292 The Origin and Tendencies of Parasitism in Fungi. ■ 



than uninfected ones, hence no injury is occasioned by the 

 parasite ; on the other hand the host-plant apparently benefits 

 to some extent, and the case appears to approach the symbiotic 

 condition where a fungus and an alga constitute a lichen. 



The earliest known and most primitive of fungi are truly 

 aquatic, and their spores, known as zoospores on account of 

 their power of spontaneous movement, required the constant 

 presence of water to secure their dispersion. The great wave 

 of parasitism set in when the fungi commenced to adapt them- 

 selves to dry land conditions. Their extension on dry land was 

 considerably restricted, so long as zoospores, requiring the 

 presence of water for their distribution, were alone produced. 

 At this stage a second or supplementary formation of spores or 

 conidia was gradually evolved, in addition to the primitive 

 sexual fruit producing zoospores. This later conidial condition 

 in most cases acquired parasitic tendencies. By this means a 

 marked division of labour was introduced into the life-history 

 of the fungi as a whole, the business of the later evolved conidial 

 condition of the fungus being to extend the geographical range 

 of the species, by producing immense numbers of conidia 

 throughout the season when the host is in an active state of 

 growth, in the case of parasitic species. On the other hand, 

 the older or sexual forming fruit only appears late in the season, 

 when the host-plant is on the wane, and remains in a quiescent 

 state until the following season, when the host plant is again 

 infected, and the same cycle of development is repeated. Thus 

 it is seen that the primary function of the original type of fruit 

 is to tide the fungus over that portion of the year when its 

 host-plant is not in active growth. On the other hand the 

 extension in geographical distribution of a fungus is due to its 

 modern conidial form of reproduction, which, instead of being 

 dependent on water for their distribution, are dispersed by 

 wind, animals, insects, etc. 



The Quarterly Journal of the Geological Society for May 31st (which, as is 

 customary, was late in pubHcation) contains a number of papers of par- 

 ticular interest to readers of ' The Naturalist.' Dr. A Smith- Wood ward 

 describes a fine skull of Megalosaurus bradleyi, n. sp., from the Great Oolite 

 of Minchinhampton ; Mr. R. H. Rastall has an elaborate paper on the 

 Skiddaw Granite and its Metamorphism ; Mr. W. G. Fearnsides has a 

 similiarly detailed piece of work, accompanied by numerous sections and 

 maps, dealing with the Tremadoc Slates and Associated Rocks of South- 

 East Carnarvonshire ; Mr. A. M. Finlayson writes on the Metallogeny of 

 the British Isles, and also on the Problems of Ore-Deposition in the Lead 

 and Zinc veins of Great Britain. There is also Prof. Sollas' presidential 

 address, referred to elsewhere. 



Naturalist, 



