THE MORPHOLOGICAL COMPOSITION OF PLANTS. 31 



parent-frond is comparatively irregular in form, and without 

 a mid-rib; and along with this very imperfect integration, 



we see that the secondary fronds growing from the edges are 

 distributed very much at random, and are by no means 

 specific in their shapes. A considerable advance is displayed 

 by Pliylloplwra rubens, Fig. 39. Here the frond, primary, 

 secondary, or tertiary, betrays some approach towards regu- 

 larity in both form and size; by which, as also by its 

 partially-developed mid-rib, there is established a more 

 marked individuality; and at the same time, the growth of 

 the secondary fronds no longer occurs anywhere on the edge, 

 in the same plane as the parent-frond, but from the surface 

 at specific places. Delesseria sanguined, Fig. 40, illustrates a 

 much more definite arrangement of the same kind. The 

 fronds of this plant, quite regularly shaped, have their parts 

 decidedly subordinated to the whole; and from their mid- 

 ribs grow other fronds Avhich are just like them. Each of 

 ? these fronds is an organized group of those morphological 

 units which we distinguish as aggregates of the first order. 

 And in this case, two or more such aggregates of the second 



