of Lysigenous Cavity-formation . 4 1 5 
longer than usually, were the normal tearing averted. In 
other words, the tearing shortens only by a few days or weeks 
what would otherwise be the life-period of the cells. 
5. Effect of Prevention of the Extension of 
Surrounding Tissues. 
As shown on page 406, it is possible for a cavity to begin 
schizogenously in secondary growth by the tension called 
forth in the contraction of cells or tissues due to loss of turgor 
while the surrounding tissues maintain their fixed position 
and size. It is also conceivable that if, in stems in which such 
a relation exists, the full primary extension of the vascular 
zone and the cortex be prevented by the early application of 
a gypsum-cast, there will arise less tension between pith and 
vascular zone when the former loses its turgidity during 
secondary growth. If the tension be thus averted it is quite 
possible that the pith-cells would live longer, since they 
would not be torn apart. And I am quite certain that many 
of my plants have demonstrated that this actually occurs. 
Triticum repens , Althaea tanrinensis , and Eryngium planum , 
which form a central cavity shortly after the cessation of 
primary growth, have had the cavity-formation deferred, but 
only for a short time, by laying around the stem an envelope 
of gypsum a few days before primary growth ceased. In 
Triticum repens the cast was applied to the rhizome. The 
lower internodes of Vicia Faba and Dahlia variabilis , in 
which the cavity appears subsequently to the beginning of 
secondary growth, have with similar treatment given essen- 
tially the same results. 
But in many plants about whose stems gypsum-casts have 
been placed, the cavity-formation has been deferred for weeks 
and even months, with attendant phenomena which render it 
impossible that it should be the prevention of tension which 
has preserved the pith. 
The first group of plants to be considered includes those 
which form a lysigenous cavity in the pith during primary 
