2go The Origin and Tendencies of Parasitism in Fungi. 



orchid just under the epidermis. In due course the fungus 

 produced fruit on the surface of the leaf, coming through 

 wounds made in the epidermis to admit of its exit. The spores 

 of this crop were in turn injected into the orchid leaf, mixed with 

 the natural food of the fungus. This method was constantly 

 repeated, always using the preceding crop of spores for infection 

 purposes. In course of time the fungus had become so accus- 

 tomed to its new kind of food that the spores were injected 

 mixed with distilled water instead of the original normal food 

 solution, and in course of time produced fruit. In the case of 

 two kinds of fungi experimented with, after the sixteenth crop 

 had been produced, the spores when placed on the orchid leaf, 

 germinated, entered the tissues and acted in every way as true 

 parasites. No infection followed placing the spores on any 

 other kind of living plant, save the particular species of orchid 

 to which they had gradually become accustomed- 



Among the true parasites, every grade of parasitism is 

 represented. In what may be termed the incipient stage, the 

 fungus attacks and promptly kills its host-plant, thus limiting 

 its own period of existence to a matter of hours only. To this 

 category belongs Pythium debaryanitm, the ' damping off ' 

 fungus. Going to the other extreme, where all the niceties 

 of a parasitic mode of life have been carefully worked out, we 

 meet with fungi that manage to live at the expense of the host- 

 plant, or plant upon which they are parasitic, without appar- 

 ently causing it any injury, or even any inconvenience. The 

 fungus causing ' smut ' or ' slean ' of oats illustrates this ad- 

 vanced stage of parasitism. The spores of the fungus, present 

 in the soil, infect the oat seedling when it is only a few days old, 

 and grow up with the host-plant until it has completed its 

 vegetative period of growth, without causing the slightest 

 injury; in fact the presence of the fungus in the tissues of the 

 oat plant causes the latter to grow more vigorously than 

 neighbouring plants that are not infected, and an expert can 

 pick out smutted plants by their robust habit and deeper 

 green colour, long before the smut appears externally. When 

 the young ovaries are formed, they are attacked by the myce- 

 lium of the fungus, and in due course, instead of an oat grain, 

 a mass of sooty powder, the spores of the fungus, is produced. 

 Between the two extreme examples given, every grade in the 

 progress of parasitism may be studied, even in our Qwn country. 

 This tendency towards parasitism on the part of many fungi 



Naturalist, 



