MacDougal . — The Water-balance of Desert Plants . 73 
Late in February, 1910, the plant was removed to the open and the rate 
immediately rose to 6 g. daily, and with the coming of the arid fore-summer 
rose to 31 g. daily, or one part in 150 of the weight at the beginning of the 
period taken into account. The rate now fell to 7 g. in the rainy season, 
3 g. in October, 19TO, 1 g. in November, and 0-5 g. in December to February, 
1911, or one part in 5,000 of the total weight. The loss in December to 
February, 1908-9, was one part in 3,000 of the water-balance and about 
one part in 4,000 of the water-balance two years later (1910-11). The 
weight on March 20, 1911, was 2-220 kg., showing a loss of 2-916 kg. or 
56-5 per cent, of the original weight in the total period of desiccation ex- 
tending over thirty months. 
A chemical analysis of the plant made in April, 1911, showed total 
solids of 8-097 g. per 100 c.c. of sap, and 3-149 g. of ash, with an average 
osmotic activity of 2-3 atmospheres at 25 0 C. This plant, as well as No. 3, 
may be supposed to have reached the limit of endurance, and disintegration 
had set in, although a high concentration of the sap contents had not been 
reached. 
The record of this plant includes some data of importance as bearing 
on the capacity of such plants to absorb moisture through their aerial 
surfaces. The weight in the open on February 28, 1911, after a drizzling 
rain lasting through the night, was 2-430 kg., which was 8 g. more than on 
February 20, 1911. The loss during the eight days would have been 
about 4 g., so that an estimated absorption of 12 g. by the spines and 
external structures must have taken place. The plant showed no adhering 
drops or films of water, and the weighing was done at noon on the 28th. 
Echinocactus No. 3 was taken from the soil on March 6, 1908, and 
placed on a base of loosely-piled black volcanic rocks in the open, its 
estimated weight being 5-480 kg. It weighed 3-893 kg. when brought into 
the laboratory on November 5, 1908, and during the next month gained 
14 g., which may be attributed to absorption of water vapour by the dead 
and dried spines. The daily rate of loss was o-8 g., or one part in about 
5,000 in the period from November to February. 
The plant had now been deprived of a water-supply for a year, and 
when placed in the soil exhibited the usual phenomena of growth and flower 
formation during the summer of 1909. The roots were embedded in soil in 
a suitable box and the preparation set under a glass shelter without sides, 
an arrangement which would allow desiccation to proceed as usual. The 
plant was freed from the soil on November 5, 1910, cleaned, and the roots 
cut away to simulate the conditions in November, 1908, and the weight was 
found to be but 4 kg., showing that practically all accretion of dry material 
had been used in the construction of roots, although some expansion of thg 
head had taken place in 1909. Still supported under the shelter, but 
separated from its roots and soil, the rate of loss was 1 -6 g. daily from 
