Tilden: pilinia and stigeoclonium. 633 



I. Wille, N. Engler and Prantl's Die Naturlichen Pnanzenfamilien. 

 I Teil. 2 Abteilung. 46 Lieferung. 101 1890. 



I. Wolle, F. Fresh Water Algae of the United States. 114. 1887. 



I. Wood, H. C. Jr. A Contribution to the History of the Fresh- 

 Water-Algae of North America. 211. 1872. 



EXPLANATION OF PLATES. 



Plate XXXI. 



Fig. 1. Pebble "1" from Bellefonte spring, two-thirds natural size. 



Thalli forming an almost continuous stratum. 

 Fig. 2. Pebble "2". Thalli forming isolated discs. 



Plate XXXII. 



Fig. 1. Portion of mature thallus in Pilinia stage. Row of plate cells 

 bearing upright filaments the terminal cells of which are de- 

 veloping gonidangia. (X 300). 



Fig. 2. End of branch showing dichotomous branching like that of 

 a Chaetophora. (X 300). 



Fig. 3. Another example of dichotomous branching. (X 300). 



Fig. 4. Bristle terminating upright filament. (X 300). 



Fig. 5. Bristle developed directly from basal cell. (X 300). 



Fig. 6. Branch showing how vegetative cells taper down to width of 

 bristle. (X 300). 



Fig. 7. Branch showing cells with contents dividing up into megazoo- 

 spores. (X 300). 



Fig. 8. Reproductive cell given off from upper portion of filamentary 

 cell at right angles to filament. (X 300). 



Fig. 9. Similar cell given off from lower portion of filamentary cell. 

 (X 300). 



Fig. 10. Cell containing but one megazoospore. (X 300). 



Fig. 11. Cell containing two megazoospores. (X 300). 



Fig. 12. Cells showing spores crowded together. (X 300). 



Fig. 13. Cell containing four megazoospores. (X 300). 



Fig. 14 and 15. Gonidangia appearing large and roomy. (X 300). 



Fig. 16. Gonidangium appearing crowded. (X 300). 



Fig. 17. Megazoospores. (X 300). 



Fig. 18 and 19. Sporiferous branches. (X 300). 



Fig. 20. A crystal plate of calcium carbonate showing apertures made 

 by Pilinia filaments around which the lime is secreted. (X 300). 



Fig. 21. A transverse section of crystal plate. (X 300). 



Fig. 22. Branch with crystal fragment in natural position. (X 300). 



Fig. 23. Branch showing enlarged terminal cells. (X 300). 



Fig. 24. A group of cells, terminated by a bristle, which may be a sporife- 

 rous branch. (X 300). 



Plate XXXIII. 



Fig. 1. Portion of mature thallus in Stigeoclonium stage. (X 287). 

 Fig. 2. Upper portion of primary filament showing ordinary elongated 



cylindrical cells alternating with groups of branch-bearing 



short cells. (X 160). 



