4 BRITISH FUNGI 



these conidia, each capable of infecting a plant, are produced 

 daih' throughout the season, it can be readil}^ understood how 

 quickly a disease can spread, not onh- from one plant to another 

 in the same garden, but from garden to garden, and even from 

 one country to another. Conidia are very short-lived, usually 

 only retaining the power of germination for a few days, after which 

 they perish. Now if I have succeeded in making myself under- 

 stood so far, myj previous statement that the use of conidia or 

 summer-spores is solely to enable the fungus to extend its area of 

 distribution will be clear. All epidemics of fungi, that is, those 

 exceptionally abundant outbreaks of fungus growth which so 

 frequently prove destructive to cultivated crops, are invariably due 

 to tlie rapid development and extension of the conidial stage of the 

 fungus. 



To return to our mildewed rose bush. If the white mildew patches 

 on the shoots are examined during the autumn, minute blackish 

 dots, smaller than the head of a small pin, may be seen on the white 

 cottony patches of mildew. These small black balls are the ancient, 

 sexual, or winter form of fruit. Their structure is complicated, and 

 cannot be understood without microscopic examination. For the 

 present it must suffice to state that each little ball or fruit contains 

 se\-eral spores in its interior. These spores, unlike conidia, will not 

 germinate at once, but require a period of rest before the}- will do so, 

 in fact, they will not germinate until the spring following their 

 production. When spring arrives the little balls decay, liberate 

 their contained spores, which are carried about by wind, etc. ; 

 those that happen to alight on young rose leaves set up an infection, 

 which results in the production of a patcli of mildew, and the cycle 

 of development, first conidia, then winter-spores, is repeated. 



The above account briefly indicates the general outlines of the 

 division of labour, in so far as the methods of extending the area of 

 distribution and the continuation in time is concerned, of many 

 thousands of different kinds of fungi. 



At this stage it may be well to attempt to define the meaning of 

 the terms conidium ( = singular of conidia) , and spore. A conidium 

 is a reproductive body, equivalent in value to the seed of a flowering 

 plant, as a pea or an acorn, but it is asexual in origin, that is, it is 

 not the result of an act of fertihzation. A spore is the result of an 

 act of fertilization, the sexual organs being equivalent in function 

 to the stamens and pistil in flowering plants. In the great majority 

 of fungi the actual act of fertilization is arrested or obsolete now, 

 but the general structure of the fruit-body is the same as when 

 fertilization occurred, and the bodies produced in such structures 

 are still called spores. Unfortunately this distinction between 

 conidia and spore is not consistently followed ; the reproductive 

 bodies of the gill-bearing fungi, and of the Basidiomycetes col- 

 lectively, are by common consent called spores, although they are 



