of Lysigenous Cavity -formation, 421 
The evidence for this conclusion is, that in all those cases 
mentioned in the last paragraph of statement No. 6, the 
vitality of the cells in question was never prolonged more 
than a week or two except in the case of J uncus ; that in 
plants in which the pith normally collapses it died without 
being torn when the tearing was prevented by surrounding 
the stems with casts ; that the pith, which does not die till 
secondary growth has begun, was preserved alive when the 
casts were not applied till primary growth had ceased, the 
casts in this case not affecting the tension between pith and 
more peripheral zones ; that the pith was never preserved 
long unless the stems encased made good growth ; and, finally, 
that in stems grown for a period within casts the pith died 
without collapsing on removal of the casts, though the tension 
on the pith was thereby not increased. 
