1905] McCALLUM—REGENERATION IN PLANTS 249 
annuals, like Helianthus, whose axillary buds finally develop 
branches, the removal of the apex from young plants causes the 
buds to develop at once. Silphium integrijolium has a leafy stem, 
unbranched until late in the season when the flower branches arise; 
but if the apex is early removed, the minute axillary buds promptly 
produce branches. 
Not only does the 
growing apex exert an 
influence felt by the 
growing points below 
it, but those along the 
shoot exert a similar 
influence upon those 
lowerdown. VocHTING 
(18) showed that in 
isolated pieces of Salix 
stem only the buds 
toward the upper end 
of the piece develop. Fic. 3.—Young shoot of Salix amygdaloides. The 
apex was cut off at a and four branches developed 
PFEFFER (15) found  jclow this. 
that if the upper buds 
are placed in plaster those lower down start. As a series of expeti- 
ments on polarity will be published in an article to follow this one, 
only brief mention will be made here of the experiments in this 
connection. The plant used was Salix. 
Experiment 43.—Four pieces of two-year old stem, 35°™ long, 
ae Placed with the basal ends in 6°™ of water. Two were erect, 
= me Temaining parts in the moist air; the upper 8°™ of the other 
- Aa In a bell jar through which a current of hydrogen passed. 
rise ~ days the buds at the upper part of the first two started to 
— and, so far as could be observed, simultaneously with them 
in h ‘ n the other two pieces just below the part in hydrogen. Those 
to Yetogen were not killed, and when the gas was removed started 
 . In a few weeks their shoots had surpassed those below 
- ich had now almost ceased growing. 
30°m Periment 44.—Twelve similar pieces of stem were selected, 
long. On three the buds were left only on the upper third; 
