1948 



A TEXTBOOK OF THEORETICAL BOTANY 



natively the roots may be tuberous, as in Dahlia, or stem tubers may develop 

 on a rhizome as in Crepis bulbosa and Helianthus, those of H. tuberosus, the 



Jerusalem Artichoke, being 

 edible. Runners or stolons are 

 often produced, as in Achillea. 

 The leaves may form a 

 rosette at the base of the plant 

 as in the Daisy and Dandelion, 

 or they may be produced alter- 

 nately up the stem. They are 

 often large in relation to the 

 plant. In some species the 

 leaves may become spiny or 

 in extremely xerophytic types, 

 needle-shaped. Narrow, par- 

 allel veined leaves occur in a 

 few genera. Though stipules 

 are absent, auricles occur at 

 the leaf bases in some genera 

 and decurrent leaves are 

 widely distributed. 

 The inflorescence (Fig. 1878) is with few exceptions a capitulum con- 

 taining numerous small flowers called florets, surrounded and protected 

 by an involucre (Fig. 1879). The disc may be either flattened or convex. 



The florets (Fig. 1880) may be all alike, or there may be a central group 

 of disc florets surrounded by marginal ray florets, but in all instances the 

 youngest flowers lie towards 



Fig 



1878. — Doronicum pardalianches. Leopards' 

 Bane. Capitulum with well-marked differ- 

 entiation of small disc florets and marginal 

 ray florets with liguliform corollas. 



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the centre of the capitulum. 

 Small scaly bracts or paleae 

 often occur between the 

 florets, usually subtending 

 them. 



The capitula themselves 

 may be arranged in racemes, 

 panicles or spikes, forming 

 thereby compound inflores- 

 cences which may themselves 

 simulate capitula. In most 

 of these cases the individual 

 capitula have only a few 

 florets or may be reduced to 

 one only, as in Echinops. 



The flowers (Fig. 1881) 

 are epigynous and usually 

 pentamerous; they may be actinomorphic or zygomorphic, and may be 

 either hermaphrodite, monoecious or even sterile. 



Fig. 1879. — Taraxacum. Transverse section of 

 a capitulum with florets all sub-similar, 

 surrounded by a ring of involucral bracts. 



