100 ORGANOGRAPHY. 



duced by an elongation of the horizontal or parenchymatous 

 system of tho stem or its divisions, and consists at first of a 

 minute conical central cellular mass, which is connected Avitli 

 the pith; around this, spiral and other vessels and wood-cells 

 are soon developed, also in connexion with similar parts of 

 the wood, and on the outside of these, in a cellular substance 

 which ultimately becomes the bark, we have little conical pro- 

 jections of parenchyma developed, which are the rudimentary 

 leaves. As growth proceeds these parts become more evi- 

 dent, and a little conical body is formed at the apex of the stem, 

 or laterally in the axil of leaves, and the formation of the bud is 

 completed (j^y, 192). 



The buds of temperate and cold climates, which remain dor- 

 mant during the winter, and which are accordingly exposed to 

 all its rigours, have generally certain protective organs de- 

 veloped on their outer surfaces in the form of modified leaves, 

 which are commonly called scales. These are usually of a 

 hardened texture, and are sometimes covered with a resinous 

 secretion, as in the Horsechestnut and several species of Poplars; 

 or with a dense coating of soft hairs or down, as in some 

 Willows. Such scales, therefore, by interposing between the 

 tender nidimentary leaves of the bud and the air a thick coating 

 of matter which is a bad conductor of heat and insoluble in water, 

 protect them from the influence of external circumstances, by 

 which they would be otherwise destroyed. Buds thus protected 

 are sometimes termed scab/. In the buds of tropical regions, 

 and those of herbaceous plants of temperate climates which arc 

 not thus exposed to the influence of a winter, such protective 

 organs would be useless, and are accordingly absent, and hence 

 all the leaves of the bud are nearly of the same character. Such 

 buds are called naked. In a few instances, we find even that 

 the buds of perennial plants growing in cold climates are naked 

 like those of tropical plants. Such is the case with the Alder 

 Buckthorn {Rhamnus Frangtda), some species of Viburnum, &c. 



These external modified leaves, or protective organs of the 

 bud, are commonly, as we have just mentioned, termed scales, 

 but they have also received the names of teymenta, perulce, &c. 

 That such scales arc really only modified leaves adapted for 

 a special purpose, is proved not only by their position with re- 

 gard to the true leaves, but also from the gradual transitional 

 states, which may be frequently traced from them to the ordi- 

 nary leaves of the bud; this is very clearly exhil)ited in the 

 ^senilis Pavia. Thus, as stated by Lindley: — "In tliis plant 

 the scales on the outside arc short, hard, dry, and brown; 

 those next them are longer, greenish, and delicate; within these 

 others l)ccomc dihitcd, are slightly coloured pink, and oc- 

 casionally bear a few im])erfect leaflets at their apex; in suc- 

 cession are developed leaves of the ordinary character, except 



