182 FOUNDATIONS OF BOTANY 



with nitrogen to make various proteid compounds, either 

 for immediate use or for reserve food. Many other com- 

 plicated transformations occur. 



(3) The power to cast off waste or used-up material 

 (excretion). Getting rid of surplus water (Sect. 174) and 

 of oxygen (Sect. 178) constitutes a very large part of the 

 excretory work of plants. 



(4) The capacity for growth and the production of off- 

 spring (reproduction). These are especially characteristic 

 of living protoplasm. It is true that non-living objects 

 may grow in a certain sense, as an icicle or a crystal of 

 salt or of alum in a solution of its own material does. 

 But growth by the process of taking suitable particles 

 into the interior of the growing substance and arranging 

 them into an orderly structure (Fig. 126) is possible only 

 in the case of live protoplasm. 



(5) The possession of the power of originating move- 

 ments not wholly and directly caused by any external 

 impulse (automatic movements). Such, for instance, are 

 the lashing movements of the cilia of the swarmspores 

 of slime moulds, or the slow pendulum movements of 

 Oscillatoria (Sect. 269), or the slow vibrating movements 

 of the stipules of the " telegraph plant " (Desmodium), 

 not uncommon in greenhouses. 



(6) The power of shrinking or closing up (contractility). 

 This is illustrated by the action of the contractile vacuole 

 of the slime moulds and of many animalcules and by all 

 the muscular movements of animals. 



(7) Sensitiveness when touched or otherwise disturbed, 

 for instance, by a change of light or of temperature 

 (irritability). 



