EVOLUTION UNDER DOMESTICATION. 



71 



ries on the trees; these drop, germinate, and take root, and then the planters choose the 

 best and strongest of those "suckers," as they call them, for replanting. Now that is a 

 natural selection, which, I think, has had great influence on the vigor of the trees, and, 

 probably, if the planters made nurseries and germinated all the seeds from a tree, whether 

 they were constitutionally strong or weak, they would probably not get as good results. 

 But \ think the paper of Professor Cook will certainly do a great deal to open the eyes 

 of coffee planters in the West Indies to the question, and probably something will be 

 done to test his theory in every way. I think the West Indies are much obliged to Pro- 

 fessor Cook for taking up these tropical subjects. 



W. M. Hays: I am exceedingly interested in this paper. We need studies in the 

 theory along this line. I have had charge of some experiments for a dozen years in wheat, 

 which, as I have already said, is close-fertilized, close-pollinated; and I want to emphasize 

 one of the general features he brought out in his paper by an illustration which the wheat 

 makes possible. We have in Minnesota two varieties of wheat that are almost universally 

 grown, the common Red Fife and Velvet Chaff or Blue Stem wheat. On the University 

 farm, where I am located, Fife wheat has averaged, we will say, 22 bushels for ten years, 

 and under exactly similar conditions Blue Stem wheat has averaged 24 bushels. We take 

 large numbers of these and plant the seeds, take choice seeds from each, selecting the 

 choicest plants, and selecting from those the choicest seeds, and plant large blocks, we 

 will say 5,000 for convenience, one seed in a place, four inches apart each way. We have 

 devised a machine for planting them, so a man puts one seed in each of fourteen cups 

 and throws the fourteen seeds over at one time. Another man throws the machine forward 

 four inches, so that the wheat is planted under very uniform conditions. At harvest the 

 choicest plants one way and another are gotten at, those that yield best and have good 

 quality. Those are tested in the nursery for three years, by growing 100 plants from each 

 of these mother plants. We will say we start with 100 mother plants, chosen as the best 

 plants out of 5,000. These are run for three years, and the best 100 plants are chosen each 

 year. At the end of three years, then, we have the measure of each 100 mother plants, not 

 in terms of its own yield, but in terms of the yield of its progeny, of the average of its 

 progeny. These plants are taken and the number is counted and the whole is threshed, 

 and the total weight, of the wheat is divided by the exact number of plants harvested. 

 We will say, for example, that one mother- plant yields a progeny that average 

 7 giams, another one 6 1-2 grams, another one 6 grams, and so on, variations running 

 down, we will say, from 7 grams down to 4 grams. Then we pick out the best from that 

 and take varieties. These varieties are grown then for three or four years alongside the 

 plants ol the two foundation varieties. The possibilities of getting a high yielding variety 

 lie, as President Northrop quoted somebody in expressing the idea, in the projected effi- 

 ciency of each of those 100 original mother plants we start with. We gradually throw away 

 those with the least efficiency and finally take a comparatively few from the field that have 

 the greatest projected efficiency, the greatest ability to project their peculiar heredity into 

 varieties that will yield well in the field. We will assume for the purpose of the point 

 I wish to make that we can raise the yield this way three bushels in each case; the Fife 

 wheat we can raise from 22 to 25 bushels, and the Blue Stem from 24 to 27 bushels. Now, 

 we can raise that by using large numbers and getting the plants that will make the largest 

 yield, that have the highest projected efficiency, if you please, and then we can go a little 

 further. If we use larger numbers we may add a little to that 25 and 27 bushels, and I 

 may say that it has proven perfectly practicable to make varieties from single plants of 

 wheat. Whether these will remain with their high ability for a long period of time, of 

 course only time can tell, and it may be better perhaps to make the varieties from a 

 number of foundation mother plants; but we have certainly run for ten years, and their 

 ability to yield well has kept up. Assuming, then, that the yield is 25 bushels in one case 

 and 27 in the other, we go back now to the matter of hybridizing these two varieties. The 

 average between these two varieties would be 23 bushels. When we hybridize them we 

 get in many cases plants that on the average are away down the scale, that perhaps would 

 not have a yielding ability of over 10 or 15 bushels; in some cases we may get 20 bushels 

 or even 23 bushels, possibly in some cases higher: but if we get a single piant with a 

 higher yield, that is sufficient, because in the hybrids we take single plants again, and if 

 we can get an occasional plant that has a projected efficiency that will give us a yield 

 higher than 23 bushels, we can then get from that hybrid varieties that yield still 

 more than from either of the simple stocks from which we started. Now, this experience 



