186 M. Miillci' o?i the Germination o/Isoetes lacustris. 



The most interesting point about this organ is^ that^ after the 

 coat of the nucleus is bursty the germ-plant no longer remains at 

 the bottom of the ovule, and the leaf has not merely part of its 

 apex but almost its whole length situated outside the opening 

 (figs. 16j 17, where the drawing exhibits the condition more ac- 

 curately). At a subsequent period only does the germ-plant 

 reach the bottom of the ovule by means of the root, running 

 downward and piercing through the coat of the nucleus below 

 (fig. 20^). This rising of the germ-plant in the nucleus cer- 

 tainly depends upon its being specifically lighter, the germinal 

 body evidently not being heavy enough to retain the plant at the 

 bottom of the nucleus. 



It has already been mentioned above (§ 4.), that the future 

 furrow of the leaf exists in a rudimentary condition very early, 

 as a fold, in the embryo. 



4. The Leaf-scale. — Of this also it has been previously seen 

 that its rudiments are formed very early, since the mother-cell 

 of it appears in that stage when the separation of the germinal 

 body into alimentary organ, root, vagina, &c. scarcely exists 

 (fig. lie). As such it is seen to remain for a long time, without 

 essential alteration of its form (figs. 11 c, 12 f, 13 d, 16 d). In 

 the mean time however a process of cell- formation has taken 

 place similar to that previously occurring in the mother-cell of the 

 embryo. New cells have been formed. By this means the shape 

 of the mother-cell has been somewhat changed ; it has become a 

 body densely filled with cellular tissue. This stage of the scale 

 is found in that germ-plant which is represented in PI. II. fig. 15. 

 The scale which previously had the appearance of a globule has 

 now become a smooth disc which stands close against the cell of 

 the second leaf lying below it (figs. 16 c, 17 c). 



During the continuous growth of the germ-plant it attains its 

 highest stage of development, when the vessel of the first root 

 begins to show itself (PI. III. fig. ISh.) It is then a flat, broad, 

 more or less reniform disc which is somewhat folded together, so 

 that the succeeding leaflet is almost entirely surrounded by it, 

 whence one might be led to imagine that it only existed on ac- 

 count of its connexion with that succeeding leaflet. 



It is composed of very delicate parenchymatous cells which 

 contain nothing in the young condition of the plant, when the 

 cytoblasts of the cellular tissue have disappeared, though some- 

 times these are to be found persisting for a longer time. The 

 scale is often toothed on the border with extraordinary regu- 

 larity. In such cases one cell projects from the border as a 

 sharp tooth while the next remains unextended, and then the 

 third cell again projects as the second tooth. I have however 

 also found the scale very irregularly toothed. This is indeed a 



