APPENDIX A 535 



individual flower is already known in the case of the Sunflower, by the study 

 of its development (Chapter XIII., p. 239, Fig. 188). Each flower is there seen 

 in the normal position, i.e. in the axil of a bract ; it consists of 5 petals, 5 

 stamens, and 2 carpels. The transverse section of the flower approacliing 

 maturity shows these parts arranged as in a floral diagram. The odd ])etal 

 is anterior ; the stamens alternate with the petals, and the carpels are antero- 

 posterior (Fig. 188, viii.). The ovary is inferior, 

 unilocular, and contains one ovule. This structure O 



is fundamental for all Compositae (Fig. 441). ^•r-'-^^'ii:--^ 



As in similarly crowded inflorescences (for in 

 stance the cyathium of the Spurges, p. 515), the 

 crowding brings with it reduction of the individual 

 llowers, but it does not go so far in the Compositae 

 as in the Spurges, The most usual modification is 

 the reduction of the calyx, its protective function 

 having devolved upon the involucre. Sometimes 

 it is absent, as in the Daisy ; or it may be re- 

 presented by two or three teeth, as in Bidens '^' ^^^' 



/r-- ^ T^\ -n i if ,1 -J • J 1 1 I'loral diagram for Coiupositat". 



(i'lg. 238, E). But most frequently it is developed (After Kichlcr.) 



as a means of fruit-dispersal, taking the form of a 



" pappus " composed of bristles, which spread like a parachute (Fig. 234, 

 p. 290). The bract subtending each flower is often abortive, as in the 

 DandeHon and Daisy. The flowers themselves though typically hermaphrodite 

 are liable to become unisexual by abortion. These are all features of reduc- 

 tion, following on the aggregation of the flowers in the compact inflorescence. 

 The florets may develop in three different ways, though all are fundamen- 

 tally of the same construction, having the general formula, S, (5, or o or a), 

 P. 5, A. 5, G. (2). The first type is radially symmetrical, with five equal petals. 



This is probably the original type, and is characteristic of the florets of the disc 

 (Fig. 442, III., IV.). A second type is seen in the ray-florets (Fig. 442, v.), in which 

 the corolla is tubular below, but the three anterior petals are elongated into a 

 long strap-shaped ray, as shown by the three distal teeth ; the two obliquely 

 posterior are reduced or absent. These ray-florets are frequently female, 

 or neuter. A third type is the ligitlate floret, in which the corolla is split on 

 one side, and all the five petals, as shown by the five distal teeth, are elongated 

 into a strap-shaped ray ; but here all five join in its formation (Fig. ^44). 

 According to the type of flower the Family is divided into two Sub- 

 families : (i) The Tubuliflorae, in which the flowers are all tubular, or the outer 

 may be developed as ray-florets (Fig. 442). They have watery juice. K\- 

 amples are the Groundsel, Daisy, Sunflower, and Centaury. (ii) The 

 Ligidiflorae, in which all the flowers are ligulate (Fig. 444). They have 

 milky juice. Examples are Dandelion or Hawk- weed. 



(i) Tubuliflorae. 



(42) The Common Groundsel {Senecio vulgaris. L.) is one of the commonest 



weeds of cultivated ground. It is annual and herbaceous, with branched 



leafy stem, bearing a few heads drooping when young, erect when old. 



The single head, examined in full flower, shows a green involucre of bracts, the 



