214 AKXOTT, ON CYCLOTBLLA. 



Summary. — I think, then, from the above remarks, that 

 there can be no doubt but that what has been called 

 " Chlorococcus " is nothing more than the gonidia of some 

 lichens, which, having been conveyed by the movements of the 

 atmosphere, had been deposited on a favorable surface, where 

 they soon begin to increase by various modes of segmen- 

 tation, which continue for an unlimited period. But under 

 suitable conditions, chiefly drought and warmth, the gonidium 

 throws out from its external envelope a small fibre, which, 

 adhering and branching, ultimately encases it and forms a 

 " soridium." At this stage gonidium may continue also for 

 an indefinite period in a dormant condition, but, circum- 

 stances favoring, segmentation of the gonidium goes on 

 within the soridium, while the branches of the fibre penetrate 

 within the divisions, till at last a young thallus is formed. 

 But a check may occur during any of these stages, and yet 

 vitality be prolonged for a period of months and even years. 



Of this, I believe, any one may satisfy himself if he will 

 be careful to watch an old wall or tree, and check his 

 observation by the microscope from time to time. In every 

 particular, the whole of these stages are passed through by 

 those gonidia whose pedigree is known, which, having burst 

 through the cortical layers of the lichen-thallus, still re- 

 main attached to its surface. 



There are two other points which, although they require 

 more observations to give any certain value to them, it will 

 be as well to mention here : 



The first is the occurrence among the fibres of dilatations 

 which contain a number of small, actively moving bodies, of a 

 reddish-brown colour (as at fig. 11, a, a). They apparently 

 have a motion different from the ordinary molecular move- 

 ment. 



The other is, that there are to be found among the crushed 

 soridia some small, moving, green cells, like minute zoo- 

 spores, but I cannot satisfy myself as to their origin. 



On Cycloteu.a. 

 By G. A. Walker-Ahnott, LL.D. 



My object is not to give here a monograph of the genus 

 Cyclotetta, but to endeavour to clear up the synonyms of our 

 British species, which to me appear to be in a little con- 

 fusion. 



