THE PERFOLIATE YELLOW-WORT— continued. 
the laws of priority, it must be replaced by Blackstonia , the name by which William 
Hudson in his “Flora Anglica ” (1762) worthily commemorated an excellent 
English botanist. 
Of John Blackstone comparatively little personal information exists. He 
appears to have been apprenticed to an apothecary in the Strand, perhaps from 1733 
to 1740, and to have frequently visited Francis Ashby of Breakspears at Harefield, 
Middlesex. In 1737 he published a little book entitled “ Fasciculus plantarum circa 
H arefield sponte nascentium,” with an appendix on the geology and other character- 
istics of this district. This book was dedicated to Sir Hans Sloane. In 1740 he 
was established in business as an apothecary “at the Griffin near Salisbury Court, 
Fleet Street”; and in 1746 he published his “Specimen Botanicum,” a list of 
localities for the rarer plants of England, arranged, as the Harefield list had been, in 
alphabetical order. This work, so far as its nomenclature is concerned, is described 
by Pulteney as “ the last book published in England, on the indigenous botany, 
before the system of Linnaeus had gained the ascendancy over that of Ray.” 
Blackstone died in 1753. 
Though not absolutely confined to calcareous soil, the Perfoliate Yellow-wort is 
chiefly found on such formations. It is an annual plant, and there seems formerly 
to have been some tendency to regard as distinct the more luxuriant and branched 
forms and the depauperated examples, which are often very small, slender, and 
unbranched. The whole plant is glabrous and glaucous, and Lord Avebury states 
that the smooth connate leaves serve as an obstacle to small crawling insects. 
Several stems may proceed from one root : they may reach eighteen inches in height 
and be slightly branched ; and they are circular in section. There is at first a 
rosette of radical leaves with rounded points ; but these often wither ; while the 
connate, acute, cauline ones are known by the misleading term “ perfoliate.” Sepals, 
petals, and stamens all usually number eight, each in one whorl, the calyx-lobes 
being deeply divided ; and the corolla, having but a short tube, is often described 
as rotate. The flowers have neither scent nor honey, but they only expand between 
nine and ten in the morning and close at about four. They are protogynous. 
The corolla persists, and the capsule, when ripe, bursts through the corolla-tube. 
The flowering season is from June to September. 
Our only British species ranges over most of Central and Southern Europe and 
into North Africa and Western Asia ; and there are four other Europaean species, all 
mainly southern. The cool grey foliage and bright blossoms, spreading, as it seems, 
with eagerness in the full glare of the sun, suggest this geographical distribution. 
The Yellow-wort shares the tonic bitterness of the F'amily and is said to yield 
a yellow dye. 
