108 EXPERIMENTS WITS PLANTS 



extensively, the farmer to a lesser degree. The gar- 

 dener has various mixtures for various purposes: for 

 plants requiring much water he makes a clay loam 

 (loam is a soil containing about equal parts of sand 

 and clay mixed with humus: a clay loam contains 

 more clay than sand, a sandy loam more sand than 

 clay) . For plants which require but little water, such 

 as Cacti, he makes a sandy loam: for Ferns he uses a 

 soil composed very largely of humus. For young 

 plants he makes an open, porous soil, which he re- 

 places by a heavier soil as they grow older. In this 

 way he succeeds in raising from a small pot of soil as 

 large a plant as the farmer ordinarily produces by the 

 use of a thousand times as much earth. The farmer 

 is much more restricted in this respect, but he mixes 

 humus with the soil by plowing in straw, stable ma- 

 nure or green plants: he also adds ashes, clay or sand 

 to the soil when necessary. 



What kind of soil is best for cuttings? Wliy? 

 Which crops need a liglit soil; which a heavy soil? 

 Classify the soils of your region according to the 

 following scheme: 



The red or yellow color of soils is due to the iron in 

 them: the black color to humus. Point anv differ- 



