Selby: Studies in etiolation 



75 



throughout the stem are otherwise equal, being simply those arising 

 from turgidity. When such a stem is laid in a prostrate position 

 and the embryonic cells of the apical portions of the stem produce 

 a curvature in making an adjusting response, the stretching tension 

 set up in the concave side of the stem acts as a stimulus inducing 

 the formation of the mechanical tissue as described. 



The writer wishes to express his great obligations to Dr. D. T. 

 MacDougal, Director of the Laboratories of the Garden, for ma- 

 terial aid and constant encouragement in the course of this work, 

 and to make further acknowledgment of special assistance in the 

 interpretation of results. The illustrations are chiefly from draw- 



Marioll 



are due. 



Ohio Agricultural Experiment Station. 



