^ FLORA OF TASMANIA.
h a . so m a n y e n em ie s th a t th e y d o n o t p e r p e tu a te it s rac e. I n th e ea se o f t y
E r i n = . - : —
ru le , an d p e rm a n en c e th e e x c ep tio n , or a t Yarictics, a g a in ,
p . . H y b r id iz a tio n , or
IS a p h en om en o J ¡ , g ,,,e r a lly su p p o sed , e v e n in g a rd en s, w h e r e
g o n s m I e ir cnm s ta n c e s th e m o s t fa v ou rab le to th e p rod n c tm n o f a
th e y ar e so o f te n ^ H y b r id s are a lm o s t in v a r ia b ly b a r r en , a n d th e ir
h y b r id , and u n fa v ou rab le t o 1 g . v h o u s t e n d e n c y o f h y b r id iz a tio n b e tw e en v a r ie tie s
r c ? r y . ; : = £ - ^
“ ,” ,"" r . “ i r s . i • ■ - *■•■■“ “ • ' ' T ' "
p. 828.
o r b y th a t o f a n y o th e r p la n t,* th e y e v e n tu a lly r ev e r t to o n e o f th e ir p a r e n t s : o n th e o th e r h an d ,
th e n um b e r o f v a r ie tie s i s in ca lcu la b le , th e p ow e r to v a r y fu r th e r is u n im p a ir ed in th e ir p r o g en y ,
an d th e s e t e n d t o d ep a r t fu r th e r a n d fu r th e r in sen s ib le p rop e r tie s fr om th e o r ig in a l parent.
I n c o n fo rm ity w ith m y p lan o f s ta r tin g from th e va r iab le an d n o t th e fix ed a sp e c t o f N a tu r e ,
I ha v e n ow s e t d ow n th e p r om in en t fe a tu r e s o f th e V e g e ta b le K in g d om , a s su r v e y ed from th is p o in t
o f view . F r om th e p r e c ed in g p aragrap h s th e e v id en c e appear s to h e c e r ta in ly in fa v ou r o f p r o n en e ss
to ch a n g e in in d iv id u a ls , an d o f th e pow e r t o ch a n g e c e a s in g o n ly w ith th e lif e o f th e in d iv id u a l;
an d w e h a v e s t ill to a c c o u n t for th e fa c t th a t th e r e ar e lim its to th e s e m u ta t io n s , an d law s th a t c o n tr
o l th e c h a n g e s b o th a s t o d e g r e e a n d k in d ; th a t sp e c ie s are n e ith e r v isio n a ry n o r e v en arbitrary
c r e a tio n s o f th e n a tu r a lis t ; th a t th e y a r e , in sh o r t, r e a lit ie s , w h e th e r o n ly tem p o r a r ily so o r n o t.
1 3 . G r a n tin g th e n th a t th e te n d e n c y o f N a tu r e is fir st to m u ltip ly fo rm s o f e x is t in g p la n ts b y
g rad u a ted ch a n g e s , an d n e x t b y d e s tr o y in g som e to is o la t e th e I’e s t in ar ea an d in ch a ra c te r , w e are
n ow in a c o n d itio n to s e ek som e th e o r y o f th e m o d u s o p e ra n d i o f N a tu r e th a t w ill g iv e tem p o ra ry
p e rm an en c e o f ch a ra c te r t o th e s e c h a n g e lin g s . A u d h e r e w e m u s t appeal to th e o r y or sp e c u la t io n ;
for o u r k n ow led g e o f th e h is to r y o f sp e c ie s in r e la tio n to o n e a n o th e r , and to th e in c e s s a n t m u ta tio n s
o f tb e ir en v ir o n in g p h y s ic a l c o n d itio n s , is far to o lim ite d an d in c om p le te t o afford d a ta for d em o n str
a tin g th e e ffe c ts o f th e s e in th e p r o d u c tio n o f a n y o n e sp e c ie s in a n a tiv e sta te .
