370 Mr. Hogg's Observations on the Spongilla fluviatilis, 



being deprived of light, after many days received no green tint, but continued 

 of a light buff or a yellowish white colour. Thus, then, by the exactly similar 

 influence of light upon thechromule*, or colouring matter in plants, and like- 

 wise by the etiolation, or blanching of vegetables by the absence of light, so 

 well known to every one, very favourable proofs may, from these analogous 

 phenomena, be most reasonably adduced with regard to the vegetable nature 

 of the Spongilla JiuviatUis. 



The circumstances that led me to the investigation of those appearances 

 are described in a paperf, which at the date of my former letter to you had 

 not been read before the Royal Society, to whom I was induced to communi- 

 cate it. I therefore did not consider myself then at liberty to make any men- 

 tion of them to you ; although they, together with some observations on the 

 seedlike bodies of the Spongilla, already described in that letter, created in my 

 mind considerable doubts as to the animality of that substance. Renewed and 

 similar observations upon several fresh and living masses of the River Sponge, 

 during the summer which has just passed, have now confirmed me in the cor- 

 rectness of those doubts, and in the certainty of those facts which afford the 

 stronger proofs of the real vegetability of that Sponge. Of such proofs, indeed, 

 which I was then about to pronounce as quite conclusive on that point, are the 

 effects that I had noticed, caused by the presence and absence of light, upon 

 the colours of that substance, the germination of its seedlike bodies, sporidia, or 

 sporules, and their subsequent plantlike mode of growth and of increase ; and 

 whilst engaged in these researches, I was greatly surprised in discovering (on 

 the 12th of August, 1838,) the only traces that could with any degree of pro- 

 bability be advanced in favour of the supposed animality of the Spongilla, 

 namely, certain remarkable germlike bodies swimming about in the basin of 

 water, wherein a beautiful mass of that Sponge, growing with great vigour and 

 attached to a stone, was contained. At first I was disposed to think that they 



* Prof. DeCandolle uses this term to signify that matter which produces the colours in flowers, the 

 green in leaves and other parts of plants, and is contained in their cells in the shape of globules. — 

 See Organographie Veg^tale, torn. i. p. 19. Paris, 1827. 



■\ See a short notice of this paper in the Philosophical Magazine, vol. xiii. p. 457, for December 

 1838 ; and another entitled, " De 1' Action de la Lumidre sur la Couleur de I'Eponge de Rivifere," in the 

 Bibliothique Universelle de Geneve, torn. xix. p. 207. (Janvier, 1839). 



