110 STRUCTURAL BOTANY. 



branching thorns of the Honey-locust originate just above me axil, from < ccessory bnda 

 Prickles differ from either spines or thorns, growing from the epidermis -upon stems or 

 leaves, at no determinate point, and consisting of hardened cellular tissues, as hi the 

 Rose, Bramble. 



329. By a more gentle transformation, leaves pass into Bracts, 

 which are those smaller, reduced leaf-forms situated near and 

 among the flowers. So gradual is the transition from leaves 

 to bracts in the Peony, e. g. that no absolute limits can be as- 

 signed. Equally gradual is the transition from bracts to sepals 

 of the flower affording a beautiful illustration of the doctrine 

 of metamorphosis ( 330, etc.) Bracts will be further consid- 

 ered under the head of Inflorescence. 



Review. 317. Early aim of the botanist? 319. Prove that scales are transformed leaves. 

 Three varieties of such scales. 320. Nature of the cotyledons? Proof? Why so de- 

 formed? 321. What are the " leaves" of Acacia? 322. Give the nat.ure of ascidia The 

 four examples given. What of the leaves of Dioiuea? 323. Use of air-bladders? 324. 

 Use of the tendril ? Is this a new organ ? Whence that of Pea ? Lathyrns ? Gloriosa? 

 In Clematis what organs serve as tendrils? In Greenbrier? In the Grapevine? 327. 

 Nature of the spines in Berberis? Goafs-thorn 'Locust ? 328. The thorn of a differ- 

 ent nature. When do trees lose their thorns ? What are prickles ? 329. Nature of 

 Bracts ? 



CHAPTER XXIV. 



METAMORPHOSIS OF THE FLOWER. 



330. It has already been announced ( 37) that a flower is a 

 metamorphosed, that is, a transformed branch. No new princi- 

 ple or element was devised to meet this new necessity in the 

 life of the plant, viz., the perpetuation of its kind ; but the leaf, 

 that same protean form which we have already detected in 

 shapes so numerous and diverse, THE LEAF, is yet once more in 

 nature's hand moulded into a series of forms of superior elegance, 

 touched with colors more brilliant, and adapted to a higher 

 sphere as the organs of reproduction. 



331. Proofs of this doctrine appear on every hand, both in 

 the natural and in the artificial development of plants. We 

 mention a few instances. The thoughtful student will observe 

 many more. 



332. In most flowers, as in the Poppy, very little evidence 

 of the metamorphosis appears, simply because it has been so** 

 complete. Its sepals, petals, stamens, and pistils how unlike ! 



