Experimental Crops at RotJiamstcd. 
active growth, by means of a delicate balance made for the 
purpose ; which, though carrjinj^ so heavy a weight, was capable 
of indicating a change of a few grains. The plants were of 
course supplied with water as it was needed. The earlier 
results, both with agricultural plants and trees, are published in 
the ' Journal of the Horticultural Society of London,' and to the 
reports there given we must refer the reader for the details of 
the inquiry as far as they are yet recorded.* 
Referring here only to the results obtained with some of the 
agricultural plants, it will be sufficient for our present purpose to 
summarise them as follows : — 
1. The amount of w^ater given off by the plants during 
growth was found to bear relation to the quantity of the total 
dry matter, or the total non-nitrogenous substance, fixed or 
assimilated ; and within somewhat narrow limits the same re- 
lation was observed in the case of both graminaceous and legu- 
minous corn-crops. 
2. In relation to a given quantity of water exhaled, twice or 
three times as much nitrogenous substance is fixed by a legu- 
minous, as by a graminaceous corn-crop. 
3. In the growth and ripening of either graminaceous or 
leguminous corn-crops, probably on the average from 250 to 
300 parts of water are given off for 1 part of total dry substance 
fixed or assimilated. 
Before considering the application of this estimate to any 
special cases, it may be well to give an illustration of its bearing 
in general terms. Several plots in the experimental wheat-field 
give an average of about 3 tons of total produce (corn and 
straw) per acre per annum ; and if we assume one-sixth of this 
to be water, we have remaining 2^ tons of dry substance 
ripened by the end of July, or the middle of August, each year ; 
and if we further assume that 300 parts of water may be exhaled 
for 1 part of dry substance fixed, we have 300 x 2'5 = 750 tons 
of water evaporated per acre by the growth of such a crop. 
Owing to the difficulty of eliminating surface evaporation 
other than through the growing herbage, in experiments on 
the exhalation from a sod of mixed grasses, we cannot so safely 
adopt a figure to represent the probable average amount of 
water given off for 1 part of dry substance fixed in their case 
as in that of their ripened allies, wheat and barley. We will 
* ' Experimental investigation into the amount of ■water given oflF by plants 
during their growth, especially in relation to the fixation and source of their 
various constituents.' — (' Jour. Hort. Soc. Lond.,' vol. v. part i. 1850.) 
' Report upon some experiments undertaken at the suggestion of Professor 
Lindley, to ascertain the comparative evaporating properties of Evergreen and 
Deciduous Trees.' — (' Jour. Hort. Soc. Lond.' vol. vi. parts iii. and iv. 
