Let us examine a somewhat different set of facts in the case of another pair of nearly allied species _Lychnis diurna_ and _vespertina_. The two plants have much in common. Both are dioecious perennials, with somewhat similar flowers, the one crimson, the other white. Each however has its peculiarities which are discernible in almost any part of its structure, whether flower, leaf, fruit or seed, distinctions which would enable a person thoroughly familiar with the plants to determine at once from which species even a small piece had been taken. There is so much resemblance however as readily to support the surmise that the two were mere varieties of one species. Bentham, following Linnaeus, in fact actually makes this suggestion, with what propriety we will afterwards consider. Now this case is typical of many. The two forms have a wide distribution, occurring sometimes separately, sometimes in juxtaposition. _L. diurna_ is a plant of hedgerows and sheltered situations. _L. vespertina_ is common in fields and open spaces, where _diurna_ is hardly ever found; but not rarely _vespertina_ occurs in association with _diurna_ in the places which that plant frequents. In this case I do not doubt that we have to do with organisms of somewhat different aptitudes. That _L. vespertina_ has powers which _diurna_ has not is shown very clearly by the fact that _diurna_ is sometimes entirely absent from areas where _vespertina_ can abound.[9] But in order to understand the true genetic relations of the two plants to each other it is necessary to observe their behaviour when they meet as they not unfrequently do. If the _Lychnis_ population of such a locality be examined it will be found to consist of many undoubted and unmodified _diurna_, a number--sometimes few, sometimes many--of similarly unmodified _vespertina_, and an uncertain but usually rather small proportion of plants obviously hybrids between the two. How is it possible to reconcile these facts with the view that specific distinction has no natural basis apart from environmental exigency?