40 THE BOOK OF NATURE STUDY 



STRUCTURE OF WINTER BUDS. Ash. Winter buds show a 

 wonderful adaptation of structure to function. Their outer 

 scales are developed from very different organs. Some are 

 formed from the part of the leaf attached to the stem, the 

 " leaf -base " as it is called ; this is the case in the Ash, 

 Horse-chestnut, Sycamore, and in most rosaceous trees. Or 

 bud scales may represent stipules, structures which occur in 

 pairs, as lateral branches of the leaf-base. The bud scales of 

 the Oak, Beech, Poplar, Alder are modified stipules. In the 

 Alder and Poplar the stipules are fewer than in the Oak and 

 Beech. Again, bud-scales may represent true leaves, as in the 

 Lilac and Honeysuckle. Some of these winter buds may now 

 be examined more in detail. The bud of the Ash is covered by two 

 or four thick, olive-green scales. These overlap and enclose the 

 young leaves covered with down. In the apical bud, these 

 young leaves are all foliage-leaves ; in the axillary buds, both 

 foliage and floral leaves are found. As a rule, one axillary bud 

 develops into a branch ; the opposite one into a flowering shoot. 

 All these leaves, bud-scales, foliage, and floral -leaves are borne 

 by a central structure, the stem. It is by means of the scales 

 and the down that the young leaves are protected from the 

 cold and damp of winter. The bud scales are of the nature of 

 leaf-bases, for they show rudimentary leaves at the tip. The 

 dark colour is due to a layer of flattened hairs, which secrete 

 a resinous substance, that helps to protect the leaves from damp. 



Horse-Chestnut. The Horse-chestnut has almost the largest 

 buds of any tree. Each is protected by eight or ten scales, and 

 is very sticky owing to the resin secreted. To take off the 

 scales without breaking them, the bud may first be dipped in 

 methylated spirits. If all the scales are removed and placed 

 side by side, the difference in colour and size is striking. The 

 most external are dark brown and small ; inside these come 

 structures which are green and herbaceous, and within these are 

 the true foliage-leaves, covered with down. Inside these foliage- 

 leaves are the floral-leaves. All these sets of leaves are borne by a 

 stem. This bud shows a gradual transition from bud scales 

 on the outside, to true foliage-leaves, something intermediate 

 between scales and leaves being present between the bud-scales 



