158 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



catching insects, as Saracenia, Drosera, Pinguicula, Nepenthes, 

 &c, which are scattered over the vegetable kingdom and possess 

 no immediate affinities between them, shows that this power of 

 digestion of nitrogenous food is a general one— as, indeed, is 

 normally effected on the germination of seeds and sprouting of 

 tubers when the solid reserve food-materials are dissolved and 

 assimilated — but the insectivorous habit has become developed in 

 some unknown way in particular groups of plants only, or in 

 isolated members of families. Saracenia and Nepenthes, it may 

 be observed, are cases of analogy, as the former is a metamor- 

 phosed leaf-blade, the latter, according to Sir J. D. Hooker, an 

 altered water-gland situated at the extreme tip of the blade only. 



Leaf-scales. — Arrested forms of leaves, called bud-scales, 

 appear on subterranean bulbs, as of lilies. These act as store- 

 houses of nutriment, and become analogous with tubers and 

 fleshy roots. They can also be formed aerially (L. bulbiferum). 

 In other cases they act as protectors to the young growths within 

 the autumn-formed leaf-buds. In these it is usually the petiole 

 only which expands without the blade (horse-chestnut, currant, 

 ash), or else the stipules form bud-scales, the true leaf taking no 

 part whatever (lime, elm, oak, &c). 



Bracts. — Leaves again become scale-like when the repro- 

 ductive organs are developed. They are then called bracts. 

 These may be green and formed out of the petiole only (hellebore), 

 or blade only (ranunculus). They may be coloured and petaloid, 

 and so add to the attraction of the flowers (everlastings, some 

 Aroidece, some salvias, &c). In other cases they mimic a flower 

 by their regular form and whorled character (Comus, Danvinia, 

 Eupho rb ia J acquinifo I id) . 



Floral Whorls. — It has long been an established fact that 

 all the members of flowers are metamorphosed leaves, or rather 

 homologous with leaves ; and while transitions from one kind to 

 another are normal in some few cases, it is a common thing for 

 one organ to assume more or less perfectly the form of another 

 in abnormal or monstrous conditions. 



The changes may be metaphorically described as f 1 pro- 

 gressive" and " retrogressive," as the parts of any outer whorl 



