( 691 ) 



like GuiGNARD and Boxxier, will think the use of these terms 

 admissible. Although we incline towards this latter opinion, we shall 

 not dwell on this point here. 



But we think it desirable to point out that a closer study of 

 unfertilised ovules, especially of dioecious plants will perhaps yield 

 surprising results. Since we know through Loeb that chemical stimuli 

 may cause the development of an egg, the possibility must be granted 

 tliat this may also be the case with higher plants. When a normal 

 fertilisation does not take place, such chemical stimuli would at any 

 rate render a beginning of de\elopment possible. Looked at from 

 this point of \iew the case of Dasylirion is perhaps important, but, 

 as we stated already at the beginning of this communication, only 

 an investigation in the natural place of occurrence of the plant can 

 give an answer to this and allied questions. 



Astronomy. — "On the parallax of the nebulae". By Prof. J. C. 

 Kapteyn. 



Up to the present time we know hardly anything about the distance 

 of the nebulae. On the whole they do not allow of the most accurate 

 measurement, and as a consequence direct determination of parallax 

 is generally to be considered as hopeless. A few endeavours made 

 for particularly regular nebulae have not led to any positive result. 



The proper motions (p. m.) seem more promising, at least for the 

 purpose of getting general notions about the distances of these objects. 



Spectroscopic measurements of radial motion show tliat the real 

 velocities of the nebulae are quite of the order of those of the stars. 

 Therefore, as soon as we tind the astronomical proper motion of 

 any nebula, we conclude, witli some degree of probability, that its 

 distance is of the order of that of the stars with equal p. m. 



Meanwiiile it may be considered to be a fact, most clearly brought 

 out just by the observations presently to be discussed, that as yet 

 p.m. of a nebula has not been proved with certainty in a single case. 

 It does not follow that these p. m. are necessarily very small. The 

 time during which the position of these bodies has been determined 

 with precision, is still short, the errors of the observations are large. 

 The effect of these errors on the annual p. m. may easily amount 

 to 0"2 or 0"3. 



We might endeavour to lessen the influence of the errors of 

 observation by determining not the individual motions but the mean 

 p. ra. of a considerable number of nebulae. 



