a to lls or baiTier r e e fs, a s t lie M a ld iv e s , L a c ca d iv e s, an d K e e lin g I s la n d , c o n ta in few sp e c ie s, and
tlio s e tb e sam e a s g row o n tb e n e a r e s t c o n t in e n t s . I n tb e P a c ific O c ean , a g a in , th e g rou p s o f isla n d s
m o s t r em ai'k ab le fo r th e ir a sc e r ta in ed n um b e r o f v e r y p e cu lia r g e n e r ic ty p e s are th e S a n dw ich grou p ,
G a la p a g o s, J u a n F e rn a n d e z , L o o ch o o and B o n in , a ll o f w h ic h ar e r is in g , an d m o s t h a v e a c tiv e v o lca
n o s ; th o s e w ith th e le a s t am o u n t o f p e cu lia r ity ar e th e S o c ie ty g rou p an d F ijis , b o th o f w h ic h are
s in k in g . I n th e p r e s e n t s ta t e o f o u r k n ow led g e i t is n o t sa fe t o la y m u c h str e ss o n th e s e ap parent
fa c ts , e sp e c ia lly a s th e N ew H eb r id e s an d N ew C a led on ia , w h ich l i e v e r y c lo s e to g e th e r , an d b o th , I
b e lie v e , c o n ta in m u c h p e c u lia r ity , a r e in o p p o s ite g e o lo g ic a l c o n d itio n s , th e H e b r id e s r is in g an d Ca le d
on ia s in k in g ; an d th e F r ie n d ly * an d F ij i g ro u p s, e q u a lly nea i’ o n e a n o th e r , a n d w ith , I su sp e c t,
v e ry sim ila r v e g e ta tio n , a r e a lso r ep r e sen ted a s b e in g in o p p o site c o n d itio n s . O n th e o th e r h an d ,
w h o le o f th e g r o u p in c lu d in g th e L ow A r ch ip e la g o an d th e S o c ie ty I s la n d s , e x t e n d in g o v e r m o r e th a n
2 0 0 0 m ile s , I o b se rv e b u t o n e r is in g s p o t , f n am e ly , E liz a b e th Is la n d , a m e r e sp e ck o f la n d , bu t
w L ich i s th e o n ly k n ow n h a b ita t o f o n e o f t h e m o s t r em a rk ab le g en e r a o f Composit<B.%
2 5 . M a n y o f t h e ab o v e fa c ts in th e g en e r a l d is tr ib u tio n o f sp e c ie s c a n n o t b e w h o lly a c co u n ted
fo r b y th e su p p o sitio n th a t n a tu r a l c a u se s h a v e d isp e r sed th em o v e r su ch e x is tin g o b s ta c le s a s se a s,
d e se r ts, an d m o u n ta in - c h a in s ; m o r eo v e r , som e o f th e s e fa c ts are op p o sed to th e th e o r y th a t th e
c r e a tio n o f e x is t in g sp e c ie s h a s ta k e n p la c e su b s eq u en t to th e p r e sen t d is tr ib u tio n o f c lim a te s , and
o f la n d and w a te r , a n d to th a t o f theii* d isp e r sion h a v in g b e e n e ffe c ted b y th e n ow p r e v a ilin g aq u a tic ,
a tm o sp h e r ic , a n d a n im a l m e a n s o f tran sp o rt.
S im ila r c lim a te s a u d c o u n tr ie s , e v e n w h en a lto g e th e r fa v ou rab ly p lac ed for r e c e iv in g c o lo n is t s
from e a c h o th e r , a n d w ith co n d itio n s su ita b le to th e ir r ec ip ro ca l e x ch a n g e , do n o t, a s a ru le , in t e r c
h a n g e sp e c ie s. C a u se s n ow in o p e ra tio n w ill n o t a c c o u n t fo r th e fa c t th a t o n ly 2 0 0 o f th e N ew
Z e a la n d F low e r in g P la n t s a r e c om m o n t o A u s tr a lia , a n d s t ill le s s fo r th e c o n tr a s tin g o n e th a t th e
v e r y c om m o n e s t, m o s t n um e r o u s , a n d u n iv e r sa lly d is tr ib u ted A u s tr a lia n g en e r a and sp e c ie s, as
C a su a r in a , E u c a h jp tu s , A c a c ia , B o r o n ia , H e lic h r y sum , M e la leu c a , e t c ., and all th e A u s tr a lia n L e g u -
m in o s a (in c lu d in g a E u r o p e a n g e n u s a n d sp e c ie s ) , ar e a b sen t from N ew Z ealand. C au se s n ow in
o p e r a tio n c a n n o t b e m a d e t o a c c o u n t for a la r g e a ss em b la g e o f F low e r in g P la n ts c h a r a c te r istic o f
th e In d ia n p e n in su la b e in g a lso in h a b ita n ts o f tr o p ic a l A u s tr a lia , w h ile n o t o n e ch a r a c te r istic A u s tr
a lia n g e n u s h a s ev e r b e e n fo u n d in th e p en in su la o f In d ia . S t ill le s s w ill th e s e c a u se s a c c o u n t for
th e p r e sen c e o f A n ta r c tic a n d E u r o p e a n sp e c ie s in th e A lp s o f T a sm a n ia an d V ic to r ia , or for th e
r eap p ea ran c e o f T a sm a n ia n g en e r a o n th e iso la te d lo f ty m o u n ta in o f K in a -B a lo u , in B o rn eo .
