206 STUDIES IN PLANT REGENERATION 
supply of food for expenditure in organogeny — formed any shoots ; 
and in those which did, the appearance of roots antedated that of 
shoots by a period varying from two weeks to five months. This 
fact will be referred to later on. 
Another point that deserves attention here is the lack of a rigid 
polarity in the root-parts mentioned. In none of the species in 
which shoots were acquired anew were these restricted to the 
basal end. In the horseradish the cambium of either or both 
surfaces proved active ; in the parsnip the end in contact with the 
moist sand seemed commonly more effective in regenerating shoots, 
without regard to gravity ; and in the Pelargonium these arose from 
the middle of the root. Furthermore, in one of the two cases in 
which roots were in the narrower sense regenerated, that is, in the 
thin transverse sections of the sweet potato, these developed from 
both sides, The evidence, therefore, seems to warrant the con- 
clusion that polarity evinced by root-pieces without buds is less 
fixed than is generally believed. 
REGENERATION IN STEMS 
With the exception of internodes, parts of stems from which 
buds are absent have been little used in studies in regeneration. 
This may be because investigators have concerned themselves al- 
most exclusively with the question of root-development on stems. 
In the stumps of some trees, though, the power to produce shoots 
from a callus derived from (һе cambium 15 а phenomenon very 
well known but not readily subjected to experiment. Neverthe- 
less, some stems afford abundant scope for experimentation as 
to shoot-production. Experiments have been carried on with 
dicotyledonous stems, modified stems of various types, monocoty- 
ledons and a conifer. In the dicotyledonous stems, of which 
Muhlenbeckia platyclados and Phyllocactus (sp?) were taken as 
one type, aerial shoots of potato as a second, and the potato- 
tuber as a third, the first point upon which information was 
sought, was the behavior of stem-pieces of considerable size from 
which the buds had been cut. A comparison of such regenera- 
tion with cases in which one or more buds had been left was also 
instituted ; and finally the regeneration of the internode alone was 
investigated. 
