STUDIES IN PLANT REGENERATION 291 
these always originated in the pericambial region above its level. 
Wiesner * and Hansen,t however, have confirmed Cruger's results 
and there is no doubt that organs may arise in both ways. The 
pulvinus of the primary leaf of the bean was cut off, so as to 
simplify the anatomical study, and the leaves were planted. 
Every twenty-four hours up to the ninth day on which, in some 
cases, roots became visible, specimens were removed and killed. 
Microtome sections showed that the callus-formation begins in the 
cortical region just outside the bundles on the second day. There 
may be several centers of such formation in the rind, which start 
independently but later unite. Оп the fourth day activity is notice- 
able in the pith cells, as well, of which there are a few rows sur- 
rounding the cavity of the hollow petiole. Тһе callus resulting 
from the growth in these two regions eventually, about the seventh 
day, covers over the entire cut end of the petiole so that the hol- 
low is no longer visible. Roots may grow out in both of the ways 
described above. Sometimes the callus remains sterile and the 
roots appear only from the petiole above. At other times they 
start in the part of the callus which covers the cavity, so that 
there can be no question here of a derivation from a cambial tissue 
ata higher level. Тһе stages іп the formation of callus and roots 
closely coincide with the processes as described by Stoll,j Titt- 
man,$ Sorauer|| and others, so that there seems no need of a 
further description here. 
Experiment 38. — The callus was allowed to form fully, and 
was then cut off on the eighth day. Others were repeatedly re- 
moved after the same lapse of time, and it was found that a single 
leaf could form eight such calluses before it disintegrated. 
Experiment 39. — Bean leaves which had formed calluses and 
roots were transferred to a rich loam, to a soil saturated with cul- 
ture solution, and to a one per cent solution of grape sugar, to 
m 
dui J. Die Elementarstruktur und das Wachstum der lebender Substanz 
E A. Vergleichende Untersuchung über Adventivbildungen im Pflan- 
zenreich. Abh. Senckenb. Naturf, V 12: 157 sg. 1881 
Stoll, В. Z. c. 752 and pi. г ; 
{ Tittmann, Physiologic Untersuchungen ері Callu 
lingen holziger Gewachse. Jahrb. wiss. Bot. 27: 164. 5. 
. and 
ча Sorauer, P. Handbuch der а. 2 Auflage 1: 660 seg. ап 
sbildung ап Steck- 
