102 
The Australasian Scientific Magazine, [Oct. i, 1885. 
the annual series of changes. But there are abundance of facts which serve 
to show that such an alternation is part of the vegetable economy. 
In the same manner in which Linnaeus proposed a Calendar of Flora, he 
also proposed a Dial of Flora, or flower clock ; and this was to consist, as 
will readily be supposed, of plants, which mark certain hours of the day 
by opening and shutting their flowers. Thus the day-lily ( Hemerocallis 
fulva), opens at five in the morning; the Leontomn taraxacum, or 
common dandelion, at five or six; the Hieradum latifolium (hawkweed), 
at seven ; the Hieradum pilosella , at eight ; the Calendula arvensis, or mari- 
gold, at nine; the Mesetiibryanthemun neapolitanurn, at ten or eleven ; and 
the closing of these and other flowers in the latter part of the day offers a 
similar system of hour marks. 
Some of these plants are thus expanded inconsequence of the stimulating 
action of the light and heat of the day, as appears by their changing their time 
when the influences are changed ; but others appear to be constant to the 
same hours, and independent of the impulse of such external circumstances. 
Other flowers by their opening and shutting, prognosticate the weather. 
Plants of the latter kind are called by Linnaeus, meteoric^ owers, as being- 
regulated by atmospheric causes ; those which change their hour of opening 
and shutting with the length of the day, he terms tropical ; and the hours 
which they measure are, he observes, like Turkish hours, of varying length 
at different seasons. But there are other plants which he terms equinoctial; 
their vegetable days, like the days of the equator, being always of equal 
length : and these open, and generally close, at a fixed and positive hour 
of the day. Such plants clearly prove that the periodical character, and 
the period of the motions above described, do not depend altogether on 
external circumstances. Some curious experiments on this subject were 
made by Decandolle. He kept certain plants m two cellars, one warmed 
by a stove and dark, the other lighted by lamps. On some of the plants 
the artificial light appeared to have no influence (Convolvulus arvensis , 
Convohndus cneorum , Silene frutkosa ), and they still followed the clock 
hours in their opening and closing. 
The night-blowing plants appeared somewhat disturbed, both by per- 
petual light and perpetual darkness. In either condition they accelerated 
their going so much that in three days they had gained half a day, and thus 
exchanged night for day as their time of opening. Other flowers went 
slower in the artificial light (Convolvulus purpurens). In like manner 
those plants which fold and unfold their leaves were variously affected by 
this mode of treatment. The Oxalis stticta and Oxalis incarnata kept their 
habits without regarding either artificial light or heat. The Mimosa 
leucocephala folded and unfolded at the usual times, whether in light or in 
darkness, but the folding up was not so complete as in the open air. The 
Mimosa pudica (sensitive plant) kept in darkness during the day-time, and 
illuminated during the night, had in three days accommodated herself to 
the artificial state, opening in the evening and closing in the morning • 
restored to the open air she recovered her usual habits. 
Tropical plants in general, as is remarked by our gardeners, suffer from 
the length of our summer daylight ; and it has been found necessary to 
shade them during a certain part of the day. 
It is clear from these facts that there is a diurnal period belonging to the 
constitution of vegetables ; though the succession of functions depends in 
part on external stimulants, as light and heat, their periodical character is 
a result of the structure of the plant ; and this structure is such, that the 
