LECTURE XI 

 ON THE DYNAMICS OF REGENERATIVE PROCESSES 



i. SACHS'S HYPOTHESIS OF THE FORMATION OF ORGANS 



THE investigation of the physicochemical conditions for the for- 

 mation of organs in the egg meets with the difficulty that the germ is 

 too small for a thorough experimental analysis of the processes which 

 occur there. It seems to me that it will be easier to use for such an 

 analysis another series of morphogenetic processes; namely, regen- 

 eration. In many plants and animals when an organ is cut off, a new 

 organ is formed which is identical with the lost organ. The only scien- 

 tific hypothesis of morphogenesis which we thus far possess, namely, 

 that of Sachs,* starts with the processes of regeneration. 



Sachs takes it for granted that the variety in the form of organs 

 is determined by a corresponding variety in their chemical constitution. 

 As an illustration of the relation between chemical constitution and 

 the formation of organs, he uses his experiences with the influence of 

 light upon the origin of blossoms. If plants, e.g. Tropceolum majus, 

 are put into the dark in spring, their flowering buds which are already 

 formed are not able to develop. In the dark the assimilating power 

 of the green plant is inhibited, and Sachs concluded that the specific 

 substances which are required for the formation of the blossoms cannot 

 be formed by the leaves in the dark. In the light, however, these sub- 

 stances are formed in the leaves, and are carried by the sap from the 

 leaves to the nearest flowering buds. Growth was not restricted in 

 the dark, as was shown by the formation of large (etiolized) shoots 

 in the dark by the same plants. From this fact Sachs concluded that 

 if only the quantity and not the quality of the material circulating in 

 the sap determined the nature of organs, the Tropceolum should have 

 formed flowers; for the mass of the shoots formed in the dark was a 

 multiple of the mass of material required for the production of flowers. 



* Sachs, Staff und Form der Pflanzenorgane. Gesammelte Abhandlungen iiber Pflan- 

 zenphysiologie, Vol. 2, p. 1159, Leipzig, 1892. The reader will find a rather complete survey 

 of the literature on Regeneration in Morgan's book on this subject (T. H. Morgan, Regen- 

 eration, New York, 1901). 



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