984 STUDIES IN PLANT REGENERATION 
interpretation without this assumption. The vegetative points of 
root and shoot normally appropriate the food-material (not further 
specialized). When the connection with these growing points is 
interrupted either by mechanically hindering their development 
or by cutting the conducting system, the material flows to other 
previously dormant vegetative points and rouses these into activ- 
ity. The new structures then appear at a nearby meristem if such 
exists. Ifa preformed growing point is absent, the heaping up of 
the food at the base of the interrupted conducting tissue, be it cut 
vein or the end of the petiole, causes the organs to grow here. 
The other factors which have by different writers been con- 
sidered causal in calling forth regeneration may be briefly enume- 
rated. Noll* regards the form disturbance as the energizing 
influence; Kiister,+ the removal of the hindrances to growth ; 
Wiesner,} the impulse from the dead cells at the wound to the ` 
living cells beyond. Іп a series of ingenious experiments con- 
ducted mainly on the cotyledonary buds of the bean, McCallum $ 
has certainly succeeded in proving that no one of these factors is 
alone responsible in calling forth the development of these buds, 
which he regards as regeneration. His work, however, seems 
open to criticism on the score that he nowhere considers the pos- 
sibility of two or more of these conditions working in concert to 
bring about these results ; and for that reason his decisions that 
the ** wound-stimulus is not in itself any part of the cause" and 
that the growth is not brought about “ through any disturbance 
created in the nutritive or water relations" do not carry convic- 
tion. To his own conclusion, moreover, that the regeneration is 
due to the removal of * some influence which an Organ . . , 18 
able to exert over other parts and so prevent their growth," the 
same comment would apply as to the explanations which he criti- 
cises. Even when this condition is present, the formation of one 
or the other kind of organ may fail to take place; and on the 
other hand, the regeneration may occur without the separation 
* Noll, Е. Über die Kórperform als Ursache von formativen und Orientirungs- 
reisen. Sep. Abd. aus den Sitzungsb. Niederhein. Ges. 900. 
Т Küster, E. Pathologische Pflanzenanatomie 2 6. 
А i Wiesner, J. Die Elementarstruktur und das Wachstum der lebender Substanz 
-6, 
102. 
2 McCallum, W.B. /.‹. 243, 262, 
