8 J. D. Hooker, Introductory Essay to the Flora of Tasmania. 
and genera may respectively consist of only undefinable groups. 
of genera or of species. For instance, both Graminee and : 
p are, in the present state of our knowledge, absolutley 
limited orders, and extremely natural ones also; but their gen- — 
era are to a very eminent degree arbitrarily limited, and their — 
species extremely variable. Orchidee and Leguminose are also 
well-limited orders (though not so absolutely as the former), but 
they, on the contrary, consist of comparatively exceedingly 
well-marked genera and species. Melanthacee and Scrophulart- 
nee, on the other hand, are not limitable as orders, and contain 
very many differently constructed groups; but their genera, and 
to a great extent their species also, are well-marked: and limita- 
ble. The circumstance of a group being either isolated or hav- 
ing complex relations, oa anaes no indication of its members — 
having the same charac 5 
gain, as with sussiit so with genera and ‘orders, we find 
that upon the whole those are the*best limited which consist of — 
plants of complex floral structure: the. orders of Dicotyledons 
are better limited than those of es and the genera 
of Dichlamydez than those of Achlamydezx.* 
always recognized ; these may be called eer orders ; Orchide and Graminee 
are exam les. _An ny naturalist, endowed with fair powers ‘of Shear vation and general- 
D 
uninstructed person to recognize the se affinity of Clematis and Ranunculus, or 
of Acacia and Cytisus, though tite os realy 7 closely related as the “Orchids and 
Grasses mentioned above. We do not why some orders are subjective and 
some objective; but if ae theory of ceeaion by waite is a rss one, we ought 
mrough it to reac ses a solu 
ere oO many ssoepligns to this to admit of our concluding at once Lisi 
it is attributable to any simple and uniform law of variation; but it 
the i 
eee ee. oy groups being most preva rps her classes (i. ¢., 
‘ony most a in tice oO =e woul a Jak oes appear an 
rogr were it ae the cons t the higher 
eipeor., 3 thes the 
surpassed the ae ph of gen - ct species, in indi- 
in bulk and at pg And lastly, i all the highest orders é plants 
n genera of as simple organization as any of the 
t ‘that physical superiority which is manifested in 
ter securing a of r rape jn more pave ragie 
even in eel "of bulk, is in 
tan tet peoand angry comapAZEY OF or specialization of organ. 
