CXXXII.— THE BLACKTHORN OR SLOE. 
P run us spinosa Linne. 
S O closely related are the “ stone-fruits ” which constitute the Tribe Drupace^ or 
Prunoide^e that almost all of them have, at one time or another, been included 
in the genus Prunus. All are woody plants, with scattered, simple leaves which have 
generally some sugar-excreting glands or “extra-floral nectaries” on their stalks; 
white, pink, or red flowers ; calyx and corolla of five leaves each and both deciduous 
in the fruit stage ; numerous stamens rising from the margin of a cup-like recep- 
tacular tube which encloses the monocarpellary ovary without adhering to it ; and 
two ovules of which only one as a rule reaches the mature condition of a seed. 
While, however, the Peaches, Almonds, and Apricots have a woolly skin or 
“epicarp” to the fruit, the Cherries and Cherry-laurels have smooth and polished 
drupes ; and the Plums — the genus Prunus in its most restricted sense — have their 
fruits covered with a glaucous “ bloom ” or coating of wax-particles. There are 
further differences in the “stones” or “endocarps” of the fruits, which are 
corrugated in Peaches, pitted with holes in Almonds, and smooth in the other 
groups ; in the inflorescences ; and in the folding of the foliage-leaves in their buds. 
In the Cherries and Cherry-laurels the leaves are conduplicate, folded, that is, down 
the midrib like the two halves of a sheet of note-paper ; whilst in the Plums they 
are convolute^ or rolled up with one margin inside, as in a scroll. 
Among the remains of Stone-Age folk found in the Swiss lake-dwellings are the 
stones of the fruits of Sloes and Bullaces, suggesting that these types were then used 
as food and, perhaps, cultivated ; but what we should call distinctively a Plum is not 
found and may not at that time have been evolved by the cultivator’s selective art. 
It is, at the present day, difficult to draw the line between Sloe, Bullace, and Plum, 
or to say that hedgerow trees of the two latter groups are anything more than 
escapes from cultivation. We may, however, discriminate between the three by the 
following characters. If the bark is dark grey or black, the branches spread in all 
directions, every twiglet ending in a thorn; if the flowers come out before the leaves 
and have smooth stalks, while the leaves are small, finely-toothed, and smooth 
beneath, and if the fruit is globular, purple-black, not more than half an inch in 
diameter and very austere in taste, it is the bush we call a Blackthorn when it is in 
flower or leaf, and a S:loe when in fruit. If the bark is brown, the branches straight 
and downy, with but few thorns, the leaves larger, broader, more coarsely serrate 
and downy below ; if the flowers and leaves expand at the same time, the flower-stalks 
are downy, and the globular fruit is purple or yellow, nearly an inch in diameter and 
less austere, we call the tree a Bullace or Damson. Or, lastly, if the bark is brown, 
the branches are straight and thornless, the flower-stalks smooth, the leaves downy 
only along their veins, and the fruit oblong and over an inch in length, we call it a 
Plum, and admit that it is almost certainly an escape from cultivation. 
