Oil the Movements of Petals g 



potropic and gamotropic movements. Here, as in earlier publi- 

 cations, he concludes by saying that the exact causes are unknown. 



In a paper published in 1890, Hermann Vochting treats of the 

 influence of temperature upon the flower movements of Anemone 

 stellata — those of the flower pedicel especially — but he also men- 

 tions that the opening and closing are connected with the unequal 

 growth of the upper and under sides of the basal portion of the 

 floral leaves. 



Friedrich Oltmanns (1895) gives to light the most important 

 place in causing nyctitropic movements of flowers, the more in- 

 tense the light, the earlier the closing or opening, a certain quan- 

 tity of light being necessary for the withering of ephemeral flow- 

 ers or the closing of periodically moving ones. He makes the 

 statement that Royer, De Candolle, Dutrochet, and Meyen have 

 all thought light an important factor, while Pfeffer considers 

 that heat works with light in causing flowers to open in the 

 morning. 



Kerner and Oliver (1895) say that the opening of flowers is 

 promoted by sunshine, but whether it is light or heat is to them 

 a question. Kerner says that the amount of pollen produced and 

 the number of flowers on a plant directly afifect the length of 

 time a flow^er stays open. As to the physical cause, the sun's 

 rays affect the tension of the tissues, but just how is not known. 

 The movement of flowers — the change in the position of the 

 petals — is onl}^ another expression of heat energy. The author 

 suggests that, since anthocyanin converts light into heat, if the 

 petals or sepals are white on the inside, the under surface must 

 be tinged red, violet, or blue in order to cause opening. 



From Strasburger and Schimper (1898) it is to be inferred 

 that light and temperature variations are the cause of opening 

 and closing. The same two factors are said by Ludwig Jost 

 (1898) to cause nyctitropic movements. They work together, 

 the two sides of a petal reacting in an opposite manner due to 

 internal causes. His experiments were made principally upon 

 tulip and dandelion flowers. He gives three possibilities as to 

 the growth of the two sides. The first is PfefTer's : the growth 

 of the concave side is hindered by the growth of the convex side, 



199 



