320 New combe. — Geo tropic Response at Various 
grass stems. In these experiments the intermittent klinostat was used, 
exposing grass stems alternately for the same interval to various equal 
angles above and below the horizontal. In twenty-seven cases in the 
thirty-four the stems bent toward the horizontal axis of revolution, thus 
indicating that the positions below the horizontal caused a stronger response. 
A year ago I carried out a limited number of experiments from which 
the inference was drawn that the conclusions of Sachs and of Stone were 
wrong, and that those of Czapek and Miss Pertz were right. A report of 
my results was made incidentally in a paper 1 dealing with the limitations 
of the klinostat. At the same time Fitting 2 published a paper merely 
mentioning results which induced him to support Sachs’ view, that stimuli 
at equal angles above and below the horizontal are equal. Fitting’s method 
seemed adequate, and on other points his results were the same as my own. 
I could not doubt the results shown by my plants, but I resolved to subject 
the apparatus I had had made to a critical examination. This examination 
showed faulty construction, as the result of which the two positions of 
alternate stimulation, instead of being always i8o° apart, were but 177 0 
apart, all of the shortening being on one side of the vertical plane. This 
regrettable error was corrected, and another series of experiments carried 
through as detailed in the following lines. 
On the alternating rack .— This device was the same as that described 
in the first part of this paper. The plants were fastened to the hinged 
board, and the latter was alternated from one side of the vertical plane 
to the other, and stopped in positions such as to give the longitudinal axes 
of the plants in the two positions equal angles with the horizontal plane, 
in one position above, in the other below the horizontal. In all these 
experiments the plants were so placed as to serve as checks on any 
irregularities in the apparatus, some of the pots or damp chambers being 
reversed with respect to the others. Thus, for example, while, in one 
position of the alternating stimulation, some of the roots were 45 0 above 
the horizontal, the neighbouring reversed container would have its roots at 
the same time 45 0 below the horizontal. 
Seedlings of Pisnm sativum , to the number of thirty-eight, were 
employed for the behaviour of their primary roots when alternated at 
intervals of to minutes from 45 0 above to 45 0 below the horizontal. In 
the two experiments the duration was in one case 7 hours and in the other 
9 hours, at a temperature of 23 0 . Eleven roots bent slightly as though 
responding to the position above the horizontal, three as though responding 
to the position below the horizontal, and the other twenty-four remained 
straight. Twelve seedling roots of Lupinus albus in a similar experiment 
1 * Limitations of the Klinostat as an Instrument for Scientific Research.’ Science, NewSer. xx, 
1904, p. 376. 
2 Geotropische'Untersuchungeri. Vorl. Mittheil. Ber. d. d. hot. Gesellsch., xxii, 1904, p. 361. 
