GROWTH 201 



invented by Frost (Minnesota Botanical Studies, No. XVII, 1894); the 

 thread from the plant is carried over a toothed wheel so arranged that it 

 closes an electric circuit after definite amounts of growth, thus marking a 

 continuous record upon a revolving cylinder which may be removed to any 

 desired distance. Another, in which a descending pointer marks on black- 

 ened rods carried before it by clockwork, is described by Golden and 

 Arthur (Botanical Gazette, 22, 1896, 463). Another, in which an arc- 

 marking pointer records on a continuously turning cylinder, is that of Cor- 

 bett (Ninth and Twelfth Reports of the West Virginia Experiment Station, 

 1900). Another, substantially similar in principle to the last, but utilizing 

 the levers and clockwork of a Richard thermograph, is described by Mac- 

 Dougal, 291. Still another form, on a photographic principle, has been 

 invented by Kohl (Berichte der deutschen botanischen Gesellschaft, 20, 

 1902, 210); in this the growth of the plant permits the descent of a slide, 

 carrying a tiny electric light in front of a minute opening, down the front 

 of a box which contains a revolving cylinder covered with photographic 

 paper. But this instrument would seem liable to serious practical errors. 

 I have myself devised a precision form, working upon the same general 

 principle as Frost's, but eliminating the threads; and this will later be sup- 

 plied among my normal apparatus. It will have the advantage that the 

 part in connection with the plar>t will not exceed a watch in size, and will 

 be practically water-proof, while the recording cylinder can be placed at any 

 distance. Also I have devised a simpler student form, in which a paper 

 carried on the rim of a magnifying wheel revolved in the usual way is marked 

 each hour by the hand of a cheap watch. 



Adapted auxographs in many forms have been described, especially in 

 this country: one recording upon a smoked-glass plate carried on a movable 

 carriage released at intervals by clockwork, by Bumpus (Botanical Gazette, 

 12, 1887, 149); one recording upon a cylinder released at intervals by an 

 electrical device, by Barnes (Botanical Gazette, 12, 1887, 150); one utiliz- 

 ing a small hanging balance to carry a pointer recording on a blackened 

 arm moved by a simple clock, by Stone (Botanical Gazette, 17, 1892, 105); 

 one where a hanging tin cylinder on which a pointer is recording is moved 

 slightly once an hour by the hand of a clock, by F. Darwin (Darwin and 

 Acton, 1905, 156); one in which a glass pen hanging from the rim of a 

 magnifying wheel turned by growth of the plant marks on a cylinder re- 

 volved by a simple clock, by myself (Botanical Gazette, 27, 1899, 260, and 

 in a much improved form in first edition of this book, 103): and it is this 

 instrument, with a change in the clock, which is supplied by the Cambridge 

 Botanical Supply Co.; one in which a pointer connected with the plant 

 marks on a vertical blackened strip moved once an hour by a simple clock, 

 by Lloyd (Torreya, 3, 1903, 97, and School Science, 1903), forming one 

 of the best of the simple instruments; one very similar to the latter in prin- 

 ciple, but somewhat more elaborate, by Schouten in Flora, 97, 1907, 116. 

 I have myself constructed a later form, an improvement over that described 

 in the first edition of this book. It has proved very satisfactory, especially 

 for class demonstration, since its principle is so obvious, and the results 



