Shirreff has proved, are well worthy of extensive cultivation. Not until equal attention be paid to the variability and selection of weeds, can the argument from their constancy under unintentional culture be of any value. In accordance with the principles of selection we can understand how it is that in the several cultivated varieties of wheat the organs of vegetation differ so little; for if a plant with peculiar leaves appeared, it would be neglected unless the grains of corn were at the same time superior in quality or size. the selection of seed-corn was strongly recommended (9/46. Quoted by Le Couteur page 16.) in ancient times by Columella and Celsus; and as Virgil says,--
I've seen the largest seeds, tho' view'd with care, Degenerate, unless th' industrious hand Did yearly cull the largest."
But whether in ancient times selection was methodically pursued we may well doubt, when we hear how laborious the work has been found by Le Coutour and Hallett. Although the principle of selection is so important, yet the little which man has effected, by incessant efforts (9/47. A. De Candolle 'Geograph. Bot.' page 932.) during thousands of years, in rendering the plants more productive or the grains more nutritious than they were in the time of the old Egyptians, would seem to speak strongly against its efficacy. But we must not forget that at each successive period the state of agriculture and the quantity of manure supplied to the land will have determined the maximum degree of productiveness; for it would be impossible to cultivate a highly productive variety, unless the land contained a sufficient supply of the necessary chemical elements.
We now know that man was sufficiently civilised to cultivate the ground at an immensely remote period; so that wheat might have been improved long ago up to that standard of excellence which was possible under the then existing state of agriculture. One small class of facts supports this view of the slow and gradual improvement of our cereals. In the most ancient lake-habitations of Switzerland, when men employed only flint-tools, the most extensively cultivated wheat was a peculiar kind, with remarkably small ears and grains. (9/48. O. Heer 'Die Pflanzen der Pfahlbauten' 1866. The following passage is quoted from Dr. Christ in 'Die Fauna der Pfahlbauten, von Dr. Rutimeyer' 1861 s. 225.) "Whilst the grains of the modern forms are in section from seven to eight millimetres in length, the larger grains from the lake-habitations are six, seldom seven, and the smaller ones only four. The ear is thus much narrower, and the spikelets stand out more horizontally, than in our present forms." So again with barley, the most ancient and most extensively cultivated kind had small ears, and the grains were "smaller, shorter, and nearer to each other, than in that now grown; without the husk they were 2 1/2 lines long, and scarcely 1 1/2 broad, whilst those now grown have a length of three lines, and almost the same in breadth." (9/49. Heer as quoted by Carl Vogt 'Lectures on Man' English translation page 355.) These small-grained varieties of wheat and barley are believed by Heer to be the parent-forms of certain existing allied varieties, which have supplanted their early progenitors.
Heer gives an interesting account of the first appearance and final disappearance of the several plants which were cultivated in greater or less abundance in Switzerland during former successive periods, and which generally differed more or less from our existing varieties. The peculiar small-eared and small-grained wheat, already alluded to, was the commonest kind during the Stone period; it lasted down to the Helvetico-Roman age, and then became extinct. A second kind was rare at first, but afterwards became more frequent. A third, the Egyptian wheat (T. turgidum), does not agree exactly with any existing variety, and was rare during the Stone period. A fourth kind (T. dicoccum) differs from all known varieties of this form. A fifth kind (T. monococcum) is known to have existed during the Stone period only by the presence of a single ear.