198 STUDIES IN PLANT REGENERATION 
set of experiments has been conducted ; and finally, existing the- 
ories as to the cause of the kind of organs produced in regenera- 
tion have been discussed in the light of these and other experiments 
with a view of determining their plausibility. 
REGENERATION IN ROOTS 
Roots afford excellent material for the study of regeneration 
because, while in many plants the roots normally produce buds, 
in a number of others, there is a marked tendency to form 
shoots only upon injury. Vöchting * showed conclusively that 
in cuttings of woody roots (poplar, Paulownia, elm, etc.), new 
roots are formed at the apical, and shoots at the basal (proxi- 
mal) end of the part. The same polarity is normally mani- 
fested іп root-pieces of Taraxacum, used by Goebel,t Wiesner, $ 
and Küster || and of Scorzonera hispanica (Rechinger,$ Goebel 1), 
though experiments have shown that this polarity could be partially 
reversed. For example, Wiesner succeeded in inducing shoot- 
formation from both ends of a Taraxacum root-cutting by a cul- 
ture in light. Goebel demonstrated also that when the growth at 
the shoot-pole is arrested by a covering of sealing-wax or plaster, 
or when the callus is repeatedly cut off at this end, the distal end 
produces the shoots. It is noticeable, however, as Tittmann ** 
remarks, that the polarity is simply changed at one of the two 
poles; and that no case is known in which doth poles produce Ше 
opposite type of organ from the normal. 
In the work on roots several distinct types were used. Of 
these the horseradish (Roripa Armoracia) was chosen to begin 
with ; this series of experiments was followed by one on the sweet 
potato (/ротоеа Batatas) and dahlia (Dahlia variabilis), as examples 
of thickened secondary roots ; a number of fleshy tap-roots, carrots 
* Uber Organbildung im Pflanzenreich 1: 
84 seq. 
t Goebel, K. Allgemeine Regenerationsprobleme: Flora 95: 400. Erganzungs- 
band 1905. 
iWeisner, J. Die Elementarstruktur und das Wachstum der lebender Substanz. 
112: 1992. 
4 Küster, E. Pathologische Pflanzenanatomie. 
I 903. 
|| Rechinger, C. Untersuchungen über die Grenzen i Тын im Pflanzen- 
reich: Abh. жі, -bot. Ges 93. 
ebel, К. Uber перон са im Pflanzenreich. Biol. Centralb. 1902. 
- Tittman, H. Physiologische Untersuchungen uber талатын an Steck- 
lingen holziger Gewichse. Jahrb. wiss. Bot. 27: 168 5 
