214 



KNOWLEDGE. 



[Skptembek 1, 1896. 



In this flower, and in most other CompositiP, the pollen 

 is not deposited on a zone round the style, as in the 

 t'ainp;innlacc;p, hut is set free above its immature tip, 

 which is provided with small stilT hairs. As the style 

 develops and lengthens, this circular array of bristles acts 

 like a chimney-sweep's brush, and pushes in front of it 

 the pollen filling the upper part of the corolla-tube, leaving 

 it on the surface of the ilower-head : thus the pollen 

 grains cannot fail, in this exposed position, to come into 

 contact with the abdomen or legs of an insect settling on 

 the llower in search of honey or pollen. 



Subsequently, the apex of the style divides into two 

 branches, just like the previous cases, laying bare the 

 receptive surfaces, which up to that moment had been 

 protected by their mutual pressure from contact with 

 pollen from the same lloret (Fig. E, i., ii., m., iv.). 



The differentiation in the daisy of some of the marginal 

 florets into ray-tlorets, with their characteristic ligulate 

 corolla, has reached a yet higher stage in the large Ligu- 

 late section of the Compositre, some of which possess 

 characteristics of the Campanulacea> which are wanting 

 in the daisy. Thus, in the pale blue flower-heads of the 

 chicory {Cichorium inti/lnis) all the florets are ligulate, but 

 the calyx seems to be a little less degenerate than in most 

 other Composit;r, for it consists of little scales which 

 certainly approach the nature of sepals more closely than 

 the hairs and bristles which usually take the place of the 

 calyx in this order. A striking quality which the chicory 

 tribe possesses, in common with the Campanulacese, is 

 the presence of late.i\ or milky juice, in their tissues. 

 Everyone who has plucked a dandelion will be familiar 

 with the appsarance of the dense white juice welling up 

 from the wound ; and it is highly probable that this forms 

 another of the characteristics which the two groups of 

 plants derive from a remote common ancestor. 



To sum up : the points in which the Compositte resemble 

 the Campauulace.T are the following : — 



1. The valvate fpstivation of the corolla — i.e., the petals 

 in the flower-bud are placed edge to edge, and do not 

 overlap in any way. 



2. The occurrence of inulin ( Dahlia , Jerusalem artichoke) 

 and of latex (chicory, dandelion). 



3. The ovary is inferior to the corolla. This condition 

 always points to the flower having reached a high state of 

 development. 



■1. The tendency in some of the Campanulacefe for the 

 anthers to adhere by their sides to form a tube, becomes 

 a general rule in the Composite. In Eupntorium the 

 pollen is shed on to the lateral surface of the style as 

 in Campanulaceae, although in most Compositffi it is 

 discharged above the tip of the style. 



5. The phenomenon of protandry as explained above. 



G. The ovule is anatropous — i.e., the ovule, though 

 straight itself, is bent on its own stalk so that the micropyle 

 (the pore through which the pollen-tube penetrates) is 

 close to the place where the ovule is attached to the 

 placenta. 



It still remains necessary to give some explanation of 

 the differences between the two orders. These, although 

 of importance, do not, I think, present any msuperable 

 difficulties. 



The Campanulaceae differ from the Compositae in the 

 following particulars ; — 



1. The arrangement of the veins in the corolla. 



2. The plurality and horizontal direction of the ovnles. 

 (In the C'ompositif there is only one ovule in the ovary, 

 and it is erect.) 



3. The fruit in Campanulacere is a capsule with two or 

 three divisions, and not an achene. 



4. The collecting hairs on the style are arranged in lines 

 and not in a ring. 



5. The seed contains endosperm. 



6. The prevailing colour of the flowers is blue, while 

 that of the Compositio is yellow. 



Most of these differences (2, ;!, and 5) result from the 

 crowding together of great numbers of flowers into 

 compact heads. In all such cases the number of ovules 

 tends to become reduced. Moreover, the fact that there 

 are two stigmatic branches to the style in Composite 

 seems to indicate that their ancestor possessed an ovary 

 with two loculi or compartments, just as in the rampion 

 and sheep's bit. And, furthermore, the suppression of 

 endosperm in the seeds of the Compositic is not, after all, 

 a hard-and-fast distinction between the two orders, for the 

 seed of Tai/eti's, a Composite plant, still contains some 

 endosperm, and can therefore be termed albuminous. 



The other points hardly seem to constitute deep-seated 

 differences in the essential structure of flowers, but may 

 be regarded rather as superficial and responsive adaptations 

 to secure fertilization by difl'erent insects or to differences 

 in the climatic surroundings. 



But the question will very naturally arise, " If the 

 Compositfo arc descended from an ancestral type some- 

 what like the harebell, how is it that the prevailing colour 

 of Composite flowers is yellow, while nearly all the 

 Campanulacefc have blue flowers '?" 



To this question. Grant Allen, in his " Colours of 

 Flowers " (pp. 81-85), has suggested a very plausible and 

 ingenious answer, the gist of which I venture to reproduce 

 as an extremely probable solution of the difficulty. 

 Observation of analogous cases (RubiaceiB, etc.) tends to 

 show that when flowers with highly specialized colours, 

 such as blue, become dwarfed and crowded together, they 

 show a tendency to revert through lilac, pink, and white 

 back again to the more primitive yellow. This retro- 

 gression in colour is probably due to the fact that the 

 crowded florets are no longer dependent on the visits of 

 only one species of insects to secure cross-fertilization, 

 and hence the reversion in many flower-heads to the 

 yellow of their distant ancestors, since it is the colour which 

 appeals to a great number of miscellaneous insects. In 

 accordance with this principle. Grant Allen considers that 

 " the primitive ancestral Composite had reached the stage 

 of blue or purple flowers whOe it was still at a level of 

 development corresponding to that of the sheep's bit 

 ( Jiisioiie I." Thus the Cynaroid or thistle group of the 

 Compositie are all purple or blue, and the florets are fairly 

 large. In the group of the Corymbifers yellow becomes 

 general; but the least evolved type, the hemp-agrimony, 

 is still purple. Yet, while in many members of the group 

 both ray-florets and disk- florets are a uniform yellow, the 

 daisy shows endence of a progressive step in its develop- 

 ment of colour, for not only are the ray-llorets white, but 

 their edges have begun to show signs of pink. Lastly, 

 the delicate blue colour of the chicory may perhaps 

 indicate a similar forward development, which in this 

 plant has reached the higher notes of the scale of 

 colour. 



The Compositfe have often been bracketted together 

 with the Teasel tribe, the Dipsacaceas, and even a genetic 

 connection between them has sometimes been assumed. 

 But when we come to balance all the facts of the case, this 

 alliance is more apparent than real. It would take too long 

 in this article to dwell upon the technical but essential 

 differences which distinguish the Dipsacacere from the 

 Composite, such as the presence of an epicalyx, a simple 

 style and a terminal undivided stigma, the imbricate 

 asstivation of the corolla, the stamens being only four in 



