226 SCIENCE OF THE STUDY -OF TREES. PART IT. 
plants, are not many; but, still, some, such as the canker, &c., require to 
be noticed, when the species subject to them come under review. 
D. Accidents. Some trees and shrubs are more liable than others to be 
blown down, or have some of their branches broken off by high winds, or 
by the weight of snow; and these species should be pointed out to the 
inexperienced planter. Some, also, are said to be less liable to be struck 
by lightning than others ; for example, the beech. 
7. Geographical Distribution. The different countries will be mentioned where 
each species is found naturally ; and, where practicable, the different lo- 
calities, soil, elevation, and other particulars will be given. It will also be 
stated, as far as is known, in what countries each species is cultivated, and 
to what purposes it is applied. 
8. History. This subject may be included under two heads ; viz. retrospective 
and prospective. P 
A. The Retrospective History of every species or variety will commence 
with its first discovery, or record by botanists; and its progress will be 
traced in every country, but more especially in Britain, from that period 
to the present time. Though the history of some trees and shrubs com- 
mences with the time of the Romans, yet that of others is comparatively 
obscure ; and, of some of the finest ornaments of our gardens, little more 
can be stated than that they are races or varieties, perhaps hybrids, raised 
by cultivators whose names are unknown. 
B. Lhe Prospective History, or probable progress, of our knowledge of 
species may be included under the heads of doubtful species, unnamed 
species, and expected additions. 
a. Doubtful Species. In almost every genus, containing several species, 
there are some of the names which are of doubtful application, which 
under this head we shall bring together, with their authorities, in order 
to direct the attention of botanists and cultivators to the subject. 
b. Unnamed Species. The introduction of new species of trees and 
shrubs into British gardens is constantly going on, and numbers are also 
as constantly being raised from seed in the country. Jn general, neither 
of these kinds of additions to our ligneous flora can be received into 
books till they have flowered; when they are named, figured, and re- 
corded in some botanical work. It often happens, however, that the 
genus to which a new plant belongs is discovered, from the general 
habit of the plant, long before it has flowered; and in such a case, 
though the species may not be introduced into botanical catalogues, 
plants of it may be distributed among cultivators by those who have 
introduced it, and it may be propagated for sale in the nurseries, under 
some provisional name. Such species, and also varieties raised in the 
country from seed, or otherwise procured, deserve notice in a work 
like the present, and we shall devote this head to the subject. 
c. Expected Additions. The species of some genera are so numerous, 
and their geographical distribution is so extensive, that from these cir- 
cumstances alone we may reasonably anticipate the discovery and 
the introduction of additional species. Of other genera, many species 
suitable for our climate, though not yet introduced, have been described 
by botanists as indigenous in different parts of the temperate hemi- 
spheres. It will be useful to direct attention to both these points, with 
a view of stimulating travellers and others to procure the additional 
species that are known; and wealthy individuals, or societies or asso- 
clations, to send out collectors to discover those species which may be 
yet unknown. 
9. Use. Trees and shrubs are used in the arts of construction, of machinery, 
and of fabrication ; in the chemical arts of dyeing and colouring; in domestic 
and rural economy ; and in medicine. 
A. The Arts of Construction are, civil, military, and marine architecture ; 
engineering, carpentry, joinery, cabinet-making, carving, and modelling ; 
