STUDIES IN PLANT REGENERATION 224 
explanation for this phenomenon involves a consideration ог с 
various theories of regeneration, and may, therefore, be deferred 
until this subject is discussed. 
The experiments throw some light also on the dependence of 
organogeny upon the presence of a cambium, and upon callus forma- 
tion. That the structures regenerated do not necessarily derive 
their origin from a cambium, as Stoll,* Frank,+ and their followers 
assert, has been demonstrated by the results with isolated root- 
regions from which the cambium has been carefully cut away, and 
from the anatomical study of the bean petiole. It will be recalled 
that the central part of the parsnip, consisting only of wood and 
pith, was able to produce a callus and roots. Root-meristems, 
too, were seen to arise in the callus covering the hollow of the 
bean petiole. Апа, as to shoots, isolated rind-tissues of the parsnip 
were found to produce a callus from which buds arose (Fig. 4). 
The absence of any cambium or transverse bundles in this region 
was confirmed by a microscopical examination at the time the 
buds appeared. Coulter and Chrysler found a similar develop- 
ment of shoots from isolated cortical regions of Zamia.{ There 
can be no doubt, therefore, that both roots and shoots may arise 
from callus that has no direct connection with cambium or bundles. 
That both sorts of organs can also spring from a cambium without 
the intermediation of a callus seems equally clear. Rechinger 5 
describes such a derivation of shoots in the horseradish, and of 
course the origin of roots in such a manner is a common occur- 
rence. Тһе cells of both these tissues agree іп being undifferen- 
tiated, rich in protoplasm, and capable of rapid division — three 
characteristics which seem to supply the structural basis for the 
appearance of primordia of root and shoot. || 
Before closing this section of the work, it may be worth while 
to record the result of an experiment performed on the alga Peni- 
‘cillus capitatus іп the summer of 1004 at the Flatts Harbor іп 
Жос 701. 
Т Frank, A. B. Die Krankheiten der Pflanzen т: 70. 
t Coulter, J. M., and Chrysler, M. A. Regeneration in Zamia, Bot. Gaz. 38: 
452. 1904. 
323. 
|| A few instances are known, as for example in the epidermis of Begonia leaves, 
where organs arise from mature cells without even the intermediation of a callus. 
* 
