306 BOTANICAL GAZETTE • [april 



increase in the number of spaces occurred; in one, following a 

 change from air to water, there was a marked increase within a 

 distance of 1 5 mm. ; in the other a noticeable increase occurred 

 within 9 mm., following a change from low to high temperature. 

 From these experiments there is no clear evidence that either water, 

 temperature, or rate of growth has any effect upon the number or 

 size of chambers produced. 



Partitions between air chambers and outer wall of stem. 



— The changes in environment used in these experiments appear 

 to have no effect upon the regular course of development of the 

 partitions, which seems to be an increase in the number of layers 

 from one to three. No observable difference could be noted in the 

 outer wall of the stems. 



Palisade layers. — The curious banding, which is sometimes 

 seen in Scirpus, occurred in experiment 5. The albescent spaces 

 and the basal region contained no palisades. The dark green 

 portions contained two layers of palisades, and the pale green 

 spaces one layer, or two with only part of the cells chlorophyllous. 

 The environmental changes in the experiment seem to have no 

 effect upon the development of palisades, and cannot be held 

 responsible for the banded appearance. 



Reduced atmospheric pressure 



Experiments 



During February 19 16 a series of experiments was started in 

 the temperate house of the University of Chicago, to test the 

 effect of low atmospheric pressure upon the air chambers of water 

 plants. The apparatus is shown in fig. 2 and described in the 

 legend. The temperature of the house was controlled by the 

 general heating system, and a recording thermometer showed a 

 variation of a degree about 20-2 i°C. The barometric pressure 

 was obtained in experiment 1 .from the records of a government in- 

 strument outside the greenhouse, and the figures were reduced to 

 metric readings at 21 C. In experiments 2 and 3 the pressure read- 

 ings were obtained from the barometer in the Botany Building, and 

 corrected for temperature only. The pressure in the experimental 



