NUT A TION, 



547 



The phenomenon in question, as later observations have shown, occurs very commonly 

 indeed in orthotropic organs, and those which grow rapidly in length, but it is certainly 

 an unwarranted exaggeration on the part of Darwin, who designates it circumnutation, 

 to consider this as a universal property appertaining to all growing organs ; above all, 

 it is certainly not true of normal and vigorously growing roots. That Darwin 

 ascribes circumnutation to the latter depends on imperfect observation, since it 

 may easily be demonstrated that his roots were improperly cultivated and diseased. 

 I had, long before Darwin's observations, shown that the roots of terrestrial plants 

 growing in moist air soon become diseased, assume abnormal conditions, and may 

 then exhibit pronounced nutations which, however, are not to be observed in normal 

 primary roots of seedlings growing in damp earth or in water. 



The nutations which take place during the unfolding of most foliage leaves are 

 very conspicuous : so long as these belong to the bud at the apex of the shoot, 

 their posterior side (outer, and subsequently under side) grows more strongly, 

 a fact upon which the formation of buds depends. When now the oldest external 

 leaves of a bud are about to unfold, the growth in length commences — and to this 

 we may in this case consider the growth in surface of the lamina as due — to 

 become stronger on the inner side (the subsequent upper side) than that of the 

 dorsal side, and this continues till the leaf has assumed a horizontal or oblique 

 position, in which it then becomes fixed. In most simple leaves the process 

 presents little that is remarkable; in the large complex leaves of the Ferns and 

 Cycads, on the contrary, the young leaves are rolled inwards at the growing-point 

 like a helix, the lateral parts of the lamina each for itself showing lateral involution 

 at the same time. With increasing growth the leaf-stalk and midrib, and likewise 

 the lateral parts of the leaf, now become extended straight, beginning from below 

 and proceeding upwards, so that in the middle stages of unfolding the upper younger 

 part of the leaf is still coiled up like a helix, whereas the lower is already unfolded 

 and extended flat. At last the uppermost part of the leaf also becomes completely 

 unrolled and extended ; however, in some Ferns the upper end of the leaf continually 

 retains this involution, because a growing-point exists at its apex by means of which 

 such a leaf is capable of a so-called unlimited growth in length. 



The long, filiform, and even branched tendrils of the cucurbitaceous plants 

 behave, with respect to their nutation, quite like the leaves of Ferns. Concealed 

 in the young state between the leaves of the bud, they are coiled up into a helix 

 with numerous turns; subsequently, proceeding from below upwards, they become 

 completely unrolled and extended straight. The matter does not end here, 

 however, but during the growth in length which still continues for several daj'S 

 nutations make their appearance, causing the tendril to bend over in all directions 



bent in turns towards the east, west, north, and south, quite independently of the position of the sun. 

 and altogether independent of the light (e. g. Allium Porrum, A. Ccpa, Brassica uapKs, Linuin 

 usitatissinnitn), since it occurs even in profound and constant darkness.' These short statements of mine 

 were based on very detailed investigations, which, however, have not been published : cf. note 4, loc. cit. 

 also. Dutrochet, moreover, had already observed nutations in Pisum (' Comptes rend.' T. xvil, 

 1843, p. 989), Darwin subsequently made evident the significance of the nutation of twining and 

 tendril-bearing plants, but did not recognise as such the spiral and spontaneous nutation of twining 

 plants, whence arose his entirely false theory of twining. 



N n 2 



