98 Origin of the British Flora. 



a later comer needing the same station finds the ground 

 pre-occupied. All the proved cases will now be brought 

 together; but, as this chapter is merely a record of facts, 

 it does not seem advisable at present to deal with the 

 converse side of the question, that is to say with the 

 noticeable absence of many of our most common living 

 species. This deficiency, also, may be apparent only, not 

 real, and till we have a fuller knowledge of the fossil 

 plants it is undesirable to throw out suggestions which 

 to-morrow's work may show to be founded on nothing 

 more than the incompleteness of our search. 



The exotic plants which have as yet been recorded as 

 British fossils are only six ; but I may repeat, in a more 

 general sense, the remarks already made, with regard to 

 the plants of one locality, and say that in reality the pro- 

 portion of exotic species must be considerably greater. 

 These are the plants for the determination of which it is 

 most difficult to obtain the necessary material. Botanists 

 seldom collect plants in fruit, and, if they do, the ordinary 

 method of preserving specimens is not suitable, as most of 

 the seeds that are ripe, or nearly ripe, fall out and are lost 

 in drying. My own collection of recent seeds and fruits 

 includes only a small proportion of exotic forms ; but I 

 have examined various fossil seeds which certainly do not 

 belong to any living British plant, and are quite determin- 

 able, if only sufficiently complete continental collections 

 were available. 



Papaver somniferum has only been found at Cowden 

 Glen, and in face of the great uncertainty as to the age 

 of the peaty deposit at that place I do not feel prepared 

 to accept it as a true fossil, though the opium-poppy was 

 apparently grown in Switzerland in Neolithic times. 



Acer monspessulanum occurs in Interglacial deposits at 

 Selsey, in Sussex, and at Stone, in Hampshire. It now 



