WILD. Cissus sicyoices and Bajania pleio- 

 neura. 



YAMADOU. An oil expressed from the 

 seeds of Myristica sebifera. 



YAMS. Lindley's name for the Biosco- 

 reacece. 



YANGTJA. A name given by Spruce to 

 a Brazilian plant now referred to Cybistax: 

 which see. 



YAN-SOUN. The Egyptian name for 

 Anise. 



YAOBA. A Caribbean name for Sauva- 

 gesia erecta. 



YAPON. The South Sea Tea, Hex vomi- 

 toria. 



YARI-YARI. A Guiana name for the 

 strong elastic wood of Buguetia quitarensis. 



YARR. A Scotch name for Spergula 

 arvensis. 



YARRAWARA. An aboriginal name for 

 the Black Butt, one of the largest of the 

 Eucalypti of New South Wales. 



YARROW. Achillea Millefolium. 



YARURf. A Demerara name for Paddle- 

 wood, the strong but light and elastic 

 timber of Aspidosperma excelsum. 



YAW- WEED. Morinda Royoc. 



YEAST. See Yeast-Plant. 



YEAST-PLANT. It has long been known 

 that the particles of which Yeast is com- 

 posed germinate, and are multiplied with 

 extraordinary rapidity when placed in a so- 

 lution of sugar kept at a proper tempera- 

 ture. It was therefore at once allowed that 

 the substance was organised, whether be- 

 longing to the animal or vegetable king- 

 dom; and while some pronounced it an alga, 

 others as confidently asserted that it was a 

 fungus. Dr. Hassall and others observed , 

 that a particular mould grew pretty uni- 

 formly on a solution of malt, but we believe 

 that Mr. Hoffmann, in union with Mr. Ber- 

 keley, first watched the growth of single 

 yeast-globules in a drop of water surround- 

 ed by air enclosed in a glass cell, and ascer- 

 tained that a Penicillimn and a Mncor grew 

 immediately from the globules. They were 

 also convinced that these were not the 

 only moulds to which the yeast-globules 

 gave rise. It was clear, then, that yeast 

 consists of a mixture of different moulds 

 in a peculiar condition due to their deve- 

 lopment in a fluid, and that when a fit 

 opportunity offers, these globules are 

 capable of being developed into their ordi- 

 nary form. The globules, however, pre- 

 serve their character without, developing 

 their perfect forms when the fluid in which 

 they float is drained away, and in this con- 

 dition the mass is called German Yeast— a 

 substance largely imported into this coun- 

 try, and on accountof its freedom from the 

 bitter principle of hops, and some peculiari- 

 ties in its action on fermentable substances, 

 often preferred to ordinary fluid yeast. It 

 is a singular fact respecting yeast in this 

 condition, that a sudden fall from a great 



height will sometimes completely destroy 

 its power of vegetating. 



Yeast is of very different qualities, ac- 

 cording to the nature of the liquor in 

 which it is generated; and though there is 

 little difference, if any, to the naked eye, 

 the yeast-merchants distinguish several 

 varieties, which, according to their respec- 

 tive energy and activity, are employed for 

 different purposes. It has not yet been 

 ascertained whether these different varie- 

 ties are composed of the germs of different 

 species of Fungi, or of the same species in 

 different proportions. 



It is often said that yeast works by cata- 

 lysis, but this is merely the substitution 

 of a technical phrase for the simple fact that 

 yeast promotes fermentation. There is no 

 doubt, however, that it acts partly by 

 presenting a large surface over which the 

 fluid is spread, and thus favouring thedisen- 

 gagement of the carbonic acid gas, formed 

 in the process of fermentation, exactly as 

 that gas is set free when a lump of sugar 

 or a piece of bread-crumb is placed in a 

 glass of effervescent wine which apparent- 

 ly has previously parted with all the gas 

 which it contained. It is moreover con- 

 jectured, that as chemical action always 

 takes place when there is an interchange 

 of two fluids of different densities sepa- 

 rated by a membrane, the decomposition j 

 of a fermentable fluid containing yeast i 

 is favoured by this interchange, which is i 

 known to chemists and physiologists under I 

 the names of endosmose and exosmose. 



Substances which are hostile to the 

 growth of fungi, generally, are hostile to 

 fermentation. Hence a mixture of sul- 

 phites of soda, or the ignition of sulphur, 

 are used to arrest the process where it is 

 necessary. 



In the manufacture of wine we have 

 observed occasionally a species of Mucor 

 (M. clavatus) to be developed in large 

 fleecy clouds, to the great improvement of 

 its quality. [M. J. B.] 



YEBLE. (Fr.) Sambucus Ebulus. 

 YELANGA. All Indian name for the 

 Wood-apple, Feronia Elephantum. 

 YELLOW. The colour of gamboge. 



YELLOW-BERRIES. The dried unripe 

 berries of Rhamnus infectorius, imported 

 in large quantities from the South of 

 Europe and the Levant for the use of 

 dyers. 



YELLOW HERCULES. Xantlwxylon 

 clava-Herculis. 



YELLOWNESS. A disease in plants, in 

 which the green parts assume a yellowish 

 colour. The same as Flavedo. 



YELLOW-ROOT. Xanthorrhizaapii folia ; 

 also Hydrastis canadensis. 



YELLOW-WEED. Reseda Luteola. 



YELLOW- WOOD. Xanthoxylon ; also 

 Tobinia. —, CAPE. Podncarpus Thunbergii. 

 — , EAST INDIAN. Chloroxylon Swietenia. 

 —, QUEENSLAND. Oxleya Xanthoxi/la. 

 — , PRICKLY. Xanthoxylon clava-Her- 



