BRANCHING (Fr. branche, branch. It. Sp. bronco, branch, claw, from Low Lat. bronco., claw, possibly from Lat. bra[e]chiont, arm. claw). There are two general types of branch ing, known as the 'dichotomous' and the `mono podial.' In the former, the apex of the axis forks, the old axis ending at the point of branch ing. In some cases three branches may arise in this way, resulting in 'trichotomy,' or even more than three branches may arise by the divi sion of a growing tip, but the term dichotomy is a general one, covering all cases of branches arising in this way. without reference to the number. Thallus bodies are particularly inclined to dichotomous branching. and hence its chief display is among the alga! and fungi, the liver worts, and the prothallia of ferns. Among seed plants there are cases which resemble dichotomy, as in the branching of the lilac, but this is `false dichotomy,' because, although two branches seem to arise front the apex of an axis in forking fashion, they are really lateral branches, the apex of the old axis remaining between them undivided but arrested in growth.
In monopodial branching the branches arise laterally from the axis. This type is character istic of the seed-plants, but it is found in the lower groups as well. In this case the tip of the main axis may continue to grow vigorously. and a central shaft may develop, as in the pines mid firs; such a habit is called 'exeurrent,' the main shaft 'running through' the whole branch sys tem. In other cases, as in the elm, some of the lateral branches are more vigorous than the main axis, which is presently lost sight of, and the trunk seems to be replaced above by a set of large divergent limbs, a habit called 'deliques cent,' meaning that the main axis is 'dissolved' into branches. Sometimes what appears to be the main axis is really a series of strong lateral branches which simulate it. A strong lateral branch appears just behind the tip of the axis, pushes it aside in its growth, and continues the direction of the main axis; then a lateral branch from this first branch does the same thing, and so on, until the principal axis consists of a series of strong lateral branches, as in the linden. Such an axis is called a 'sympodium,'
and this sympodial development is apt to be characteristic of groups of plants.
The branching, of roots is never so symmetrical as that of stems, the brandies arising from any point, while those of the stems are related very definitely to the nodes• at which the leaves ap pear. Another characteristic of root-branching is that the branches arise from the edit rill woody cylinder and burrow their way through the cor tex; while in stems the brandies arise super ficially. of eourse involving also the deeper tis sues. The root type of branch origin is said to be 'endogenous' ('inside origin'). and the stein type is 'exogenous' ('outside origin'). This is the proper application of the terms 'endogenous' and 'exogenous,' which were formerly misapplied to the stems of monocotyledons and dicotyledons respectively.
Leaves also frequently branch, and when the branches are quite distinct the leaves are said to be compound. This branching is determined by the venation. which is the system of vein branch ing. Accordingly. branching leaves may be either palmately or pinnately compound. See LEAF. BRANCHIOPODA, bran'k1-6p'ecda (Gk., gill footed, from bronchia, gills + rca;s, pons, foot), or ELTIIYLLOPODA. A suborder of Entomostraca, with numerous branchkr, or gills, attached to the feet; water-Ileas. The term has been used by different authors in a most con fusing manner, but the latest writers regard the group as a division of Phyllopoda. Used in this sense the Bra nchiopoda may lie defined as phyl lopods with numerous distinct trunk-segments and numerous pairs of swimming-feet. There are three families containing about a half-dozen genera and not many species. The families are distinguished by the carapace. which is wanting in one, shield-shaped in the second, and bivalve in the third.