s 
&. 
a 
6 J.D. Hooker, Intypductory Essay to the Flora of Tasmania. 
species, the rough, rusty-leaved form of Ceylon, and the smooth, 
silvery-leaved form of the northwestern Himalaya. A white 
botanists are not agreed as to their limits, and often fail to refer 
the offspring with certainty to their parents, each being distin- 
uished from one or more others by one or a few such trifling 
characters, that each group may be regarded as a continuous 
series of varieties, between the terms of which no hiatus exists 
suggesting the intercalation of any intermediate variety. The 
genera Rubus, Rosa, Salix, and Saxifraga, afford conspicuous ex- 
amples of these unstable species; Veronica, Campanula, and 
Lobelia, of comparatively stable ones. 
4. Of these natural groups of varying and unvarying species, 
some are large and some small; they are also variously distrib. 
uted through the classes, orders, and genera of the Vegetable 
Kingdom; but, asa general rule, the varying species are rela- 
tively most numerous in those classes, orders, and genera which 
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