548 



LECTURE XXXII. 



successively like the flower-stems described above. "The advantage which not only 

 these but also all other tendrils derive from this nutation we shall consider more 

 closely later, when considering their phenomena of irritability. There I shall also 

 show more in detail, that the still in part obscure movements of twining shoot- 

 axes, such as those of the Hop, Bindweed, Aristolochia, Akehia, Menispermum and 

 many others depend in part at least simply on nutations, or are introduced by 

 such; if tips of shoots, 20-30 cm. long, of twining plants which have not as yet 

 coiled round a support are cut off, and placed singly in tall glass cylinders 

 with a little water, they grow on actively for some days, becoming coiled in the 

 form of a spiral which not rarely exhibits 3-4 or more turns. However, I shall 

 return to the details, merely mentioning' this phenomenon now as a particular case 

 of nutation \ 



As tendrils and twining plants derive advantage from nutation (which is indeed 

 indispensable for the life of these plants), so also numerous plants derive other 



advantages from the often active nutations 

 of their stamens. It is a very common 

 phenomenon, especially in large flowers 

 with long stamens, that the stamens, when 

 the anthers are about to empty their 

 pollen, undergo various curvatures as they 

 ■ grow, as is perceived unusually clearly 

 for example in the Indian Cress (Tro- 

 paolum), and still more in Didamnus (Fig. 

 347). These nutations of the stamens are 

 frequently accompanied by corresponding 

 movements of the style, and usually serve 

 the purpose of giving the anthers that 

 position in the flower which is necessary in 

 the transference of the pollen by insects 

 from one flower to the stigma of another. 



The nutations thus present us with 

 instructive examples of how a capacity of 

 the plant conditioned by growth, and for and by itself useless, is found to be very 

 common, and how certain plants then develope this movement further and make it 

 useful for themselves, sometimes in order to live as climbing plants, sometimes in 

 order to ensure their fertilisation. 



The majority of twining shoot-axes exhibit torsions — i.e. where angles or grooves 

 project on the segments of the st^m and at first run parallel with the axis of growth, 

 they are subsequently found on the fully grown internodes in the form of spiral 

 lines running round the shoot-axis. It is easy to see on internodes which are grow- 

 ing how the torsion gradually arises and proceeds ; but it would be very difficult 

 without geometrical discursions to show the processes of growth through which the 



1 Concerning the spiral nutation of twining stems, statements in some detail are found in my 

 'Noth Uber Schlingpflanzen' (Arb. des bot. Inst, in Wzbg. B. II, 1882, p. 719) : furtlier on, how- 

 ever, in the fifth series of the present lectures, I shall make these more complete on the basis of my 

 most recent observations. 



FIG. 347.— Nutation of the stamens oiDictamttus 

 yraxinella : those the anthers of which have not 

 yet opened are curved downwards, those with 

 opened anthers upwards. 



