20O 



PLANT PHYSIOLOGY 



for ordinary use. It is in reality a refinement of SACHS' early arrangement 

 in which a pointer, attached to a weight on a thread passing from the plant 

 over a pulley-wheel, descended along a scale. A crude form of this is given 

 by DARWIN and ACTON, 150. Third, there is the arc-pointer, invented by 

 SACHS (Lehrbuch, 2d edition, 1870, 632); in this a weighted thread attached 

 to the tip of the plant passes over a pulley-wheel carrying a light pointer 

 which moves over a graduated arc. This form is most effective for educa- 

 tional use, being especially valuable for lecture demonstrations. A good 

 form of it is supplied by ALBRECHT, and another by the STOELTING Company, 

 while a simple make-shift form was pictured by BESSEY in his "Essentials 

 of Botany" (Holt & Co., 1896), 89. Another is given by MAcDouGAL in his 

 "Elementary Plant Physiology," 18, though his OELS form, 19, exhibits a 

 too heavy turning weight. A modification of this, in which the pointer is 

 replaced by a ra*y of light reflected from a mirror carried on the pulley-wheel, 

 or an arm thereof, has also been used (MAcDouGAL, op. cit., 21). Fourth, 

 there is the elaborate balanced crescograph of BOSE, described in his book 

 "Plant Response" (London, Longmans, Green, & Co., 1006), an instru- 

 ment the elaboration of whose combination of levers, mirrors, floats, and 

 hand-recording cylinder seems to preclude the possibility of accuracy. 



Auxographs (Autographic, or Recording, Auxanometers). Of these many 

 forms have been devised. Of precision forms the first was invented by 

 SACHS about 1872 (" Gesammelte Abhandlungen," 691, figured in his "Lec- 

 tures," 557). It consisted of a large vertical excentrically placed cylinder 

 turned by a weight-and-pendulum clock, and having on one side a smoked 

 paper, which was scratched by a pointer carried on a wheel connected with 

 the plant by a thread. A defect in the record was introduced by the arc, 

 instead of the vertical, movement of the pointer. This was overcome in WIES- 

 NER'S instrument (Flora, 1876, 467, figured in his "Elemente der wissen- 

 schaftlichen Botanik," 3d ed., i, 269), in which the pointer was replaced 

 by a large wheel which permitted the vertical drop of a weighted marker 

 suspended by a thread from its circumference, and he also used a compact 

 spring clock. Some improvement in compactness, and in simplifying the 

 mode of guiding the pointer, was made by PFEFFER (whose instrument is 

 pictured in DETMER, 378, and a simple form on the same principle is fig- 

 ured by NOLL in the Bonn Text-book). These instruments all made the 

 record upon a continuously revolving cylinder, but BARANETZKY (in his " Die 

 tagliche Periodicitat der Langenwachsthum," 1879, 21, figured in VINES' 

 "Lectures," 399) introduced a fixed cylinder moved horizontally at regular 

 intervals by an electrically released clockwork, thus making the record 

 appear as a series of descending steps. PFEFFER improved BARANETZKY'S 

 instrument in details, and produced the form now regarded as the standard 

 autographic auxanometer. It is figured in PFEFFER'S "Physiology," 2, 21, 

 and is supplied by ALBRECHT of Tubingen. Other accurate forms have also 

 been constructed. A form using the "occasional release" principle, but 

 with a return to the old arc-marking pointer, is F. DARWIN'S form, described 

 and figured in DARWIN and ACTON, 154, and supplied by the Cambridge 

 Scientific Instrument Company. Another form of great exactness was 



