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PART III. — VEGETABLE PHYSIOLOGY. 



destitute of a cell-wall. The movement is a slow, creeping one, 

 accompanied by constant changes of form, or the throwing out 

 of processes resembling the pseudopodia of Rhizopods. It is 

 undoubtedly the most primitive form of locomotion, and is 

 exhibited only by the simplest living forms, or by more complex 

 ones in the earlier stages of their development. It is illustrated 

 in the Myxomycetes, Fig. 466. 



Ciliary motion is accomplished by means of delicate hair-like 

 or lash-like projections of the protoplasm, called cilia. In these 

 organs, the ordinary protoplasmic contractility has acquired a 

 high degree of development to suit them to the functions of loco- 

 motion, and by their rapid bending to and fro, the cell to which 

 they are attached is propelled through the water in which it 

 lives. While amoeboid movement is slow and creeping, this is 

 conspicuous for its rapidity, and is to be regarded as a higher 

 development. It is observed in many mature plants belonging 

 to the lower orders, examples of which are illustrated in Figs. 484 

 and 485, and in the reproductive spores of the great majority of 

 flowerless plants. See Figs. 486, 487, 488 and 489. 



The mechanism by which the slow, gliding, or sometimes 

 jerky movements of Diatoms and Desmids is accomplished is 

 not yet understood, though there can be no doubt it is attribut- 

 able to the same fundamental property of contractility that lies 

 at the foundation of all other spontaneous movements in plants. 



Movements not Locomotive. (1) First to be noticed among 

 these is the movements of the protoplasm within the cell-wall. 

 In some cells, for instance, those of the stems and leaves of 

 Chara and Nitella, the leaves of Vallisneria, many hairs, such as 

 the stinging hairs of the Nettle, those on the filaments of Trades- 

 cantia, etc., the phenomenon is conspicuous, and there are few 

 things more wonderful than to watch them under the microscope. 

 While, however, they are more obvious in these examples, there 

 is no doubt that they take place more slowly in all living cells. 

 As regards their nature, they are streaming movements in the 

 bands and plates of protoplasm that cross the cell, in the endo- 

 plasm and about the nucleus, or gliding movements of the great 

 mass of the protoplasm around the interior of the cell, or some- 

 times crossing from one wall of the cell to the other. In cells 

 containing chlorophyll-bodies, the latter very commonly assume 



