SENSITIVENESS OF STAMENS. 423 



Sachs has given the name Phototonus to the normal motile 

 condition resulting from alternation of day and night. ' " A 

 plant in this condition, if placed in the dark, will remain for some 

 time (hours or even days) in a state of phototonus, which then 

 disappears gradually ; the plant is therefore under normal condi- 

 tions in a state of phototonus even during the night. In the 

 same manner a plant which has become rigid in continued dark- 

 ness retains its rigidity for some time (hours or even days) 

 after being exposed to light. The two conditions therefore 

 pass over into one another only slowly." 



1093. Temporary rigidity is produced in the case of the Sensi- 

 tive plant by an exposure to a temperature of 15 C. The same 

 effect is produced by a temperature above 50 C., according to 

 Bert's observations at about 60 C. It is stated by him that the 

 sensitiveness of Mimosa is destro3 r ed by exposure to a green 

 light, while plants placed under bell-jars of the following colors 

 remained healthy : white, red, yellow, blue, and violet. 1 



1094. Sensitiveness of stamens. No better illustration of 

 this is afforded than that given by stamens of the common Bar- 

 berry. The six stamens lie curved under the arching petals, but 

 if a filament is lightly touched it is jerked suddenly forward, 

 bringing the anther into apposition with the pistil. 



1095. The filaments of certain Composite are sensitive. The 

 case of the common Chicory has been thus described : The 

 anthers are conjoined to form a tube supported upon five dis- 

 connected filaments which are at first more or less curved out- 

 wards. If the filaments in this condition are lightly touched 

 they instantly straighten, carrying the anther-tube up a little 

 higher, and thus bringing the pollen all along the style which is 

 enclosed. After a short time they resume their former curved 

 condition, retracting the anther-tube to the place which it occu- 

 pied before. It is to be observed that the irritation of a single 

 filament excites only that one, and thus the tube of anthers may 

 be pushed over to one side for a few minutes, again recovering 

 itself after a little while. 



1096. Sparmannia Africana has a cluster of beaded filaments 

 surrounding the pistil and variously intermingled with the sta- 

 mens. When these are touched lightty they open out from the 

 centre with considerable rapidity, and remain thus expanded 

 for a certain period, after which they revert to the closed posi- 

 tion. Somewhat the same phenomenon is to be observed in 



1 Comptes Rendus, Ixx., 1870, p. 339. 



