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 unbranched, 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'teryz 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 !” 
