SECTION 16.] 



MOVEMENTS. 



149 



they restore an equal bulk of life-sustaining oxygen needful for the respiration 

 of animals, needful, also, in a certain measure, for plants in any -work they 

 do. For in plants, as well as in animals, work is done at a certain cost. 



6. PLANT WORK AND MOVEMENT. 



458. As the organic basis and truly living material of plants is identical 

 with that of animals, so is the life at bottom essentially the same ; but in 

 auimals something is added at every rise from the lowest to highest organ- 

 isms. Action and work in living beings require movement. 



459. Living things move ; those not living are only moved. Plants 

 move as truly as do animals. The latter, nourished as they are upon or- 

 ganized food, which has been prepared for them by plants, and is found 

 only here and there, must needs have the power of going after it, of collect- 

 ing it, or at least of taking it in ; which requires them to make spontaneous 

 movements. But ordinary plants, with their wide-spread surface, always 

 in contact with the earth and air on which they feed, the latter every- 

 where the same, and the former very much so, might be thought to have 

 no need of movement. Ordinary plants, indeed, have no locomotion; some 

 float, but most are rooted to the spot where they grew. Yet probably all 

 of them execute various movements which must be as truly self-caused as 

 are those of the lower grades of animals, movements which are over- 

 looked only because too slow to be directly observed. Nevertheless, the 

 motion of the hour-hand and of the minute-hand of a watch is not less real 

 than that of the second-hand. 



460. Locomotion. Moreover, many microscopic plants living in water 

 are seen to move freely, if not briskly, under the microscope ; and so like- 

 wise do more conspicuous 

 aquatic plants in their embryo- 

 like or seedling state. Even at 

 maturity, species of Oscillaria 

 (such as in Fig. 488, minute 

 worm-shaped plants of fresh 

 waters, taking tins name from 

 their oscillating motions) freely 

 execute three different kinds 



of movement, the very delicate investing coat of cellulose not impeding the 

 action of the living protoplasm within. Even when this coat is firmer and 

 hardened with a siliceous deposit, such crescent-shaped or boat-shaped 

 one-celled plants as Closterium or Navicula are able in some way to move 

 along from place to place in the water. 



461. Movements in Cells, or Cell-circulation, sometimes called Cy- 

 closis, has been detected in so many plants, especially in comparatively 



488 



Fig. 488. Two individuals of an Oscillaria, magnified. 



