STUDIES ім PLANT REGENERATION 235 
from the influence of the parts above and below, which he соп- 
siders necessary. When cuttings are made of stems from which 
the buds have been excised, the parts are certainly removed from 
the influence of both growing roots and shoots; yet, except in 
the potato-tuber, only roots are capable of being replaced. The 
tuber moreover, though separated from the roots of the plant of 
which it formed a part, itself does not acquire roots. That this 
disability is not due solely to correlations as one might think, is 
proved by the fact that even when the buds (which usually root 
immediately upon their development) are repeatedly cut away, the 
tuber is still unable to supply the loss of roots. Accordingly, 
isolation from either type of organ is not alone sufficient to call 
forth its production. Furthermore the bud can be induced to 
appear on the leaf of Sedum tortuosum and other plants without 
such detachment. Here by simply making a narrow transverse 
cut through the midrib, shoots and sometimes root-rudiments 
form on the leaves while they still retain their connection with 
both root and shoot of the growing plant. The same fact proved 
true of the roots formed both in his own experiments and in those 
of Klebs.* 
= Аз has been shown above, the replacement of roots either as 
direct restorations or as outgrowths from the cambium of the main 
or secondary roots (''Ersatzbildungen") is a more generalized 
faculty throughout the plant than the acquisition of shoots when 
rudiments are lacking ; also when both kinds of organs grow anew 
the roots have almost always been seen to precede the shoots by 
a period of time that may be considerable. The explanations of 
regeneration above mentioned do not account for either of these 
phenomena. It is undoubtedly true that the aggregation of food 
at the end of an interrupted conducting system is, as Goebel 
maintains, one of the factors favoring regeneration. Yet again in 
the case of the stems with excised buds and in many leaves, 
though food unquestionably gathers at the cuts, this is not effective 
in bringing about the development of a shoot meristem. More- 
over, in the cases of the inflorescences and fruits which regenerate, 
whatever current of food material occurs must be upward toward 
the developing flowers andseeds. Nevertheless, in all the instances 
Ке 2-2 22222 
* 5. dc 103. 
