30 DISEASES OF GLASSHOUSE PLANTS 
matter were richer in fungi than those whose waters 
were clearer. Water from brooks and ponds was also 
highly contaminated, but a slight reduction in the 
number of fungus species results from thoroughly clearing 
away the vegetation on the banks. Water which had 
passed through an uncovered tank was more highly 
contaminated than that from a covered tank. The 
importance of a pure water supply is obvious, and every 
nursery should possess a deep artesian well, suitably 
protected from contamination by surface drainage. 
(b) Straw Manure.—Straw manure has frequently 
been regarded with suspicion as a possible source of 
infection with plant diseases, and investigations at 
Cheshunt Experimental Station have indicated that such 
may be the case (7). Some disease-causing fungi thrive 
on this material and readily permeate large masses 
when they gain access to them. Our investigations were 
concerned primarily with the introduction of cucumber 
anthracnose caused by Colletotrichum oligochetum, but 
they also showed that other plant parasites may be 
introduced in this manner. Straw manure from different 
sources was examined, and while many were found to 
be free from plant pests others were badly contaminated. 
Manure from country farms was mostly free from disease, 
but that obtained from town stables was frequently 
contaminated. Heaps of straw manure lying adjacent 
to those of decaying plant debris on commercial nurseries 
were found to be contaminated. 
Growers should exercise particular care in the choice 
of their straw manure, and that which is obviously 
contaminated with half-rotten potatoes and roots should 
be avoided. 
(c) Imported Plants—Growers whose land is free 
from disease should be warned against importing plants 
from other nurseries, but where this is unavoidable the 
imported plants should be isolated until it is certain 
they are free from disease. Jt must be clearly understood 
that it is easier to keep disease away from a nursery than to 
