32 PLANT LIFE 
however, we can generally distinguish between 
what is primitively and what is secondarily 
simple, and all that need be said here about 
the matter is that in any classification of this 
sort most people more or less unconsciously 
adopt an anthropomorphic standpoint and 
standard. Provided we recognise this for 
ourselves, we shall avoid confusion of thought, 
and our mental picture will be the clearer. 
Within the genus Chlamydomonas, which 
we selected as an example of a primitive 
plant, we find that some, at any rate, of the 
species are able to manifest a change of form 
and character according to the circumstances 
under which they are growing. This fact 
will serve as a starting-point from which 
to trace the development of complication of 
form and structure in the plant kingdom. 
Individuals belonging to certain species, 
e.g. Chlamydomonas Braunii, when cultivated 
on appropriate nutritive media, such as a 
relatively concentrated solution of mineral 
salts, or on a damp substratum, cease to 
multiply in the ordinary way. Instead of 
the cells which have been formed by the 
division of a parent-cell becoming separated 
and swimming away, they remain cohering 
together. Their cellulose walls swell up and 
form a gelatinous mass in which, as in a 
matrix, the cells (2.e. the nucleated proto- 
plasmic units) which have arisen by the 
repeated fission of parent cells remain em- 
bedded. Even the cilia may become en- 
