N"ewcomb'e, Gravitation sensitiveness not confined to apex of root. 107 



Observation was next made attheend of 2.5hours. The two roots 

 which previously were found straight had now beut outward 15 ° 

 and 20° respectively, while one root formeiiy curved had wholly 

 straightened. 



During all these tests, the damp Chamber always con- 

 tained several centimeters of free water in addition to that 

 held in the filter-paper lining the Chamber; as stated before, my damp- 

 chambers were closed against the loss of water. 



Fig. 5. 

 Seedling of Vicia faba. Method of bending when opposed by bar of cork. 



The foregoing result would seem to demonstrate the geo- 

 tropic sensitiveness of the part of the root behind the apical 

 3 mm. There can be no doubt that the curves are not plastic. 

 Some, however, may hesitate to pronounce against the possible 

 participation of hyclrotropism and thigmotropism in producing the 

 curves when the corkbars were employed. Such doubters are re- 

 ferred to my papers on The Rheotropism of Eoots ! ) and Thigmotro- 

 pism of Terrestrial Roots 2 ), in which it is shown that, even in un- 



1° °l 



Fig. 6. 

 Seedling of Vicia faba. Tip kept from bending by 2 bars of cork. 



injured roots of Vicia faba and Cucurbita pepo, such curves as 

 are recorded in this paper are never produced by cork in con- 

 tact with one side either of the tip or the part behind the tip 

 of the root. 



To make the matter doubly sure, two other experiments were 

 set up quite similar to the last, except that strips of cork were 

 brought into contact with both sides of the tip of the root, as shown 

 in Fig. 6 : Six seedlings of Vicia faba had each 3 min of the tip 

 removed, and the seedlings were tuen prepared in the damp-cham- 

 ber with their tips between cork bars as indicated. revolved for 

 7 hours at 8 g in temperature 24.5° and then observed. Only 



*) Bot. Gazette. XXXIII. 1902. 177. 



2 ) Beih. z. Bot. Oentralbl. XYH. 1904. 61, 



