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316 BOTANICAL GAZETTE [april 



temperature; while the reverse changes resulted in a decrease in 

 the rate. 



4. Temperature seemed to be a more important factor than water. 



5. The increase in diaphragm distance which followed a change 

 from water to air, and from high to low temperature, did not 

 seem to be sufficiently great to be considered a direct result of the 

 change, inasmuch as there is a normal tendency to increase from 

 tip to base. 



6. There appeared to be an inverse relation between diaphragm 

 distance and rate of growth. 



7. Environmental conditions may influence diaphragm distance 

 by their effect upon growth. 



8. A decreased growth rate would indicate a lowering of the 

 vital activities of the plant, and would result in the formation of 

 fewer diaphragms, thus increasing the distance between them. 



9. This decreased vitality was shown normally in the decrease 

 in growth rate toward the close of the growth period, and was 

 accompanied by an increase in diaphragm distance. 



10. This plant grew fairly well under 10-20 mm. pressure, 

 while under 60-80 mm. pressure there was almost as good growth 

 as under normal pressure. 



1 1 . There appeared to be an increase in diaphragm distance at 

 low pressures. Apparently this was due to the retarding effect of 

 diminished pressure upon growth. 



12. Lowered pressure appeared to have no effect upon (1) the 

 total number of air chambers or their size, (2) the thickness of the 

 mass of tissue on the outside of the stem or of the partitions between 

 the chambers, and (3) the number of palisade layers. 



13. These experiments lead one to conclude either that water 

 with its low oxygen content is not the direct cause of the air spaces 

 in aquatics, or that Scirpus validus is a very non-plastic organism, 

 retaining its characteristic growth and structure under wide varia- 

 tions in environmental conditions. 



14. A lowering of the atmospheric pressure below 630=*= mm. had 

 a retarding effect upon the growth of Cyperus alternifolius ( ?) , but 

 there is no evidence that it had any effect upon the air spaces. 



Wellesley College 

 Wellesley, Mass. 



