62 Notes on Greenhouse Plants, S^c. 



if the substances necessary for the perfection of one or more 

 parts of a plant predominate in the soil, its principal devel- 

 opment will take place in that direction. So also with an 

 analysis of the soil ; the chemist, by the aid of fire and other 

 energetic agents, may show us what actually exists in the 

 soil, but this is not enough for practical purposes ; we must 

 also know whether the various substances are in such a state 

 of combination as to be readily accessible to the roots of 

 plants, for it has been proved that a soil may possess abun- 

 dance of all the ingredients required by any particular crop, 

 and yet be unproductive, owing to their not being in a suffi- 

 ciently soluble form to be dii-ectly available for the purposes 

 of vegetation. The roots of plants can take up and carry into 

 circulation only such matters as are at the time either gas- 

 eous or soluble. 



Scientific writers dwell much upon the chemical constitu- 

 tion of soils, but practical experience teaches us that their 

 mechanical texture is of equal importance. The physical 

 condition of the soil is seldom connected with the analysis 

 of the chemist, but in practice much depends on this prop- 

 erty. So much depends upon the decomposing power of the 

 atmosphere, that its presence or absence in a soil is sufficient 

 materially to afi"ect its productive capabilities. The soil is a 

 great laboratory, in which, by the aid of air and moisture, 

 chemical changes are constantly going on, preparing the dif- 

 ferent kinds of food for admission to the roots. Exclude air, 

 and this preparation is stopped ; the most valuable ingredients, 

 although present, may now remain inert, and useless to veg- 

 etation, because not in a fit condition to be absorbed by the 

 roots of plants. 



A practical illustration of the advantages derivable from a 

 due observance of the state of the soil, is afforded by the 

 improvement in the cultivation of plants in pots during the 

 last twelve years. Previous to this, it was almost a universal 

 practice to render all soils for potting as finely divided as 

 possible, and its value was reckoned in proportion as it at- 

 tained this condition. Various kinds of soils and manures 

 were collected and mixed with mathematical exactness, but 



