EXPLANATION OF PLATES. 



All of figures on Plates XXXIV-XXXIX, with the exception of the photo-micro- 

 graphs, are photographs of plants floating in water, in aquaria, or in specimen jars. 



Plate XXII. 



Fig. I. Polamogeton am^ricanus, seed, i}2 i-itaesnatiual size. 



Fig. 2. Potamogcton americanus, seedling ^ days old, 1J-2 times natural size. 



Fig. 3. Potamogeton americaniu, seedling 14 days old, ij 2 times nattu'al size. 



Fig. 4. Polamogeton amcricanus, seedling of four months, J , natural size; A, winter buds. 



Fig. 5. Potamogeton americamis. germinating winter bud, natural size; the last two winter buds 

 belated in development. Aquarium specimen, Januarj' 24, 1914. 



Fig. 6. Potamogeton amerieanus, rootstock with winter bud A, natural size. September. 



Plate XXIII. 



Fig. 7. Potamogeton amplifoUus, rootstock, yi natural size; A, A, A, young shoots which continue 

 to grow slowly through winter. November. 



Fig. 8. Potamogeton hcterophyllus, submerged plant, X natural size; A, tuberous rootstock; B, B, 

 submerged shoots; a, b, and c, details of leaves. May 4. 



Fig. 9. Potamogeton heterophyllus , rootstock not tuberous, natural size. July 7. 



Fig. 10. Potamogeton heterophyllus, tuberous rootstock, natural size. July 7. 



Fig. II. Potamogeton heterophyllus, tuberous rootstock, natural size; A, A, incipient shoots 

 November 17. 



Plate XXIV. 



Fig. 12. Potamogeton heterophyllus, typical habit of land form, 1^2 times natural size. Terminal 

 portion of rootstock tuberous. July 7. 



Fig. 13. Potamogeton heterophyllus, terminal portion of rootstock showing tendency to become 

 tuberous, i^ times natural size. July 7. 



Fig. 14. Same, more advanced stage, i^i times natural size. July 7. 



Fig. 15. Potamogeton heterophyllus, aquarium specimen, natural size; A, tuberous intemode placed 

 in aquarium in November; B, B, new shoots and rootstock. January 26. 



Plate XXV. 



Fig. 16. Potamogeton heterophyllus, aquarium specimen, natural size; A, B, C, D, new shoot and 

 tuberous rootstocks in various stages of growth. March 14. 



Fig. 17. Potamogeton heterophyllus, aquarium specimen, natural size. 



Fig. 18. Potamogeton perfoliatus, winter shoot showing elongation of intemodes, natural size; A, 

 leathery scale ; a, detail of scale. June. 



Fig. 19. Growing tips of same. 



Plate XXVI. 



Fig. 20. Potamogeton crispus, recumbent branch, showing development 01 new shoots on old stem, 

 )4 natural size. March. 



Fig. 21. Po^awojc/on cm/'Mj, spicular bur, i_^^ times natural size. Aquarium. July. 



Fig. 22. Potamogeton crispus, denticulate bur, %■ nattiral size ; a, detail of leaf with denticulate 

 base, 2 times natural size; i, line delimiting starch storage. 



Fig. 23. Po/oTOO^e/on cm/;M^, sprouting bur, 1J2 times natural size. March. 



Fig. 24. Potamogeton crispus, denticulate bur with sprout, natural size. Aquarium. July. 



Fig. 25. Potamogeton crispus, spicular bur with sprout, ^2 natural size. Aquarium. July. 



289 



