September 1, 1896.] 



KNOWLEDGE. 



213 



inevitably receive on its legs and abdomen some of the 

 pollen adhering to the style, since it uses the style as a 

 support durmg its search for the honey beneath the 

 spreading bases of the stamens. Subsequently, the bee 

 will visit a rather older flower in which the stigmas are 

 expanded on a level with the entrance to the bell, so that 

 the pollen adhering to the bee's body must necessarily be 

 transferred to the sticky stigmatic surface. But if, after 

 all, the flower should fail to be cross-fertilized by insects, 

 then it takes to self-fertilization as a last resource, and the 

 stigmas curl right back so as to expose their receptive 

 part to the zone of pollen round the stj'le. 



In the rampiou (Phyteuma), another member of the 

 CampanulaceiB, we find indications of an advance on the 

 simpler harebell type. The flowers are no longer on 

 separate stalks, but are collected in heads ; we may regard 

 this habit as a step in the direction of economy, for an 

 insect can evidently visit and cross-fertilize a greater 

 number of flowers thus arranged without wasting so much 

 time as if they were each isolated and needing separate 

 visits. The corolla in the rampion is no longer an open 

 bell but a narrow cylindrical tube ; the lower part ulti- 

 mately splits into five ribbons, while the upper part, with a 

 toothed margin, remains a tube for a longer time. The 

 pollen is shed (as in the harebell) by the anthers apon 

 the style within the corolla-tube, and adheres in a broad 

 zone to the lateral collecting hairs. The gradual lengthen- 

 ing of the style, as well as the contraction of the corolla 

 caused by the splitting of the lower part, exposes the zone 

 of pollen for the visits of bees, while the stigma itself 

 remains immature for a day or so longer before unfolding its 

 branches (Pig. C, i.). In the absence of visits from insects. 



C«3 



Fio. C. 



- Single (loret of Rampion. I. Stigmas immature 

 expanded above the zone of pollen. 



II. Stigmas 



i 



V 



self-fertilization may, however, occur in the rampiou 

 precisely as in the harebell, by the excessive curling back of 

 the stigmatic branches on to the pollen adhering to the 

 style beneath (Fig. C, ii.). The presence of an involucre 

 — /.('., a group of floral bracts round the compound 

 flower — as well as the reduction of the stylar branches 

 from three to two, enhances the resemtslance to the 

 Compositii', which has already become foreshadowed 

 by the grouping of the flowers in heads. 



In the spherical flower-head of the sheep's bit 

 {Jasione montana) — a pretty little blue ilower, frequent 

 in mountain districts — the kinship of the flower to 

 the Composite type becomes still more manifest. 

 Here the anthers, instead of being separate from each j-j„ 

 other, are now " syngenesious " * — that is to say, 

 they are united by their edges, forming a closed ring 

 round the style— but the union is not yet perfect, for only j 

 the bases of the anthers have become coherent. The 

 inflorescence, however, is almost identical with that of the 

 Composit:!', for the flowers are crowded together in capitate 

 umbels with involucres, and the stylar branches (as well 



as the cells of the capsule) have become reduced in number 

 from three to two. Indeed, the similarity is so close that 

 Linnipus himself classed it with the Composita?. 



The flowers of these three members of the Campanulaceae 

 naturally show more afiinity between themselves than with 

 the flowers of the usual Composite type. But the gap 

 seems less wide if we consider the structure of one of the 

 more primitive Compositse, sach as the IQac hemp-agrimony 

 (Enpatorium cannabinum). Only a few flowers occur in 

 each head, but many of these small heads are grouped 

 together to form a large inflorescenop. iloreover, the 

 florets in each little head are not so tightly packed together 

 as in most Composite. Each 

 floret presents in the main a 

 similar structure to the more 

 advanced bellflower type, being 

 tubular with five well -marked 

 teeth ; but the green calyx 

 becomes reduced here to a 

 number of bristly hairs, and 

 the anthers are now completely 

 united to each other, side to 

 side. However, there is no 

 diS'erentiation as yet into ray 

 and disk-florets ; all are alike 

 and all have the same lilac 

 colour. The branches of the 

 style are long and hairy, and as 

 they grow in length they sweep 

 out the pollen from the anthers. 

 Subsequently, when mature, the 

 branches separate widely, ex- 

 posing the stigmatic surfaces 



(Fig. D). If the flower fails to be fertilized by insects, then 

 the long curling styles come into contact with the pollen 

 still adhering to the collecting hairs of younger and 

 immature styles of neighbouring florets ; thus the florets of 

 the same head become fertilized with each other's pollen. 



Finally, the " wee crimson-tipped " daisy {Bellis peirnnis) 

 has carried the dift'erentiation of its flowers to a still greater 

 extreme. Here the florets are of two kinds : white ligulate 

 ray-florets and yellow tubular disk-florets (Fig. E, i. ). More- 

 over, all trace of a calyx, even in the form of hairs or scales, is 

 entirely absent. The ray-florets have become considerably 

 modified from the simple tubular type, which continues to 

 be exempUfied in the disk-florets ; the lower part of the 

 tube still exists, but the upper part has split open, spreading 



Fig. 



Hemp 

 view. 



D.— Single 

 Agrimony. 

 II. Section. 



Iloret of 

 I. Side 



* Sifinpht/anilra^ another member of the Cainii.iimlai' 

 wise syngenesious stamens. 



lias like 



. v.. — I. Section of Daisy. II., Til., IV., Successirc staples in the 

 growth of n disli-llorct. 



out into a flat, ligulate (strap-shaped) corolla. But the 

 five minute teeth on the end of the strap betray the parent 

 character. The corolla has been modified in tin's way 

 chiefly for the sake of making the ilowor more conspicuous, 

 but also in order to protect the pollen from rain and dow. 

 At night, or when a shower is impending, these flat straps 

 bend over and inwards and effectually cover over the 

 exposed pollen. 



