REJUVENESCENCE IN NATURE. 239 



mordial utricle of the mother-cell (analogous to the 

 nucleus of it) is here totally dissolved and reconstructed. 

 For the former view, for a total solution and reformation 

 of the primordial utricle, it seems to me that no sufficient 

 reasons can be found, at all events in ordinary vegetative 

 cell-formation ; but if a total solution of the primordial 

 utricle does not take place, but merely an interruption of 

 its continuity in the periphery of the place of division, 

 the hypothesis of a completion of the primordial utricle 

 for each of the daughter-cells, through a formative move- 

 ment issuing and advancing from the parts already 

 formed, which is demonstrated by observation in Clado- 

 phora and Spirogyra, appears to me not improbable, even 

 for the seeming simultaneous division. The principal 

 distinction between these two cases depends evidently on 

 the age of the cell at which the division takes place. 

 There are cells which never become old, but in their 

 earliest age, by dividing, give up their existence again, or 

 rather continue it in a new generation, till age is finally 

 attained in a last generation, which never undergoes 

 division. This is the condition in the cells of the young 

 tissues of the higher plants, which often divide again 

 when scarcely formed, still small, and thin-walled, with 

 comparatively large nuclei, and abundant viscid con- 

 tents. To such cells, which have not yet lost the 

 character of youth, belongs the apparently simultaneous 

 cell-division. Hofmeister* expressly remarks that this 

 kind of cell-formation takes place everywhere that the 

 volume of the mother-cell does not very considerably 

 exceed (at least about sixteen times) the circumference of 

 the nuclei of the new daughter-cells to be formed. On 

 the other side, there are cells (probably only in the lowest 

 stages of the Vegetable kingdom) which may be said 

 never to be young, since they display from their earliest 

 origin the characters of old cells ; for instance, a nucleus 

 (perhaps sometimes altogether deficient) very small in 



* 'Die Eiitstehung des Embr. der Phanerog.,' p. 1. 



