 

 way because of root competition, and shading cast 

 by established trees. Some species of shrubs and trees 

 actually produce more annual growth under heavy 

 than light browsing. Other species, however, may be 

 killed when small by heavy browsing, although they 

 tolerate considerable browsing when mature. Detri- 

 mental effects of both browsing and grazing become 

 evident in an area in the form of excessive invasion 

 of new species which are little used as food, and dis- 

 appearance or stunting of the food species that are 

 desirable (Graham 1954). 



Some tropical acacias have evolved foliar nectaries 

 or other food bodies as well as enlarged hollow stip- 

 ules, spines, or other structures to attract stinging 

 ants. In return, the plants obtain protection from 

 Iierbivorous mammalian and insect enemies (Brown 

 1960). 



Interspecific mutualism is nicely demonstrated by 

 the flagellate Trichonympha, an obligate in the gut 

 of several species of wood-eating termites (but not in 

 the family Termitidae) where it digests cellulose 

 (Cleveland 1924). Trichonympha and related species 

 also occur in the alimentary trace of the wood-eating 

 roach Cryptoccrcus (Cleveland 1934). The termite 

 and roach reduce the wood to small fragments, pass- 

 ing them through the alimentary canal to the hind- 

 gut where the protozoans digest the cellulose, chang- 

 ing it into sugar. The host benefits the protozoa by 

 removing harmful metabolic waste products and 

 maintaining anaerobic conditions in the intestine 

 (Hungate 1939). 



The ruminant stomach and the horse coecum con- 

 tain enormous numbers of ciliates and bacteria, some 

 of which digest cellulose. The micro-organisms repro- 

 duce the equivalent of their biomass each day. This 

 provides the host with about 20 per cent of its nitro- 

 gen requirement (Hungate 1960). 



Cooperation and disoperation 177 



