PROTOPLASM AND ITS PROPERTIES 181 
slime moulds live. Their movement is caused by a thrust- 
ing 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 ameba-shaped bodies unite, as at J, 
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 amceba-like 
period, and after they have formed the larger masses, n. 
193. Characteristics of Living Protoplasm.!— The behay- 
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.” 
