7 6 MacDougal ’ — The Water-balance of Desert Plants . 
The weight was now 31-570 kg., the total loss during the entire period of the 
experiment extending over twenty-nine months being but 42-48 kg., or less 
than 12 per cent, of the original. During this time some apical growth had 
ensued and eighteen fruits were retained. This plant, with No. 6, was set up 
for further observation. 
Echinocactns No. 10 was taken from the soil November 7, 1908, freed 
from its roots, and set on a tin box near the south side of the laboratory in 
the open. Its net weight was 14-588 kg. and it lost 6i-6g. daily during 
the first month, or one part in 220, about ten times the rate of plants 
in a shaded room. The rate during the next six months was 30 g., the total 
being 4-860 kg., out of the original noted above. This rate was one part in 
430, which is about five times that of Nos. 6 and 7 during the same period 
in the shade. 
The analysis of the expressed juice of the sap of the cortex gave the 
following data : 
Specific gravity ........ 1-035 
Acidity calculated as H 2 S 0 4 per 100 c.c. . . . 0-1064 
Total solids per 100 c.c. of sap ..... 7-060 
Ash content of sap per 100 c.c. ..... 3-009 
A similar analysis of a turgid plant taken up on September 9, 1909, 
gave the following : 
Specific gravity of sap 1 -0095 
Acidity calculated as H 2 S 0 4 per 100 c.c. of sap . . 0-0887 
Total solids per 100 c.c. of sap ..... 2-092 
Ash content of sap per 100 c.c. ..... 0-792 
Echinocactus No. 13 was taken from the soil and freed from its roots 
on February 18, 1910, after which its net weight was found to be 49-390 kg. 
It was now mounted on a base of loosely piled black volcanic rock near 
a Carnegiea taken up at the same time. Definite points were located for 
calibration, and the greatest length was 585 mm. and the greatest diameter 
413 mm. The rate of loss was i5o*5g. daily from February to May, this 
being one part in over 300 total weight. The total loss of 12-490 kg. up to 
May 12, 1910, was accompanied by a decrease in length of 25 mm. and of 
diameter amounting to 43 mm. The rate of loss fell to 102 g. daily in July, 
some new spines being formed and flower buds developed at this time. The 
rate fell to 33 g. daily by October 3, 1910, at which time the total loss was 
12-845 kg. This rate amounted to one part in 873. Although the plant 
had lost over one-fourth of its total water-balance, eighteen flowers had 
been formed and eight small fruits matured. The length had decreased to 
500 mm., a further shrinkage of 60 mm. in length and of the diameter to 
325 mm., a loss of 45 mm. The lowest rate, 9-3 g. daily or one part in 
nearly 2,900, was found in the period of thirty-five days ending November 9, 
