46 



INVESTIGATION INTO THE AMOUNT OF WATER 



been an average of about 100,000 grains of water given off by 

 them during their growth, an amount far greater than was anti- 

 cipated when the arrangements for the experiments were made ; 

 and it will readily be understood that, with such quantities as 

 these, it was seldom necessary to conduct the weighings with the 

 nicety for which we were prepared. 



The first and second columns of the Table show the sources 

 of the water given off, from which it is seen that an amount 

 varying from 10,000 to 30,000 grains has been derived from 

 the soil, the remainder having been supplied as the experiment 

 proceeded. It should be remarked, however, that before the 

 commencement of the experiment, 30 fluid ounces, or between 

 14,000 and 15,000 grains of water were added to each of the 

 jars of soil, which, by exposure to the air for some time with 

 shelter from the rain, and by the process of sifting, had become 

 somewhat dry. The figures in the. Table therefore overstate, by 

 nearly the quantity just mentioned, the amount obtained from the 

 normal soil. Nevertheless it is believed that the wheat and the 

 barley plants suffered to somg extent during the latter period of 

 the experiment for want of a freer supply of water, and that to 

 this cause may in part be attributed a defective development of 

 their seeds as compared with those of the beans and peas. 



We have not prepared any detailed account of the periodical 

 supply of water, which was regulated both as to time and quan- 

 tity, in part by the amount given off by the plants, and partly 

 also by their apparent or supposed requirements. It may be 

 stated, however, that none was added during the first few weeks 

 of the experiments, and that the doses given varied from 

 250 grains to as much as 1, 2, 3, 4, 6, or even 12 thousand 

 grains as the growth of the plants progressed. 



A somewhat more detailed view of the. amounts of water given 

 off by the plants may be of interest, and we have accordingly 

 supplied, in Tables 2 and 3 (pp. 47, 48), statements both of the 

 total and the average daily loss during periods, in the main, as 

 nearly approaching to one month each, as the details of our 

 registry w r ould permit. 



The relationship of evaporation to rapidity of growth is, it is 

 true, as yet a problem, but it may nevertheless be assumed as a 

 general fact — and especially between plant and plant of the same 

 description — that the comparative rate of the evaporation of 

 water, or its amount within any given period, to some extent 

 indicates the comparative activity of the processes of the plants ; 

 yet, since, w ith the advance of the season, and increased intensity 

 of heat and light, the surface for evaporation was also constantly 

 increasing, it is difficult to determine whether the increasing loss 

 up to a certain period, as indicated in the tables, is. to any extent, 



