246 



HUTCHINSON'S POPULAR BOTANY 



protoplasts, as though aware that the nipping frosts of winter will have 

 to be faced by these nurslings of the Vegetable World, provide them 

 with jackets which effectually keep out the cold, and which may be 

 thrown off with the milder spring's return. These jackets are botanically 

 known as scale-leaves or bud-scales (fig. 302). 



In some plants as the Horse-chestnut (sEsculiis hippocastanum} the 

 scales are covered with a gluey substance, resulting from the conversion 

 into mucilage of a layer of epidermal cells beneath the cuticle, which 

 increases their efficiency as bud protectors : while in many speaies of 

 "Willow (Salix) and not a few other plants the scales are provided with 

 a coating of soft hair or down. When bud-scales are not developed, 

 the leaf-like appendages stipules at the bases of the young leaves 

 frequently serve as protectors : or the leaves 

 themselves may be covered with wool. In the 

 majority of cases the Indiarubber-plant (Ficus 

 elastica) may be cited as an example these pro- 

 tective coverings drop off when the leaf is strong 

 enough to bear exposure to sun and weather 

 (fig. 304) ; but in others they persist throughout 



A ^W~ the life of the plant. The membranous stipules 



iW\ of the Tulip-tree ( Liriodendron tulipifera) close 



% A over the young leaf like the shells of a walnut; 



and on pulling them apart the folded leaf may 

 \ be seen curled up, and looking as snug as a kitten 



A in a basket (fig. 307). These stipules shrivel and 



% fall off directly their work is done. 



Another and more familiar form of protective 

 bud-scales is the brown, drj-, chaffy-looking growth 

 which covers the tender green fronds of many 

 Ferns, and which may be well studied in the 

 Common Scale-fern (Asplenium ceterach), one of 

 the prettiest of our mural species. The closely packed overlapping scales, 

 which are of a rust-coloured brown, completely cover the under surface 

 of the fronds ; and in this case are persistent, for the plant grows in exposed 

 situations and cannot afford to dispense with its chaffy undervest as it grows 

 older. When dry winds prevail or the sun is in his fiercer moods, the fronds 

 roll up, and thus make the most of their protective scales. The leaves of 

 evergreen plants, which, though they have to brave the rigours of winter, 

 lose their scales at an early period, are provided with a specially tough and 

 water-tight epidermis, and their smooth glossy surfaces are admirably 

 adapted to prevent the accumulation of snow upon them. Good examples 

 are offered by the Common Holly (Ilex aquifolium) and the Sweet Bay-tree 

 (Laurus nobilis). 



Buds are usually formed either at the ends of branches, when they are 



FIG. 302. CHRISTMAS ROSE 

 (Helleborus niger). 



The sm Ter figure shows a leaf-bud 



before opening ; in the larger figure it 



has emerged from the bud-cale. 



