334 BOTANY. 



ranged under three tribes ; our more common species only are given 

 below. 



Tribe A. Monarthrodactylcp, with the terminal segments of the 

 leaves one-colled. 



N.flcxttis, N. translucent, N. gelatinosa. 



Tribe B. Diartlirodactyla, with the ultimate segments of the 

 leaves two-celled. 



N. gracUis, N. tenutssimti. 



Tribe C. Polyartkrodactylas, with the ultimate segments of the 

 leaves three to six-celled. 



N. cnpUlata, N. inti'icata. 



The genus Tolypella contains about a dozen known species, most of 

 which are American. 



Order Chareee. In this order the atom and leaves are sometimes 

 naked, and sometimes corticated ; the leaves are in whorls of six to 

 twelve, and their bracts or leaflets are always one-celled. The sporo- 

 carps arise upon tlie upper side of the leaves, and each has a crown of 

 one whorl of five cells. 



These plants resemble the Nitelleue in size and habit. The species 

 aro separated into two genera, Lyc7mothamnus and Cfiara. The former 

 has no representatives in America; it may be distinguished by the an- 

 theridia being by the Bide of the carpogonia instead of below them, as 

 is the case in Chara. 



The species of Cftara are arranged under three tribes ; there are 

 about a dozen representatives in America, the more important of which 

 are here given. 



Tribe A. Astephana, with no circle of stipules. No American 

 representative. 



Tribe 2t. Haf&otbphanet, with a circle of stipules consisting of a 

 simple series of cells. 



Ch. coronata, Oh. Hydropitys. 



Tribe C.Dip J otephanix, with the stipular ring double. 



Ch.f<Ktida, Ch.fragttix, Ch. gyinnopns. 



(b) The genus Chra is a very old one ; some species occur in the Sec- 

 ondary (Jurassic) strata, and in the Tertiary (of Europe) they are very 

 abundant, no less than thirty-seven species being recorded by Schim- 

 per.* According to Lesquereuxf no fossil species of Characere have 

 yet been discovered in America, which is a remarkable fact, for at 

 the present time the plants of this group are as abundant here as in 

 Europe, and the sporocarps possess great durability and are likely to 

 be preserved as fossils. 



* "TraitS de Paleoutologie Vegetale," par W. Ph. Schimper, Paris, 

 1869-1874. 



t " Contributions to the Fossil Flora of the Western Territories; 

 Part II., The Tertiary Flora," by Leo Lesquereux, Washington, 1878. 



