THE FORMATION OF PLANTATIONS, 105 
to grow slowly and unprofitably, as their timber value is usually 
in direct proportion to the rapidity of their growth, ceteris 
paribus. Coniferous trees, on the other hand, generally produce 
better timber when their growth has been slow, and are therefore 
better adapted for planting at high altitudes, although they take 
longer time to come to maturity. In this country (Scotland) 
timber of any kind can hardly be profitably grown over 1500 feet 
above sea-level, and, in the vicinity of the sea, that altitude is 
probably too great. Much depends, however, upon the latitude ; 
the nearer the equator the greater the altitude at which plants will 
grow. Climate is perhaps the most important factor in vegetable 
growth, for the elements of cold, heat, light, and moisture 
come under its head. More especially must it be considered 
in relation to all introductions from other countries, for it is the 
only important distinction which exists between different countries, 
and therefore powerfully affects plant life when moved from its 
native habitat. Owing to the insular position of Great Britain, 
it enjoys a warmer and more temperate climate than many 
countries which lie between the same degrees of latitude; but 
although it possesses the advantage of being usually free from 
extremes of cold and heat, it has the disadvantage of being very 
variable, especially during the spring months, when vegetation is 
very susceptible of atmospheric influence. In consequence of 
this, introductions from countries possessing more regular and 
equable climates than ours are often excited into growth by a 
spell of mild weather during March and April, and in the event 
of this being succeeded by a few days of cutting wind, or frosty 
nights, the effect on such plants is very injurious, and often 
engenders disease and unhealthy growth. This is frequently 
noticeable in the larch and silver fir, as shown by the unhealthy 
condition of their foliage, and the consequent attacks of aphides 
and other insects which generally accompany a weak and sickly 
growth. To prevent the result of this excitability as much ag 
possible, such trees should be planted in situations where the 
variations of temperature are felt as little as possible, such as 
on slopes facing the north, cool soils, or in any other situations 
where the plants would be less likely to start early into growth, 
Duration and intensity of sunlight also exercise a great influence 
on tree growth, especially in regard to the proper ripening of the 
wood. Trees like the larch, which continue growing late into 
autumn, cannot fail to be injuriously affected by a cold wet 
