66 BET. G. HENSLOW HOMOLOGY AKD 



the segmented laminae are alone present; while in A. hepatica it 

 appears to be the homologue of the petiole alone which constitutes 

 the calyciform involucre. 



Bracteoles would seem to be little else than mid-ribs invested by 

 parenchyma, like an ultimate segment of fennel, and might thus be 

 called costal. 



On the other hand, bracts may abnormally revert to true but 



small leaves. Such is not unfrequently the case in species of 



Plantago, in the involucres of Composites and UmbellifereB, and at the 



base of the umbells of Primula. 



Classifying bracts homologically, we may group them as follows : — 



Kecognising bracts as homologous with or issuing from some 

 one of the above sources, they may assume a diversity of forms 

 and characters adapting them for diverse characters. 



1. Foliaceous. If bracts are of a green colour and herbaceous 

 texture, whatever be their homology, they may justly be presumed 

 to have leaf-functions ; and the cases mentioned above will illus- 

 trate this condition, which is extremely common. 



2. Petaloid. This state of bracts and bracteoles is very frequent. 

 Petaloid bracts may be grouped conveniently under three heads. 



(1) Assisting in the colorisation of the inflorescence, such being 

 mainly effected otherwise by the floral whorls, the bracts them- 

 selves not resembling flowers. 



(2) A number of coloured bracts may together mimic a flower, 

 the true floral perianth being insignificant or wanting. 



(3) Bracts may pass by insensible graduation into the true floral 

 whorls, there being no hreah between true bracts on the exterior 

 and true petals within the flower. 



As examples of the first case there are species of Monarda 

 and Salvia, such as S. splendens and S. Bruantii, in which the 

 calyx is scarlet as Avell as the bracts. Leycesteria, Bougainvillia 

 spectabilis, Musa coccinea, Bromelia, Tillandsea, and Etiphorbia 

 furnish others, while Anthurium, Richardia, and other Aroids, have 

 brightly-coloured or white spathes. 



As examples of involucrate bracts simulating flowers, there 

 are Hederoma [Darwinia) tidipifera, species of Cornus, Xanthosia, 

 Rhodanthe, Helichrgsum, and other kinds of the so-called " Ever- 

 lastings" of Compositce, Euphorbia jacquineceflora, and other species 

 of that genus. 



Instances of complete graduation from small exterior-coloured 

 bracts up to the petals with no distinct intermediate calycine 

 whorl, may be seen in Cactus Jenlcinsonii and other members of 

 that order, such as Epiphyllum splendidum ; as also in Calycanthus 

 and Chimonanthus. 



