194 The Botanical Gazette. [May, 
plete be so encased that it cannot grow farther, the cells must 
retain a smaller size than normal. The matter cannot, how- 
ever, be so easily disposed of; the question of the interaction 
of the tissues, each striving to expand, still remains. We 
will consider first the effect on the division of cells; second, 
the manifestation of turgor between tissues; third, the defin- 
itive size of cells; and fourth, the thickness of membrane. 
The results of my experiments in those cases where the 
material was suitable to the purpose have coincided with those 
obtained by Pfeffer® in the roots of seedlings in which he found 
that cells behind the growing point and in the elongating zone 
divided after the zone was put into a cast. The cells would 
thus be found shorter (but more numerous) than they were 
when the cast was applied. Yet this division without expan- » 
sion does not progress very far, and it is only the cells that 
are near the stage of division before being put into the cast 
that divide within the cast. In cross-sections no division sub- 
sequent to the application of the cast has been found. It 
should be stated, however, that my preparations were not 
made to give, and were not often of a nature to give exact 
relations in this direction. , 
The displacement of tissues due to resistance to growth has 
been recorded in Aristolochia sipho by De Bary.’° In this 
plant the pith is compressed by the approach of the fibrovas- 
cular bundles toward the center, the impelling cause being 
thought to lie in the resistance of the leathery cortex. b 
similar movement of the fibrovascular bundles towar = 
center has been induced in many of my plants by the page 
ance of the cast. The conditions for this displacement - 
that the gypsum must be laid around the stem before p 
fibrovascular zone has formed a bridge of mechanical pi 
that the pith contains intercellular spaces or has lost the m 
of its turgor, that th rtex is in an active con j 
gor, that the corte Thus the pith 
the elements of the bundles are radially elongated — : 
vessels generally collapsed; the cortical cells are 
elongated and often assume the shape of palisade cells. 
®*Pfeffer: Druck und Arbeitsleistung, 127. 
*°De Bary: Vergleichende Anatomie, 549. 
