432 THE FRUIT. DEVELOPMENT OF THE FLOWER. 



the Cruciferae has been derived from one which bore two antero- 

 posterior stamens. 



While the petals in our object develop very slowly, the rudi- 

 ments of the stamens enlarge rapidly. They are, therefore, very 

 readily visible, while the petals are hard to see. Our knowledge 

 of the distribution of parts in the fully-formed flower helps us to 

 avoid confusion, and materially facilitates orientation. After the 

 origin of the inner staminal pairs, the apex of the floral axis 

 commences to bulge in the form of a two-lipped crater, some- 

 what laterally compressed, in the base of which the growing point 

 must therefore be now sought. This crater increases in height 

 but slowly, while the stamens develop very quickly, and soon 

 form the largest structures enclosed within the sepals. The 

 petals, on the other hand, still remain very small, and cannot 

 be off-hand recognised within the bud when made transparent. 

 They show more clearly, as small tongue- shaped flaps, in buds 

 which have been carefully crushed under the cover-glass. The 

 petals first begin to grow, and then somewhat rapidly, in buds 

 which (without stalk) are more than one mm. high, and in which 

 all parts of the stamens are recognisable. These relations, how- 

 ever, as well as the destiny of the pistillar rudiment, can no 

 longer be followed upon entire buds, but only upon sections, 

 or upon dissected buds. 



Let us prepare longitudinal sections through the apex of the 

 entire inflorescence between the fingers. In order to isolate 

 the parts, we dissect the buds with needles under the simple 

 microscope. The sections, as well as the separated parts, can 

 with advantage be treated with potash. We can then determine 

 that the deeply two-lipped rudiment of the pistil, after it has 

 attained a certain height,- begins to close above ; that, simultane- 

 ously with the lower parts of the ovary, a partition wall arises from 

 the punctum vegetationis, and thus divides the ovarian cavity into 

 halves ; that finally out of the angles on each side of this partition 

 wall three ovular rudiments arise. The placentae are therefore 

 at the angles of this partition wall. The ovular rudiments are 

 at first conical and not bent ; they produce under their apex an 

 annular wall-like prominence the inner ovular integument ; 

 they then begin to bend, while at the same time on their posterior 

 surface a second protuberance, the outer ovular integument, 

 arises close under the first. While this increases in strength, the 

 ovule bends more and more. The integuments, growing by their 



