THE ASH OF PLANTS. 211 



oils of the onion, mustard, horse-radish, turnip, etc., like- 

 wise require sulphates for their organization. 



Phosphates. — The phosphorized substances (prota- 

 gon., lecithin, cMorophyl) require to their elaboration that 

 phosphates be at the disposal of the plant. Knop has s h own 

 that hypophosphites cannot take the place of phosphates. 

 The albuminoids which are probably formed in the foliage 

 must pass thence through the cells and ducts of the stepi 

 into growing parts of the plant, and into the seed, where 

 they accumulate in large quantity. But the albuminoids 

 penetrate membranes with great difiBculty and slowness 

 when in the pure state. The di- and tri-potassic phosphates 

 dissolve or form water-soluble compounds with many 

 albuminoids, and, according to Schumacher {Physik' der 

 Pflanze, p. 128), considerably increase thedifEusive rate 

 of these bodies, and thus facilitate their translocation in 

 the plant. 



Potassium. — The organic acids, viz., oxalic, malic, 

 tartaric, citric, etc., require potassium to form the salts 

 of this metal, which exist abundantly in plants, e. g. , 

 potassium oxalate in sorrel, potassium bitartrate in the 

 grape, potassium malate in garden rhubarb ; and without 

 potassium it is in most cases probably impossible for the 

 acids to accumulate or to be formed. Mercadante culti- 

 vated sorrel {Oxalis acetosella and Etimex aceiosa), in ab- 

 sence of potassium-salts; sodium, calcium, and magnesium 

 being supplied. The plants failed to fructify, and their 

 juices contained but one-eighth as much free acid (or acid 

 saltsj") as exists in the sap of the same kind of plants veg- 

 etating under normal conditions. The acids — oxalic, with 

 a little tartaric — were united to calcium (Berichte, 1875, 

 II, p. 1200). The organic acids may result from the de- 

 composition of carbhydrates (starch or sugar), or they 

 may be preliminary stages in the production of the carb- 

 hydrates. In either case their formation is an index to 

 the constructiye processes by which the plant originates 



