0}i the Movements of Petals ii 



it, and finally in water or salt solution, when it straightens out 

 again. He considers that this shows that movement is due to 

 the life and activity of the protoplasm. 



Detmar, in his recent Plant Physiology (1903), devotes some 

 space to nyctitropic movements of flowers, citing a few experi- 

 ments with Leontodon hastilis, Tulipa gesneriana. Crocus vermis, 

 Adonis vernalis, and Taraxacum taraxacum. Those with Leon- 

 todon heads show, as he thinks, that light variations are very 

 important in the opening and closing, while in the experiments 

 with all the others, temperature variations alone cause the move- 

 ments. His experiment, cited for Leontodon hastilis, was about 

 as follows : he cut off during the day several stalks possessing 

 open flowers and put them in water in the dark. They closed 

 as usual in the evening and opened again the next morning (in 

 ■the dark). The following night they closed, but would not open 

 the next morning until placed in the light. In the evening they 

 closed again, thus proving to his satisfaction that light in no way 

 affects opening. 



The view held by Ludwig Jost in his recent Plant Physiology 

 (1904) is that not all flowers act nyctitropically to temperature 

 variations ; some react to light variations. I infer from his state- 

 ments that it is variations in light that cause opening and closing 

 in composite heads, while in Crocus it is temperature. He states 

 that darkness has the same effect on composites as coolness has 

 on Crocus, and that light has the same effect as heat. He adds 

 that, generally in nature, it is the receiving of light accompanied 

 by a rise in temperature, or the taking away of light with lower- 

 irjg of temperature, that causes these movements. 



In the Prantl-Pax Lehrbuch dcr Botanik (1904), rising tem- 

 perature and light are said to cause the inner side of floral leaves 

 (such as Tulipa, Crocus, Adonis) to grow more than the outer; 

 hence the flower opens. Lower temperature and light cause the 

 outer to grow more, and the flower closes. There is a caution 

 not to confuse these movements with those of ephemeral flowers. 

 The author seems to make two divisions of floral movement : 

 those caused by outside forces (autonomous), and those caused 

 by internal forces, turgor changes, brought about by stimuli act- 

 ing on the protoplasm and influencing growth (paratonic). 



201 



