168 TRANSACTIONS LIVEEPOOL BIOLOGICAL SOCIETY. 



that is, the colour of the spores is used as a means of 

 recognition, and it is the common belief that this artificial 

 method has led to an undue multiplication of the " species " 

 of that genus — one of the largest genera of plants. If 

 colour then be fallacious as a subordinate character else- 

 where, on what grounds are we to account for its apparent 

 ordinal importance among Algae? The nature of the 

 pigments themselves answer the question. The colours 

 of land plants other than the green colour of vegetation, are 

 produced by pigments which play no role of importance in 

 their vital processes, while here in Algae they are bound 

 up with the essential process of nutrition — the pigments 

 are adaptations, associated with the chlorophyll itself to 

 the amount and nature of the sunlight reaching the Algae. 

 The colour is therefore of most profound biological impor- 

 tance in this case, and it follows that its variation is 

 naturally accompanied by variations of structure both of 

 thallus and of reproductive organs equally profound. The 

 biological significance of colour is a subject that has been 

 seized upon by easily satisfied speculators who are mostly 

 incapable of a due study of the pigments, and who 

 concern themseles with fanciful interpretations of their 

 "meaning." The present case is one which fortunately 

 does not lend itself to such treatment, and the coast is clear, 

 if the play upon words may be pardoned, of such literature. 

 This short digression from the strict subject of distribution 

 may be excused on the ground that a consideration of the 

 subject itself has here led to the recognition of a very 

 striking case of correlation between physiological and 

 structural variation. He who runs may read the lesson 

 to be learnt from it. 



The saying, that the character of vegetation changes 

 entirely with every twenty-four degrees of latitude, is less 



