K0TE3 AND MEMORANDA. 81 



form. It is in this stage that it is described and figured by Acha- 

 rius (t. X. f. 8). When the ceplialodium so increases, the tissue 

 of the lichen under it no longer appears in the form of pseudoparen- 

 chymatous cortex, and no longer encloses gonidia, but consists only of 

 hyphae very much interlaced, and it is only on the parts placed near 

 the borders of the cejihalodium, that there can still be observed a 

 progressive transition of the round cells of the cortex into the com- 

 pletely developed filaments of the hypha, which degenerate progres- 

 sively into radical hairs (rhizines) of a dark brown colour. As soon 

 as the final transformation of the tissue of the bark of the lichen into 

 filaments of hypha is accomplished, all connection between the cepha- 

 lodium and the thallus of the lichen disappears. At the point where 

 the separation of the cephalodium has taken place, the cells of the 

 cortical layer of the lichen assume a brown hue ; below them extends 

 a layer of gonidia which, whilst it touches some of the radical hairs 

 of the cephalodium, has no longer any connection with them. Under 

 the layer of the gonidia of the thallus is arranged the medullary 

 layer, whose filaments are clearly distinguished from the radical hairs 

 by their more transparent colour, as well as by the thickness of their 

 membrane. The cells of the hypha of the cephalodium, disposed 

 under its gonidia, having degenerated into radical hairs, are trans- 

 formed into pseudoparenchymatous cortex which covers its inferior 

 face. As soon as the cephalodium becomes entirely independent of 

 the lichen, it grows more and more horizontally, and finally receives 

 the oblong, or orbicular and flattened form. 



We may conclude that the cephalodia owe their origin to the 

 parasitic nature of Nostoc, which is always found in damp places, 

 where the lichen is usually met with. Not that the Nostoc alone 

 takes part in the formation ; other algfe also share in it perhaps, as 

 Schwendener and Bornet have shown in Stereocaulon. It is possible, 

 that if Peltigera aphthosa were gathered in some other locality, other 

 algfe than Nostoc might perhaps also be found. A coloured plate of 

 nine figures accompanies the paper. 



Mr. Soiby's New Micro-spectroscope. — This instrument, which 

 was briefly noticed in its original form at page 148 of vol. i., has 

 since been modified and improved, and was exhibited at the meeting 

 of the Society, on 8th January. 



The principal advantages of the instrument are the small size 

 (half the ordinary size) combined with great dispersive power and 

 excellent definition, with large field of view over the whole spectrum. 



To obtain this, a change in the ordinary mode of construction has 

 •been adopted, the achromatic object-glass focussing the slit being 

 placed, not below the prism as usual, but above it, close to the eye, 

 A much longer focus can therefore be obtained for the object-glass, 

 and consequently better definition. To collect the light coming 

 from the slit, a cylindrical lens is fitted behind the prism and gives an 

 even, bright light far into the extreme ends of the spectrum, so that 

 no shifting of slit or micrometer arrangement is required. Without 

 any trouble of re-adjustment the object-glass also focusses a micro- 

 meter scale which extends over the whole spectrum, and consequently 



VOL. ir. Or 



