MANUEES. 



289 



ilieir food from the atmospliere ; and the lower 

 they are hi the scale of creation, the more evident 

 thia appeai-s. The first traces of vegetation on 

 the oooled-down masses of lava in volcanic re- 

 gions are various species of cryptogamic plants, 

 which have scarcely such appendages as roots ; 

 there, however, they thrive, deriving their whole 

 sustenance from the atmosphere : by their dis- 

 solution they leave organic matter in the fissures, 

 which, in turn, supports a higher order of vege- 

 tation to perform the same important office, 

 until a sufficient body is at last accumulated to 

 give support to the largest shrubs and trees; 

 thus showing, as we rise in the scale of vege- 

 table life, the vast importance — nay, the positive 

 necessity — of organic matter being present to 

 secm-e healthy development. The operation of 

 rendering the most sterile soUs in course of time 

 fertile, may be instanced in the case of planting 

 with trees soils naturally possessed of little 

 or no organic matter ; yet on such soils do trees 

 not only grow, but in time produce thousands 

 of tons of valuable timber, leaving the soil much 

 richer in vegetable matter than it was prior to 

 their being planted. Dm-ing the first few years, 

 trees so circumstanced make little progress; but 

 as they increase in size, and as their annual ex- 

 foliation increases, so do they in bulk and mag- 

 nitude. These facts are quite sufficient to prove 

 that vegetables have the power of feeding largely 

 on the atmosphere, and deriving from it the 

 gi-eat bulk of their sustenance. According to 

 some, more than three-fourths of the solid matter 

 found in plants is derived from the air, and not 

 from the soil. Seeing, therefore, that plants 

 derive so much of their food from the air, it may 

 not be unimportant to inquire from whence and 

 how their food is provided. We believe that it 

 arises from the soil in the shape of gaseous 

 matter disengaged by the great chemical opera- 

 tions constantly going on in the great laboratory 

 of nature, and mixing in the atmosphere, and 

 fed upon by the leaves of plants. The supply 

 necessary to keep up this enormous demand is 

 almost provided by plants themselves, even when 

 in a state of nature, by the annual shedding of 

 then' foliage and decaying parts ; but when in 

 an artificial state, where greater development is 

 required, then it becomes necessary for man to 

 add to these sources such materials, or what are 

 called manures, as he deems best fitted for their 

 wants and circumstances. 



Before noticing those manures individually, 

 which experience has proved to be of most con- 

 sequence to the horticulturist, we may observe 

 that, according to our highest authorities on 

 vegetable chemistry, all plants are composed of 

 oxygen, hydrogen, carbon, and nitrogen, or 

 azote, with a small proportion of saline bodies. 

 All manures, therefore, should include these 

 elements, as a deficiency of either may prevent 

 the formation of those parts in the vegetable, 

 for which its peculiar organisation is contrived, 

 and on which much of its healthy existence 

 depends. 



All manures must be rendered soluble, as no 

 solid substance can enter into a plant. Hence, 

 manures deposited in the soil must undergo a 

 species of dissolution, and become wateiy or 



gaseous before they are capable of being ab- 

 sorbed either by the roots or leaves of plants. 

 Sir H. Davy thought that such parts as became 

 gaseous, and passed into the atmosphere, af- 

 forded little benefit to plants, as the gases soon 

 become diffused through the mass of suiTound- 

 ing air. More recent authorities think otherwise, 

 and say that plants feed as much by the leaves 

 as by the roots, and that their food is sup- 

 plied by the gases which evolve around them, 

 and which of necessity must arise from the soil. 

 The application of manure to the soil no 

 doubt acts in two very different ways, yet both 

 indispensable to vegetable existence ; first, by 

 being taken up by the roots, after it has as- 

 sumed an aqueous form ; and, secondly, by be- 

 ing taken up by the leaves, when it becomes 

 resolved into a gaseous state. The first of 

 these has been long admitted, the other has 

 more recently been recognised. To insure that 

 effect in the former, the manure is buried in the 

 soil near to where the roots are situated. To 

 secure the latter, it may be thought that the 

 manure should be spread upon the surface, or 

 probably applied to the leaves in a more direct 

 manner. Neither of these are absolutely neces- 

 saiy, although of the effect there can be little 

 doubt. A certain portion of the manure, when 

 reduced to a proper state, is taken up by the 

 spongioles at the termination of the roots, 

 while another portion, becoming disengaged 

 from the soil, escapes into the air which sur- 

 rounds the plant, and is fed upon by the leaves. 

 Hence one of the great advantages of frequently 

 stirring the soil between rows of crops, and 

 which is done by most people for the suppres- 

 sion of weeds ; by others , as they say, to pro- 

 mote evaporation, and for the admission of the 

 rays of heat to the roots — few thinking that this 

 very necessary operation tends to facihtate the 

 escape of fertilising gases from the boU, to be 

 fed upon by the leaves, which would be pre- 

 vented from escaping if the surface was allowed 

 to remain hard and unbroken. No doubt, a 

 great amount of these gases is dissipated into 

 the atmosphere, and may be lost ; or they may 

 be returned, for aught we know, by various 

 atmospheric operations — such as becoming 

 mixed with rain, dew, &c., and in this state be 

 brought to act upon the foliage in a way un- 

 known to man. Nor is it necessary that these 

 gases should become amalgamated with either 

 rain or dew ; they may remain in a gaseous 

 form, and be carried to the foliage, if not of the 

 plant from under which they arose, of others 

 equally important, by the action of the air 

 itself. The effects of gaseous food taken up by 

 the leaves must of course be much less appar- 

 ent in the open air than it is within the more 

 limited atmospheres of pits and hot-houses; and 

 that they are actually less is admitted. The 

 principle, however, remains the same. The heat 

 and moisture afforded by the tank system of 

 heating is, so far as these two elements go, 

 quite satisfactory ; but plants do not thi-ive, by 

 any means, so well in houses so heated, as in 

 others heated by the use of stable manure in a 

 state of fermentation ; nor do plants, in pits 

 heated by leaves, tanners' bark, fiax refuse, or any 



