TYPES OF DTMORPHIC SPECIALIZATION. 39 



as thougii the relations that determine the expression of the char- 

 acters had a definite pohirity or repulsion so that the contrasted 

 extremes of a series are manifested rather than the intermediate 

 degrees. Arropic species, on the other hand, are composed of indi- 

 viduals of only one kind, manifesting individual variations, of course, 

 but with no definite tendency to the contrasted forms of expressions 

 shown in sexual or dimorphic characters.^ . 



On the basis of these distinctions the cotton plant and its relatives 

 would be reckoned as arropic species, since there is no sexual or other 

 differentiation into distinct types within the species. At the same 

 time it is obviously desirable to have a ready means of designating 

 different forms of structural speciaHzation in plant individuals whether 

 they belong to ropic or to arropic species. Plants that show obvious 

 differences of leaves and flowers are sometimes called heterophyllous 

 or heteranthous, but these terms record merely the fact of diversity, 

 which is often indiscriminate or intergratled, without any definitely 

 established tendency to contrasted expression of characters. 



For the designation of cases of definite dimorphic or polymorphic 

 specialization the word "ropic" may be used in combination with 

 other terms to indicate the part affected. Thus the variety of 

 Hibiscus cannahinus with the definite dimorphism of the leaves may 

 be described as phylloropic. Cotton, cofl'ee, cacao, and the Central 

 American rubber tree (Castilla) may be described as cladoropic, since 

 they all show definite specialization of two or more forms of branches. 

 Cacao and some varieties of cotton are phylloropic as well as clado- 

 ropic, for the two types of vegetative branches are accompanied by 

 definitely different types of leaves, which do not appear in coffee. 

 According to Went^, Castilla also has two kinds of leaves. 



The banana plant and the Indian corn are familiar illustrations of 

 a dimorphic condition of the flowers and may be termed anthoropic, 

 each plant bearing two definitely different kinds of flowers. A more 

 complicated case of specialization of floral differences appears in the 

 Central American rubber tree. The male or staminate individuals 

 bear only one kind of flowers, but the female or pistiUate trees bear 

 two kinds, each pistillate inflorescence being subtended by two small 

 staminate inflorescences, not of the same form as those that are found 

 on the purely staminate trees. The species as a whole shows a defi- 

 nite specialization of the sexes, but the female trees may be described 

 as anthoropic because of the two definitely different kinds of flowers. 



Many terms are used by students of plant pollination to indicate 

 whether the stamens and pistils are present together in the same 



1 Cook, O. F. Aspects of Kinetic Evolution. Proceedings of the Wasliington Academy of Sciences, 

 vol. 8, 1907, p. 369. 



-Went, F. A. F. C. Der Dimorphismus der zweige von Castilloa elastiea. Ann. Jardin Botanique 

 Buitenzorg, vol. 14, pp. 1-17. 

 221 



