1915] LONG—GROWTH IN CACTI 403 
The most striking fact brought out by the experiments is the 
inhibiting effect of acids upon both growth and hydratation, quite 
the opposite result from that obtained by Borowrkow with 
Helianthus. The discrepancy may be due in part to the stronger 
concentrations used in the experiment with Opuntia Blakeana, 
Mm INCREMENT 
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Fic. 1.—Growth of new joints of Opuntia Blakeana 
Borowikow’s concentrations ranging from N/1oo to much lower. 
It might be argued that N/s50 or even N/1oo HCI could be toxic 
in other ways than in their effect upon water imbibition. The 
same could hardly be held, however, concerning N/50 malic acid, 
as this is considerably below the concentration of the same aci 
