84 M. Miiller on the Ge^minaiion of Isoetes lacustris. 



It is a dense envelope consisting of brown cellulose, which is 

 covered on both surfaces, inside and out, with reticulated, rami- 

 fying ridges which give it the appearance of being composed of 

 cellular tissue in which the cells only, but in their entire diameter, 

 are homogeneously thickened (PI. II. fig. 1). These ridges — by no 

 means rare phsenomena in the ovules of Lycopodiacese generally 

 — have their analogues, like the whole primine, in the outer coat 

 of the pollen-grains of many sexual plants. They usually project 

 so much from the surface of the primine that they give the ovule 

 a very wrinkled appearance. Indeed the conditions of their ra- 

 mifications and elevations are so constant in the species of Isoetes, 

 that, recently, some new — and as Prof. Kunze thinks good — spe- 

 cies have been discriminated by this character. On the surface 

 of the primine here also, as in Selapnella, run the furrows of the 

 tetrahedral union, appearing with more or less distinctness, in 

 consequence of which the ovule itself exhibits a more or less per- 

 fect tetrahedral shape. At these furrows the primine subse- 

 quently splits in the germination (fig. 1). 



2. The Secundine. — This has a wholly similar structure to the 

 preceding, to the inner surface of which it is pretty firmly ap- 

 plied ; but in germination it may very easily be isolated. Like 

 the primine it is a thick brown coat produced by the deposition 

 of cellulose, but it is quite homogeneous, and only exhibits here 

 and there on the outer surface, impressions of those ridges which 

 beset the primine. How these two membranes, each indepen- 

 dently — as it appears — can be formed by the deposition of cellu- 

 lose, will certainly remain a problem until the com'se of develop- 

 ment of the oophoridia is known. 



3. The Nucleus. — This forms a special, thick envelope, which 

 is the more exti'adrdinary that it is composed of a layer of broad, 

 colourless, loosely united delicate cells, only here and there filled 

 with uncoloured globules. When this layer of cells is examined 

 on the outer surface, the form of the cells appears to be some- 

 what cubical with truncated angles (fig. 2) . Almost all over the 

 coat occur also other cells, essentially distinct from the delicate 

 kind. These lie grouped round a centre. This consists of a very 

 large cell which soon becomes divided into four by two septa 

 crossing one another (figs. 2, 3). This large cell in many cases 

 bears considerable resemblance to a stomate, but must not be 

 imagined to be one. Yet it shares with many stomates the pecu- 

 liarity, that it projects as a papilla from the surface. It is poly- 

 hedral, usually oval (fig. 3), but very often constricted in four 

 places at the sides, so that the papillary projection appears to be 

 composed of four spherical cells (fig. 2). All the walls of these 

 large cells are excessively thickened on both sides, evidently by the 

 deposition of cellulose. The thickening itself is emarginate on 



