Royal Academy of Berlin. 237 



the embryonal sac ; when therefore Mirbel speaks of a P4risperme 

 farineux, he uses this term in the old indefinite sense, for since the 

 embryo-trophic mass is formed in the same sac with the small cylin- 

 drical embryo, it must be named, according to the minute distinction 

 of modern Carpology, endosperm and not perisperm. 



From the smallness of the seed of Pistia, Bonpl. nothing could be 

 ascertained for certain as to the structure of the embryo itself. How- 

 ever in the Pistia (Stratiotes) Jacq., where the seeds are twice the 

 size, he succeeded in convincing himself of the presence of the 

 aroideal fissure, which was doubted by Lindley, and which in Pistia, 

 as in Calla, &c, has a longitudinal direction, and not, as in Lemna, a 

 transverse one, round the radicular end of the embryo. M. Horkel 

 further found that the gemmule is not a pointed convolution of leaves, 

 such as Mirbel and Turpin have figured it, but is a round thick disk, 

 situated obliquely in the radicular extremity of the embryo, and is 

 connected for some length with the wall of the embryo situated oppo- 

 site to the rima. 



As up to the present time there have been no observations made 

 on the germination of Pistia, the following, although in some degree 

 imperfect, as only dried germinating plants were at M.Horkel's dis- 

 posal, will still add some little to our knowledge of the germination 

 of this plant. We must expect a more perfect history from such 

 botanists only who have occasion to study its germination within the 

 tropics, or we must have at our disposal at least an entire series of the 

 plant in the various states of its germination well preserved in spirit. 



The germination begins in Pistia as in Lemna with the separation 

 of a thickened part of the membrana interna, occurring round the 

 micropyle, and consisting of long radiating cells, with which in Pistia 

 the superincumbent portion of the testa, through which the micro- 

 pyle canal passes, also separates in the form of an operculum ; and 

 in Pistia as in Lemna remains stationary at its original place, the ra- 

 dicular end of the embryo, which in both plants is raised in the form 

 of a sac, so that the spreading gemmule leaf in the interior of this 

 sac (in Lemna it is the entire discoidal plantula seminalis), remains 

 for a long time hidden, until at last it is forced through the widened 

 fissure, and thus shows itself as the first leaf of the germinating plant, 

 and soon afterwards the radicula primitiva is thrown out at the side 

 opposite to the rima, only not so high. This is also in the beginning 

 covered by a disk-like prolongation of the embryo, which is pierced 

 at a later period, when the radicula with its end covered as in Lemna 

 with a calyptra, becomes evident. The simple radicular of the germi- 

 nating plant, which at a later period are formed in abundance, have 



