Plate II. 

 All figures refer to Naiasflexilis. 



Fig. 27. Mature male flower, showing the long pedicel; X 25. 



Fig. 28. A male flower which has discharged the pollen, showing the 

 lateral rupture of the floral envelope; X 25. 



Fig. 29. Longitudinal section of a nearly mature flower, showing a com- 

 plete division of the anther into two loculi- X 40. 



Figs. 30, 31. Germinating pollen-spores; X 400. 



Figs. 32, 33. Pollen-tubes, showing the granular protoplasm at the ex- 

 tremity. In fig. 33, the two generative nuclei, k, can be seen. 



Figs. 34-39. Successive stages in the development of the ovule, seen in 

 longitudinal section; X about 400, (except fig. 37, which is magnified about 

 200). The carpel is not shown except in figs. 34 and 37. The archesporial 

 cells are shaded; t, the tapetum, in}., in'., inner and outer integuments. 



Fig. 40. Young female flower, showing the young spiny lobes, :x:, and 

 stigmatic lobes, y; one of the latter is still very small; X about 200. 



Fig. 41. Section of young ovule, with the archesporium divided by longi- 

 tudinal as well as transverse walls. 



Figs. 42, 43. Young embryo-sacs, with two and four nuclei; X 450. 



Fig. 44. A mature female flower; X 25. 



Fig. 45. One of the stigmatic lobes; X 200 



Fig. 46. A spiny lobe; X 200. 



Fig 47. Longitudinal section of the ovary of a mature flower, showing 

 the stylar canal and papillae, />/ X about 60. 



Fig. 48. Young papillae from the upper part of the ovary; X 400. 



Fig. 49. Older papillae from the same place. 



Fig. 50. Upper part of mature embryo-sac, showing one of the synergidae, 

 s; the egg, o; and the two polar nuclei in close contact, k; X 400. 



Fig. 51. The two synergidae from a similar one. 



Fig. 52. Egg apparatus from a slightly younger embryo-sac than that 

 shown in fig. 50. 



Fig- 53- (^) Upper part of the embryo-sac at the time of fertilization; pi. 

 the pollen-tube, with two generative nuclei; 0, the egg. 



{b) The large endosperm nucleus, probably formed by the fusion of the 

 two polar nuclei. 



