AGRICULTURE AND PLANTING. 



On the' Structure of Vegetables. 



concentric layers, surrounding the medulla or pith. We may consider wood as 

 being formed of fibres, more or less longitudinal, connected together by a cel- 

 lular tissue, interspersed with vesicles communicating with each other; which 

 diminish gradually towards the center, where they forrn the pith, 



6. The Medulla, or pith, or innermost substance of trees, is soft and ves[T, 

 cular, and differs from cellular texture by its snow white colour. In young tlfes 

 it is most copious; but, as the plant grows, it diminishes and at length disappears. 

 Thus it is evident that the medulla is necessary in the beginning of the life of 

 plants, but not for its continuation. Perhaps nature reserves a superfluous nutri- 

 tious humour in the medulla, if from any cause the young plant should become 

 dry; that it then may be absorbed and converted into aliment. The pith thus • 

 appears to be the firfl or most essential rudiment of the new plant, like the brain 

 or spinal marrow, medulla oblongata, which is the fipst visible part of the figure, 

 I believe, of every animal faetus, from the tadpole to mankind. Hence it is obvi- 

 ous that the wood, bark, and all the parts ofJigneous or of gramineous vegetables, 

 are but collections o^ fibre and cellular tissue. 



But the grasses, fungi, &c. differ from the ligneous vegetables, as contain- 

 ing a smaller proportior/af ligneous fibres. 



Whatever part of a plant we examine, we observe these and no more. 

 The root, its- ascending stalk, and descending fibre, are one, and not three sub- 

 stances. This reduces the entire vegetable to one body, and what appears in the 

 flower to be many parts, are only the extremities or terminations of the six above 

 mentioned. 



The roots of plants consist of the same parts as the stem, although 

 less conspicuous; they are branches, enlarging the quantity of surface that the 

 plant exposes to the contact of the earth, and constituting, at the same time, its 

 means of mechanical fixation and support. The root imbibes the nutritious juices 

 from the earth, by means of its absorbent pores or oscula, as long as it remaiiut ' 



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