286 



THE STRUCTURE OF FLOWERS." 



carpels; and, secondly, a retrogressive series from carpels to 

 bracts, and thence to leaves ; finally deducing some important 

 conclusions. 



Progressive Changes in Bracts. — Bracts are in many 

 cases very obviously modifications of leaves, being sometimes 

 simply complete leaves reduced only in size, as in Epilohiam ; 

 or a bract consists either of the blade alone, as in Buttercups, 



or else of the petiole only, 

 but now expanded and 

 blade-like in form, as may 

 be well seen in Hellebores, 

 where transitional states 

 occur between the normal 

 pedate leaf and true lan- 

 ceolate bracts (Fig 61, 

 a, h, c). 



When bracts are 

 coloured otherwise than 

 green, they then approach nearer to members of the repro- 

 ductive or floral series rather than the veg'etative, and in 

 many cases are actually continuous in a spiral series with 

 the sepals and petals, as in Cactus, Cahjcanthus, etc., and so 

 assist in rendering the flower attractive. Several species of 

 the genus Salvia, e.g. S. splendens, S. Bruantii, as well as of 

 Bromeliacece, are remarkable for having brilliantly coloured 

 bracts at the base of the flower. In some cases the bracts 

 may be so arranged as to mimic a corolla, and indeed func- 

 tionally replace it, as in species of Cornus (Fig. 62), Danvinia 

 (Fig. 63), and the so-called Everlastings. 



The presence of bright colours in bracts, as also in sepals, 

 to be described, I take to be due to the same influence as 

 of the normal attractiveness in corollas ; viz., the visits 

 of insects : the immediate cause being nourishment ; the 



Fig. 61. — Transitional form?, a, h, from a leaf to a 

 true bract, c, of HdLtborus viriUis. 



