(10/150. Godron 'De l'Espece' tome 2 page 91 describes four varieties of Robinia remarkable from their manner of growth.)
In foliage we have variegated leaves which are often inherited; dark purple or red leaves, as in the hazel, barberry, and beech, the colour in these two latter trees being sometimes strongly and sometimes weakly inherited (10/151. 'Journal of a Horticultural Tour, by Caledonian Hort. Soc.' 1823 page 107. Alph. De Candolle 'Geograph. Bot.' page 1083. Verlot 'Sur La Production des Varietes' 1865 page 55 for the Barberry.); deeply-cut leaves; and leaves covered with prickles, as in the variety of the holly well called ferox, which is said to reproduce itself by seed. (10/152. Loudon's 'Arboretum et Fruticetum' volume 2 page 508.) In fact, nearly all the peculiar varieties evince a tendency, more or less strongly marked, to reproduce themselves by seed. (10/153. Verlot 'Des Varietes' 1865 page 92.) This is to a certain extent the case, according to Bosc (10/154. Loudon's 'Arboretum et Fruticetum' volume 3 page 1376.), with three varieties of the elm, namely, the broad-leafed, lime-leafed, and twisted elm, in which latter the fibres of the wood are twisted. Even with the heterophyllous hornbeam (Carpinus betulus), which bears on each twig leaves of two shapes, "several plants raised from seed all retained "the same peculiarity." (10/155. 'Gardener's Chronicle' 1841 page 687.) I will add only one other remarkable case of variation in foliage, namely, the occurrence of two sub- varieties of the ash with simple instead of pinnated leaves, and which generally transmit their character by seed. (10/156. Godron 'De l'Espece' tome 2 page 89. In Loudon's 'Gardener's Mag.' volume 12 1836 page 371, a variegated bushy ash is described and figured, as having simple leaves; it originated in Ireland.) The occurrence, in trees belonging to widely different orders, of weeping and fastigiate varieties, and of trees bearing deeply cut, variegated, and purple leaves, shows that these deviations of structure must result from some very general physiological laws.
Differences in general appearance and foliage, not more strongly marked than those above indicated, have led good observers to rank as distinct species certain forms which are now known to be mere varieties. Thus, a plane-tree long cultivated in England was considered by almost every one as a North American species: but is now ascertained by old records, as I am informed by Dr. Hooker, to be a variety. So, again, the Thuja pendula or filiformis was ranked by such good observers as Lambert, Wallich, and others, as a true species; but it is now known that the original plants, five in number, suddenly appeared in a bed of seedlings, raised at Mr. Loddige's nursery, from T. orientalis; and Dr. Hooker has adduced excellent evidence that at Turin seeds of T. pendula have reproduced the parent form, T. orientalis. (10/157. 'Gardener's Chronicle' 1863 page 575.)
Every one must have noticed how certain individual trees regularly put forth and shed their leaves earlier or later than others of the same species. There is a famous horse-chestnut in the Tuileries which is named from leafing so much earlier than the others. There is also an oak near Edinburgh which retains its leaves to a very late period. These differences have been attributed by some authors to the nature of the soil in which the trees grow; but Archbishop Whately grafted an early thorn on a late one, and vice versa, and both grafts kept to their proper periods, which differed by about a fortnight, as if they still grew on their own stocks. (10/158. Quoted from Royal Irish Academy in 'Gardener's Chronicle' 1841 page 767.) There is a Cornish variety of the elm which is almost an evergreen, and is so tender that the shoots are often killed by the frost; and the varieties of the Turkish oak (Q. cerris) may be arranged as deciduous, sub-evergreen, and evergreen. (10/159. Loudon 'Arboretum et Fruticetum:' for Elm see volume 3 page 1376; for Oak page 1846.)
SCOTCH FIR (Pinus sylvestris).