PERIODS OF REST. 369 



of pressure on the various functions, by which it appears that in 

 ordinary air, under a pressure of six atmospheres, Mimosa per- 

 ished quickly. In an atmosphere under high compression seeds 

 germinated, if at all, very slowly. 



974. Influence of temperature upon respiration. Respiration 

 can go on at low temperatures, even near the freezing-point of 

 water. The rate of respiration increases witli rise of tempera- 

 ture, as will be seen from the following figures for germinating 

 beans : l 



Amount of carbonic acid 

 Temperature. given off" each hour. 



2C 10.56 mgr. 



6 21.22 " 



18 32.34 " 



20 39.60 " 



30 47.52 " 



975. Influence of light upon respiration. It is not yet known 

 positively whether light has any effect upon respiration. In 

 some experiments there has been a slight increase, 2 in others a 

 diminution, 3 in the rate, with increased illumination ; but it is 

 not certain whether all other factors were excluded. 



If the produced carbonic acid does not escape readily from the 

 tissues, respiration goes on more slowly. 4 



976. Periods of rest. Although all plants require oxygen for 

 the performance of their normal functions, it by no means follows 

 that when a plant is supplied with oxygen the normal activities 

 will be necessarily exhibited. In the case of certain bulbs, seeds, 

 etc., even with the most favorable surroundings, there ma}- be 

 no signs of respiratory or other activity until after the lapse of 



1 Rischawi: Versuchs-Stationen, xix., 1876, p. 338. 



2 Wolkoff and Mayer: Landwirthschaftliche Jalirbiicher, 1874, Heft iv. ; 

 Cahours : Comptes Rendus, Iviii., 1864, p. 1206. 



3 Dumas: Annales de Chimie et de Physique, ser. 5, tome iii., 1874, 

 p. 105 ; Borodin : Just's Botaii. Jahresbericht, iv., 1878, p. 920. 



4 For the bearings of this upon alcoholic fermentation, which, according to 

 Melsens, is not arrested until a pressure of 25 atmospheres of carbonic acid 

 is reached, see Pasteur: Annales de Chimie et de Physique, ser 3, tome Hi., 

 1858, p. 415; and Xageli: Die niederen Pilze, 1877, p. 31. 



Alcoholic Fermentation. This process is so intimately connected with 

 that of respiration that it requires a brief description at this point. Reduced 

 to its simplest terms, it consists of the changes which are produced in a solu- 

 tion of sugar by the growth of a microscopic organism. This is some one of 

 the Saccharomycetes (a group of low fungi which are propagated by a process 

 of budding). By the growth of this fungus the solution of sugar is broken up 

 into various products, the most noteworthy being alcohol and carbonic acid. 



24 



