STUDIES ON THE PLANT CELL.— II. 



BRADLEY MOORE DAVIS. 



The Activities of the Plant Cell. 

 I. Vegetative Activities. 



Every cell passes through a history whose events repeat in a 

 broad way activities that have become established in the organ- 

 ism by the experience of its ancestors. The most important of 

 these events is nuclear division, which is accompanied in most 

 plants by cell division, the important exceptions being certain 

 groups whose protoplasm is multinucleate throughout all, or 

 almost all, vegetative conditions {e. g., coenocytic Algas and 

 Fungi, Plasmodia and multinucleate cells in various tissues). 



Protoplasm, whose nuclei can no longer divide, becomes inca- 

 pable of reproducing itself and must take a dependent position 

 in the organism, where the length of its life will be determined 

 by the good fortune of its environment and its vitality. Such 

 protoplasm becomes strictly vegetative in its functions, and while 

 these activities may be very highly specialized and of the utmost 

 importance to the organism as a whole, nevertheless such a cell 

 has lost certain of the constructive, and in consequence repro- 

 ductive, possibilities characteristic of living matter. ^ The most 

 evident and important of these constructive activities have to do 

 with the increase of nuclear material (chiefly chromatin), which 

 leads to its distribution through nuclear division, and the devel- 

 opment of a complicated mechanism (the spindle) to effect this 

 result. 



As Weismann first pointed out, from the standpoint of cell 

 studies, there is a stream of germ plasm flowing with every spe- 

 cies, protoplasm relatively fixed in its characteristics and poten- 

 tially immortal. The chief peculiarities of germ plasm are its 

 reproductive powers and the generalized structure that enables it 

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