330 
THE PRINCIPLES OF BOTANY. 
below the graft produce the ordinary yellow laburnum of 
large size, those above exhibit often small purple laburnum 
flowers, as well as reddish flowers intermediate between the 
two in size and colour. Occasionally the same cluster has 
some flowers yellow and some purplish. 
These remarks are sufficient to show that the stock and 
the graft exert an influence on each other, and also that 
different species, nay, and often different genera may be 
grafted on the same stock, though still it may be asserted as 
a rule that different families of plants may not be so inter¬ 
mixed ; thus, the apple may be grafted on the quince, or on 
the white thorn; but we shall try in vain to effect a union 
by grafting of the apple with the oak or the walnut. We 
should not omit to mention that in the case of fruits grafting 
hastens their fruiting powers, besides perpetuating a desired 
variety. 
In the case of fruits there is no doubt but that differences 
in soil and climate exert a great influence upon their pro¬ 
perties and the products derived from them; thus at home 
we find that the same sorts of apples taken from a friend^s 
orchard will differ in every essential particular; and so even 
neighbouring orchards will make a different sort and quality 
of cider, and this quite apart from treatment. Again, the 
grape in different parts of the world produces very diverse 
wines. So, again, in medicinal or food products, we knoAV 
that they vary from the same causes, and even our ordinary 
cereal crops will in the same county be richer in feeding 
properties in one year than in another. In all cases climate 
has the greatest influence, and hence we sometimes hear talk 
of acclimatisation as regards plants, but in as far as our own 
experience goes, it is easier to make an artificial climate 
suitable for tender plants as for less hardy animals; thus, 
the hot-house, green-house, drainage, and good cultivation, 
all are ameliorators of climate; but as yet we know of no 
process that will enable us to harden tropical plants so as to 
enable them to withstand northern rigour unless they pos¬ 
sessed the capability before. 
It is interesting to find that, in this respect, the same law 
affects both animals and plants, and in both we find that 
true acclimatisation fails. Thus, though the Italian grey¬ 
hound is bred in Britain, the offspring, like the parents, 
must be provided with jackets against the cold; and in our 
zoological gardens houses for tropical animals are obliged to 
be kept warm in summer. So it is with plants. AVhen 
Cobbett would persuade his countrymen to grow maize 
or Indian corn, he probably knew that North America and 
