152 



THE STRUCTURE OF FLOWERS. 



or ineclianical irritations. Thus Fig. 45* shows the effect of 

 electrical action on the threads of protoplasm ; a represents 

 a cell of a hair of Tradescantia Virgi- 

 niaca ; h the same, after the application 

 of an electrical current. The following 

 are Dr. Weiss's observations upon this 

 phenomenon : — 



" A constant electrical current is 

 without influence upon the protoplasmic 

 excitation ; whereas the alternate shocJisf 



* From Weiss's Anatomie der Fflanzen, p. 95. 

 t Pfeffer has noticed that the weight, 'per se, 

 '''Lwl£1'a°"'o™°a' ::t o* the body in contact [if .ery slight?] is of 

 dition ; b, under electrical no consequence to tendrils. Thus cotton-wool 

 action (after Weiss). weighing '00025 grain produced no effect if 



carefully placed on them ; but it did when a gentle impact was caused 

 by slight currents of air. Tentacles of Drosera have a sensitiveness very 

 similar to that of tendrils, inasmuch as small splinters of glass only 

 produced irrilation of the glands when they caused a rubbing as the 

 result of concussion (see Journ. Boy. Micr. Soc, 1886, p. 285). 



Pfeffer concludes that the conduction of sensitiveness is not alto- 

 gether due to a continuity of protoplasm, as it does not extend to the 

 epidermis. Since, however, the outer cell-wall of the epidermis can 

 grow when in contact with a foreign body, it would seem to clearly 

 indicate that under such circumstances it still retained its protoplasm ; 

 and that the modern view of the cell-wall being at first a protoplasmic 

 layer, and not altogether a dead secretion from the protoplasm within 

 it, is correct ; for otherwise it is difficult to imagine how it could adapt 

 itself to the surfaces of foreign objects at all. 



Heckel, in studying the movements of the stamens in Sparmannia, 

 Cistus, and Helianthemum, discovered that the epidermis plays an 

 important part : " L'epiderme, contrairemeat a ce que voulait Morren 

 {Ann. des Sci. Nat., t. xix., p. 104), est done dans quelques cas Torgane 

 principal et visible du mouvement. Je me suis mieux assure du role 

 qu'il remplit, en enlevant cet epiderme quand les dimensions des filets 

 mobiles le permettaient sans mutilation profonde (Cistus ladaniferus) : 

 tout mouvement alors etait suspendu " {Bull, de la Soc. Bat. de Fr., torn, 

 xxi., 1874, p. 212). See below, p. 163. 



