com p a n ied w ith a g r ea te r t e n d e n c y t o p e rm a n en c e in f o rm ; th u s A c o ty le d o n s , M o n o c o ty le d o n s , an d
D ic o ty le d o n s are a n a sc e n d in g se r ie s in c om p le x ity an d in c o n s ta n c y o f fo rm . I n D ic o ty le d o n s ,
S a lic e s , U r tic e a , C h en o p o d ia c e a , an d o tlie r O rd e r s w ith in c om p le te or a b s en t flo ra l en v e lo p e s, va ry
o n th e w h o le m o r e th a n Leguminos<B, L y th r a c e x , M y r ta c e e s , or R o s a c e a , y e t m em b e r s o f th e s e p re s
e n t , in a ll c o u n tr ie s , g ro u p s o f n o to r io u s ly v a r y in g sp e c ie s , a s E u c a ly p tu s in A u s tr a lia , R o s a in E u ro p e ,
an d L o tu s , E p ilo b ium , a n d R u b u s in b o th E u r o p e an d A u s tr a lia . A g a in , e v e n g en e r a are d iv id e d : o f
th e la s t n am ed , m o s t o r all o f t h e sp e c ie s are v a r ia b le ; o f o th e r s, a s E p a c r is , A c a c ia , a n d th e m a jo r ity
o f s u c h a s c o n ta in u pw a rd s o f s ix or e ig h t sp e c ie s, a la r g e r or sm a lle r p ro p o r tio n o n ly a r e variable.
B u t th e p r om in e n t fa c t is , th a t th is e lem e n t o f m u ta b ility p ervad e s th e w h o le V e g e ta b le K in g d om ;
n o c la s s n o r o rd e r n o r g e n u s o f m o r e th a n a few sp e c ie s c la im s a b so lu te e x em p tio n , w h ils t th e g ran d
to ta l o f u n s ta b le fo rm s g en e r a lly a ssum ed t o b e sp e c ie s p r o b a b ly e x c e ed s th a t o f th e stab le .
5 . T h e ab o v e r em a rk s are eq u a lly ap p licab le to aU th e h ig h e r d iv is io n s o f p la n ts . S om e
g en e r a an d o rd e r s ar e a s n a tu r a l, a n d as lim ita b le b y ch a ra c te r s, a s are som e sp e c ie s ; o th e r s '
a g a in , th o u g h th e y c o n ta in m a n y v e r y w e ll-m a rk ed su b o rd in a te p la n s o f c o n s tru c tio n , y e t ar e so
c o n n e c ted b y in t e rm e d ia te fo rm s w ith o th e rw is e v e r y d iffe r en t g en e r a o r o rd e r s, th a t i t is im -
p o s s ib le t o l im it th em n a tu r a lly . A n d a s som e o f th e b e s t m a rk ed an d lim it e d sp e c ie s c o n s is t o f
a se r ie s o f b a d ly m a rk ed a n d illim ita b le v a r ie tie s, so som e o f th e m o s t n a tu r a l* a n d lim ita b le orders
a n d g en e r a m a y r e sp e c tiv e ly c o n s is t o f o n ly u n d e fin a b le g ro u p s o f g en e r a or o f sp e c ie s. F o r in s ta n c e ,
b o th G r am in e a a n d C om p o s ita are, in th e p r e s en t s ta t e o f o u r k n ow led g e , a b so lu te ly lim it e d O rd e rs,
an d e x tr em e ly n a tu r a l o n e s a l s o ; b u t th e ir g en e r a ar e t o a v e ry em in e n t d e g r e e arb itra r ily lim ited ,
a n d th e ir sp e c ie s e x tr em e ly v a r ia b le . O r c h id e a a n d Leguminosc e a r e a lso w e ll- lim ite d O rd er s (th o u g h
small genera and the fact that monotypic genera seldom have their variations recorded in systematic works, hut an
examination of h is data and methods compels me to acquiesce in his statement. I t has also been remarked (Boiy de
Saint-Vincent, Voy. aux Quatre lie s de FAfrique) that the. species of islands are more variable than those o f continents,
an opinion I can scarcely subscribe to, and opposed to Mr. Darwin’s facts, inasmuch as insular Floras are characterized
by peculiar genera, and by liaving few species in proportion to genera. Bisexual trees and shrubs are generally
more variable than unisexual, which however is only a corollary from what is stated above regarding plants of simple
structure o f flower, On the whole, I think herbs are more variable than shrubby plants, and annuals than perennials.
