350 



H. M. Vernon 



aquariai, but be foimd tbat for tbis purpose it was necessary to 

 diminisb tbe ligbt to which tbey were exposed by means of green 

 or blue sbades. 



In tbe present series of observations , the red weeds did not 

 appear to keep in sucb a bealtby state as was tbe case witb Ulva^ 

 and at tbe end of eight days tbe tips of tbe fronds were generally 

 tiuged witb orange, a sure sign of decay. Tbis was not tbe case in 

 tbe followiog experiment bowever, in wbicb a frond of Gelidium^ 

 2 grams in weigbt, wbicb was attacbed to a small piece of stone, 

 was placed in a jar of 3Y2 litres of water. Aualyses of tbis water 

 were made frorn tioie to time, tbe amount of weed being diminisbed 

 proportionally to tbe water reraoved. 



Free NH3 Organic NH3 



Originai water .314 mgm. .139 mgm. 



After 4 days .421 .176 



- 11 - .223 .153 



- 21 - .171 .245 



- 28 - 069 .426 



From tbese analyses it would seem tbat tbe red weed was able, 

 after acting for some days, to slowly absorb some of tbe Iree ammonia 

 present. It is possible, bowever, tbat tbis apparent absorption was 

 due to tbe diatoms and alga? wbicb bad begun to multiply in tbe 

 water on standing. Tbe organic ammonia gradually increased in 

 amount, as was tbe case witb Ulva. After 21 days, tbe relative 

 weigbt of tbe Gelidium was increased, it now being .8 gm. in only 

 700 ce. of water. It also began to sbow signs of decay, but, never- 

 tbeless, tbe free ammonia was absorbed witb greater rapidity, whilst 

 tbe organic ammonia more rapidly increased. 



As in tbe case of Ulva, a few observations were made in wbicb 

 the water was exposed to tbe action of the alga previous to the intro- 

 duction of the fertilised ova. They gave the following results. 



Number 



of 



Expt. 



Weight of alga per litre 



"/oLarvse 

 formed 



o/o Variation 



in Size of 



larvae 



o/o Variation in amount 

 of 



free HN3 organic NH3 



94 



132 



95 



96 



1.0 gin. of Gelidiuììi corneum 



.6 gm. 

 2.0 gm. of Dudresìiaya lìurpurifera 



.7 gm. of Dictyota 



91 

 87 

 13 

 92 



— 4.1 



± 0.0 



— 18.1 



— 6.8 



1 Ann. Mag. N. H. (2) Voi. 14. 1854 pag. 371. 



4- 9 

 + 27 

 + 179 

 -f- 40 



