AGRICUI.TURAL BOTANY, ClIK^MISTRV AND PIIVSIOI.OCtY OF PLANTS IO95 



quantity of zyniogene constantly diminishes and that of enzyme increases; 

 consequently the action of the fresh juice will be stronger, but during stor- 

 age it will no longer increase, and as the intensity of activity depends on 

 the continual formation of enzymes by the zymogenes, the weakening of 

 the action will be evident. These considerations lead to the following con- 

 clusions ; the nearer spring approaches, the more the action of the freshly 

 expresses juice of the tubers will gain in intensity ; on the other hand, the 

 activity of the juice prepared in winter increases but little during storage, 

 but is maintained for a long time ; the activity of the juice prepared later 

 increases rapidly, but is of shorter duration : finally the activity of the juice 

 prepared towards the end of spring shows no increase and becomes less 

 and less lasting. 



Other investigations have brought out the fact that the proportion 

 of amylase in the potato (ii'' the freshly prepared juice) is dependent neither 

 on the variety nor on the soil, but depends on complex factors the elucidation 

 of which requires further research. 



The activity of the amylase is almost entirel}- independent of the size 

 of the tubers. 



Finally it was ascertained that, between the tubers of healthy plants and 

 those from plants suffering from leaf curl, there is no correlation in the ab- 

 solute val^^eofthe amylase content ; on the other hand, the ratio enzyme to 

 zymogene differs in healthy and in diseased tubers. In the health}' potato 

 there is comparatively more zymogene, and therefore more of it m reserve, 

 than in the diseased ones ; the activity of the juice of the healthy tubers 

 is stronger and more constant than that of the diseased tubers. These in- 

 vestigations therefore confirm the observations according to which the 

 curl of the potato leaf is accompanied, not only by mycological, but also 

 by chemical transformations. These researches likewise refute the thesi."? 

 of Massee, according to which, the quantity of amylase is less in the selected 

 potato and consequently resistance to disease would be weakened by selec- 

 tion ; if this were true, the amylase content in the diseased potatoes should 

 also be less. Contrary to this view, however, the observations of the writers 

 agree in their general character with those of Doby, inferred from the chem- 

 ical composition of the healthy and diseased tubers, and the ratios of 

 concentration of their oxydases, according to which the proportion of the 

 enzyme hydrolysing starch is not in direct relation to the state of health. 

 These experiments have shown that changes indeed take place but they are 

 of so subtle a nature that only minute analyses could make them clear. 



Further studies are required to elucidate such questions as to whether 

 the chemico-pathological changes are brought about by pathogenic plant 

 parasites, and to what extent the optimum of amylase and the activation of 

 the latter by foreign substances differ in healthy and in diseased tubers. 



