LUTHER BURBANK 
with the hardy plants, I am somewhat handi- 
capped in the attempt to deal with the more 
tender ones. 
This is notably true of the orange and its allies 
of the citrus family. 
These fruits very naturally interested me from 
the outset, not only because of their economic im- 
portance, but because the five familiar species of 
the family, namely the orange, lemon, lime, shad- 
dock, and citron present inviting diversities of 
form and habit, and yet are so closely allied that 
they cross very readily, and thus give the plant 
experimenter precisely the opening that he is 
always seeking. 
It is probable that all these citrus fruits sprang 
from one original species growing somewhere in 
the region of northern India. 
But although the habitat of these plants has 
always been restricted to sub-tropical climates, 
yet they have become so diversified as to form 
fairly good species, and the different traits of the 
various members of the clan are fairly fixed. Not, 
indeed, that any of them may be raised advantage- 
ously from seed, for here they show the same 
diversity that is shown by the other orchard fruits. 
But all varieties of oranges, for example, differ 
quite radically from any variety of lemons, and 
the seeds of the orange will not produce the 
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