1918] BAKKE—WILTING 83 
wilting occurs at a definite point and that permanent wilting 
represents the most intense wilting possible, without serious 
rupture of the water columns of the plant. These studies have 
been amplified in the present investigation. The experimentation 
involved in the present study was performed in the greenhouse 
of the University of Chicago during the summers of 1915 and 
1916. The large Russian variety of the common sunflower (Heli- 
anthus annuus) was used, the seed’ being from W. W. BARNARD of 
Chicago. The experiments involving the porometer were per- 
formed in the laboratory of Plant Physiology of Iowa State College. 
The plants were the same variety, but seed was secured from the 
Iowa Seed Company of Des Moines, Iowa. 
Series of 1915 
METHOD 
The seeds used in the tests for 1915 were planted in sheet iron 
containers 66 inches, on June 31. Germination was forced by 
placing the containers in a warm house. When the cotyledons 
had made their appearance, the seedlings were thinned out so that 
only 3 remained. The cultures were then removed to a cooler place, 
where the plants were allowed to grow until they were approxi- 
mately 6 weeks old and about 40 cm. high. The soil used in this 
Series consisted of 4 parts of compost and 1 part sand. The water- 
holding capacity was calculated to be 47 per cent. The plants 
remained in the same containers throughout the entire period of the 
experiment. They were watered from time to time until the - 
morning of July 13, when they were heavily watered, and after 
that no more water was added until the morning of July 16, when 
the plants were lightly watered and the soil surface covered with 
Plasticine. Two plants were used as checks in testing out wilting 
by the Briccs and SHantz method. 
The values for the indices of foliar transpiring power were 
obtained according to the original Livingston method; the stand- 
ard water apparatus was the same as described by BAKKE and 
Livincston. Throughout the series, cobalt paper squares made 
from Munktell’s Swedish no. oo filter paper were used. As 
the work was carried on in the greenhouse, the usual bicycle lamp 
