[ ^99 ] 



XXXI. Siipplementary Observations on f/ie Dcrelopmenf nf the T/iecd, and on 

 the Sexes of Mosses. In a Letter tu H. H. Sully, Esq., F.R.S. Sf L.S. 

 Bt/ William Valentine, Esq., F.L.S. 



Kead May 7tli, 1839. 



J_ FIND, upon resuming' the examination of Mosses, which I had given up, 

 that I have not done Mohl justice in the note attached to my paper "on the 

 Development of the Theca and on the Sexes of Mosses," pu!)lished in the 

 preceding volume of the Society's Transactions. In tliat note I liave stated, 

 that I thought Mohl was mistaken where he describes the sporules as being 

 developed by fours in a motiier-cell, believing that he had taken the several 

 masses of granular contents, which may be in many instances observed in a 

 sporule, as so many distinct sporules. I am now bound to confirm the accu- 

 racy of Mohl's observation in this respect ; and I beg, tlirough you, to offer to 

 the notice of the Society a remarkable instance of the tetrahedral union of the 

 sporules as an appendix to my former paper. The subject of the following 

 account is ŒiUpodium Grljfithianitni, which, from my residence being near 

 Snowdon, where it is found plentifully, I was enabled to examine in a recent 

 state. 



A transverse section of a very young theca (Tab. XXXV. fig. 9.) sliows 

 several concentric layers of cells in strict contact witii each otiier. The 

 outer layer is slightly tinged with brown, and is the true theca : the two 

 next, tiie outer of which is pellucid, and the inner tinged with green granules, 

 constitute the thecal membrane. The succeeding layer of cells also contains 

 green granules, and the next is pellucid ; these two form the sporular mem- 

 brane. Independent of the number and sequence of the layers, by which we 

 may decide in this state of the theca which will ultimately form the distinct 

 sporular and thecal membranes, the presence of the green granules suffi- 

 ciently identifies them ; for if we examine a longitudinal section of a ripe 



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