1958 



A TEXTBOOK OF THEORETICAL BOTANY 



oils, e.g., Sunflower fruits; others possess ethereal oils and resins. Many are 

 used medicinally, others produce insect powders, e.g., Chrysanthemum 

 roseum (Pyrethrum) and C. carneiim. Colouring matters are obtained from 

 Carthamiis tinctorius (Saffiower), and Adenostemma tinctorium is used to 

 make rouge. 



Many are used as vegetables and we have already referred to those most 

 commonly used. Innumerable species are grown in gardens and of these 

 many have been altered almost out of recognition as a result of horticultural 

 practices. One has only to consider the variety of shape and colour of the 

 capitula exhibited by Dahlias and Chrysanthemums to recognize the truth 

 of this statement. 



We cannot close our account of this family without describing some 

 details of the pollination mechanism, which shows considerable variation 

 in the difi^erent tribes. Hermann Mtiller, many years ago, made an exten- 

 sive study of this subject and his work has been confirmed and amplified by 

 the later studies of Small. 



Fig. 1887. — Eupatorium camiabinum. Hemp Agrimony. A and C, 

 Reduced capitula with involucres, showing the sweeping hairs 

 which carry up pollen from the anthers. B, Older flower with 

 stigmatic surfaces exposed at the base of the hairy arms of the 

 style. Pollen dropping from the styles, as shown at C, may 

 bring about geitonogamy. 



We will select as our first example a member of the tribe Eupatorieae, 

 e.g., Eupatorium camiabinum (Fig. 1887) (Hemp Agrimony). Each capitulum 

 usually contains four or five dull-red florets, but since some hundreds of 

 capitula are aggregated into a dense corymb the inflorescence becomes 

 very conspicuous. In the development of the florets the anthers discharge 

 their pollen into the centre of the corolla and it is then pushed upwards by 

 the sweeping hairs developed on the upper portion of the style, which 

 develops late. Thus in the first stage of anthesis the upper part of the 

 style with the sweeping hairs is exposed so that any insect visiting the 



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