150 The Botanical Gazette. [April, 
1. Embryonal tissue preserves for a long period in a gyp- 
sum cast its capability for growth. 
2. In gypsum casts the differentiation of tissue advances 
nearer the growing point than normally, thus necessarily 
shortening the zone capable of elongation. 
3. The cells of the embryonal tissue do not divide when 
their extension is prevented, but the cells of the tissue adja- 
cent to the embryonal tissue do, in some plants at least, divide 
at a size somewhat less than their normal. 
The following pages contain further observations on the 
questions already stated and besides show the effect of exter- 
nal mechanical resistance on 
1. The duration of the growing period of cells; 
2. The duration of the life period of cells; 
3. The permanent condition assumed by cells. 
This work was begun in Leipzig under the direction of 
Professor Pfeffer and completed in Michigan University since 
the author's return. 
Methods. 
The method used to arrest growth by mechanical means 
has been the employment of gypsum casts.* An organ to be 
encased had fitted about it an envelope of stiff paper clos 
at the bottom by a divided cork, by molding clay, or by cot- 
ton wool. A thick mixture of gypsum and water was stirred 
up and poured into the envelope and there allowed to harden. 
Two precautions are necessary to the securing of good rest . 
the cast must have a diameter several to many times that ° 
the organ encased to prevent springing by the energy of tur- 
gor;° the cast must have a length of three or more centimeter, 
since experience has shown that disturbing factors come into 
play in proximity to the limits of the gypsum envelope: 
: t 
At the cl i ration was 
ose of the experiment, the prepa ast and 
from the gypsum, two longitudinal trenches were SU" ___— | 
described 
°Pfeffer has used this method in researches for some time and has 
it in Berichte d. k. saechs, Gesellsch, d. Wiss., Dec. 1892: Ueber Anwendung 
en. - : reach 
ét Krabbe found the outward pressure of turgor under a ligature pfefit 
oo atmospheres in the stems of dicotyledonous trees (l. ¢.), # reach 2 
cas 
; e 
Some cases twelve atmospheres, while in the stems of some seedlings 3) 
Sure was six and one-half atmospheres. (Druck u. Arbeitsleistung, P- 
