188 STECKBECK— ON COMPARATIVE HISTOLOGY 



conducted through the vascular bundles of Mimosa pudica, and con- 

 cluded that the transmission was due to a pulsation of water. Du- 

 trochet, as well as some of the succeeding observers, attempted to com- 

 pare propagation in vegetable tissue to that by nerves in animals. 



Burnett and Mayo (8) described the structure of the leaves of Mimo- 

 sa pudica and their movements, when stimulated or when the plant 

 enters the condition of night sleep. These observers noted the flush 

 changes which pass over the primary and secondary pulvini when the 

 leaves are stimulated. They believed that the under half of the pri- 

 mary pulvinus of Mimosa is more irritable than the upper. 



De Candolle (13, p. 647) showed that in many cases even the coty- 

 ledons of sensitive plants are irritable, as illustrated in Mimosa pudica. 



Meyen (33) agreed with Dutrochet that the propagation of stimuli 

 in sensitive plants is effected by the water movements in the elements 

 of the xylem. This same view was later emphasized by Sachs, Pfeffer 

 and others. 



The structural details of pulvini were probably first described and 

 figured by Sachs (40, p. 793). 



Briicke (7) studied the changes in the turgor relation of the pulvini 

 during stimulation, and recognized that the curvature of the pulvinus 

 of Mimosa pudica was connected with the flacidity of the responsive 

 half of the pulvinus produced by the escape of water. 



Millardet (34) and Bert (2) concluded that the changes of expansion 

 in the antagonistic halves of the pulvinus were alike in both halves, but 

 differed quantitatively, and also in progress of time. 



Bert studied the rate of propagation of stimuli in sensitive plants. 



Pfeffer has contributed a great deal to our knowledge of irritability. 

 His "Die periodischen Bewegungen der Pflanzen" is one of the most 

 important of his works (37). 



Darwin (11) made very extensive studies on the sensitivity of plants. 

 He was the first to apply the term " Nyctitropism " to the sleep move- 

 ments in plants. The irritable movements of the cotyledons of various 

 sensitives were emphasized by Darwin. 



Gardiner (17) believed that in all irritable organs the movements 

 are brought about in consequence of a definite contraction of the pro- 

 toplasm of the irritable cells and that during such contraction some 

 of the cell sap escapes to the exterior. 



Haberlandt (18) put forth the view that the stimuli are carried by 

 special cells in the phloem of the vascular bundles. Hanstein before 

 Haberlandt came to the conclusion that the sieve tubes are structures 



