78 FRANCIS DARWIN. 



on the other hand, he considers that the possibility of its being 

 an active secretion is not excluded. 



As to the function of the filaments I can say nothing. In 

 the case of Dipsacus^ I made the suggestion that the filaments 

 serve to absorb the putrif'ying fluid which collects in tiie 

 cups, and the ammonia from the dew and rain which falls on the 

 seedling leaves. I was inclined to take this view by the wish 

 of suggesting some function for the filaments ; it is however, 

 quite speculative and should have been kept, perhaps, more dis- 

 tinct from the purely physiological part of the paper. And 

 since the fact of the occurrence of contractile filaments in so 

 different a position as a stalk of an Agaric, will naturally throw 

 doubt on my view of the functions of the filaments in Dipsacus. 

 I may take the opportunity of stating that the speculations as 

 to function should be considered as resting on a different footing 

 from the main question — Are the filaments protoplasmic or not ? 

 It seems to me necessary to state this clearly, as in more than 

 one notice of my paper the absorption of nitrogenous matter 

 has been described as though it were the best grounded of my 

 conclusions. 



Finally, the very fact that contractile filaments occur in such 

 different plants as an agaric and a teasel lends great probability 

 to the idea that the phenomena is of more general occurrence 

 than our present knowledge would have us believe. 



The following observations relate to the teasel only, although 

 they are of interest in relation to the filaments of the Agaric. 



The experiments were made on teasel ])lants growing in pots 

 out of doors and which were removed to the workroom. The 

 leaves used were the very young ones growing in the centre 

 of the rosette of leaves on seedling, or rather second year plants, 

 which from having failed to produce a flowering stem, retained 

 the condition of first-year plants. Thin transverse sections were cut 

 with a razor, the specimens mounted in distilled water under cover 

 glasses, and irrigated with the various reagents in the usual way. 



Irrigation with 1 percent, solution of common salt (NaCI) pro- 

 duced no effect on the filaments ; after ;)llowing the filament to 

 remain in the salt solution for a quarter of an hour the preparation 

 was irrigated with -y^^ per cent, of sulphate of quinine, and 

 contraction followed immediately. A filament irrigated with 

 sugar, 1 per cent., did not contract in seven minutes, but did so 

 in half a minute with -p'u per cent, camphor solution. 



On a subsequent occasion sections were mounted at 10.31 a.m. 

 in 8 per cent, sugar solution, and when filaments were protruded 

 they were irrigated with -,'„ per cent, sulphate of quinine solu- 

 tion at 11. 2U, and contraction of a filament took place slowly at 

 11.25. These experiments, which are fully confirmed by subse- 

 quent trials on salt and sugar solutions, struck me forcibly, 



