CHAPTER III. — SPECIAL PHYSIOLOGY OF MOVEMENT. 735 



CHAPTER III. 

 SPECIAL PHYSIOLOGY OF MOVEMENT. 



§ 10. Introductory. The movements to be specially con- 

 sidered here are such as may be characterized as vital ; that is, 

 they are essentially manifestations of the life of the protoplasm. 

 This statement is rendered necessary by the fact that movements 

 do occur in plants which are dependent upon purely physical 

 causes; instances of these are afforded by the rupture of pollen- 

 sacs and other sporangia, the twisting and untwisting of awns (as 

 in the fruits of Erodium, p. 612, and Stipa, p. 548), the bursting 

 of fruits (as in the Balsam, Impatiens Noli-me-tangere, and the 

 Squirting Cucumbers, such as Ecbalium, Momordica, and Elater- 

 ium). These movements may be due, in the simpler cases, either 

 to expansion and contraction of hygroscopic cell-walls resulting 

 from variations in the moisture of the air, or to the imbibition 

 with water and the consequent swelling-up of mucilaginous sub- 

 stances in the cells ; in the more complicated oases tlje movement 

 depends upon tensions set up between diiferenfc layers of tissue in 

 consequence of unequal expansion. 



The vital movements are either spontaneous or induced. In the 

 former case they are the result of causes operating in the or- 

 ganism itself; in the latter, they are the result of causes acting 

 upon the organism from without. 



The following are the principal phenomena of movement ex- 

 hibited by plants ; the streaming movement of protoplasm 

 (cyclosis) ; the expansion and contraction of contractile vacuoles ; 

 the locomotion of entire organisms; the movements of cellular 

 members. 



§ 11. Automatism. The spontaneous movements may be 

 conveniently considered under the two heads of movements of 

 protoplasm, and m,ovements of cellular m,emJ}ers. 



A. Movements of Protoplasm. Under this head are included 

 such spontaneous movements as can be directly observed in the 

 protoplasm. The first to be noted is the streaming movement, 

 which can be frequently observed either in naked protoplasm (&.g. 

 Plasmodia of Myxomycetes), or in the protoplasm of ccenocytes 

 clothed by a cell- wall (e.r/. hyphes of Fungi), or in that of cells 

 (e.g. leaf of Elodea and Vallisneria, internodal cells of Characece, 



V. s. B. 3 B 



