314 APPENDIX IV 



rays, as are also the smaller vessels of the autunm-wood. The pith-rays are 

 rather broad and, under the microscope, distinct. The pale patches of large 

 wood-cells (wood-parenchyma) surrounding the pores and, with them, con- 

 stituting these crescent-shaped areas, are very characteristic of the Sub-Order 

 PapiUondcece, to which nearly all European LeguminSsce belong. 



Considering that they belong to a very distantly related Order, the Elms 

 have woods which in much of their microscopic appearance, especially in the 

 autumn-wood, much resemble the Laburnum. The rings are well defined by 

 the zone of large pores, which consists of several rows in our English Elms, 

 but of little more than a single row in Ulmus americdna (Plate XVI.). The 

 pores aie oval, but irregular, in form. The small pores of the autumn-wood 

 are grouped three to fifteen together, surrounded by soft tissue, in festoons, 

 which form almost continuous wavy concentric bands. The numerous pith- 

 rays, which are brown in colour, are not very conspicuous under a low power. 

 They do not avoid the pores in this species. 



The wood of the Chestnut, Castdnea (Plate XVII.), has its amiual rings 

 very sharply defined by the wide ring of large pores ; and the wood itself is 

 more spongy in the spring half of the year's growth than in the other. The 

 large pores are oval, are somewhat loosely arranged in the zone, and decrease 

 in size outwards. They are followed in the autumn-wood by very charac- 

 teristic, obHque, branching, or "dendritic" groups of small vessels surrounded 

 by soft tissue. The pith-rays are numerous, so fine as to be hardly dis- 

 tinguishable, and bending round the large pores. 



The Oaks, of which the American White Oak {Quercus diba) is represented 

 in Plate XVIII., belong, like the Chestnut, to the Order Cupvliferce ; and, 

 though readily distinguished from the latter wood, have many points of 

 structure in common with it. The annual rings are similarly defined by the 

 zone of large spring pores. These pores are somewhat irregular in size and 

 form, and are more crowded than those of Castdnea. The small pores of the 

 autumn- wood are grouped in dendritic lines, and surrounded by wood-paren- 

 chyma, much as in the other tree, but are often blocked by thyloses. The 

 distinctive character of Oak wood, however, is the presence, in addition to 

 numerous fine pith-rays, of the very broad compound rays which are readily 

 visible to the naked eye. (Compare Figs. 19 and 27, pp. 24-31, and the descrip- 

 tion there given.) 



The Hickories (Hicoria), one of which is figured in Plate XIX., are American 

 trees belonging to the Order Juglanddcece, the Walnut group. Their annual 

 rings are well defmed by a single, loose, undulating row of large, round, or 

 sHghtly oval pores in the spring- wood. The pores are not numerous, and 

 diminish in size in the outer spring- wood, and still more in the autumn-wood. 

 The pith-rays are very numerous and very fine, and avoid the large pores. 

 The autumn-wood is traversed by very fine wavy white Hues of soft tissue. 



The wood of the Persimmon {Diospyros virginidna), the North American 

 representative of the Ebonies (Plate XX.), though not related to the last- 

 mentioned wood, has many structural points in common with it ; but in old 

 trees becomes much darker— nearly black, in fact. The rings are well marked 



