1 88 PHYSIOLOGY OF NUTRITION 



autolysis occurs in plant parts containing amygdalin, a strong odor of hy- 

 drocyanic acid is developed. 



Some of the glucosides that accumulate in plants appear to be respiratory 

 chromogens, others are very efficient activators (hormones). 



§11. Organic Acids. x — All living cells always contain some organic acids, 

 the cell sap always giving an acid reaction. It is supposed that these acids 

 arise through incomplete oxidation of carbohydrates. Numerous studies have 

 been carried out upon oxalic acid in the form of its calcium salt, 1 and it appears 

 that marked accumulation of this salt occurs in most plants only in light and 

 with normal or high transpiration, while very little is formed in darkness and 

 when transpiration is low. 



Various external and internal conditions have great influence upon the forma- 

 tion and decomposition of organic acids in plants. 2 The amounts of these acids 

 decrease somewhat in light, as is shown by the table below, which presents the 

 relative acid contents of several plants, in darkness and in light. 



Relative Acid Content 



Plant In Darkness In Light 



Convallaria majalis (rhizome) 72 68 



Phaseolus multiflorus (roots) 60 64 



Etiolated wheat seedlings 238 230 



The acid content is lower with higher temperatures. Thus, for example, 

 plants of Sempervivum tectorum, with an acid content of 358, were placed in 

 diffuse light for three hours, with temperatures of 4-6°C, 22-25°C, and 35- 

 38°C, and at the end of this period the acid content had fallen to 336, to 327, 

 and to 301, respectively. 



If carbohydrates are artificially supplied, an increase in the acid content 

 occurs. The roots were removed from etiolated seedlings of Phaseolus and 

 some were placed in distilled water, others in a solution of glucose, in dark- 

 ness. After three days the acid content of those on water was 185, while that 

 of the plants in glucose solution was 257. Grape sugar thus produces an in- 

 crease in the acid content of seedlings. 



[Active roots appear to give off organic acids, into the soil, when the supply 

 of oxygen is low. With a plentiful supply of oxygen they appear to give off 

 only carbon dioxide.] 



§12. The Importance of Water in Plants. y — Physiological processes can- 



1 Kohl, Friedrich Georg, Anatomisch-physiologische Untersuchung der Kalksalze und Kiesels&ure in 

 der Pflanze. Ein Beitrag zur Kenntnis der Mineralstoffe im lebenden Pflanzenkorper Marburg, 1889. 

 Monte verde, N. A., On the deposition of the oxalates of calcium and magnesium in plants. [Russian.} 

 81 p. St. Petersburg, 1889. Rev. in Bot. Centralbl. 43: 327-333, 1890. Wehmer, Carl, Entstehung und 

 physiologische Bedeutung der Oxalsaure im Stoffwechsel einiger Pilze. Bot. Zeitg. 49: 233-246, 240-257, 

 271-280, 289-298, 305-313. 321-332, 337-346. 3S3-363, 369-374. 385-396, 401-407, 4I/-428, 433-439. 

 449-456, 465-478, 511-518, 531-539, 547-554. 563-569, 579-584, 596-602, 611-620, 630-638. 1891. 



2 Puriewitsch Konstantin A., Bildung und Zersetzung der organischen Sauren in Samenpflanzen. Kiev, 

 1893. 



x This section is numbered §10 in the German; the numbering of the 7th Russian 

 edition is here followed. — Ed. 



v This section appears for the first time in the 7th Russian edition. — Ed. 



