PRESIDENT'S ADDRESS. 9 



the last issued ; 900 species of Cratsegus from the United 

 States are now recognised, and in the Proceedings of the 

 Royal Irish Academy a Report on the Mosses of Ireland is 

 given, 118 new species having been added since 1872. The 

 immense number of so-called American species of Cratsegus 

 reminds one of the great number of species of brambles and 

 roses which have been described by some of our botanists, 

 and which doubtless present points of difference amongst 

 themselves, but as to how far each so-called species would 

 permanently reproduce itself and remain constant is a 

 difficult question. Some of the low forms of life are very 

 uncertain in their appearance, for instance, a fresh water 

 Alga (Hydrodictyon reticulatum) , which is rarely seen in 

 this country, was found in the autumn of 1914 in the 

 lake at Kew, in enormous quantities, so that it had to be 

 cleared from the water. It has been found that many of our 

 cultivated varieties of fruit trees, apple, pear, plum, &c., 

 are self sterile and only produce fruit when fertilized with 

 pollen from some other variety. It is therefore necessary 

 to pay attention to this fact when planting orchards. 



GEOLOGY. 



A full report of the excavation of the Dewlish Elephant 

 Trench is published in our last volume of Proceedings, which 

 makes it clear that the trench was formed by natural forces 

 and not by human agency, though there are differences of 

 opinion as to the method, and some minor points, such as 

 the way in which the brilliant polish on many of the flints 

 was produced appear to me to require further elucidation. 

 I have specimens of extremely similar polished flints from a 

 fissure at Portland, but did not see them in situ.* I under- 



*It had occurred to me whether the rubbing together of the flints 

 under pressure in the fissure could have produced the polish, and 

 Captain G. R. Elwes has now shown by actual experiment that a 

 brilliant polish can be produced on some pebbles by merely rubbing 

 them together for a considerable time. 



