190 Retrospective Criticism. 
fields, and principally on a gravelly soil. Hypéricum piilehrum I have always considered as a 
tolerably common plant, but it is marked with a star. Among those plants collected in Herts, the 
Aspérula odorata and Menyanthes trifoliata certainly deserve no place. The alpine plant, the 
Bartsia alpina, from its having been found in Epping Forest, only shows that plants may be found 
within a few miles of London, which botanists have never thought of collecting so far from their 
usual places of growth. Thus the Stratidtes aldides fills a pond on Wandsworth Common ; the 
Tofitldia palistris has been found, I believe, by the foreman (Mr. Bevis?) of the garden at Syon 
House, on Wimbledon Common, with other rarities. I found the Erythre‘a pulchélla Smith ina 
boggy part of a common that runs by the side of the road leading from Kingston to Leatherhead ; 
and, what is more singular, on a strong clay soil, as this plant is usually found by the sea-side, and 
consequently on a sandy soil. In the next page, I find that the Ixddia prociimbens is mentioned 
by Mr. Daniel Stock as a plant new to him and to the botanists there. I should conceive that there 
is no good-sized common or heath where this plant may not be found. If this plant had been rare 
in Suffolk, Sir J. Smith would have mentioned it in his English Flora. —T. M. Oct. 1. 1829. 
Plants with white Flowers. — Various lists of varieties of plants with white flowers have been 
given in your valuable Magazine, and much interest (if we may judge from the numerous corre- 
spondents who have appeared) seems to be taken on the subject ; but, afterall, very little has been 
brought to bear upon the point, as your correspondents have mostly given bare lists, without 
stating the nature or quality of the soil, or peculiar habitat of their plants: so that, from the mere 
enumeration of varieties of plants, without reference to the circumstances I have mentioned, we 
gain little advantage, and no conclusion can be drawn. Having myself frequently met with varie- 
ties of plants in botanical rambles, I have tried to ascertain what causes operate to change the 
colour of the blossom, and I find that it is sometimes merely the effect of a peculiar habitat ; some- 
times the nature of the soil on which the plant grows appears to be the only reason ; and occa- 
sionally an accidental circumstance has given a richness to the soil, and manuring it has caused 
an alteration in the appearance of its vegetation : e. g. the common bird’s-foot trefoil (Ldtus cor- 
niculatus), which in dry upland pastures is of a brilliant yellow, on the red marly banks of the 
Severn assumes a deep sanguine orange hue; and a friend informs me that he has observed it on 
the lias marl, a few miles on the western side of Worcester, perfectly white : in this case the soil 
affects the flowers of the plant. The bluebell (Scilla niitans) is not uncommon, in the vicinity of 
Worcester, with white blossoms ; but I have uniformly observed, wherever it so occurs, that the 
spot is uncommonly shady, or that a wood has, at no very distant time, occupied the place. In these 
cases, the peculiar locality has an effect upon the plant; and in a deep shady wood on the western 
side of the Malvern Hills, where, this summer, I found a number of luxuriant plants of the Paris 
guadrifdlia, in one spot of the thicket where a straggling sunbeam was admitted through the trees, 
and glanced upon one of the plants, the blossom was withered and shrunk, and the four leaves 
variegated. In illustration of the accidental luxuriance of plants, I may mention that I found the 
O'rchis mbdrio, ina moist field near Worcester, double its usual height, and with flowers of a deli- 
cate light pink ; and around the plant, at this particular spot in the marsh, I noticed some swine’s 
dung had been dropped. In the list of plants (p. 161.) I have noticed in this neighbourhood, vary- 
ing in the colour of their flowers, though I have mentioned the particulars above, yet, in many 
instances, I cannot satisfactorily account for the variation. I think, however, the nature of the 
soil should always be examined and noted; and I would suggest to your correspondents to observe 
this in their botanical communications. — Edwin Lees. Sept. 17. 1829. 
Gryphe'a arcuata.— 1 wish your F.R.S. had not sent you his drawing of 
two of the most common fossil shells in England, the Gryphee‘a arcuata. 
(fig. 20. p.95.) Their position must be accidental, for they have lids like 
oysters ; indeed Linnzeus classes them with oysters. — R. B. Jan. 4. 1830. 
Cuciillus sfmplex, — Sir, At p.95. of your Magazine, you have favoured us with a drawing of 
two fossil shells, which, your correspondent says, ‘‘ appear to be the Cuciillus simplex of Rumphius 
(tab. 59. tit. B.).” I think, if he refers to Sowerby’s Zecent and Fossil Conchology, he will find the 
said fossils to be Gryphites ; and, accerding to Lamarck, very distinct from Cuculle*‘a. I am, Sir, 
&e.— A Subscriber. Jan. 7. 1830. 
Meteorological Observations. —Sir, I feel obliged by Mr. Tatem’s notice (p.95.) of my remarks 
on his meteorological observations ; and, in compliance with his wish, I shall, with much plea- 
sure, explain the course adopted by me in making out my register. I have already briefly alluded 
to this at p. 204, Vol. II. ; but perhaps I have. not been sutliciently explicit. In the article Me- 
teorology, p. 159. of Brewster’s Encyclopedia, it is assumed that the mean temperature, by daily 
observations at 10 A. M. and 10 P.M. with an ordinary thermometer, coincides with the mean of 
the daily extremes ; and the mean taken in this manner, compared with the mean of the daily 
extremes for 71 months, gives only a difference of 0°3°, and in some years there is not the smallest 
fractional difference ; and my own observations corroborate what is there stated. For example: 
at 10 a.m. I find the thermometer indicate 50°, and at 10 p.m. 40°. These results are marked in 
separate columns, and the mean 45° extended in a column by itself. On examining my night and 
day thermometer at 10 p.m., 1 find the minimum 38°, and the maximum 52° ; the mean of which 
is also 45°. Should any fractional difference occur, the mean of means is taken for the true 
mean; but knowing that such difference is extremely slight, I have repeatedly recommended 
taking the mean, as stated above, with an ordinary thermometer, with a view to encourage gar- 
deners to keep registers, who may not have self-registering thermometers. Every ten days the 
true mean is added, and divided by 20 for the mean of that decade. ‘The monthly mean is obtained 
by dividing the sum of the true daily means by the number of days in the month, and the annual 
mean by dividing the sum of these by 12. The mean of the barometrical range is taken in the 
same manner. ‘lhe dew point is ascertained at 2 o’clock by plunging a thermometer in a glass of 
water, cooled, if necessary, by frigorific mixtures, noting the temperature when the dew ceases to 
appear on the outside of the glass. Spring water at 47° often effects this in summer without any 
DBSTURE: I also employ Leslie’s differential thermometer for a check, but the calculations are 
tedious. 
The annual average temperature at this place for the last seven years I find to be 47°79 ; and at 
Wycombe, according to Mr. Tatem, it appears to be 46°43°. (Vol. II. p. 96.) Annat Gardens, where 
my register is kept, are 4°46° farther north than Wycombe ; and, according toa formula given by 
Mayer (Brewster's Encye , p. 156., art. Meteorology), which, in many instances, I have found to 
approximate nearly to the truth, the annual mean temperature here should be 47°5°, which is 
within 02° of the seven past seasons, According to the same authority, the annual mean tem- 
