LIST OF ILLUSTRATIONS AND EXPLANATION OF PLATES. 55 



PLATE 19: 



189. First longitudinal division in protonema. 



190. Seven-celled protonema with two-sided initial. X 360. 



191. Side view of tig. 190. 



192. Six-celled protonema; beginning of two-sided initial. 



193. Same as fig. 192, showing length of rhizoids. 



194. Apical growth established; one antheridium. 



195. More advanced apical growth, drawn from a specimen plasmohzed in salt 



solution in order to show the walls. 



196. Long, six-celled protonema with two-sided initial just established. 



197. Protonema with irregular apex. 



198. Dwarf male prothallus. Westport, Maryland, September 25, 1905. Four 



prothallial cells, three antheridia. 



199. Normal male, becoming cordate. 



200. Group of marginal initials just established. X 210. 



PLATE 20: 



201. Papillar outgrowth on dorsal surface of female prothallus. X 210. 



202. Two-celled archegonial rudiment, d, in sagittal section of prothallus. X 360. 



203. Upper surface of prothallus; single initial giving place to a group. X 210. 



204. Apical growth with a group of initials; horizontal section. X 360. 



205. Vertical transverse section of prothallus, 0.05 mm. back of notch, /. <?., about 



the line i-i in fig. 204. 



206. Three-celled archegonial rudiment, d, in sagittal section of prothallus, cut along 



the line 2-2 in fig. 204. X 360. 



207. Three-celled archegonial rudiment, d; first cleavage in neck-rudiment. X 360. 



208. Archegonial rudiment; neck and central cell. X 360. 



209. Cutting off neck canal-cell. X 360. 



210. Longitudinal section showing cleavage in neck cell. X 360. 



211. Longitudinal section of young archegonium showing neck bending over. X 360. 



212. Surface view of neck of nearly mature archegonium. X 360. 



213. Ditto; young archegonium. X 360. 



214. Archegonial rudiment, d y one cell. X 360. 



215. Longitudinal section of prothallus, showing neck canal cell with two nuclei. 



X 360. 



216. Formation of ventral canal-cell. X 360. 



217. Axial cells of archegonium complete; neck immature. X 360. 



218. Neck canal-cell with three nuclei. 



219. Mature archegonium; stained with iron haematoxylin. Ventral wall complete. 



X 360. 



220-222. Transverse sections of mature neck at summit, middle, and base, respec- 

 tively. X 360. 



223. Egg-cell ready for fecundation. 



224. Fertilized egg in longitudinal section of archegonium. Unsuccessful sperms in 



mucilage of neck. X 360. 

 PLATE 21: 



225. Longitudinal section of antheridial rudiment, one-celled. X 360. 



226. Ditto, two-celled. X 360. 



227. Surface view of a lobe of an old male prothallus. First division in central cell 



of antberidium above. X 210. 



228. Ditto; three-celled antheridium. 



229. Side view of antheridium with long basal cell. 



230. Antheridium nearly mature; vertical section. X 360. 



231. Rhizoids of female prothallus. X 210. 



232. Optical section of three-celled antheridium; cleared in glycerin. X 360. 



233. 234. Octants of embryo. Transverse sections of prothallus, 233 being 15 n 



anterior to 234; b, stem-octant; d, rudiment of first leaf; r, root-quad- 

 rant; ?t, foot. 



2 35> 2 3 6 - Sagittal sections of embryo and calyptra, 25 M apart; b, stem initial; d, mar- 

 ginal cell of first leaf; n, foot. 



237. Longitudinal section of old antheridium. 



