1922] 



PFEIFFER MONOGRAPH OF THE ISOETACEAE 103 



spore sculpture words prove at times a difficult mode of con- 

 veying an exact picture of the various markings. Recourse has 

 therefore been had to photographs, which will serve to counter- 

 act the shortcomings of verbal description. 



In the case of microspore markings, the point should be borne 

 in mind that in such tiny structures the degree of magnification 

 plays an unusually large role. This is true in much smaller de- 

 gree of the megaspores. The description for microspores has 

 been based on what may be seen with a magnification approx- 

 imating 100 diameters, that for megaspores, about 50 to 60 diam- 

 eters. 



ISOETACEAE Reichb. 



Isoetaceae Reichb. H. G. L. Consp. Reg. Veg. 43. 1828; 

 Dumortier, Anal. Fam.< PI. 68. 1829 ; Bartling, Ord. Nat. PI. 

 13-14. 1830; Endl. Gen. PI. 68-69. 1838-40; Schnizlein, Icon. 

 Fam. Nat. Reg. Veg. 35 . 1843-46; Ledeb. Fl. Rossica 4: 495. 

 1853; Underwood, Our Native Ferns & Fern Allies, 121. 1882; 

 Boissier, Fl. Orient. 5: 746. 1882; Kuhn in Martius, Fl. Brasil. 

 I 2 : 646. 1884 ; Luerrsen, Farnpfl. Deutschl. 845. 1889 ; Kuntze, 

 Rev. Gen. PL 2 : 828. 1891-93 ; Ascherson & Graebner, Syn. Mit- 

 teleur. Fl. 1: 163. 1896-98; Sadebeck in Engl. & Prantl, Nat. 

 Pflanzenfam. I 4 : 756. 1901-02; Small, Fl. Southeastern U. S., 

 ed. 1, 24. 1903, and ed. 2, 30. 1913; Clute, Fern Allies, 207. 1905; 

 Piper, Contr. U. S. Nat. Herb. 11: 88. 1906; Eaton in Gray, 

 Man. Bot., ed. 7, 58. 1908 ; Coulter & Nelson, Bot. Rocky Mts. 

 24. 1909 ; Underwood in Britton & Brown, 111. Fl., ed. 1, 45. 1896; 

 Maxon in Britton & Brown, 111. FL, ed. 2, 50. 1913; Rydb. Fl. 

 Rocky Mts. 1053. 1917. 



Aquatic to terrestrial herbs with a short unbranched, lobed, 

 subterranean axis producing many dichotomous roots and grass- 

 like leaves, the enlarged bases of which contain solitary, sessile, 

 adaxial sporangia, more or less covered by a thin extension of 

 tissue or velum. Sporangia of two sorts, producing large tet- 

 rahedral megaspores and minute powdery microspores, respec- 

 tively. 



ISOETES L. 



Isoetes L. Sp ; PL 1100. 1753; Gen. PL 486, gen. no. 1048. 

 1754; Amoen. Acad. 3:25, gen. no. 1109. 1756; Syst. Nat., ed. 

 10, 1330, gen. no. 1048. 1759; ed. 12, 697, gen. no. 1184. 1767; ed. 



