248 THE YEAR-BOOK OF AGRICULTURE. 



though the latter exhibits a very slight twist to the left. The woody fibre twists to the right 

 in Pinus strobus, Ostrya Virginica, the chestnut of Europe, the European and American 

 Salices, Populus pyramidalis, Cornus Florida, Liriodendron, (in Indiana and Illinois, though 

 in cultivated specimens the twist was found to be the other way ; but more observations are 

 required,) the peach, plum, and cherry-trees, and in the European Cercis siliquastrum, the 

 only leguminous tree known to twist to the right. The twist to the left hand is the more 

 common : it occurs in most Coniferae, especially in Juniperus Virginiana, Taxodium distichum, 

 Pinus sylvestris, (of which young trees twist, however, in the opposite direction,) Picea ex- 

 celsa, &c, Bctula and Alnus, Ostrya vulgaris, and Castanea Americana, (both in opposite 

 directions to the nearly-allied species of the Old World,) Quercus robur, Populus angulata, 

 Catalpa, JEsculus, Hippocastanum, the pear-tree, and, more than any other, the pomegranate ; 

 also most leguminous trees. Most American oaks, the sassafras, Acer nigrum, the apple- 

 tree, &c. twist about as often to the right as to the left. 



The cause of the apparent twisting is not easily ascertained. It is not occasioned by an 

 actual twisting of the whole stem, but belongs to the growth of the successive annual layers. 

 Prof. Braun connects it with the growth of the wood-cells, the ends of which, at their com- 

 mencement, are nearly horizontal, but become wedge-shaped as they elongate ; and if these 

 wedges assume the same direction in the whole circumference of the stem, as they are apt to 

 do, the wood-cells would assume a certain obliquity ; so that this twist of the wood is con- 

 nected with the intimate nature or disposition of the cells themselves. But this is not suf- 

 ficient to explain the higher grades of the obliquity, which sometimes reaches an angle of 

 forty-five degrees. It would here be desirable to ascertain whether the cambium cells divide 

 in this oblique direction and high angle. Our common Tupelo, or Pepperidge, or Ifyssa, would 

 be a good subject for (he investigation, since the obliquity of its wood is generally very considerable, 

 and the layers of a certain number of years incline in the opposite direction from those of the 

 preceding layers. 



Observations on the Correspondence between the Leaf-Venation and Rami- 

 fication of the Plant. 



Prof. M'Cosh, in a paper before the British Association, observed that this correspondence 

 might be illustrated under two general heads: 1. Between the disposition of the branches 

 on 'heir axis, and that of .the veins on the midrib, or other veins from which they spring. 

 In trees where the leaf has no leaf-stalk, the tree is feathered from the ground; and, on the 

 other hand, when the leaf has a leaf-stalk, the tree has a bare, unbranched trunk. It had 

 been objected that the beech-leaf has no loaf-stalk ; whereat the tree has often an unbranched 

 axis. This objection he had been able to answer to the satisfaction of the gentleman who 

 urged it. Tt is customary, in planting out beeches, to strip off the lower branches, and cut 

 over the axis, and hence the form which the plant often assumes in lawns; but the beech, 

 when uneaten by cattle, and not drawn up by being planted in the heart of a wood, is feath- 

 ered or branched from the base. This may be seen from its mode of growth in hedges. Ho 

 would have it to be understood, however, that this correspondence does not imply that the 

 tree and leaf necessarily assume precisely the same shape. Thus, when the leaf is pinnate, 

 there is no correspondence between the form of the leafage and the form of the tree. Be 

 was inclined to think that when the leaf is pinnate, as in the ash and mountain-ash, the tree 

 ite; thai is, instead of sending forthtone main axis from top to bottom, it sends 

 off, in a scattered way, branch after branch, till the axis is lost. 2. The branofa goes off 

 i much the same angle as the vein poes off from the midrib or lateral vein 



There was little difficulty in establishing this in plants with w ly straotare, or in aerbaceout 



j.lant- which have a true branch and not a mere flower-stalk. The only exceptions which 



he had found in plants with true branches were those with deourrent leaves such as thistle*, 

 where the natural angle be affected by the deourrency of the leaf. But there was 



■ difficulty in establishing the correspondence in herbaceous pleats, which either have no 



1 ranch, OT in which it is difficult to say whether we havo a branch of merely ■ peduncle Or 

 leaf-stalk; the more BO, H had not laid down any rule by which to distinguish 



