354 Floral Mechanism of Welwitschia mirabilis, Hooker. 



the tissues of the thigh may also help to prevent the damping of the crest of 

 the pulse waves. The leg arteries are probably held in a more supported 

 state, less labile, and for this reason also the pulse will be conducted to the 

 leg with less diminution in force. Size of lumen, resonance and lability are 

 three factors which may all take a part in the production of this phenomenon. 

 We have brought forward in this paper experiments which demonstrate these 

 factors at work. 



This research was carried out with the aid of a grant from the Eoyal 

 Society Government Grant. 



On the Floral Mechanism of Welwitschia mirabilis, Hooker. 

 By Arthur Harry Church, Lecturer in Botany, University of Oxford. 



(Communicated by Prof. A. C. Seward, F.R.S. Received December 23, 1913,— 



Read February 5, 1914.) 



(Abstract.) 



1. In the preparation of sectional schemes for the flowers of Welwitschia 

 mirabilis, in different stages of development, several points of interest were 

 noted as tending to throw light on the previous history of this unique floral 

 form. 



2. Evidence is adduced to show that the primary structural features of the 

 flowers are referable to an anthostrobiloid condition closely comparable with 

 that of Cycadeoidea, now expressed in a phase of minimum reduction, and to 

 be regarded as an example of heterophyletic convergence to a simple floral 

 construction in the gymnospermic condition. 



3. Secondary features of biological interest are mainly consequences of 

 xerophytic specialisation in the inflorescence ; condensation of the whole 

 system to a " cone " necessitates the extreme flattening of the flower in the 

 transverse plane, which has led to confusion in the interpretation of the facts 

 of development ; the andrcecium is represented by a true whorl of six 

 members. 



4. Similarly, secondary clisanthy in the cone mechanism necessitates special 

 features in the individual flowers, and accounts for the long exserted micro- 

 pylar tube of the ovulate flower, and the protrusion mechanism of the staminal 

 tube in the sterile flower. 



