508 MANUAL OF BOTANY 



In certain lowly organisms such as Chlamydomonas there is 

 to be seen in the protoplasm a clear space or vacuole, which 

 exhibits a more or less regular pulsation, appearing slowly as 

 a nearly spherical cavity, and then suddenly disappearing, 

 recalling the active contraction of animal protoplasm. These, 

 like the last-mentioned plants, are instances of movement in 

 consequence of internal changes and not of external stimula- 

 tion. 



In the higher plants evidence of this special automatism is 

 not lacking. Setting aside what is common to all plants, the 

 inherent power of living substance to construct itself from food 



Fig. 1195. 



Fig. 1195. A portion of a branch, with a leaf, of i;«mtirf!umj7j„-ans. Theleaf, 

 which is compound, consists of a large terminal leatlet, a, and two smaller 

 lateral ones, h, 6. There are also two other rndimentary leaflets, marked c, 

 near the terminal leaflet. 



materials, to carry on respiration and other vital functions, 

 which are of course evidence of automatism, we have in a few 

 cases distinct power of automatic movement. The protoplasm 

 of the cells of the leaves of Vallisneria, of the internodal cells 

 of Chara, of the poUen-tubes of many plants, of the cells of the 

 staminal hairs of Tradescantia, and others quoted in discussing 

 the structure of the cell, is in constant rotation round the ceU, 

 or movement within it in definite directions. 



These instances impress upon us the belief that aU protoplasm 

 is the seat of active molecular movement, the intensity or vigour, 

 however, varying very greatly in different cases. Indeed the 



