PROTOPLASM AND ITS PROPERTIES 181 



slime moulds live. Their movement is caused by a thrust- 

 iag out of the semi-liquid protoplasm on one side of the 

 mass, and a withdrawal of its substance from the other 

 side. At length many amoeba-shaped bodies unite, as at I, 

 to form a larger mass, m, which finally increases to the 

 protoplasmic network shown at n. This eventually col- 

 lects into a roundish or egg-shaped firm body, inside of 

 which a new crop of spores is produced. It is not easy to 

 trace the manner in which the nourishment of these simple 

 plants is taken. Probably they absorb it from the decay- 

 ing matter upon which they live during their amoeba-like 

 period, and after they have formed the larger masses, n. 



193. Characteristics of Living Protoplasm.^ — The behav- 

 ior of the slime moulds during their growth and transfor- 

 mations, as just outlined, affords a fair idea of several of 

 the remarkable powers which belong to living protoplasm, 

 which have been summed up as follows : 



(1) The power to take up new material into its own 

 substance {selective absorption). This is not merely a proc- 

 ess of soaking up liquids, such as occurs when dry earth 

 or a sponge is moistened. The protoplasmic lining of a 

 root-hair, for example, selects from the soil-water some 

 substances and rejects others (Sect. 65). 



,(2) The ability to change certain substances into others 

 of different chemical composition (metabolism, Sect. 176). 

 Carbon dioxide and water, losing some oxygen in the 

 process, are combined into starch; starch is changed into 

 various kinds of sugar and these back into starch again;- 

 starch becomes converted into vegetable acids, into cellu- 

 lose, or into oil ; or the elements of starch are- combined 



1 See Huxley's Essays, Vol. I, essay on " The Physical Basis of Life." 



