SHOWING MENDELIAN RESULTS. 295 
extent by human agency, as owing to its good form and its excellent timber 
it is superior to either U. glabra ог U. montana as a hedge-tree, 
АП the different seedlings reared, about 5300 in number, each lot of which 
has a well-known tree for its parent, have been planted out this year in tho 
experimental forestry plot on the University Farm at Cambridge ; and if they 
grow up, Г have по doubt that we shall see all the possible existing varieties 
of elms amongst them. 
These experiments seem to show that what are called varieties are often 
simply Mendelian combinations of two existing species. I may here point 
out, that where there is only one species of tree existing in a country or 
territory, such varieties are unknown. Гог example, the beech, a single 
species, throughout Europe, has no varieties of the kind so common in elms. 
Allthe varieties of beech are of another kind, what I may call * sports," 
where we may suppose the variation to be due to some malformation or mis- 
direction of growth in the individual plant. These are as follows :— Variations 
in eolour, as the purple, copper, golden, and variously variegated beeches ; 
variations in form of the leaf, all more or less bizarre, as var. heterophylla 
(the fern-leaved beech), in which the leaves become mere shreds; var. 
quercoides, with deeply pinnate leaves ; var. eristata, leaves small and crowded 
in tufts ; pendulous, fastigiate, and twisted-stem beeches, in which there is 
malformation in the habit of the tree. The beech shows in no way the kind 
of variation that has arisen in elms, as it has not had another species with 
which to make combinations. 
In the common ash (only one species oceurring in northern and central 
Europe) the varieties known are all mere sports, similar to those mentioned 
for the beech. 
In the case of the oak, birch, and lime, in which there are two species 
existing in the same region, the variations are like those in the elm. In 
southern Europe, where the number of species of oak increases, the number of 
varieties increases likewise, to an alarming extent, as no less than 35 varieties 
are described of Quercus Ilex, which is so often associated with Q. Suber. 
These investigations have also served to guide me to a correct appreciation 
of the poplars, which have been so long a puzzle to systematists. I may here 
advert to the Black Poplars. We have in cultivation in this country Populus 
nigra, the European Black Poplar; Populus serotina, Hartwig; a hybrid, the 
Black Italian Poplar, always a male tree; and a number of female trees, 
which, like the last, are generally supposed to be forms of the American 
species, P. deltoidea *. There are also the poplars put on the market by 
French nurserymen, as P. Eugenei, P. regenerata, &c. 
The American Black Poplar (Р. deltoidea) was introduced into France 
about 1700, and arrived in England some years later. 
* I exclude from consideration here P. angulata, another American species, occasionally 
met with in England, very distinct and easily recognizable. 
Y2 
