TRANSACTIONS OF SECTION D. 



695 



function by the Wolffian duct, may have been effected subsequently to the 

 formation of the Miillerian oviduct. And further comparison of the Dipnoi with 

 the Elasmobranchii suggests that the former may have struck off from the 

 HolocephaUc branch of the latter before the differentiation of the ancestors of its 

 existing members. 



The following diagram expresses the relationship of the reproductive system of 

 fishes, as estimated upon the foregoing considerations : — 



NephrAnJizdir 



11. On the Recent Visitation of Plutella Crucifera. By W. Freaii. 



TUESDAY, AUGUST 25. 



The following Papers were read: — 



1, On the Artificial Production of BJiytJim in Plants. 

 By Pkancis Darwin and Dokothea F. M. Pertz. 



The apparatus employed is a new form of klinostat designed by the Cambridge 

 Scientific Company. The plant to be experimented on is fixed to a spindle, which, 

 by means of a clockwork escapement, makes a sudden semi-revolution every half 

 hour. Thus the plant is subjected to a series of alternate and opposite influences 

 from light or gravitation as the case may be. To take the case of gravitation, 

 the plant will tend to curve upwards during the first half hour, and during the 

 second interval (when the horizontal spindle has made half a turn) it will tend to 

 curve geotropically in the opposite direction. 



Under these conditions it is found that a rhythmic state is induced which 

 closely resembles the periodicity in rate of growth which is set up in plants by 

 the alternation of day and night. 



A remarkable result is obtained by stopping the clockwork — that is to say, by 

 substituting a continuous for a changing stimulus. The plant continues to curve 

 with an acquired rhythm just as if the clockwork were still in action ; it has, ia 

 fact, learned and remembered the half-hourly period. This is precisely similar to 

 certain natural rhythms — for instance, to the ' sleep ' of flowers, which for a short 

 time continue to open and shut although kept constantly in the dark. 



2. On Floating Leaves. By Professor Mxall, F.L.S. 



