FOOD OF PLANTS IN GENERAL. 491 



We should do very wrong and depart from our fundamental principles 

 if we were from the foregoing considerations to deduce a theory of vege- 

 table nutrition, and were to apply it to explain the mode of nourishment of 

 particular plants. In order to obtain a correct theory of the nutrition of 

 plants, we must first learn to know the plant in its other relations, and 

 in this place the fundamental principle of the independent existence of 

 the life of the cells must be taken into consideration. Every cell lives 

 for itself. What is necessary for one cell is not to those around. One 

 cell may stand in direct relation with inorganic nature ; another, 

 through its extensive union with other cells, may stand in an indirect re- 

 lation between the plant and nature ; it may receive its nourishment not 

 immediately from the common sources of nourishment, but already assi- 

 milated and modified through the agency of other cells. Both conditions 

 may occur to the same cell during different periods of its life : thus live 

 the generality of the cells throughout the body of the plant : branches, 

 leaves, flowers, and even parasites themselves, live only, or almost only, 

 on matter already assimilated. Each bud, each twig, is a new individual, 

 which sucks from the mother plant matter already become organic, and 

 which appears incapable of assimilating inorganic matter. At this 

 point it must first form root-cells, by which means it is placed in circum- 

 stances to receive and assimilate and convert inorganic matters into or- 

 ganic combinations. But even these root-cells possess only for a short 

 time the capability of assimilating inorganic substances for the use of the 

 plant. The older root-cells receive from those of more recent origin 

 matter already assimilated. 



A question which has been referred to in the foregoing paragraphs 

 awaits an experimental solution. It may be thus expressed : 



Are there truly, as Unger and Endlicher have asserted, hysterophytes ; 

 and if so, how many groups of plants belong to them, and in what way 

 is their independence of a preceding vegetation demonstrated ? There 

 can be no doubt that parasites are hysterophytes, that is, that they can 

 by no possibility originate until the subject on which they root them- 

 selves is formed. This may be asserted with respect to a large number 

 of fungi, which are only developed on soil formed from the decay of for- 

 mer organisms. The difficulty of the cultivation of turf-moor plants 

 on other soil than their own, seems to arise from a similar relation. The 

 nutrition of the true parasites, from the assimilated juices of the subjects 

 on which they appear, seems to be established. From these to the Algce 

 and Lemnacece there is a continuous series of transitionary forms : 

 they can vegetate perfectly where water, carbonic acid, and ammonia are 

 present ; and it could only be presumptuous ignorance which should at 

 present decide whether some of the remaining plants may not derive 

 nourishment, in part or entirely, from organic matters. From what has 

 been already said, it is at least clear that, with respect to cultivated plants 

 and those on which available observations have been made, the or- 

 ganic substance of the soil is not to be regarded as the principal source 

 from whence they derive their nourishment, because its amount is not 

 adequate to the necessities of plants. 



With respect, however, to the turf-moor plants, experiment alone can 

 decide whether their nourishment, demanding, as it does, much carbon, is 

 not essentially received from organic substance as such ; for we know 

 that on moors organic substance is present in large quantities in a dis- 

 solved state, and we have as yet no proof that the plants do not receive 

 all which is presented to them in a dissolved form. 



