THE BEGINNINGS OF LIFE. 



217 



Simple livi 



tive 



Mace to 



niateriai 



place 



e 



^ble to divid 



^e a cell-wall 

 may arise in 



to be 



only a 



-X condition, 

 independent 



[pressed were 

 Q he said ' ;- 



ich forms its 

 the crab does 



■elopes form 



fact must 

 uireii' 



av 



) 



in 



T is acq 



ical activity 

 uct deposited 



g 



» 



I 

 f 



I 



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» 



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cell-coat^ as a product of cellular activity, always stands 

 in inverse proportion to the physiological activity of 

 the cell. In youth, thin^ soft, and extensible, the cell 

 coat allows abundant nutrition and advancing growth; 

 subsequently, thickened and therewith hardened by the 

 deposit of lamellae^, it compresses the contents within 

 continually narrower boundaries, more and more ex- 

 cludes intercourse with the external world, and puts 

 a term to growth/ 



Taking that view of the case, therefore^ which would 

 alone seem tenable in our present state of knowledge, 

 it could not be imagined that any changes occurring 

 in a simple living unit, or plastide^ would be essen- 

 tially altered in character because its external layers 

 had become condensed into a so-called cell-membrane. 

 It is useless, also, to resort to the nucleus as an element 

 possessing a mysterious power of its own, and to attri- 

 bute, as was formerly the case^ all the important phe^ 

 nomena occurring within a Cell to the effects of its 

 influence. We are told by Nageli^ that whole families 

 of plants are devoid of anything like a nucleus, and 



^ This more especially refers to the thickening and condensation of 

 the wall which takes place in many vegetable cells. 



^ Speaking of the occurrence of this previously supposed necessary 

 element of the cell, Braun says (loc. cit. p. 174): — ' Nageli's extensive 

 researches have demonstrated its occurrence in all divisions of the 

 vegetable kingdom; only in particular families of the Algse, as, for 

 example, in the Palmellacese, Chlorococcacese, Oscilatorinese, and Nosto- 

 chineae, as also in the large-celled Cladophorce, and the unicellular Algae 

 with unlimited growth of the cell {Vancheria, Codimn, Cmderpd), no 



trace of a nucleus has yet been discovered/ ; 



