[99] In order to get a closer insight into the causes of this confused condition of ordinary races, Rimpau made some observations on Rivett's wheat. He found that it suffers from frost during winter more than the local German varieties, and that from various causes, alien seeds may accidentally, and not rarely, become mixed with it. The threshing-machines are not always as clean as they should be and may be the cause of an accidental mixture. The manure comes from stables, where straw and the dust from many varieties are thrown together, and consequently living kernels may become mixed with the dung. Such stray grains will easily germinate in the fields, where they find more congenial conditions than does the improved variety. If winter arrives and kills quantities of this latter, the accidental local races will find ample space to develop. Once started, they will be able to multiply so rapidly, that in one or two following generations they will constitute a very considerable portion of the whole harvest. In this way the awnless German wheat often prevails over the introduced English variety, if the latter is not kept pure by continuous selection. The Swiss wheat-breeder Risler made an experiment which goes to prove the certainty of the explanation given by Rimpau. He observed on his farm at Saleves near the lake of Geneva that after a lapse of time the "Galland wheat" deteriorated and assumed, as was generally believed, the characters of the local sorts. In order to ascertain the real cause of this apparent change, he sowed in alternate rows in a field, the "Galland" and one of the local varieties. The "Galland" is a race with obvious characters and was easily distinguished from the other at the time when the heads were ripe. They are bearded when flowering, but afterwards throw off the awns. The kernels are very large and yield an extraordinarily good, white flour. During the first summer all the heads of the "Galland" rows had the deciduous awns but the following year these were only seen on half of the plants, the remainder having smooth heads, and the third year the "Galland" had nearly disappeared, being supplanted by the competing local race. The cause of this rapid change was found to be twofold. First the "Galland," as an improved variety, suffers from the winter in a far higher degree than the native Swiss sorts, and secondly it ripens its kernels one or two weeks later. At the time of harvest it may not have become fully ripe, while the varieties mixed with it had reached maturity. The wild oat, _Avena fatua_, is very common in [101] Europe from whence it has been introduced in the United States. In summers which are unfavorable to the development of the cultivated oats it may be observed to multiply with an almost incredible rapidity. It does not contribute to the harvest, and is quite useless. If no selection were made, or if selection were discontinued, it would readily supplant the cultivated varieties.