184 M. MUller on the Germination of Isoetes lacustris. 



In Selaginella this may be seen very distinctly, as it manifests 

 itself as a darker point in the interior of the germinal body. 

 Perhaps a similar condition may exist here. The vessels them- 

 selves are darker where they emerge from the interior of the 

 alimentary body ; they run gradually out into the more anterior 

 cells of the matrix, becoming continually more transparent. 



In all the stages up to this point the root still remains inside 

 the coat of the nucleus. Now however it breaks through this. 

 Its escape takes place exactly opposite to the point where the 

 first leaflet emerged (fig. 20 g) . If the plant is extricated from 

 the coat of the nucleus in this stage, it presents the appearance 

 shown in fig. 20 c. We have here no longer any doubt of the 

 existence of a root ; it has become considerably elongated, but 

 internally it has not altered essentially since the stage of fig. 18, 

 where it still remained within the ovule. The external layer of 

 cells still appears in the likeness of an epidermis, the internal 

 cells have not altered in size or form, the point of vegetation at 

 the apex remains still composed of the small-celled tissue, and 

 the vessels alone have become elongated. 



This condition however does not persist long ; for as we pass 

 next, in fig. 21 «, to a stage where the second leaflet begins to 

 emerge from the vagina (fig. 21 d)> in the first place the epider- 

 moid, external layer of cells has disappeared, since the membranes 

 of the internal cells having acquired greater consistence, no di- 

 stinction between the outer and inner cells now exists. More- 

 over the cells are empty and transparent, differing from what was 

 the case in the former stages, where they were always densely 

 filled with a very delicate, clear cytoblastema ; only the cells of 

 the point of vegetation, situated at the apex of the root, are now 

 provided with cytoblastema. Since these cells are here still small 

 and extremely delicate, the cells of the outermost layer, which 

 are of firmer texture, again appear like an epidermis (fig. 21 e), 

 which has now altogether ceased to be the case with those cells 

 lying further back. These latter are now much elongated in 

 proportion to what they were in the former stages, and the result 

 of this is an elongation of the whole root generally. This ex- 

 plains why they are quite empty, since their contents have been 

 applied in all probability to the enlargement of the membranes. 



The vessels have equally undergone a change. These are no 

 longer seen to run as two distinct cords through the interior 

 layers of the cells of the root ; they are rather blended into a 

 single mass which now runs almost to the point of vegetation of 

 the root. But notwithstanding this combination, each vascular 

 bundle runs forward in an independent condition. If one of 

 these is extracted from the root, it appears, in the shape of the 

 figure 21 b, as a longish utricle of an extremely delicate, hyaline 



