26 MCRPiiOLOGICAL DEVELOPMENT. 



J-8 



gregate of the third order is thus produced. Bui though, 

 along with increased definiteness in the secondary aggregates, 

 there is here an integration of them so extensive and so re- 

 gular, that they are visibly subordinated to the whole they 

 form ; yet the subordination is really very incomplete. In 

 some instances, as in J. complanata, Fig. 47, the leaflets de- 

 velop roots from their under surfaces, just as the primitive 

 frond does ; and in the majority of the group, as in J. 

 capitata, Fig. 48, roots are given off all along the connecting 

 stem, at the spots where the leaflets or frondlets join it : the 

 result being, that though the connected frondlets form a 

 physical whole, they do not form, in any decided manner, 

 a physiological whole ; since successive portions of the 

 united series, carry on their functions independently of the 

 rest. Finally, the most developed members of the 



group, present us with tertiary aggregates that are phyaio- 

 logically as well as physically integrated. Not lying prone 

 like the kinds thus far described, but growing erect, the stem 

 and attached leaflets become dependent upon a single root or 

 group of roots ; and being so prevented from carrying on their 

 functions separately, are made members of a compound indi- 

 vidual there arises a definitely-established aggregate of the 

 third degree of composition. 



The facts as arranged in the above order, are suggestive. 

 Minute aggregates, or cells, the grouping of which we traced 

 in 182, showed us analogous phases of indefinite union, 

 which appeared to lead the way towards definite union. We 



