REJUVENESCENCE IN NATURE. 233 



of the formation of two cells inside each mother-cell, it 

 will be equally correct in the other to call it a forma- 

 tion of one cell inside each mother-cell. In many cases, 

 indeed, it is altogether indifferent as regards the develop- 

 ment of the plant, whether such division takes place or 

 not. Compare, for example, H. von MohPs description 

 of some of the epidermal cells of Viscum album* which 

 is equally fitted to illustrate the inessentiality of individual 

 cell-divisions, and the agreement of the behaviour of the 

 membranous layers of new cells produced by division, 

 with that of simultaneous thickening layers of undivided 

 cells. In like manner it is often indifferent in the forma- 

 tion of reproductive cells, whether the contents of the 

 mother-cell are transformed into a spore or gonidium 

 undivided, or divided into two cells. Thus in Coleocliaete 

 scutafa, two gonidia are sometimes formed in one parent- 

 cell (by division of the contents) instead of one ; in 

 Aphanocluete repens (p. 184), on the contrary, it often 

 appeared to me that only one gonidium existed instead 

 of two (through omission of the dividing process) ; in 

 Stigeoclonium there occurs, in addition to the ordinary 

 formation of gonidia, a formation of microgonidia, in 

 which several gonidia are produced, instead of one, in a 

 mother-cell (see p. 139). 



As to the great, even universal extent of the occur- 

 rence of division, and, in fact, halving of the 'cells, in the 

 development of the tissues of the vegetable organism, all 

 the most trustworthy of modern phytotomists, particu- 

 larly Mohl, Nageli, linger, and Hofmeister, are agreed, 

 although they differ, in some respects, in their ways of 

 conceiving the dividing process ;f even Schleiden, who, 



* ' Ueber die Cuticula von Viscum album? (Bot. Zeit., 1849, p. 593, 

 t. ix, p. 59.) 



f Note the following passages : " These researches have led me to the 

 conclusion, that all vegetative cell-formation is a parietal cell-formation" 

 (= cell-division). (Nageli, ' Zeitschrift,' 1847, p. 49, Transl. in Ray 

 Society's publications, 1849, p. 121.) "As regards, in the first place, 

 vegetative cell-formation, I believe \ am justified by comprehensive researches 

 in the Algae, Fungi, Floridcse, Mosses and Charse, in the Vascular Crypto- 



