188 OBSERVATIONS ON THE DISEASES OF PLANTS 



titles than alkalies, and thus the former are increased not merely 

 absolutely, but also relatively. And in our ag-ricultural plants 

 the protein conibiiiations are strikingly increased and indeed 

 modified, by which means they show most plainly tlie influence 

 which has been exercised by tlie manured soil. 



No evil consequences will appear in those parts of the plant in 

 which matters are collected in a dry condition, as in the seeds 

 of our cereals or pulse, or which, as they are formed, are gatliered 

 and consumed. Where, on the contrary, the processes to which 

 parts of plants are subjected after their collection, require for 

 their success a peculiar kind of admixture, a deviation from this 

 will show itself in unfavourable results, as in the use of beet for 

 tlie manufacture of sugar gro\vn on ground newly and richly ma- 

 nured, or of barley for malting from fields which are extremely 

 fertile. Finally, where the parts in question contain constantly 

 a large quantity of uncombined water, where the proteinous 

 matter consists of dissolved albumen or casein, and the normal 

 albumen is perhaps changed througii the influence of cultivation 

 into casein, wliich is still more liable to decomposition, all requi- 

 sites are present for the most manifold putrefaction and decom- 

 position, and tlie most fatal consequences will often arise from 

 slight outward influences, so that it will depend on casual acci- 

 dents in what particular shape the process of destruction may 

 appear. 



This last-mentioned case is exactly what takes place in po- 

 tatoes. The albumen may slightly exceed its normal quantity m 

 the tubers, w hicli are always rich in uncombined water, or may 

 be changed into casein, in consequence of \\hich they are highly 

 subject to decomposition. It may then depend on different out- 

 ward influences whether disease attack the starch especially, as in 

 the wet rot, or the cell walls, as in the dry rot. Now^ if we com- 

 pare the phenomena of the potato murrain with the chemical 

 investigations which have been made, there can be no doubt that 

 the disease actually consists in an abnorm;il proportion of pro- 

 teinous matter in the potatoes, and that tiiis deviation probably 

 answers to a greater quantity of phosphates in the diseased tubers. 

 All potato diseases, of which we have anything like perfect de- 

 tails, are characterised as deviations from the normal process of 

 vegetation which have arisen from cultivation. The dry rot, 

 which was so prevalent in 1842-43, and the disease which since 

 1845 has made such dreadful and such constant havoc in our 

 fields, the only diseases which have been carefully and scientifi- 

 cally examined, are both characterised by a putrefactive process, 

 induced by the abnormal condition of the proteinous matter, 

 afl^ecting in the first the starch, in the second the cell walls. 



In a word, observation shows these diseases to be such as must 