I t would be curious to ascertain the relative variableness of social and scattered plants. The individuals of a social
plant, in each area it is social upon, are generaUy very constant, but individuals from different areas often differ much.
The Finns sylvesiris, Muyhus, and uncinata are cases in point, if considered as varieties of o n e ; as are the Cedars of
Atlas, Algeria, and the Himalaya.
* It should he home in mind that the term natural, as applied to Orders or other groups, bas often a double
significance; every natural order is so in the sense of each of its members being more closely related to one or more
of its own group than to any of another; but the term is often used to designate an easily Hmited natural order, that
is, one whose members are so very closely related to each other by conspicuous peculiarities that its diflei-ential characters
can be expressed, and itself always recognized; these may be caUed ohjective Orders; Orcliidea and Graminea
are examples. Any naturaUst, endowed with fair powers of obseiwation aud generalization, recognizes the close affinity
between a pseudobulbous epiphytical, and a terrestrial tuberous-rooted Orchid, or between the Bamboo and
■\Vheat, though the differences are exceedingly great in habit and in organs of vegetation and reproduction. Other
orders are as natural and may be as well limited, but having no conspicuous characters in common, and presenting
many subordinate distinct plans o f structure, may be regarded as subjective. Such are Ranunculacecs and Zeyu-
mi7iosx, o f which a botanist must have a special and extensive knowledge before he can readily recognize veiy many
of their members. No-degree of natural sagacity \riR enable an uninstructed person to recognize the close affinity of
Clematis and Ranunculus, or of Acacia and Oytisus, though these are really as closely related as the Orchids and
Grasses mentioned above. We do not kuow why some Orders are subjective and some objective; but if the theory
of creation by variation is a true one, we ought through it to reach a solution.
n o t so a b s o lu te ly a s th e fo rm e r ), b u t th e y , o n th e con tr a r y , c o n s is t o f c om p a r a tiv e ly e x c e e d in g ly w e ll-
m a rk ed g en e r a a n d sp e c ie s. M e la n th a c em a n d S c r o p h u la r im a , o n th e o th e r h an d , a r e n o t lim ita b le
a s O rd e r s, a n d c o n ta in v e ry m a n y d iffe r en tly c o n s tr u c t e d g r o u p s ; b u t tb e ir g en e r a , a n d to a g r e a t
e x te n t th e ir sp e c ie s a ls o , are w e ll-m a rk ed an d lim ita b le . T h e c ir cum sta n c e o f a g rou p b e in g e ith e r
iso la ted o r h a v in g com p le x r e la tio n s , is h e n c e n o in d ic a tio n o f i t s m em b e r s h a v in g th e sam e ch a ra c te r s.
