ZEA MAYS 



135 



longitudinally throughout its length. Two vascular bundles ex- 

 tend from its unequally branched apex through the walls of the 

 ovary to its base, where they are continuous with other bundles 

 supplying the spikelet. These are surrounded by slender sheath 

 cells that are densely cytoplasmic with elongated nuclei. The 

 pollen passes down the silk between these dense cells until it 

 reaches the ovarian cavity. The surface of the silk is hairy; and, 

 throughout most of its length, is receptive to pollen so that the 

 major portion of it may be regarded as a stigma. 



Fig. 56. I, longisection of young carpellate spikelet; i, the same, at the time the carpel 

 wall has begun to develop; t,, longisection of the fertile carpel showing nucellus still in erect 

 position ; 4, longisection of the carpellate spikelet at the time of pollination : c and c\ develop- 

 ing ovary walls, c' is the portion of the carpel from which the style or silk will develop; 

 CO, ovarian cavity; e s, embryo sac; g, lower glume; g', upper glume; hit, integuments; 

 /w, lemma of fertile flower ; /w', lemma of sterile flower ; mic, micropyle; mmc, megaspore 

 mother cell ; or, ovule; ova, owiry ; w, ovary wall ; />, palea of fertile flower ; /?', palea of 

 sterile flower ; pp, primordium of carpel ; ra, rachilla ; s c, stylar canal ; s fl, sterile flower ; 

 j/^, silk or style ; jr, rudimentary stamen ; fi, vascular bundle ; vZij, one of the vascular bundles 

 of the silk; vsc, sheath cells of the silk. (Diagram 4 reduced to approximately one-sixth 

 the size of diagrams 1-3. Redrawn after Miller, Jour. Agr. Rw.) 



Development of the Ovule. — Although the older interpreta- 

 tion that the pistil consists of a single carpel is accepted by some 

 morphologists, the more generally held view is that it is tri-car- 

 pellate. Randolph (15) has summarized this concept in describing 

 the formation of the ovary and the development of the ovule. The 

 ovary consists of three undi verged carpels, and a single ovule 

 arises near the base of the ovary on the side adjacent to the rachilla. 



