STRUCTURE.] MOKPHOLOGY OF OVULES. 393 



the chalaza. This opinion is also supported by the instances 

 which have been noticed of the descending metamorphosis of 

 the ovule. MM. Henry and Marquart have noticed the 

 retrograde or descending metamorphosis in the ovules of the 

 Salix cinerea, and have represented, in drawing, a catkin, 

 the carpels of which were filled with a number of longitudi- 

 nally folded leaves occupying the normal situation of the 

 ovules ; doubtless these were the organs which should have 

 constituted the ovular membranes. Hence, then, it may be 

 concluded that the axis has its termination at some point 

 within the ovule ; this I would consider to be situated at the 

 chalaza; here, the vessels which have ascended through the 

 woody tissues of the stem, and have penetrated the cellular 

 structure of the placenta, are suddenly stopped, as it were, 

 in their course, and are spread out in ramifications to the 

 nucleus and its tegumentary membranes ; thus forming the 

 true organic placenta/' 



It is, however, to be remarked that if the ovule is really 

 a leaf-bud, (the last which the axis of growth is capable of 

 producing) its integuments are not formed in the same order 

 as leaf-bud scales. In a leaf-bud of two scales the outer 

 forms first, then the second, and within the second the 

 growing point. But in an ovule the growing point, if the 

 nucleus be it, appears first, then the interior integument, and 

 afterwards the exterior. It is, moreover, not to be forgotten 

 that in the monstrous Aquilegia figured in the Elements of 

 Botany, p. 88. t. 180, each ovule actually grows into a true 

 leaf, and not a leaf-bud, the nucleus being the apex of 

 the leaf. This does not seem quite consistent with the 

 theory that ovules are leaf-buds ; and further evidence must 

 be sought before the question can be regarded as settled. 



In almost all cases the ovule is enclosed within an ovary, 

 as would necessarily happen in consequence of the convolute 

 nature of the carpellary leaves : but if the convolution is 

 imperfect, as in Reseda, the ovules are partially naked ; and 

 if it does not exist at all, as in Cycads and Conifers, the ovules 

 are then entirely naked, as was first shown by Brown, and, 

 instead of being fertilised by matter conveyed through the 