O f th e s e sp e cu la tio n s b y far th e m o s t im p o r ta n t an d p h ilo so p h ic a l is th a t o f th e d e lim ita tio n
o f sp e c ie s b y n a tu r a l s e le c tio n , for w h ich we are in d eb ted t o tw o w h o lly in d ep en d en t an d o r ig in a l
th in k e r s , M r . D a rw in an d M r . W a lla c e .f T h e s e a u th o r s a ssum e th a t a ll a n im a l and v e g e ta b le forms
are v a r ia b le , tlia t th e av e ra g e am o u n t o f sp a c e an d a n n u a l su p p ly o f fo od fo r e a ch sp e c ie s (or o th e r
grou p o f in d iv id u a ls) is lim it e d a n d c o n s ta n t, b u t th a t th e in c r e a se o f all o rg a n ism s te n d s to p ro ce ed
an n u a lly in a g e om e tr ic a l r a tio ; au d th a t , a s th e sum o f o r g a n ic lif e o n th e su r fac e o f th e g lo b e d o e s
n o t in c r ea se , th e in d iv id u a ls a n n tia lly d e str o y ed m u s t be in ca lcu la b ly g r e a t ; a lso th a t ea ch sp e c ie s is
ev e r w a r r in g a g a in s t m a n y en em ie s , an d o n ly h o ld in g it s ow n b y a s len d e r ten u r e . I n th e ord in a ry
co u r se o f natm-e th is a n n u a l d e s tru c tio n fa lls u p o n th e e g g s o r se ed s a n d y o u n g o f th e o rg a n ism s,
and a s i t i s effe c ted b y a m u lt itu d e o f a n ta g o n is tic , ev e r -ch a n g in g n a tu ra l cau se s, ea ch m o r e d e stru c tiv
e o f o n e o rg a n ism th a n o f an y o th e r , it op e ra te s w ith diffe r en t e ffe ct o n ea ch grou p o f in d iv id u a ls,
in ev e ry lo c a lity , an d a t ev e ry r e tu i-n in g sea son . H e r e th e n w e h a v e an in fin ite n um b e r o f ^•arying
c o n d itio n s , an d a su p e rab u n d an t su p p ly o f var iab le o r g a n ism s, to a c com m o d a te th em s e lv e s to th e s e
c o n d itio n s . N oav th e o r g a n ism s ca n h a v e n o p ow e r o f su r v iv in g a n y ch a n g e in th e s e c o n d itio n s,
e x c ep t th e y are en d ow ed w ith th e m e a n s o f a c c om m o d a tin g th em s e lv e s to it . T h e ex e r c ise o f
th is p ow e r m a y b e a c com p a n ied b y a v isib le (m o rp h o lo g ica l) ch a n g e in th e fo rm o r s tru c tu r e o f th e
in d iv id u a l, or i t m a y n o t , in w h ich ca se th e r e is s t ill a ch a n g e , b u t a p h y s io lo g ic a l o n e , n o t ou tw a rd ly
* A very able aiic! careful experimenter, M. Naudin, performed a series of experiments at the Jardin des Plantes
at Paris, in order to discover tbe duration of tlie progeny of fertile hybrids. He concludes that the fertile posterity
of hybrids disappears, to give place to the pure typical form of one or other parent. “ II se pent sans doute qu’il
y ait des exceptions à cette loi de retoui-, et que certains hybrides, à la fois très-fertiles et trcs-établis, tendent à faire
souche d’espèce ; mais le fait est loin d ’être prouvé. Plus nous observons les phénomènes d’hybridité, plus nous
inclinons à croire que les espèces sont indissolublement liées à une fonction dans l’ensemble des choses, et que c’est
le rôle même assigné à chacune d’elles qui en détermine la forme, la dimension et la durée.” (Annales des Sc. Nat.
sér. 4. V. 9.)
t Journal of the Linnean Society of London, Zoology, vol, iii. p. 45.
c 2