THALLUS OF SPHAEROCARPOS DONNELLII AUST. 
4. The apical growth of the mature thallus is due to a group of cells 
occupying the apical notch. These cells have the appearance of four-sided 
apical cells. The lateral segments which they cut off either resemble the 
mother cell, or go to the formation of the thallus lobes. The dorsal and 
ventral segments add to the thickness of the thallus in the median portion. 
5. The marginal lobes of the thallus are formed by the division of lateral 
segments of the apical cells. Under natural conditions, successive lateral 
segments merge together in their development to produce a more or less 
continuous marginal wing. Under cultural conditions, the more rapid 
elongation of the median portion of the thallus causes the separation of the 
structures derived from individual lateral segments into distinct leaf-like 
lobes, attached laterally along a central midrib. . 
6. Branching of the thallus is due to a division of the apical group of cells 
into two such groups, a lobe occupying the region between. The formation 
of lobes is not necessarily related to branching. 
Department of Botany, 
University of Wisconsin 
LITERATURE CITED 
1. Allen, C. E. The basis of sex inheritance in Sphaerocarpos Donnellii Aust. Proc. Amer. 
Phil. Soc. 58: 289-316. 1919. 
2. Campbell, D. H. Notes on Sphaerocarpus. Erythea 4: 73-78. 1896. 
3. . The structure and development of the mosses and ferns. 3d ed., pp. 75-82, 
New York, 191 8. 
4. Douin, C. Le Sphaerocarpus terrestris Sm. Rev. Bryol. 30: 44-57. 1903. 
5. . Nouvelles observations sur Sphaerocarpus, Rev. Bryol. 36: 37-41. 1909. 
6. Douin, C, and Douin, R. Note sur les Sphaerocarpus. Rev. Gen. Bot. 29: 129-236. 19 17. 
7. Goebel, K. Archegoniatenstudien. XI. Weitere Untersuchungen iiber Keimung und 
Regeneration bei Riella und Sphaerocarpus. Flora 97: 192-215. 1907. 
8. Haynes, C. C. Sphaerocarpos Mans sp. nov., with a revision of the genus and illustra- 
tions of the species. Bull. Torrey Club 37: 215-230. 1910. 
9. Leitgeb, H. Untersuchungen iiber die Lebermoose. Heft 4: 63-74. 1879. 
10. Marchal, E., and Marchal, E. Recherches experimentales sur la sexualite des spores 
chez les Mousses dioiques. Mem. Cour. Classe des Sci. Acad. Roy. Belgique 2^: 
1-50. 1906. 
11. Mottier, D. M. Notes on the apical growth of liverworts. Bot. Gaz. 16: 141-143. 
1,891. 
EXPLANATION OF PLATES IX-XII 
All drawings, except figures 68, 69, and 70, were made with the aid of a camera lucida. 
In these cases the drawings were freehand sketches of plants as seen under a binocular 
microscope. Figures 25, 35, 36, 37, 68, 69, and 70 were made from living plants. Magni- 
fications given are approximate. 
Fig. I. Undivided germ tube. X 150. 
Fig. 2. First division of the germ tube: sp, spore wall. X 150. 
Fig. 3. Second division of the germ tube. X 150. 
Fig. 4. Third division of the germ tube: sp, spore wall; r, rhizoid. X 150. 
Figures 1-4 are shaded to indicate the distribution of the dense cell contents. 
Figs. 5-9. Further divisions of the germ tube, prior to the formation of the germinal 
disc: sp, spore wall; 6, basal cell. X 150. 
Fig. 10. Beginning of the formation of the germinal disc: a, possible apical cell. 
X 350. 
