HYGIENIC CONDITIONS OF GLASSHOUSES § 15 
The tomato, one of the most important crops under 
glass, is especially sensitive to the drainage factor, and 
serves as an example of the way in which plants react 
to the water conditions existing round or near the roots. 
Generally speaking, tomato plants thrive best in a well- 
drained alluvial soil, such as is found in many parts of 
the Lea Valley. It is well known that the tomato 
produces its highest yields in soils where it may be given 
abundant water which readily drains away through the 
subsoil, and some of the best crops have been produced 
in the neighbourhood of sandpits, where the water may 
be seen literally pouring away. On the other hand, 
the application of too much water on lands where the 
drainage is poor will give rise to a poor, unhealthy crop. 
While the best results are obtained with abundant 
water accompanied by efficient drainage, it is of 
paramount importance that where these conditions do 
exist the water supply must be sufficient to keep the 
soil uniformly moist and yet allow for loss by drainage. 
Should a deficiency occur even for a day in the water 
supply of a tomato nursery the effect on the plants will 
be evident at a later date. Where insufficient water 
is provided over a number of days “ blossom end rot” 
of the tomato fruits is almost sure to appear a few weeks 
later. When the result is as marked as this, however, 
the bad effect of insufficient watering is obvious; but 
in many cases the outward signs are not so evident and 
are to be looked for in a reduced yield and vitality. 
Lands, however, in which the drainage is too rapid are 
in the minority, and by far the greater amount of trouble 
arises from insufficient drainage. The existence of 
insufficient drainage in the subsoil is not always apparent, 
but careful observation on the grower’s part will generally 
reveal it. This is the case when on apparently ideal 
soils, with a suitable inclination, there exists a hard pan 
or impervious stratum of soil at some distance below 
the surface. The existence of such may be a limiting 
factor in the health of the crop, for if the pan is saucer- 
