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THE AMERICAN NATURALIST [Vol. XLVII 



caused to swell slightly by merely tickling them with a 

 sharp-pointed instrument, but no seeds were produced. 



3. Abortive seed probably without embryos was pro- 

 duced by singeing young buds with a hot platinum wire, 

 by the exposure of young plants to chloroform gas, and 

 by cutting away a portion of the pistil and pollinating 

 the stub both with and without the accompaniment of a 

 germinative fluid. 



4. Abortive seed was produced by shortening the pis- 

 tils of a flower and grafting the stigma end of another 

 pistil on to the stub and pollinating the same. 



5. The ringing of the branches below a cluster of buds 

 did not assist in the production of seed. 



6. No seed was produced by the simple methods of 

 emasculation and decapitation of blossoms, except in one 

 doubtful case of N. plumbaginifolia. 



7. It is likely that an agent inhibitory to the growth of 

 pollen grains is present in the stigmatic fluids of certain 

 species of the genus Nicotiana; at least, the pollen grains 

 of N. suaveolens did not germinate in N. Forgetiana 

 stigmatic fluid when placed within a Van Tieghem cell. 



8. The exposure of young N. rustica var. texana plants 

 to acetone gas caused the transformation of the corollas 

 and the stamens of most of the terminal flowers into 

 leafy tissue ; otherwise, except in the mentioned case of 

 the chloroform, no results were secured by the use of 

 anaesthetic and toxic gases. 



9. The injection of chemicals into the stems of tobacco 

 plants was valueless in the production of seed. 



10. As no unquestionable case of parthenogenetic seed 

 was produced in the several hundred trials, it seems very 

 improbable that parthenogenesis exists in the genus 

 Nicotiana— at least in the species tested. The seed ob- 

 tained in the crosses which came true to the mother 

 species is probably polyembryonic— the stimulus of de- 

 velopment being imparted either by the penetrating pol- 

 len tubes or by a substance exuded from the same. 



