M. Miiller on the Germination of Isoetes lacustris. 83 



lament that from the same causes I am unable to do so here, and 

 therefore I beg the indulgent reader at least to follow with me 

 the germinating Isoetes lacustris. 



2. The Ovule. 



No explanation is necessary when I name the spore propaga- 

 ting the species an ovule. I have already used this expression in 

 the same sense in my essay on the development of the Lycopo- 

 diacese*, for the germinating spore, and consequently also with 

 Spring called the sporangium of Selaginella which incloses the 

 spore of this kind^ the oophoridium. The reasons why I then 

 thought that I ought so to do were morphological and physio- 

 logical, since the course of development of the oophoridium proved 

 a distinct axial nature, and the plant, unlike the other vascular 

 and cellular asexual vegetables, developed, not eooti^a but intra 

 uterum. This last reason is decidedly the more important here, 

 and is fully applicable to Isoetes. But whether the first ground 

 is tenable in this genus may perhaps be doubted by many per- 

 sons, who, with H. V. Mohl, would regard the germinating spore 

 as a leaf-product. I regret especially in regard to this point that 

 my history of the development does not extend up to this stage, 

 for I do not for a moment doubt that the oophoridium of Isoetes 

 is equally an axial structure, and does not belong to the leaves as 

 Mohl thinks. It is not of much importance that it is inclosed 

 as in a sheath by the base of the leaf in Isoetes. The leaves 

 are so smooth all round that one may thence conclude that their 

 bases are not applied to the formation of the oophoridia. The 

 simphest view of the matter is to assume that a mother-cell of 

 the root-stock itself grows up into the excavated base of the leaf 

 exactly as the mother-cell of the oophoridium does in Selaginella-\ . 

 In bringing forward — and certainly with good reason — the con- 

 dition of this latter plant as an analogical proof here, I think that 

 I fully make good my view. It is evident then that the sporangia 

 also of the spores which do not germinate are of an axial nature, 

 as is the case in Selaginella. To complete the comparison be- 

 tween the ovule of the sexual plants and that of the Lycopo- 

 diacese, a third reason, an anatomical one, presents itself in Iso- 

 etes, for the ovule of the Isoetes, exactly like that of sexual plants, 

 consists of three coats, to which may in a similar manner be ap- 

 plied the simple names primine, secundine and nucleus, without 

 regarding the special anatomical distinctions. 



1. The Primine. — This coat is not composed of cellular tissue. 



* Ann. of Nat. Hist. Ser. 1. vol. xix. 



t Ann. of Nat. Hist. Ser. 1. vol. xix. PI. IV. fig. 7 c ilr fig. 9 a. 



6* 



