OO BIOLOGY OF PLANTS. 



penetrated the soil, to a depth of thirty feet, and that the tap 

 roots of clover and some other plants extend to a depth of 

 three feet or more. 



(3) The soil should be finely pulverized; especially the 

 surface to the depth of six inches ; in order that the seed corn, 

 grain, or potato shoot may be placed in earth finely divided, 

 into which the tender fibres of the root may easily and quick- 

 ly shoot, and air, water and heat operate with facility. 



If the soil is lumpy, large pores or intervals will exist, 

 across which, the delicate fibres of the roots will extend them- 

 selves, become exposed to injury, and unable to discharge 

 their functions in a vigorous manner. 



Professor Hitchcock accounts for the superior fertility of 

 the alluvial soils of New England, on this principle. Such 

 soils do not contain so large a quantity of vegetable matter as 

 those less fertile, but their materials are in a much more fine- 

 ly divided state, and hence their fertility. This condition 

 of vitality is liable to be disregarded by the farmer, because 

 the expense of preparing the soil, in the first instance, is much 

 increased, and because the time of sowing and of harvesting, 

 are too far removed to impress the mind with its necessity 

 and utility, i c j 



(4) The. soil should he covered at the proper depth. The 

 requisite depth varies according to the nature of the seed, but 

 generally the smoother and finer the surface, the less the depth 

 required. Grain covered one fourth of an inch in depth by 

 finely pulverized earth, where it will feel the influence of heat, 

 moisture and air combined, will be much more likely to ger- 

 minate, the vitality will be much sooner excited, the roots 

 will become more powerful and the stalks, leaves and fruit 

 much more abundant. 



The Baron Von Vought has made a numerous collection of 

 plants, in which the seed was, in the one case, covered only 

 two lines in depth, and in the other a little more than one inch 

 and a half ; and these plants show, " what a striking differ- 



