1 7 . T h o u g h w e r a r e ly fin d th e sam e sp e c ie s r u n n in g in to th e sam e v a r ie tie s a t w id e ly su n d e r ed
lo c a litie s (u n le s s sta rv ed or lu x u r ia n t fo rm s b e ca lled v a r ie tie s ), y e t w c d o o ften fin d a g rou p o f sp e c
ie s r ep r e sen ted in m a n y d is ta n t p la c e s b y o th e r g rou p s o f a llied fo rm s ; au d i f w e su p p o se th a t in d iv
id u a ls o f th e pai-ent ty p e h a v e fo u n d th e ir w a y t o th em a ll, th e thcoi-y th a t e x is t in g sp e c ie s h a v e
o r ig in a ted in v a r ia tio n , a n d th a t v a r ie tie s d ep a r t fu r th e r from th e p a r en t fo rm , w ill a c c o u u t fo r su ch
g ro u p s o f a llied sp e c ie s b e in g fo u n d a t d is ta n t s p o t s ; a s a lso fo r th e s e g ro u p s b e in g c om p o sed o f
r ep r e s en ta tiv e sp e c ie s and g en e ra.
1 8 . N o g en e r a l r e la tio n s h a v e y e t b e e n e s ta b lish ed b e tw e en th e p h y s ic a l co n d itio n s o f a c o u n tr y
a n d th e n um b e r o f sp e c ie s o r v a r ie tie s w h ic h i t c o n ta in s , fu r th e r th a n th a t th e tro p ica l an d tem p e ra te
r e g io n s ai-e m o r e f e r t ile th a n th e p o la r , a u d th a t p e r en n ia l d r o u g h t i s em in e n tly u n fa v ou rab le to
v e g e ta t io n . I t i s n o t ev en a s c e r ta in ed w h e th e r th e tr o p ic a l c lim a te s p ro d u c e m o r e sp e c ie s tb a n th e
tem p e r a te .
1 9 . T h o u g h w e c a n u o t ex p la in th e g en e r a l r e la tio n s b e tw e e n th e v e g e ta tio n an d p h y s ic a l c o n d it
io n o f a n y tw o c o u n t r ie s th a t c o n tr a st in th e s e r e sp e c ts, w e m a y co n c lu d e as a g en e r a l ru le th a t
th o s e t r a c ts o f la u d p r e s en t th e g i’e a te s t vain e ty in th e ir v e g e ta t io n th a t h a v e th e m o s t v aried c om b in
a t io n s o f co n d itio n s o f h e a t , lig h t , m o is tu r e , a n d m in e r a l ch a ra c te r s. I t is , in th e p r e sen t s ta te
o f o u r k n ow led g e , im p o s s ib le to m ea su r e th e am o u n t o f th e f lu c tu a tio n s o f th e s e c o n flic tin g c o n d
it io n s in a g iv e n c o u n tr y , n o r i f w e co u ld ca n w e e x p r e ss th em s ym b o lic a lly or o th e rw is e so a s to
m a k e th em in t e llig ib le e x p o n e n ts o f th e am o u n t o f v a r ie ty in th e v e g e ta t io n th e y affec t ; b u t th e fo llow
in g fa c t s in g e n e r a l d istr ib u tio n appeal* to m e to b e fa v ou rab le t o th e id e a th a t th e r e is su ch a
c o n n e c tio n .
T h e r e ar e c e r ta in p o r tio n s o f th e su r fac e o f th e g lo b e ch a ra c te rized b y a r em a rk ab le u n ifo rm ity
in th e ir p hæ n o g am ic v e g e ta tio n . T h e se m a y b e lu x u r ia n t ly c lo th ed , an d ab ou n d in in d iv id u a ls, b u t
are a lw a y s po o r in sp e c ie s. S u c h are th e c o o le r tem p e r a te an d su b a r c tic la k e r e g io n s o f N o r th
A m e r ic a , F u e g ia an d th e F a lk la n d I s la n d s , th e P am p a s o f B u e n o s A y r e s , S ib e r ia an d N o r th
R u s s ia , I r e la n d an d W e s te r n S c o tla n d , th e g r e a t G a n g e tic p la in , an d m a n y o th e r tr a c ts o f lan d .
