4i2 Newcombe. — On the Cause and Conditions 
become hollow through the etiolated zone, because there is in 
such segments an expansion great enough to tear the central 
cells. This expansion is to be traced to the effect of the 
expansion in the adjacent inflated parts of the leaf. If how- 
ever, instead of a yielding opaque band, gypsum 1 is used to 
enclose zones of the leaf, the whole tissue of the enclosed part 
will remain alive, though the cavity will exist as normally 
both above and below the limits of the cast. By this process 
the central mass of cells has been kept alive within the cast 
eleven or twelve days after it had died outside of the limits 
of the cast. 
Similar results have been obtained by enclosing the aerial 
shoots of jfuncus ejfusus in gypsum. For eleven weeks some of 
these young shoots were wholly encased in gypsum, at the 
end of which period they showed the peripheral zone of living 
cells thicker radially by two rows of cells than in normal shoots. 
In this case, cells that weeks before would have passed over 
into the dead, stellate form had, so far as cause can be dis- 
cerned, been kept alive because they had not been subjected 
to the usual stretching from the normal growth of the stem 2 . 
The formation of the intercarinal canals in Equisetum 
limosum was delayed for a week or more by the application 
of a gypsum-cast to the base of a young shoot. The stem 
did not, outside the cast, increase subsequently in diameter ; 
hence the cast prevented only longitudinal extension of the 
enclosed internodes. In Zea Mats the formation of the 
lysigenous canal in the vascular bundles was prevented in 
1 The method of applying these casts is described by Pfeffer, in Berichte 
d. K. Sachs. Gesellsch. d. Wissenschaften, December, 1892. The author, who 
learned the method from Pfeffer, has described it in Botanical Gazette, April, 
1894, in an article entitled The Effect of Mechanical Resistance on the Develop- 
ment and Life-period of Cells. 
2 It is probable that another factor comes into play in this case ; that is, that the 
cells live longer, not only because they are not stretched by adjacent tissue, but 
because they are prevented from making their own active and normal growth. 
This question has been discussed by the author in The Effect of Mechanical 
Resistance on the Growth of Plant-Tissues, Leipzig, 1893, and in The Effect of 
Mechanical Resistance on the Development and Life-period of Cells, Botanical 
Gazette, April and May, 1894. 
