346 



There is a likelihood of some of these being refound ; but, on the other 

 hand, there are some ' very rare ' species which, in a few years' time, must 

 be added to this list. Such are some Ferns and those semi-maritime plants 

 which still maintain their ground in the Isle of Dogs, e. g. Petroselinum, 

 segetum, Aster, Samolus, Scirpus maritiinus, Sclerochloa distans. 



III. Comparison with the ' Cybele Britannica.' — In vol. iv. of the Cybelc 

 the number of species for the whole of Great Britain is reckoned as 1,425. 

 Adopting the same specific limits, and fitting the foregoing enumeration to 

 Mr. Watson's list {Cyb. Br. iv. pp. 175-233), we have in Middlesex 826 

 species. 



In the list just referred to the plants are distinguished as respectively be- 

 longing to certain ' types of distribution ' (explained in Cyb. Br. iv. pp. 

 499-519, and better in Comp. pp. 23-32) ; of these the following table 

 shows the numbers for the whole of Great Britain, and for Middlesex : — 



At pp. 234-281 of the same vol. of the Cyhde is a list of the 1,425 British 

 species, arranged in a series according to their relative frequency, tested 

 by the occxirrence in, or absence from, the 38 sub-provinces into which Great 

 Britain has been divided by Mr. Watson. 



The list begins with the commonest plants, or those which occur in aU the 

 sub-provinces. We want in Middlesex the following : — 



