32 FAMILIAR TREES 



calyx, have their parts mostly in fives, and have 

 stamens and pistil in the same flowers. The style in 

 this species is imbranched, and the ovary contains 

 only two seeds. The small globular fruits of the two 

 species are similar externally, but those of R. Fran- 

 gula reach a larger size. Both are fleshy and berry- 

 like, and become ultimately black. 



It is a somewhat exceptional fact that these many 

 differences in external anatomy are associated with 

 quite as wide a divergence in the character of the 

 wood of the two shrubs, though there is a resemblance 

 in colour. The soft spongy wood of the Alder Buck- 

 thorn is largely used, under the name of " Black Dog- 

 wood," for the manufacture of gunpowder charcoal. 

 It has a yellowish- red heart, with a narrow light 

 yellow sapwood ; but there is nothing very remarkable 

 about its appearance under the microscope. The 

 harder and heavier wood of R. catharticus, however, 

 is not only more orange at the heart and more greenish 

 in its sapwood, but shows a distinct zone of pores in 

 the spring wood of each annual ring, and remarkable 

 flame-like groups of pores tapering outwards through 

 the autumn wood in a manner well nigh unique. 



If this tree has no great beauty of its own, 

 it is the source of one of the loveliest sights of 

 our English summer; for the Brimstone Butterfly 

 (Gonep'teryx Rhamni) feeds in its larval stage 

 upon the leaves of the Alder Buckthorn; and we 

 may apply to this lovely insect the language used 

 by Burke with reference to Marie Antoinette : 

 "Surely never lighted on this orb, which she 

 hardly seemed to touch, a more delightful vision ! " 



