I 



P^of. F. Cohn on the Contractile Tissue of Plants. 199 



a homogeneous tissue for the more special (but by no means the 

 exclusive) performance of one or other of those functions. The 

 hypothesis now contended for is, that plant-cells possess irrita- 

 bihty and contractility as do animals, though in a much less 

 complete manner, and without the mechanism of the specially 

 devised tissues — muscle and nerve. And whoever will deny to 

 plants the property of responding by movements to the act of 

 irritation because they possess neither muscles nor nerves, by 

 similar reasoning should deny their capability of taking up 

 nourishment because they have neither mouth nor stomach, or 

 their power to circulate the sap because they have no heart, 

 or their faculty of respiration because they are destitute both of 

 lungs and gills. In short, the plant has, by the medium of the 

 simple cell alone, to accomplish all that is effected in the higher 

 animals by different organs in a more complete and efficient 

 manner. 



31. In the foregoing discussion, Cohn has contented himself 

 by assigning to vegetable tissue the property of irritability and 

 the power of responding to irritation, or the function of con- 

 tractility ; and he would leave to a more imaginative dissertation 

 the task of claiming for plants the possession of localized sensa- 

 tion, of consciousness, and of volition — properties which, in his 

 apprehension, are absent also in the lowest forms of animal 

 existence. 



If sensation, as manifested in animals, could be predicated of 

 tissues which respond by movements to external irritation and 

 in consequence of it, no difficulty would be found in proving its 

 existence in the vegetable kingdom, and particularly by reference 

 to the influence of light upon the green parts of plants, the 

 leaves and stems, in the production of correlative movements. 



32. The movements of the contractile filaments of Centaurea 

 must be acknowledged as having a special purpose when the 

 process of fructification in this plant and its allies is studied. 

 The anthers in Cynarese reach maturity before the stigma. 

 When the apex of the style has as yet not advanced in length 

 beyond the surrounding ring of anthers, the pollen already dis- 

 tends, and exudes from, the cavities of the anthers. If at this 

 period, when the irritability of the filaments is at its maximum, 

 the floret be touched, the filaments are immediately shortened, 

 and the anthers, as a consequence, are simultaneously retracted; 

 a quantity of lumpy pollen is at the same time seen to be ex- 

 truded from the apices of the anthers. However, this pollen is 

 not in a condition to fructify the stigma, in consequence of the 

 peculiar disposition of hairs upon the nodule supporting the 

 fissured apex, which prevent the passage upwards of the pollen 

 to the yet closed stigma-orifice ; and it is not until after the 



