1894.] The Influence of Mechanical Resistance. 157 
mentioned for Caltha palustris and Zea mais. The same is 
true of the only other plant in which the question was studied, 
viz., Cucurbita pepo. In this plant after elongation of the 
internodes the innermost cortical cells thicken into a heavy 
zone of sclerenchyma. In internodes confined in casts this 
zone has been delayed in development into sclerenchyma for 
several weeks, though it could there be identified as a band of 
thin-walled cells. Older preparations have shown this band 
becoming slowly thick-walled, the progress continuing after 
the full thickness of wall had been obtained in parts above 
and below the cast; though in the oldest preparation ex- 
amined these cells had not become so thick as in normal parts 
of the same stem. 
University of Michigan, Ann Arbor. 
[Zo be continued. | 
