M. Miiller on the Germination of Isoetes lacustris. 85 



both sides. Frequently also it passes over, the point running out, 

 into the walls of the contiguous cells. All the cells of these re- 

 markable groups are of a brown colour, which is deepest in the 

 large cell, the colouring gradually fading outwards till it reaches 

 the extremely delicate cellular tissue bounding the group ; this 

 tissue contrasting the more with the group that its walls are 

 composed of much firmer and more distinctly defined membranes. 

 Moreover the cells lying immediately round the large cell are 

 distinguished by the irregularity of their form from those situated 

 beyond them. Many such groups occur upon the coat of the 

 nucleus. Frequently they are far apart, often near together, or 

 again arranged in groups, so that we find no special regularity 

 in the whole. But at one point the condition is more constant, 

 for they especially occur upon that part of the surface of the coat 

 where the primine and secundine subsequently open (fig. 1 a). 

 At the point of the orifice usually appears one large cell (fig. 1 a) 

 with its accessory cells, and it appears to me that it is exactly 

 this place which subsequently gives way in the breaking through 

 of the germ. It is conceivable that the coat is most brittle here, 

 and therefore gives way so much the more readily when it is 

 pushed up in a cone by the rising embryo. The presence of all 

 these groups at the point of the ovule may be just as easily ex- 

 plained. I imagine that the thickening of this surface is merely 

 to afford an additional defence to the contents of the nucleus and 

 to the embryo against external, hurtful influences. For the 

 bursting of the primine, which is always followed by that, of the 

 secundine, appears to depend upon various circumstances. Now 

 if this dehiscence happened at an epoch when the contents of 

 the nucleus had not yet attained to substantial independence 

 sufficient to enable it to defend itself from the surrounding water, 

 and the coat of the nucleus was yet so delicate that it would be 

 powerless against the intrusion of any moisture, the conclusion 

 is not very distant ; certainly it would not be exactly beneficial 

 to the contents of the nucleus. This seems to me to be the sim- 

 plest, because the most natural explanation. The peculiar de- 

 hiscence of the primine and secundine also speak in favour of it. 

 These two membranes only retract gradually during the process 

 of germination, and remain attached to the nucleus until the 

 embryo is very substantially developed, and all and every of the 

 contents of the nucleus, which we shall presently become ac- 

 quainted with, have disappeared. Where the root subsequently 

 breaks through, those groups of cells do not make their appear- 

 ance. By the time however that the breaking-through ensues, 

 the young plant is already supplied with nutriment in a different 

 way, as we shall discover in the course of this description ; it is 



