September 8, 1904] 



NATURE 



469 



the organ of graviperception is in the tip of the root ; and 

 it is there — generally in the root-cap — and there only, that 

 statoplasts are found. But these facts do not entirely 

 iiarnionise with the statolith theory, as I shall show later 

 ■on in the section devoted to experimental evidence. Here 

 1 will only add that the group of statocytes in the root are 

 strongly suggestive of some special function, and those who 

 •denv that they form an organ of graviperception must find 

 some other use for them ; and this will be no easy task. I 

 must not omit to mention the ingenious experiments of 

 Piccard (04), which prove (if they prove anything) that the 

 root-tip is not the seat of the graviperception, but that this 

 ■quality is found in even greater perfection in the growing 

 region of the root. But until the whole of the other experi- 

 mental evidence is proved to be illusory, I must suspend 

 judgment on I'iccard's results and treat the question pro- 

 visionally from our previous standpoint. 



The e.xistence of statoliths in regions which have ceased 

 ■to be capable of ordinary geotropic curvature is at first 

 sight a difficulty. Thus Miss Pertz has found in the pith 

 ■of the watercress (Xasturtiiim officinale) the most perfect 

 statoplasts, and this in winter, when the capacity for 

 geotropic curvature was probably absent. Again, she has 

 found movable starch in the xylem elements and in the 

 cortex of a number of trees. In this case we must remember 

 .that, according to Meischke (gg), Jost (oi), and Baranetzky 

 '(01), woody branches of several years' growth are capable 

 ■of geotropic curvature. If so, graviperceptive organs must 

 ■exist. We must remember, too, that in the regeneration 

 of cuttings, \'6chting (78) has shown that gravitation has 

 an influence in certain ca^es ; such cuttings must therefore 

 have organs of graviperception. Or, if this is not granted 

 ■as necessary, it seems to me conceivable that falling starch- 

 grains, though made use of, and in a certain sense 

 rspecialised, for graviperception, should nevertheless e.xist 

 iind serve other purposes in the economv of the plant. But 

 ithis question needs further detailed work. 



Lastly, as part of the general question of distribution, 

 it must be clearly pointed out that in a large number of 

 plants, such as Algae and Fungi, no statoliths are known 

 ■to exist, though their complete absence has not been proved.^ 

 Here we must either believe in Noll's minute and hitherto 

 imseen statoliths or in a different mechanism, such as hydro- 

 static pressure. There is no more impossibility in this state 

 of things than in the presence of statoliths in Palaemon and 

 their absence in higher animals. And I am glad to note 

 that both Pfeffer and Czapek are not disinclined to believe 

 in the possibility of various forms of graviperception. 



Experimental Evidence. 

 A flaw runs through a great part of the experimental 

 ■evidence, which may be illustrated by an experience of my 

 •own. 1 found - that seedlings of Setaria and Sorghum 

 could be nearly deprived of statoplasts by means of a high 

 itemperature, and, further, that such destarched plants were 

 markedly less geotropic than normal specimens. Here 

 seemed a proof of the theory ; unfortunately, however, it 

 turned out that the plants in question were also rendered 

 less heliotropic. These facts make it impossible to allow 

 Nemec's gypsum experiment to be convincing. He caused 

 ■a loss of starch by enclosing roots in plaster of Paris, and 

 found that they had in great part lost their geotropic power. 

 But he did not discover whether this loss depended on dis- 

 appearance of part of the sense-organ or on general loss of 

 ■curving power, though he has since (02) made the interest- 

 ing observation that roots so treated are capable of hvdro- 

 ■■tropism. Again, Kemec found in resting seeds of Vicia 

 Faha that the statoliths are undeveloped, and that they 

 appear synchronously with the power of geotroping. Would 

 not a similar thing be true of the apheliotropism of Sinapis 

 roots — i.e., might it not be found that they were not helio- 

 tropic until the starch appeared? 



The same objection must be brought against Haberlandt's 

 otherwise convincing observation' that Linum growing out 

 1 See Nemec (Beihefte Bot. Central., B. xvii. 1904, p. 59I, where he 

 -describes the c.-ises and the occurrence of statoliths in the'mosses and liver- 

 worts. Giesenhagen (01) has described heavy bodies at the tips of the 

 rhizoids of Chara which fall to the physically lower side. 

