200 Prof. F. Cohn on the Contractile Tissue of Plants. 



filaments have lost their irritability that the stigma and pollen 

 are mutually fitted for the process of fructification. This extru- 

 sion of pollen on primary contact has, upon such grounds, been 

 designated "pollution" by Meyer. From the above facts, it 

 follows that the several florets in the flower of Centaurea, although 

 they have their anthers and stigma in immediate contact, are 

 nevertheless incapable of self-fructification, are only apparently 

 hermaphrodite, and, in point of fact, dichogamic. 



It is further remarkable that the pollen-grains remain united' 

 in lumps, and therefore less diffusible in the currents of air as 

 dust; and consequently the. fructification, in these as in many 

 other plants, is effected by the agency of insects. When an 

 insect alights on a flower of Centaurea, it produces by its con- 

 tact a retraction of the irritable filament and anther, and at the 

 same moment a discharge of pollen from the apex of the latter, 

 which adheres to the legs of the insect, and serves to fructify, 

 not the stigma of that particular floret, which as yet is, in fact, 

 unfit for the process, but the female organ of some other floret, 

 arrived at maturity, in the same or, it may be, in some other 

 flower. 



The researches of Kohlreuter and others prove that this process 

 prevails throughout the entire family of Cynarete, and affords an 

 explanation of the frequency of bastard forms in this section of 

 the Composite, and particularly in the genus Cirsium. Conrad 

 Sprengel has pointed out that the sexual organs in Carduus 

 nutans do not simultaneously reach maturity, and that therefore 

 the florets are dichogamic. Kohlreuter also states that the fila- 

 ments in Cichorium intybus and Hieracium sabaudum are equally 

 irritable with those of Centaurea ; and the frequency of bastard 

 forms in the Hieracese renders it probable that their florets are also 

 dichogamic. The same condition is moreover presumable in the 

 case of other plants with syngenetic stamens, particularly in that 

 of the Campanulacese, Lobeliacere, Violacere, &c. 



Kohlreuter has likewise announced the fact of the irritability 

 of the filaments in Cactese and Cistinese; and those of the former 

 tribe offer themselves as peculiarly adapted to further researches 

 on this matter, and particularly with relation to the effects of 

 electricity on the contractile tissue of plants. The physiology of 

 contractile tissues is still in its infancy; but we anticipate that its 

 more profound investigation will only supply additional evidence 

 in favour of the proposition which we believe is the starting- 

 point for general physiology and the science of development, 

 viz., that the principle of life, both in the animal and vegetable 

 kingdom, is one and the same, multifariously diversified by dif- 

 ferent gradations in organization, and that all vital phenomena 

 of living organisms are referable to the life of the cell. 



