Physiology of Plants. 73 



firmed with much greater exactness by Boussingault, 

 whose careful culture-experiments showed that plants 

 do not use the free nitrogen of the air, that they will 

 flourish in soil artificially deprived of organic matter if 

 nitrates are added, that all the carbon in the plant is 

 derived from carbon dioxide, and that various alkaline 

 salts (sulphates, phosphates, &c.) are indispensable to 

 vigorous growth. These were the chief results estab- 

 lished, after much vacillation, at the date 1860. 



Even the most easy-going observers could not fail 

 to notice that many flowers open and close with the 

 growing and waning light of day, that many Movement 

 leaves have a position at night which is and Feeling 

 different from that which they have at noon, in Plants - 

 that many plants climb by their stems, like the hop, or 

 by their leaf-stalks, like the clematis, or by their ten- 

 drils, like the pea and the vine. Of such movements, 

 as well as of others less obvious, there are records in 

 ancient works. 



Yet the history of the subject can hardly be called 

 instructive until within the Victorian Era. There were 

 hundreds of isolated observations, but few experiments; 

 there was almost no success in distinguishing the differ- 

 ent kinds of movements (e.g. growth-movements and 

 periodic movements) ; and almost no one succeeded in 

 taking a comprehensive or unified view of the subject. 



John Ray (1693) puzzled over the case of the sensi- 

 tive plant which had been imported from America, and 

 directed particular attention to the influence of temper- 

 ature on the opening and closing of flowers, and even 

 on the bending of stems towards the light ; the French 

 Academician Dodart deserves credit for first detecting 

 any problem in the familiar fact that a stem grows away 

 from, and a root towards, the centre of the earth; and 

 Stephen Hales tackled the general question of the con- 

 ditions of growth. 



About 1750 Linnaeus constructed his floral clock an 

 arrangement of flowers opening and closing with regu- 

 lar periodicity which made a strong impression on the 

 popular imagination, and he seems to have been the 

 first to apply the term " sleep" to the nocturnal changes 



