On the Movements of Petals 5 



Whether this was a theory or had really been found out from 

 experimentation, I am not able to ascertain, as I do not have 

 access to the original paper. 



Linne in 175 1 gave many instances of flower movement. He 

 made a list of forty-six species with the time of opening and 

 closing of each. These he called "sun flowers" ("solares flores") 

 and divided them into (a) those which the conditions of shade, 

 humidity of the air, and atmospheric pressure afifect directly 

 ("meteorici") ; these do not open during cloudy or rainy weather; 

 (&) those that open in the morning but close before evening, at 

 different times according to the light ("tropici") ; (c) those that 

 open and close at a certain hour of the day ("aequinoctiales"). 

 These last he grouped into his "Floral Clock" according to the 

 hours of the day at which they open and close their flowers, 

 every hour being represented by two or three opening or closing 

 flowers ; composites were also included here since the ray florets 

 act much as the petals of simple flowers. It is quite significant 

 of the importance of the subject that it should have been known 

 even thus well over two hundred years ago. 



According to Rover, Duhamel (a contemporary of Linne's) 

 attributed opening to heat and turgescence, but said that heat 

 rarified the cell sap, quite contrary to the later view that tur- 

 gescence is due to an excessive flow of liquids to certain regions. 



Dutrochet in 1836 gave as the cause of the opening and closing 

 of four-o-clocks (Mirabilis jalapa and Mirabilis longiHora) , the 

 morning glory (Iponioea purpurea) , and the dandelion (Taraxa- 

 cum taraxacum) turgescence and the filling of the fibrous tissue 

 with oxygen. He attempted to explain the process in this way: 

 on the external side of the corolla nerves, parenchymatous tissue 

 is arranged in longitudinal rows, while on the internal side there 

 is fibrous tissue, the two tissues tending to curve in opposite di- 

 rections and thus draw along the other tissues surrounding them. 

 Opening and closing result from the alternately predominant 

 action of one or the other tissue. The parenchymatous tissue 

 tends to curve outward by filling with water, thus causing open- 

 ing in flowers of Mirabilis ; the fibrous tissue curves outward by 

 the chemical action of the oxygen in the water, causing closing 



195 



