STUDIES IN PLANT REGENERATION 239 
making extracts of the organ in question, and injecting these into 
parts in which they are lacking. А series of experiments with this 
object in view has been started but no results ready for publica- 
tion have as yet been obtained. There are certain inherent diffi- 
culties in manipulation, which make the success of the operation 
uncertain; but further work may suggest means of obviating these, 
or at least of minimizing their influence. 
Such an explanation as the one above outlined would not 
necessarily preclude the action of any of the conditions that have 
been assigned as the causes of regeneration. It simply indicates 
that, as the regeneration is lacking in cases for which these theo- 
ries fail to account, there may be necessary, in addition, specific 
substances which can be provisionally looked upon in the light of 
enzymes, 
SUMMARY 
1. Every organ of the plant without buds that has been used 
as a cutting has been found to be capable of a certain amount of 
regeneration, 
2. In Ше cases of the roots that regenerated shoots, these 
were not confined to the basal ends of the cuttings, but were 
found on the apical cut-surface as well (horseradish) or upon the 
surface which at the time was under the sand (parsnip) or, finally, 
in the middle of the root (Pelargonium). 
3. The separate tissue regions of the root exclusive of the cam- 
bium were found capable of regeneration. From the central part 
of the horseradish, shoots were developed, and both the rind and 
the central cylinder of the parsnip regenerated, though the latter 
produced only roots. 
4. Parts of six other kinds of roots were able to form roots, 
either as regenerations or as outgrowths through the rind in the 
normal way, but did not develop shoots. 
5. When the bud-producing regions were cut away боа а 
number of stems, these formed roots from the base, but were unable 
to replace the shoots. Though such parts lived over a period 
in which, on the plant, they would alter their form and become 
secondarily thickened, they did not undergo any change when 
treated in the manner described. In the Muhlenbeckia, however, 
when a single bud was left, such thickening, though of an unusual 
sort, did occur. 
