WITH ^^OTES oisr other species. 145 



Plate XV. 



Fig. 18. Chlamydospores of A. Americana. X 200. 



Fig. 19. Ciilamydospores of Achlya sp. X 74. 



Fig. 20. G-ermiaatioa of chlamydospores of .4.c7iJi/(Z sp. X 74. 



Fig. 21. Origin of oogonium, o, and aattieridium, a, from aa tiyphi of 4. Amrimna. X 3)0. 



Fig. 23. A divided oogoaial branch of A. apioalata, beiring three oogoaia. X 200. 



Fig. 23. A proliferous oogonium of A. polyandra. X 200. 



Fig. 24. An oogonium of .4. Americana which has reverted to the vegetative condition and given rise to new sexual 

 organs. X 540. 



Fig. 25. Antheridial branches of 4 J.m5?'icaii terminated by oo'oniumlike swellings. X 350. 



Fig. 26. Four stages in the development of the oojpheres of J. apiculciti ; a, th3 parietal layer still intact, the pro- 

 toplasm accumulating into masses, at 11.50 a.m.; &, the parietal layer ruptured and withdrawn into the three 

 distinct masses, at 12 m. ; c, the separation of small portions from the main protoplasmic masses, at 13.10 p.m.; 

 d, the reabsorption of these masses, at 13.18 p.m. X 350. 



Fig. 27. A still later stage thiu 38, d, the oSspheres quite roun ded off, at 13.33 p.m.; showing also the antheridial 

 branches. X 350. 



Fig. 28. An oogonium of -4.. papillosa which has reverted to the vegetative condition and produced three hyphae with 

 sporangia, one of them fully shown at f . X 200. 



Fig. 29. Germination in situ of the oospores of A. Americana ; a, two spores with young germ tubes ; b, one oospore 

 with a fully developed hypha and empty sporangium. X 540. 



Plate XVI. 



Figs. 30-36. Cytology of the sexual organs of A Americana. From Corros.-subL-Haematoxylin preparations. 



Fig. 30. Young oogonium with its central vacuole formed, its nuclei irregularly scattered. X 510. 



Fig. 31. Oogonium after the formition of its basal wall, the protoplasaa more withdrawn from the centre and the 



nuclei approaching in pairs. X 540. 

 Fig, 83. The nuclei larger, fewer, and fainter, and the vacuoles formed in the protoplasmic layer. X 800. 

 Fig. 33. The vacuoles have disappeared and the protoplasm is more contracted. X 800. 

 Fig. 31. The oospores are formed, and the antheridia have produced fertilization-tubes which contain protoplasm and 



nuclei, but remain closed ; a and b, two sections from the same oogonium. X 540. 

 Fig. 35. A fully developed oosphere with its single nucleus. X 800. 

 Fig. 36. Two oospheres before the final nuclear fusions. X 800. 

 Figs. 37-39. Saprolegnia monoica. 

 Fig. 37. Sexual organs, mature . X 540. 

 Fig. 38. Both sexual organs from the same branch. X 549. 

 Fig. 39. An intercalary oogonium. X 300. 

 Figs. 40-43. Saprolegnia mixta . 

 Fig. 40. Two small oogonia, one with and one without an antheridiura, the latter formed inside an empty sporangium. 



From Mississippi. X 200. 

 Fig. 41. An oogonium with antheridia. From Pennsylvania. X 200. 



Fig. 42. An abnormally branched sporangium, not rare in this species. From Pennsylvania. X 74. 

 Figs. 43-45. Saprolegnia ferax. From Kentucky. 



Fig. 43. An oogonium, on a branch growing through a sporangium. X 540. 

 Fig. 44. A cylindrical oogonium. X 540. 

 Fig. 45. Two oogonia on a forked branch. X 200. 



