THE MORPHOLOGICAL COMPOSITION OF PLANTS. 27 



irregularly tubular; as in Enteromorpha intesiinalis, Fig. 27. 

 And often, as in Enteromorpha compressa, Fig. 28, and other 



2S 



species, this tubular frond becomes branched. Figs. 29 and 

 30 are magnified portions of such fronds, showing the 

 simple cellular aggregation which allies them with the pre- 

 ceding forms. 



In the common Fuci of our coasts, other and somewhat 

 higher stages of this integration are displayed. We have 

 fronds preserving something like constant breadths and 

 dividing dichotomously with approximate regularity. Though 

 the subdivisions so produced are not to be regarded as 

 separate fronds, but only as extensions of one frond, they 

 foreshadow a higher degree of composition; and by the com- 

 paratively methodic way in which they are united, give to 

 the aggregate a more definite, as well as a more complex, in- 

 dividuality. Many of the higher lichens exhibit an 

 analogous advance. While in the lowest lichens, the different 

 parts of the thallus are held together only by being all 

 attached to the supporting surface, in the higher lichens the 

 thallus is so far integrated that it can support itself by 

 attachment to such surface at one point only. And then, in 

 still more developed kinds, we find the thallus assuming a 



