p e r a te r e g io n s , a u d o f th e tem p e r a te sp e c ie s o f b o th h em isp h e r e s on th e m o u n ta in s o f in te rm ed ia te
tr o p ic a l la titu d e s .
O n th e o th e r h a n d , w e h a v e su ffic ien t e r id e n c e o f m a n y o f w h a t are n ow th e m o s t trop ica l
Orde rs o f p la n t s h a r in g in h a b ite d th e n o r th t em p e r a te zo n e b e fo r e th e g la c ia l e p o c h ; a n d i t is diffic
u lt t o c o n c e iv e h ow th e s e O rd e rs c o u ld lia v e su rv iv ed so g r e a t a r ed u c tio n o f th e tem p e ra tu r e o f th e
g lo b e a s sh o u ld h a v e a llow e d th e p r eg la c ia l tem p e r a te F lo r a to c ro ss th e E q u a to r in an y lo n g i-
tu d e . I t i s e v id e n t th a t, u n d e r su c h c o ld , th e m o s t tr o p ic a l O rd e r s m u s t h a v e p e r ish ed , an d th e ir
r e -c r e a tio n a fte r th e g la c ia l ep o ch is a n in a dm is s ib le h y p o th e s is .*
2 9 . I t r em a in s th e n t o e x am in e w h e th e r , su p p o sin g th e g la c ia l ep o ch s o f th e n o r th e rn and
s o u th e r n h em isp h e r e s t o h a v e b e en c o n tem p o r a n e o u s, th e r e la tio n s o f la n d and s e a m a y n o t h a v e b een
su ch a s th a t a c e r ta in m e r id ia n m a y h a v e r e ta in ed a tr o p ic a l tem p e ra tu r e n ea r th e E q u a to r , au d th u s
h a v e pr e se rv ed th e tr o p ic a l fo rm s. S u c h c o n d itio n s m ig h t p e rh ap s b e a tta in ed b y su p p o sin g tw o
la r g e m a s s e s o f la n d a t e ith e r p o le , w h ic h sh o u ld c o n tr a c t an d jo in tow a rd s th e E q u a to r , fo rm in g
o n e m e r id io n a l c o n t in e n t , wliUe o n e eq u a to r ia l m a ss o f la n d sh o u ld b e p la c ed a t th e op p o site m e r id ian .
I f th e fo rm e r c o n t in e n t w e r e tra v e r sed b y a m e r id io n a l ch a in o f m o u n ta in s , a n d so d isp o sed th a t th e
p olar o c e a n ic cu r r en ts sh o u ld sw e ep tow a rd s th e E q u a to r for m a n y d e g r e e s a lo n g b o th it s sh o r e s, it s
eq u a to r ia l c lim a te w o u ld b e th r o u g h o u t fai' m o r e tem p e r a te th a n th a t o f th e op p o site eq u a to r ia l m a ss
o f la n d , w h o s e c lim a te w o u ld b e tr o p ic a l, in su la r , an d h um id .
