84 The Great World's Farm 



that in the case of a white iris, which was watered with 

 a bkie sohition, the white petals were streaked with color 

 in from ten to fifteen hours. 



A more trustworthy experiment made upon a willow 

 seemed to show that the water in this case rose from the 

 roots at a very much more rapid rate — thirty-four inches 

 an hour. But the willow, having its roots always in or 

 near water, has no need to be economical. 



In a plant of maize, whose roots were in earth, the 

 rate was much less, being little more than fourteen inches 

 per hour; in a sunflower it was twenty-five inches; but 

 in a tobacco-plant it was forty-seven and one-half inches 

 per hour. The tobacco transpires so freely that its leaves 

 droop as soon as gathered, and these experiments were 

 made in such a way as to encourage transpiration to the 

 utmost. 



In some plants the sap rises with extraordinary rapid- 

 ity; as, for instance, the water-liana. This is one of the 

 many gigantic, rope-like creepers or "vines" of tropical 

 America, and owes its name to the fact that clear, cool 

 water fit for drinking can be obtained from its stem — by 

 those, at least, who know how to proceed. 



These climbers mount up among the trees far over- 

 head, so that to cut off the top of one is quite impossible. 

 A length of some seven feet has to be cut out where it is 

 within reach, and this piece wih yield about a pint of 

 water; but it must be cut first at the top, otherwise, if 

 cut first near the ground, almost the whole of the water 

 will have rushed away into the vine high overhead before 

 the second cut can be made. 



This plant, therefore, seems to dispose of a pint of 

 water in less than a minute, and almost all by transpira- 



