RELATIONSHIPS W I T H THE FLORAS OF OTHER REGIONS.
235
pregnant fact is that the genera are, almost without exception, much more strongly
developed in America than they are in Australasia and the Antarctic islands. But if we
take the vegetation generally of the southern coldest zone and regions the preponderance
of what may be termed American types, in contradistinction to those which are more
fully represented in the Australian region, is not so great; and if the bulk of Antarctic
vegetation seems clearly traceable to America, the isolation in South America of such
essentially Australasian types as Lebetanthus (Epacrideae) and Leptocarpus (Restiacere)
is not easily explained.
FURTHER DETAILS OF T H E DISTRIBUTION OF SOME OF T H E MORE
PROMINENT N A T U R A L ORDERS.
each natural order and genus and species in the Enumeration some particulars
are given of its general distribution, as well as any peculiarities of its distribution that
could be expressed in a few words; and this information is amplified and augmented in
the preceding Tables, while the succeeding paragraphs are devoted to a fuller exposition
of the general and special features of the leading natural orders in the vegetation of
Mexico and Central America. Something of interest might be written respecting the
composition and distribution of each natural order, and much more concerning those
treated of, but it would be more in place in a work dealing with the phytogeography
of the world than here.
UNDER
Ranunculacece.
All the seven genera of this order in Mexico and Central America are of wide range,
and there is, perhaps, no other large order of dicotyledons in which so high a proportion
of the genera has so wide a range. Of the forty-nine species, twenty-seven are endemic,
eighteen others restricted to America, leaving only four that extend to other parts of
the world. Two genera, Aquilegia and Delphinium, find their southern limit in
America in Guatemala and Mexico respectively.
Cruciferce.
W e have of this ubiquitous, mainly herbaceous, order of temperate and cold regions
twenty genera, two of them endemic, and five others restricted to America; and of the
remainder eleven are widely diffused and two common to the Mediterranean region.
Forty-two out of seventy-six species are endemic, and only four extend beyond America.
Sisymbrium is the most numerous in species.
Cistinece.
Helianthemum offers one of the most notable connections with the Mediterranean
region. It is also represented by one or more species in extratropical South America.
Lechea and Hudsonia are peculiar to North America, the former extending southward
BIOL. CBNTR.-AMBE., Bot. Vol. IV., August 1887.
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