452 Laws observed in the Distribution of vegetable Forms. 
to it with England, France, and Germany. Among the dicoty- 
ledons the ratio is only 1 in 200; which proves once more how, 
in the two hemispheres, the grasses and the cyperaceze are the 
most diffused, on account of the extreme flexibility of their or- 
ganization. It would be desirous that learned zoologists should 
endeavour to examine the analogous numerical ratios presented 
by the distribution of the different families of animals on the 
globe. 
In the austral hemisphere the vegetable forms of the torrid 
zone advance more towards the pole than in the boreal hemi- 
sphere. The fern-trees in Asia and America are rarely to be 
found beyond the tropic of Cancer; whereas in the austral part 
of our globe the Dicksonia antarctica, the trunk of which is six 
metres in height, pushes its migrations as far as Van Diemen’s 
Land under the latitude of 42°: it has even been found in New 
Zealand, in Dusky Gulph, under the parallel of Lyons. 
Other forms net less majestic, and which were thought to be- 
long exclusively to the equinoctial Flora, the parasite orchides 
(epidendra, dendrobia) are found mixed with the arborescent 
ferns far beyond the tropic of Capricorn, in the centre of the 
austral temperate zone. These phenomena of the geography of 
plants prove how vague is what has been generally said of the 
great diminution of temperature in the southern hemisphere, 
without distinguishing between the parallels more or less near 
the pole, and without any regard to the division of heat among 
the different seasons of the year. Those regions towards which 
the equinoctial forms extend, possess, on account of the i immen- 
sity of the seas which surround them, a true island climate. 
From the tropic of Capricorn to the parallel of 34°, and per-= 
haps still further, the mean heats of the year (2..e. the quantity 
of heat received by any given point of the globe) do not differ’ 
considerably in the two hemispheres. On casting our eyes over 
the three continents, New Holland, Africa, and America, we find 
that the mean annual temperature of Port Jackson (lat. 33° 51’) 
is 19° 3’ of the centigrade thermometer: that of the Cape of 
Good Hope (lat. 33° 55’) 19° 4’; that of the town of Buenos 
Ayres (lat. 34° 36’) 19° 7’. We may be surprised at this great 
equality in the distribution of heat by the 34° of austral latitude. 
Meteorological observations, still more precise, prove that in the 
boreal hemisphere, under this very parallel of 34°, we find a mean 
temperature of 19° 8’. On advancing towards the antare ic pole, 
perhaps even to the parallel of 57°, the temperatures of the twe 
hemispheres differ less in winter than summer. The Malouine 
Islands, situated in 51° and a half of south latitude, have less in- 
tense cold in winter than is experienced at London. The mean 
temperature of Van Diemen’s Land seems to be 10°; it freezes 
during 
