Page:The New International Encyclopædia 1st ed. v. 19.djvu/886

* UKEAS. 758 UREDINALES. direct action of the chloride of the acid radicle on urea; thus mono-acetyl urea is formed accord- ing to the following equation: NH, NHCOCH, CO +CH3COCl=CO -fHCl NH, NHj Urea Acetyl chloride Acetyl urea. Other methods., however, must be employed for the purpose of introducing more than one acid radicle; thus symmetrical di-acetyl urea is obtained b}- the action of acetamide upon car- bonyl chloride, the reaction taking place accord- ing to the following chemical equation: NHCOCH3 COCI2 -f 2CH3CONHJ =00 -f 2HC1 NHCOCH3 Carbonyl Acetamide Dj-acetyl urea, chloride Among the important ureides is that of car- bonic acid, called allophanic acid. Its form- NH, / ula is CO. It is an exceedingly NHCOOH weak acid, its alkaline salts being decomposed even by carbonic acid. The substance biuret, formed by heating urea somewhat above 150° C. (see Ukea), is the amide of allophanic acid, NH / its formula being CO. See also Uric NHCONHj Acid. When the alkyl ureas ( i.e. the compound ureas formed by replacing hydrogen in urea by alcohol radicles) are boiled with alkalies, decomposition ensues resulting in the formation of amines, am- monia, and carbonic acid. Methyl urea, for in- stance, is thus hydrolyzed according to the fol- lowing chemical equation: NHCH, / CO + HjO ^CHjNHj + NH5 +COj NHj Methyl urea Methylamine. The ureides are more or less readily saponified by the action of alkalies ; acetyl urea, for in- stance, being decomposed according to the fol- lowing equation: NHCOCH3 NH, / / CO + NaOH = CO -f CHjCOONa NH, NH, Acetyl urea Urea ,Sodium acetate. UREDINALES, u-red'i-na'lez (Neo-Lat. nom. pi., from Lat. uredo, blight, blast, from iirerc, Skt. us, to burn). A group of fungi familiarly called 'rusts' which live as parasites on flower- ing plants. It includes very many species, which have complicated and diverse life-histories, but are identified by the teleutospore stage, this being normally a resting period in the life history. The teleutospores are formed after a period of active vegetation and previous to some unfavorable season, as winter. They are one to several-celled, and exhibit such a variety in structure that they serve to distinguish the various genera. After the return of a favorable GEBM TUBE OF A RDST ENTERING A LEAF THHOCGH A STOMA. season each cell of tlie teleutospore produces a short filament (promycelium), each of whose cells, generally four in number, develops a small spore (sporidium) which serves to infect the proper host. There are some rusts, confined to one host, that never produce more than two forms EPST. 1, Section of leal of barberry with cluster cups (nscidia) below and epermogonia above; 2, uredoepores- and one teleutospore: 3. germinating teleutospore with four-celled promycelium. of spores (teleutospores and sporidia), that alter- nate with one another. Most rusts, however, have other forms of spores. Conspicuous among them are the uredospores, somewhat similar to