950 DESCRIPTION OF THE ENGRAVINGS. 



sporangium lying between them, enveloped in mucus. 3. Staurastrum (Desmidium, Ehr.) 

 eustephanum, e, V. 4. Spii'ota^nia condensata (Breb.), x200: the frond is seen with its 

 spiral band of endochi'ome, and surrounded by a mucous hyaline sheath. 7. Staui'astrum 

 (Desmidium, E.)senarimn. 8 & 11. Docidimn Ehrenbergii (Ralfs), X 100: 8. Conjugating 

 fronds, the sporangium in an early stage of development ; 11 shows the process of develop- 

 ment by fission, the young segments partially gi-own. 9. Docidium clavatum (Kg.), X 100. 

 10 & 30. Euastrum pectinatum (Breb.), x200: 10. A single frond; 30. The spinous 

 sporangium, the empty segments adjacent. 12, 13. Tetmemorus Brebissonii (Ealfs), X 

 200 : 12. f. V. ; 13. s. v. 14, 15. Penium margaritaceum (Breb.), x200 : 14. f. v. var. a ; 

 15. s. V. of two empty fronds, var. y, the sporangium between them. 16, 17. Staurastrum 

 alternans (Breb.), x400: 16. f. v. ; 17. e. v. 18 & 23. Xanthidium cristatum (Breb.), 

 X400: 18. f. v.; 23. e. v. 19 & 36. Scenodesmus quadricauda (Ealfs), x400: 19. A 

 frond of two cells ; 36. one of four cells. 20, 21, 24, 25 & 31. Staurastrimi polymor- 

 phum (Breb.), x400; 20. e.v. (of five-rayed var.); 21 & 31. f.v. ; 24. A frond multi- 

 plying by self-division ; 25. Sporangium with its fm-cate spines, and around it the empty 

 and previously conjugated fronds. 22. Micrasterias denticulata (Breb.), X 100, sporan- 

 gium of. 26. Cosmarium caelatum (Ralfs), x300: front view of frond midtiplying by 

 self-division, the young segments partially grown and their sm-face still smooth. 27. Pe- 

 diastrum tetras (Ralfs), x400, f.v. of a frond. 28, 29. Tetrachastrum oscitans (Dixon), 

 XlOO: 28. f. v.; 29. tr. v. of e. f. 32 & 35. Hyalotheca dissiliens (Breb.): 32. x200, 

 tr. V. with investing hyaline gelatinous sheath; 35. X400, f.v., also showing the sheath. 

 33,34. Cosmarium midulatum (Corda), x400: 33. f. v. ; 34. Sporangivun with the 

 empty fronds. 37 & 40. Desmidium quadrangulatum (Ralfs): 37. x200, f. v. of fila- 

 ment; 40. X300, tr. V. 38,39. Didymoprivun Borreri (Ralfs), x400: 38. tr. v. ; 39. 

 Portion of a filament, f. v. Diatoms : — 41, 42. Lithodesmium undulatum ; 43. Eucampia 

 Zodiacus. Desmid : — 44. Micrasterias Americana. Diatoms : — 45. Podosira monilifor- 

 mis attached to Polysiphonia ; 46, 47, 49, 50. Biddulphia pulchella; 48. Denticella 

 Biddulphia. 



PLATE III. (Desmids). 



Figure 1. Gonatozygon Ealfsii (De Bary), three joints of, x300; 2. Same, conju- 

 gated, showing sporangium, x300. 3. Genicularia spirotsenia (De Bary), single joint of, 

 X 150 (vide De Bary, op. cit. iv. 1. p. 717), x300. 4. Leptocystinema Kinahani (Archer), 

 X200, showing front and side views of the band of endocln'ome, and two joints with 

 nascent halves. 5. Aptogonum Baileyi (Ralfs), x400; 6. Same, e. v. 7. Desmidium 

 Aptogonum (Breb.), portion of a filament, x400; 8. Same, e.v. x400. 9. Spondjlosium 

 depressum (Breb.), x300: five joints, one dividing. 10. S. pulchellum (Archer), x450: 

 five joiuts of a filament. 11. Euastrmm oblongum (Ralfs), x200. 12. E. insigne (Hass.), 

 X200. 13. E. binale (Ralfs), X 400. 14. Cosmarium pyramidatum (Breb.), X 300; 

 15. Same, e. v. x300. 16. C. cylindi-icum (Ralfs), x300; 17. Same, e. v. X300. 18. 

 Staurastrum avicula (Breb.), X3(X); 19. Same, e.v. x300. 20. S. teliferum (Ralfs), 

 X300; 21. Same, e.v. x300, 22. S. spongiosum (Breb.), x300; 23. Same, e.v. x300. 

 24. S. quadrangidare (Breb.), x300; 25. Same, e. v. 26. S. globulatum (Breb.); 

 27. Same, e.v. 28. S.gracde (RaKs), x300; 29. Same, e.v. x300. 30. S. vestitum 

 (Ralfs), x300; 31. Same, tr. v. x300. 32. S. fiu-cigerum (Breb.), X200; 33. Same, e.v. 

 X200. 34. S. margaritaceum (Menegh.), X 300 ; 35. Same, e. v. X 300. 36. Arthro- 

 desmus Incus (Hass.), X 400. 37. Triploceras verticiUatiun (Badey). 38. Docidiiun 

 Bacidum (Breb.), X 200. 39. Closterium didymotocum (Corda), X 100. 40, C. turgiclum 

 (Ehr.), xlOO. 41. C. lineatum (Ehr.), XlOO; 42. Same, conjugated, showing the double 

 sporangium, xlOO. 43. C. attenuatum (Ehr.), xlOO. 44. C. rostratiun (Ehr.), xlOO. 

 45. Penium interruptum (Breb.), x200. 46. Docidium Elu-enbergii (Ralfs), X 200, after 

 W. Archer (Nat. Hist. Review, vii. p. 375) : commencement of groveth of lateral tube 

 preparatory to the formation of zoospores. 47. Same, the zoospores emitted and forming 

 an external cluster (p. 716). 48-54. After De Bary (op. cit.) ; all X 190, showing develop- 

 ment of sporangimn of Cosmarium Botrytis (Menegh.) : 48. The inner membrane with 

 contents escaping by bursting the outer wall of the sporangium ; 49. The same escaped, 

 somewhat further developed, preparatory to segmentation of the contents, the external 

 membrane doubled ; 50. The same, division finished ; 51. The same, H hour after ; 

 52. The same, at a later stage ; 53. Germ-cells, ordinary vegetative division begun ; 

 54. Product of the first division of a germ-cell, each new half (but not imtil now) having 

 assumed the characteristic form of the species. 55-60. After De Bary (op. cit.), all x390, 

 showing development of sporangimn of Cosmarium Meneghinii (Breb.) : 55. Empty out- 

 side coat of a sporangium with an open slit or fissure by which the inner membrane (with 

 contents) has come out; 56. The emerged inner membrane and contents; 57. A pair of 

 germ-cells formed therein ; 58. The same, one escaping ; 59, 60. Products of the germ- 



