468 



NA TURE 



[September 8, 1904 



has been conclusively proved by Kreidl's' beautiful experi- 

 ment that in the Crustacean Palasmon the sense of verticality 

 depends on the pressure of heavy bodies on the inside of 

 cavities now known as statocysts, and formerly believed to 

 be organs of hearing. The point of the experiment is that 

 when the normal particles are replaced by fragments of iron 

 the Palsemon reacts towards the attraction of a magnet 

 precisely as it formerly reached towards gravity. 



It is unfortunate that Noll's arguments in favour of the 

 existence of a similar mechanism in plants were not at once 

 followed by the demonstration of those easily visible falling 

 bodies, which, in imitation more flattering than accurate, 

 are called statolillis, after the bodies in the statocysts of 

 animals. Personally 1 was convinced by Kreidl, as quoted 

 by Noll, that here was the key to graviperception in plants. 

 But it was not until the simultaneous appearance of Haber- 

 landt's" and Nemec's^ papers that my belief became active, 

 and this, I think, was the case with others. The whole 

 incident is an instance of what my father says somewhere 

 about the difificulty of analysing the act of belief. I find it 

 impossible to help believing in the statolith theory, though 

 I own to not being able to give a good account of the faith 

 that is in me. It is a fair question whether the analogy 

 drawn from animals gives any support to the theory for 

 plants. The study of sense-organs in plants dates, I think, 

 in its modern development, at least, from my father's work 

 on root-tips, and on the light-perceiving apices of certain 

 seedlings. And the work on the subject is all part of the 

 wave of investigation into adaptations which followed the 

 publication of the " Origin of Species." It is very 

 appropriate that one of the two authors to whom we owe 

 the practical working out of the statolith theory should 

 also be one of the greatest living authorities on adaptation 

 in plants. Haberlandt's work on sense-organs,* especiallv 

 on the apparatus for the reception of contact stimuli, is 

 applicable to our present case, since he has shown that the 

 organs for intensifying the effect of contact are similar in 

 the two kingdoms. No one supposes that the whisker of a 

 cat and the sensitive papilla of a plant are phylogenetically 

 connected. It is a case of what Ray Lankester called homo- 

 plastic resemblance. Necessity is the mother of invention, 

 but invention is not infinitely varied, and the same need has 

 led to similar apparatus in beings which have little more 

 in common than that both are living organisms. 



But, whether we are or 'are not affected in our belief by 

 the general argument from analogy, we cannot neglect the 

 important fact that Kreidl proves the possibility of gravi- 

 sensitiveness depending on the possession of statoliths. We 

 must add to this a very important consideration — namely, 

 that we know from Nemec's work'' that an alteration iii 

 the position of the statoliths does stimulate the statocytc." 

 Such, at least, is, to my mind, the only conclusion to be 

 drawn from the remarkable accumulation of protoplasm 

 which occurs, for instance, on the basal wall of a normally 

 vertical cell when that wall is cleared of statoliths by 

 temporary horizontality. The fact that a visible disturb- 

 ance in the plasmic contents of the statocyte follows the 

 disturbance of the starch-grains seems to 'me a valuable 

 contribution to the evidence. 



There is one other set of facts of sufficiently general 

 interest to find a place in this section. I mean Haberlandt's 

 result,' also independently arrived at by mvself, that when 

 a plant is placed horizontally and rap'idlv' shaken up and 

 down^ in a vertical plane the gravistimiilus is increased. 

 This IS readily comprehensible on the statolith theory, since 

 we can imagine the starch-grains would give a greater 

 stimulus if made to vibrate on one of the lateral walls, or 

 if forced into the protoplasm, as Haberlandt supposes. I 

 do not see that the difference in the pressure of the cell-sap 

 on the upper and lower walls (i.e., the lateral walls morpho- 

 logically considered) would be increased. It would, I 

 imagine, be rendered uneven ; but the average difference 

 would remain the same. But in the case of the starch- 

 grains^ an obvious new feature is introduced by exchanging 

 a stationary condition for one of movement. And though 

 I speak with hesitation on such a point, I am inclined to 

 see in Haberlandt's and my own experiments a means of 



1 Kreidl (03). 2 Habeilandt (00). ■< Nemec (co). 



■• Haberlandt (01). 5 NJmec(oi, p. 153). 



" Id est, the ceils containing slatolilhf. 



" Haberlandt (03) and F. Darwin (03). 



NO. 18 19, VOL. 70] 



distinguishing between the pressure and statolith theories. 

 Noll,' however, considers that the shaking method is not 

 essentially different from that of Knight's experiment, and 

 adds that the result might have been foreseen. 

