184 OBSERVATIONS ON THE DISEASES OF PLANTS 



success, SO also in pathological researches we must direct our 

 attention exclusively to the alterations which the individual cells 

 exhibit. In every living cell the substances proper to it are 

 arranged on one simj)Ie plan. The wall of tlie cell is formed of 

 firm, perfectly insoluble cellulose, which, after it has been pene- 

 trated witli this or tiiat matter, and has in consequence lost its 

 purity, is in a condition to exhibit different appearances on the 

 application of re-agents, but abstractedly always the same, and 

 that a non-nitrogenous substance remains, in which, together 

 with carbon, hydrogen and oxygen are present in the proportions 

 in which they constitute water. This cell-wall is lined within by 

 a coat of greater or less thickness, either yellowish or free from 

 colour, consisting of a semi-tluid, somewliat coagulated, gela- 

 tinoso-granular substance, wliich is formed of a proteinous matter 

 rich in nitrogen, and called by II. v. Mold* the primordial sac. 

 Finally, the inner cavity of the cell contains a highly mixed 

 fluid, the medium of whose fluidity is water, in which a few nitro- 

 genous, i^roteinous compounds are present, together with many 

 which are non-nitrogenous, as gum, sugar, pectin, &c., soluble 

 salts, and in a fixed form starch, inulin, and crystals. 



The relation of the greatest consequence as regards the life of 

 the cells seems to be that of the nitrogenous lining to the other 

 substances, especially the non-nitrogenous, and the vigorous 

 health of the cells to depend entirely on the normal condition of 

 this stratum. When the cell is old and begins to perish (as for 

 instance in the wood-cells), tiiis coat gradually disappears, or is 

 so closely united with the cell-:wall tliat it becomes inseparable, 

 while at the same time it penetrates it in a soluble state, and thus 

 by degrees the original reaction on the cellulose is perfectly 

 masked by the constantly increasing re-action on the proteinous 

 combinations. 



If we now examine the first deviations from normal phenomena 

 which are exhibited in the occurrence of internal diseases, as for 

 instance in smut (^Uredo segetmit), in decay, as in the stems of 

 Cacti, juicy fruits, &c., or in the potato murrain, we find in 

 every case that the nitrogenous lining of tlie cells first becomes 

 discoloured, assumes a darker tint, a firmer consistence, a more 

 evident granulation, and that it begins at the same time to per- 

 colate and saturate the cell-wall, so that it ceases to exhibit its 

 pure reaction on the cellulose. These phenomena are so general 



* It is matter of regret that the best organic chemists are so little agreed 

 as to the normal constitution of cells. Schleiden's view is so much more 

 simple than that which regards the proteinous lining as the original cell, 

 that it bears the stamp of truth about it. Mulder's admirable work is, in 

 our opinion, impaired very materially by his trusting so much to the fancies 

 of Hartiff.— Tr. 



