34S STATE BOARD OF AGRICULTURE. 



(Chlorophyll) which enables them in the presence of sunlight to assimilate 

 the raw food materials of the soil and air and thus to prow. Funsi, however, 

 do not possess this green coloring matter, hence are forced to depend on organic 

 substances such as rotting leaves, wood, straw, manure, and the humus of the 

 soil (Saprophytic Fungi) or on the tissues of living plants (Parasitic Fungi). 

 Familiar examples of the former are seen in the common mushrooms and the 

 shelf or bracket-like fungi which grow on decaying stumps and logs. (Fig. 41.) 

 These are mostly plants of considerable size some of them being valued for food. 

 The fungi which exist at the expense of living plants, however, are mostly very 

 small organisms and require the use of the microscope in studying them. They 

 make up, however, in numbers and rapidity of growth for their insignificant 

 size, consequently these parasitic fungi are able to cause incalculable injury to 

 cultivated crops each season. 



In its early stages of growth a fungus consists of a delicate mass of cobweb- 

 like threads which branch in all directions in search of nourishment in very 

 much the same manner as the fine rootlets of other plants. This network of 

 slender threads is known as mycelium or spawn and serves the purpose of root 

 and stem. It may be found at almost any time by overturning old boards or 

 decaying leaves lying on the ground. In the case of the parasitic or disease 

 producing fungi the mycelium invades the tissues of the plant on which it lives 

 (known as the host plant) and causes in some cases swellings and distortions of 

 the affected part, or in other cases the cells of the host plant are killed as soon 

 as attacked, thus leading to the death of the diseased organs or of the entire 

 plant. In some cases, however, the mycelium lives on the surface of its host 

 merely sending little sucker-like branches into the affected part as in the powdery 

 mildews. 



SPORES. 



Fungi are reproduced and spread by means of minute bodies called spores. 

 Spores may be formed in a variety of ways after the mycelium becomes estab- 

 lished. The most simple method is that in which the mycelium gives rise to 

 branches which bear one or more spores at the apex or along the sides, or, in 

 some cases, the branch itself becomes changed into a chain of spores by the 

 formation of little partitions or septa, the cells thus formed finally separating 

 from each other and each constituting a spore. More complex methods usually 

 consist of the formation, by the mycelium, of fruiting bodies often dark in color, 

 which are hollow and either give rise to spores from the inner surface directly 

 or to small spore sacks (asci) each containing a number of spores which when 

 mature are discharged by the breaking of the surrounding wall. 



Spores are so small and light that they can readily float in the air for some 

 time as an almost invisible dust and may also be carried on the bodies and feet 

 of birds and insects. In some cases they are produced in such enormous num- 

 bers as to form a cloud of smoke-like dyst when disturbed, as in the powdery 

 masses of corn smut. Some idea of the amazing number of spores produced by 

 such a fungus may be gained only by knowing their measurements. Thus a 

 mass of such spores the size of an ordinary match head could contain about ten 

 million of these microscopic bodies, enough to cover an acre and a half at the 

 rate of one spore to the square inch. 



When the spores of fungi are surrounded by favorable conditions of moistwre 

 and heat they may germinate usually by pushing out a slender germ tub©. In 

 the case of the parasitic fungi this germ tube enters the tissues of its host plant 

 and forms the beginning of the mycelium. In this manner the host plant be- 

 comes infected. A great many fungi possess two 1'ornis of spores. One kind, 

 known as summer spores, is produced in great aluindance during the growing 

 season. They are capable of germinating as soon as mature and thus serve to 

 spread the disease from one plant to another. The other kind of spores, known 

 as resting or winter spores, is formpd usually late in the season and remains 

 over winter in a dormant condition often in o" attached to the dead tissues of 

 the host plant. When spring arrives and the host plant is pushing out its first 

 tender growth these resting spores germinate and thus start the disease anew. 



In the case of some parasitic fungi the mycelium is perennial in the stems of 

 the host plant remaining dormant during winter but becoming active again the 

 next spring, as the leaf curl fungus of the peach and the black knot of the plum. 



