M.—AGRICULTURE. 249 
to conquer the waste, are always liable to fail through soil troubles, 
plant diseases or insect attacks. Over large parts of our Empire 
there is a continuous struggle for possession between insects and men, 
and the margin of victory, even when we get it, is never very great. And 
there are new troubles as yet only dimly seen that may easily cause great 
difficulty in future. The remarkable development of rapid transport has 
carried all over the world not only the blessings but also the evils of this 
earth. Pests and diseases of animals, and particularly of plants, have 
only to appear in one corner of the globe to spread elsewhere with great 
rapidity despite all regulations to the contrary, often causing enormous 
losses. Among the most serious troubles of modern times are the virus 
diseases of plants. These diseases are apparently not caused by any 
recognisable living organism, nor are they simple physiological 
disturbances; they cannot yet be attributed to any definite causal 
agent. They spread rapidly, being frequently carried by small insects, 
sometimes by mere contact, and they cannot be cured, one can only 
stand by and see the plants perish. All kinds of crops are affected : 
sugar-cane, tobacco, cotton, sugar-beet, groundnuts, bananas, potatoes, 
maize, timber trees (e.g. Sandal), large and small fruits (e.g. peach and 
raspberry) and most greenhouse and horticultural plants. And it is not 
so much sickly plants as healthy ones that suffer; the disease may come 
suddenly and with great virulence into a healthy prosperous region and 
_ devastate the most important crop. In Gambia the Rosetta disease cut 
down the crop of groundnuts to about one-third of the normal yield.’ 
In the United States in 1926 two virus diseases reduced the crop of potatoes 
by no less than 16 million bushels. In this country the total loss cannot 
be estimated, but the figures recorded for various attacks vary from 
_ 35 to 75 per cent. loss of crop. Worse still is the deterioration of stocks : 
stocks apparently healthy. and vigorous may become worthless in two to 
_ four years. Cotton growers are becoming seriously perturbed. In the 
Gezira last year the losses were considerable, although until recently the 
leaf-curl disease was unknown there. Sugar-beet in the south-western 
region of the United States is so seriously imperilled by the curly-top 
_ disease that the Government has set aside $300,000 for its investigation. 
Tn this country special grants are made to Rothamsted, Cheshunt, Bangor, 
_ and other institutions to study these diseases. Tobacco is now being 
_ badly attacked, also tomatoes and potatoes; the latest sufferers are the 
narcissi and daffodils in our own gardens; these cease to flower and 
' shortly perish. Virus diseases are quite recent as serious plagues; if they 
are old they have hitherto been unimportant or unnoticed. Clearly 
_ Pandora’s box is not yet empty. 
__ Now a cynic might say that it is no bad thing thus to discover a way 
_ of making one blade of grass grow where two grew before. If these 
_ troubles affected only certain areas or groups of growers the more fortunate 
_ producers might regard them with sympathetic equanimity. Unfortu- 
nately, however, they may befall any farmer, good or bad, and the better 
_ the farmer the greater the loss may be. Plant pathology has not yet 
_ had its Arnold Theiler to show the way of insuring health to farm crops, 
. 7 Gambia Report, 1925. 
