124 



MISS M. E. J. CHANDLER ON THE 



fvol. lxxix, 



VII. Summary and General Conclusions. 



The relationship postulated between the different species of 

 Stratiotes may be summarized in the following diagram, which is 

 merely a suggestive phylogeny, and is not intended to illustrate 

 the precise limits in time of any of the species : — 



Subsidiary Line 

 of Evolution. 



Main Line of 

 Evolution. 



S. aloides. 



8. websteri. 

 S. thalictroides. • Bovey ? 



S. websteri. 



8. intermedins. 



8. tuberculatus. 



Time-Scale. 



Recent 



Pleistocene. 

 Upper Pliocene. 



Lower Pliocene. 

 Upper Miocene. 



S. kaltennordlieimensis. Lower Miocene. 

 Upper Oligocene. 



S. acuticostatus. 



8. neglectus. 



8. headonensis. 



Upper Middle 

 Oligocene. 



Lower Middle 

 Oligocene. 



Upper Eocene. 



Researches on Stratiotes have a botanical as well as a geological 

 significance. From the botanical point of view, it is interesting 

 to trace the varied history of a genus which is rnonotypic at the 

 present time. In regard to the geological value, it is hoped that 

 Stratiotes may eventually prove to be a useful time-index in cor- 

 relating isolated freshwater deposits, for the following reasons : — 



(1) We know that some species had a fairly wide geographical range : for 

 instance, S. ivebsteri and 8. kaltennordheimensis (pp. 128 & 130). 



(2) There is also good reason for supposing that each species had a limited 

 range in time : thus, in beds so near one to the other as the Bembridge and 

 Hamstead Series, there are distinct, though closely related, forms. 



(3) Finally, where Stratiotes occurs, it is abundant and readily recognized. 



There is one particular case in which it seems possible that this 

 plant may prove of use in correlation. S. websteri is known from 

 the Hamstead Beds and the Gyrena Marls of the Maj^ence Basin, 

 both of which are Middle Oligocene. It also occurs in the Bovey 



