140 LEAVES AND BUDS. 



the shoot sometimes grow in the ordinary way, but the stem 

 stops growing and these leaves enclose the young leaves 

 formed inside the bud. Naked resting-buds of this kind 

 occur in herbaceous plants, their structure being essentially 

 like that of a Brussels Sprout, Lettuce, or Cabbage. 



In most woody plants, however, the bud is covered by 

 special scales (bud-scales), each representing a leaf or part of 

 a leaf and being usually thick, hard, corky, gummy, resinous, 

 or hairy, and these scales protect the delicate and sappy 

 young leaves within from injury by rain and frost, but 

 especially from loss of water. In cold weather the roots are 



REVOLUTE INVOLUTE 



CONDUPLICATE 



Fig. 48. Vernation of Leaves. 

 (In each case the young leaf is shown cut transversely.) 



hardly able to absorb any moisture from the soil, so that loss 

 of water at such a time, when there is little or no transpira- 

 tion-current flowing up in the stem, would be fatal to the 

 young shoot inside the bud. When a cold dry east wind 

 comes after the buds have expanded in spring, the young 

 leaves are often killed, whereas an equally cold but moist 

 westerly wind hardly affects them. 



The scales of resting-buds may represent whole leaves (Privet, Lilac), 

 leaf -bases without stalk or blade (Sycamore, Horse Chestnut), stipules 

 of leaves which develop a blade (Alder, Elm, Hazel), or stipules of 

 leaves which do not develop a blade (Oak, Beech). 



