THE TBMPBEATUEE OF PLANTS, AND OF THE GROUND. 
37 
1848, bloomed in tlie Gardens of the Horticultural Society, and was grown in a shallow 
pan twelve or fourteen inches in diameter ; the stem was wound round on the top of 
the soil, so that the foliage covered the surface of the pot evenly. The flower-stems 
grow three inches or more high. 
The plant is about as hardy as a Verbena, and should be treated in exactly the same 
manner, and increase is effected both by cuttings and seeds. 
The generic name is derived from abros, delicate, in allusion to the delicacy of the 
involucrum. 
TPIE TEMPERATURE OF PLiVNTS, AND OF THE GROUND. 
By Jolm Towers, Esq. 
About the years 1824 to 1828, some very interesting researches were made, on the first 
of these subjects, in Germany, and in the Botanic Garden of Geneva, and the results 
communicated to one of the German universities. M. Haider, in 1826, had stated that 
some trees, during severe winters, are at a lower temperature than 32°, or the freezing point 
of Fahrenheit's thermometer. The winters of the German continent are usually very 
severe ; and this fact may, therefore, be readily admitted ; as may also that of the watery 
sap being in a state of congelation without danger of vital injury. We were further told 
that the winter of 1828 being severe, the temperature of a poplar was observed during 
that year, and the following notices recorded : — The temperature of the air and of the 
tree were nearly equal in February ; that of the tree became higher in March, April, and 
May ; but the temperature of the air was higher during the other months of the year. 
If we retrace the extreme degree of cold which was witnessed in England in 1838, 
1841, and 1844, when on several occasions the mercury receded below zero, it will not 
be difficult to believe that the sap of trees and shrubs would be reduced so as to become 
far below 32° of Fahrenheit : it is also familiar to the recollection of every gardener, 
that plants in cold frames are frequently so frozen, that the soil of the pots becomes a 
solid and immovable mass. If vital action be strong, its princijple is found sufficient to 
protect the tissues of the hard-wooded tribes ; but in other cases wherein the tissues are 
lax and watery, a disruption of the cellular membrane leads to the inevitable destruction 
of the plant, and then it becomes subjected at once to chemical decomposition. To 
return from this digression. We are told that at the beginning of January, 1828, the 
poplar gave a temperature higher by 10° than that of the external air, which excess the 
writer assigned to a great disengagement of heat when the aqueous juices of the tree 
congealed ; but, he adds, " when it thawed, the heat of the tree was 4° and even 8° above 
that of the air." The observations made during two successive winters have shown that 
the thermometer, in the interior of trees, may descend below zero without injury to 
vegetation. On the 26th of January, 1828, the thermometer marked 1-| plus Fahrenheit ; 
on the 27th, it rose to 34^ ; the change in the tree was less sudden, since on the second 
of those days it remained at 32°, the exact freezing point. 
Several trees were cut, and they were found frozen to a certain depth. The j^^sculiis 
Hippo castanum w^as frozen 8^ lines ; Fraxinus excelsior, 12^ lines; Salix fragilis, 17 
lines. The water of a pool close at hand, was frozen at the same time to the depth of 
8-j^inches. It appeared that the frost had penetrated just in proportion as the trees 
contained more or less water ; and this circumstance will partly account for the rapid and 
total destruction of Pelargoniums and other juicy shrubs which remain in the open ground 
after bedding out in parterres, &c. The -writer alluded to, observes that at the beginning 
of April " nearly all trees contain eight per cent more of aqueous fluid than £yt the end of 
January." Hence, he concludes, that to this cause must be assigned that more general 
loss of shrubs which takes place in the early spring, than in the depth of winter. 
The foregoing passages contain the substance of the interesting article alluded to ; 
but they are not verbatim extracts. 
