220 OPENING OF THE PASSAGE TO THE INTERIOR OF THE FLOWER. 



and growth. The active energy of the heat is converted into another form of 

 movement which ultimately alters the position of the petals, and we see the flowers 

 opening. This explanation, further, harmonizes with the ascertained fact that 

 under the influence of light and warmth the watery contents of certain cells in 

 dead tissues undergo a rapid alteration, and that even in portions of flowers whose 

 cells contain no living protoplasm changes in tension are brought about. It also 

 agrees with the conception that the periodic opening and closing of flowers stands 

 in relation to those chemical changes and molecular re-arrangements which we know 

 as Respiration, Metabolism, and Growth. It has been demonsti-ated that flowers 

 which exhibit periodic movements do not cease their growth on their first opening, 

 but continue to stretch both in length and breadth. The perianth-leaves of Winter 

 Aconites (c/. p. 114), Meadow Safirons, Anemones, and Gentians, and the ligulate 

 florets of the capitula of the Daisy, Marigold, and Leopard's Bane grow in length 

 considerably every night. Only so long as this growth continues is an opening 

 or closing possible, these movements cease simultaneously with growth. 



The suggestion already offered as to the significance of anthocyanin (vol. i. 

 p. 520) agrees with the idea that light is converted into heat in the tis.sue of the 

 sepals. It was made probable, in the page cited, that the variously-coloured 

 pigments known as anthocyanin possessed amongst other properties that of 

 converting light into heat. It is particularly interesting to note that the white 

 sepals of periodically opening and closing Anemones (Anemone al^nna, baldensis, 

 nemorosa, sylvestris, trifolia, &c.), show a red, violet, or blue tinge on the under 

 side. Quite similarly coloured are the ligulate florets of many Composites (e.g. 

 Anacyclus oJjUcinarum, Bellis jyerennis, Calendula pluvialis, Hieracium Pilosella). 

 It is of course the under-surfaces of the sepals, petals and marginal florets of closed 

 flowers and capitula which ai-e alone visible. When they are closed they appear 

 red, violet, or blue; when open, white (yellow in Hieracium Pilosella). The first 

 rays of the morning sun fall first on the laj^ers of cells coloured by anthocj^anin, 

 and we readily understand what an important part this substance may play in 

 converting the light into heat. 



Seeing that the opening of flowers and flower-buds stands to the rays of the 

 morning sun in the relation of effect to cause, we may infer that the shutting at 

 evening is connected with the waning light and heat. It is also to be expected 

 that closed flowers may be made to open at will by appropriate illumination and 

 warmth, and conversely. This at any rate holds good for a number of plants. It 

 has been already remarked of Gentiana nivalis (cf. p. 116) that in tlie course of an 

 hour, when the sun alternately shines and is obscured by clouds, it will repeatedly 

 open and close. This is also the case with several other Gentians, with Tulips, 

 Meadow SaflProns, and a Flax (Linum. catharticum). In them, also, is the effect 

 of earlier rising and later setting of the sun in northern latitudes especially con- 

 spicuous. But in the majority of flowers with periodic opening and closing, the 

 matter is not quite so simple. True, the majority of species of Flax and Wood- 

 sorrel, and the marginal florets of Composite heads respond to illumination and 



i 



