

1920] SNOW— DIAPHRAGMS 3 1 5 



in the experiment, and the graphs for nos. 7, 8, and 9 are so nearly 

 alike that it is evident that this amount of pressure has the same 

 effect on the growth of Cyperus as full atmospheric pressure. 



After the experiment was over, cross-sections were made at the 

 same distances from the top in the two sets of culms, but no evi- 

 dence that diminished pressure had any effect upon the air spaces 

 could be observed. 



Experiment 5 



k experiment was set up May 10, using the same apparatus 

 le last experiment. The pressure was kept for 3 days at 

 1 2 atm. (380=*= mm.) and for 2 weeks at about 7/10 atm. 



(530=*= mm.), after which it varied around 1/3 atm. (250=*= mm.) 

 for 6 days. Growth was not measured, but after May 31 cross- 

 sections were made. A careful study of these show that at 30 mm. 

 from the base the experimental culm was a little more lacunose 

 than the control, at 50 mm. still more so, but at 70 mm. it showed 

 less difference. At 95 mm. the experimental culm ended in the 

 usual tuft of leaves, while the control grew much higher, and at 

 95 mm. showed a structure exactly like that of the experimental 

 culm at 50 or 70 mm. The shorter culm evidently had not differ- 

 entiated as much as the longer one, and the difference in the 

 sections was therefore only apparent and not due to the effect of 

 diminished pressure. 



From these two experiments one must conclude that, although 



atmospheric pressure reduced below 630=*= mm. had a retarding 

 effect upon the growth of Cyperus, there is no evidence that it had 

 any effect upon the air spaces. 



1 



Summary 

 • The zone of growth of Scirpus validus is very short, possibly 



2-3 mm. 



■ 



2. The direct contact of the surrounding medium with the 

 growing region is prevented by a closely fitting sheath of scale 

 leaves. 



3- In these experiments the rate of growth, in general, was 

 increased by a change from air to water, and from low to high 



