DYNAMICS OF REGENERATIVE PROCESSES 20I 



growing, the specific formative substances of the root flow from the 

 assimilating leaves to the root at the lower end of the stem; while the 

 shoot-forming substances flow from the leaves upward to the apices 

 of the twigs. If a piece be cut out from the stem or the root, the cut 

 surfaces form an obstruction where these substances now gather." In 

 such a piece the root-forming substances will therefore gather at the 

 basal end of the twig, and cause here the formation of roots; and the 

 shoot-forming substances will collect at the apical end where they favor 

 the formation of shoots. Sachs's hypothesis finds a beautiful confirma- 

 tion in the phenomena of regeneration in leaves. The leaves are the 

 factories in which the carbohydrates, and perhaps all the specific sub- 

 stances in the sense of Sachs, are formed. The dissolved substances 

 flow from the leaves to the base, and from here to the stem. If pieces 

 be cut from a leaf, e.g. in a Begonia, shoots as well as roots are formed 

 at the basal end of the leaf where the substances flow. Goebel has 

 added a great many beautiful observations on regeneration in plants 

 which support Sachs's conclusion. 



The observations of pathologists on compensatory hypertrophia 

 support also in my opinion the idea of Sachs.* If, e.g., one kidney is 

 removed, the other increases in mass. The same seems to hold also 

 for other glandular organs. Pathologists assume that this is due to 

 the greater work now done by the remaining gland. If the hypothesis 

 of Sachs is apphcable here, it is possible that certain substances which 

 caused the growth of these glands circulate only in limited quantities 

 in the blood. If a gland be removed on one side of the body, these sub- 

 stances will all flow through the remaining organ which will, therefore, 

 begin to grow. 



2. Heteromorphosis and Regeneration in Tubularia 



The only way which seems to lead directly to any information concern- 

 ing the dynamics of regeneration lies in our finding means to substitute 

 at desire one organ for another. The results thus obtained no longer 

 rest upon surmises, but allow us to determine the variables of which 

 the process of regeneration is a function. Sixteen years ago I under- 

 took to bring about such substitutions of one organ for another at 

 desire. I succeeded in a number of hydroids and an ascidian, and 

 called the process heteromorphosis f to discriminate between this 

 phenomenon and the substitution of an organ by an identical one 



* Loeb, Untersttchungen zur physiologischen Morphologic der Tiers, Wiirzburg, 1890 

 and 1891. (Translated in Studies in General Physiology, Chicago, 1905.) 

 t Loeb, loc. cit. 



