ULVACE.E. 



[ 660 ] 



UREDINEI. 



ULVACE^. A family of Confervoid 

 Algae. Marine or freshwater Algae, consist- 

 ing of membranous, expanded, saccate or tu- 

 bular, sometimes filiform fronds, composed of 

 spherical or polygonal cells, united together 

 firmly into layers, either single or double. 

 Reproduced by roundish spores formed from 

 the whole contents of cells, or by ciliated 

 zoospores formed in twos, fours, or many in 

 each cell. British genera : 



I. ULVA. Frond plane, simple, or lobed, 

 formed of a double layer of cells closely 

 packed, producing zoospores. 



II. ENTEROMORPHA. Frond hollow, 

 simple or branched, of a single layer of cells 

 closely packed, forming a sac or tube ; with 

 zoospores. 



III. MONOSTROMA. Frond flat or sac- 

 cate, simple or lacerate-lobed, forming a 

 single layer of cells, which are scattered in 

 a homogeneous membrane ; with zoospores. 



IV. PRASIOLA. Fronds membranous, 

 lacerate-lobed, formed of a single layer of 

 cells arranged in simple or compound lines, 

 or in groups multiple of four. Spores from 

 the whole contents of cells, motionless. 



V. SCHIZOGONIUM. Fronds filiform, 

 dilated here and there into flat ribands con- 

 taining two or four rows of cells. Spores 

 formed from the whole contents, motion- 

 less. 



ULVINA, Kiitz. A supposed genus of 

 Algae, founded on the " mother" of Vinegar. 

 (See VINEGAR PLANT). 



BIBL. Kiitz. Sp. Alg. p. 147- 



UMBILICARIA, Fe'e (Gyrophora, Ach.). 

 A genus of Lecidinese (Gymnocarpous Li- 

 chens). U. pustulata grows on rocks in 

 various parts of Britain. It is remarkable 

 for the tubercles or hollow papillae occurring 

 on its surface. The apothecia are flat, and 

 at first black, at length tuberculate. Sper- 

 mogonia also occur, in the form of little 

 tubercles containing a nucleus of densely 

 packed sterigmata, enclosed by a thin black 

 rind. The species in which the disk of the 

 apothecia is concentrically plicate form the 

 proper Gyrophorce of Ach. ; they occur on 

 mountain rocks. 



BIBL. Hook. Brit. Flor. ii. pi. 1. p. 223; 

 Tulasne, Ann. des Sc. nat. 3 ser. xvii. p. 207. 

 pi. 5. figs. 5-12 ; Schaerer, Enum. crit. p. 25. 



URATES. See URIC ACID and URATES. 



URCEOLARIA, Ach. A genus of Par- 

 meliaceae (Gymnocarpous Lichens), included 

 under Parmelia by Fries, but agreeing in 

 almost every particular with LECANORA. 

 U. scruposo, the commonest species, grows 



on heaths, walls, and rocks. The disk of the 

 apothecia is black, and the border crenated. 

 The spores are cellular or multilocular (PI. 

 29. fig. 17). The spermogonia are scattered 

 over the thallus, sometimes in the outer wall 

 of the (thallodal) border of the apothecia ; 

 they are very inconspicuous, on account of 

 the light colour of their ostiole. 



BIBL. Hook. Brit. Flor. ii. pt. 1. 

 p. 175; Tulasne, Ann. des Sc. nat. 3 ser. 

 xvii. p. 172. pi. 4. figs. 5-14 ; Schaerer, Enum. 

 crit. p. 85. 



URCEOLARIA, Duj. A genus of Infu- 

 soria, consisting of U. stellina, D. (= Tri- 

 chodina pediculus, E.), and three doubtful 

 species described by Miiller. 



BIBL. Dujardin, In/us. 525. 



URCEOLARINA, Duj. A family of In- 

 fusoria. 



Char. Body variable in form, alternately 

 top-shaped or hemispherical, or globular, 

 sometimes ciliated all over, furnished at the 

 upper and anterior end with a marginal row 

 of very large cilia, spirally arranged, and 

 leading to the marginal mouth ; sometimes 

 swimming, sometimes temporarily fixed by 

 means of the cilia of the posterior end. 



This family includes the genera Ophrydia, 

 Stentor, Urceolaria, and Urocentrum. 



BIBL. Dujardin, Infus. 518. 



UREA. This substance occurs normally 

 in the urine of man and the carnivora, in 

 small quantity in that of the herbivora ; also 

 in the amniotic liquid, and the vitreous and 

 aqueous humours of the eye. Pathologically, 

 it is found in the blood, dropsical effusions, 

 vomited liquids, and doubtfully in the saliva, 

 the bile, and perspiration. 



When pure, it forms colourless four-sided 

 prisms, sometimes longitudinally striated, 

 and with one or two oblique terminal facets. 

 The crystals are readily soluble in water and 

 alcohol, but not in pure aether. 



When nitric or oxalic acid is added to a 

 solution of urea, the nitrate or oxalate sepa- 

 rates in the crystalline form. 



The nitrate of urea, when rapidly formed, 

 consists of irregularly aggregated scaly cry- 

 stals (PI. 9. fig. 18 c) ; when more slowly 

 formed, rhombic or hexagonal plates, or di- 

 stinct prisms (PL 9. fig. 18 , 6). The cry- 

 stals of the nitrate of soda (PI. 6. fig. 19) bear 

 some resemblance to those of the urea salt. 



The crystals of the oxalate of urea somewhat 

 resemble those of the nitrate, the rhombic 

 form being evident. 



BIBL. That of CHEMISTRY, Animal. 



UREDINEI. Since the article Caeomacei 



