46 APPENDIX. 



" In perennial plants we observe a second effort, which is directed towards 

 preparing and storing up nutritious matter, for the consumption of the plant. The 

 preparation of this nutriment is effected by the physiological action of the leaves, 

 under the influence of the roots. The stronger and larger the former are, the 

 more is this preparation of food delayed. 



" The nutritious matters are stored in the colored stratum of the bark in shrubs 

 and trees, and in the tubers in the potato and salep plants. Not only, however, 

 the nutrient matters, but also the cells, owe their origin to the physiological action 

 of the leaves. 



" On considering these things, it follows, that the potato plant requires more 

 care than is usually devoted to it. Hitherto the whole cultivation consisted in 

 clearing off weeds, and hoeing up the earth round the stems. Both of these 

 measures are, indeed, necessary, but they are not alone sufficient ; for the plant is 

 cultivated, not on account of its fruit, but for the sake of its tubers, and our treat- 

 ment should be modified accordingly. 



" The chief points to be attended to, with a view to the attainment of this object, 

 namely, the increase of tubers, are 



1. To increase the power in the roots, and 



2. To check the transformation which occurs in the leaf. 



" We obtain both ends simultaneously, if, in the 5th, 6th, and 7th week after 

 setting the tubers, and in the 4th and 5th week after planting out germs furnished 

 with roots, or at a time when the plants reach the height of 6 to 9 inches above 

 the soil, we pinch off the extreme points of the branches or twigs to the extent of 

 half an inch downwards,* and repeat this on every branch or twig, in the 10th 

 and llth week, no matter at what time of day. 



" The consequences of this check to the development of the stem and branches, 

 is a stimulous to the nutrient matters in the plant in the direction of the increase, 

 both of roots and of the multiplication of the branches of the stem above ground, 

 which not only favors the power of the root, but also strengthens the leaves and 

 stalks to such a degree, that the matters prepared by the physiological action of 

 these parts are increased and applied to the formation ox tubers, while at the same 

 time the direct action of the sun's rays on the soil is prevented by the thick foliage, 

 and thus the drying up of the soil and its injurious consequences are avoided. 



The checking of the transformation in the leaf is equivalent to the interruption 

 of the natural change of the leaves into calyces, corollas, stamens, and pistfls, which 

 is effected at the expense of the nutrient matters collected in the plant ; and these, 

 when this modification of the leaves is arrested, are turned to account in the forma- 

 tion of tubers. 



" Led by these views, I made, in 1846, experiments on single potato plants, 

 carefully marked by pinching off the ends of the branches. They were so readily 

 distinguished in their subsequent growth from the plants beside them, by more 

 numerous branches, larger and darker foliage, that in truth no marking was neces- 

 sary. 



"The produce from these plants of tubers was abundant, and the tubers were 

 perfectly healthy ; while the plants next them which had not been so treated, gave 

 uniformly less produce, at the same time the tubers were rough on the surface, 

 and in many instances attacked with the prevailing disease. This experiment was 

 incomplete, and did not give a positive result, but it was yet encouraging for me. 



" In the middle of April, 1847, an experiment was made on a low-lying field 

 with the round white potatoes, generally cultivated here, a variety which had not 

 suffered much from the disease which first appeared here 1845. The potatoes 

 were planted in the usual way by an experienced farm servant. 



** After weeding them in the end of May, I renewed my experiment by pinching 

 off the points of the branches of every second row, and repeated this in the end of 

 June. The result surpassed all expectations. The stocks of the plants not treated 



* Any one would be bitterly disappointed, who on the principle, that " there cannot be too 

 much of a good ( hing," should take off more than is here recommended, in order to use it as 

 fodder. 



