200 Dr. H. Karsten on the Sexual Life of 



had good reason for supposing, with Ehrenberg, that the car- 

 bonate of lime of which they are composed was derived from 

 decayed Foraminifera ; but at the same time a strict proof would 

 have been wanting, and we might have adopted the opinion ex- 

 pressed by Haidinger in his paper on the Metamorphism of 

 Rocks *, and concluded that, though, according to Ehrenberg, 

 chalk does contain very many organic bodies, it does itself con- 

 sist of rounded forms, which are a chemical deposit from water 

 containing soluble salts of lime. Now, however, that their real 

 origin appears to be established, it is no longer requisite to 

 assume the existence of any unknown crystalloidal force differing 

 from simple crystallization ; and we can clearly perceive that, 

 though presenting characteristic differences, chalk is in every 

 respect analogous to what we should have, if the mad now 

 being formed at great depths in the Atlantic, by the accumula- 

 tion of various minute organic bodies, were to be subsequently 

 more or less altered by molecular changes or chemical actions of 

 a well-known character. There is, however, one striking differ- 

 ence ; for the Atlantic mud contains many Diatomacese, spicula 

 of Sponges, and other silicious organic bodies, which are very 

 rare in, or absent from, the chalk : it contains, however, sili- 

 cious concretions ; and this contrast in the state and aggrega- 

 tion of the silicious matter in the two otherwise analogous depo- 

 sits makes me very much inclined to conclude, with Ehrenbergf, 

 that the silex of the flints was derived from disseminated silicious 

 organic bodies, which has collected round various centres of 

 segregational attraction, — though there are some difficulties to 

 remove before that opinion can be finally adopted. 



XX. — On the Sexual Life of Plants, and Parthenogenesis. By Dr. 



H. Karsten, Lecturer on Botany at the University of Berlin. 



[Concluded from page 99.] 



Embryogeny. 



The elongated pollen-cells on the stigma of Ccelebogyne ilici- 

 folia exhibit no peculiarity in the onward course they pursue to 

 the nucleus of the ovule. The amylum and the vesicles with 

 nitrogenous contents (mucus-vesicles) become dissolved as the 

 pollen grows ; and when the pollen-tube has reached the large 

 embryo-sac, it is seen to be filled with fluid, which also in all 

 probability contains a number of vesicles, freely swimming about 

 in it, some with and others without nuclei. 



* Haidinger's Wiener Mittheilungen, 1848, iv. 103; Neues Jahrbuch 

 fur Mineralogie, 1849, 213. 



t Abhaiullungen d. k. Ak. d. Wiss. zu Berlin, 1838, 82. 



