THE OREEN OI<^LLS OP CONYOI.UTA ROSCOFFENSlF^. 197 



drawn — tliat the green cells o£ Convoluta are withont cell- 

 Avalls, for it is well known that the nucleus of the plant-cell 

 presides over cell-wall formation. An enucleated fragment 

 of a plant-cell; though capable of performing certain vital 

 processes — e. g. photosynthesis — is unable to form a new wall. 



We may therefore regard the suppression of cell-wall as the 

 first result of a pi-ogressive nuclear degeneration. Enough, 

 however, of the nucleus is loft to preside over cell-division, 

 which proceeds rapidly after infection ; as this division goes 

 on less and less nuclear material remains, till finally partial 

 cells, incapable of independent life and probably also incapable 

 of further division, alone are left. 



It is noteworthy that we have come across no evidence of 

 mitosis in the dividing green cells of the animal. 



A significant phenomenon is revealed by a reference to 

 Figs. 9 and 10, pi. 13, and to the description thereof. Here, 

 as at {Nu., gc), ai-e isolated green cells, in each of which a 

 nucleus is recognisable; in other parts of the section are 

 ingrowing rows of cells budded off from the outermost cell, 

 and of these rows only the outermost cells contain a distinct 

 nucleus; others contain only deep-staining granules; and 

 others, again, no nuclear substance whatever (Fig. 9, pi. 13). 



A parallel suggests itself between the green cells of Con- 

 voluta and the led blood-cells of the higher vertebrates. As 

 the red discs are enucleate partial cells budded off from the 

 nucleated red cells, so may the green cells be regarded as 

 enucleate partial cells budded off from the outermost row of 

 nucleated green cells, and as the red discs are of limited life 

 and specialised (respiratory) function, so are the green cells 

 of limited life and of specialised (photosynthetic) function. 



The green cell devoid of a nucleus of its own would not, 

 however, appear to be shut off from all nuclear influences. 

 For the enucleate green cell may be connected by a finely 

 drawn process with another green cell still possessed of 

 nuclear substance (PI. 13, fig. 9). Moreover, such green 

 cells as are without nuclear material are accompanied each 

 by a large attendant nucleus of animal origin ; this close 



