MOVEMENTS DUE TO SWELLING, ETC. 405 



HAACKE. 1892. Flora, 75, 455. 



KLEIN. 1898. Ber. d. bot. Gesell. 16, 335. 



KNOCH. 1899. Bibliotheca botanica, Heft 47. 



KRAUS. 1894-5. Abhandl. d. naturf. Gesell. Halle, 16, 35 and 257. 



KUNKEL. 1878. Arb. bot. Inst. Wiirzburg, 2, i. 



[MOLISCH. 1904. Leuchtende Pflanzen. Jena.] 



MUNK. 1876. Archiv f. Anat. u. Phys. p. 30. 



PFEFFER. 1892. Energetik (Abh. kgl. Gesell. Leipzig, 18). 



RICHARDS. 1896. Annals of Botany, 10, 531. 



VERWORN. 1901. Allgem. Physiologic. 3rd ed. Jena. 



LECTURE XXXII 



MOVEMENTS RESULTING FROM SWELLING AND CONTRACTION 

 AND FROM COHESION OF IMBIBITION WATER 



MANIFESTATIONS of movement in plants are everywhere apparent to an 

 attentive observer, but these movements are not all of equal interest to the 

 physiologist. Our native plants for the most part cast their leaves and even in 

 some cases their branches in autumn, and these deciduous parts may be carried 

 away for long distances by wind and water. Examples of a similar kind are seen 

 in the case of fruits and seeds, but the distribution of these structures differs 

 in this, that it is useful to the plant, and that it is facilitated by special con- 

 trivances, e.g. by special wings for distribution by air currents, floats for distri- 

 bution by water and by hooks for transport by animals. Such movements are, 

 however, effected without any expenditure of energy on the part of the plant, 

 they are purely passive movements, very important, it is true, from the bio- 

 logical point of view, but outside the domain of strict physiology. There are, 

 however, passive movements which do interest the physiologist, such as the 

 downward bending of branches by their own weight or, conversely, the straighten- 

 ing of the branches of submerged plants by water support. In the cell also 

 we have to take into account the passive movements of chlorophyll bodies, e. g. 

 in Vallisneria, consequent upon the rotation of the protoplasm, or, in other 

 cases, where protoplasmic movement distributes the chloroplasts in definite 

 situations. Although we have to study in the following pages primarily the 

 active movements of plant organs, still we must not neglect the purely passive 

 ones, all the more so since no sharp line of demarcation can be drawn between 

 the two types. Observation of the gradual bending upwards of a shoot laid 

 horizontally teaches us that it is due to curvature taking place at a certain dis- 

 tance from the apex. This movement may certainly be termed active, since the 

 plant in this case actually does the work, but this work is performed only in a 

 definite spot, at the point of curvature ; the distal end of the shoot is lifted in 

 a purely passive manner. 



Under active movements we may distinguish two main categories : (i) loco- 

 motory movements of entire organisms, met with only among the lower plants ; 

 (2) movements exhibited by higher plants which grow in fixed positions. This 

 distinction is not a hard and fast one, since the protoplasm within the cells of 

 a higher plant moves in precisely the same way as the entire organism does, say 

 in the case of Amoebae or Myxomycetes ; indeed, in certain cells it may pass 

 out of the cell- wall and move through the water for a certain time, just as do 

 the cells of Flagellata during their entire life. Many analogies between these 

 two categories of movements are forced on our attention, and so, obviously, the 

 classification we have indicated is to be considered not as expressing a funda- 

 mental difference in nature, but rather a useful subdivision for teaching pur- 

 poses. 



