HISTORICAL. 7 



acidification of the plant tends also to increase the carbon dioxide output and 

 to raise the ratio. Oxygen is necessary for the production of acid, and so neces- 

 sary that in atmospheres with less than the normal oxygen-supply this process 

 is greatly impeded. Acidification is favored when the oxygen-supply is 

 increased above normal, and hence his general statement that acid is best 

 produced in an atmosphere rich in oxygen. On the other hand, a supply of 

 oxygen is necessary for the deacidification. It has been shown by other inves- 

 tigators, without question, that oxygen is needed for both processes; but 

 whether Astruc's interpretation is wholly applicable to the conditions found 

 in succulents is perhaps doubtful. There is much more detail in this contribu- 

 tion of Astruc which might be given, but it is not necessary to do so here. 

 On the whole it is a corroboration of the results of Aubert. 



Very recently Spoehr has published a paper which gives the first definite 

 account of the steps in the deacidification processes, following exposure of 

 malic acid to light. The photolytic action of light on malic acid results in the 

 formation of a number of degeneration products, as follows: formaldehyde, 

 acetaldehyde, formic acid, acetic acid, glycolic acid, oxalic acid, and carbon 

 dioxide. Step by step the malic acid breaks down to simpler derivatives 

 accompanied by a constant evolution of carbon dioxide. That the disruption 

 of the acid should be rapid at first, becoming gradually slower, is to be expected 

 from the greater stability of the simpler acids, especially formic acid. The 

 oxalic acid is apparently formed from the acetaldehyde, which is one of the 

 early products of the deacidification processes. Some of this oxalic acid is 

 removed from the sphere of photolytic action by reason of its precipitation as 

 a calcium salt, but the rest suffers a further splitting, since oxalic acid is highly 

 sensitive to light. A great deal of this work was done in vitro from ordinary 

 chemical preparations, but there are some interesting observations on the 

 plant-juices themselves. Among the most important is the account of an 

 attempt to determine whether deacidification is brought about through the 

 action of an enzyme. Very careful experiments gave a wholly negative result, 

 and it appears, therefore, that this process can not be due to any enzymatic 

 catalyst. Indeed, it is not wholly dependent upon the living protoplasm, 

 since the expressed juice when placed in the sunlight diminishes in acidity with 

 the formation of carbon dioxide. The product, after exposure to light, 

 evinces an increased power to reduce Fehling's solution; but, as the author 

 points out, this should not be necessarily interpreted as indicating the forma- 

 tion of reducing sugars. Many of the substances formed by photolysis would 

 account for this response to the Fehling test. Attention is also called to the 

 interesting theory of Borowikow on the influence of acid media upon the hydra- 

 tation of colloids and the consequent effect on growth. The possible connec- 

 tion of this hydratation with the acidity question is suggested, to which fuller 

 reference will be made in the appropriate place. In this connection, it is inter- 

 esting to note that Aubert stated that less water is transpired by organs richest 

 in malic acid, a circumstance which appears in keeping with Borowikow's 

 suggestions. However this may be, even if the acidification of the colloids 

 did not result in conditions which greatly affect growth, at least this increased 

 hydratative power might be a very important factor in maintaining a sufficient 

 water-balance to keep the cells alive and active. 