T h e s e au d a m u lt itu d e o f a n a lo g o u s fa c ts h a v e le d t o th e s tu d y o f tw o c la sse s o f a g en ts,
b o th o f W’h ic h m a y b e r e a so n a b ly su p p o sed t o h a v e had a p ow e r fu l e ffe ct in d e t e rm in in g th e d is tr ib u tio
n o f p la n ts J th e s e are c h a n g e s o f c lim a te s , and c h a n g e s in th e r e la tiv e p o s itio n s au d e lev a tio n s
o f la n d .
2 6 . O f th e s e , th a t m o s t e a sy o f d ir e c t ap p lica tion is th e effec t o f h um id ity in e x t e n d in g th e
* I find that there is a remarkable difference between the Floras of the New Hebrides and Caledonia on the
one hand, and those o f the Fiji islands and those to the east of them on the other. In the former, New Zealand
and Australian types abound; in the latter, almost exclusively Indian forms. The differences between the Floras of
Fiji, Samoa, Tonga, Tahiti, and that o f India, are in species and not in genera, and many species are common to all.
t Mr. Darwin has left Aurora Island (another of the group) uncolourcd, on account of the doubtful evidence
regarding it, which however is in favour of its being in the same condition as Elizabeth Island. From a list of
species communicated by Mr. Dana, it appears to contain no peculiar plants.
X Fitckia. See Lond. Journ. Bot. 1 845, iv. p, 640. t. 23, 24.
ra n g e o f sp e c ie s in to r e g io n s ch a ra c te r iz ed b y w h a t w o u ld o th e rw is e b e to th em d e s tru c tiv e t em p e r a tu
r e s.
I h ave , in th e ‘ A n ta r c tic F lo r a ,’ sh ow n th a t th e d is tr ib u t io n o f tr o p ic a l fo rm s is ex ten d ed
in to c o ld r e g io n s th a t are h um id a n d eq u a b le fu r th e r th a n in to su c h as a r e d ry an d e x c e s s iv e ;
an d , c o n v e r se ly , th a t t em p e r a te fo rm s ad v an c e m u ch fu r th e r in to h um id an d eq u a b le tr o p ic a l r e g io n s
th a n in to d ry an d e x c e s s iv e o n e s ; a n d I h a v e a ttr ib u ted th e e x t e n s io n o f T r e e -fe rn s, E p ip h y ta l
O r ch id s, M y r ta c e® , e t c ., in to h ig h so u th e rn la t itu d e s , to th e m o is t an d eq u a b le c lim a te o f th e so u th
tem p e r a te zo n e . I h a v e a lso sh ow n h ow co n sp icu o u s ly th is k in d o f c lim a t e in flu en c e s th e d is tr ib u tio
n o f m o u n ta in p la n ts in In d ia , w h e r e tr o p ic a l fo rm s o f L a u r e l, F ig , B am b o o , an d m a n y o th e r
g en e r a , asc en d th e h um id ex tr a tr o p ic a l m o u n ta in s o f E a s t e r n B e n g a l an d S ik k im to fu lly 9 0 0 0
f e e t e le v a tio n ; a n d tem p e r a te g en e r a , a u d in som e ca s e s sp e c ie s, o f Q u e r cu s, S a lix , R o sa , P in u s ,
P nm u s , C am e llia , R u b u s, K ad su ra , F ra g a r ia , J S s c u lu s , e tc ., d e sc en d th e m o u n ta in s e v e n t o th e le v e l
o f th e sea , in la t. 2 5 ° . I n a tr o p ic a l c lim a t e th e c om b in ed e ffe c ts o f an eq u a b le c lim a t e and
h um id ity in th u s e x te n d in g th e d istr ib u tio n o f sp e c ie s, o f te n am o u n t t o 5 0 0 0 f e e t in e le v a tio n or
d ep r e ssio n (eq u iv a len t t o 1 5 ° F a h r . o f iso th e rm a ls in la t itu d e ) , a m o s t im p o r ta n t e lem e n t in our
sp e cu la tio n s o n th e com p a ra tiv e r a n g e o f sp e c ie s u n d e r e x is t in g or p a st c o n d it io n s ; a n d w'hen to
th is is added th a t th e ave ra g e r a n g e in a ltitu d e o f e a ch H im a la y a n tr o p ic a l an d tem p e r a te an d a lp in e
sp e c ie s o f F low e r in g P la n t is 4 0 0 0 f e e t , w h ich is eq u iv a len t to 1 2° o f iso th e r r a a ls o f la titu d e , w’e can
u n d e r sta n d h ow an e le v a tio n o f a v e r y few th o u sa n d f e e t m ig h t , u n d e r c e r ta in c lim a t ic c o n d itio n s,
suffice t o e x ten d th e r a n g e o f an o th e rw ise lo c a l sp e c ie s o v e r a t le a s t 2 5 ° p a ra lle ls o f la titu d e , and
h ow a p ro p o r tio n a lly sm a ll in c r e a se o f e le v a t io n in a m e r id io n a l ch a in w h e r e it c ro sse s th e E q u a to r ,
m a y en a b le tem p e r a te p la n ts to e ffe c t an e a sy p a ssa g e from o n e tem p e r a te zo n e to th e o th e r .
