238 EVAPOEATION OF EVEKGKEEN AND DECIDUOUS TEEES. 



ments was an attempt to ascertain more exactly the precise effect 

 of different kinds of water on the growth and evaporating power 

 of the same plant ; in this case six plants of Spearmint were suf- 

 fered to gi-ow in weighed bottles of water for eight weeks ; the 

 results were as follows ; — 



Spearmint. 



1. In Hyde Park water . . . 



2. Ditto 



3. Ditto, with J an oz. of soil 



4. Ditto, with ^anoz. of garden! 



soil j 



5. Distilled water .... 

 C. Hyde Park water, coucen-) 



trated by evaporation . . j 



Original 

 Weight. 



Grains. 



127 



110 



74 



92 



114 



81 



Grains. 

 128 

 139 

 168 



284 



41 



94 



Water Eatio of 



water increase to 



Evaporated Evaporation. 



Grains. 

 14190 

 13140 

 10731 



14950 



8803 



4344 



1 to 110 

 1 to 94 

 1 to 63 



1 to 52 



1 to 214 



1 to 46 



It was the common belief of many naturalists at this time that 

 the increase in weight of plants was in direct proportion to the 

 quantity of water which passed through them, or rather to the 

 proportion of it which became fixed in their organs in the process 

 of being absorbed by the roots and given off by the leaves. In 

 the experiment just mentioned, the last plant increased most in 

 proportion to the quantity of water evaporated, bvit the fourth 

 was the one which grew most luxuriantly, and it was also the one 

 which absorbed the largest quantity of water in comparison to 

 its weight. The plant fed with distilled water grew least of all, 

 whilst that fed with spring water containing a portion of garden 

 soil was by far the most flourishing. 



These experiments of Woodward's led Dr. Stephen Hales to 

 make a number of curious and interesting observations on the 

 evaporating power of the leaves of plants, which he published in 

 1727, in the first volume of his celebrated Statical Essays. Those 

 which more immediately relate to the present subject will be 

 found in the first chapter, " on the quantity of moisture imbibed 

 and perspired by plants and trees." Hales's most celebrated 

 experiment was made in 1724 with a healtliy full-grown Sun- 

 flower, more than a yard high, and wliich had been purposely 

 planted when young in a suitable flowerpot. The mode in which 

 the experiment was conducted is best given in his own words : — 

 " 1 covered the pot with a plate of thin milled lead, and cemented 

 all the joints fast, so that no vapour could pass, but only air, 

 through a small glass tube, 9 inches long, which was fixed pur- 

 posely near the stem of the plant, to make a free communication 

 with tlie outward air and that under the leaden plate. I 



