348 SCIENCE PROGRESS. 



the walls of the cells of which consist in large part of them. 

 He held that the mineral salts were intercalated with other 

 substances in the body of the cell-wall. 



In a latter paper of Fremy's (lo) written in 1848, he 

 o-ives some account of his researches on the localisation of 

 the bodies, which in his earlier work he had only indicated 

 as existing in plant tissues. The hitherto unnamed sub- 

 stance he calls pedose, and declares it to be a constituent 

 of the membrane so closely connected with the cellulose, and 

 so easily changed by various reagents, that he had found it 

 impossible to separate the two. Like cellulose it is insoluble 

 in water. Fremy found it in the cell-walls of green fruits, 

 such as the apple ; in those of the roots of many plants 

 especially such as are succulent, like the carrot and 

 turnip ; also in the fibres of the cortex of the axis. The 

 pectine of other authors he considers to be a derivative of 

 pectose. 



Mulder extended the localisation of pectose to the col- 

 lenchyma, and the thin-walled parenchyma of Opuntia 

 Brasiliensis, and says that it occurs also in the external 

 parts of the thickened walls of the laticiferous vessels or 

 cells of Euphorbia Caput- Medusa'. Referring to Payen's 

 researches he suggests that the pectic acid and calcic pectate 

 of the latter are derivatives of pectose. Harting (11) suggests 

 that the thickening matter of collenchyma, bast fibres and 

 many other thickened parenchymatous cells, as well as the 

 substance of most thin-walled cells consists of pectates or of 

 pectose, which he supposes to be isomeric with pectic acid. 

 Both these writers point out that while cellulose gives a blue 

 colour in treatment with iodine and sulphuric acid pectose 

 remains uncloured under the same conditions. 



These views, however, did not remain unchallenged. 

 Other writers, among whom may be mentioned Poumarede 

 and Figuier, denied the existence of pectic acid and con- 

 sidered that the wall is essentially homogeneous at first if 

 not always, and that pectose and cellulose are essentially 

 identical. 



The substance forniino^ the middle lamella beino: most 

 easily recognisable and the latter layer being in so many 



