42 VEGETABLE PHYSIOLOGY 
cellulose and leaves the framework of the cell apparently 
unaltered ; if consists then, however, not of pure pectose, 
but of a compound of pectic acid with some of the copper of 
the reagent. 
Pectine swells up and dissolves in water, forming a 
viscous liquid which soon becomes a jelly. It exists in 
considerable quantity in many ripe fruits and in some 
mucilages. It gives no precipitate with the neutral acetate 
of lead, but is thrown down by the basic acetate in the form 
of white floceuli. If it is boiled for some hours in water, it 
is converted into parapectine, which is precipitated by 
neutral lead acetate. Further boiling with dilute acids 
converts it into metapectine, which can be precipitated by 
barium chloride. 
The acid series shows peculiarities similar to those of the 
neutral one. Its most insoluble member is pectic acid, which 
will not dissolve in water, alcohol, or acids ; it forms soluble 
pectates with alkalies, and insoluble ones with the metals 
of the alkaline earths, of which calcice pectate is the most 
widely distributed. It dissolves in solutions of alkaline 
salts, such as the carbonates of sodium and potassium, 
alkaline phosphates and most organic ammoniacal salts, 
forming with them double salts which gelatinise more or 
less freely with water. Its solution in alkaline carbonates 
is mucilaginous, but when ammonic oxalate is the solvent 
it is perfectly limpid. 
The member at the other end of the series is meta- 
pectic acid, a body with an acid reaction, freely soluble in 
water and forming soluble salts with all bases, especially 
those of calcium and barium, which precipitate pectic acid. 
Metapectates are coloured yellow when they are warmed 
with an excess of alkali. This body and its compounds 
are probably very prominent in the gums; when ‘acted 
on by dilute sulphuric acid they split up, one of their 
products being a crystallisable dextro-rotatory sugar which 
is apparently arabinose. Metapectic acid does not form a 
jelly, its solutions always being limpid. 
