296 MR. A. HENRY ON ELM-SEEDLINGS 
The differences between the two true species are as follows :— 
P. nigra (Europe). Leaf: non-ciliate in margin ; without glands at the 
base ; cuneate at the base ; long-acuminate at the apex. 
P. deltoidea (№. America). Leaf: densely ciliate in margin ; with two 
glands at the base on the upper surface; truncate at the base ; euspi- 
date at the apex. 
Soon after the American species was introduced in the eighteenth century 
into France, a first cross accidentally arose, which became known in France as 
P. nigra helvetica or * Peuplier suisse," and when imported into England was 
called the Black Italian Poplar. Arising as а single tree (which has been 
always reproduced by cuttings) it happened to be a male. Selected at once, 
on account of its astounding vigour, characteristic of first crosses in trees, it 
is amply distinct from either of the parents, not only by its rapid growth, but 
by its habit,—slender ascending branches and straight cylindrical stem. 
Scarcely any other tree produces such a volume of timber per year; and its 
economie importance in France and Belgium, and even in England, is 
extreme. 
It is characterized as follows :— 
P. nigra x deltoidea (Р. serotina), First cross. Leaf with a few cilia 
irregularly disposed on the margin ; glands at the base variable, 0, 1, 
or 2 on each leaf ; in shape like Р. deltoidea, but appreciably 
different. 
Some time after the first cross was obtained, further crossing occurred from 
time to time, and we now have at least two forms of a female tree, which 
differs not only from Р. serotina, but also from P. deltoidea ; and these are 
comparatively valueless, as they grow slowly, and differ in habit from the 
Black Italian Poplar. I need not pursue the history of these poplars further ; 
but P. Eugenei, Г. regenerata, &e. are all later products. 
So far as I can judge, but my investigations are not yet finished, the 
Cricket-bat Willow, which is known only as a female tree, and which 
originated in Norfolk about 1700, is the first cross between Salix alba and 
S. fragilis, —bat, like most first crosses, much more strongly resembles one 
parent than the other. It is, in fact, so close to S. alba in its botanical 
characters that it is universally considered to be a variety of that, viz. ©. alba 
сетива. If it were a variety simply, e.g. a. geographical race, how explain 
its occurrence in one sex only ? The economic importance of this tree, which 
grows twice as fast as ©. alba, is very considerable. 
The history of the Lucombe Oak is very enlightening, as Loudon obtained 
accurate particulars of it, and we are in no doubt as to the facts. The 
Lucombe Oak was raised at Exeter in 1763 from an acorn of a Turkey Oak 
(Q. Cerris) which had been pollinated by a Cork Oak (Q. Suber) growing 
