1885.] 



MICROSCOPICAL JOURNAL. 



231 



sieve, while the diatoms will go 

 through and will float on the surface 

 of the water ; let it stand about a 

 quarter of an hour, ■when the diatoms 

 will have settled on the edge of the 

 plate, and there form a'greenish-black 

 border, which you can take ofl' and 

 put under the microscope. 



ProvisioiiarKey to (lassification of 

 Algjp of Fresh Water. — V. 



BV THE EDITOR. 

 [ Continued from f. 174. ] 



III. ORDER CONFERVOIDEyE Kirch- 

 ner. 



c. Ulvin^. Group 3. 



Synopsis of Ge?tera. 



1. Foliaceous ; cells in a single 



layer. 

 Thallus crustaceous. 



Protodertna^ 69. 

 Thallus attached, erect, leaf-like. 



Prasiola^ 70. 

 Thallus membranaceous, crisped, at- 

 tached or floating. Ulva^ 71. 

 Thallus filiform. Schizomeris^ 72. 



2. Membranaceous, tubular or ves- 



cicular. 

 Thallus vescicular, globular. 



Physodictyon^ 73. 

 Thallus tubular. 



Enteromorpha^ 74. 

 Thallus open or saccate ; cells round- 

 ed, not close. Monostrotna, 75. 



69. Genus Protoderma Kiitzing. 

 Thallus crustaceous, indefinitely 



expanded, closely adherent to the sub- 

 stratum ; cells angular, irregularly 

 arranged, closely connected. Prop- 

 agation unknown. 



70. Genus Prasiola Agardh, 

 Thallus leaf-like, erect, spreading 



from an intricate mass of colorless 

 filaments forming a root-like attach- 

 ment. Cells angular, more or less 

 arranged in groups of 2-8-16, sep- 

 arated by clear spaces. 



Division of cells in two directions. 



[Sometimes the thallus arises 

 from a slender petiole-like attachment 

 and expands into a broad, palmate 

 eaf.] 



71. Genus Ulva Linn. 



Thallus membranaceous, expand- 

 ed, undulately curled or crisped, 

 composed of a single stratum of 

 cells, angular from mutual pressure. 



Division in two directions. Prop- 

 agation by zoospores, 4-8-16 formed 

 in a single cell. 



[ Ulva is a marine genus, not often 

 represented in freshwater. The fronds 

 closely resemble Prasiola^ and it is 

 doubtful whether Prasiola may not 

 be regarded as the fresh-water repre- 

 sentative of Ulva. See also Meris- 

 mopedia.^ 



72. Genus Schizomeris Kiitzing. 



Thallus filiform, cylindrical, attach- 

 ed, cells in a single plane, dividing first 

 in one direction, later in two direc- 

 tions forming groups of four. Frond 

 constricted here and there. 



73. Genus Physodictyon Kiitzing. 

 Thallus vescicular, globular ; cells 



angular. 



74. Genus Enterotnorpha Link. 

 Thallus tubular, branched, attached 



while young, later free ; cells in a 

 single layer forming the tube. Propa- 

 gation by zoospores. 



75. Genus Monostroma Thuret. 

 Frond plane or saccate, simple or 



lobate ; cells somewhat rounded 

 (sometimes quarternate) . 



[The frond may be either flat and 

 open, or in the form of a tube. The 

 cells are not so closely aggregated as 

 in the preceding genera, and they 

 are frequently surrounded by special, 

 hyaline envelopes, enclosing 1-2-4 

 cells. We are not acquainted with 

 the genus, but take the description 

 and figures of Cooke for authority.] 



Family VII. Pithophorace-*; 

 Wittrock. 



Filaments like Cladophora^ but 

 with some of the cells distinctly 

 swelled in their upper part. The 

 spores are formed in such cells, the 

 entire endochrome of the cell passing 

 into the upper, turgid portion, which 

 is club-shaped, leaving the lower part 

 colorless. 



Genus 76. Pithophora Wittrock. 



Character same as the family. 



