on a horse-chestnut or lime-tree, an incomparably larger number of flowers must be fertilised by pollen brought from other flowers on the same tree, than from flowers on a distinct tree.  But we should bear in mind that with the horse-chestnut, for instance, only one or two of the several flowers on the same peduncle produce a seed; and that this seed is the product of only one out of several ovules within the same ovarium.  Now we know from the experiments of Herbert and others that if one flower is fertilised with pollen which is more efficient than that applied to the other flowers on the same peduncle, the latter often drop off (10/41.  ‘Variation under Domestication’ chapter 17 2nd edition volume 2 page 120.); and it is probable that this would occur with many of the self-fertilised flowers on a large tree, if other and adjoining flowers were cross-fertilised.  Of the flowers annually produced by a great tree, it is almost certain that a large number would be self-fertilised; and if we assume that the tree produced only 500 flowers, and that this number of seeds were requisite to keep up the stock, so that at least one seedling should hereafter struggle to maturity, then a large proportion of the seedlings would necessarily be derived from self-fertilised seeds.  But if the tree annually produced 50,000 flowers, of which the self-fertilised dropped off without yielding seeds, then the cross-fertilised flowers might yield seeds in sufficient number to keep up the stock, and most of the seedlings would be vigorous from being the product of a cross between distinct individuals.  In this manner the production of a vast number of flowers, besides serving to entice numerous insects and to compensate for the accidental destruction of many flowers by spring-frosts or otherwise, would be a very great advantage to the species; and when we behold our orchard-trees covered with a white sheet of bloom in the spring, we should not falsely accuse nature of wasteful expenditure, though comparatively little fruit is produced in the autumn.

Anemophilous plants.

The nature and relations of plants which are fertilised by the wind have been admirably discussed by Delpino and Hermann Muller; and I have already made some remarks on the structure of their flowers in contrast with those of entomophilous species. (10/42.  Delpino ’Ult.  Osservazioni sulla Dicogamia’ part 2 fasc. 1 1870 and ’Studi sopra un Lignaggio anemofilo’ etc. 1871.  Hermann Muller ‘Die Befruchtung’ etc. pages 412, 442.  Both these authors remark that plants must have been anemophilous before they were entomophilous.  Hermann Muller further discusses in a very interesting manner the steps by which entomophilous flowers became nectariferous and gradually acquired their present structure through successive beneficial changes.) There is good reason to believe that the first plants which appeared on this earth were cryptogamic; and judging from what now occurs, the male fertilising