30 STUDIES IN SHE VEGETATION OF THE STATE 



3. Observations upon the Water Content of Plants Dying from 

 Drought and the Corresponding Water Content of the Soil. 



The relative amount of water in plants dying from drought 

 is usually varied by the same causes that vary the amount 

 of water in the healthy plant. This varies with the natural 

 woodiness or succulency of the plant and is greatly modified 

 by the physical conditions under which the plant develops. 

 The discussion of the wilting plant in the previous chapter 

 might be made to include the dying plant, for there can be 

 no definite line of demarcation between the two conditions. 

 The wilting is but the beginning of disturbances of function 

 in the plant which if continued result in its death. Owing 

 to the difiSculty of examining the roots of the plant at every 

 stage of the process of wilting and dying, it is almost impos- 

 sible to tell when a plant ceases to obtain water from the 

 soil, and actually begins to die. So long as this is the case 

 there will be an uncertainty about the results obtained in 

 estimating non-available soil water. The plant must cer- 

 tainly live for some time after it ceases to take water from 

 the soil. The length of this period depends directly upon 

 the store of water in the plant and its ability to hoard it. 

 The ordinary mesophyte seems to be deficient in both re- 

 gards, yet in a number of species studied, such plants lived 

 even after the roots had died, that is, until the soil appar- 

 ently aided the roots in extracting water from the resistant 

 living cells of the stems. This happened usually under 

 conditions where the evaporation of water took place very 

 slowly, and the death o"f the plant was prolonged. 



Grasses when turgid contain a lower per cent of water 

 than many other herbaceous plants, and when dying they 

 show a still greater proportionate difference. It was impos- 

 sible to experiment along all lines, and the data given here 

 are from observations made at various times in connection 

 with the other lines of experimentation. A grass containing 

 15 per cent of water or less is dead almost beyond a doubt; 

 with from 15 to 20 per cent its condition is uncertain and it 

 is doubtful if it could be revived; above 20 per cent, life 

 usually remains in most grasses. A succulent plant 



