352 METAMORPHOSIS 



conclusion in the next lecture. We need only add at present that the capacity 

 for life in embryonic cells is retained only if they be active and have the power 

 of growing and dividing ; if this capacity be lost they are doomed sooner or 

 later. We have already shown that in seeds and similar structures the inactive 

 protoplasm for long (but not indefinitely) retains its power of development ; 

 active merismatic regions die off much more rapidly if they be prevented from 

 growing. Root apices, for example, confined within plaster of Paris died off in 

 about ten weeks according to PFEFFER'S experiments (1893, 356). 



Bibliography to Lecture XXVII. 



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BARANETZKY. 1879. Mem. de 1'acad. de St. Petersbourg, vn, 27. 



BUSGEN. 1901. Allg. Forst- u. Jagdzeitung (August). 



FISCHER, A. 1890. Jahrb. f. wiss. Bot. 22, 73. 



GODLEWSKI. 1889-90. Anzeiger d. Akad. in Krakau. 



GOEBEL. 1880. Bot. Ztg. 38, 753. 



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[GOEBEL. 1905. Flora, 95.] 



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Nov. 1901). 



KiiSTER. 1898. Fiinfstuck's Beitr. z. wiss. Bot. 2, 401. 

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LECTURE XXVIII 

 PERIODICITY IN DEVELOPMENT. II 



REFERENCE was made incidentally in the last lecture to the periodic alter- 

 nation of foliage and reproductive-leaves in ferns and flowering plants, and the 

 reason for the difference in form and anatomical structure of these two types 

 of leaf, we found, lay in the different functions fulfilled by them. The repro- 

 ductive-leaves have assigned to them the formation of sporangia, the specific 



