Some Questions which they Suggest. 65 



cell of the growing points in plants. We now see a 

 differentiation of parts arising without any such cell to 

 divide, and without any septa to mark off the future organ. 

 The protoplasm is the master: the cell-walls are its 

 humble servants, and we have another illustration of how 

 the contents are apt to rule the containing structure, and 

 the soft to rule and mould the hard. The divisions of the 

 cell-walls are a secondary and subordinate phenomenon. 



ISOMORPHISM. We crave our readers' leave to return to 

 the fact already mentioned, that unicellular organisms 

 have a tendency to imitate the forms of cellular organisms, 

 and that whereas we have in the series and chain of cellular 

 plants such marked outward forms as those of the moss, 

 the lycopod, the conifer, the cactus, &c., we have in the 

 chain of unicellular plants very similar outward forms, so 

 that we seem to have two chains branching off from one 

 another, with links here and there which closely corre- 

 spond with one another. This phenomenon is one found 

 frequently to present itself to the attention of the philo- 

 sophical systematist, and like all the phenomena of 

 Nature is well worth pondering. It has been stated very 

 forcibly by Mr. Brady, in respect to the Foraminifera, 

 a group of organisms deeply studied by him : " A 

 purely artificial classification is ill-adapted to the 

 conditions presented by a class of organisms like the 

 Foraminifera, largely made up of groups of which the 

 modifications run in parallel lines. This ' isomorphism ' 



exists not merely between a single series 



in one of the larger divisions, and a single series in 



