STRUCTURE.] SCHLEIDEN's THEOEY. 383 



indisputably proved by Agardh, Schykoffsky, and Schleiden ; 

 the latter even maintains that in no cases is there any sutural 

 production of ovules, or marginal placentae, but that the 

 placenta is a mere form of the growing point finally deve- 

 loped within the cavity of a carpel. Schleiden believes that 

 the formation of the ovule in Taxus, where it terminates a 

 branch, and is naked, and where the leaves are arranged in 

 the customary spiral direction, even to the extreme summit, 

 and where no one leaf implies in the slightest degree an 

 adaptation to the female part more than another, is incom- 

 patible with the sutural theory; and he also adverts to the 

 difficulty of explaining by it such a structure as that of 

 Armeria, in which five carpels surround a single ovule, rising 

 from the bottom of a cell upon a cord, which curves down- 

 wards at its apex, and thus suspends the ovule free in the 

 centre of the cavity ; he therefore supposes the ovule, and 

 consequently the placenta, to be in all cases a production of 

 the axis. The following is an extract from his valuable paper 

 on this subject : 



"Although we cannot doubt that in plants possessing a 

 free central placenta, or in those where, as in the Buckwheats 

 (Polygonacese,) Taxus, Juglans, Myrica, 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 ; arid 

 I do not consider the explanation to be very difficult. We 

 find in many Arads that the axis is expanded at its summit 

 into a kind of disk upon which is a number of buds or ovules, 

 arranged like the flowers in the capitulum of Composites and 

 other families. We next observe these disks expanded into 

 lobed processes, and adherent to the edges of the carpellary 

 leaves in all parietal or pseudocentral placenta ; such a modi- 

 fication of the axis as this is what occurs in Dorstenia. The 

 parietal placenta may be explained equally well, and perhaps 

 with greater simplicity, as a mere ramification of the axis. It 

 will not therefore surprise us that the buds or ovules of these 

 branches grow only upon their inner side, viz. that side 

 directed towards the axis ; for the same is observed in the 

 inflorescence of many plants, for instance, in ^Esculus. 



