13 



Our species of Isoetes appear to be very sensitive to salt water, 

 and I have been unable to find any under its direct influence, save 

 a few plants of Engehnanni in a mud hole near a dyke next the 

 silt marsh, where inundated only by the highest tides. 



8b. I. ECHINOSPORA ROBUSTA Engelm. 



Stouter, with 25-70 leaves, bearing more stomata. 



So far as herbarium specimens are concerned, this differs from 

 llraunii only in the above characters, but the collector who has a 

 general idea of Isoetes, can usually determine when he has this va- 

 riety, by its appearance. It must manifestly differ in more than size, 

 or a plant might be Braunii one year and robusta the next. Though 

 it is impossible to separate all small plants with certainty, a goodly 

 percentage can be so separated by the appearance of the plants, but 

 it is difficult to satisfactorily define these differences in a descrip- 

 tion. 



Lake Champlain, Pringle; Epping, N. H., A. A. Eaton. 



8c. I. ECHINOSPORA BooTTii (A. Br. ) Engelm. 



Leaves io-i2.5cm long, stiffly erect, of a soft, delicate green : 

 spinules of spores long and slender. 



Not certainly known except from Boott's original localities near 

 Boston. 



8d. I. ECHINOSPORA MURICATA (Durieu) Engelm. 



Leaves 10-15, ver >" slender, the submersed ones i5-4ocm. long, 

 ascending, in spirals, stomata few : spores 400-480 ft with slender 

 spinules often mixed with short or elongated crests. 



After the fall of the water in summer, the long leaves disap- 

 pear, and are succeeded by short, bright green ones 5-7011. long. 

 In this state the plants would not be taken for the same unless the 

 transition had been observed. There is a specimen from Boott's 

 herbarium, collected in this stage, in the National Herbarium. 



Maine : Moosehead Lake, Harvey; various localities, Fernald. 

 New Hampshire : Kingston, East Kingston, Newton, Epping, New- 

 market, A. A. Eaton. Vermont: Norwich (fide Dodge). Massa- 

 chusetts : Woburn creek and Abajona river, Boott. Connecticut : 

 Groton, Graves. 



9. I. EATONI Dodge. 



The largest New England species, exceeded in size by none 

 now known in the world, and equalled only by Engelmanni valida 



