I 3 6 PLANT PHYSIOLOGY 



By way of summary we must admit that in this latter case, as also in the 

 case of the root, apical perception has been shown to be extremely probable. 

 In most stems it is by no means generally established, however, for often 

 portions of stems deprived of their apices may exhibit geotropic curvatures. 

 Certain shoots studied by MIEHE (1902) are of special interest in this connexion, 

 for in them it was apparent that there existed a very obvious dependence of 

 geotropic sensitivity on their apices, although doubtless geoperception did not 

 take place in them ; the apices were of import in these cases only in as much 

 as they determined the sensitivity of the whole organ. 



We may now turn to the wider question as to what the primary effect of 

 gravity is and how that leads to perception. 



443, 11. 7-8, for movement, for ... (1898), it is read, movement. CZAPEK 

 (1898) has shown that it is possible to remove a large part of the root apex 

 without destroying perception. This takes place quite normally, e.g. if only 

 one longitudinal half be retained, and it is then quite immaterial how this 

 half is orientated. Hence it is 



11. 13-16, for Many of the . . . hypothesis read Another statocyst hypo- 

 thesis has been simultaneously elaborated by HABERLANDT (1900) and NEMEC 

 (1900). 



1. 28 P. 444, 1. 41, for observations (HABERLANDT, &c. . . . CZAPEK, 1905.] 

 read observations, so that this theory must doubtless be granted a high heuristic 

 value, although it has not as yet been uniformly adopted. Investigators 

 whose forte lies more in anatomical studies have accepted it with enthusiasm, 

 and in cases where difficulties were met with, have sought to surmount them 

 with the aid of supplementary hypotheses. They draw attention more espe- 

 cially to the fact that such mobile starch-grains are never absent from the higher 

 plants, that they are to be found nowhere else in such plants. Conversely, no 

 starch, or at least no mobile starch, is found in organs which do not react 

 geotropically. Still, however, there are geotropic organs without starch (e. g. 

 certain Fungi, root-hairs) or without mobile starch (Caulerpa) ; in such cases 

 other known or hypothetical bodies must be regarded as statoliths, or the 

 statolith function must be accorded to non-mobile starch-grains. In fact, 

 every starch-grain imbedded in sensitive protoplasm must be able to induce 

 perception, and that too without change of position. To regard such apparatus 

 as reduced or rudimentary, and to claim that statocysts with mobile starch 

 have a greater functional capacity, is to look at the matter with the eye of 

 faith ! 



Regarded more from the physiological standpoint, the hypothesis must 

 be more sceptically received. In the first place, it must be noted that, in its 

 original form, it is contradicted by physiological experiment ; for it could 

 be shown, both by rotation experiments and by intermittent stimulation, 

 that a geotropic curvature arises when there is no unilateral accumulation of 

 starch-grains. Since, however, HABERLANDT has more recently suggested 

 that such an aggregation is unnecessary, and since he has laid the chief stress 

 on a unilateral pressure excited by the starch -grain, his theory can no longer 

 be attacked experimentally. We cannot see that this improves matters, for 

 the theory at the same time becomes incapable of demonstration. Certainly 

 attempts have been made to show that the unilateral pressure must proceed 

 from starch-grains, not from any other constituents of the cell ; but the methods 

 (e. g. high or low temperatures) which are employed in removing the starch- 

 grains are all open to the suspicion of affecting at the same time the sensitivity 

 of the protoplasm. 



We must content ourselves with these few observations on the voluminous 

 literature which has gathered round HABERLANDT'S and NEMEC'S hypothesis : 



