- 3 - 
finding all the nutrients they need. As the roots absorb water, 
more must be added to maintain the level correct. The water 
must also be aerated as often as necessary, and its acidity 
maintained at the right value. 
By this means, under ideal conditions, the roots have all 
that they need, in exactly the right proportions, and growth is 
therefore vigorous and rapid. No soil diseases or pests are 
present to harm the roots. By suitable tests, the quantity of 
nutrients in the water can be maintained constantly correct, so 
that the development of the plant proceeds unhindered. Ideally, 
the method should in fact produce perfect plants of maximum size. 
In practice there are found to be certain difficulties, some of 
which have been indicated above. Another is the fact that the 
nutrient solution is an ideal medium for the growth of algae, 
the microscopic water plants that turn ditchwater green. These 
can fairly effectively be dealt with by keeping the water shaded 
from light; green algae cannot grow in the dark. There are 
however other microscopic organisms that can grow in the dark 
and may cause complications: bacteria, protozoa, etc. These 
should be controllable by cleanly methods. 
So far as local experiments have gone, they show that proper 
aeration of the water is the chief difficulty. Mechanical aera¬ 
ting devices, such as those used in large aquaria, may meet this 
need. For some plants, blowing air through the water occasionally 
with a bicycle pump may be enough, but others seem to need more. 
The acidity question is said not to be serious if the solution 
is changed from time to time as it becomes exhausted. It is 
probable that many plants can be grown by this process with 
quite simple equipment by the ordinary person interested in 
gardening, but for larger undertakings the method probably offers 
more difficulties, which will only be discovered and corrected 
by full scale experiments. 
It is possible that the method will in time be developed 
for general use in the commercial production of fresh vegetables 
of many kinds, and for cut flowers, as has already been done 
in various places in America. But it is certain that conditions 
will have to be very carefully controlled by scientific methods; 
like most improvements of technique, hydroponics needs greater 
knowledge and skill for its effective use. 
But he would be a rash man who would prophesy the future 
of horticulture. Besides the salts and the trace elements above 
mentioned, biochemists are now beginning to understand the 
functions of hormones or growth-promoting substances, minute 
quantities of which have a profound influence on the behaviour 
of plants. It is possible that the existence of these in natural 
manures may account for the advantage of the latter over artificial 
fertilizers. Perhaps the really effective use of hydroponics 
may have to wait for a fuller understanding of these more subtle 
needs of the growing plant. 
There are some good books on Hydroponics, published 
in America. One of the first was "Soilless Growth of Plants” 
by Bllis Sc Swaney (Reinhold Publishing Corporation, New York, 
1938). Later books are "Growing Plants in Nutrient Solutions" 
by Turner Sc Henry (John Wiley & Sons, New York, 1939) and 
"Soilless Culture Simplified" by A. Laurie (McGraw-Hill Publish¬ 
ing Co. Ltd., 19h0). A newly published work by Dr. W.F. Gericke, 
originator of the method, called "The Complete Guide to Soilless 
Gardening" has been published this year by Putnam & Co., London, 
price 12/6. 
