CHAPTER VIII. 



THE SHAPES OF BRANCHES. 



221. AGGREGATES of the first order supply a few examples 

 of forms ramified in an approximately-regular manner, under 

 conditions which subject their parts to approximately-regu- 

 lar distributions of forces. Some unicellular Algae, becoming 

 elaborately branched, assume very much the aspects of small 

 trees; and show us in their branches analogous relations of 

 forms to forces. Bryopsis plumosa may 

 be instanced. Fig. 200 represents the 

 end of one of its lateral ramifications, 

 above and beneath which come others of 

 like characters. Here it will be seen that 

 the attached and free ends differ; that 

 the two sides are much alike; and that they are unlike the 

 upper and under surfaces, which resemble one another. The 

 more highly developed members of the same group of Algce, 

 the Siphonea, show a marked radial symmetry coexisting 

 with very elaborate branching, e.g., Neo- 

 meris, Cymopolia, and others. 



222. Fig. 201 shows us how, in an 

 aggregate of the second order, each proxi- ^ 

 mate component is modified by its rela- 

 tions to the rest; just as we before saw 

 a whole fungus of the same type modified 



56 145 



