88 MacDougal, — The Water-balance of Desert Plants . 
in 9,000 of the total weight in a shaded room in winter, and the maximum 
in the open was one part in 640 after the plant had suffered several months’ 
depletion. Seedlings of this plant lifted from the soil in November lost 
weight at the rate of one part in 12 daily for three days, the average 
during the next nine days being one in 40, which then rose to one part 
in 30 in midwinter, and fell later to one part in 227 in the period when 
some of the individuals were dying. This expected high rate of loss by 
desiccation would contribute to the enormous mortality of seedlings in 
the open. Germination takes place in the summer rains in July, and the 
tender plant lets must then endure a period of four months of extreme 
aridity, but with falling temperatures. 
The resting corms of Brodiaea lost one part in 11 by evaporation from 
the dead outer coats the first day after removal from the soil in November, 
and this rate fell at once to one in 53, then to one part in 164, and finally 
to one part in 200. The latter rate was calculated for the period including 
the formation of new corms. This rate of loss is probably greater than that 
which would be exhibited by corms in situ in the soil. 
The minimum rate of loss of Ibervillea during the relatively humid 
cool winter season was one part in 4,500 to one part in 32,000. The 
maximum in a well lighted room during the arid fore-summer was one 
part in 573 to one part in 2,oco. This applies to the period in which new 
stems were being formed. 
The behaviour of a plant in successive seasons with especial relation 
to the state of depletion of its water-balance of succulency was a matter 
which received some attention. Echinocactus No. 1 showed a maximum 
rate of 29 g. daily in 1908, and 15*6 g. a year later, after it had lost but 
3 kg. or 7 per cent, of its weight. The minimum rate in March, 1908, was 
10 g. daily, while a year later, in the corresponding season, it was less than 
4 g. after a loss of but 3 kg. or about 7 per cent, of its weight. 
Echinocactus No. 6 lost at the rate of o-6 g. daily during 155 days 
including the winter of 1908-9, and 37 g. daily during a corresponding 
period of 173 days a year later, after it had decreased 1-370 kg. or 3-8 per 
cent, of its earlier weight. A year later the rate was 2-8 g. for a period of 
188 days after a loss of but i-6oo kg. more. The maximum rate in June, 
1909, was 10 g. daily, and in June and July, 1910, 7 and 7-7 g. daily, after 
a loss of 1-865 kg. or less than 7 per cent, of its total weight. Echinocactus 
No. 7 lost 9 g. daily in 56 days in midwinter of 1908-9, while the rate was 
2-3 g. daily for 109 days in the corresponding period of 1909 and 1910, after 
a loss of 2-653 kg. or 7*5 per cent, of the earlier weight. 
The above data were taken from plants kept in the laboratory, in which 
corresponding seasons would be fairly equalized. 
Echinocactus No. 13 lost at the rate of 150 g. daily during 83 days 
ending May 12, 1910, and 10 g. daily in the 42 days ending March 20, 1911, 
