Physiological Studies in Plant Anatomy 43 
11. Owing to the depression of transpiration extension goes on 
in the etiolated plant equally by day and night; in the green plant 
extension goes on mostly by night. 
12. Earlier theories advanced to account for this particular group 
of etiolation phenomena are reviewed from the new standpoint, and 
some further experiments briefly described, which do not support an 
alternative hypothesis that elongated growth in etiolation is due to 
the absence of a growth inhibiting secretion formed by the chloro- 
plasts in the light. 
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