= 
en 
1893.) Cell Union in Herbaceous Grafting. 291 
The short account here given is from the examination of 
potato callus, as it showed all the parts clearly. Froma lon- 
gitudinal section it was seen that all the cells injured by the 
knife died, the parenchymatous tissues immediately beneath 
were vigorous and were stimulated to renewed growth. 
Elongation towards the cut surface occurred in the cells, and 
by forming successive transverse walls each elongated cell 
gave rise to several small cells, which rapidly inereased in 
thickness of cell wall, and became rounded. These small 
tells pushed the dead cells in advance as they grew, and soon 
the parenchyma cells, which give rise to them, and the cell 
Contents are richer in protoplasm. The outer callus cells 
Matic tissue into ordinary central parenchyma is very gradual. 
.“xamination of the tip showed the first stages in the for- 
mation of callus to be similar to those in effecting union of 
= by grafting. Hansen, who has carefully studied the for- 
» regards a cut made in a stem, when vegeta- 
€ favorable, as a stimulus to extensive and 
In the cut necessary to grafting we have 
stimulus th, the parenchyma cells respond to the 
y developing meristematic tissue which in most 
n 
fases effects the union. 
MAY exist € other of an external wound. The callus 
Produces He =e graft, and parenchyma which in one place 
Cent locality, losity to protect an exposed injury, in an adja- 
Css j ¥ effects a union between stock and scion, the 
‘ M each case being similar. 
curs in om We find that union in herbaceous grafting oc- — 
= * two ways: It is accomplished either by long a 
Causing Bere holding old cell walls together and gradually 
Permanently to cohere, or through the develop- _ 
