4 
232 . The Botanical Gazette. [June, 
Similarly to the cells of the pith, the life-period of the cor- 
tical cells has also been prolonged. Lamium garganicum, 
Urtica dioica and Vicia faba have shown dead cells in the cor- 
tex outside the limits of the casts, when within the casts all 
cells have remained alive. 
There have come under my observation two species of 
plants in which, sometimes but not always, cortical cells are 
crushed within the casts before any dead ones appear outside 
the casts. These plants are Ricinus communis and Dahlia 
variabilis. This result is apparently brought about by the 
growth of the fibrovascular zone, the turgor there present be- 
ing sufficient to cause the less resistant cells of the cortex to 
collapse, whereas similar cells outside the limits of the casts 
live for some time longer, though the tissue which they form 
becomes looser and looser by the separation of cells. 
In all of the foregoing cases in which the life-period of 
cells has been more than normally prolonged, the cells were 
prevented from attaining their full size by confining their 
growth before they were fully extended. But in certain cases 
the death of cells may be deferred by checking the growth of 
surrounding tissue after the cells in question have reached 
their full extension. In Sambucus nigra and Helianthus tub- 
erosus, for instance, where the pith lives for several wpe 
after secondary growth has begun, a cast applied after the 
pith has grown to its definitive size will preserve the pith ea 
for several weeks after it dies above and below the limits © 
the cast. 
Summary. 
I. Meristematic tissue of growing points, intercalary ye 
and cambium will preserve for a considerable period tts si ve 
tional capability when growth is prevented by an exe 
mechanical resistance. ; ped bY 
Il. When in such meristematic tissue growth ts checké: 
mechanical resistance, the tissue remains apparently unalte 
the cells do not divide, nor the walls become thicker, mr 
composition of the walls undergo change. : : soutien 
Especial attention may be eed to the biologica! pone 
cance of the two facts just stated, and to the em’ or in- 
what takes place when growth ceases because of CO + of the 
sufficient moisture. It is manifestly to the per tissue 
plant-organism not only that the life of anid this tis- 
should be retained but that the primary condition 0 
ved; 
the 
