MKTABOLIC PROCESSES IX TlfE PLANT. 327 



131. The Behaviour of the Free Organic Acids in the Crassulaceae, 

 and Some Other Plants. 



Many Crassulaceae and other plants, especially succulent ones, 

 are very remarkable in the fact that the quantity of free organic 

 acids in their sap (we have in these cases specially to deal with 

 Malic acid) is much less in the daytime than at night. The 

 extremely complicated relations in question have been by no 

 means thoroughly examined in all directions. But a few facts 

 have been established, and shall be experimentally confirmed 

 below, after I have first stated very briefly the views which I 

 have formed on the basis of previous investigations as to the 

 behaviour of organic acids in the Crassulacea?. 1 In the tissue 

 (especially in the leaf tissue) of the Crassulaceae and some other 

 plants, two processes are constantly and under all circumstances 

 going on side by side, which appear to be of the utmost signifi- 

 cance in connection with the acidity of the sap. On the one hand, 

 production of acid is always taking place, and on the other, acid 

 is always undergoing decomposition. The amount of acid at any 

 given moment is therefore the resultant of these two processes.* 



1 1 is a fact of great importance that, under certain conditions, 

 considerable quantities of free acid can accumulate very rapidly 

 in the cells of the Crassulaceae, and one which is undoubtedly of 

 biological significance for the plants. These, viz., grow generally 

 in dry and often very calcareous localities. They need therefore 

 special means for increasing the osmotic capacity of their cell 

 contents, so that large quantities of water may collect in their 

 tissues, and at the same time for rendering possible combination 

 of the excess of lime transferred to their cells from the soil. 

 The organic acids serve both these ends. 



The acids are produced from carbohydrates under the influence 

 of Oxygen. They originate from oxidation of the products of 

 assimilation. That such considerable quantities of acid should 

 accumulate in the tissue of succulent plants is related to their 

 organization. Succulent plants, viz., in virtue of the possession of 

 a thick cuticle, relatively few stomata, and fleshy tissue, maintain 



* Besides the decomposition of free organic acids in the tissue of the 

 Crassulaceae there is continually going on in them a combination of the acids 

 with bases (Kraus). Hence large quantities of certain salts gradually collect 

 in the cells, and the production of these compounds, which however we must 

 here leave out of consideration, is also naturally not without significance as 

 regards the acidity of Crassulaceous plants. 



