PROTOPLASMIC MOVEMENT. 407 



4. Mechanical Stimuli. 



All sudden mechanical disturbances of any importance act 

 as mechanical stimuli — pressing, pulling, bruising, and tearing 

 to pieces. The phenomena are really the same as those called 

 forth by electrical excitation. 



More than one hundred years ago Rosel ^ observed that when 

 touched Amoebae draw themselves together. Colourless blood 

 corpuscles, Rhizopods, &c., after violent pressure draw in their 

 processes and often become varicose. The streaming of the 

 Plasmodia of Myxomycetes is easily slowed or brought to a 

 standstill for some time by any disturbance whatsoever."- The 

 protoplasmic threads in the staminal hairs of Tradescantia will, 

 after strong sudden bruising, tear apart, " draw themselves 

 together into short clubs or balls, and fuse partly with the 

 protoplasm, which is heaped up around the nucleus, and partly 

 with the protoplasm lining the cell- wall " — the primordial 

 utricle. After ten to fifteen minutes the normal arrangement 

 and movement commences again. ^ The rotation in Chara cells, 

 as was observed by Gozzi,* and afterwards by Dutrochet,^ and 

 others, stops after the tying of a ligature round the cell or sharply 

 bending. But rotation soon commences again in the two halves. 

 Dutrochet^ observed a stoppage of some minutes after cutting or 

 tearing the cell. It is without doubt due to mechanical excitation 

 that freshly-made preparations of Chara, Vallisneria, &c., only 

 exhibit motionless protoplasm. The movement recommences 



vi, p. 1, 1867. Borodin, ' Mel. Biol. Petersb.,' vi, 1S07 ; vii, 1869. Frank, 

 ' Jahrb. f. wissensch. Bot.,' viii, p. 216, 1871. 'Botan. Ztg.,' 1871, No. 14 

 and 15. Jul. Sachs, 'Ber. d. sachs: Ges. d. Wiss. Mathem-phys. CI.,' xxii, 

 1859 ; ' Lehrb. d. Bot.,' 4 Aufl., p. 722, 1874. 



^ Rosel von. Rosenbof, ' Der monatl. herausgeg. Insectenbelustigungen, 

 dritter Theil, p. 621, Niirnberg, 1755. 



" H. de Bary, 'Die Mycetozoen,' 2 Aufl., p. 49; Hofmeister, 'Lebre von 

 der Pflanzenzelle,' p. 26. 



' Hofmeister, loo. cit., p. 50. 



* Gozzi, in 'iBrugnatelli Giornale de fisica,' 2 Dec, p. 199, 1818. 



« Dutrocbet, ' Coinpt. rend.,' ii, p. 780, 1837. 



« Dutrocbet, * Compt. rend.,' ii, p. 780, 1837. 



