358 SCIENCE PROGRESS. 



the wall consists in dissolving away the pectose and leaving 

 the cellulose. Sections of the tissue may be boiled for half 

 an hour with two per cent, solution of hydrochloric acid. 

 After repeated washings in water, they should be again 

 boiled for some time in two per cent, solution of the hydrate 

 of potassium or sodium and again washed thoroughly. The 

 tissue will then stain a deep blue with iodine and phosphoric 

 acid, but not with basic stains. 



There is only one substance which behaves like the 

 pectic compounds with basic stains — the gelose of the 

 Algae. This can be distinguished from the former bodies 

 by being soluble in hydrochloric acid diluted with an equal 

 volume of water, but being insoluble in alkalies. 



By means of these methods of procedure, Mangin has 

 ascertained that in Phanerogams, Pteridophytes and Mus- 

 cineae hardly any soft tissue is devoid of pectic bodies in 

 its cell-walls. These are found conspicuously present in 

 parenchyma, collenchyma, bast and meristem tissues, pectic 

 acid and pectose being the compounds generally occurring. 

 Pectic acid, as Payen pointed out, usually exists in the 

 tissues in combination with calcium as calcic pectate. 

 Mangin demonstrated this fact by steeping the tissue, cut 

 into small pieces, in dilute hydrochlorate acid, or preferably 

 in a mixture of one part hydrochloric acid and three parts 

 of alcohol. The pectate was decomposed, the calcium 

 being converted into calcium chloride and the pectic acid 

 liberated. This beino- insoluble was washed with water till 

 all the hydrochloric acid was removed. It was then dis- 

 solved in a weak solution of potassic hydrate or carbonate 

 and the solution filtered. On neutralising with a dilute acid 

 the pectic acid was thrown down in gelatinous flocks. 

 Mangin found, as Payen had done before, that the middle 

 lamella, von Mohl's " intercellular substance," consists almost 

 or quite entirely of calcic pectate, which serves as a kind of 

 cementing medium, joining contiguous cells together. 

 When by any reagent it is dissolved, the cells separate 

 from each other. 



The dissociation of the tissues by the process of dis- 

 solving the calcic pectate can be effected more gradually 



