248 The Ohio Naturalist. [Vol XIV, No. 4, 



down as is fixed in the construction of these materials, i. e., that 

 the complete oxidation results in a quantity of water equal to that 

 required during photosynthesis and chemosynthesis, the amount 

 of water comprises but little more than three-fifths or 60 to 65 

 percent, of the weight of the dry matter of plants. The ecological 

 water requirement it will be seen is greatly in excess of the actual 

 quantity of water used; the quantity of water lost by transpira- 

 tion is not related to the synthetic process. Transpiration aids 

 the gaseous exchange, but the rate and amount of COj entering 

 is not in proportion to the water evaporating through the stomata. 

 The dift'usion of the gas is independent of it, and the supply of COo 

 is usually less than could be utilized by the chloroplasts. The 

 results obtained in green and dry weight of plant depend upon and 

 vary within the limiting conditions of the CO2 gradient in the air, 

 the light intensity, and the general temperature conditions as 

 well as the duration of period of the growth. 



Unfortunately the number of investigations on hydrolytic 

 reactions in plants during their entire life cycle is small, and it 

 would be therefore unsafe to make any extended discussion of 

 the results. The greater percentage of organic matter in tissues 

 is often due to hydrolytic reactions, but the total quantity of 

 water used in this manner is unknown, since no means are yet 

 available for the determining the extent and the degree of hydra- 

 tion, and the number of times which degradation or metabolic 

 transition products function in hydrolytic reactions. In many 

 cases the action consists merely in an absorption of water which 

 is followed by a splitting up of the substance. The difi^erent 

 hydrolytic enzymes which act upon glucosides, and such catalytic 

 agents as saccharase, amylase, cytase, lypase, protease are active 

 in this stage of metabolism. In other stages the h^^drolytic pro- 

 cesses are reversible and accelerate synthetic combinations, some 

 of the products showing profound differences in reaction and with 

 relation to the infiuence of external factors. The number of such 

 intermediate compounds is large; their molecular structure is not 

 sufficiently well known, and the knowledge of this construction 

 action is yet very scanty. Hydrolytic reactions occur in all 

 stages of growth, from gemiination to maturity and decay. 



The attention of physiologists has been attracted thus far 

 especially to the dependence of these reactions on temperature. 

 However, the principle of temperature coefficients fails to hold 

 rigidly, for wherever components are co-ordinated into a system 

 of reciprocal relations, and obscured by the effects of limiting 

 conditions, such as in the cycle of changes collectively spoken of 

 as growth, the character and the rate of any one single reaction 

 is not that of more elementary chemical processes. Beyond a 

 certain ])oint, further temperature increases do not cause more 

 growth. The favorable range of temperature has not as yet been 



