816 THE CROSSING OF FLOWERS. 



growing together in a clump, will not all blossom together, and consequently 

 innumerable crossings take place between the flowers of the individuals of this 

 same species. The first ripe stigmas of the earliest plants of Rumex obtusifolius 

 within an hour's walk can only receive their pollen during the first two days from 

 other species of Dock, and therefore, when they first blossom, hybridization only 

 can occur. It has already been stated that plants of Marjoram (Origanum vulgare, 

 a Labiate), which bear pseudo-hermaphrodite female flowers, blossom fully eight days 

 before those with truly hermaphrodite flowers. To this we might add that the 

 plants which blossom first in any given district cannot obtain pollen from the same 

 species, and that consequently, if the stigmas are, nevertheless, pollinated l)y insects, 

 the pollen must have been obtained from some other species. In Compositee, 

 whose capitula contain both truly hermaphrodite and pseudo - hermaphrodite 

 female flowers, the latter always mature some days before the former, and con- 

 sequently the pioneer flowers in a given locality can only obtain pollen from 

 species which bloom still earlier, so that again hybridization occurs. In the 

 floral region of the Black Sea many Fleabanes grow side by side (Inula Oculus- 

 Christi, ensifolia, Oerr)ranica, salicina, &c.), and in the summer they blossom 

 in definite succession, so that one species always begins to fade when another is 

 in its prime. Each capitulum of these Inulas consists of tongue-shaped pseudo- 

 hermaphrodite female flowers on the circumference and tubular hermaphrodite 

 flowers in the centre. The former unfold earlier than the latter, and for each 

 species there is a certain period, if only two days, when the pollen, brought by 

 insects to the stigmas of the pistillate flowers on the circumference, can only have 

 been obtained from another species, since their own pollen is not obtainable. Many 

 other examples of the same kind might be quoted, all pointing to the fact that 

 hybridization at the commencement of flowering and the subsequent legitimate 

 crossing depend mainly on the incomplete dichogamy obtaining in these plants. 



It is the same with plants which have true hermaphrodite flowers. In hetero- 

 styled species either the long-styled or the short-styled flowers may develop first. 

 The long-styled flowers of Primula Auricula and the short-styled flowers of 

 Prir}iula longiflora are the earlier, consequently, the stigmas of the first long-styled 

 Primula plants can only be fertilized with pollen from other species. This is 

 often actually effected by insect-agency, and gives rise to numerous Primula hybrids. 

 The same thing is repeated in hermaphrodite flowers which are not heterostyled. 

 When a plant is protogynous, as, for example, the open-flowered Pasque-flower, 

 Pulsatilla patens, the earliest flowers can receive no pollen from anthers of their 

 own species, because not one is open, but it would be possible for them to be 

 provided with the pollen of other species of the same genus which inhabit the same 

 locality but blossom earlier. This, of course, only holds good for the commenceTnent 

 of the flowering period, and only for those plants of the species which are the first 

 to open their flowers in a given place. At a later period of flowering legitimate 

 crossing will occur, because by that time the earliest plants have shed their pollen, 

 and it may be collected and transferred by insects. Among hermaphrodite plants 



