232 



FLOWERS AND THEIR WORK. 



? FLOWER" 



,-J FLOWER 



--GLAND 



INVOLUCRE 



BUD 



Fig. 81. Inflorescence of Euphorbia. 



The inflorescence of the garden Geranium (Pelargonium) and of many 

 Narcissi resembles an umbel, but the flowers in the apparent umbel 

 are really arranged in little cymose clusters, so that the whole in- 

 florescence has been termed an umbellate cymose head. 



The apparent flowers of the Spurge (Euphorbia) are really inflor- 

 escences, which are sometimes termed cyathiums (Fig. 81). Each is 



surrounded by a cup-shaped invo- 

 lucre formed by the union of tive 

 bracts. Four crescentic glandular 

 scales occur at the margin of the in- 

 volucre between four of the bracts. 

 Inside the cup there appear to be 

 a number of stamens and a single 

 ovary borne on a stalk. The latter 

 is really a carpellary flower, and 

 each of the former corresponds to 

 a single staminate flower, as is 

 indicated by the fact that each 

 stamen is articulated to a short 

 stalk, and that at this point a small 

 scaly bract occurs. In some allied 

 plants a small perianth is present 

 at the base of every stamen, which 

 clearly shows that each of them cor- 

 responds to a single reduced flower. 

 The occurrence of bracts, and the positions which they occupy, are 

 features of great importance in determining the nature of compound 

 or mixed inflorescences. Bracts are usually green, and smaller and 

 simpler than the foliage-leaves. In some Sages they are brightly 

 coloured, and take on the attractive function of a corolla. They are 

 absent from most Cruciferae and Papilionaceae, and the flowers (florets) 

 of most Umbellif erae and Compositae are bractless. Sometimes a series 

 of specially modified leaves which do not subtend flowers, and which 

 therefore are, strictly speaking, not bracts at all, are grouped around 

 the inflorescence. Thus the end of the Daisy or Dandelion has a ring 

 or involucre of green "bracts" around it, although the individual 

 flowers have none. In the head of the Sunflower, however, each 

 flower arises in the axil of a true scaly bract. Sometimes, as in 

 Narcissus, Arums, and Palms, the entire inflorescence is enclosed when 

 young by a single large ' ' bract " or spathe. The latter, however, is 

 simply the uppermost leaf on the stem, and it is not a true bract at all, 

 for the inflorescence is terminal and not axillary. 



Th"! student will usually have little trouble in making out the 

 nature of any inflorescence if the foregoing paragraphs have been 

 mastered. Specimens of all the plants mentioned should be examined 

 carefully. 



Examine the inflorescences of Buttercup (cymose), Foxglove, Bluebell, 

 Wallflower, Candytuft, Cherry, Cowslip, Ivy, Cow Parsnip, Pelar- 

 gonium, Stitchwort, Chickweed, Sweet William, Elder, Willow, 

 Plantain, Sunflower, Daisy, Spurge. 



