390 HORTUS GRAMINEUS WOBURNENSIS. 



different, and will be found to agree with daily experience in the 

 garden and on the farm. 



The proportion in which they 

 stand to each other, with re- 

 spect to the weight of nutri- 

 tive matter per acre, and in 

 exhausting the land. 



The effects of some plants are only to impoverish the soil for an 

 immediate succession of the same plant ; while others have the 

 property of exhausting the land, not only for an immediate suc- 

 cession of themselves, but likewise for every other kind of 

 vegetable. 



A consideration of the difference in the composition of compo- 

 nent parts of the nutritive matter of different species of plants, it 

 appears, will account in some measure for this property. 



It has been already mentioned (p. 3) that the nutritive or 

 soluble matter of vegetables consists, for the most part, of five 

 distinct vegetable substances — mucilage or starch, saccharine 

 matter, gluten or albumen, and bitter extractive or saline matters. 

 A plant, therefore, whose nutritive matter consists of one or two 

 of these principles only, will impoverish the soil in a greater degree 

 for an immediate succession of the same plant, than a different spe- 

 cies of vegetable that has its nutritive matter composed of a greater 

 variety of these substances. Hence, plants that have the greatest 

 dissimilarity in the number and proportion of vegetable principles 

 which constitute their nutritive matter, will be found best fitted to 

 succeed each other in alternate cropping. The different varieties 

 of wheat consist almost entirely of starch and gluten ; while barley, 

 pease, and turnips, contain a greater proportion of saccharine 

 matter which is wanting in wheat: and are consequently best qua- 

 lified to precede or follow that grain, in alternation with green 

 crops. Oats, rye, and beans, afford nutritive matters similar to 

 wheat, though in less proportion ; and a crop of either of these will 

 have a like effect on the soil to that of wheat, though in a less de- 

 gree, but totally different from those of barley, pease, and turnips. 

 The former plants, therefore, as they impoverish the soil only for 

 an immediate succession of themselves, may be termed partial 

 impoverisfiers ; and the latter, exhausting the land for themselves. 



