Marine Algae of the Cape Peninsula 



55 



the brown, and still more the red pigments absorb the light at the 

 blue end. This is significant when we remember that as light 

 passes through water it is refracted unequally, the red end of the 

 spectrum being first cut off, so that the light which penetrates to 

 the deeper layers of water is bluish in tint. The red pigment is 



A r 



L 



'5£2S'^?'^^ra^5S?^^^C9^X^ 



Fig. 1. — Reduced from a life size drawing of Caulerpa UguUta, 

 sliowing rhizome-like base (R) bearing rhizoids (r) as liapterons, 

 a young frond with growing tip (G), and an old frond (OF) 

 proliferating and bearing new assimilating fronds (AF). The 

 wrinkled basal part of the fronds is characteristic. 

 The line AB represents 2 inches. 



(Drawing by M. G. Thoday) 



especially able to absorb this bluish light. I am not aware that 

 any definite experiments have been made to determine exactly what 

 limits of light intensity are characteristic of the different seaweeds, 

 but a simple observation was kindly made for me by Prof. Thoday 

 with an exposure metre at Camps Bay, on a rock pool about ten 