2 7 . T o e x p la in m o r e fu lly th e p r e sen t d is tr ib u tio n o f sp e c ie s a n d g en e r a in area, I h a v e re cou rse
to th o s e a r g um en ts w h ich are d ev e lop ed in th e In tr o d u c to r y E s s a y t o th e N ew Z ea la n d F lo r a , and
w h ich r e s t on g e o lo g ic a l ev id en c e , o r ig in a lly e s ta b lish ed b y S ii’ Chai’le s L y e ll, th a t c e r ta in sp e c ie s
o f an im a ls h a v e suririvcd g r e a t r e la tiv e c h a n g e s o f sea an d la n d . T h is d o c tr in e , w h ich I in
th a t E s s a y en d ea v ou r ed t o exp an d b y a s tu d y o f th e d istr ib u tio n o f e x is t in g S o u th e r n sp e c ie s,
h as, I v en tu r e to th in k , acquir ed a d d itio n a l w e ig h t s in c e th e n , from th e fa c ts 1 sh a ll b r in g foi-ward
u n d e r tb c n e x t h ead o f G e o lo g ic a l D is tr ib u t io n , a n d w h ich s e em t o in d ic a te th a t m a n y e x is t in g
O rd er s and G en e ra o f p la n ts o f th e h ig h e s t d e v e lo pm en t m a y h a v e flo u r ish ed d u r in g th e E o c e n e
a n d C r e ta c eou s pe r iod s, an d h a v e h e n c e su rv iv ed c om p le te r e v o lu tio n s in th e tem p e r a tu r e an d g e o g
rap h y o f th e m id d le an d tem p e r a te la t itu d e s o f th e g lo b e .
^ 2 8 . M r . D a rw in h a s g r e a tly ex ten d ed in a n o th e r d ir e c tio n th e s e v iew s o f th e a n t iq u ity o f m a n y
E u r o p e a n sp e c ie s, and th e ir p ow e r o f r e ta in in g th e ir f a c ie s u n ch a n g ed d u r in g m o s t e x te n s iv e m ig r a tio
n s , b y h is th e o r y o f th e sim u lta n e o u s e x ten s io n o f th e g la c ia l tem p e ra tu r e in b o th h em isp h e r e s, and
its c o n s eq u en t effec t in c o o lin g th e tro p ica l zo n e . H e a rg u e s th a t, u n d e r su ch a co ld c o n d itio n o f th e
su rface o f th e g lo b e , th e tem p e r a te p la u ts o f b o th h em isp h e r e s m ay h a v e b e en a lm o st co n fin ed to th e
tro p ica l zo n e , w h en c e afterwards, ow in g to an in c r em en t o f t em p e ra tu r e , th e y w ou ld be d r iv en u p th e
m o u n ta in s o f tlie trop ic s, au d back a g a in to th o s e h ig h e r tem p e ra te la titu d e s w h e r e w e n ow find m o st
o f th em . 1 ha v e a lread y (N ew Zealand E ssa y ) a v ailed m y s e lf o f th e h y p o th e s is o f an a u stra l g la c ia l
p e riod, to a c co u n t for A n ta r c tic sp e c ie s b e in g fou n d o n th e a lp s o f A u str a lia , T a sm a n ia , a n d N ew
Z e a la n d ; an d i f a s c om p le te ev id en c e o f su ch a p r op o r tion a lly c o o led s ta t e o f th e in te r tro p ica l
r e g io n s w e r e fo v th c o n iin g as th e r e is o f a g la c ia l c o n d itio n o f th e t em p e r a te zo n e s, i t w ou ld am p ly
suffice to a c co u u t for th e pr e scu c c o f Eu rop ean and A r c tic sp e c ie s in th e A n ta r c t ic and so u th tem -
d