DORSIVENTRAL SHOOTS. POSITION OF ORGANS 85 



that is to say, the wood grows more towards the upper or towards the 

 under side and thus the pith acquires an excentric position. I may 

 mention here, quoting Wiesner, the following facts regarding the plagio- 

 tropous shoots of trees and shrubs : 



(1) The Coniferae are hyponastic. 



(2) Broad-leaved trees with feebly developed or no anisophylly show 



at first a radial condition of the wood, whilst later it is epinastic 

 and finally is hyponastic. 



(3) Broad-leaved trees with strong anisophylly are at first hyponastic, 



then become epinastic, and finally hyponastic again. 



(4) In many shrubs, for example Lycium barbarum and Berberis 



vulgaris, the axes remain radial. 



We do not know the causes which bring about the epinasty and 

 hyponasty ; it is only clear that plagiotropous growth excites it. The 

 phenomena of varying predominance in growth of the upper and the under 

 side are exhibited not only by the wood but appear also elsewhere. We 

 see them in the secondary rind in many woody plants and in the peripheral 

 fundamental tissue upon the upper and the under side of young shoots. 

 The creeping shoots of Nuphar luteum have a radial terminal bud, but 

 they subsequently become dorsiventral and creep upon the soil under the 

 influence of unilateral illumination, as will be shown in the Fifth Section ; 

 the leaf-scars upon the upper side are then far apart but are more 

 closely set on the under side. The needles in many Coniferae (spruce, 

 yew, and others) show like features, only not so strongly, and they 

 are also to be found on the plagiotropous shoots of Elatostemma and 

 Goldfussia anisophylla. 



2. RELATIONSHIPS OF POSITION. 



The dorsiventral construction expresses itself, in the second place, in 

 the different relationships of position of the lateral shoots of the two sides. 

 By ' dorsal side ' in creeping, climbing, and swimming shoots we mean the 

 upper side, the ventral side is the under side. A peculiarity of the 

 vegetative point which we meet with in a number of dorsiventral shoots 

 belonging to the most different divisions of the Vegetable Kingdom is often 

 associated with the difference in these two sides, namely, a strong 

 incurving or involution of it which secures the protection of the embryonal 

 tissue. A similar feature is observable in the leaves of ferns, species of 

 Drosera, and other plants. In Fig. 40 there is a representation of such 



Allgemeine Morphologic, p. 604 ; Kny, Uber das Dickenwachstum des Holzkorpers, in Sitzungsber. 

 d. Gesellsch. naturforsch. Freunde zu Berlin, 1877 ; Wiesner, Untersuchungen iiber den Einfluss der 

 Lage auf die Gestalt der Pflanzenorgane, in Sitzungsber. der Wiener Akad. 1892. Wiesner has 

 introduced the terms ' epitrophy ' and ' hypotrophy ' for epinasty and hyponasty, as the latter have 

 been applied in a different sense. 



