124 



HISTORY OF THE VEGETABLE KINGDOM. 



probable that plants undergo a change in their 

 functions; or that, during this period, they per- 

 form a process analogous to breathing, giving out 

 their excess of carbonic acid, and taking in a 

 quantity of oxygen; wliereas, during the day, 

 tlieir digestive process consists in decomposing 

 carbonic acid and water, and liberating a quantity 

 of superfluous oxygen. 



The action of light is tlie chief agent in the 

 expansion of the blossoms of flowers. Many 

 plants do not fuUy expand their petals except 

 when tlie sun shines; and hence tliey alternately 

 open them during tlie day, and shut tliem up 

 during the night. Tliis is distinctly observable 

 in the case of the garden pea, and other papilion- 

 aceous flowers, which spread out their wings in 

 fine weather to admit the rays of the sun, and 

 again fold them up as the night approaches. It 

 may be exemplified also in all compound flowers, 

 as in the dandelion and hawkweed. But the 

 most remarkable case of the kind is that of the 

 celebrated lotus, or lily of the Nile, as described 

 by Theophrastus and Pliny. This plant is re- 

 presented as raising and expanding its blossom 

 during the day, and closing and sinking down 

 beneath the sui'face of the water at night, so as 

 to be beyond the grasp of the hand, and thus 

 remaining till morning again calls it up to the 

 air and light. 



But though the opening and shutting of the 

 blossoms of plants takes place on the change 

 from day to night; yet all plants do not open 

 and shut them at the same time exactly. Plants 

 of the same species are, however, wonderfully 

 regular, even to an hour, other circumstances 

 being the same; and hence has been constructed 

 what botanists call " Flora's Time piece." Flowers 

 requiring a slight stimulus of light, open early 

 in the morning, others requiring more and more 

 open in succession until noon. Many do not 

 fully expand till mid-day, or a little later ; and 

 some, whose extreme delicacy cannot bear the 

 action of full light at all, open only at night; 

 of this nature is the cactus grandiflora, ov night 

 blowing cereus. 



Some, however, have doubted whether light 

 be the sole agent in this expansion of the blos- 

 soms, as it has been observed that equatorial 

 flowers open always at the same hour ; and that 

 tropical flowers change their hour of opening 

 according to the length of the Aa,y. It has been 

 observed also, that the flowei's of plants that 

 liave been removed from a warmer to a colder 

 climate, expand at a later hour in the latter. A 

 flower that opens at six in the morning at Sene- 

 gal, will not open in France or England till eight 

 or nine, nor in Sweden till ten. A flower that 

 opens at ten at Senegal, will not open in France 

 or England till noon, or later, and in Sweden it 

 will not expand at all. Neither will a flower 

 open at all in I'jngland or France, which delays 



its expansion in Senegal till noon or later. Thi."; 

 seems as if a certain amount of heat were as 

 necessary as light, though the opening of such 

 as blow only at night cannot be attributed to 

 either of these stimulants. It is higlily proba- 

 ble that the expansion of some flowers depends 

 as much on other conditions of the air, as 

 on the presence or absence of light and heat, 

 such as its moisture or dryness, and its electric 

 condition. Hence it is, that their opening or 

 shutting betokens meteorological changes. Thus, 

 if the Siberian sow-thistle shuts at night, the 

 ensuing day will be fine; and if it opens, it will 

 be cloudy and rainy. If the African marygold 

 continues shut after seven o'clock in the morn- 

 ing, rain may be soon expected; and if the con- 

 volvulus arvensis, calendula fluvialis, or anagallis 

 arwnsis, are even already open, they will shut 

 upon the approach of rain, the last of which, 

 from its nice susceptibility in this respect, has 

 been called " the poor man's weather glass." 



Some flowers not only indicate the same in- 

 fluence by expanding under his presence, but 

 they also follow him in his course, by bending 

 or turning gradually from the east to the west as 

 the day advances; and thus, looking towards the 

 east in the morning, towards the south at noon, 

 and to the west in the evening, while during the 

 night they again return to their eastern position, 

 to meet the rising luminary. Such flowers have 

 been called heliotropes, on account of their thus 

 following the course of the sun; and the move- 

 ment they thus make has been called by the as- 

 tronomical term of their nutation. The ancients 

 had remarked this circumstance long before they 

 had made any considerable progress in botany; 

 and it had even been interwoven into their 

 mythology, having, according to their legends, 

 originated in one of the metamorphosis of early 

 ages. Clytia, inconsolable for the loss of the 

 affections of Sol, by whom she had been for- 

 merly beloved, and of whom she was still en- 

 amoured, is represented as brooding over her 

 griefs in silence and solitude; where refusing all 

 sustenance, and seated upon the cold ground, 

 with her eyes invariably fixed on the sun during 

 the day, and watching for his return during the 

 night, she is at length transformed into a flower, 

 retaining as much as a flower can retain it, the 

 same unaltered attachment to the sun. This is 

 the flower which is denominated the heliotrope 

 by the ancients, and described by Ovid as " the 

 flower A\hich turns to the sun." But it must 

 be remarked that the flower thus alluded to by 

 Ovid, cannot be the heliotrope of the moderns, 

 because Ovid describes it as resembling the violet; 

 much less can it be the modern sun-flower, which 

 is a native of America, and could not conse- 

 quently have been known to the Latin poet; so 

 that the true heliotropinm of the ancients yet 

 remains unascertained. Bonnet has remarked 



