36d 



Dr. Matthews inquired if the species described was an ally of that nostoc 

 which grew in a night during damp weather, forming blood-red patches on 

 a stone. 



Dr. Cooke said that the organism referred to by Dr. Matthews was not a 

 nostoc but another alga, and the nostocs were as wide apart from these algae 

 as butterflies and beetles. The red patches were caused by an agglomera- 

 tion of cells ; it was always found to consist of simple free cells dividing in 

 two directions, and they had never at any time been reckoned to have any 

 affinity whatever. Nostocs also belonged to the green, and not the red 

 group of algae. 



Dr. G. D. Brown asked for information as to an alga found in a pond 

 having the appearance of pale sea green spores . On examining a drop of 

 the water he found almost exactly what had been described. 



Dr. Cooke said the form to which Dr. Brown had referred was not a true 

 nostoc, but a member of the same family, some of them being found float- 

 ing. This one had the structure of a nostoc except the jelly, but was 

 free swimming; it belonged to the following genus, and came next in 

 order to the one which had been described. It was one of those peculiar 

 kinds which made their appearance in waters at certain times, and diffused 

 themselves through the whole water, giving the appearance sometimes called 

 " breaking of the waters." Attention had been given to it for some years. 



Mr. E. T. Newton said it was not unusual to find in these things an 

 alternation of generation. Did heat, or dampness, or dryness cause these 

 changes ? 



Dr. Cooke said that the changes which he had described formed the 

 ordinary mode of reproduction in the genus ; all went through the same 

 stages, the gelatine was always there and the threads were always there. 

 Whilst observers confined themselves to |in. objectives it was supposed 

 that all the cells were alike, but by using higher powers it was found that 

 they became granular, then enlarged, then split away, and then began to 

 germinate and form new threads inside the old gelatine, and the formation 

 of a hormogone was found to be a usual process under favourable — that 

 was under damp conditions. Many of the nostocs lived either in water or 

 close to it, so that they would frequently get wetted. Of course if it got 

 dried up it would shrivel up to a mere spot, and would be unable to carry 

 on its existence. 



Mr. Buffham asked what Dr. Cooke thought the heterocysts really were ? 



Dr. Cooke said he never allowed himself to think on these questions. 



Mr. Buffham thought that the extension of knowledge had led to the 

 increase of the number of species, showing sexual generation, and he could 

 hardly help thinking that these might have some such function. 



Dr. Cooke said there was at present no evidence as to what they were, 

 and under those circumstances it would, he thought, be unsafe to make 

 any suggestion. The heterocysts were left behind in the jelly, and apparently 

 decayed away. 



A vote of thanks to Dr. Cooke for his communication was unanimously 

 passed. 



