412 BOTANICAL GAZETTE [December 



f 



Asclepias tuberosa. 



Fig. 8. Gland from receptacle ; r, receptacle ; /, pedicel ; X 390. 



Fig. 9. Young stamen ; p, pollinum ; by elongated elements preliminary to a 



bundle; X 48. 

 Fig. 10. Young stamen, older than 7?"^, g\ e, end of vessel ; //, beginning of 



hood and horn ; X 48. 

 Fig. 1 1. Longitudinal section of stamen ; e^ end of vessel ; n, horn ; d, hood ; 



p, pollinium ; X 48. 

 Figs. 12-15. Cross sections throughyf^. //in planes indicated; /, pollinium ; 



Cy corpusculum ; w^ wing ; a, alar chamber ; X 94. 



Asclepias Cor?iiiti, 

 Fig. 16. Dorsal view of young stamen with concentric hood and papillate 



horn ; X 23. 



Asclepias tuberosa. 



Fig. 17. Longitudinal section of stamen ; hood and horn forming rapidly ; 



X 23. 



Fig. 18. Longitudinal section through mature stamen showing bundle loop- 

 ing far up into the hood; X 23. 



Fig. 19. Section from Jig, 18 through hood (region indicated) showing 



aerenchyma ; s, air space ; X 203. 



Asclepias Cornuii, 



Fig. 20. Part of flower with slice removed by tangential cut ; 5, stamen ; 0^ 



ovary ; w, mass arising from the stamineal ring ; X 23. 



Fig. 21. Longitudinal section of basal part of stamen ; s, sepal; p, petal; n^ 



stamen ; ?n, mass arising from stamineal ring ; X 94. 



A sclepias verticil la ta. 



Fig. 22. Pollen grain \ g, generative cell ; /, tube nucleus; b, undetermined 



bodies ; X 1500. 

 Fig. 23. Generative cell leaving the wall of the pollen grain ; X 1500. 

 Fig. 24. Generative cell before division, without a wall ; g, generative cell ; 



/, tube nucleus ; X i 500, 

 Fig. 25. Division of generative cell, no wall about it ; X 1500. 

 Fig. 26. Division of the generative cell ; X 1500. 

 Fig. 27. Two male cells shortly after their formation ; X 2200. 



Asclepias tuberosa. 



Fig. 28. Longitudinal section of head ; s^ stigma ; c, styler canal \ g, glandu- 

 lar epidermis which forms the corpusculum ;/ may be functionless 

 stigma ; /, conducting tissue ; b, bundle ; X 136. 



Fig. 29. Ovule witharchesporial cell ; X 1275. 



Fig. 30. Ovule containing two archesporial cells ; X 2200- 



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