FORM, COLOUR, TEMPERATURE. 27 



part, in regular series. In this circumnutation move- 

 ment results from the fact that the cells grow in 

 series, not all simultaneously. 



Form, colour, temperature, are properties as fre- 

 quently observed in non-living as in living subjects. 

 These may, perhaps, be looked upon, and spoken of 

 most conveniently, as obvious properties because 

 the form, colour, and temperature are their own 

 expressions. This statement is not exactly true, 

 but this form of language does not convey any 

 untruth that will vitiate our use of this term for 

 present purposes. Strictly speaking, " the colour of 

 an object" is a condition of its surface, and what 

 we see and describe, is the reflection of light from 

 it, and the kind of light so reflected is an expression 

 of the molecular structure of its surface ; "the tempe- 

 rature of a body " is an expression of the condition 

 of the vibrations of its molecules ; " the form of an 

 object " is the result of the forces that produced it. 



The largest possible scope has been given in this 

 chapter to the term " expression," and this has been 

 done with a definite object. Expression is the 

 objective sign of a property of the subject. In 

 biological inquiries we are obliged to study vital 

 processes by their expression in objective signs. 

 Life itself is studied by the results, or objective 

 expressions of nutrition, and growth. It is, then, 

 obviously desirable that we should study all the 

 objective signs, or modes of expression of these 

 vital processes. The subject of expression is dwelt 

 upon in the wide signification here given to the 

 term, because it appears doubtful if, in biological 