N o w a ll th e s e r e g io n s are - ch a ra c te r iz ed b y a g r e a t u n ifo rm ity in m o s t o f th e ir p h y sic a l ch a ra c te r s,
a n d an a b sen c e o f th o s e v a r y in g c o n d itio n s w h ic h we a s sum e to b e s tim u la n ts t o v a r ia tion in a lo c a lit
y . O n th e o th e r h an d , i t is in th o s e t r a c t s th a t h a v e th e m o s t b rok en su r fa c e , v ar ied com p o sitio n
o f r o ck s, e x c e s s iv e c lim a te (w ith in th e lim it s o f v e g e ta b le en d u r a n c e ), an d a b u n d an c e o f lig h t , th a t
th e m o s t sp e c ie s are fo u n d , a s in S o u th A fr ica , m a n y par ts o f B r a z il an d th e A n d e s , S o u th e rn
F r a n c e , A s ia M in o r , S p a in , A lg e r ia , J a p a n , a n d A u str a lia .
2 0 . T h e P o la r r e g io n s are ch ie fly p eo p led fr om th e co ld er t em p e r a te zo n e s, a n d th e sp e c ie s from
th e la t te r w h ic h h a v e sp read in to th em are v e r y v ariab le, b u t o n ly w ith in com p a ra tiv e ly sm a ll lim it s ,
p a r ticu la r ly in sta tu r e , co lo u r , an d v e s tu r e . M a n y o f th e s e po la r an d co ld e r tem p e r a te p la n ts are
a lso fo u n d , to g e th e r w ith o th e r sp e c ie s c lo s e ly a llied t o th em , o n th e m o u n ta in s o f th e warm tem p e ra
te , an d ev en tr o p ic a l zo n e s ; to w h ich i t is d ifficu lt t o co n c e iv e th a t th e y ca n h a v e b e en tran sp o r ted
b y a g en c ie s n ow in o p e ra tion .
2 1 . T h e F lo r a s o f is la n d s p r e s en t m a n y p o in ts o f in te r e s t. T h e to ta l n um b e r o f sp e c ie s th e y
co n ta in s e em s to b e in v a r ia b ly le s s th a n an eq u a l c o n t in e n ta l ar ea p o sse sse s, and th e r e la tiv e n um b e r s
o f sp e c ie s t o g en e r a (or o th e r h ig h e r groups) is a lso m u ch le s s th a n in sim ila r c o n tin e n ta l areas.
T h e fu r th e r an isla n d is fr om a c o n t in e n t, th e sm a lle r i s it s F lo r a n um e r ic a lly , th e mor e
of organs in plants, where many are present, and where those of low morphological importance may have a comparatively
high physiological significance.
p e cu lia r is it s v e g e ta tio n , a n d th e sm a lle r i t s p ro p o r tio n o f sp e c ie s t o g en e r a . I n th e ca se o f v e ry
iso la ted isla n d s, m o r eo v e r , th e g en e r ic ty p e s a r e o ften th o s e o f v e r y d is ta n t c o u n tr ie s , a n d n o t o f th e
n e a r e s t la n d . T h u s th e S t . H e le n a an d A s c e n s io n fo rm s are n o t so c h a r a c te r istic o f tro p ica l A fr ic a
a s o f th e Cape o f G o o d H o p e . T h o s e o f K e r g u e len ’s L a u d a r e A n ta r c t ic A m e r ic a n , n o t A fr ic a n n o r
In d ia n . T h e S a n dw ich I s la n d s c o n ta in m a n y N o r th -w e s t Am e r ic a n an d s om e N ew Z ea la n d fo rm s.
J a p a n p r e sen ts u s w ith m a n y g en e ra an d sp e c ie s u n k n ow n e x c ep t to th e e a s h v a r d o f th e R o c k y
M o u n ta in s , in N o r th A m e r ic a .* S o to o A m e r ic a n , A b y s s in ia n , an d e v en S o u th A fr ic a n g en e r a and
sp e c ie s are fo u n d in M ad e ira and th e Can a ry I s la n d s ; an d F u e g ia n o n e s in T r ista n d’A cu n h a .
2 2 . T h e r e is a st r ic t a n a lo g y in th is r e sp e c t b e tw e en th e F lo r a s o f is la n d s an d th o s e o f lo fty
m o u n ta in -r a n g c s , n o d o u b t in b o th ca s e s ow in g t o th e sam e c a u se s. T h u s, a s J ap an co n ta in s
va r io u s p e cu lia r N .E . A m e r ic a n sp e c ie s w'hich are n o t fo u n d in N.W". A m e r ic a n o r e lsew h e r e o n th e
g lo b e , an d th e Canar ie s an d A z o r e s p o s s e s s A m e r ic a n g en e r a n o t fo u n d in E u r o p e n o r A fr ica , so th e
lo f ty m o u n ta in s o f B o rn eo c o n ta in T a sm a n ia n a n d H im a la y a n r ep r e s e n ta tiv e s ; th e H im a la y a s c o n ta
in A n d ea n , R o c k y M o u n ta in , an d J a p a n e se g en e r a a n d s p e c ie s ; a n d th e a lp s o f V ic to r ia an d T a s m
a n ia c o n ta in a ssem b la g e s o f N ew Z ea la n d , F u e g ia n , A n d e a n , an d E u r o p e a n g en e r a an d sp e c ie s.
