LIGHT. 149 



latitudes. Trees become harder, smaller, and less luxuriant 

 the higher the latitude, for durinij; the period of their growth, 

 the sun is a threat part ol' the time above the hoiizon. That 

 this is owing to llie action of light, is proved by the fact, that 

 bv transporting vegetables into high latitudes, from equatorial 

 regions, and keeping t!iem in an atiuos{)here, at the tempera- 

 ture of their n.iturAl situation^^, by means of the hot-house, 

 thev flourish diiring the summer, hut during the short days, 

 and long niglits of winter, they droop, cxlii biting their 

 sufTorin^I from t!ic due influence of the sohir r.ivs. 



217. Ila^jpall's theory above noticed, receives conflrm'ition 

 from the fict, tluit those vi'getables which C(»nsist entirely of 

 cellular substance, arc produced only in the absence of the 

 light of the sun, such as muslirooms ; their growth ceasing at 

 the coming of light. And it is a common notion among gar- 

 deners (wiiether true or not, I will not pretend to say,) that 

 melons, cucumlM^rs, and like pulpy fruits, increase much 

 more at niglit than during the day. Although Fungi grow 

 only in darkness, they will never produce spores capable of 

 geriuination, without the action of the sun's light, and it is 

 said, that in cases where the light of day never enters, there 

 may be Fvmgi, but they never increase or perpetuate them- 

 selves by the prndcietion of spores, but only by spreading. 



218. It is during the direct action of the sun's rays, and by 

 their agency, that the most important vegetable products are 

 generated. It is by their influence, that water and carbonic 

 acid are decom;)ospd. the oxygen being mostly liberated, and 

 the elements cf)mbining in other proportions, for the forma- 

 tion of the vari nis oils, resins, &c., including the most ira- 

 portant and abundant of the vegetable products. What is gen- 

 erally tcrmnl the sleep of plants, tliat is, the folding up of 

 compound leaves, and the closing of flowei's, is no doubt in 

 most instances, occasioned bv the want of the stimulating ac- 

 tion of the solnr rays ; for wo see leaves and flowers, that 

 were folded up during the night, expand with the first rays 

 of the niorning sun. 



219. Wc have upon record, many instances of the singular 

 phenomenon of flowers durinir twilight, emitting flashes of 

 tight. It is said the daughter of I^innieus first ol)served this 

 emission, exiiibited by the Tropccolum Majus or Garden Nas- 

 turtium. The flrvshcs occur only during twilight, in the 

 morning or evening ; those of the evening being much the 

 most brilliant. Tiie plants, from whose flowers these flashes 

 have l>orn obsorvod to issue most frequently, are flu* Marigold, 

 Calendula officinalis^ Orange Lily, Lilium Bulbifcrum, Af- 



13* 



