NUTRITION : MYCORHIZA. 321 



corhiza have the fungus on the outside of the roots. These often occur on 

 the roots of the oak, beech, hornbeam, etc., in forests where there is a great 

 deal of humus from the decaying leaves and other vegetation. The young 

 growing roots of the oalc, beech, liornbeam, etc., become closely covered 

 with a thick felt of the mycelium, so that no root hairs can develop. The 

 root is also thickened. The fungus serves here as the absorbent organ tor 

 tlie tree. It also acts on the humus, converting it into available plant food 

 and transferring it over to the tree. 



605. Nutrition of the dodder. — The dodder (cuscuta) is an example of one 

 of the higher plants that is parasitic. The stem twines around the stems of 

 other plants, sending haustoria in their tissues. By means of these the nutri- 

 ment is absorbed. 



606. Carnivorous plants. — Examples of these are ine well-known venus 

 fly-trap and the common sundew. 



607. Nutrition of bacteria. — Bacteria are very minute plants, in the 

 form of short rods, which are either straight or spiral, while some are 

 minute spheres. They are widely distributed ; some cause diseases of plants 

 and animals, others cause decay of organic matter, while still others pla)- an 

 important role in converting certain nitrogen compoimds into an available 

 form for plant food. They absorb their food through the surface of their 

 body. They may be obtained in abundance for study in infusions of plants 

 Or of meats. 



