PLATE II. 



Fig. 1. — The same portion of the same plant shown in PL I, photographed eight 

 days later than fig. 1. The emasculated flowers b and c have not yet fallen, while 

 the seed pods resulting from flowers 3 and 4 have attained considerable size. 



Figs. 2, 3, 4, and 5. — Photomicrographs of pollen grains and pollen tubes in sections 

 of flowers that fell because of premature pollination. 



Fig. 2. — Section of a tobacco stigma showing pollen grains which have germinated 

 and sent their tubes into the style. Flower from which this section was made was 

 emasculated and pollinated May 25, 11 a. m., two days before it would have opened. 

 May 27, 11 a. m., it was found fallen and was fixed for microscopic study. ( X 250 

 diameters. ) 



Fig. 3. — Pollen tubes farther down the style. Figs. 2 and 3 are sections of the 

 same pistils. ( X 315 diameters. ) 



Fig. 4. — Mass of pollen tubes near the point where they enter the ovary from the 

 style. The flower from which this section was made was one of experiment 21 

 (see Table I). ( X 160 diameters. ) 



Fig. 5. — Pollen tubes in ovary on the placenta at attachment of ovules. Figs. 4 

 and 5 are from different sections of the same ovary. ( X 75 diameters. ) 



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