[ 241 ] 



XXX VI. Some Observations on the Development of the Organic 

 zation in Phcenogamous Plants, By Dr. M. J. Schleiden. 



[Continued from p. 189.] 



A LTHOUGH we cannot remain one moment in doubt that 

 in plants possessing a true placenta centralis libera (still 

 less in such where, as in the Polygonece, Taxus, Juglans, My^ 

 rica^ the placenta cannot be supposed to exist as a separate 

 organ), the nucleus of the ovule is only the summit of the axis, 

 yet the question suggests itself as to how the parietal placenta is 

 to be understood ; and I do not consider the explanation to be 

 very difficult. We find in many of the Aroidece that the axis is 

 spread out at its summit, forming a kind of disc ; upon this 

 surface are a number of buds as ovules, similar to the arrange- 

 ment which is found, in the Synaiitherce and other families, to 

 take place among the flower-buds ; we next observe these discs 

 expanded into lobular processes, and adherent to the edges of 

 the carpellary leaves in all parietal or pseudocentral placentae, 

 a modification of the axis which is met with in Dorstenia^ 

 the parietal placentse may be explained equally well, and per- 

 haps with greater simplicity and consistency, as a mere rami- 

 fication of the axis. It will not therefore surprise us, that 

 the buds of these branches (ovula) grow only upon their inner 

 side, viz., that directed towards the axis, since the same is ob- 

 served in the inflorescence of many plants, for instance, in 

 JEsculus, Lastly, we find the axis expanded somewhat in the 

 shape of a basin in those plants in which the entire wall of 

 the simple ovarium is occupied with ovules, as may also be 

 seen in the similar modification of the stalk in many Rosacece 

 and in Ficus, There cannot however be any reason adduced 

 why such deviations in the form of the axis should be assumed 

 as occurring in a lower internodium between the leaves and 

 bud, whilst they are denied existence in a higher one between 

 the carpellary leaves and ovule-butf, or are said to be impos- 

 sible. 



But we find in nature, that in parietal placentae the edges 

 of the leaves are never laid upon one another in their entire 

 length, and adhere in that manner, but become united from 

 below upwards by the subsequent growth of a more or less 

 distinctly interposed substance. This interposed substance 

 is very evident in the Fuviariacece and Crucifera, in which 

 it appears much later than the carpellary leaves, stands ex- 

 actly within them, and in the latter family forms the spu- 

 rious partition, by its gradual extension towards the middle 

 4nd its subsequent adhesion. The placenta shows itself to 



Phil Mag, S. 3. Vol. 12. No. 74. March 1838. 2 C 