3 0 . T h e h y p o th e s is o f fo rm e r m o u n ta in ch a in s h a v in g afforded to p la n ts th e m e a n s o f m ig r a tio n ,
b y c o n n e c tin g c o u n tr ie s n ow iso la te d b y sea s o r d e se r t p la in s, is d er iv ed from th e e r id en c e afforded
b y g e o lo g y o f th e ex tra o rd in a ry m u ta t io n in e le v a tio n th a t th e ea r th ’s su r fa c e h a s e x p e r ien c ed sin c e
t h e app ea ran c e o f e x is t in g fo rm s o f a n im a ls a n d p la n ts . I n th e A n ta r c tic E lo ra I su g g e s ted a s an
h y p o th e s is th a t th e p r e sen c e o f so m a n y A r c t ic -A m e r ic a n p la n ts in A n ta r c tic A m e r ic a m ig h t be
a c c o u n ted fo r b y su p p o sin g th a t th e n ow dep r e ssed p o r tio n s o f th e A n d e a n ch a in lia d , a t a forme r
p e r io d , b e e n so e le v a ted th a t th e sp e c ie s in q u e s tio n h a d p a ssed a lo n g i t from th e n o r th to th e sou th
tem p e r a te z o n e ; f a n d th e r e are som e fa c ts in th e d is tr ib u tio n o f sp e c ie s c om m o n t o th e m o u n ta in
F lo r a s o f th e H im a la y a an d M a la y I s la n d s , a n d o f A u str a lia an d J ap an , th a t w o u ld w e ll a c c om m o d
a te th em s e lv e s t o a sim ila r h y p o th e s is . O f su c h su bm e rg ed m e r id io n a l la n d s w e h a v e som e slen d e r
* The question of the state of the mean temperatui-e of the globe during comparatively recent geological periods
is yearly deriving greater importance in relation to the problem of distribution. Upon this point geologish are not
altogether clear, nor at one with the masters of physical science. Lyell (Principles, ed. ix. chap. vu.) attributes the
glacial epoch to such a disposition of land and sea as would sufficiently cool the temperate zones; aud he impUes
that this involves or necessitates a lowei-ing of the mean temperature of the whole globe. Another liypothesis is,
that there was a lowering of the mean temperature of the globe wholly independent of any material change in the
present relations of sea and land, which cold induced the glacial epoch. A third theoiy is that such a redisposition
of land and sea as would induce a glacial epoch in our hemisphere need not he gi-eat, nor necessitate a
decrement of the mean temperature of the whole earth.
t The continuous extension of so many species along the Cordillera (of which detailed evidence is given in the
Antarctic Flora) from the Rooky Mountains to Fuegia, is a most remarkable fact, considering how great the break
is between the Andes of New Granada and those of Mexico, and that the intermediate countries present but few
resting-places for alpine plants. That this depression of the chain has had a powerful effect in either limiting
the extension of species which have appeared since its occurrence, or in inducing changes o f climate which have
extinguished species once common to the north and. south, is evidenced by the fact that a number of Fuegian
and South Chili plants extend northward as alpines to tbe veiy shores of the Gulf of Mexico, but do not inhabit
the Mexican Andes, whilst as many Arctic species advance south to the Mexican Andes, hut do not cross the intermediate
depression, and reappear- in the Bolivian Andes.
e r id e n c e in tb e fa c t th a t, in th e m e r id ia n s o f A u s t r a lia a n d J a p a n , w e h a v e , first, th e n o r th -w e s t
c o a s t o f A u s tr a lia s in k in g , to g e th e r w ith th e L o u is ia d e A r c h ip e la g o t o it s n o r th ; th e n , ap p ro a ch in g
th e L in e , th e N ew I r e la n d g rou p is s in k in g , a s are a lso th e C a r o lin e I s la n d s , in la t . 7° N . B e y o n d
th is , h ow ev e r , in la t . 1 5 ° N . , a r e th e M a r ia n n e I s la n d s (r is in g ), o f w h o s e v e g e ta t io n n o th in g is
k n o w n ; in 2 7 ° N . , th e B o n in I s la n d s (a lso r i s in g ) ; an d in 3 0 ° N . is J a p a n , w ith w h ic h th is b o ta n
ic a l r e la tio n sh ip ex is ts .
I t i s o b je c ted b y M r . D a rw in to th is lin e o f a r g um en t (as to th a t a t p. x v c o n c e rn in g th e
P a c ific I s ia n ils ), th a t a ll th e s e s in k in g ar eas are T olcanio is la n d s , h a v in g n o tr a c e s o f o ld e r r o ck s on
t h e m ; h u t I d o n o t se c th a t th is a lto g e th e r in v a lid a te s th e h y p o th e s is , for m a n y o f t h e lo ft ie s t m o u n ta
in s th r o u g h o u t th e M a la y a n A r ch ip e la g o , N ew Zea lan d , an d th e P a c ific I s la n d s , are v o lc a n ic ; som e
are a c tiv e , a n d m a n y a tta in 1 0 - 1 4 ,0 0 0 f e e t in e le v a tio n , w h ils t th e low e r p o r tio n s o f som e o f th e
la r g e s t o f th e s e isla n d s are fo rm ed o f ro ck s o f various age s.
071 th e G en e ra l P h en om en a o f th e D is tr ib u tio n o f P la n ts in T im e .
