REJUVENESCENCE IN NATURE. 231 



cells formed by vegetative growth into spore-sleep (see 

 Chlamidomonas, p. 215), the cell is regarded as one and 

 the same before and after this transition, in spite of the 

 difference of the condition ; but if the earlier envelope is 

 broken open or cast off in the transition to the new state, 

 the cell in its altered condition is regarded as a new one. 

 The loosening of the new cell from the old cell-membrane 

 takes place either by a contraction of the whole internal 

 body (including the primordial utricle), as, for instance, 

 in the formation of spores of most of the CEdogonia; or 

 it seems, vice versa, to be a swelling up of the contained 

 mass by occurrence of a secretion of cellulose, which 

 separates the primordial utricle from the cell-membrane, 

 as in the gonidia of (Edogonium, Draparnaldia, &c. The 

 reason of the loosening of the contents of the special 

 mother-cell shaping themselves into a pollen-cell, from the 

 wall of the former, is explained by Hofmeister* by the 

 specific nature of the substance secreted all over the 

 outer surface of the primordial utricle, which substance, 

 not adhering to the thickening layers of the walls of the 

 special mother-cells, forms the primary (subsequently the 

 inner) membrane of the pollen- cell. The following cases 

 may be cited, differing in the behaviour of the new cell 

 to the membranes of the mother-cell : 



a. The new cell slips out of the membrane of the 

 parent-cell : as in the active gonidium of Vaucheria, 

 (Edogonium, Bulbochcete, Braparnaldia, Stigeoclonium, 

 Chcetopliora, Coleochcete (see p. 183) ; the motionless 

 gonidium of Chantransia (p. 183) ; the spore of the 

 Eucoidese (p. 183). 



b. The membrane of the parent-cell peels off the new 

 cell : as in germinating cell developing from the spore 

 of Mosses and Ferns, which throws off a mere incrusting 

 membrane; and of theZygnemacese, which breaks through 

 a multiple spore-coat (p. 180). 



* Hofmeister, ' Uebcf die Eiitwiekliiug des Pollens,' (' Bot. Zcitung,' 

 184.8, p. 431.) 



