1902] A MORPHOLOGICAL STUDY OF ASCLEPIADACEAE 413 



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Fig. 31. Ovule with integument just beginning to show; /, integument ; n, 



nucellus ; X 1500. 

 Fig. 32. First division of the mother cell ; X 2200. 

 Fig. 33. Division of the daughter cells ; X 2200. 

 Fig. 34. Row of four megaspores with the fourth surpassing the others; X 



780. 

 Fig. 35. Disorganization of the first three megaspores ; X 780. 

 Fig. 36. Djinination of the first m^gaspore ; n, nucellus ; m, micropyle ; X 



2200. 

 Fig 37. Row of four megaspores, two of which are about equally active ; X 



2200. 



Asclepias Sullivantii. 



Fig. 38. First daughter cell not yet divided ; fourth megaspore enlarging ; nt-^ 



micropyle ; 71, nucellus ; X 2200 

 Fig. 39. First daughter cell dividing; third megaspore disorganizing ; X 



2200. 

 Fig. 40. Division of first daughter cell just completed ; X 2200, 

 Fig. 41, Dominance of the second megaspore ; X 2200. 

 Fig. 42. First division in the embrj^o sac ; m, disorganized megaspores ; X 



2200, 



Asclepias titberosa. 



Fig. 43, Normal embr3'0 sac ; union of polar nuclei ; X 1500- 



Fig. 44. Kmbryo sac which has reached the surface of the ovule ; e^ t%^\ 



df disorganizing cells ; X 1500. 

 Fig. 45. Eight antipodals ; X 1500. 

 Fig. 46. Complete union of the polar nuclei before fertilization; e, ^gg ; w, 



endosperm nucleus ; X 1500. 

 Fig. 47. Tip of pollen tube entering the stigma ; s, male cells ; /, tube 



^ nucleus ; X 2200. 



Asclepias Corniiti. 



Fig. 48. Double fertilization; u, micropylar polar ; ^, egg ; s, synergid; /, 



tracheid ; X 1500. 

 Fig. 4g. Third division of the endosperm ; X 1500. 

 1^ Fig. 50. Eight-nucleate endosperm ; ^, egg ; X 1500. 



Fig. 51. Sixteen-celled endosperm ; e, ^gg ; s, synergid ; X 1500. 



Fig. 52. Two-celled embryo ; endosperm massed about embryo ; s, synergid ; 



X 1085. 



