324 M. Miiller on the Germination of Isoetes lacustris. 



stead of breaking forth outward from the vascular cylinder, turned 

 inward and perforated the rhizome. According to this there- 

 fore a proper vascular cylinder must be present in the rhizome, 

 and as such must be understood the internal medullary layer*. 

 This is not clear to me. From MohFs illustrations I do not 

 know in what relation the vessels, occurring in the lower part of 

 the medullary layer, stand to the leaves. According to these 

 figures the upper vessels most certainly stand in connexion with 

 the leaves, and they admit of its being conceived that the above 

 ground of explanation which I have deduced from the course 

 of development actually hits the fact; that the vessels of the 

 youngest roots correspond to the youngest leaves. 



The gradual death of the young embryos appeared to me very 

 peculiar : I have represented it in the figures (fig. 24 e, /, g) . The 

 root of the first leaflet went first, and the coats of the primine 

 with the secuudine still adhered to the first leaflet (fig. 24 e). 

 Then this also was lost (fig. 24/), and by this means the third 

 leaflet became more free. Next the root of the second leaflet 

 disappeared (fig. 24^), and after that the leaf itself. At last 

 only the third leaflet remained : this lived, fresh and growing 

 for some time ; but the true vital foundation appeared to have 

 departed from it, and after several weeks' vegetation it died like 

 the rest. 



Now that we have become fully acquainted with the course of 

 development of Isoetes up to this point, I consider the observa- 

 tion of the further progress will be very easy, if any one, in whose 

 neighbourhood Isoetes occurs, will take the pains to fish up 

 young embryos out of the water, and continue the examination 

 from the point at which I have ceased. The embryos are pro- 

 bably not difficult to find in their natural condition. I imagine 

 that they must grow socially, in great numbers close together, 

 since they will in any case germinate simultaneously out from 

 the oophoridia of the decaying parent plant, as often happens in 

 aquatic plants. 



7. Retrospect. 

 A. Special course of development of Isoetes. 



1. The foundation of all cell-formation of the embryo is a de- 

 licate granular mass which exists very early in the ovule and 

 completely fills it (fig. 4). 



2. This mass becomes transformed into starch, and is thus 

 brought into a condition for solution (fig. 5). 



* See the illustrations, by H. v. Mohl, Linnsea, 1840, t. 3. (Also in 

 Vermischt. Schrift. plate 5.) 



