536 
Proceedings of the Royal Society 
7 The variations of spores or sporidia in the same species. 
8. The occurrence of different forms of reproductive corpuscles 
in the same perithecium. 
The author’s paper includes also descriptions of two new parasitic 
Micro-Licliens — 
Lecidea Endocarpicola, and 
Ahrothallus Moorei : 
and of one non-parasitic Micro-Fungus — 
Peziza lichenoides. 
He contributes also to a fuller knowledge of the minute anatomy 
of various lichenicolous parasites, whose names and specific char- 
acters have already been published, but which are nevertheless 
as yet little known, e.g . — 
Sphceria Hookeri. Gassicurtia silacea. 
Spilomium G-raphideorum. Microthelia Collemaria. 
6. On the Theory of the Formation of Ammonia when 
Nitrogen and Aqueous Vapour are passed over Mag- 
nesium. By A. K. Catton, M.A. 
In a paper recently communicated to the Society by Mr Main 
and myself, we showed that when nitrogen and aqueous vapour 
are passed over magnesium ammonia is formed. We took for 
granted the theory of the reaction to be that the magnesium de- 
composes the aqueous vapour, and that the hydrogen thus pro- 
duced, when in the nascent state, combines with nitrogen and 
forms ammonia. In a discussion which followed the reading of 
the paper, Mr Dittmar maintained that such was not the theory of 
the reaction, but that nitride of magnesium is first produced, and 
then decomposed by the aqueous vapour into ammonia and 
magnesia. 
I gave what appeared to me a conclusive answer to this suppo- 
sition — which I was certainly surprised to find seriously maintained 
■ — for it seemed in every point of view so entirely untenable, that 
I did not think it worthy of notice in our paper. 
As, however, the formation of ammonia in the manner we 
