This section is from the book "On British Wild Flowers Considered In Relation To Insects", by John Lubbock. Also available from Amazon: Nature Series On British Wild Flowers Considered In Relation To Insects.
This is a very extensive order, containing no less than thirty-seven British genera (Carrot, Chervil, Parsley, Parsnip, etc.) and a very large number of species. The plants belonging to this group possess two great advantages - namely, firstly, the association of the numerous small flowers into comparatively large flat heads, by which they are made much more conspicuous: and, secondly, they all secrete honey in the centre of the flower on a flat disk (Fig. 84, 85) which is thus accessible to all insects, even those with the shortest lips. This is an advantage, as it effects a considerable saving of time, enabling the insects to visit a given number of flowers more rapidly, and consequently rendering their fertilisation more certain than if they had stood singly. But though the order is so rich in genera and species, it is comparatively uniform, and the divisions are for the most part characterised by the form and structure of the fruit. The flowers are generally small; the petals five, inserted round a little fleshy disk; the stamens, also five, alternating with the petals.
Fig. 83. - Wild Chervil (Charophyllum sylvestre).
The self-fertilisation which, in small flowers such as these, would otherwise naturally occur, is provided against by the fact that the flowers are generally pro-terandrous, the stamens ripening before the pistil, and the latter not being mature until the former have shed their pollen; as, for instance, is shown in the following enlarged figures of the Wild Chervil (Chaero-phyllum sylvestre). Fig. 84 represents a floret in the earlier (male) condition, showing three ripe (a') and two still immature (a), while the stigmas have not yet made their appearance: in Fig. 85 is represented the same flower in a more advanced condition, the stamens having fallen off, and the stigmas (si) being now mature. In some cases, flowers in both conditions may be found in the same head or umbel; in others, as, for instance, in Myrrhis, the flowers of one head are all firstly in the male condition, and subsequently in that with mature stigmas, none of them arriving at the second stage until they have all passed through the first.
Fig. 84. - Flower of the Wild Chervil in the first (male) state.
Fig. 85. - Ditto, in the second (female) state.
It will be seen that in these florets the petals are not symmetrical, the outer ones being considerably larger than the others, and in many Umbellifers the florets themselves, on the outer edge of the umbel, are considerably larger than the inner ones. This distinction is carried still further in the Com-positae, where also the florets are so closely packed together that the whole flowerhead is commonly, though of course incorrectly, spoken of as a flower.
H. Muller has recorded 73 species of insects as frequenting the Wild Chervil. In some cases the number was even greater, as for instance in Heracleum, on which he has observed no less than 118. That the number depends on the con-spicuousness of the umbel he illustrates by the following series, arranged in the order of the con-spicuousness of the flowers, - viz., I. Heracleum, 2. AEgopodium, 3. Anthriscus (Chserophyllum) sylvestris, 4. Daucus, 5. Carum, 6. Chaerophyllum temulum, 7. Torilis. On these he found the following number of species of insects:
The position of the honey on a flat disk, which renders it accessible to most insects, has the opposite result as regards the Lepidoptera, which therefore, as might naturally be expected, are but rare visitors of the Umbelliferas. I have sometimes wondered whether the neutral tints of these flowers have any connection with the number of species by which they are frequented.