NATURE, FORMATION, AND ACTIVITIES 



the outside, forming a protective mat. This 

 fungal mass is inhabited both by mycelium 

 infected scale insects, the only function of 

 which consists in feeding the protecting fun- 

 gus, and by noninfected scale insects which 

 take care of the reproduction. In this case 

 protection is traded for food. Further in- 

 formation on the phenomena of symbiosis in 

 nature is found in the work of \'uillemin 

 (1889), Waksman (1937), C'hristensen 

 (1951), and Gaullery (19r)2). 



Competition 



Different living organisms may feed on 

 the same substances, with a resulting con- 

 flict. Obviously, in nature, microorganisms 

 capable of utilizing the same food will com- 

 pete for whatever concentrations of that food 

 are available. If two organisms can utilize 

 the same nutrient with the same ease, other 

 factors will regulate which one of the two 

 will have the supremacy. For example, at 

 high temperature, thermophilic organisms 

 will be favored; in the absence of free oxy- 

 gen, anaerobic organisms will be favored. 



Predatorines8 



Any living organism that consumes an- 

 other living organism is a predator. Ex- 

 amples of such an association are most com- 

 mon among animals but are not restricted 

 to the animal kingdom. Carni\'orous plants 

 with specialized leaves capture insects. The 

 leaves of Sarracenia and Nepenthes are 

 shaped like an urn and are filled with a 

 licjuid, diluted by rain water. If an insect 

 is trapped in the urn, the motion of the in- 

 sect starts the secretion of proteolytic en- 

 zymes, the pH of the licjuid becoming acid. 

 Bacterial action is not essential for the de- 

 composition of the insect, since the sterile 

 liciuid has definite proteolytic i^roperties. 

 In other plants, such as Droscra, the insect 

 is trapped by mucilaginous tentacles which 

 can also produce proteolytic enzymes. In 

 plants of the genus Dionea, the leaf folds 

 along its central nervation and traps the 



insect in a forest of hard bristles, proteolytic 

 enzymes being produced. 



Predatoriness is common among protozoa, 

 but even some of the fungi are predators. 

 Some of these organisms specialize in catch- 

 ing nematodes; others can trap protozoa. 

 This process has been studied extensively b}^ 

 Drechsler (see Duddington, 1957). Certain 

 fungal species have developed different types 

 of nematode traps. These may be mycelial 

 loops strong enough to hold a nematode if 

 the worm sticks its head through one of 

 them. The mycelium will then invade the 

 body of the nematode and digest it. Possibly 

 the fungi secrete a substance which attracts 

 nematodes and incites them to stick their 

 necks in the loops. It is interesting to note 

 that Pi-amer (1959) has shown that the 

 nematode-trapping fungi form traps only 

 under the stimulation of a substance found 

 in many animal tissues including those of 

 nematodes. 



The biological significance of predatori- 

 ness is clear in the case of a fox catching a 

 chicken but harder to explain logically in 

 the case of higher plants and fungi. The 

 insect-catching plants are indeed able to 

 carry out photosynthesis and they rarely 

 live in such poor soil that no nitrogen would 

 be a\^ailable to them. The nematode-trap- 

 ping fungi are able to utilize the organic and 

 inorganic nutrients of the soil. Still they are 

 performing what seems to us the nonessen- 

 tial function of predators. It may be of in- 

 terest to note here that Vuillemin first ap- 

 plied, in 1889, the designation "antibiosis" 

 to phenomena of predatoriness, standing 

 between strict saprophitism and parasitism, 

 as a "snake devouring its prey." 



Parasitism 



Predatoriness differs from parasitism in 

 that a predator destroys its prey outright, 

 whereas a parasite usually feeds on the living 

 host. It is common practice to differentiate 

 between facultatiN'e and obligator}^ parasites. 

 The term obligatory parasite may be only an 



