CO SYMBIOSIS— DISJUNCTIVE 



37. Termites and Ambrosia Beetles as Symbionts.— Termites, 

 commonly called white ants, cultivate funo;i in a way comparable to 

 tliat practiced by leaf-cuttinji; ants. The termites, however, cultivate 

 their fungi on excreta instead of leaf pulp. Several kinds of fungi 

 have been identified from termite nests; species of Xylarla, Collybia, 

 Entoloma, etc. The termites feed on the mycelium. 



Still another somewhat similar symbiotic relationship is that be- 

 tween ambrosia beetles and fungi. The ambrosia beetles are wood- 

 boring beetles as distinguished from bark-boring beetles. They bore 

 tunnels into the wood, sometimes rather simple and sometimes much 

 branched. In these tunnels they plant the mycelium of a fungus. 

 The fungi cultivated by the ambrosia beetles are not yet known but 

 they probably are some of the lower fungi rather than mushrooms. 

 The beetles feed upon the mycelium, which often grows so luxuri- 

 antly that it completely clogs up the tunnels, and beetles have been 

 known to become imprisoned and to suffer death as a penalty for not 

 being able to eat fast enough to gain an exit through their food 

 supply. 



38. Insectivorous Plants.— In all of the examples of antagonistic 

 symbiosis so far discussed animal symbionts obtain food from plants. 

 This condition is just reversed, however, in the case of a limited 

 number of plants which have the power of digesting and absorbing 

 animal food. These plants are called insectivorous or carnivorous 

 plants. The best understood perhaps of these insectivorous plants 

 is the sundew ( Drosera) . Several species of sundew are common in 

 the bogs of the northern United States and Canada. Drosera 

 rotimdifolia, the commonest species, is a small plant with a rosette 

 of radical leaves. In summer it sends up a stalk about 6 inches long 

 which bears from one to two dozen small white flowers. The leaves 

 are rounded or oval in shape, about a centimeter broad, and with 

 hairy petioles of 2 to 5 cm. in length. 



The leaves of Drosera, which are attractively red in color, are 

 beset on the upper surface with glandular hairs which are rather 

 short at the center of the leaf but progressively longer toward the 

 outside. Each hair has on its knob-like end a sticky drop of semi- 

 liquid substance which glistens in the sun like dew, thus giving the 

 name, sundew, to the plant. When an insect, either by chance or 

 attracted by the brilliancy of color or by the sweetish secretion, 

 comes in contact with any of the hairs it sticks fast. The other hairs 

 of the leaf now begin to bend inward toward the insect until a con- 



