REJUVENESCENCE IN NATURE. 145 



we have seen in the lower stages, where each cell strives 

 to vegetate for itself alone. The development of different 

 ranks of cells, with which is connected the realisation of 

 the organic differences in the vegetative sphere, in the 

 higher plants, is chiefly attained by the above-mentioned 

 production of daughter-cells of different kinds in one and 

 the same mother-cell, therefore by differing sister-cells. 

 We will examine this condition in a few examples of the 

 simplest kind, so as to indicate the path by which nature 

 advances in the production of the multiplicity of cell- 

 formation of one and the same plant. 



We meet with the first separation of vegetative per- 

 manent cells from series of generations terminating in 

 reproductive cells, in the Nostoc-hke Algae. The 

 necklace-like filaments of Nbstoc, composed of a row 

 of cells, exhibit at one or both ends, as also here and 

 there in the course of the filament, particular cells 

 distinguished from the rest by size, regular rounding, 

 thick membrane, and pale, homogeneous contents ; 

 while the remaining, smaller, thin-coated cells, filled With 

 darker and often granular contents, continue to multiply 

 in rapid succession by division, until they finally, in the 

 last generation, fall apart as germ-cells, exhibiting no 

 perceptible difference from the preceding generations. 

 The large terminal and interstitial cells just named 

 remain almost imchanged, neither undergoing further 

 vegetative division, nor taking part in the propagation.* 



The origin of these peculiar boundary-cells can only 

 take place by certain of the cells dividing into two unlike 

 daughter-cells, one of which becomes a vegetative per- 

 manent cell, the other a mother-cell of a series of uniform 

 generations of cells, terminating in fructification. It is 

 probable that the very first cell (the germ-cell) divides in 

 this way into two unlike cells, f and then, when a filament 



* These cells have been hitherto incorrectly regarded as seed-cells, 

 (spermaiia, Kg.). 



t Very youag plants of Nostoc (or Hormosiphon I'), exhibited a short fila- 

 ment enclosed by a gelatinous vesicle, having a boundary-cell only on one 

 side, and this lying outside the gelatinous vesicle. 



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