PLATE 21 

 Prasiola mexicana J. Ag. 



Ih ill. Tniv. Calif., no. 911S1, collected near Eugene, Oregon, Vjy Professor 

 A. R. Sweetser, May, 190:5. 



Fig. 1. Habit of typical plant. X 0.5. 



Fig. 2. Surface view of thallus lobe. X 375. 



Fig. 3. Transverse section showing double layer of tetrad-type of aplaiio- 

 spore (?) formation. X 375. 



Fig. 4. Similar section showing both tetra<l and "authcridial " typo of 

 aplanospore (?) formation. X 375. 



Fig. 5. Similar section to that of figure 3, but less regular. X 375. 



Herb. Univ. Calif., no. 91182, collected near Portland, Oregon, by H. A. 

 Foster. 



Fig. (). Transverse section showing single layer of tetrad-type of aplano- 

 spore (?) formation. X .375. 



Fig. 7. Transverse section showing "antheridial" type of aplanospore (?) 

 formation. X 375. 



No. 1545, U. S. Geol. Surv., collected in the Diamond Range, Nevada, by 

 Sereno Watson and type collection of Ulva merismopedioides Wood. 



V'ig. 8. Surface view of lobe of thallus. X 375. 



Fig. 9. Transerve section showing double layer of tetrad-tyi^e of aplano- 

 spore (?) formation. X 375. 



Fig. 10. Similar section showing "antheridial" type of aplanospore (?) 

 formation. X 375. 



Prasiola nevadensis S. and G. 



No. 6507, collected in Crane Creek, Foresta townsite, Mariposa County, 

 California, by W. A. Setchell, June, 1914. 



Fig. 11. Habit of young plant. X 0.5. 



Fig. 12. Habit of young plant. X 0.5. 



Fig. 13. Habit of older plant. X 1. 



Fig. 14. Surface view of lobe of thallus. X 375. 



Fig. 15. Surface view of lobe of thallus. X 375. 



Fig. 16. Surface view of portion of thallus. X 375. 



Fig. 17. Transverse section showing cells probably on the way to aplano- 

 spore (?) formation. X 375. 



Fig. 18. Similar section showing tetrad-type of aplanospore ( ?) formation. 

 X 375. 



All the figures of this plate were drawn by Dr. Helen M. CJilkcy under the 

 direction of W. A. Setchell. 



[304] 



