16 INJURIOUS EFFECTS OF PREMATURE POLLINATION. 



Dividing these into two groups, namely, those pollinated more than 

 one da}- before opening and those pollinated one day or less than one 

 day before opening, they show that the former set 4 per cent of seed 

 pods which contained no germinative seeds, while the latter set 86 

 per cent of seed pods which contained germinative seeds. 



MICROSCOPIC STUDY OF TOBACCO PISTILS AND OVARIES. 



Soon after becoming detached from the plant some of the prema- 

 turely pollinated blossoms were carried to the laboratory and the 

 stigmas and pistils examined. That the pollen grains had germinated 

 and penetrated the stigma could be seen, but the growth of the pollen 

 tubes down the style could not be followed in the fresh material. 

 This led to the premature pollinating of one series of blossoms and 

 the mature pollinating of another series for microscopic study. The 

 flowers of both these series were emasculated and kept bagged so 

 that no pollen reached their stigmas except that purposely placed 

 there. By this means the rapidity of growth of the pollen tubes was 

 to some extent determined. At various intervals some flowers of each 

 series, as well as some of various ages that had never received pollen, 

 were cut and killed in Flemming's chromic-ace to-osmic acid solution 

 and carried through alcohols and imbedded, sectioned, mounted, and 

 stained with the safranin-gentian-violet triple stain. By this means 

 the pollen tubes could be found penetrating the stigmas (PI. II, fig. 2), 

 in the styles (tig. 3), entering the ovary and dispersing among the 

 ovules of the prematurely pollinated flowers (tigs, 4 and 5). 



Flowers collected twenty-two hours after being prematurely polli- 

 nated showed pollen tubes on and penetrating the stigma and some a 

 short distance into the stjde but none in the ovaries, while in ovaries 

 of flowers that had fallen because of being prematurely pollinated 

 pollen tubes were abundant. Figs. 4 and 5 show pollen tubes in the 

 ovaries of such flowers. In the sections that have been photographed 

 pollen tubes are more abundant than they appear in the photomicro- 

 graphs, but do not show because they are not in the same focusing 

 plane. 



Although the ovaries of the prematurely pollinated flowers contain 

 many pollen tubes, none has been found entering the micropyle of 

 an ovule, and in just what way the flower is destroyed has not 

 been determined; but the kindness of Dr. Webber in examining the 

 sections enables the writer to state definitely that the ovules, though 

 encompassed with pollen tubes, are much too immature for fertiliza- 

 tion, the embryo sacks being in the one and the two celled stages. 

 The study of an abnormal condition of this kind may help to explain 

 the attractive force which enables pollen tubes to find and enter ovules 

 at the proper time. 



