12 



about ttiis, however. I hâve indeed found an abstract of 

 the communication in „Naturwissensçhaftliche Kundschau" 

 of 1906, Bd. XXI, p. 615, and in it several statements occur 

 which agrce corapletely witli what I hâve observed, but 

 in other respects there are such différences, that I must 

 assume, that the reporter did not completely understand 

 the meaning of the reader of the paper; I dare not there- 

 fore rely on this abstract. 



The Podostemaceae differ on the following points from 

 the ordinary arrangement in Angiosperms, as regards the 

 development of the ovule: 1. The inner integument begins 

 to develop after the outer; this is perhaps connected with 

 the fact, that the top of the nucellus remains free in the endo- 

 stomium, a phenomenon, which has been observed in other 

 plants. 2. The peculiar development of a pseudo-embryosac 

 by the stretching and dissolution of the cell-walls of a 

 layer of the nucellus. I am not acquainted with anything 

 in the vegetable kingdom corresponding to this. One could 

 only point out, in explanation, that in many cases the 

 developing embryo-sac exercises a solvent action on the 

 surrounding tissue of the nucellus, and that in the 

 présent case a similar action is exerted on those cells of 

 the nucellus which are turned towards the chalaza; 

 thèse cells only disappear completely, when the embryo 

 proceeds to develop there. 



The phenomenon also suggests, that, to a certain extent, 

 it is comparable to that of nucellar cmbryos. By this 1 

 mean, that thèse nucellar embryos prove the existence 

 of causes, acting in the embryo-sac, which détermine a 

 ■ developing cell to become an embryo. What thèse causes 

 are, we do not know, but it is by no means inconceivable, 

 that some day we may know them completely and even 

 be able to imitate them, so that we may be able to 

 produce an embryo at will. Similarly this phenome- 



