16 DISEASES OF GLASSHOUSE PLANTS 
shaped the water will lie in the depression and harmful 
effects invariably follow. Cases similar to this have 
been investigated, and all remedial measures were of no 
avail until the pan was broken up mechanically. 
(c) Relation to Neighbouring High Land.—In choosing 
the site for a future nursery it is important to consider 
the relation of the particular area to the height of the 
surrounding land, for upon this depends two other 
important factors: (1) the height of the water table in 
the soil, and (2) the extent of drainage water passing 
through the site. 
Upon the level of the water table depends the nearness 
of stagnant water to the plant roots. Should the water 
table be high the plants become “ chlorotic ” or yellowish 
in appearance as soon as the roots reach the waterlogged 
soil. The “tops”? become weak and sickly, and the 
vitality of the plants is much reduced, with the con- 
sequence that they become an early prey to parasitic 
fungi or bacteria. 
Such conditions have been found to exist at the base 
of hills which border low-lying plains near to rivers, 
and sites in such regions should be avoided wherever 
possible. 
Upon the surface drainage water depends to an 
important extent the question of contamination with 
fungus and bacterial diseases introduced by such drainage 
water from the neighbouring high lands. 
Two cases, personally investigated by the writer, in 
which epidemics originated in this manner will serve to 
emphasize the importance of this factor. 
In the first, the tomato nursery in question was 
situated in a natural depression at the base of a wide 
ridge, and running close to the block of houses was a 
natural watercourse draining the high land. <A heap of 
soil, part of which had been used each spring during the 
previous six years for raising seedlings and young plants, 
lay at the side of the watercourse. In 1919 tomato 
seedlings raised in nurseries on the top of the ridge had 
