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Show 494 ISLAND LIFE. (rART IT. . b th preservation in these Madagascar and the Antilles, 'dy eead types so we should f ts of once WI e-spr ' localities o remnan common to Australia and . d the few genera prefer to consi er f ncient vegetation, once spread Af, · remnants o an a South nca as . h d 'ven southward by the pressure over the north. err n hemisp ere,d now findincr a refu!!e in these d types an n b '-' of .more specm Ise h' 1 nds It is sugcrestive of such 'd 1 arated sout ern a · 0 · two WI 1e Y tsieopn that t h ese gen era are either of very a.n cie. nt an exp ana Com.f ers an d 0 yea d s- or plants of low orgamsahon groups-as . f ld-wide distribution, as Melan-as the Restmcere-or o wor thacere. Pl ts n'n New Zealand.-Returning Tl v d ·c Genera of an " te JitJhn emN~e w Zealand :flora, 'th hich we are more espe- WI w now to e 1 mains to be considered the pecucially concerned, there on ! re t · · ~ These are thirtv- . whiCh charac ense ll!. J liar or endemic gcnerda tly very isolated. A few have · mber an are mos two In nu . ' A t' u s others with Himalayan, or ffi 't' vith rc IC gro P ' a m Iers ' a. severa1 are tropi'cal forms ' but the majority Austra Ian gener . ' h l'ar types of world-wide groups-as appear to be alto~et er pecu 1 .t 0 ch1dere &c. We must . Saxifracrere Composi re, r . ' Le.gummosre, b ,.,k ~he~e peculiar forms to the earliest imrni-evidentl~ trace a _, h th or from the south; and the great grants, either from t_ e dnotr . to New Zealand-an antiquity . 't are obhae o give antiqui Y we o . 'ts fauna and :flora, no less than by supported _by every £teature I~ ~ts :xtinct forms of lifel-affords . t geoloalCal struc ure, an . . f 1 t 1: :sJ le timo e for t h e ch anges I. n the oc reneral distnbution oh p .a nfl s, for those due to isolation and ~odification u~de; 1 ~ m ~~~ f hancred conditions, whiCh are mam es e . y ence o c .o . f . f these interesting endemic forms. treme pecuhanty o mc1ny o . . . ex £ tl e genus Darnrnam m TnasslC 1 Dr. Hector notes the oc:urren?edo N 1 Zealand produced the genera deposits, ';bile in the .'T uras~~ t~:n~eris e;arnptopteris, Cycadites, Echin?Palceozarma, Oleandnurn, e Ph ' e Neocomian beds contam 1 I d" f ms of t e same ag · strobus, &c., al n Ian or . 1 D . and A raucaria. The Cretaceous d. t 1 donous leaf w1t 1 arnrnm a f a true wo y e . h fl . £ dicotyledonous plants, many o deposits have produced a nc thoia ~ t'ng flora. while the Miocene and f th e genera as e exJs 1 ' . l which are o e sam. d ]ants apparently almost jdentical w1t t other Tertiary deposits pro uce p 11· New Z ealand Inst. Vol. XI. those now inhabiting the country. ~~ 1~~r the orio·in of the New Zealand 1879, p. 536.) These facts agTee we Wl 1 o flora developed in the last chapter. CHAP. XXIII.) ARCTIC PLANTS IN NEW ZEALAND. 495 The absence of Smtthe1·n Types from the Northern Hemisphere. -We have now only to notice the singular want of reciprocity in the migrations of northern and southern types of vegetation. In return for the vast number of European plants which have reached Australia, not one single Australian plant has entered any part of the north temperate zone, and the same may be said of the typical southern vegetation in general, whether developed in the Antarctic lands, New Zealand, South America, or South Africa. The furthest northern outliers of the southern flora are a few genera of Antarctic type on the Bornean Alps; the genus A.ccena which has a species in California; two representatives of the Australian :flora-Casua1·ina and Stylidi'lt,m, in the peninsula of India; while China and the Philippines have two strictly Australian genera of Orchidere-Microtis and Thel!Jmitra, as well as a Restiaceous genus. Several distinct causes appear to have combined to produce this curious inability of the southern flora to make its way into the northern hemisphere. The primary cause is, no doubt, the totally different distribution of land in the two hemispheres, so that in the south there is the minimum of land in the colder parts of the temperate zone and in the north the maximum. This is well shown by the fact that on the parallel of Lat. 50° N. we pass over 240° of land or shallow sea, while on the same parallel of south latitude we have only 4°, where we cross the southern part of Patagonia. Again the three most important south temperate land-areas- South Temperate America, South Africa, and Australia-are widely separated from each other, and have in all probability always been so; whereas the whole of the north temperate lands are practically continuous. It follows that, instead of the enormous northern area, in which highly organised and dominant groups of plants have been developed gifted with great colonising and aggressive powers, we have in the south three comparatively small and detached areas, in which rich floras have been developed with special adaptations to soil, climate, and organic environment, but comparatively impotent and inferior beyond their own domain. Another circumstance which makes the contest between the northern and southern forms still more unequal, is the much |