Wheat is not only one of the most adaptable of plants. It is also one of the most plastic and prone to variation. During the many centuries over which its cultivation has extended it has yielded hundreds of different varieties, whose origin, however, except in a few doubtful cases is unknown. Comparatively few of these varieties are in common use in this country, and even of these it was impossible until recently to say which was the best. It was even almost impossible to obtain a pure stock of many of the standard varieties. This is by no means the simple matter it appears to be. It is of course quite easy to pick out a single ear, to rub out the grain from it, to sow the grain on a small plot by itself and to raise a pound or so of perfectly pure seed. This can again be sown by itself, and the produce, thrashed by hand, will give perhaps a bushel of seed which will be quite pure. From this seed it will be possible to sow something like an acre; and now the trouble begins. Any kind of hand thrashing is extremely tedious for the produce of acre plots, and thrashing by machinery becomes imperative. Now a thrashing machine is an extremely complicated piece of apparatus, which it is practically impossible thoroughly to clean. When once seed has been through such a machine it is impossible to guarantee its purity. Contamination in the thrashing machine is usually the cause of the impurity of the stocks of wheat and other cereals throughout the country. The only remedy is for the farmer to renew his stock from time to time from one or other of the seedsmen or institutions who make it their business to keep on hand pure stocks obtained by the method above described. [Illustration: Fig. 1. Typical ears of a few of the many cultivated varieties of wheat] Comparative trials of pure stocks of many of the standard varieties of wheat, and of the other cereals, are being carried out in almost every county by members of the staff of the agricultural colleges. The object of such trials is to determine the relative cropping power of the different varieties. This might at first sight appear to be an extremely simple matter, but a moment’s consideration shows that this is not the case. No soil is so uniform that an experimenter can guarantee that each of the varieties he is trying has the same chance of making a good yield as far as soil is concerned. It is a matter of common knowledge too that every crop of wheat is more or less affected by insect and fungoid pests, whose injuries are unlikely to fall equally on each of the varieties in any variety test. Many other causes of variation, such as unequal distribution of manure, inequalities in previous cropping of the land, irregular damage by birds, may well interfere with the reliability of such field tests.