AGRICULTURAL CHEMISTRY AND GEOLOGY. 187 



atmosphere depends upon the number and surface of the leaves ; that which is taken from 

 the soil, upon the number and surface of the roots. 



37. If to two plants of the same species, during the formation of leaves and roots, an 

 unequal amount of nourishment be offered in the same space of time, their increase of mass 

 is unequal in this time. That plant which has received more food increases more, its de- 

 velopment is facilitated. The same difference in growth is manifest when two plants receive 

 the same amount of food, but in unlike forms as to solubility. 



The rapidity of the development of a plant is facilitated by furnishing it with, all the 

 necessary atmospheric and telluric nutritive matters in proper form and at the right time. 

 The conditions that shorten the time of development are the same as those that contribute 

 to its amount. 



38. Two plants, whose roots have an equal length and extension, do not flourish so well 

 near or after each other as two plants whose roots, being of unequal length, acquire their 

 nourishment at different depths in the soil. 



39. The nutritive substances needed by the plant must act together in a given time, in 

 order that the plant attain full development in this time. The more rapidly a plant develops 

 itself in a given period, the more food does it need in that time. Annuals require more rapid 

 supplies than perennials. 



40. If one of the co-operating ingredients of the soil or of the atmosphere be partly or 

 entirely deficient, or want those qualities that adapt it to absorption, the plant does not 

 develop itself in all its parts, or only imperfectly. The deficiency of one ingredient renders 

 those present ineffectual, or diminishes their effect. 



41. If the absent or deficient substance be added to the soil, or, if present, but insoluble, 

 be rendered soluble, the other constituents are thereby rendered efficient. 



By the deficiency or absence of one necessary constituent, all the others being present, the 

 soil is rendered barren for all those crops to the life of which that one constituent is indis- 

 pen-able. The soil yields rich crops if that substance be added infdue quantity and in an 

 available form. In the case of soils of unknown composition, experiments with individual 

 mineral manures enable us to acquire a knowledge of the quality of the land and the pre- 

 sence of the different mineral constituents. If, for example, phosphate of lime, given alone, 

 is found efficacious that is, if it increases the produce of the land this is a sign that that 

 substance was absent, or present in too small proportion, whereas there was no want of the 

 others. Had any of these other necessary substances been also wanting, the phosphate of 

 lime would have had no effect. 



42. The efficacy of all the mineral constituents of the soil taken together, in a given time, 

 depends on the co-operation of the atmospheric constituents in the same time. 



43. The efficacy of the atmospheric constituents in a given time depends on the co-operation 

 of the mineral constituents in the same time ; if the latter be present in due proportion and in 

 available forms, the development of the plants is in proportion to the supply and assimilation 

 of their atmospheric food. The quantity and quality (available form) of the mineral constitu- 

 ents in the soil, and the absence or presence of the obstacles to their efficacy, (physical qualities 

 of the soil, ) increase or diminish the number and bulk of the plants which may be grown on a 

 given surface. The fertile soil takes up from the air, in the plants grown on it, more carbonic 

 acid and ammonia than the barren one ; this absorption is in proportion to its fertility, and 

 is only limited by the limited amount of carbonic acid and ammonia in the atmosphere. 



44. With equal supplies of the atmospheric conditions of the growth of plants, the crops are 

 in direct proportion to the amount of mineral constituents supplied in the manure. 



45. With equal telluric conditions, the crops are in proportion to the amount of atmospheric 

 constituents supplied by the air and the soil, (including manure.) If, to the available mineral 

 constituents in the soil, ammonia and carbonic acid be added in the manure, the fertility of 

 the soil is exalted. 



The union of the telluric and atmospheric conditions and their co-operation in due quantity, 

 time, and quality, determine the maximum of produce. 



46. The supply of more atmospheric food (carbonic acid and ammonia, by means of am- 

 moniacal salts and humus) than the air can furnish, increases the efficacy of the mineral 



