326 M. Miiller on the Germination of Isoetes lacustris. 



12. The vagina has merely become a very delicate membrane, 

 and the vascular cords of the root united into one mass at that 

 time when the second leaflet issues from the vagina as a green, 

 somewhat flattened corpuscule. The root now expands only at 

 its apex by cell-formation, since its only point of vegetation lies 

 there (fig. 21). 



13. When the second leaflet has issued from the vagina, which 

 now forms a long, delicate membrane obliquely cut off" at its open 

 end, the starch of the alimentary organ has disappeared. The vas- 

 cular bundle of the first root has again separated into two por- 

 tions ; each portion however consists of several, usually two cords. 

 The root of the second leaflet now shows itself, at first only as a 

 very transparent compact protuberance (fig. 22). 



14. The further development of this radicle appears to have 

 become the principal matter in the whole plant As in the first 

 root, the vessels are first formed as two cords (fig. 23). 



15. Then they become elongated, like those of the first, with 

 all the gradations of the preceding formation (fig. 24 b). 



16. After the second root has attained its full development, the 

 third leaf makes its appearance between the two first (fig. 24 c, d). 



B. Comparison of the course of development of Selaginella and 



Isoetes. 



No comparison is possible between the earliest stages of de- 

 velopment of these two genera, since those of Selaginella are yet 

 unknown. Nevertheless they perfectly agree in one point, — that 

 the element of cell-formation is in both a granular mass, which 

 becomes converted first into starch and then into protoplasm. 

 At this point our comparison is terminated, and we begin again 

 at a considerably advanced period of development, in the young 

 plant. 



The young embryo of Selaginella consists, like that of Isoetes, 

 of three essential parts : 1. the alimentary organ ; 2. the radical 

 portion ; 3. the terminal bud. 



The alimentary organ is here a special body originally very im- 

 perfectly, but in further-developed states of the plant perfectly 

 round. This alone remains within the ovule, to attach the little 

 plant to it (fig. 25 a) . No starch is deposited in its interior ; 

 the protoplasm which must be formed from the granular mass 

 (fig. 25 d) still existing within the ovule, is taken up by it and 

 carried onward to the remaining portions of the embryo. In 

 this variation this body does not wholly represent the organ in 

 Isoetes. The most peculiar point in it however is, that it does not 

 become wholly rounded off" until a subsequent period. 



The radical portion does not lie, as in Isoetes, with the alimen- 



