APPENDIX. 103 



this period of development, when the power of 

 the roots is limited ; as also of lengthening it when 

 the extent and power of the roots are increased. 



" We observe in nature, that plants with feebly- 

 developed roots often have a weak, sickly 'aspect, 

 but yet come to maturity in flower and fruit sooner 

 than stronger individuals, well furnished with roots. 



" 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 influ- 

 ence 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 coloured 

 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 de- 

 voted to it. Hitherto the whole cultivation con- 

 sisted in clearing off weeds, and hoeing up the 

 earth round the stems. Both of these measures 

 are indeed necessary, but they are not alone suffi- 

 cient ; for the plant is cultivated, not on account of 

 its fruit, but for the sake of its tubers, and our 

 treatment should be modified accordingly. 



