VOL. LV.] PHILOSOPHICAL T^NSACTIONS. 340 



That plants do not produce their flowers all the year, but only at particular 

 seasons. That many plants are some years before they produce their flowers, 

 and hardly any, except annuals, blow the first year after they are sown. That 

 soil, climate, pruning, and many other circumstances, will bring plants to blow 

 sooner or later than they would otherwise do. That culture will increase the 

 quantity of bloom, and so occasion the expansion of flowers, which would 

 otherwise have remained within the wood. 



Now if these circumstances, which are similar to those of which the expla- 

 nation is sought, be so common, why may we not in like manner suppose, 

 " that, whenever either the male or female organs are absent, it is owing to 

 some circumstance that determines the sap into other channels, and so prevents 

 the expansion of the part." This will perhaps be thought to amount to more 

 than a conjecture ; because, besides its probability from the circumstances stated 

 above, it will perfectly explain another well attested phenomenon in the class 

 Dioecia, that is scarcely to be accounted for on any other supposition, viz. that a 

 male plant has, at a certain age, been found to change to a female one, and 

 vice versa, and also to bear flowers of both sexes, to which he may add 

 another which he had observed in the Monoecious plants, Zea and Ricinus, 

 where he often found spikes of fruit breaking out among the male flowers, 

 though they commonly come out separate from them in another part of the 

 plant. If there be any weight in these arguments, the general conclusion will 

 be this, that the flowers of all vegetables whatever are hermaphrodite in their 

 original construction, though both the organs do not appear in all cases. 

 Remarks on the Impregnation of Vegetables. By the same. p. 261. 

 Each grain of pollen is a vessel filled with pulpy matter, in which are lodged 

 a considerable number of smaller grains, which may be called the impregnating 

 corpuscles; see pi, 6, fig. 2, 3, 4, 5, 6, 7, 8, Q, 10, 11, 12, 13. These are not 

 visible with the naked eye, but may be distinguished with glasses of moderate 

 power, if the grain be transparent, or if the pulp be forced out by compressing 

 the grain between the talks. They are round, transparent, and nearly of the 

 same size in all plants. They are conveyed to the germen through the style, 

 which is furnished with internal ducts for that purpose; and in the class synge- 

 nesia, and in the small plants of other classes, where the style is slender and 

 transparent, they may be distinguished in their passage, as in fig. 19. The 

 manner of their recejitiou into the style depends on the disposition of its sur- 

 face: our observation fell chiefly on those plants that have hairy styles or 

 stigmas ; and in these the corpuscles enter by means of the hairs, which are 

 often found on the style itself, so that the stigma must not always be considered 

 as the only recipient part, though it may perhaps be so in most instances. The 

 hairs are so many tubes open at the extremity for the reception of the corpus- 



VOL. XII. K K 



