s
trigonifolius common; otherwise Cyperaceae, _Epilobium out of_
_season_! Ranunculus aquaticus is most abundant; two species of Chara, or
rather 1 Chara, and 1 Nitella, the last a beautiful species, Marsilea in
profusion, Azolla common, Lemna two or three species, one _new_, a
floating Marchantiacia, Nelumbium occurs, but only as a cultivated plant.

Of two Boreal, or European forms found in sub-tropical countries, that
form is the most northern which flowers, etc. in the coldest season,
hence Veronica and Ranunculus are more northern than _Epilobium_ in this
particular district. The most elevational plant at Cabul is
Cardaminoidea, floribus luteis, this flowers at high altitudes in August
and September, and at Cabul shows no symptom of flowering even in
October; it is there a winter plant? The same is true of Hippuris, which
to flower at Cabul requires a greater degree of cold than is obtainable
during the summer months.

What I have said of Epilobium above, is true of Typha and Arundo, both
now passed flowering, and both found in India, to a considerable extent.

Royle's idea of the comparatively greater extent of distribution of water
plants is not I think correct, in the sense he seems to entertain it; to
be so, the species should be the same, which they are certainly not. It
is only with pre-eminently aquatic forms that the annual temperature can
be more equalised than obtains with strictly terrestrial plants. The
humidity which may appear connected with the rapid evaporation in these
countries, and which obtains? in the vicinity of all bodies of water, may
account for the appearance here of Arundo, etc. All genuine aquatic
types have leaves involute in vernation?

The least valuable of all northern forms, are those associated with
cultivation, especially if they be annuals, because in the first place
they may be acclimated species, a circumstance of great importance; and
in the second, because if annual, they are confined to the cold season.
All such forms have probably migrated into these countries, they have
come from the westward: this shows us why at almost equal elevations they
are most common, the nearer we approach to the elevated regions towards
the west, because it is self-evident that the nearer we approach the
regions whence they have migrated, the more abundant and diversified will
the migrating plants be, only particular species having the power of
extending the range of migration.

When al