Food from the Soil 117 



taining much sand. Yet chalk, pure chalk, does not con- 

 tain a particle of silica. 



As before remarked, however, such a thing as a per- 

 fectly unmixed soil is hardly to be found anywhere. Even 

 on the mountains there is rarely less than ten per cent of 

 soil which has been brought from elsewhere, either by 

 wind or water, or added to it by animals. So it is on the 

 downs, and the grass finds there what it needs. 



It would be rash to say of any plant that it will not 

 grow on any soil until it has been tried; but plants cer- 

 tainly have their likes and dislikes in this matter, though 

 sometimes a good climate will make up for poor soil. 



Some plants have such peculiar tastes, or requirements, 

 in respect of soils, that they must seldom, one would 

 think, be able to gratify them; and one almost wonders 

 where the seeds come from when the opportunity for 

 growing does arrive. 



Some, for instance, are never to be seen except after 

 forest-fires; apparently because they require wood-ashes 

 to grow in. Other plants have similar likings; and it was 

 observed that after the fires of London and Copenhagen, 

 plants of the same kinds grew among the ruins of both 

 cities. 



It is very remarkable, too, what slight, and even imper- 

 ceptible, differences in the soil will make very great 

 differences in the crops grown upon them. This is espe- 

 cially noticeable in the case of vines. Tokay wine, for 

 instance, cannot be made except from grapes grown in 

 the one district from which it takes its name. The vines 

 may be grown elsewhere, but the wine is different. So, 

 too, in France; vineyards growing side by side, and sepa- 

 rated only by a narrow footpath, having the same aspect, 



