THE DISPERSION OF BRITISH PLANTS. 249 
by winds, currents, or birds, increases as the distance to be traversed 
_ diminishes ; and in Northern seas it is considered that icebergs serve 
_/ a8 means of conveyance : it is obvious, therefore, that Northern 
igration 
each other than at present. 
Viewed with regard to their rue our native* plants give the fol- 
lowing average degree of dispersi 
Species door Species. Average. 
69 erste i ; : 9°09 
124 Northern 8°82 ; 
297 Temperate, penetrating within As, VBE 
the Arctic Circle 8°79 
366 pobre, not found within 
etic Circle eas 661 5°63 
295 Southern 4°62 
| Total 1 1151. oe eA ee 
: Dispersion as affected by Station. ' 
Aquatic Plants.—It has long been noticed that: se plants, in 
eco with other fresh-water roductions, si 3 as a rule, widely 
are as 
oss Average, 
49 Aquatic Dcineiass aes Oe 
268 Seni-Auatio'o or Palustral , ‘ : fi rd 
834 Terrestrial 
te tendency i is most marked in those plants which belong a orders 
Wholly or pri eyelly composed of aquatic or palustral spe Thus 
of the 49 aquatic plants— 
Nymphaoace cer, cer gere Hydrocharidez, 
Potom maceze, Lemna and ere ai 
average 9-11 
13 belon, t 2 : ‘ 8°46 
and of the “ ene a) other orders. r 
101 Drosrcen, Pinguiculacez, Alismacee, Ty- 
uncacee, and a ee 8°16 
167 Belonging ta other orders 7-79 
tw Maritine P lants.—Professor De Condall elect the whole of the 
mes Pla umbaginac cez and Salsolaces as representatives of mari- 
ne or salt-loving plants; and finding that their mean specific area, 
= or ae suspected, to be only naturalised in Britain have 
the comparisons in this paper. 
