It is well known that two kinds of wheat are recognised by agriculturalists, one of which is sown in spring and the other in autumn, both being reaped at about the same time. It is evident that the conditions of development are very different in the two cases. To sow a spring wheat in autumn, was, so to speak, changing the condition of existence, and, consequently, attempting an experiment in acclimatisation. This was done by the celebrated Abbé Tessier. A hundred seeds of autumn wheat were sown in spring; they all came up and produced young plants, which passed through the usual stages of vegetation. Only ten plants, however, formed seeds, which only ripened upon four plants. A hundred seeds of this first crop produced fifty fertile plants. In the third generation the hundred seeds produced corn. The inverse experiment gave similar results. The acclimatisation of wheat at Sierra Leone offers still more instructive peculiarities. The first year almost all the seed ran to leaf; the ears were very few, and poorly filled. The seeds of this first crop were sown; a great number did not come, up at all. Those which survived were a little more fertile. Much patience was, however, required, and many generations passed before normal crops were obtained. We see that in Tessier’s experiment all the seeds of wheat and their germs lived, but the grain was wanting, or was more or less abortive. There was, then, a _loss of generations_. The same thing occurred at Sierra Leone. Moreover, the second time the seed was sown, some of it never came up at all. Here, therefore, the loss of individuals was added to that of generations. The history of our poultry which has been imported into America, presents equally significant facts. At Cuzco the broods are just as large as in Europe. Garcilasso de la Véga tells us, however, that in his time the eggs were few, and the chickens difficult to rear. The species has, since then, become acclimatised. When M. Roulin made his observations upon the geese imported into Bogota, it was more than twenty years since they had been first brought to that high plateau, and, even then, they had not attained their normal fecundity. They were not, however, far from it, while at first the eggs were very rare. A quarter, at the most, of the eggs were hatched, and half the goslings died before the end of the first month. Thus, on the one hand, the Bogota breeder did not obtain nearly as many eggs as he would have done in Europe, while, on the other hand, at the end of a period scarcely equal to the two-hundredth part of the life of the goose, he obtained from these eggs scarcely one-eighth of what they would have produced in Europe.