Innocent: A Century's Changes in the Sheffield Flora. 217 
If this is so, an increase or a decrease of population-density 
will be somewhat proportionate to the decrease or survival 
of plant species. The population-density in the Sheffield 
district is correlated to the geological systems, and the per- 
sistence of species is most marked upon the Carboniferous Lime- 
stone of Derbyshire where the density of population has been 
adversely affected by the decay of the lead-mining industry ; 
and probably the extension of coal-mining eastwards, into the 
Triassic and Permian tracts, will seriously affect their floras. 
The direct destruction of plants may, I think, be con- 
veniently divided into destruction by (1) children ; (2) herba- 
lists ; (3) garden and flower-lovers ; and (4) nature-students. 
Children, happily, prefer known and generally common 
species of which they can gather a great many individuals: to 
children, the decrease of Arum maculatum is perhaps due. 
Herbalists are probably responsible for the disappearance 
of many more plants than is commonly supposed, for there is 
still a great use of native herbs in the West Riding. A leading 
Sheffield herbalist, recently deceased, lamented that his col- 
lectors, owing to ever-decreasing supplies had to go constantly 
farther and farther afield. A writer, in “The Naturalist,’ 
some years ago, recorded the gathering of large quantities of 
Arctostaphylos uva-ursi, by a party of herbalists, in a North 
Derbyshire valley, and its disappearance from Salt’s recorded 
habitat is probably due to this cause. To the herbalists are no 
doubt due the decrease locally of such usually common plants 
as :— 
Chelidonium majus. 
Agrvimonia Eupatoria. 
Sanicula europea. 
Evythvaea centaurium. 
Stachys betonica. 
Euphrastia officinalis. 
Lovers of gardens are principally responsible for the dis- 
appearance of ferns, which form cheap and useful shade plants, 
and of many plants showy in character and sentimental in 
association, in this district, such are :— 
Aquilegia vulgaris. Primula vulgaris. 
Digitalis purpurea. Narcissus pseudo-narcissus. 
Nature-students are probably responsible for the decreases 
in Pinguicula vulgaris and Drosera rotundifolia, and in the 
orchids generally. 
To man directly in one or other of the above classes may be 
ascribed the disappearance of some seven species of orchids, 
and :— 
Viscum album. M. pulegium. 
Pulicaria dysenterica. | Marrubium vulgare. 
Arctostaphylos uva-ursi. Galanthus nivalis. 
Hyoscyamus niger. | Polypodium phegopteris. 
Mentha piperita. Asplenium viride. 
In manufactures the hand and water-power of former 
git June is 
