1904] Notes on the Statolith Theory of Geotrojnsm. 485 



tational stimulus remains unchanged in direction (though not in 

 intensity) is long enough to be effective in producing curvature, does 

 not concern us, since it is a question which is applicable to all theories 

 of gravitational sensibility. 



II. 



On the Presence of Statoliths in Tertiary Hoots. 



Early in our work we noticed the existence of movable starch in the 

 tertiary roots of Vicia faba, and since tertiary roots have been hitherto 

 believed to be devoid of gravitational sensitiveness, we saw that here 

 was a question for investigation. In Jost's above quoted paper 

 (p. 173) this difficulty is referred to in the following words : — 



"Further anatomical investigation is also needed in the case of 

 roots. My own work has shown us that lateral roots of secondary 

 or tertiary rank, which are not gravitationally sensitive, have just the 

 same movable starch as primary roots." 



We do not know to what secondary roots Jost refers. In the case of 

 Vicia faba there is no difficulty in finding a function for the statoliths 

 of the secondary roots, since these are well known to react to gravity. 

 In regard to the tertiary roots the difficulty is a real one. 



It is well known that, if the primary root is cut off, one or more of 

 the secondary roots ceases to grow diageotropically, and turns vertically 

 downward. It occurred to us that the tertiary roots springing from 

 such a secondary might acquire gravitational sensitiveness, and behave 

 like normal secondaries. This proves to be the case, and in this fact 

 undoubtedly lies the explanation of the presence of statoliths in 

 tertiary roots. 



Our method of procedure is to wait until the secondary roots of a 

 bean [Vicia faba) have begun to show themselves, when the primary 

 root is cut near its base, and the secondary roots, with the exception 

 of one, are at the same time removed. The seedling is then planted 

 with the stump of the primary root roughly horizontal, and the single 

 secondary root pointing vertically downwards, as shown in fig. 1. It 

 will be seen that the secondary root E 2 grows vertically for the greater 

 part of its length, and that the general direction of growth of the 

 tertiary roots is strikingly like that of normal secondaries ; and this 

 preparation alone would strongly suggest, to anyone accustomed to the 

 subject, that under these conditions the tertiaries were regulated by 

 gravitation. 



We grow our bean roots (in a dark room) in Sachs's troughs, having 

 oblique glass sides, so that the secondary root, in its attempt to grow 

 vertically, is forced to follow the glass wall. This insures that the 

 secondary root, and a fair proportion of tertiaries, shall be visible, and 

 thus their course can be recorded by painting lines on the glass. 



