THE VEGET2IBLE CELL. 77 



follow from tliem, that the discovery of eadosmose has not solved 

 the problem which lies in the movement of the sap of plants, 

 that in all probability it really does play an important, perhaps 

 the principal, part in the absorption and carrying onward of the 

 sap ; but that as yet we have no definite experiments to enable 

 us to determine accurately the share in the phenomenon which 

 is to be ascribed to this force, and that a series of phenomena 

 exist which are at all events at present inexplicable by endosmose. 



c. Wutrient Matters. 



The question, what substances serve for the food of plants, 

 includes a two-fold one : 1, What elementary materials are made 

 use of by the plant in the formation of its substance ? and 2, 

 What are the combinations in which those elementary materials 

 are taken up by plants? 



The number of elementary substances which occur in plants 

 constantly, and, therefore, must be looked upon as necessary con- 

 stituents, is very inconsiderable, viz.: 1, Oxygen; 2, Carbon; 

 3, Hydrogen; 4, Nitrogen; 5, Sulphur; 6, Phosphorus; 7, Chlorine; 

 8, Iodine ; 9, Bromine ; 3 0, Fluorine ; 11, Potassium ; 12, Sodium; 

 13, Calcium; 14, Magnesium; 15, Aluminium; 16, Silicium ; 17 

 Iron; 18, Manganese. 



Observ. These eighteen elements are not all combined in any one plant, 

 for not only can one be substituted for another, which is chemically nearly 

 allied, e, g., potassium for sodium, magnesium for calcium, &c., but al&o 

 particular of them, such as iodine and bromine occur only in certain 

 plants, of which they certainly appear to be necessary constituents. Under 

 these circumstances, these eighteen elementary subbianees are not all of 

 equal importance ; we must evidently lay the greatest weight upon those 

 which occur in all plants, since these are to be regarded as the absolutely 

 ueces&ary constituents. In this respect the firbt fotu' mentioned stand 

 highest, since the principal mass of vegetable substance is composed of 

 them, the first three furnish the material for the formation of cell-mem- 

 brane, and nitrogen is a prmcipal constituent of the proteine substances; 

 sulphur and phosphorus, although contained in inconsiderable quantity in 

 plants, play a most important part, since they in like manner appear to be 

 necessary constituents for the formation of particular proteine compounds. 

 It is different with the radicles of the alkalies and earths, for not only 

 may one basic body be replaced by another m many cases, but even a sub- 

 stitution of ammonia for a fixed base is perhaps often possible. At all 

 events, the latter appears to have been the case in certaia Mould Fungi 

 in wliich Mulder foimd no fixed basic substance; but yet in any case tbis 

 condition must be regarded as a great exception, since alkalies and earths, 

 and indeed particular earths, are necessary to the well-being of all other 

 plants. The universally distributed chlorine is a necessary constituent of 

 certain plants, while iodine and bromiae play in general a very sub- 

 ordinate part. Snicium, iron, and manganese are veiy generally diffused, 

 but in respect to their importance to the life of plants very little is known. 



