121 
harvest increases with increasing water supply up to a definite limit, 
beyond which the harvest diminishes steadily for any further increase 
in the water supply, until when the earth is completely saturated with 
water the harvest in some cases becomes almost mil. The most 
advantageous percentage of moisture in the soil varies for the differ- 
ent plants, depending on their own method of using the water, on the 
evaporation from their leaves, and on the number of plants to the 
unit of area of the field, namely, their closeness to each other. 
In reference to the needs of practical agriculture it would be 
improper to consider in such experiments as these only the water 
that has been used, since the number of plants to the unit area is of 
equal if not greater importance. It would therefore be improper 
to reason from these experiments up to the needs of another field or 
tub having a greater or less plant density. Again, as also shown by 
Wollny, more water is used in proportion as more nutriment is avail- 
uble in the ground, because the development of the organs of tran- 
spiration or the leaves is thereby increased. Therefore, in general, 
the quantity of water required to attain the maximum crop will 
increase with the richness of the soil and the closeness of the plants as 
well as the dryness and velocity of the wind. For different crops, 
moreover, the absolute quantity of water will depend upon the dura- 
tion of the whole process of vegetation, from germination to harvest. 
(See Wollny, 1881, IV, p. 109.) 
The character of the plant affects the quantity of necessary water, 
not only by the duration of the process, but by the relative quantity 
of auxiliary organs that the plant develops in order to produce the 
ripened seed, which we call the harvest. The ratio of the grain to the 
straw and chaff when the, maximum crop of grain is produced in 
each of Wollny’s seven cases is shown in the following table: 
Maximum harvest dried in air. 
Straw | 
|Grain.| and | Ratio. 
| chaff. | 
| TEA 
11, Sr RAGE BATS) Saeco c abe e eo pO Ree Dae SEO SASS TS SAEs See eee eee | 5.7 12.0 48 
SUM Fock re a NS Oe ee Ee SY cecdeee Soecnces | 11.6 15.4 | 75 
TWO, (Sherer eye Tay oD) SEs hs eo ee ok ee lB eee | Avo) eee (ROM 65 
TAY, TSWOyGEIS) [OVS Se a re ee mee | 21.9] 31.6 69 
Wee Colzaiboan wathoutimanunrom ees. 9) teases nae a 2 ee eee ee | 4.6 15.4 | 30 
Wiles @olza bean withscuano seen: sesh Sen oss aie. cc ces coceea eee |eeGOi Leas) 40 
These percentages show the success with which the plant labors 
to perpetuate its species with the least possible waste of molecular 
energy on extraneous matters. 
