xiii, c, 6 Brown and Trelease: Shrinkage and Elongation 359 
growth, running parallel to its course and being determined in greater 
part by identical causes. 
That the water balance is actually decreased at night and increased 
by day has been found by Mrs. E. B. Shreve, 8 who says of a cylindropuntia : 
“It was found, under conditions of average transpiration, such as occur 
in the greenhouse in summer, that the water intake at night is less than 
the outgo, while during the day the intake is greater than or at least 
equal to the outgo .... An examination of the water-content of stems 
from plants in the open and from the greenhouse showed that the highest 
water-content is at 5 p. m. after the close of a bright day, and the lowest 
just before daylight the next morning, with an intermediate amount at 
noon.” 
In the case of Cestrum the shortening during the day would 
appear to be very evidently connected with excessive trans- 
piration. 
That excessive transpiration may check growth or cause ac- 
tual shrinkage has been demonstrated by Lloyd 9 in Eriogonum. 
Concerning his experiments he says: 
The daily march of growth is as follows: During the early daylight 
hours until about 8 there is usually a slight rise in growth-rate. After 
that hour the rate falls to a low value, or, much more frequently, there 
ensues an actual shrinkage. This is the period during which the loss 
of water by transpiration is rapidly increasing, reaching its maximum 
at about noon. Coincidentally with the checking of transpiration, the 
growth-rates rapidly increase in value, the maximum rate being attained 
by 1 or 2 p. m., and thereafter maintained, with fluctuations, until 6 p. 
m., when the rates fall to the night values. The afternoon rates are great 
enough to more than make up for the negative behavior of the morning, 
except, as above stated, under unusual conditions. 
* * * it was found possible experimentally to alter the rates both 
positively and negatively quite independently of the constancy, increase, 
or decrease of illumination, even when this has been increased with 
respect to the growing part by insolation from three directions. There 
seems, indeed, to be no maximum insolation normally occurring in the 
field at this locality which can cause any cessation or inhibition of growth 
when conditions obtain which insure water-supply to the growing part. 
Thus, when a cessation of growth is apparent, it may be checked, and 
high rates instituted, by the removal of leaves (which divert the water- 
supply), by increasing the vapor-tension in the vicinity of the growing 
part, * * *. 
The present results on Cestrum indicate that a retardation 
or inhibition of growth during the day may be due to other 
conditions than the direct action of light. In this they agree 
with Lloyd’s results and tend to support MacDougal’s earlier 
conclusions: 10 
8 Carnegie Inst. Wash. Year Book 13 (1914) 98, 99. 
“Carnegie Inst. Wash. Year Book 15 (1916) 58. 
10 MacDougal, D. T., Influence of light and darkness on growth and 
development, Mem. N. Y. Bot. Garden 2 (1903) 307. 
