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 
