I 3 4 RELATIONSHIPS OF SYMMETRY 



much further than the point of view established by Sprengel and 

 de Candolle. We know that dorsiventral construction of the flowers in 

 most cases is connected with pollination and only occurs in lateral flowers. 



INFLORESCENCES l . 



We have here, as in the case of the flowers, two cases to look at, 

 namely : inflorescences which are laid down as radial structures, and 

 only become dorsiventral by torsion of the flower-stalks or of the 

 internodes of the axis of inflorescence ; and inflorescences in which the 

 dorsiventrality exists from the beginning. Flowers on dorsiventral 

 inflorescences are usually only shortly-stalked, and to the inflorescence 

 is assignee! the task of bringing them into the correct position for 

 pollination. With regard to biological relationships we have to distinguish 

 two cases dorsiventral inflorescences are found in both anemophilous 

 and entomophilous plants. 



i. Anemophilous plants. In the inflorescences of Urtica dioica 

 Dorstenia, some Gramineae, and others, the flowers all stand upon the 

 upper side. In Urtica dioica the branches of the inflorescence also have 

 this position. We may perhaps find the biological significance of this 

 in Urtica dioica in connexion with the fact that the anthers explode, 

 for the pollen discharged as a small dust-cloud will have a better chance 

 of being transported by currents of air when sent upwards, than it would 

 have were it shot out in other directions. Urtica urens is monoecious and 

 its inflorescences are not dorsiventral. 



Dorsiventral inflorescences of a striking kind in which the spikelets 

 are inserted unilaterally on the whole inflorescence are found in many 

 grasses, for example, Chloris, Dactylis, and others. It is scarcely possible 

 to see a relationship to the environment in these ; but if we examine from 

 the comparative biological standpoint the arrangements of the inflores- 

 cence of grasses, it is evident that the configuration of the inflorescence 

 is so moulded that it can be easily moved by the wind. The slender 

 haulm, the spikelets, which in the quaking grass are seated upon long 

 thin stalks, the delicate spreading branches in others, all serve the same 

 end, which is also followed up in the configuration of the stamens, namely, 

 to secure the easy scattering of the pollen. Now unilateral inflorescences 

 occur, as far as I know, only in grasses which have shortly-stalked spikelets, 

 and where they are displaced to one side, as in Dactylis, they offer a larger 

 surface to the wind than they would do were they distributed equally 

 all round the axis. But even in the cases where the small number 

 of spikelets prevents us looking at them from this point of view, the 



1 See Goebel, Uber die Verzweigung dorsiventraler Sprosse, in Arb. d. hot. Inst. in Wurzburg, ii 

 (iSSo). 



