METAMORPHOSIS IN PLANTS. 97 



illustration of the developmental evidence. Prof. Goebel, 1 

 to whom we owe most of our knowledge on this subject, 

 has shown that, in many cases, the scales protecting the 

 leaf-buds are really foliage-leaves which have undergone 

 modification which consists either in the abortion of the 

 leaf-blade, or in a change of form of the entire leaf. He 

 has ascertained this, not only by the study of development, 

 but also experimentally in a most ingenious way. He has 

 found, namely, that if the leaf-buds formed in any one year 

 to expand in the following year, are forced to expand in the 

 year of their formation, — which may be accomplished either 

 by cutting off the growing end of the branch bearing the 

 buds, or by removing all its leaves — the buds form no bud- 

 scales, but the structures which would have formed bud- 

 scales in the normal course now develop into foliage- 

 leaves instead. With regard to the bracts, the matter is 

 comparatively simple ; in many cases they are quite in- 

 distinguishable from the foliage-leaves, and in others their 

 relation to them can be traced by a series of intermediate 

 forms. The same kind of evidence applies also to the 

 sepals. In many cases they cannot be distinguished from 

 the bracts ; and it must be further borne in mind that, 

 inasmuch as they stand in the same relation to the flower- 

 bud as do the bud-scales to the leaf-bud, there is a certain 

 connection to be traced between them. Coming now to the 

 petals, we find that in many cases (as in the Lily) they can- 

 not be distinguished from the sepals ; moreover their peculiar 

 attributes of colour and form may be exhibited, not only by 

 the closely related sepals, but by the more remotely related 

 bracts {Bougainvillea Pointseitia). Finally, in the case of 

 the sporophylls, we have to rely upon the manifestation by 

 them of phylloid characters so frequent in the case of 

 monstrous and of double flowers, as well as upon the com- 

 paratively few cases in which the petaloid form is the normal 

 (stamens of Carina and its allies ; petaloid style of Iris). 



But if this evidence suffice to prove the existence of 

 material metamorphosis in the category of leaves, the 



1 Goebel, Vergleichende Entwickelungsgeschichte, p. 248. 



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