172 Weston.—The Development of 
28 . Swingle, D. B. ( 1903 ) : Formation of the Spores in the Sporangia of Rhizopus nigricans and 
of Phycomyces nitens. Bur. of Plant Ind. Bull., vol. xxxvii, pp. 9-40, 6 Pis. 
29 . Trow, A. H. ( 1899 ): Observations on the Biology and Cytology of a New Variety of Achlya 
americana. Ann. Bot., vol. xiii, pp. 131-79, 3 Pis. 
30 . Walz, J. ( 1870 ) : Ueber die Entleerung der Zoosporangien. Bot. Zeit., vol. xxviii, pp. 689-91, 
703 - 7 - 
EXPLANATION OF PLATES IV AND V. 
Illustrating Mr. Wesson’s paper on the Development of Thraustotheca. 
The figures were drawn from living material at the level of the stage, with the aid of an Abbe 
camera lucida. The approximate magnification of the combination of lenses used is given in each 
case, but applies to the original figures, which have been slightly reduced in reproduction. 
PLATE IV. 
Fig. 1. Young sporangium initial becoming filled with protoplasm, x 550. 
Figs. 2-5. Stages in the formation of the septum. Figs. 2-4 x 550; Fig. 5 x 1,300. 
Figs. 6-13. Stages in the development of a small sporangium, x 1,400. 
Figs. 14-17. Emergence of a zoospore from a sporangiospore. x 1,400. 
Fig. 18. Zoospore on the point of swimming away ; side view, x 1,400. 
Fig. 19. Cystospore (encysted zoospore) showing discarded cilia, x 1,400. 
Figs. 20, 21. Germination of a cystospore. x 1,400 
Fig. 22. Small plant resulting from such a germination in the presence of scanty nutriment, 
x 550. 
Fig. 23. Formation of a dwarf sporangium from a cystospore. x 1,400. 
Figs. 24, 25. Germination of a sporangiospore on nutrient agar. x 1,400. 
Fig. 26. Three-spored dwarf sporangium formed from a sporangiospore. x 1,400. 
Fig. 27. Two successively formed sporangia showing lateral dehiscence and the retention of 
a large proportion of the spores, x 550. 
Fig. 28. Retained sporangiospores, one of which is forming a dwarf sporangium. x 1,400. 
Fig. 29. Base of a dehisced sporangium, showing sporangiospores in situ , an imprisoned 
zoospore, a cystospore, and empty sporangiospores. x 1,400. 
Fig. 30. Sporangium which still retains a large number of sporangiospores, some of which have 
emitted zoospores, x 550. 
Fig. 31. Same sporangium showing development of germ-tubes when nutriment was added, x 550. 
Figs. 32-4. Stages in the development of a bispored dwarf sporangium, x 1,400. 
Fig* 35 * Portion of a hypha showing endogenous hyphae which have formed sporangia, x 550. 
Fig. 36. Abnormal columella-like growth of septum into a sporangium, x 550. 
Fig. 37. Portion of a hypha showing thick pectin septum, x 550. 
Fig. 38. Sporangium developed at high temperature showing papilla and large central vacuole, 
x 550. 
Fig. 39. Similar sporangium after dehiscence. x 550. 
Figs. 40, 41. Incomplete surface cleavage of a punctured sporangium, x 550. 
PLATE V. 
Fig. 42. Sporangium formed from a sporangial gemma. x 350. 
Fig. 43. Oogonial gemma which has been transformed into a sporangium. X 550. 
Fig. 44. Part of oogonium wall, showing pits, after treatment with zinc chlor-iodide. X 1,400. 
Fig. 45. Repeated proliferation of oogonial initial with final formation of a sporangium, x 550. 
Fig. 46. Formation of oogonium initial and antheridial branch by an oogonial gemma. X 350. 
Fig. 47. Irregular hyphal gemma, x 350. 