W e ca n u o t a c c o u n t for an y o f th e s e ca se s o f d is tr ib u tio n b e tw e e n is la n d s and m o u n ta in s e x c e p t b y
a s sum in g th a t th e sp e c ie s a n d g en e r a c om m o n t o th e s e d is ta n t lo c a litie s h a v e fo u n d th e ir w a y a cro ss
th e in t e r v e n in g sp a ce s u n d e r co n d itio n s w h ich n o lo n g e r e x is t.
2 3 . T h e r e is m u c h to b e ob se rv ed in th e c o n d itio n an d d is t r ib u tio n o f th e in tr o d u c ed or n a tu ra
liz ed p la n ts o f a co u n tr y , w h ic h m a y b e ap plied t o th e s tu d y o f th e o r ig in o f it s in d ig e n o u s v e g e ta tio
n . T h e g r ea te r p ro p o r tio n o f th e s e are th e a n n u a l an d o th e r w e ed s o f cu ltiv a te d la n d , an d p lan ts
w h ich a tta ch th em s e lv e s t o n itr o g e n o u s s o i l s ; n a tu ra liz ed p e r en n ia ls, sh ru b s, an d tr e e s o c cu r c o n s
e c u t iv e ly in rap id ly d im in ish in g p rop o r tion s. I ca n find n o d e c id ed r e la tio n b e tw e en c om p le x ity
o f stru c tu r e an d p r o n en c ss t o m ig r a te , n o r m u ch b e tw e e n fa c ilit ie s for tra n sp o r t o r p ow er o f en d u r a
n c e or v ita lity in th e se ed , and e x t e n t o f d is tr ib u tio n b y a r tific ia l m e a n s. I sh a ll r e tu rn to th is
su b je c t (wfiiich I h a v e elsew'here d iscu ssed a t le n g th w ith r e fe r en c e to th e G a lap a g o s A r c h ip e la g o f)
w h en t r e a tin g o f th e n a tu ra liz ed p la n ts o f A u stra lia .
2 4 . I ven tu r e to a n tic ip a te th a t a s tu d y o f th e v e g e ta tio n o f is la n d s wdth r e fe r en c e t o th e
p e cu lia r itie s o f th e ir g en e r ic ty p e s o n th e o n e h a n d , an d o f th e ir g e o lo g ic a l c o n d itio n (w h e th e r as
r is in g or sin k in g ) on th e o th e r , m a y , in th e p r e sen t s ta te o f ou r k n ow led g e , a d v a n c e th e su b je c ts o f
d is tr ib u tio n an d v a r ia tion co n sid e ra b ly . T h e in c om p le te n e s s o f th e c o lle c tio n s a t m y com m an d
fr om th e P o ly n e s ia n is la n d s, h a s fru stra ted m y a tt em p t s to illu s tr a te th is b ran ch o f in q u ir y by
e x t e n d in g in y r e sea r ch e s from th e A u s tr a lia n F lo r a over th a t o f th e P a c ific . I m a y ‘h ow eve r
in d ic a te as a g en e r a l r e su lt, th a t I find th e s in k in g is la n d s, th o s e (so d e te rm in ed b y D a rw in ’s ab le
in v e stig a tio n s) ch a ra c te r iz ed a s a to lls , or as h a v in g b arr ie r ree fs, to c o n ta in com p a r a tiv e ly few e r
sp e c ie s and few e r pe cu lia r g en e r ic ty p e s th a n th o s e w h ich arc r isin g . T h u s, c om m e n c in g from th e
e a st co a st o f A fr ic a , I find in th e In d ia n O c ean th e fo llow in g is la n d s m a rk ed in D a rw in ’s c h a r tj as
b ou n d ed w ith f r in g in g re efs o r a c tiv e v o lc a n o s, an d h e n c e r i s in g :— T h e S e y c h e lle s , M ad agascar,
M a u r itiu s, B o u rb o n , C e y lo n , th e A n d am a n s, N ic o b a r , a n d S um a tr a ; th e v e g e ta tio n o f a ll w h ic h is
charac te i’iz ed b y g r e a t d iv e r sity and m u ch p e cu lia r ity o f g en e r ic t y p e : wh er eas th o s e m a rk ed as
* W iilst tlicsc sheets are passing tlivoiigli the press, I have been informed by Professor Asa Gray that the
Flora of Japan aud N .E . Asia is much more closely allied to that of the Northern United States than to that of
;Vuierica west of the Rocky Mountains.
t Linn. Trans, xx. 235. % See liis works on volcanic islands and on coral reefs.