Note on Micrasterias americana. By W. M. Maskett. 9 



to be accidental, and is here not taken into consideration. The first 

 group would include Nos. 1 to 6 ; the second Nos. 7 to 14. Even 

 then, when a plant is found which will lessen the apparently more 

 distinct gap between No. 6 and No. 7, the two groups would be 

 merged into one. 



There are, however, two other considerations which seem to me to 

 forbid the subdivision into only two groups. The first is the presence 

 or absence of serrations on the middle or terminal lobe ; the second 

 is the shape of the lateral lobes and lobules. Whilst anxious, as I 

 remarked just now, for simplification of species and varieties, I believe 

 the convenience of students and observers will be consulted by em- 

 ploying subdivision wherever clearly marked, just as a farmer finds it 

 convenient to separate shorthorns from Devons, or Leicesters from 

 Cheviots. A glance at the accompanying figures will show that there 

 are three different shapes of the lateral lobes and lobules, and three 

 different characters of the edges, whether all round or on the median 

 lobe. I propose therefore the following arrangement as probably 

 correct, and at the same time likely to help a student to identify or 

 to allocate correctly any plant which he may find agreeing with the 

 series. 



Micrasterias americana Ealfs. 

 * Lateral lobes thick, lobules short. 



1. Forma genuina Ealfs. 



2. „ integra Turner (forma b Babenhorst). 

 o. „ recta Wolle. 



4. „ spinosa Turner (MS.). 



5. „ Ralfsii Turner (forma ft Ralfs) MS. 



6. „ major Wills. 



* * Lateral lobes with directly-tapering lobules : sides of 

 median lobe smooth. 



7. Forma excelsior Wallich (Turner MS.). 



8. „ Mahabuleshwarensis Hobson. 



9. „ Wallichii Grunow. 



10. „ Wallichii forma suecica (Turner MS.) 



* * * Lateral lobes with sinuous or flask-like lobules : sides 

 of median lobe smooth. 



1 1 . Forma Hermanniana Eeinsch. 



12. „ jijiensis Macdonald (1856), perhaps. 



* * * * Lateral lobes with flask -like lobules ; sides of median 

 lobe serrated. 



13. Forma ampullacea Maskell. 



* * * * * Lateral lobes with flask-like lobules : margins of all 

 the lobes smooth. 



14. Forma ampullacea var. /3 Spencer. 



