THE VEGETABLE CELL. 91 



the hydrogen than in water. Among these acids, oxalic is one 

 of the most widely diffused, — scarcely a plant being without it. 

 This acid stands very close to carbonic acid, since — supposing it 

 anhydrous — it contains no hydrogen, and differs only from car- 

 bonic acid, by containing less oxygen. It may, with Liebig 

 {^'Agricult. Ghem ,"' 6th ed.), be considered very probable, that the 

 deoxidizing process connected with the respii^ation of the green 

 organs, does not convert the carbonic acid and water at once 

 into neutral compounds, but first only a partial separation of 

 oxygen takes place, and the carbonic acid is changed into organic 

 acids, fi.rst of all into oxalic, the hydrate of which, by separation 

 of greater amounts of oxygen gas, can be transformed into malic, 

 citric, and other acids. It may be assumed of all these acids 

 that they are capable of conversion iuto sugar, starch, &e., by the 

 addition of hydrogen. If this conception is adopted, the con- 

 stant occurrence of vegetable acids appears a necessity for the 

 nutritive processes of plants ; and it will explain why plants will 

 not flourish when they do not take up a certain quantity of basic 

 substances, to combine into salts with these acicls. On the con- 

 version of an acid into a neutral substance, the base becomes 

 free again, can unite with a new portion of acid, and so in the 

 course of time, a comparatively small quantity of base may 

 bring about the formation of a very great quantity of neutral 

 compounds. 



Observ. This notion of the importance of acids in the vegetable eco- 

 nomy, has something very attractive about it, since it appears to solve a 

 series of questions, but on closer examination a number of doubts present 

 themselves. On the one side, the assumption that the acids are foimed 

 by a decomposition of carbonic aeid, appears in any case too general, 

 since in many plants with fleshy leaves, an acid is formed every night 

 (thus at a time when no carbonic acid is decomposed), which acid is again 

 decomposed by day. Here the acid is doubtless formed through oxida- 

 tion of a neutral compound. On the other hand, that theory does not 

 perfectly explam the case of the basic substances. If these had no other 

 destination in the plant than the purpose of fixing free acids, it would 

 be all one to plants whatever base was absorbed from withotit ; any one 

 could be substituted for any other. This is certamly, in some degree, 

 the case with regard to bases which are very closely chemically allied, 

 like potash and soda, or lime and magnesia, but this substitution is only 

 coiBpatible to a certain extent with the healthy growth of the plant. 

 Particular plants require particular bases, lime, potash, &c., and die when 

 they do not find them in the soil. Therefore, the specific properties of 

 the bases stand in a definite relation to the nutritive processes of plants, 

 albeit, the grounds of this relation are still unexplained. If, moreover, 

 the acids form these transitional stages between carbonic acid and the 

 neutral compounds, it is remarkable that so many plants produce an 

 acid, and especially carbonic acid, in far greater quantity than is neces- 

 sary for this purpose, depositing it, ia combination with lime, in an in- 

 soluble condition, crystallized in the celK, and yet do not subsequently 



