512 HORTICULTURE, FORESTRY, FLORICULTURE 



Upon the amounts of the various constituents present, i. e., clay, 

 fine silt, silt, fine sand, etc., will depend the porosity of the soil, the 

 readiness with which air penetrates it and water moves through it, 

 its water-holding capacity, and, finally, its temperature. 



It will be seen, therefore, that the texture and structure of a soil 

 have an important bearing on the development of the plant, affecting 

 not only the growth of the roots, leaves, stems, and flowers, but the 

 relative proportion of these and their relation to each other. 



By varying the texture of a soil, its water content is varied, its 

 capacity for heat is modified, and so on, until every important factor, 

 including food, in the ordinary acceptance of the word, is involved. 

 To these variations the plant adapts itself, and the result may be 

 excessive leaf development, with few or no flowers, or vice versa; a 

 weakened condition of the tissues, making the plant subject to the 

 attacks of parasitic enemies, especially fungi, and so on through a 

 list of other possibilities. To illustrate, we may have a rose grown 

 in a soil of a certain texture and structure. The water capacity of 

 this soil is most favorable for growth, and may be represented by 

 10. The capacity for heat, permeability to air, and the readiness with 

 which water moves through it are also ideal, and may each be repre- 

 sented by 10. These conditions may so act on the food in the soil as 

 to place it at the disposal of the plant in the most suitable form, so 

 that food supply may also be represented by 10. Suppose, now, the 

 texture of the soil is modified by the addition of clay ; the water con- 

 tent of the soil is changed, this in turn affects the access of air and 

 also the temperature, and the food supply is involved by the effects 

 of the different changes on certain soil organisms, which play an 

 important part in the matter of food. As a result of these various 

 combinations and changes, we may have the water capacity of the 

 soil represented by 12 ; capacity for heat, permeability to air, readi- 

 ness with which water moves, 8 ; food supply, 8, etc. It will thus be 

 seen that the plant in this case has an entirely different set of factors 

 to which it must adapt itself, and in doing this it may so modify its 

 development as to become unprofitable ; that is, the new set of factors 

 may give a good leaf development at the expense of flowers, or if a 

 certain leaf development is wanted, as in the case of plants like let- 

 tuce, the color and texture may be changed to such an extent as to 

 make the crop unprofitable. 



It will, of course, be recognized that in the growth of plants 

 under glass the conditions surrounding them are under far better 

 control than those outside. Hence the gardener who grows plants in 

 greenhouses has a wider range in the use of soils than he who grows 

 them outside, for if the texture is not exactly suited to the require- 

 ments of his plants, he may partly overcome the difficulty by the 

 judicious use of water and rigid attention to other conditions. There 

 is a limit, however, beyond which even he can not go, and the nearer 

 he approaches this limit the more care he must exercise in his work, 

 otherwise the plants will suffer. The nearer the ideal soil conditions 

 for each crop are attained, the less, other things being equal, will be 

 the difficulties in the way of successful crop production. 



