220 Innocent: A Century's Changes in the Sheffield Flora. 
Salt found every British species of thistle in this district, 
which is eloquent of the state of agriculture in his time. The 
thistles now missing are :— 
Carduus tenutflorus. Cnicus pratensis. 
C. marianus. C. hetevophyllus. 
Onopordum acanthium. 
The old conditions of cultivation are imperfectly understood, 
but large tracts called ‘commons’”’ appear to have been un- 
allotted open pastures, etc., and to their so-called ‘ inclosures’ 
the following extinctions are probably due :— 
Cerastium semi-decandrum. | Gnaphalium sylvaticum. 
Antennaria dioica. | Scirpus cespitosus. 
Carex ovalis. 
On Lindrick Common the destruction of the upstanding 
plants, such as gorse, by a golf club, has benefitted the uncom- 
mon stemless thistle C. acaulis, which is now abundant there. 
Another group of some ten extinctions is that of the culti- 
vation escapes, which Salt included among the wild flowers, 
and which it is unnecessary to list. 
In the last century many woods have been destroyed, and 
the local newspapers of the time contain numerous advertise- 
ments of oak trees suitable for shipbuilding ; these were for 
those “ wooden walls,’ necessitated by the ambitions of Napo- 
leon Bonaparte. With the woods have gone also the shade 
plants, their associates, and the survival value of those that 
remain is decreased. The following plants are extinct in this 
way :— 
Stellavia nemorum, Ovobanche major. 
Hypericum andvosemum. Hordeum sylvaticum. 
In the course of ages many kinds of flowering plants have 
been developed, varying in habitat, life period, fertilization, 
seed number, seed dispersal, and in many other ways. 
As to the life duration, known for every British plant, I 
guessed that it would be more useful for a plant to be a peren- 
nial, and a rather tedious ‘count-up’ shows that there were in 
the district in Salt’s time 543 Perennials, 36 Biennials, and 150 
Annuals, and there have disappeared 134 Perennials, 9 Bien- 
nials, and 25 Annuals. The greatest survival value then 
belongs not to the Perennials but to the Annuals, and indeed 
are not most of our intruding and prosperous aliens (which 
become denizens) annuals. 
Again, is it more advantageous to produce few or many 
seeds ? I was only able to work this out with the Crucifers. 
Only two species have disappeared from the immediate neigh- 
bourhood of Sheffield, viz.: Lepidium campestre, with two, and 
Teesdalia nudicaulis, with four seeds, while many-seeded 
genera like Capsella and Brassica still abound. 
Among the Labiates Lycopus europeus is the only species, 
Naturalist, 
