LAW OF PROGRESSIVE COLOURATION. 27 



that new colours always make their appearance at the 

 outer side of the petal, while the base usually retains 

 its primitive colouration. For the present, this prin- 



FiG. 6 — Vertical section of bramble-flower {Rubus). White. 



ciple must be accepted on trust. Finally, the true roses 

 (Fig- 8), whose flowers are the most developed of all, 

 have usually broad pink petals (like those of our own 



Fig. 7.— Vertical section of apple-blossom {Pyrus vialus). Pinky white. 



dog-rose, Rosa canina, R. villosa, R. riibigmosa, &c.), 

 which, in some still bigger exotic species, become 

 crimson or damask of the deepest dye. They are 



