METABOLISM AND GROWTH 221 



in the latter, hydrogen, marsh gas, leucin, and tyrosin. 

 Higher plants also appear to have the power, in absence 

 of free oxygen gas, of decomposing sugar, with the 

 formation of alcohol and carbon dioxide, and these and 

 similar phenomena led to the linking up of respiration 

 with fermentation as was suggested by Pfeffer in 1885. 

 This physiologist held that sugar was first of all decom- 

 posed into alcohol and carbon dioxide without the aid 

 of oxygen, but that, when that gas was supplied, the 

 alcohol was further broken up into carbon dioxide and 

 water. To follow out the story I have thus so very 

 briefly outlined would take me far beyond the limits 

 I have prescribed for myself ; besides, the subject becomes 

 more and more of the nature of a problem in organic 

 chemistry, and hence outside the boundaries of botany 

 in the strict sense of the term. 



GROWTH 



I must now devote a sentence or two to the work 

 that had been accomplished in a branch of physiological 

 investigation which I have not as yet touched upon at 

 all, viz. growth. 



Our knowledge of the phenomena of growth really 

 dates from the year 1873, when Sachs postulated that 

 every cell, tissue, and organ passed through certain 

 phases which he termed collectively the " grand period 

 of growth/ 1 The first phase of growth was slow, but the 

 rate gradually increased until the maximum activity 

 was reached, when there followed a gradual decline to 

 zero. Examples of this succession of phases will occur 

 to you in abundance from your knowledge of the develop- 

 ment of the root and stem from their apical meristems 

 backward to the zones where extension ceases and the 

 tissues assume their permanent size and shape. Sachs 

 not only illustrated the " grand period " in great detail, 

 but studied the variations that exhibited themselves 



