﻿The Evolution of Assimilating Tissue in Sporophytes. 



By Carlton C. Curtis. 



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author very justly ascribes an important place to the poet Goethe, 

 whose treatise on the metamorphosis of plants, however fanciful the 

 dream, it must be admitted, suggested lines of investigation which 

 have yielded such important results in every department of botany, 

 originating the study of the history of development and paving the 

 way for the spread of the idea of the transmutation of species. 

 The absurd speculations of the philosophy of Goethe and of his 

 time have passed away; still his doctrine of leaf metamorphosis, 

 though not originating with him more than with Cesalpino and 

 Linnaeus, has been generally accepted. Goethe's ideal or typical 

 plant with its six stages of development, cotyledon, leaf, sepal, petal, 

 stamen and corolla, appearing in three wave crests or expansions, 

 (leaf, petal and carpel), and three wave troughs or contractions 

 (cotyledon, sepal and stamen) has had in the popular mind some- 

 thing more substantial in its conception than the stuff of which 

 dreams are made. At the present time these organs are quite 

 generally regarded as due to the gradual metamorphosis in acro- 

 petal succession of parts which are identical in origin ; and, though 

 not ascribing the change to the clarification and refinement of the 



ascending sap, we have come to look upon the metamorphosis as a 



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progressive one from primordial leaf to carpel. As a matter of 

 fact, however, there is probably no evidence of the metamorphosis 

 of a leaf into any member of the flower, especially into one of the 

 essential parts. The evolution of plant types points to an entirely 

 distinct origin of the organs of assimilation and propagation and 

 indicates very clearly the priority of the latter in point of time. 

 Among lower forms, as the Algae, when an alternation can be 

 traced, there is no indication of assimilatory tissue in the sporo- 

 phyte, it being simply a sporangium. This is essentially true of 

 the lower Hepaticae, as in Riccia, the fertilized egg of the arche- 

 gonium is developed as a sporangium surrounded by a single 



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