l6a BOTANY OF THE LIVING PLANT 



M rianth ambers, rather than to turgor changes. For example, 

 the opening and < losing of Crocus and Tulip flowers are due to differen- 

 ti J growth on the inner and outer surfaces of the perianth members, 

 temperature being the controlling factor. A fall in temperature 

 induces closur, of the flower, while a rise results in opening. In 

 other plants, such as Dandelion, changes in light intensity are more 

 important than those of temperature. The closure of flowers at 

 night or in wet weather serves to protect the inner floral organs 

 from damage by low temperatures or by rain. In some plants, 

 such as the Night Scented Stock (Matthiola), the flowers open 



II. 

 I. 



Fig. 98. 

 Shoot of Mimosa pudica. I. with leaves in the normal day-position. II. in the 

 night-position assumed at dusk, or after stimulation. B = inflorescences. (After 

 Strasburger.) 



at night and close in the daytime, which suggests an adaptation 

 to pollination by moths. 



Sleep movements of foliage leaves are to be seen, for example, in 

 (lover, Wood-sorrel and Mimosa, all of which have compound leaves. 

 In the daytime the leaves are open and the leaflets occupy a horizontal 

 position, but with the approach of night the leaves close up. In 

 (lover this is the result of the leaflets rising, while in Wood- 

 sorrel they droop. In Mimosa the pairs of leaflets fold their upper 

 surfaces together, and the pinnae converge, while the petiole falls 

 into a pendant position (Fig. 98). These movements are made 

 possible by the presence of structures (pulvini) which act like hinges 



