40 DIMORPHIC LEAVES IX RELATION TO HEREDITY, 



inflorescences, separated in different flowers of the same plant or on 

 difl'erent plants, or whether these organs are alike or different among 

 themselves or ripen at the same or at different times. Yet these 

 terms do not indicate whether the different conditions arise bv gradual 

 changes in the expression of the characters or whether the other floral 

 parts are different, as well as the stamens and pistils. 



Technical terms can often be avoided in describing the details of 

 structure or behavior in any one species or genus of plants, but they 

 become a practical necessity in the scientific task of comparing and 

 contrasting the behavior of different types of plants. Distinctions 

 need to be carefully drawn so as to recognize as definitely as possible 

 the different kinds of diversity that arise because of the different ways 

 in which the expression of the characters is determined. In some 

 cases it is plain that the external conditions are able to influence the 

 expression of characters during the development of a branch, while in 

 other cases determination of characters of branches and leaves seems 

 to be entirely independent of the environment. It is desirable, there- 

 fore, to review briefly the terms that have been applied by morpholo- 

 gists to the structural diversities that most nearly resemble the present 

 cases of dimorphic leaves and branches. 



Goebel refers to upright shoots of conifers and similarly specialized 

 trees as orthotropes, and lateral or horizontal shoots as plagiotropes; 

 he also considers that the specialization of the lateral shoots (lateral- 

 ity) is of two kinds, called "labfle induction" when the lateral 

 branches are able to assume the functions of uprights, as in Picea, 

 and "stabile induction" when such substitutions can not be made. 

 There is also a distinction to be drawm between two kinds of "stabile 

 induction" of laterality. In some cases the lateral branches are 

 readily able to regenerate upright shoots from lateral buds, as in 

 cotton, while in other cases the lateral branches seem to have no 

 power of replacing the uprights, even from latent buds. This ex- 

 treme type of specialization shown in coffee, Castilla, and cacao has 

 also been demonstrated by Goebel in Phi/llanthus lathyroides.^ 



The terms clinomorphy and anisophylly have been used by Wiesner 

 for adaptive modifications of leaf forms connected wdth differences of 

 position or exposure, but not in relation to dimorphism or contrasted 

 expression of characters as a definite fact of heredity.^ 



» Goebel, K. Einleitiing in die Experimentelle Morphologie der Pflanzen, 1908, pp. 80-8S. 



2 In Biologic der Pflanzen. Vienna, 18S0. Wiesner states: " Many format ive processes in plants are induced 

 by the inclination of the organs to the horizon. All phenomena of development induced through position, 

 not explainable through the effects of gravitation alone, should be comprehended under the name clino- 

 morphy. Clinomorphy appears if an organ in the course of its development is so inclined to the horizon 

 that one can distinguish an upper and an under side, and consists in the fact that the upper half takes 

 another fjrm than the lower." (P. 28.) 



"Anisophylly is only an inequality of the foliage of the shoot in relation to position and is shown in Uw 

 under leaves of a shoot becoming larger and heavier than the upper." (P. 33.) 

 'I'll 



