M. Miiller on the Germination of Isoetes lacustris. 187 



disc, but not rounded off like the former, rather apiculate above, 

 and furnished with horn-like projecting cells of considerable 

 size. 



The second scale, that of the second leaflet, is also a disc, and 

 the one which I found as such deviated again from the forms of 

 both the preceding, being of a more or less oval shape and fur- 

 nished with some minute projecting cells at the apex. 



By the sight of these scales I was reminded instantly of that 

 accessory organ which I found in the Selaginelke, and of which 

 I have given a complete history of development. I at once con- 

 cluded these to be of the same morphological import. In a trea- 

 tise by Mettenius on Azolla^ which appeared just at that time, 

 he compared the scale of Isoetes with a ligule, while he referred 

 the organ of the Selaginellce to an axillary stipule. I will not 

 venture to decide either for the one or the other, but I think, as 

 I have said, that they are of similar origin and also of similar 

 import. 



To complete the characterization of the scale I will add the 

 description of Mettenius {op. cit.), since this observer has ex- 

 amined it on the mature plant, which I have not : — " In Isoetes 

 this scale occurs on the fertile and barren leaves. In young 

 leaves it is seated on the surface, in old ones apparently in an 

 excavation, since its lower part is ensheathed by the substance of 

 the leaf, and only the upper scale-like portion lies free upon the 

 inner face of the leaf. The point of attachment of the scale is 

 broader than the proximate ensheathed portion, and is formed 

 of a cellular tissue distinctly defined from the parenchyma of the 

 leaf. The nerve of the leaf runs up behind the point of attach- 

 ment, and the cellular tissue surrounding this contains numerous 

 spiral-fibrous cells, which extend down to the point of attachment 

 of the sporangium. ^^ 



5. The Vagina. — We found the first rudiment of this in the 

 stage of fig. 116; there were then only isolated spherical cells, 

 elevated above the surface indicating the vagina ; subsequently 

 they are raised up with the matrix of the root in such a manner 

 that they are now connected in an uninterrupted line with the 

 furrow of the first leaflet (figs. 12 d, IS c, 15 g) . At this time these 

 single cells surround, as a cup, the second leaflet projecting out 

 beyond them (figs. 17 A, 18 i, 20 h) . They then become multiplied 

 by division, and thus very delicate and minute, so that this tissue 

 is now distinguished in a marked manner from that surrounding, 

 by its greater delicacy (fig. 21 g). Thereby it may be observed that 

 a peculiar delicate membrane, composed of a simple layer of cells, 

 is in course of formation. 



* Linneea, 1847, p. 270. 



13* 



