172 



DEPARTMENT OF THE NATAL SERyiCE 



, 6 GEOHGE V, A. 1916 



Using the figures given in tlie previous report, the following data are available 

 for variations of iodine content with age in the same species growing under the same 

 conditions. 



Species. 



Laminaria bullata 



Laminaria saccharina.. j- 



Fucus .furOHus 



Fucus evanescenx. 



Obtained August, 1913. 



0060 .. 



156 (small plant) 

 0']76 (medium sized) 

 0'015 (average) 

 016 (average) 



Obtained June, 1914. 



'270 (young plants) 

 175 (old plants) 



'206 (young jilants) 

 078 (old plant ) 



042 



028 



Obtained August, 1914. 



0'017 (average) 

 0'015 (average) 



These figures show the effect of age and a distinct effect of period of year (this 

 has already been pointed out by Scurti for Sargassum and Cystoseira). The data for 

 Nereocystis confirm these variations. A determination of ash was carried out with 

 one set of samples of Nereocystis; the results are only approximate since some 

 inorganic salt was vaporized before the carbon was completely ignited. 



The specimens obtained near Haddington island were preserved in formol, and 

 I have shown elsewhere that in such cases iodine is lost in the subsequent evaporation 

 to the extent of about 10 per cent. 



Careful examination of the above figures shows, in spite of the marked individual 

 variation which is their most striking characteristic, that the percentage of iodine is 

 almost always less and the percentage of water greater in the float than in either the 

 fronds or stipe. The ash determinations show a similar difference. The iodine con- 

 tent in Nereocystis appears, on the average, to diminish with growth, the highest 

 values for frond and stripe being obtained for the smallest plants. The water con- 

 tent of frond and stipe shows dimunition with age (this is especially true for the 



