124 THE VEGETABLE WORLD. 
“ The regularity of these phenomena,” says De Candolle, “has 
struck all observers, but although the cause evidently is referable 
to the action of light, it is still difficult to verify it with precision. 
ae I have subjected the Marvel of Peru to continuous 
lamplight, and by that means have obtained an inflorescence 
altogether irregular; but having also placed them where they 
were lighted during the night, and kept in darkness during the 
day, I noticed that at first their flowering was very irregular. 
They soon became accustomed, however, to their new circumstances, 
and ended by blowing in the morning, that is, at the end of the 
day artificially made for them, and closing in the evening as their 
period of obscurity approached.” : 
Heat, however, appears to have a certain influence on the time 
and the duration of the blowing of flowers; and it is observed that 
these phenomena vary in different countries, according to their 
latitudes, and in the same country according to the seasons. The 
Floral Clock drawn up by Linnzeus at Upsal goes slower than the 
clock arranged by De Candolle at Paris. 
In a few flowers the time of blowing is modified by the state of 
the atmosphere. These may be called meteoric plants. The 
Siberian Sow Thistle (Sonchus dentatus) never closes in the even- 
ing, it is said, when it is going to rain the next day. Several of 
the Chichoracee do not open in the morning when it is going to 
rain. The Caltha pluvialis is said to close its petals when the 
weather indicates rain, but its flowers remain open in sudden 
storms, which seem to take it by surprise. Facts of this kind, 
which are, however, neither numerous nor very trustworthy, have 
been used in the arrangement of a floral weather-glass. 
The duration of inflorescence varies much in different species. 
In the Peach, Almond, and Apricot, among trees, and in the 
Hyacinth and Tulip among herbs, it remains in blossom for a 
few days only. But the Winter Hellebore remains covered with 
flowers the whole winter, and the Shepherd’s Purse (Capsella) 
flowers from April till November. 
The period at which flowering commences varies in the —_ 
way according to species. Linnzeus arranged a table of the flowering 
of different vegetables in the climate of Upsal, in Sweden, for the 
year 1755, and gave to this list the name of the Floral Calendar. 
