184 Transactions of tJie [Sess. 



thallus gonidia of the Lichen, and are cast out along with the spores 

 of the Fuugi, so that when these spores germinate, the hyphaj again 

 enclose the gonidia. In this way, in botli the animal and the Lichen, 

 there is a provision by which the symbiotic Algaj are brought into 

 the closest possible relationship with the reproductive cups, and 

 every facility is offered for the continuance of the association through 

 the successive generations. The hymenial layers of the apothecia 

 may be exposed, as in gymnocarpous Lichens, or there may be an 

 encircling perithecium, as in angiocarpous Lichens, and the spores 

 which form in asci by free cell-formation escape by a small orifice at 

 its extremity, that escajie being effected by rupture of the ascal wall, 

 brought about by swelling resulting from the penetration of moisture 

 to the hymenium. — (' Encyc. Brit.,' 9th edit. Art. " Parasitism.") 



The only other point that may be noted in connection with Lichens 

 is that their multiplication is sometimes effected by sorecUa, in which 

 case one or several gonidia become surrounded by definite hyphse, 

 the gonidia divide, and the cortex of the parent ruptures, so that the 

 soredia escape, and finally develop into a new Lichen. This type of 

 multiplication is, from a symbiotic standpoint, closely correlated with 

 the contemporaneous escape of fungoid spores and gonidia from the 

 hymenial region of the reproductive cups of Lichens, and in a similar 

 way corroborates the intimacy of the association of the algoid and 

 fungoid constituents — an association which is capable of being pro- 

 longed through many generations without the production of any 

 manifest pathological changes on either side. 



XIV.— THE NUTHATCH (SITTA EUROPj^A). 



By Mr A. B. HERBERT, President. 



(Read March 27, 18S4.) 



This pretty bird, with its peculiar and amusing habits, has always 

 been a favourite with me from my youth. The male and female are 

 much alike in colour, the back and head being of a delicate ash 

 shade, approaching to pale blue ; the under parts cloudy white, with 

 a slight roseate tint and marks of brown. Meyer's illustration before 

 you gives a very fair idea of the bird. It is an extremely rare bird 

 in Scotland, and I expect also in the north of England, for had 

 one of such colours and habits been common in Yorkshire, it would 

 not have escaped the acute observation of Waterton. It is very 

 local in its habitat, for on the west side of my native town of Coven- 

 try, especially in the old avenue at AUesley Hall, I seldom failed 



