8o Mac Doug at.—- The Water-balance of Desert Plants. 
affected by the seasonal changes in an obvious manner. No changes 
of mode or discontinuity in the rates of loss, such as were seen in Echino - 
cactus , were recorded. The extremest stages of desiccation were accompanied 
by highly increased total solids and ash content of the sap. 
Carnegiea seedlings. Twenty young plants, seven months old, were 
taken from the flat in which the germinations had taken place, and put in 
a dish in the laboratory, November 4, 1910. The net weight of the lot was 
27-244 g., and the loss during the first three days was 6-865 g. at the rate of 
2-286 g. daily, this being one part in 12 of the total. Much of this may be 
attributed to the desiccation of the exposed root-surfaces, although all of 
the finer branches had been removed. The rate of loss was 0-5 g. daily, or 
one part in 40 during the next nine days, while in the next 79 days ending 
February 3, 1911, the rate was 0-85 g. or one part in 30, an increase for 
which no adequate cause may be given. February 24, i9ii,the net weight 
was 12-499 g., the loss in the preceding 21 days having been 0-055 g. indica- 
ting a rate of one part in 46. The total loss was 14-745 g. or 54 per cent, of the 
original weight. Four of the seedlings were wilted beyond revival, and as 
many more were in a doubtful condition, the above may be taken as 
roughly representing the average resistance of the seedlings. From this it 
may be seen that the seedling loses water at such a rapid rate during even 
the cooler season as to exhaust its effective balance in about 100-120 days. 
The death of some of the individuals ensues when something less than 54 per 
cent, of the total water-balance is lost. This is, however, a greater degree of 
endurance than that exhibited by adult plants, as may be seen by reference 
to page 79. The older individuals are not able to withstand a loss greater 
than about 23 per cent, of their original turgid weight. 
Thirty-six resting corms of a native Brodiaea were taken from the soil 
on October 30, 1910, and brought into the laboratory to obtain data which 
might be of interest in comparison with those furnished by the seedlings of 
Carnegiea. The net weight of the lot was 46-7 g., and the loss during the 
first 24 hours was 4-9 g., which was one-eleventh of the total. This doubt- 
less represents the desiccation of the outer dried coating of the bulbs. The 
loss during the following day was 0-78 g. or one part in 53 - During the 
next week, ending November 9, 1910, the loss fell to 0-31 g. daily or one 
part in 130. The loss during the week ending November 16, 1910, was 
i-68og., 0-24 g. daily, or one part in 200. The total loss was 18-425 g. or 
39*5 P er cent, of the original weight during 96 days. During the latter part of 
this period young corms were developed, and the contents were slowly with- 
drawn from the older ones. The desiccation of the other structures 
described in this paper resulted in depletions in water-balance followed by 
shrivelling and contraction of the affected members. The reaction of 
Brodiaea , however, is seen to consist in the formation of new smaller corms 
which are plump and turgid, although each one contains but the fraction of 
