256 Journal of Agricultural Research voi. xviii, No. s 



embryo and endosperm. Kuwada (9) made a cytological study of the 

 pollen mother cells of a number of varieties of corn. He found that 

 there was a considerable variation in the size and number of the chromo- 

 somes even in the same race. The haploid number varied from 9 to 12, 

 the higher number as a rule being found in the varieties of sugar corn 

 and the lower numbers in the varieties with more starch. In a later 

 paper (10) he reported that the diploid number of chromosomes varied 

 from 20 to 22 in the cells of the root, but that the number was constant 

 for any one plant. Weatherwax {15-17) since this work has been in 

 progress has reported extensively on the development, structure, and 

 evolution of both the pistillate and staminate spikelets of the corn plant. 

 Further mention of his work will be made in the discussion of the results 

 reported in the present article. 



EXPERIMENTAL METHODS 



The varieties of corn used in this work were Pride of Saline, Freed 

 White Dent, and Sherrod White Dent. The material was collected in 

 the field at Garden City, Kans., during the seasons of 1914 to 1917, and 

 at Manhattan, Kans., in 191 8. All the material used in this investiga- 

 tion was fixed in inedium chrom-acetic solution, washed, dehydrated, 

 cleared in xylol, and embedded in paraffin in the usual manner. The 

 sections for the most part were cut 15 to 20 microns in thickness and 

 stained with safranin, gentian violet, and orange G. The drawings of 

 the developing spikelet were made with the aid of a Bausch and lyomb 

 projection apparatus, and those showing the development of the embryo 

 sac and fertilization were made by the aid of the camera lucida. 



In order to study the time elapsing between pollination and fertiliza- 

 tion, the young ears were bagged before the silks appeared. After the 

 silks had practically all appeared, they were hand-pollinated with freshly 

 collected pollen. After pollination the ears were again bagged and kept 

 covered until the specimens were collected for fixing. The ears which 

 furnished the material for study were collected at stated hourly intervals 

 after pollination had been made. In this manner the time elapsing 

 between the time of pollination and fertilization could be determined. 



For the study of the course of the pollen tvibe, the silks at certain 

 periods after pollination were cut into short lengths and then tied into 

 small bundles by means of fine threads. These bundles were then fixed 

 and embedded in the same way as the other material. By cutting the 

 bundles lengthwise, a large number of silks for a portion of their length 

 could be obtained in longitudinal section. Since the bundles were 

 taken consecutively from the tip of the silk to the ovary, the course of 

 the pollen tube could be observed in any portion of the silk. 



