SECTIONAL TRANSACTIONS.— M. 4I7 



different qualities of South African grease wools, and are now being applied to commer- 

 cial bulk samples, which are always mixtures. They have also been applied to woola 

 from various parts of the world and to tops, and the results suggest that a common 

 basis of comparison may be arrived at for the raw wool production of the world and 

 for the early stages of its manufacture. 



(d) Dr. J. E. Nichols. — Some Aspects of Empire Wool Production. 



(e) Discussion. 



Friday, July 26. 



Mr. G. Frecheville. — Crop Rotations and the Maintenance of Soil Fertility. 



Mrs. N. L. Alcock. — The International Aspect of Plant Diseases. 



Each country must be responsible for the health of its exports. There are two 

 methods of safeguarding Plant Trade : — 1st. The Method of Embargo. In a general 

 form this kills all trade. Each country will exclude certain specific diseases. 

 2nd. Some form of health certificate. 



Great Britain has chosen the latter method and realises that, to make it effective 

 it includes : — 



(a) Safeguarding imports — care must be taken to prevent the entrance of disease. 



(6) Insisting on a reasonable standard of health in the country, in growing crops, 

 nurseries, &c. ; inspection in the field for certain crops such as potatoes. 



(c) Knowledge of where disease exists entailing a general disease survey. 



(d) Inspection of Exports by competent Mycologists. 

 Safeguarding Imports. 



Imports are in two categories (certificated). 



(a) Imports which are likely to prove dangerous on account of the fact that they 

 come from countries where the flora and fauna are different from our own, or because 

 they are known to carry some special pest not already in Great Britain. 



(6) Imports from countries where the flora and fauna are identical : the diseases 

 and pests are exactly the same as in Great Britain. These are less dangerous. 



Imports in category (a). — -These plants are re-examined and in the majority of 

 cases are looked at a second time by competent inspectors during the growing season. 



Imports in category (b). — If these carry a certificate ensuring a high standard 

 of health it is merely necessary to carry out sample inspection to ensure the certificate 

 is maintaining its declared standard. 



There remains of course, a group c. Plants without a certificate. These aie 

 always inspected and are treated additionally in accordance with the needs of the case. 



Plants for export obviously have to be treated in accordance with the rules of the 

 country to which they are going. The value of a Health Certificate must depend on 

 the competence of those giving it. In the case of large quantities the sampling 

 method must be employed. The careful examination of a sample is better than the 

 casual inspection of the whole. 



If given by competent men the value of a Health Certificate wiU lie, not so much 

 at the moment of export, as in the weU-known fact that inspection and certification 

 tend to raise the general standard of plant products all along the Line. The best 

 growers in Great Britain are the best in the world. The effect of a good Plant Disease 

 Service tends to approximate the less good to the standard of the best. 



It seems obvious that the ideal to be striven for is an agreed imperial system of 

 inspection and certification which Avill be standardised in its basic features, but which 

 will be sufficiently flexible to admit of modifications to suit varying regional needs. 



Dr. Winifred Brenchley. — The Dormancy of Weed Seeds in the Soil as 

 affected by Ctdtivation and Fallowing. 



Numerical estimations are being made of the effect of cultivation and fallowing 

 on the number of viable weed seeds in the soil of Broadbalk permanent wheat field, 

 Rothamsted. Counts are made of the number of seedlings derived from numerous 

 measured samples taken annually after harvest. Excluding poppy, the number of 

 living seeds on unfallowed land ranged from 27 to 62 millions per acre, according to 



1929 E E 



