94 



ORGANOGRAPHY. 



a bad conductor of heat and insoluble in water, protect them 

 from the influence of external circumstances, by which they 



Fig. 183, 



Fig. 184. 



i^c 



Fig. 183. Branch of Oak with alternate leaves and leaf-buds in their axils. 



a, a. Buds, b, b. Leaves. Fig. 184. Longitudinal section of the end 



of a twig of the Horse-chestnut (^scm/ms Hippocastanum), ]>ef ore the 

 bursting of the hud. After Schleiden. a. The pith, b, b. Tlie wood, 

 c, c. The hark, d, d. Scars of leaves of former years, e, e. The vascular 

 bundles of those leaves. /, /. The axillary buds of those leaves, with 

 their scales and the vascular bundles belonging to them. g. Terminal 

 bud of the twig ending in a rudimentary flowering panicle, h, h. Scars 

 formed by the falling off of the lowest scales of the bud, and above 

 these may be seen the closed scales with their vascular bundles, i. Me- 

 dullary mass leading from the pith into the axillary bud. 



would be otherwise destroyed. Buds thus protected are some- 

 times termed scalg. In the buds of tropical regions, and those 



herbaceous plants of temperate climates which are 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 these buds 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, and which are ex- 

 posed during the winter, are naked like those of tropical and 

 herbaceous plants. Such is the case with the Alder Buckthorn 

 {Bhamnus Frangida), 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 name of tegmenta. That such 

 scales are really only modified leaves adapted for a special 



