( 831 ) 



remarked, that much to my regret, I have only ripe seeds of 

 Tristicha, but no younger stages. In the 78th Versammlung 

 Deutscher Naturforscher und Aerzte in 1906 at Stuttgart R. von 

 Wettstein made a communication : "Ueber Entwickelung der Samenan- 

 lagen und Befruchtung der Podostemonaceen". So far he has not 

 published anything about this, however. I have indeed found an 

 abstract of the communication in "Naturwissenschaftliche Rundschau" 

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

 agree completely with what I have observed, but in other respects 

 there are such differences, that I must assume, that the reporter did 

 not completely understand the meaning of the reader of the paper ; 

 I dare not therefore rely on this abstract. 



The Podostemaceae differ on the following points from the ordinary 

 arrangement in Angiosperins, 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 endostomium, a phenomenon, which has been observed 

 in other plants. 2. The peculiar development of a pseudo-em bryosac 

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

 nucellus. 1 am not acquainted with anything in the vegetable king- 

 dom 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 

 present case a similar action is exerted on those cells of the nucellus 

 which are turned towards the chalaza ; these 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 embryos. By this I mean, that these 

 nucellar embryos prove the existence of causes, acting in the embryo- 

 sac, which determine a developing cell to become an embryo. 

 What these 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 phenomenon in Podostemaceae seems 

 to me to prove, that there are causes acting in the ovule, which 

 favour the development of such a large cavity as the embryo-sac, so 

 that in those cases, in which the embryo-sac itself does not develop 

 greatly, because it is enclosed and separated off in the upper part 

 of the ovule, the cavity is formed by other cells, lying underneath 

 the embryo-sac. 



3. The development of the embryo-sac departs widely from the 

 normal, in that no antipodal cells and no antipodal polar nucleus 



56* 



