234 
POPULAE SCIENCE EEVIEW. 
species of oak, ash and birch, hickories, iron-wood, blue-bark, butter-nut, 
pines, hackmatack, cedars, hemlock, balsam fir, poplars, and wild cherries ; 
spruces increase to the eastward. Of essentially American species which 
form the great mass of the Canadian flora, the Solidagos Asters, and other 
showy compositse, are conspicuous. It is along the southern and south-western 
frontier of Canada that there exists the greatest number of plants of the true 
American flora, which is a Continental flora, developed chiefly inland, and 
decreasing toward the Atlantic sea-board. There are many examples of this 
in Nova Scotia, but in that locality the preponderance of northern species is 
much greater than in the corresponding latitudes in Canada, and many of our 
common plants are in western Canada, either entirely northern, or strictly 
confined to the great swamps, whose cool waters and dense shade form a 
shelter for northern species. This effect of the swamps in modifying the 
distribution of species seems to have been hitherto overlooked. Dr. Lawson 
observed that, in localities in which boulders were largely distributed, there 
were always certain plants which he terms ftoitMer-plants to be found. — Vide 
The Transactions of the Nova Scotian Institute of Natural Science, vol. ii. 
part i. 
The Origin of our Local Floras. — On this subject an article appeared in 
our last number. This contribution was accompanied by a plate, in the 
execution of which the lithographer did not exactly carry out the directions 
of the artist concerning certain variations of shading. We therefore beg to 
call our readers’ attention to the following erratum, which arose from the 
want of correspondence between the drawing and the description in the 
text : — Page 36, lines 6 and 7 from top, instead of “ The unshaded and 
most deeply shaded parts of Plate II.” read “ Areas I. and II. of Plate II.” 
New British Lichens. — The Kev. W. A. Leighton records the discovery of 
some lichens new to Britain. The most remarkable of those recorded 
this botanist is Thelocarpon Laureri. This curious species was first dis- 
covered by Flotow, in 1824, in marshy places near Glatz in Germany, and 
his specimens appear to have lain in his herbarium, undetermined, until 
1846, when M. Laurer again found the lichen on turf fences, and drew 
M. Flotow’s attention to it. The latter gentleman then described it under 
the name of Sphceropsis. Mr. Leighton’s specimens were discovered upon a 
single decorticated larch rail at Middletown, near Craig-Breidden, in Shrop- 
shire, in June last ; and in August it was found growing parasitically upon 
the thallus of Boeomyces rufus on Stipertones Hole, and also on larch rails near 
the cemetery, Shrewsbury. In all these localities it occurred in very small 
quantity, and subsequent repeated researches have hitherto faded to detect 
more of it. Its extreme minuteness is doubtless the cause of its having 
been heretofore overlooked ; but now that attention has been drawn to it, it 
wdl most probably be found to be by no means uncommon. At first sight 
it resembles the granules of the thallus of Trachylia tigillaris, in a young 
scattered state, but the microscope and dissection show such appearances to 
be mere resemblances. — ^Vide Annals of Natural History, December. 
The Development of Composite Flovjers has recently been minutely studied 
by Professor Wolfgang, who gives the following information concerning it : — 
The flowers which constitute the head are developed subsequently to the 
leaves of the involucre, in a direction from the circumference of the receptacle 
