ANOMALIES OF PLANT DISPERSION.

Dominion, Volume 1, Issue 24, 23 October 1907, Page 10

ANOMALIES OF PLANT DISPERSION.

. Why is it that the kauri tree is practically' confined to a district north of the thirtyeighth parallel of latitude, though south of this line for a considerable distance thoro are no climatic conditions which should inhibit the growth of this trcs in many places? That is a question which Dr. L. Cockayne discusses in an interesting pamphlet on Now Zealand coastal vegetation, contributed a year ago to the Transactions of tlio New Zealand Institute, and now reprinted by the Government. Dr. Cockayno points out that at Wellington, more than threo degrees to the south of tho kauri limit, this tree grows famously in cultivation, producing cones regularly. Even at Christchurch, in the South Island, in , the Domain, where —9 degrees C has been frequently' recorded, the kauri grows well and has fruited. Also, a young plant has withstood the cold , of winter in tho garden of the biological laboratory, Canterbury College, in a position where it could get no sun, and where a plant of Veronica elliptic.! collected by Dr.. Cockayne in Campbell Island was killed outright. Finally, so far south .is Duncdin, the kauri is by no means difficult to cultivate. In its restricted natural area;, and capacity for wider growth, it is not unique. The nolmtukawa is the characteristic tree of certain coastal rock formation!; of the northern part of New Zealand, and lino much ,thc same distribution as the kauri, yet; without any apparent reason, it also' doer> not extend beyond a certain latitude, although it is perfectly hardy near the shores of Cook Strait, being a frequent plant of gardens in Wellington and elsewhere. ' The karnka,* a plant probably more susceptible to frost than either of the above, occurs spontaneously as far south as Banks Peninsula, but further docs not £o, although quite hardy on tho Otago Peninsula. "Han;,- cdior examples could be cited. The explanation would soeni to ho that many plants would extend further to tho north or the south, but they encounter competitors better equipped for the, struggle—i.e., more in harmony with the surroundings than themselves. A plant which is" slightly mcra suited than another for a particular station must evidently : become tho victor in the struggle for existence, although both outwardly may anocav equally matched in every particular; The diverse origin of the New Zealand flora is another factor in the problem.