Dec. 1, 1919 Pistillate Spikelet and Fertilization in Zea mays L. 257 



EXPERIMENTAL DATA 

 MATURE PISTILLATE SPIKELET 



The pistillate spikelet of corn at the time the silk emerges from the 

 husk has the appearance in longitudinal section shown in Plate 19. 

 The two empty glumes of the spikelet are thickened at their base but 

 are thin and membranous at their tips. The spikelet bears two flowers, 

 but in most cases one of these aborts, so that in each spikelet there is 

 only one functional flower. Each of the flowers of the spikelet consists 

 of a pistil and three stamens. The stamens in both flowers, however, 

 remain rudimentary, so that the only part of the fertile flower that 

 functions is the pistil. The development and disorganization of the 

 stamens as well as the development and abortion of the pistil of the 

 sterile flower have been described in much detail by Weatherwax (16). 

 Each flower is subtended by a lemma or flowering glume. Between the 

 two flowers and adjacent to each other are located the two palets. The 

 palets and lemmas are much shorter and more membranous than the 

 empty glumes. With the exception of the pod corns, the bracts of the 

 spikelet cease growth at the time of fertilization and thus never com- 

 pletely inclose the ovary. The bracts remain at the base of the grain 

 and form the chaff of the cob. If fertilization is not effected, however, 

 the bracts of the spikelet continue to grow in length and will completely 

 inclose the ovary of the fertile flower. In pod corn, the bracts continue 

 to grow after fertilization and completely inclose the mature grain. 



When the spikelet is mature the lodicules of the fertile flower are not 

 present or are not easily seen. According to Weatherwax {16) the 

 lodicules in early stages of growth are present in both flowers, but those 

 of the functional flower are crowded out before it is mature, while those 

 of the sterile flower remain intact and can readily be observed even when 

 that flower has a functional pistil. 



The pistil of the fertile flower consists of the ovary and the elongated 

 style or "silk." The silk is unevenly cleft at its tip, and this branched 

 portion has been termed the stigma of the pistil by most authors. 

 A small rounded knob or protuberance is located at the top of the ovary 

 near the base of the silk. In the center of this knob is a funnel-shaped 

 depression, apparently leading to the cavity of the ovary. However, 

 an examination of a section through this region shows that the depression 

 is only superficial and that the opening ^hich at one time led to the 

 cavity of the ovary has been closed. The cells composing the wall of 

 this cavity have never completely united (Pi. 19, sc). This incomi)lete 

 union of the wall of the ovary was noticed by True {14) but was first 

 termed the stylar canal by Guignard (4). The origin of this canal will 

 be discussed in detail when the embryonic development of the spikelet 

 is considered. 



134795"— 19 2 



