194 Prof. F. Colm on the Contractile Tissue of Plants. 



22. Another interpretation offers itself when the above ob- 

 servations are viewed in comparison with those made respecting 

 the contractile tissue in animals ; and although, in the higher 

 animals, contractility is found in association with highly organ- 

 ized muscular fibre and nerve-tissue, yet, in the lowest animal 

 organisms, contractility and irritability exist even without the 

 formation of distinct cells, as in the sarcode of Hydra, of Amceboe, 

 &c. ; consequently these properties as exhibited in plants become 

 more correctly comparable with such similar endowments in the 

 animal kingdom. The comparison of vegetable contractile tissue 

 with true muscular structure can, indeed, be only by way of 

 analogy, and not of homology. 



23. The greatest analogy obtains between the smooth organic 

 muscles of animals and the contractile tissue of plants. The 

 effect of contraction on muscle is to shorten and thicken it : 

 this effect is speedy, but the subsequent elongation more gra- 

 dual ; this latter likewise proceeds in a curvilinear manner, 

 similar to what may be seen in the contractile filament of the 

 plants. However, the contraction of muscular tissue exceeds in 

 extent that witnessed in the contractile substance of the plant. 



Again, in muscle, contractility is opposed to elasticity; for, 

 like the filament, muscular fibre is endowed with a small amount 

 of elasticity. The degree of elasticity of muscle is smaller, and 

 the extensibility greater, in the contracted than in the extended 

 condition ; and, though not demonstrated, it appears probable 

 that the contracted filaments are more readily and largely ex- 

 tensible than the outstretched ones. 



Further experiments are needed to decide whether the elastic 

 property of the contractile filaments in all cases follows the same 

 laws as Weber has clearly proved to exist in muscles. 



The most powerful excitant of muscle is electricity, by the 

 medium, however, of the nerves. Its operation is nevertheless 

 similar in the case of the motile filaments. Mechanical con- 

 tact operates alike in the two structures, and affects the entire 

 length of the contractile organ. But, besides electricity, there 

 are several other stimulants of muscular energy, such as warm 

 and cold water, vegetable poisons, prussic acid, ether, and chlo- 

 roform, not yet experimented upon in the case of the stamens of 

 Centaur -ea, but which, judging from their action on Mimosa 

 pudica, may be presumed to react on their irritability much as 

 they do on that of muscles. 



24. With the facts now advanced, the differences subsisting 

 between the motory phenomena of contractile filaments and of 

 muscular fibre may be examined and compared. Now, the ex- 

 tended condition is considered to represent the passive and 

 normal state of muscle, and its contraction an active condition 



