§ 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-regular distributions of forces. Some unicellular _Algæ_, 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 _Algæ_, the _Siphoneæ_, show a marked radial symmetry co-existing with very elaborate branching, _e.g._, _Neomeris_, _Cymopolia_, and others. [Illustration: Fig. 200.] § 222. Fig. 201 shows us how, in an aggregate of the second order, each proximate component is modified by its relations to the rest; just as we before saw a whole fungus of the same type modified by its relations to environing objects. If a branch of the fungus here figured, be compared with one of the fungi clustered together in Fig. 195, or, still better, with one of the laterally-growing fungi shown in Fig. 196, there will be perceived a kindred transition from radial to bilateral symmetry, occurring under kindred conditions. The portion of the pileus next to the side of attachment is undeveloped in this branched form as in the simpler form; and in the one case as in the other, the stem is modified towards the side of attachment. A division into similar halves, which, as shown in Fig. 196 _e_, might be made of the whole fungus by a vertical plane passing through the centre of the pileus and the axis of the supporting body, might here be made of the branch, by a vertical plane passing through the centre of its pileus and the axis of the main stem. Among aggregates of this order, the _Algæ_ furnish cases of kindred nature. In the branches of _Lessonia_, Fig. 37, may be observed a substantially-similar relationship. As their inner parts are less developed than their outer parts, while their two sides are developed in approximately equal degrees, they are rendered bilateral. [Illustration: Fig. 201.]