=831. The helicoid cyme.=—Where successive lateral branching takes place, and always continues on the same side a curved flower cluster is formed, as in the forget-me-not and most members of the borage family. This is known as a _helicoid cyme_ (fig. 453, _C_). Each new branch becomes in turn the “false” axis bearing a new branch on the same side. =832. The scorpioid cyme.=—_A scorpioid cyme_ (fig. 453, _B_) is formed where each new branch arises on alternate sides of the “false” axis. =833. The forking cyme= is where each “false” axis produces two branches opposite, so that it represents a false dichotomy (example, the flower cluster of chickweed). =834.= Some of these flower clusters are peculiar and it is difficult to see how the helicoid, or scorpioid, cymes are of any advantage to the plant over a true cyme. The inflorescence of the plant being determinate, if the flowering is to be extended over a considerable period a peculiar form would necessarily result. In the _helicoid cyme_ continued branching takes place on one side, and the result in the forget-me-not is a continued inflorescence in its effect like that of a continued raceme (compare shepherd’s-purse). But we should not expect that all of the complex and specialized structures from simple and generalized ones are beneficial to the plant. In many plants we recognize evolution in the direction of advantageous structures. But since the plant cannot consciously evolve these structures, we must also recognize that there may be phases of retrogression in which the structures evolved are not so beneficial to the plant as the more simple and generalized ones of its ancestors. Variation and change do not result in advancing the plant or plant structures merely along the lines which will be beneficial. The tendency is in all directions. The result in general may be diagramed by a tree with divergent and wide-reaching branches. Some die out; others remain subordinate or dormant; while still others droop downward, showing a retrogression. But in this backward evolution they do not return to the condition of their ancestors, nor is the same course retraced. A new downward course is followed just as the downward-growing branch follows a course of its own, and does not return in the trunk. CHAPTER XLIII. POLLINATION. Origin of heterospory, and the necessity for pollination.