The general rule which correlates this polymorphic change is that its direction changes at a given temperature.
Klebs has, however, recently canvassed the conclusions of both these investigators; and as the result of his own observations declares that algae, so far from being as polymorphic as they have been described, vary only within relatively narrow limits, and present on the whole as great fixity as the higher plants.
Bartlett, that every ruff assumes tufts and frill exactly the same in colour and markings as those he wore in the preceding season; and thus, polymorphic as is the male as a species, as an individual he is unchangeable.
One of these sub-species, merope, which ranges from the west coast to Victoria Nyanza, is polymorphic and occurs under three forms, namely (a) hippocoon, which mimics the Danaine Amauris niavius; (b) trophonius, which mimics the Danaine Limnas chrysippus; (c) planemoides, which mimics the Acraeine Planema poggei.
Panicum, a very polymorphic genus, and one of the largest in the order, is widely spread in all warm countries; together with species of Paspalum they form good forage grasses in the South American savannas and campos.