PROGRESSIVE METAMORPHOSES. 



289 



compoiind blades are retained (see Fig. 24, p. 93). In 

 Pedicularis the blades are present as a minute fringe on the 

 edge. In Ranunculus, Potentilla, etc., the broad base of the 

 petiole is the only part present, for in abnormal conditions 

 the blade may be borne above (Fig. QQi). Similarly, in a 

 gamosepalous calyx the teeth as a rule seem to be all that 

 remain to represent the blades ; for in Trifolium rejpens, when 

 virescent, true unifoliate blades are developed on elongated 

 pedicels, all arising from the border of the calyx-tube (Fig. 

 Q7), in which the teeth become pinnately nerved blades. 



-Ranunculus with foliaceous 

 sepal. 



Fig. 67.— Foliaceous calyx of Trifolium 

 repens, with stipulate leaflets (after 

 Baillon). 



The venation may in some cases assist in furnishing a clue 

 as to the real nature of a part. Thus in Hellebore, as already 

 seen (Fig. 61), the bracts are homologous with petioles, 

 their venation being palmate, and not pinnate as in the 

 divisions of the blades of the leaves. It is the same in the 

 sepals, which are presumably therefore homologous with 

 petioles as well. The sepals of Galtlta resemble them in 

 their venation, but in this plant the leaf is of a more 

 primitive type, not being lobed, and has also a palmate 

 venation. 



A similar difference between the venation of the sepals 



u 



