86 M. Miiller on the Germination of Isoetes lacustris. 



sufficiently independent to be able to defend itself against the 

 water. 



With regard to the coat of the nucleus, this appears to be 

 called the spore-cell by some authors, for instance by Mettenius*. 

 In the passage referred to, he describes the ovule of Isoetes la- 

 custris as follows : — " In Isoetes lacustris the flattened surface of 

 the large spore, which has the three ridges, is separated from the 

 remainder of the periphery of the spore by an annular border, as 

 has already been observed by Bischoff (Kryptog. Heft iii. p. 81), 

 and the stratified composition of the outer coat, is still more evi- 

 dent than in Lycopodium [Selaginella) . The spore-cell is imme- 

 diately surrounded by a thin layer of membrane, then follows one 

 tough and darker ; both are of a granular structure ; as the third 

 and outermost layer succeeds one consisting of distinct pieces, 

 readily separable, somewhat more transparent, and possessing 

 papillose elevations on its surface." In numerous investigations 

 I have found but the three coats which I have described above. 

 The description of Mettenius is therefore obscure to me. Since 

 he also describes three coats, I may guess that by the spore-cell 

 he means my third coat, the nucleus. But then the characters 

 do not agree, for my coat of the nucleus is not a cell, if by a cell 

 is meant a simple vesicle not (disregarding the contents) again 

 composed of a reticulated tissue. And yet the spore- cell of this 

 observer must be my nucleus, since in this it is that the embryo 

 finally makes its appearance, for he probably will not have meant 

 the first cell of the embryo by this expression. Perhaps he has 

 only examined dried ovules of Isoetes, and the coat of the nucleus 

 may have had a different shape in these. I have examined them 

 only in the living condition, and in these the innermost coat was 

 never a granulated simple cell. 



In a note on the same page Mettenius reproaches me with 

 having, in Selaginella, confounded the spore-cell with the inner- 

 most layer of the innermost coat of the spore, and at page 270 

 he says further, that he saw the spore in germination become 

 gradually transformed into a sac composed of a single cell. From 

 these words, my coat of the nucleus must be his spore-cell, and 

 this becomes perfected into an independent sac (coat of the nu- 

 cleus) only at a later stage, perhaps in germination. In Selagi- 

 nella, I cannot now recollect, except in Selaginella gracillima, to 

 have found such ; in Isoetes lacustris I have constantly met with 

 it in the germinating spore. In any case it would be very inter- 

 esting to have an accurate demonstration of the development of 

 this cellular coat. 



To avoid misconception, I observe, that by the nucleus I mean 

 * Linnnea, 1847, p. 269. 