 - F- Darwin (03). 



■■i Haberlandt (03). It seems, however, that the starchless plants had some 

 Vheliotropic capacity. 



NO. 18 19, VOL. 70] 



of doors in late autumn or winter is both devoid of stato- 

 plasts and incapable of geotropism, and that the power of 

 curvature returns on bringing the plants indoors, when 

 the starch reappears. The full value of these experiments 

 cannot be made clear without going into more detail than 

 is here admissible. They are particularly interesting 

 because, as Haberlandt remarks, so far as they prove the 

 truth of the statolith theory, they also disprove the pressure 

 theory. This may also be said of other e.xperiments 

 mentioned in the present sc-tion. 



We must, I think, object on similar grounds to Nemec's 

 observations, suggestive though they are, on the absence 

 of geotropism in certain individual leaves and roots which, 

 through unknown causes, had no statoliths.' 



The same must be said of the above-mentioned experi- 

 ments of Haberlandt, in which geotropism is increased by 

 rapid shaking in a vertical plane. I attempted " to avoid 

 this fault in the similar experiments with a tuning-fork 

 made independently, which showed that the effect of vibra- 

 tion in increasing reaction is far greater in the case of 

 geotropism than in heliotropism. 



Haberlandt (00) made the interesting observation that 

 plants deprived of their endodermis by means of an operation 

 lose the capacity of geotropism. Here, again, we ought to 

 know how the operation affects sensitiveness other than 

 geotropic ; and, as Haberlandt grants, it may perhaps be 

 said that the operation is too serious to allow of the found- 

 ation on it of a very convincing argument. 



The question how far the statolith theory is applicable to 

 the root is a difficult one. It involves the old and apparently 

 insoluble difficulty of distinguishing between the removal 

 of the tip of the root, considered as a perceptive organ, and 

 the effect of the shock of the operation. The question is, 

 moreover, complicated by contradictory evidence. Accord- 

 ing to Czapek, cutting off a small part of the root-tip, an 

 operation which does not remove the whole of the stato- 

 liths, interferes with geotropism in the same way as does 

 actual amputation.^ 



Nemec, on the other hand, finds evidence for the operation 

 depending on the removal of the sense-organ ; for accord- 

 ing to him the power of geotroping does not return with 

 the appearance of general symptoms of recovery, such as 

 cell division and the growth of a callus, but only with the 

 actual reappearance of statocytes. 



Nemec's most recent experiments* are confirmatory of 

 this result. He finds that Lupin roots, from which 5 mm., 

 I mm., and i^ nmi. respectively are cut off. behave differ- 

 ently. The 5 mm. lot were clearly geotropic in seven 

 hours, while no curvature occurred in the others. After 

 a further interval of thirteen hours the i mm. lot had curved. 

 Microscopic examination showed that statoplasts had 

 appeared in these roots, but not in the ik mm. lot, which 

 showed no geotropism. It is particularly interesting that 

 according to Nemec the statoplasts appeared in a new 

 growth which was visible as a slight conve.xity of the cut 

 surface.'^ 



.^n experiment by Nemec with the roots of V. Faha must 

 also be mentioned. One millimetre was cut from the tips 

 of each of a number of roots, and they were all placed hori- 

 zontally. They were examined after fifteen hours, when 

 considerable variety in the result of the operation was 

 evident ; some of the roots had bent geotropically, while 

 others were still horizontal. On cutting sections it was 

 found that the geotropic roots had statoplasts, the hori- 

 zontal ones none. It may of course be said that the result 

 depends on the effect of shock lasting longer in some 

 individual roots, since, as Czapek has well said, the only 

 proof of the disappearance of shock effect is the act of 

 curving. But since the operation was approximately the 

 same in all the roots, it is hard to believe in such a malicious 

 coincidence as that the shock was smaller in all those roots 

 which produced statoplasts. But it may be said that shock 

 prevented both geotropism and statoplast-formation in 

 certain roots. 



1 Nimec(o,). 

 - F. Darwin (03). 

 ^ Czapek (oz. p. 118). 

 ■* NSmec (04, pp. 46. 53)- 



^ This agrees, as Nemec says, with Wachtel s fgg resu who found geo- 

 tropism returning before the whole tip was regenerated. 



