1894. ] The Influence of Mechanical Resistance. 233 
sue should be retained, instead of the passing of such tissue 
over into a permanent state where growth could not be re- 
sumed when the obstacle to growth should be removed. 
If it should be found—what neither Pfeffer, Krabbe nor I 
have once observed—that in some plants the cell-walls of the 
meristem become slightly thicker during the enforced rest of 
this tissue, as Kriiger!® found thickenings to arise in the ra- 
dial walls of the cambium of some plants during the winter - 
rest, the importance of the biological truth would not be al- 
tered, that the meristem retains its functional capability. 
That the cell-contents may change during mechanical re- 
sistance was shown by Pfeffer1® in the case of the primary 
foot of Vicia faba, where there was a considerable rise of 
turgor after the root was enclosed in a gypsum cast. This 
Mise of turgor does not take place in all plants, as Pfeffer 
showed. 
TIL, The period between the formation of a cell and the ar- 
rival at its definitive condition is lengthened by an external 
resistance preventing or impeding growth. 
Under this general statement is included a group of phe- 
nomena the details of which may be the better emphasized 
by greater individual prominence, such as the following: 
1. The zone of eiongation in roots and stems passes more 
slowly into its definitive length. 
- Differentiation of the fundamental parenchyma into col- 
lenchyma, sclerenchyma and sclerenchymatous parenchyma pro- 
ceeds more slowlLy. 
3: All the thick-walled and lignified elements of the bundles 
develop more slowly. 
' It has already been stated that De Vries discovered this 
“/ clements of the xylem. The observations here recorded 
Show that it holds true for the hard bast also. — 
hy he formation of cork ts deferred. : : 
a 's Statement isin accord with the results obtained Len 
three plants under experiment and also with Gerbers 
a 9 Placing ligatures about stems. Since, as has been 
do si - this article and in the investigations of others, cells 
ot di 
vide under pressure till they have reached or. nearly 
18] —_—$<—<—$—$—— eee 
Zeitung 80: i die Wandverdickungen der Cambiumzellen. Botanische 
’Pioffer. D A me . ; 
ty * Vruck-und Arbeitsleistung, 65. : : 
iger het Ueber die jahrliche Kork cxoduction im Oberflachen-periderm ein- 
~ Inaug. Diss, Halle 1884. 
