Nov. 25, 1869] 
NATURE 
107 
can be improved by any method whatever, unless the 
alterations in the density and the curvature are perfectly 
simultaneous.” This is an entire misconception. Ifa 
lens has too short or too long a focus, it may be amended 
either by an alteration of curvature, or an alteration of 
density ; if the curvature be irregular, and the rays do 
not converge to a point, then any increased regularity of 
curvature will be an improvement. So the contraction of 
the iris and the muscular movements of the eye are 
neither of them essential to vision, but only improvements 
which might have been added and perfected at any stage 
of the construction of the instrument. Thus it does not 
seem at all impossible for spontaneous variations to have 
produced all the delicate adjustments of the eye, once 
given the rudiments of it, in nerves exquisitely sensitive 
to light and colour; but it does seem certain that it could 
only be effected with extreme slowness ; and the fact that 
in all three of the primary groups, Mollusca, Annulosa, 
and Vertebrata, species with well-developed eyes occur so 
early as in the Silurian period, is certainly a difficulty in 
view of the strict limits physicists now place to the age 
of the solar system. A. R. WALLACE 
THE PLANTS OF MIDDLESEX 
Flora of Middlesex; a Topographical and Historical 
Account of the Plants found in the County; with 
Sketches of its Physical Geography and Climate, and 
of the Progress of Middlesex Botany during the 
last Three Centuries. By Henry Trimen, M.B.,F.L.S., 
and W.T. Thiselton Dyer, B.A. Pp.xli.,428. (London: 
Hardwicke, 1869.) 
0] ENS first local Flora published in England gives a list 
of the plants of Hampstead Heath. It was prepared 
by Thomas Johnson, Apothecary on Snow Hill. Early on 
the morning of the 1st August, 1629, and accompanied 
by a few friends, he left London and proceeded on a 
simpling expedition to Hampstead, by way of Kentish 
Town and Highgate. A heavy shower arrested their 
progress for a little, but nothing daunted they made their 
way into the woods, and then on to the heath. The day’s 
excursion was brought to a close in a country inn at 
Kentish Town, where the party dined together. 
Johnson enumerated seventy-two plants as the result of 
the day’s simpling. In subsequent expeditions he added 
sixty-nine others, so that in 1632 his Exwmeratio Plan- 
tarum tn Eviceto Hampsted. cresc. contained 141 species. 
This rare little volume, with its forgotten names—those of 
Gerarde and Lobel—is the earliest precursor of the Flora 
of Middlesex. Since its publication, the materials have 
been gradually accumulating for illustrating the Flora of 
the Metropolitan district, and one of the most valuable 
features in the work before us is, that its authors have, 
with great care and singular success, investigated and ex- 
pounded all the ancient as well as the more recent plant- 
lore bearing on the subject. 
The bi-nominal system of nomenclature and the Lin- 
nean classification introduced, somewhat more than a 
century ago, a new era into the science of Botany, and 
relegated to comparative obscurity the older authors. 
The difficulty of determining the value of their names, 
and the practice of neglecting all ante-Linnean synonymy, 
have caused their labours to be set aside. The authors of 
this volume have made the works of these earlier writers 
critically certain by the help of the Herbaria of Merrett, 
Petiver, Plukenet, Ray, and specially of Buddle, and of 
the manuscripts relating to them now preserved in the 
British Museum. 
We have here given for the first time an authentic 
biography, so to speak, of the different plants so far as they 
are connected with Middlesex. ‘The name of the observer 
who first recorded each plant, the date of the record, and 
the place where it was observed, are specified ; while the 
chronologically-arranged localities where it has been at 
different times gathered, enable one frequently to trace its 
increasing rarity, and in not a few cases the biography 
terminates with the record of its complete extirpation, 
Thus Turner, the father of British Botany, first (1562) records 
Penny-royal (Alentha Pulegium, Linn.) from “ beside 
Hundsley upon the Heth beside a watery place ;” after him 
Gerarde (1597) tells us that it grew “on the common neere 
London called Miles ende, whence poore women bring 
plentie to sell in London Markets ;” and then, through 
Blackstone, to our own time when it was found in plenty 
beside the Hampstead ponds, but finally disappeared from 
the county about twenty years ago. London Rocket, 
which Morison says might have been reaped like a crop 
of wheat on the ruins near St. Paul’s after the Great Fire, 
was, up to the beginning of the present century, a common 
plant in Middlesex, but is now completely lost. The 
history of Czcudalws, from the Isle of Dogs, is much 
shorter. Known in England only in this locality, it 
flourished apparently in a wild state for twenty years, 
until building operations destroyed the habitat about 
twelve years ago. 
Every page of the volume supplies similar interesting 
details in the history of Middlesex plants, This feature 
of the work is as novel as it is important. There is 
abundant evidence that the authors, in addition to their 
faithful and even loving exposition of the labours of their 
predecessors, possess a sound critical acquaintance with 
the species of British plants. Even in this aspect, the 
volume is not behind the best of our county Floras, 
The influence of the geological condition of a district 
upon, the organised bodies connected with it has lately 
been receiving the attention it deserves. Important con- 
clusions have resulted from the Government inquiry into 
the relations subsisting between the diseases of man and 
the geological structure of the south-eastern corner of 
England. The connection between the indigenous vegeta- 
tion and the geology of its habitat is not less interesting, 
and, when data have been sufficiently accumulated to 
warrant safe deductions, will yield valuable information. 
M. Thurmann, in an elaborate essay on the botany of the 
Jura, has shown that vegetation is influenced by the 
manner in which the particles of the rocks are combined, 
rather than by the nature of the materials of which they 
are composed. He has consequently classified rocks into 
two great groups, based on their mechanical constitution : 
the one he calls “ Eugéogénes ” (plentiful-detritus-yielding) 
and the other “ Dysgéogénes” (sparing-detritus-yielding). 
The essential differences between the two groups are in 
respect to their hardness, their power of absorbing and 
retaining moisture in small masses, their permeability in 
extensive deposits, and the rate at which they form detritus 
resulting from the possession of these characteristics. 
Mr. Baker has applied the conclusions of the French 
