PLUMS, WILLOWS, ETC. 247 



periderm is usually very dark red to nearly black as it 

 ages, with peeling thin papery lamina in P. Cerasus and 

 P. Avium, or splitting into long fissures in P. domestica 

 &c., whereas in Pyrus it passes to greyer and duller hues 

 and is more inclined to crack into scales. The smoother 

 periderm of Prunus is also apt to drag out the lenticels 

 into horizontal streaks. 



In critical cases recourse may be had to the wood. In 

 Prunus the annual rings are accentuated by the crowding 

 of more numerous vessels in the spring wood, and the 

 medullary rays are sharp, though thin : in Pyrus the 

 vessels are uniform in distribution as well as in size, and, 

 like the medullary rays, so fine that a lens is necessary 

 to see them clearly. 



Buds only showing one scale, really 

 composed of two fused, as indicated 

 by the keeled margins. Leaf-scar 

 crescentic, with 3 leaf -trace bundles. 



[Other buds only exposing one scale are rare, e.g. 

 Guelder Rose, pp. 168 and 169. 



The Willows are so prone to vary and hybridise that 

 it is impossible to do more here than indicate the prin- 

 cipal types ; even good species are not always determinable 

 by the twigs and buds, but the following are the chief 

 forms met with in Britain. Care must be taken in winter 

 that the presence of superficial fungi is not confounded 

 with hairiness. 



The true terminal bud is usually aborted in the 

 Willows. The lateral bud always starts with one scale, 

 anterior, and completely covering the whole. This is 

 doubtless composed of two fused leaves, because minute 

 buds are sometimes found in their axils, to right and left 

 of the ordinary bud. 



