ISOETACEAE (QUILLWORT FAMILY) 61 



usually scattered among the gynosporangia, the spores 25-30 n (average 28 /*) 

 long, minutely tuberculate. Borders of ponds and streams, s. N. H. to N. J. 

 Our largest species. 



9. I. GravSsii A. A. Eaton. Polygamous; leayes 20-150, 12-30 cm. 

 long, 2-3 mm. in diameter, erect, reddish or dark green ; sporangia with an 

 abundance of light brown cells, $-| covered by the velum ; gynospores 361- 

 405 fj. in diameter, the upper hemisphere depressed, covered with short truncate 

 single columns ; androspores 22-30 xi (average 26 /x) long, high-cristate or tuber- 

 culate. Mass, to Ct. 



10. I. Dodgei A. A. Eaton. Leaves 10-75, the submersed 20-45 cm. long, 

 1.5-2 mm. wide, erect or spiral; emersed 10-15 cm. long, interlaced; stomata 

 many ; bast-bundles usually present ; sporangia sprinkled 



with light cells, ^-\ covered by the velum ; gynospores 



600-675 /x (average 560 /x) in diameter, sparsely beset with 



irregular often anastomosing walls ; androspores 22-44 it 



(average 32 /x) long, wrinkled. (7. riparia, var. canadensis 



Engelm.; /. canadensis A. A. Eaton.) Firm soil, borders ' g p ^ x 15 



of ponds and streams, Me. to B. C., southw. to Pa. FIG. 29. 



Var. Robblnsii A. A. Eaton. Leaves 15-30, 10-38 cm. long, 1-1.5 mm. wide, 

 dark green, rigidly erect, fine-pointed ; sporangia $-J indusiate, covered with 

 brown cells ; gynospores 460-600 xi (average 600 /x) in diameter, thickly beset 

 with anastomosing jagged walls ; androspores 28.7-32.8 xi long, rough or slightly 

 papillose. (/. canadensis, var. Robbinsii A. A. Eaton.) Borders of ponds 

 and streams, s. Mass, to N. Y. 



11. I. Engelmanni A. Br. Leaves 10-40, 1-4 dm. long, 1-2 mm. in diame- 

 ter, light green ; sporangia unspotted, \ or less indusiate ; gynospores 350-570 xi 



(average 450 /*) in diameter, honeycomb-reticulated with 

 thin walls ; androspores 24-29 /x long, smooth. Ponds, 

 etreams, and ditches, mostly in clay, N. H. and Vt. to Pa. 

 and Mo; mostly near the coast. FIG. 30. Var. GRACILIS 

 80 I EnzelmanrU Engelm. is an attenuate form in shade or deep water. 

 Gynospm-e x 15 Var - v ^ lida Engelm. Plants larger ; leaves 50-100, 3-6 dm. 



tall, 2-3 mm. wide, often with 6 bast-bundles ; sporangia 

 ^-f indusiate ; gynospores 320-570 xt (average 480 xt) in diameter ; androspores 

 24-30 xt (average 28 xi) long, blunt-spinulose. N. J. to Va. 



Var. fontana A. A. Eaton. Trunk 1-2 cm. in diameter ; leaves 30-50, 

 15-20 cm. long, 2 mm. wide, erect, with many stomata and six large and sev- 

 eral small bast-bundles ; velum narrow ; sporangia sparingly spotted with light- 

 brown cells ; gynospores 400-750 xi (average 600 /x) in diameter, covered with 

 coarser more or less broken alveolations ; androspores as in the type. Pa. and 

 Va. ; local. 



12. I. melan6poda J. Gay. Polygamous; leaves 15-60, 1.6-3.6 mm. broad, 

 12-45 cm. tall, chestnut or black at base, with numerous peripheral bast- 

 bundles ; sporangia less than indusiate, thickly spotted ; 



gynospores 250-400 xi (average 330 xi) in diameter, nearly 



smooth or with low often confluent tubercles ; androspores 



23-30 xi (average 25 xi) long, spinulose. Inundated fields and 



shallow ponds, 111. and la. to Okl. and Cal. FIG. 31. Variety 31. I. im-iain>|>,i:i. 



PALLIDA Engelm. of the Southwest, occasionally found mixed Gynospore x 15. 



with the type in our range, differs only in having pale leaf-bases. 



13. I. ButlSri Engelm. Dioecious; leaves 8-60, 7.5-22 cm. long, 0.5 mm. 



in diameter, rigid, triangular-setaceous, with wide dissepiments, narrow air- 

 canals, and four stout bast-bundles ; sheaths granular on the 

 backs ; velum none or very narrow ; sporangia mostly spotted ; 

 gynospores 400-630 xi (average 570 xi) in diameter, roughened 

 with very small warts or fragmentary crests ; androspores 28-:>4 xi 



Gynospore x 15 long, coarsely tubercled. Moist hillsides and shallow depres- 

 sions, 111. and Kan. to Tenn. and Okl. Ki<;.:'.2. Var. IMMACUL\TA 



Engelm. is a form without spots on the sporangia, growing with the typical 



form of the species. 



