510 Comparative Physiology. 



broken small, and when the texture of the soil is such as to 

 preserve that condition for a length of time, the powers of the 

 stomach are such that a much greater effect will be produced, 

 than in adverse circumstances where many times the quantity 

 of food has been deposited. The same quarter of the garden or 

 nursery grounds, especially if the soil is a strong loam inclining 

 to clay, if cropped in separate portions and at different times, 

 will have one part, which was worked dry and got a few dry 

 days after working, producing an excellent crop, while another 

 portion equally well worked and manured, which has unfor- 

 tunately been subject to saturating rains before the particles of 

 soil were dried sufficiently, will be found much worse. If small 

 seedling crops have been sown there is frequently a total 

 failure ; and with stronger crops the growth is weak and yellow, 

 compared with that where, the soil being worked dry and keeping 

 open, the proper action of the stomach is preserved. It is in 

 this way that turf buried, or deposit of roots left from previous 

 crops, acts ; or trenching of the soil and bringing up a new 

 surface, which from long lying has recovered its powers of con- 

 stitution, and is not so apt to run off into powder and close up 

 the pores, as old effete long-worked soil does ; it is from these 

 deposits and the renewed constitution of the soil preserving an 

 open porous state, that such astonishing effects are at times pro- 

 duced. I have often seen the crops twice as large from these 

 circumstances alone, and the trees as large in one piece of the same 

 quarter at one year's growth as in another piece at two years' 

 growth, when there was no difference of the manure and other 

 preparations. If the soil is too loose and sandy, or from long 

 working falls into powder too easily, or if it is a strong clay not 

 admitting of breaking freely into pieces, no manure will remedy 

 these defects, unless deposited in such quantities as to alter the 

 texture of the soil; and it is the same with good land, which has 

 unfortunately been battered with heavy rains immediately after 

 pulverisation, especially on clayey loams, which in good seasons 

 and under proper circumstances often produce the best crops. 

 Farm-yard manure acts much in the way of keeping the soil 

 open and absorbing moisture, and this is one of the reasons why it 

 will be found generally superior to concentrated manures, unless 

 where carriage is expensive ; by its gradual decay it keeps the 

 soil porous : and concentrated manures will always be found of 

 most value, especially those like guano containing much nitrogen, 

 when mixed up with bulky substances, as sawdust of deciduous 

 wood, peat-moss, scourings of ditches, or refuse of gardens, 

 weeds, &c. 



The changes on the substances absorbed by the spongioles 

 of plants are probably confined to the rejection of insoluble sub- 

 stances, changes in the substances taken up being more proper 



