^2 



DROSERA ROTUNDIFOLIA. 



[COAP. II. 



The Inflection of the Exterior Tentacles as directly caused 

 by Objects left in Contact with their Glands* 



I made a vast number of trials by placing, by means of a 

 fine needle moistened with distilled water, and with the aid 

 of a lens, particles of various substances on the viscid secre- 

 tion surrounding the glands of the outer tentacles. I experi- 

 mented on both the oval and long-headed glands. When a 

 particle is thus placed on a single gland, the movement of 

 the tentacle is particularly well seen in contrast with the 

 stationary condition of the surrounding tentacles. (See pre- 

 vious Fig. 6.) In four cases small particles of raw meat 

 caused the tentacles to be greatly inflected in between 5 and 

 6 m. Another tentacle similarly treated, and observed with 

 special care, distinctly, though slightly, changed its position 

 in 10 s. (seconds) ; and this is the quickest movement seen by 



power of animal substances, 

 which have been left close to, 

 but not in contact with, sulphate 

 of quinine. The action of salts 

 of quinine will be described in a 

 future chapter. Since the ap- 

 pearance or the paper above re- 

 ferred to, M. ZfcKler has pub- 

 lished a book on the same sub- 

 ject, entitled, ' Atonlcit6 et Zol- 

 clt^,' 1874. 



* [The researches of Pfeffor 

 (' IJnters. aus d. Hot. Instltut zu 

 Tilbingeu.' vol. I., 1885, p. 483) on 

 the sensitiveness of various or- 

 gans to contact show that the 

 conclusions as to the sensitive- 

 ness of Drosera cannot be nmin- 

 talned in their present form (ace 

 p. 24). 



I'feffcr shows. l>oth In the 

 case of the tendrils of climbing 

 plants, and also In that of the 

 tentacles of Drosera, that uni- 

 form pressure hns no stimulating 

 action; tle effect which is 

 ascribc>d simply to contact is in 

 reality due to unequal compres- 

 sion of closely neighbouring 

 points. Tendrils which move 

 after having been rubbeil with a 

 light stick fall to be stimulated 

 when they are rubbed with a 

 glass rod coated with gelatine. 

 The gelatine hns the sMme uni- 

 formity of action ns drops of 

 water falling on the tendril, 

 which are known to produce no 

 effect. If the gelatine Is sprin- 

 kled with flne particles of sand, 

 or If the water holds particles 



of clay In suspension, stimula- 

 tion results. Analogous experi- 

 ments were made on Drosera (p, 

 511). It was found impossible to 

 produce movement of the ten- 

 tacles by rubbing the glands 

 with a surface of mercury, 

 whereas bv rubbing or repeated 

 touches with solid bodies move- 

 ment is called forth. Other ex- 

 periments of Pfeffer's show con- 

 clusively that continuous uni- 

 form pressure has no stimulating 

 effect. He placed small glob- 

 ules of glass on the glands, and 

 convinced himself, by examina- 

 tion with a lens, that contact 

 was effected. Some of the ten- 

 tacles moved, Imt the majority 

 showed no movement, a lonrj ns 

 the plnnlt tcrrc i>o plnrnl thai no 

 vibration from the tabl' or floor 

 rould rrarh thrm. When they 

 were exposed to vibration, and 

 when, therefore, the glass glob- 

 ules must have rubbed against 

 or Jarred the gbind. the ten- 

 tacles moved. The results de- 

 taile<l above in the text nmst 

 presumably be set down to the 

 same cause, namely, the vibra- 

 tion of the table and floor. The 

 sensitiveness of Drosera. there- 

 fore, by no means ceases to be 

 astonishing. Instead of liellev- 

 Ing In movements caused by the 

 steady pressure of very small 

 weights, we set down the results 

 ns iK'Ing due to the Jarring r>f 

 the gland by these same minute 

 bodies. P. D.] 



