Medical Officers of the Army of India.

59

    Stachytarpheta indica is a common and favourite flower in Indian gardens,
and may have been intentionally introduced. But it is also (like Plumbago) a
plant that readily throws itself out of cultivation, and is nearly as likely to have
been unintentionally conveyed.

    Premna integrifolia may possibly have been introduced because of its
medicinal properties. It has, however, more probably arrived independently of
man. Mr. Hume found it wild, and in dense thickets; it is a common tree on
Indian coasts; it is perfectly capable of distribution by ocean-currents (fruits
almost certainly belonging to this genus occur in various ocean-drifts); it is also
probably capable of dispersal by means of frugivorous birds, as seeds of appa-
rently species of P remna have been found in the crops of such.

    On the other hand, Gloriosa is more likely to have been introduced; not
only is it a showy plant, but natives of India believe that its roots possess
powerful poisonous properties. It must be pointed out, however, that its seeds are
capable of dispersal by winds, though it may be doubted whether they are capable
of being carried so far as 130 miles, which is the distance of Anderut from the
mainland. But it was not being cultivated where it was gathered, nor was it in
cultivation elsewhere.

    Pandanus odoratissimus may have been introduced because of its sweet
scent. But it is very general in the archipelago; it is not cultivated by the
islanders, and they do not make any use of it; species of Pandanus are amongst
the most usual of ocean-distributed plants elsewhere; and it may be held as
almost certain that it has been introduced by ocean-currents.

    The grass that Mr. Hume took to be the common dubh-grass may have been
introduced purposely, since some of the islanders have a few cattle; but it is far
more likely, even if it was dubh, which it is extremely probable it was, to have
been introduced as a weed.

    While, then, all 16 may have been intentionally introduced by man, it is
more probable that 7 (Cœsalpinia, Morinda, Cynanchum, Tylophora, Ipomœa,
Premna and Pandanus) have arrived independently, and just possible that 5
others (Calophyllum, Thespesia, Mucuna, Calotropis and Gloriosa) may also
have arrived independently. The remaining 4 (Plumbago, Datura, Stachytar-
pheta and Cynodon) have either been introduced intentionally or have been intro-
duced as weeds, and so certainly owe their presence in the islands to the agency
of man.

    But, besides these four, there are 27 other species that are or may be weeds
of cultivation, and as such are extremely liable to be dispersed by man involun-
tarily. For all in the following list this is without doubt the principal means of
dispersion, and for the majority it is unquestionably the only possible means.

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