THE MORPHOLOGICAL COMPOSITION OF PLANTS. 27 



see here among compound aggregates, as we saw there 

 among simple aggregates, the establishment of a specific 

 form, and a size that falls within moderate limits of varia- 

 tion. This passage from less definite extension to more de- 

 finite extension, seems in the one case, as the other, to be ac- 

 companied by the result, that growth exceeding a certain 

 rate, ends in the formation of a new aggregate, rather than 

 an enlargement of the old. And on the higher stage, as oa 

 the lower, this process, irregularly carried out in the simpler 

 types, produces in them unions that are but temporary ; while 

 in the more-developed types, it proceeds in a systematic way, 

 and ends in the production of a permanent aggregate that is 

 doubly compound. 



Must we then conclude, that as cells, or morphological 

 units, are integrated into a unit of a higher order, which we 

 call a thallus or frond ; so, by the integration of fronds, there 

 is evolved a structure such as the above- delineated species 

 possess ? Whether this is the interpretation to be given of 

 these plants, we shall best see when considering whether it is 

 the interpretation to be given of plants that rank above them. 

 Thus far we have dealt only with the Cryptogamia. "We 

 have now to deal with the Phauerogamia or Phanogamia, 



