THE ORCHID WORLD. 
THE ROOT SYSTEM OF ORCHIDS. 
THE importance of the root system in 
orchids cannot be over-estimated, and 
a few remarks concerning" tiie utihty 
oi it to the plant may prove of interest. 
In terrestrial plants the roots usually fix 
the plant to the soil, and in the case of 
epiphytes to the trees or rocks upon which 
they are growing. These roots absorb water 
and nutritive material, while in order to satisfy 
the greater demands made upon the plant as 
the developing shoot system above ground 
increases in size, the root system must grow 
and become stronger, so as to provide a firmer 
attachment and to render possible an in- 
creased absorption of water and nutritive 
material. 
In the photograph of Cattleya Trianse re- 
produced on page 138 the very remarkable 
extent of this root expansion is visible. 
Besides securely fastening the plant to the 
v. all the roots have, by the aid of many lateral 
branches, covered an area of 8 ft. 6 m. by 
7 ft. 3 in., from which they draw their nutritive 
supply. 
The plant has been in its present position 
for four years, and the roots are very interest- 
ing to watch, for they grow as much during 
the winter months as they do in the summer. 
The roots of orchids may be divided into 
two divisions : terrestrial, or those which grow 
into the soil or compost, and aerial, or those 
which remain exposed to the atmosphere. 
We will first consider the terrestrial roots 
of an orchid. It is a well-known fact that 
primary or the first-made roots of a plant 
usually grow in a downward direction, or 
towards the earth. This is spoken of as 
geotropic irritability, and in order that the 
root system may spread thoroughly through 
the soil or compost it is necessary that the 
secondary or side roots should not be so sus- 
ceptible to this force of gravity, otherwise 
they would all grow in the same downward 
direction, and much of the nutritive material 
in the adjacent upper part of the soil or com- 
post would be unused. If, for example, a 
strong plant of Cattleya labiata be turned out 
of its pot these secondary roots may be seen 
branching out of the primary one at right 
angles and running round the inside of the 
pot in a horizontal position. 
A very large part of the constructive 
material required by an orchid is obtained by 
means of its roots, and, no matter m what soil 
or material they are in contact with, the roots 
will only absorb this nutriment in a liquid 
form. Every plant has definite specific needs, 
and to satisfy these has the marvellous power 
of selecting from the many ingredients con- 
tained in the soil not only those which are 
specially required for the well-being of the 
plant, but also those which, although non- 
essential, are always collected by certain 
species. 
The aerial roots, having a somewhat dif- 
ferent function to perform, show little or no 
geotropisin, and, instead of growing towards 
the earth, grow in all directions, and cling to 
almost anything which perchance they came 
across. 
Many of these aerial roots, beside obtaining 
nutriment, as will presently be explained, are 
provided with a distinct negative heliotropism, 
or, in other words, have a tendency to grow 
away from the light, and as soon as they 
approach any substance having a damp sur- 
face send out many small root-hairs, or 
suckers, and securely fasten themselves to this 
material. 
The power of adaptation in these roots is 
not very great, and any sudden change may 
be productive of transitory ill effects. When 
re-potting an orchid one may frequently have 
noticed that if any aerial roots are buried in 
the compost they invariably decay in a very 
short space of time. 
All aerial roots of orchids are covered with 
a very thick epidermis, or skin, which is com- 
posed of numerous cells, without any living 
contents, the walls of which are colourless, 
though in mass they frequently have a silvery 
lustre, and when immersed in water soon 
become sufficiently transparent to permit the 
inner green tissue to be visible. Some of the 
older aerial roots are continually green, be- 
cause these cells contain minute algae. This 
