Three cases are to be distinguished as to heredity. Many plants are so constituted as to be fertilized with their own pollen. In this case the visits of insects have simply to be excluded, which may be done by covering plants with iron gauze or with bags of prepared paper. Sometimes they fertilize themselves without any aid, as for instance, the common evening-primrose; in other cases the pollen has to be placed on the stigma artificially, as with Lamarck's evening-primrose and its derivatives. Other plants need cross-fertilization in order to produce a normal yield of seeds. Here two individuals have always to be combined, and the pedigree becomes a more complicated one. Such is the case with the toad-flax, which is nearly sterile with its own pollen. But even in these cases the visits of insects bringing pollen [26] from other plants, must be carefully excluded. A special lecture will be devoted to this very interesting source of impurity and of uncertainty in ordinary cultures. Of course, crosses may lie in the proposed line of work, and this is the third point to be alluded to. They must be surrounded with the same careful isolation and protection against bees, as any other fertilizations. And not only the seed-parent, but also the pollen must be kept pure from all possible foreign admixtures. A pure and accurately recorded ancestry is thus to be considered as the most important condition of success in experimental plant breeding. Next to this comes the gathering of the seeds of each individual separately. Fifty or sixty, and often more, bags of seeds are by no means uncommon for a single experiment, and in ordinary years the harvest of my garden is preserved in over a thousand separate lots.