232 SUMMARY OF CURRENT RESEARCHES RELATING TO 



a dilute solution of potassa, produciug a soluble pectate which can be 

 again decomposed by acids. 



6, 7. The Nitrogenous stihstances contained in vegetable tissues are 

 dissolved by alkalies ; and the Inorganic substances constitute the ash 

 after calcination. 



In the most complicated of vegetable tissues, woody tissue, all 

 these substances except No. 6 can be discriminated by using the tests 

 above mentioned. The following is a resume of the action of the 

 reagents named : — Dilute cold hydrochloric acid decomposes calcium 

 pectate, setting pectic acid free, which can then be again dissolved by 

 alkalies. Dilute boiling hydrochloric acid transforms pectose into 

 pectine, which may be precipitated by alcohol. The ammoniacal 

 copper (Schweitzer's) reagent dissolves cellulose. Boiling hydrochloric 

 acid renders paracellulose soluble in the cojjper reagent. Bihydrated 

 sulphuric acid dissolves the cellulose-substances. Dilute boiling 

 potassa dissolves cutose. Potassa with additional pressure dissolves 

 vasculose. Dilute nitric acid renders vasculose soluble in alkaline 

 solutions. 



Chemical Composition of Vegetable Tissues.* — E. Fremy and 

 Urbain have made a series of observations on the chemical constitution 

 of the substances named in the preceding article, chiefly as regards 

 the vascular tissues of plants. For exact details of the numerous 

 analyses made the article itself must be referred to. The following 

 are some of the more general results deduced. 



In woods the proportion of vasculose increases with their hardness 

 and density. The proportions of cellulose and paracellulose vary in 

 stems ; pine-wood appears to be composed exclusively of paracellulose 

 and vasculose. The parenchyma of the pith often contains consider- 

 able quantities of pectose and calcium pectate. Cork consists partly 

 of a peculiar substance called by M. Chevreul " suberine," and 

 composed of cutose and vasculose. In leaves and petals the paren- 

 chyma consists of cellulose and pectose, the vascular bundles and 

 vessels of vasculose and paracellulose, and the epidermis of cutose 

 and paracellulose ; the utricular tissue of petals is composed 

 almost entirely of cellulose, their spiral vessels almost entirely of 

 vasculose. 



In fruits, the epicarp, mesocarp, endocarp, and seed were analysed 

 separately. The epicarp, or skin, of such fruits as the apple is a 

 complex structure composed of three layers ; the outermost layer 

 consists of cutose, the middle one of vasculose, and the innermost of 

 paracellulose. The composition of the endocarp is very nearly that 

 of wood, cellulose combined with paracellulose and vasculose ; the 

 vasculose sometimes makes up more than half the weight, the endocarp 

 being then extremely hard. The cells of the mesocarp are composed 

 of cellulose, often associated with i)ectose. The vessels are composed 

 principally of vasculose. The stony concretions of pears are formed 

 of a combination of vasculose and cellulose. The perisperm of seeds, 

 when the starch and the nitrogenous and oily substances have been 



* Aun. Sci. Nat. (Bot.) xiii. (1882) pp. 360-82. 



