492 BOTANICAL GAZETTE [JUNE 
joint being cut off smoothly at the base and placed in the appropriate 
solution, the latter being replaced by freshly prepared solution 
every few days. All the plants were suspended by means of 
wooden clamps in the various solutions to a uniform depth of 
5 cm., and the battery jars containing the preparations were 
eqioed to full sunlight in the laboratory court. While tempera- 
ture and light conditions were thus not controlled, they were the 
same for all of the plants. The length of the new joint or bud was 
then measured at intervals of 3 or 4 days. In the swelling experi- 
ments, sections of standard size from healthy plants were cut with 
a cork borer, weighed, immersed in the different media, and kept 
in the dark in the laboratory constant-temperature room, the 
imbibed water being determined by weighing at 6-hour intervals 
during the following 24 hours. Inasmuch as there is considerable 
individual variation in swelling power in different joints from the 
same species, in all cases the experiments were conducted in such 
a way that all the joints used had equal representation in all the 
solutions of that experiment. 
It developed immediately that for Opuntia Blakeana, with the 
concentrations of acid which it was practical to use with this plant, 
which has a concentration varying between N/1o and N/2o in its 
own sap, the observations recorded above for Helianthus do not 
hold. The results of these experiments are summed up in figs. I 
and 2 and table I, growth increment being expressed in millimeters, 
TABLE I 
GROWTH OF FLOWER BUDS OF Opuntia Blakeana, MARCH 25-APRIL 24 
Total th 
Medium : jncrement Time in days 
Distilled water 2: 0c 42.0 mm. 27 
tO NEO 6s os 40.5 30 
N/ko malic acd... 1... 5... 36.0 28 
Men). oe 31:0 28 
and swelling in percentage of the original weight. In nearly all 
cases the recorded figures represent the average for a number 0 
plants, all of the hydratation experiments being carried out at 
least four times, and the majority of them twelve times. 
