258 Journal of Agricultural Research Voi. xviii, no. s 



The ovule is of a modified campylotropous type and is attached by 

 approximately one-third of its circumference to the bottom of the cavity 

 of the ovary. The outer coat of the ovule is incomplete and extends 

 about half way around it. The outer coat for its whole length, with the 

 exception of a short distance at the base, is free from the inner coat. 

 The inner coat fits closely to the ovule and covers it completely, except 

 in the region of the micropyle. Each coat of the ovule is approximately 

 two cells in thickness, except in the region of the micropyle and the 

 stylar canal where the coats may be from three to four cells in thickness. 

 The outer coat forms a wedge-shaped projection which extends into the 

 inner depression of the stylar canal. The inner coat also often shows 

 such a projection, but it is never so marked as that in the outer coat 

 (PI. 19, ovc). This projection of the outer coat into the stylar canal has 

 been observed by both Guignard {4) and Weatherwax (/<5). 



The two fibro-vascular bundles of the silk traverse the walls of the 

 ovary and unite at its base with the bundles that supply the various 

 elements of the spikelet. Extending from each of the fibro-vascular 

 bundles of the silk to the cavity of the ovary is a bundle of elongated 

 cells that are rich in protoplasm and resemble very closely the sheath cells 

 of the fibro-vascular bundles of the silk. Through these sheathlike cells 

 the pollen tube travels to the cavity of the ovary after it leaves the sheath 

 cells of the fibro-vascular bundles of the silk (Pi. 19, vbs, bsc). 



DEVELOPMENT OF THE PISTILLATE SPIKELET 



The spikelets are borne on the cob in double rows, because the spikelets 

 are paired; and since each spikelet has only one functional flower, an 

 even number of rows of grains is produced. It has been observed by 

 Kempton (7), Stewart {12), and Weatherwax (75) that frequently in 

 certain varieties both flowers of the spikelet may function, and thus two 

 grains may be produced to each spikelet instead of one. In these varie- 

 ties the grains do not always occur in regular rows on the cob but may be 

 more or less irregularly arranged. This is due to the fact that the develop- 

 ment of two grains in a spikelet tends to crowd the other grains in that 

 region more or less out of alignment. 



The origin of the paired spikelets is best observed by a study of the 

 cross section of a very young cob. Such a cross section of the tip shows 

 that it is composed of undifferentiated or embryonic cells (Pi. 20, A). A 

 short distance back of the tip numerous projections or protuberances 

 appear on the periphery of the cob. Each of these projections is a rudi- 

 ment or primordium from which a pair of spikelets will develop (Pi. 20, B). 

 Soon after the formation of these rudiments, each one becomes equally 

 divided (Pi. 20, C), and from each half a spikelet develops (Pi, 20, D). 

 The progressive development of a spikelet from its primordium is best 

 studied in longitudinal section. The appearance of the embryonic cella 



