increasing the thickness of the tree. When the stem is injured, eg., 
by animals peeling off the bark, the cambium attempts to grow over 
the wound and cover it up, but often not quickly enough, if the 
injury is of considerable area, to prevent wound-fungi, which are 
among the commonest parasites of stems, obtaining a lodgment. 
The soil is an important factor in the health of the plant. An 
excess of moisture, not so much as mere moisture but because it 
excludes air, is highly detrimental ; though the amount which can 
be comfortably tolerated varies with different species of plant. 
Equally detrimental is an excess of free acids, especially on a plant 
which gives off a relatively large amount of water from its leaves 
(transpires strongly). The roots or trees exercise great selective 
power, but too much of the mineral salts which are necessary to the 
healthy growth of a plant may prevent it thriving or set up patho- 
logical appearances. Though in this as with the amount of 
moisture what is one species’ food is another species’ poise. . Just 
as certain species of plants can successfully withstand drought 
which would be fatal to others, so can particular plants grow on a soil 
containing a concentration of mineral salts which t or Axil 
those not accustomed to it. There are certain infecti---' -asses, 
such as the “ rrlosaic” diseases of tobacco, and “pen yellows/’ in 
the United States, the “ spike ” disease of sandalwood pees in India, 
which are not/ due to fungi or bacteria, but to internal disturbances 
in the economy of the plant. They are generally assigned to faults 
in nutrition, to a surplus or deficiency of certain 'lecessary elenyents 
in the soil ; but there is considerable diversity of opinion as to the 
actual cause^. 
It has been said that a plant lives up fc; its privileges. It 
endeavours to make arrangements to meet p^tstynt difficulties such 
as continual strong wind, or a loose soil ii } which it must make 
special efforts to attain a firm foothold, but ft makes no preparation 
to meet unaccustomed attacks hence the dam«ye done by storms of 
wand or hail. If coffee or sugar is cut dy,^ Vi 7"befcto the p8T3 
planted among them has got well above [heir level, it is sure to 
suffer from wind. When trees are blown down, unless the wind 
has been much beyond the ordinary, the s^il, especially the drainage 
of the subsoil, and the health of the root must be investigated. 
When several show a tendency to topple . over it is often ascribed 
to top heaviness, which should be r signed as a cause, if indeed it 
ever can be one, only when all /others/ have been dismissed as 
improbable. ( 
From the foregoing it will be seen th£t attention must be paid to 
soil and surrounding cpqdititions\aud to any unnatural treatment, 
such as tapping, or cutting\lfAves, t d/which a tree is exposed if not 
alone itself but its neighbors of the same species are to be kept 
healthy. / /- 
Unhealthiness caused by parades is the more dangerous. If it 
assume an epidemic character, the monetary loss may be serious, 
perhaps sufficient to destroy entire industry. These references 
are to parasites of a plan^ nature only (fungi, and bacteria). 