A g a in , a s w ith sp e c ie s, so >vith g en e r a an d orde r s, w e fin d th a t u p o n th e w h o le th o s e are th e
b e s t H m ited w h ic h c o n s is t o f p la n ts o f c om p le x flo ra l s t r u c tu r e : th e O rd er s o f D ic o ty le d o n s are
b e tt e r lim it e d th a n th o s e o f M o n o c o ty le d o n s , a n d th e g en e r a o f D ich lam y d e® th a n th o s e o f A ch la r
mydca?.*
N o w m y o b je c t in dw e llin g o n th is p a ra lle lism b e tw e e n th e ch a r a c te r istic s o f in d iv id u a ls in
r e la tio n to sp e c ie s, o f sp e c ie s in r e la tio n to g en e r a , a n d o f g en e r a in r e la tio n t o O rd e rs, i s b e c a u se I
co n sid e r (In tr o d . E s s a y to FI. N . Z.) th a t i t is to th e e x tin c tio n o f sp e c ie s a n d g en e r a th a t w e are
in d e b t e d for ou r m e a n s o f r e so lv in g p la n ts in to lim ita b le g en e r a an d orders. T h is v iew is n ow , I
b e lie v e , g en e r a lly adm itted , ev en b y th o s e w h o s t ill regai-d sp e c ie s as th e im m u ta b le u n its o f th e
V e g e ta b le C r e a tio n ; an d i t th e r e fo r e n ow r em a in s to b e s e en h ow far w e are w a r ran ted in e x t e n d in g
it t o th e lim ita t io n o f sp e c ie s b y th e e lim in a tio n o f th e ir v a r ie tie s th r o u g h n a tu r a l c a u s e s .f
6 . T h e ev id en c e o f v a r ia b ility th u s d ed u c ed from a rap id g e n e r a l su r v e y o f th e p r om in en t fa c ts
e lic ite d from a s tu d y o f t h e p r in c ip le s o f c la ssific a tio n , a r e to a c e r ta in e x t e n t te s t e d b y th e b eh a v io u r
o f p la n t s u n d e r cu ltiv a tio n , w h ich op e rate s e ith e r b y h a s t e n in g th e p ro c e sse s o f N a tu r e (in rap id ly
in d u c in g v a r ia tio n ), o r b y e ffe c tin g a prolepsia or a n tic ip a tio n o f th o s e p r o c e sse s (in p r o d u c in g sports^
i. e. b e tt e r m a rk ed v a r ie tie s, w ith o u t g rad u a ted s t a g e s ) ,o r b y p la c in g th e p la n t in co n d itio n s to w h ich
i t w o u ld n ev e r h a v e b e en exp o sed in th e ord in a ry co u r se o f n a tm ’a l e v e n ts , a n d w h ich e v e n tu a lly e ith e r
kiH it o r g iv e o r ig in t o a s e r ie s o f v a r ie tie s w h ich m ig h t o th e rw ise h a v e n e v e r e x is te d .J
* There are too many exceptions to this to admit o f our concluding at once that it is attributable to any
simple and u n ifom law o f variation; but it may be explained by assuming that the degree or amount o f variation is
differently manifested at different epochs in the histoiy of the group. Thus, if a genus is numerically increasing, and
consequently running into varieties, it wOl present a group of species with complex relations inter se; if, on the con
trar\', it is numerically decreasing, such decrease must lead to the extinction of some varieties, and hence result in the
better limitation o f the remainder. The application of this assumption to the fact of the best limited groups being
most prevalent among tbe higher classes (t. e. among those most complicated in their organization), would at first
sight appear an argument against progression, were it not for the consideration that the higher tribes of plants have
in another respect proved themselves superior, in that they have not only far siupassed the lower in number of genera
and species, but in indiidduals, and also in bulk and stature. And lastly, as all the highest orders of plants contain
numerous species and often genera of as simple organization as any o f the lower orders are, it M ow s that that physical
superiority which is manifested in greater extent of variation, in better securing a succession of race, in more
rapid multiplication of individuals, and even in increase of bulk, is in some senses of a higher order than that represented
by mere complexity or speciabzation of organ.
t It follows as a coroUaiy to the proposition (That species, etc., are naturally rendered limitable by the destruc-
. tion of varieties), that there must be some intimate relation between the rate of increase and the duration of genera
(or other groups of species) on the one hand, and the limitability of their species on the other. Thus, when a genus
consists of a multitude of ibimitable foims, we may argue -with much plausibility that it is on the increase, because
no intermediates have as yet been destroyed, and that the bhth o f indiriduals aud the production o f new forms is proceeding
at a gi-eater proportional rate than in an equally large genus of which the species are limitable.
t hly friend Mi-. Wallace treats of animals under domestication, not only as if they were in very different
physical conditions from those in a state o f nature, inasmuch as every sense and faculty is continually fully exercised
and strengthened by w ild animals, wlulst certain o f these lie dormant in the domesticated, but as if they were