500 BOTANICAL GAZETTE [june 



32. Wood, H. C, Contributions to the history of the fresh water algae of 

 North America. Smithson. Contrib. 19:53-262. pis. 21. 1874. 



33. York, H. H., Sexuality of Spirogyra. Science N.S. 38:368-369. 1913. 



EXPLANATION OF PLATES XXHI-XXV 



PLATE XXIII 



* 



Fig. i. — Conjuguee majeure (princeps), in cross-conjugation; copy 

 Vaucher, pi. IV, fig. 3 ; Spirogyra nitida. 



Fig. 2. — Conjuguee portiquis Vaucher, in cross-conjugation; copy 

 Vaucher, pi. V, fig. 1 ; Spirogyra porticalis (MeulL) Cleve. 



Fig. 3. — Conjuguee condensee Vaucher, in cross-conjugation; copy 

 Vaucher, pi. V, fig. 2; Spirogyra condensata (Vaucher) Kutz. 



Fig. 4. — Conjuguee renjlee Vaucher, in cross-conjugation; copy Vaucher, 

 pi. V, fig. 3; Spirogyra inflata (Vaucher) Rabenh. 



Fig. 5. — Spirogyra gracilis in cross-conjugation; copy West (29) pi. V, 

 fig. 81. 



Fig. 6. — Zygnema intermedium Hassall, in cross-conjugation; copy 

 Hassall (17) pi. 38, fig. 8; Spirogyra Weberi Kutz. 



Fig. 7. — Spirogyra protecta and 5. majuscula hybridizing; claimed to be 

 in cross-conjugation; copy of Bessey (4). 



Fig. 8. — Zygnema orbicular e Hassall, figured in cross-conjugation; copy 

 Hassall (17) pi. 19, figs. 1, 2; Spirogyra maxima (Hass.) Wittr. 



Fig. 9. — Schematic drawing of " false cross-conjugation" as observed by 

 the writer. 



PLATE XXIV 



Fig. 1. — Microphotograph of material mounted in glycerine and unstained; 

 X225. 



Figs. 2-7. — Microphotographs of material mounted in glycerine, and 

 stained with iodine and Magdala red; X225. 



plate xxv 



Figs. 1-19. — Schematic drawings of cases of cross-conjugation observed 

 by the writer. 