 DislrihiMon. 



As far as I know, the development of statoplasts ^ has 

 not been made out. Are they at first like ordinary 

 immovable amyloplasts ; and, if so, by what precise process 

 do they become movable ? Where the two forms of starch 

 are seen in close juxtaposition the difference between them 

 is striking, and it is hardly possible to doubt that these 

 differently situated bodies have different functions. In a 

 seedling Plialaris canariensis the apical part has only fall- 

 ing starch-grains, while lower down both forms occur. It 

 suggests a corresponding distribution of graviperception \. 

 and, as a fact, the seedling is gravisensitive throughout, 

 but is especially so at the apex. If this is not the meaning 

 of the statoplasts we must find some other. For instance, 

 are the loose starch-grains connected in an unknown way 

 with heliotropic sensitiveness, which often has the same 

 distribution as that of graviperception? Or is the loose- 

 ness of starch connected in some way with food storage? 

 Is it to allow of starch being closely packed in part of the 

 cell, leaving the rest of the space free? 



Again, the most striking general fact about the distribu- 

 tion of falling starch is its presence in the endodermis." If 

 we believe that the endodermis is essentially a tissue of 

 gravisensitive cells w'e can understand the striking fact that 

 it contains loose starch only as long as the stem is capable 

 of growth curvature^* Otherwise the theories of the func- 

 tion of the endoderm, which have never been very satis- 

 factory, have the additional burthen of explaining this last- 

 ranied fact. 



According to Haberlandt (00), some monocotyledons the 

 leaves of which contain no starch have falling grains in 

 the endodermis. Nemec (01, p. 24) quotes from Sachs the 

 case of Allium cepa, where statoplasts occur in the root-cap, 

 the endoderm, and punctum of the seedling, and not else- 

 where. Then we have occurrence of starch in the pulvinus 

 of grasses and not in the rest of the haulm. Viscum is not 

 geotropic, and has no statoplasts. In the holdfast roots of 

 Hedera and Marcgravia there is no starch, and in Hoya, 

 Pothos, and Ficus the starch is not movable, and these roots 

 are not geotropic.'' 



Jost (02) brought forward, as a serious objection to the 

 statolith theory, the fact that tertiary roots possess stato- 

 liths, but are not sensitive to gravitation. This objection 

 has been overcome by the discovery " that when the primary 

 root is cut off and a secondary assumes its place and manner 

 of growth, the tertiaries springing from it are diageotropic, 

 and thus have at least an occasional use for their statoplasts. 



I have shown ' that the cotyledon of Setaria and Sorghum 

 is the seat of gravi-perception, and it is there that the stato- 

 plasts are found.' Wiesner (02) was unable to find stato- 

 liths in the perianth-segments of Clivia nohilis, which are 

 geotropic, nor in those of Clivia miniata, which are not 

 geotropic. Here would seem to be a serious objection to the 

 statolith theory, but Nemec (04. p. 58), on repeating 

 Wiesner's observations, finds, on the contrary, a confirm- 

 ation of his own views. For movable starch-grains occur in 

 the perianth of C. nohilis, but not in those of C. miniata. 

 In the case of roots the distribution of the statoplasts is 

 especially worthy of note. Physiologists have gradually 

 come to believe that my father ° was right in his view that 



I Noll (03, p. 131). 

 _ - I would suggest the word staioplait in place of the cumbersome expresr 

 sion tnova' Ic starch-grains. 



"' See Haberlandt (03) for a description of certain special cases of statocyte- 

 tissue, apparently replacing the endodermis. 



* .\ccording "to Haberlandt (03, p. 451), it is easy to be deceived in assert- 

 ing that the endoderm contains no starch. Thus Fischer failed to find it ir> 

 outgrown steins of some plants which possess it when young. Tonde'ra (o3> 

 asserts that in certain Cucurbits the falling starch is only present in the older 

 parts no longer capable of geotropism. But Miss Pertz, who has examined 

 most of the species investigated by Tondera, finds statoplasts in the young- 

 parts where he failed to find these. Tondera makes some interesting remarks 

 on the distribution of starch in the Cucurbits harmonising wiih Heine's 

 storehouse theory. It is obviously difficult in the case of the endoderm to- 

 distinguish between starch serving as a reserve and starch serving as part 

 of thei-mechanism of perception. I see no reason why the second function 

 should not be evolved from the first. 



■■i Haberlandt (03, p. 461). « Darwin and Pertz (04). " F. Parwin (99). 



s According to Nemec they occur to some extent in the hypocotyl of 

 Panicum. « C. Darwin (" Power of Movement "). 