A th ird cla ss o f fa c ts r e la te s to th e a n tiq u ity o f v e g e ta b le fo rm s and ty p e s o n th e g lo b e , a s e v id
en c ed b y fo s s il p la u t s . T h e c h ie f fa c ts r e la t in g to th e s e ar e th e fo llo w in g :—
3 1 . T h e e a r lie st F lo r a o f w h ic h w e k n ow m u ch s c ien tific a lly , is th a t o f th e C a rb on iferou s fo rm a tio
n . W e h a v e in d e ed p la u ts th a t b e lo n g e d to an e a r lie r v e g e ta t io n , b u t th e y d o n o t differ in an y
im p o r ta n t r e sp e c ts from th o s e o f th e ca rb on ife rou s fo rm a tio n .
N o w th e a sc e r ta in ed fea tu r e s o f th e co a l v e g e ta t io n m a y h e sum m ed up v e r y b r ie fly . Th e re
e x is t e d a t th a t tim e ,—
F ilic e s ; in th e m a in en tir e ly r e s em b lin g th e ir m o d e rn r ep r e sen ta tiv e s, an d som e o f w h ic h m a y
e v en h e g e n e r ic a lly , th o u g h n o t sp e c ifica lly , id en tic a l w ith th em .
L y c o p o d ia c e a ; th e sam e in th e ir m a in ch a ra c te r s as th o s e n ow e x is tin g , an d , th o u g h o f h ig h e r
sp e c ia liz a tio n o f s tem , o f g r ea te r s ta tu r e , o f d iffe ren t sp e c ie s, an d p erh ap s a lso g en e ra , from m od e rn
L y c o p o d ia c e a , y e t id e n tic a l w ith th e s e in th e s tru c tu r e o f th e ir r ep ro d u c tiv e o r g a n s an d th e ir c o n te
n ts , an d in th e m in u te a n a tom y o f th e ir tis su e s .
Conifei'a. T h e e v id en c e o f th is Order i s d e r iv ed c h ie fly fr om th e a n a tom ic a l ch a ra c te r s o f th e
D ic o ty le d o n o u s w o od so a b u n d a n tly fo u n d in th e c o a l, a n d w h ich s e em s to h e id e n t ic a l in a ll im p o r ta
n t r e sp e c ts w ith th e w o o d o f m od e rn g en e r a o f th a t Order , t o w h ic h m u s t b e a d d ed th e p ro b a b ility
o f T r iy o n o c a rp o n an d N a g g e r a th ia b e in g G ym n o sp e rm o n s, aud a llied to S a lis b u r ia .* O n th e oth e r
h a n d , i t m u s t n o t b e o v e r lo o k ed th a t n o C on ife rou s s tr o b ili h a v e b e en h ith e r to d e te c ted in th e Car b
o n ife r o u s fo rm a tio n . . 1 1
C y c a d e a . S om e fr a gm en ts o f w o od , p r e s en tin g a str ik in g s im ila r ity in a n a tom ica l ch a ra cte r s
to th a t o f C y c a d e a , h a v e b e e n fo u n d in th e ca rb on ife rou s sc r ie s.
I n th e a b sen c e o f th e fru c tifica tio n o f C a tam ite s , C a lam o d en d ro n , H a lo n ia , A n a b a th r a , e t c .,
th e r e e r e n o m a te r ia ls for a n y safe c o n c lu s io n s as to th e ir im m e fiia te a ffin itie s, b ey o n d th a t th e y all
se em to h o alliocl to P e r n s or L g c o p o d ia e e te : b u t th e sam e c a n ha rd ly b e sa id o f th e a ffin itie s o f
V o lkm a n n ia f A n th oU th e s an d o th e r s, w h ich h a v e b e en refe r red, w ith m o r e or le s s p ro b a b ility , to
A n g io sp e rm o n s D ic o ty led o n s .
T h e P e rm ia n F lo r a is for th e m o s t p ar t sp e c ifica lly d is tin c t from th e C a i'bonife rous, h u t m a n y o f
* Fliil. Trans. 1855, p. 149. t See Quarterly Journal o f Geological Society, May, 1854.