108 Newcombe, Gravitation sensitiveness not confined to apex of root. 



5 of the roots had grown, and all were straight except one which 

 had been able to make an outward curve wliile still between 

 the cork bars. 



The confining cork bars were now removed, and thepreparation 

 revolved for 2.5 hours longer at the rate of one revolution in 1.5 

 minutes. Observation then showed that all 5 of the roots which 

 had grown had .curved outward at angles of 10°. 15°. 30°, 45°. 

 and 90° respectively. 



Thirteen seedlings of Cucurbita pepo were treated preci- 

 sely as the seedlings [in the preceding experiment, having 3 

 mm of the apex removed. and cork bars fastened on both 

 sides in contact with the terminal 5 to 7 mm of the roots. 

 The speed was equal to 8 g, temperature 24.5°, and the 

 period 7 hours. At the end of this period all 13 roots showed 

 growth, and were still confined between the cork bars, and 

 were straight. On removal of the cork bars, 11 of the 13 roots 

 immediately curved outward at angles ranging from 15° to 70°, 

 while the other 2 remained straight. The revolution was imme- 

 diately resumed at the rate of once in 2 minutes, and after the lapse 

 of 3.25 hoars, the 2 roots formerly straight were curved at angles 

 of 10° and 20° outward, while one of the roots formerly curved 

 outward had entirely straightened. Thus all 13 roots had shown 

 geotropic curves. 



The method of experimentation here presented is so simple 

 that any one may follow it out. The only difticult step is the pro- 

 per amputation of the root-tips. If the experimenter will use seed- 

 lings of either Vicia faba or Cucurbita pepo, he cannot fail to ob- 

 tain curves which willconvincehim that these plants possess gravi - 

 tation sensitiveness in the part 4 millimeters distant from the apex, 

 and even farther. 



The geotropic sensitiveness of the root, having been, in 

 my opinion, demonstrated to extend through 5 millimeters of 

 some roots, we may now inquire as to several geotropic curva- 

 ture-phenomena which present themseves in various kinds of ex- 

 perimentation. 



Bearing in mind the results obtained with the centrifuge, 

 how shall we offer an hypothesis in accord both with them and 

 with the form of root-growth illustrated in Fig. 4. The latter 

 form is often seen with Cucurbita pepo, Plmseolus multiflorus, Lu- 

 pinus albus and Vicia faba when one places seedlings of these 

 species horizontally in a damp-chamber. The apex of the root, 

 as far as the zone of maximnm growth, declines 45 ° more or less, 

 but the main direction of growth is, in a considerable percentage 

 of cases, horizontal or in a straight line dipping below the hori- 

 zontal. This form must be attained by the tissue of the decli- 

 ning tip changing its direction as it passes behind the zone of 

 maximum growth. 



There are two hypotheses which are in accord with the 

 phenomena mentioned in the last paragreph: (1) The gravi - 

 tation sensitiveness j^is^strongest [at the apexjof the root and 



