270 NOSTOCHINE^E. 



coloured infusion betrays the presence of vibratile ciliae; 

 and we cannot believe that the threads turn on themselves, 

 because the granulations of the green matter do not change 

 place during the progression. I have seen threads of 

 three seeds move, but never a single seed. If you continue 

 to observe for some days, you will see the thread become 

 immoveable, increase in size, at the same time develope the 

 mucilage with which they are surrounded as with a transparent 

 sheath. Soon the seed enlarges considerably, and divides to 

 form two others, but sideways, and not in the direction of 

 the length of the threads. 



" This formation is repeated many times, and it would seem 

 natural to seek in this circumstance the origin of new 

 threads. Unfortunately the increase of the number of grains, 

 by diminishing the transparency, prevents one following the 

 increase with the same facility. Their confused mass fills 

 entirely the young Nostoc, which is developed in a very irre- 

 gular manner, and takes a variety of forms. It is but later 

 when the mucilage is most abundant, when the seeds are less 

 crowded in the interior of the Nostoc, that you begin to 

 distinguish the threads." 



The Nostochinece of the first section are mostly of a lively 

 and exquisitely delicate green colour. They are wonder- 

 fully prolific, increasing to such an extent frequently as to 

 impart their beautiful colour to extensive tracts of water, 

 as also do occasionally certain species of Oscillator-ice. One 

 species described by Mr. Thompson, Anabaina f tpiralis, and 

 which I have named in honour of its discoverer, Spirillum 

 Thompsoni, imparted its colour to the entire of an extensive 

 lake, Ballydrain, which extends over about twenty acres of 

 ground near Belfast* The Oscillatoria cenigescens of Drum- 

 mond in like manner imparted its rich green colour to an 

 extensive lough in the north of Ireland, Glaslough, whose 

 waters seemed greened as though by the reflection of trees, f 



* For an interesting paper, by Mr. Thompson, on this Alga, see 

 " Annals of Nat. Hist." vol. v. 

 See Annals Nat. Hist. vol. i. 



