io8 Deserts 



seasons of the year, according as the plant is growing, 

 or putting out buds and leaves, or not. 



Experiments made by watering plants with coloured 

 solutions are not very satisfactory, because the colour- 

 ing matter may be caught and entangled, while the water 

 moves on without them. Still, it is interesting to learn 

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

 a blue solution, the white petals were streaked with 

 colour 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 14 inches 

 per hour ; in a sunflower it was 25 inches ; but in a 

 tobacco-plant it was 47^ 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 

 rapidity; 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 pro- 

 ceed. 



These climbers mount up among the trees far over- 

 head, so that to cut off the top of one is quite im- 

 possible. A length of some seven feet has to be cut 

 out where it is within reach, and this piece will yield 

 about a pint of water ; but it must be cut Jiysi at the top, 



