THE 'NON-CELLULAR' TYPE 53 



The whole is strongly impregnated with a 

 deposit of lime, whereby the plant acquires 

 a considerable degree of strength and 

 rigidity. The remarkable cactus- or opuntia- 

 like form is produced by a wonderful weaving 

 together of the branching filaments of which 

 the whole plant is made up. There are no 

 traces of cross walls in these tubular branches, 

 but there is a considerable difference between 

 the different regions of the branches them- 

 selves. The lower part of each branch 

 system runs down the centre of the plant, 

 while the final short twigs form the outer 

 surface of the flattened segments. These 

 final branchlets are closely adherent, and the 

 flattened segment of the plant, looked at 

 from the outside, seems to be clothed with 

 a mosaic of small cells these being, of course, 

 the tips of the branches just mentioned. 

 Not only this, but the chlorophyll is almost 

 entirely confined to these peripheral branch- 

 lets, whilst the hinder and wider parts of the 

 tubes serve to store and distribute the food 

 material manufactured in the tips when 

 exposed to light. 



Halimeda, then, furnishes a wonderful 

 example of co-ordinated growth. The singular 

 completeness with which it has solved the 

 problem of attaining a very high degree of 

 specialisation with the simplest materials, 

 extends to every detail of its structure. It 

 is admirably adapted, both to utilise the light 

 and to store away the material products of 



