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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



or less bilabiate type, as shown in the Mutisiaceae. With this 

 third type we have nothing to do at present, and it enters very 

 little into European garden botany. The flowers of the first and 

 second types are aggregated into heads of three different kinds, 

 and the most obvious classification of garden Compositse is into 

 three groups, as follows : First, the homogamous ligulate type, 

 in which all the flowers of the head are ligulate, as in Crepis, 

 Lactuca, and Hieraciurn ; secondly, the homogamous tubular 

 type, in which all the flowers of the head are tubular, as in 

 Eupatorium, Vernonia, or Carduus ; thirdly, the heterogamous 

 type, in which the central flowers of the head are tubular, com- 

 posing what are called the disc, and the outside flowers, com- 

 posing what is called the rays, are ligulate. To this third group 

 belong both Aster and Helianthus. In the homogamous types 

 all the flowers of the head are usually hermaphrodite. In the 

 heterogamous heads the disc-flowers are usually hermaphro- 

 dite and the ray-flowers more or less incomplete as regards 

 their reproductive organs. A priori one would say that 

 tubular flowers and ligulate flowers represent two extremely 

 different types of structure, but we find that in point of fact 

 they change into one another very easily. The Dahlia, which 

 is nearly allied to the Sunflower, is properly heterogamous, 

 but the majority of garden Dahlias have been changed by culti- 

 vation, so that all the flowers of the head have become homo- 

 gamous and ligulate. In the common Camomile (Authcmis 

 nobilis) all these types may be seen. It is properly heterogamous, 

 but homogamous ligulate and homogamous tubular forms may 

 be found not unfrequently. Aster is properly heterogamous, but 

 there is a form of our common English seaside Aster Tripolium 

 without any ray, and the other English species, Aster Linosyris 

 never has a ray. More constant characters are found in the 

 involucre, the pappus, the anthers, and the shape of the style- 

 branches. The tribes (of which Bentham and Hooker make 

 thirteen) depend mainly on the shape of the style -branches. 

 Aster is the type of one large tribe which is called Asteroidea?, 

 Helianthus of another which is called Helianthoideae. 



In Asteroidens there are upwards of ninety genera, but many 

 of them differ from one another by very slight characters. Of 

 large well-known genera that belong to this tribe, Conyza and 

 Baccharis are homogamous, and in the latter the flowers are 



