484 SCIENCE PROGRESS. 



they stain the lignified and suberised ones. Such colours 

 are acid green, acid brown, nigrosin, and indulin. It is 

 possible by appropriate treatment with these two groups of 

 stains to obtain double-stained preparations of such cell 

 walls. 



Mangin also describes the action of certain staining 

 reagents which, while staining pure cellulose and the callus 

 of sieve tubes, leave pectic bodies colourless. Such are 

 orseille red A, naphtol black, Congo-red, azo-blue. and 

 benzo purpurin. 



Apart from their behaviour to stains we find a marked 

 difference from cellulose in the reaction of the pectoses to 

 ammonio-cupric oxide solution, in which they are altogether 

 insoluble. They are not stained blue or violet with iodine, 

 even in the presence of sulphuric acid or of the metallic 

 chlorides. When warmed with dilute nitric acid they are 

 slowly oxidised to mucic acid, which can be recognised by 

 its characteristic crystals, whereas the cellulose bodies under 

 similar conditions give rise to oxalic acid. 



Their relations to gums has been investigated by 

 Giraud (45) who says that some of the latter contain con- 

 siderable amounts of them, one yielding more than half 

 its weight of a body insoluble in water, apparently identical 

 with Fremy's pectose. It may, indeed, be that gums may 

 be derived from these pectic bodies present in the cell 

 wall, and not the result of cellulose degeneration. 



The distribution of oily reserved materials is very 

 varied, though as in so many other cases the seed is the 

 most general place of deposition. Many seeds, as that of 

 the castor oil plant, contain as much as 60 per cent, of their 

 dry weight of oil, which is non-volatile. Others contain as 

 little as 2 per cent, and between these limits very varying 

 amounts may be found. When the oil is in great prepon- 

 derance often no other form of carbonaceous reserve 

 material is present ; in cases where but little oil occurs 

 starch is usually found as well, as in so many of the 

 Leguminosse. The Cruciferae as a group often contain oil 

 in fairly large quantity. As a rule nitrogenous reserves 

 in the shape of aleurone grains accompany the oil. 



