off they developed. Though less than a 
1905] MCCALLUM—REGENERATION IN PLANTS IOI 
exclusion the essential factor might be isolated. Experiments were 
conducted on Phaseolus, Salix, Helianthus, Taraxacum, Tolmiea, and 
other plants. 
If the common scarlet runner bean, a variety of Phaseolus mul- 
tiflorus, be cut off any place along the epicotyl, there arise from 
within the cotyledons two shoots, which grow 
vigorously and may attain the size of the 
normal plants (fig. 3). Sometimes, however, 
one of these may grow weakly, or even be 
entirely suppressed. These arise from two 
minute primordia which are present, one in 
the axil of each cotyledon. Of the many 
hundred plants under observation scarcely 
a case was seen in which these primordia 
developed without the removal of the shoot, 
and in every case in which the stem was cut 
millimeter in length, in three or four days 
after the stem is removed they appear above 
the cotyledons, and in a week are often 6°™ 
long. Growth is then very rapid, and in a 
month they may be 60 or 70°™ high. In the 
axils of each of the foliage leaves on the plant 
there is, as usual, a bud. These under the con- 
dition of my experiments rarely developed. 
If the plant be allowed to grow until the 
second internode is formed, and this be cut 
off, these dormant buds in the axils of the 
leaves at its base will at once become active 
and give rise to two shoots; or if the plant 
form several internodes and the upper one . 
be removed, the buds of the nodes below (not necessarily the first 
one) at once will develop shoots. 
Here we have one of the most common phenomena in regeneration, 
namely the removal of a part stimulating to development what would 
otherwise be dormant primordia. But this same removal or isolation 
of a part is followed by the growth of organs where their primordia 
Fic. 3 
