THE MOVEMENTS OF FLUIDS IN STEMS. 203 



XXIII. The Movements of Fluids in Stems, considered in relation 

 to the Felling and Seasoning of Timber. By "W. Ramsay 

 M'Nab, M.D., F.L.S., Professor of Botany, Royal College of 

 Science, Dublin. 



Although at first sight the scientific vegetable physiologist may 

 seem to have little in common with the practical forester, still 

 we doubt not both may learn something one from the other. The 

 scientific man may lay down rules for the guidance of the practical 

 man, and often does so with great advantage ; but we think that 

 a humbler sphere may in some cases be a more useful one for the 

 scientific botanist. We cannot ignore the vast amount of empiri- 

 cal knowledge, of knowledge derived from practical experience, 

 that the forester can lay before us ; and we can make ourselves 

 useful by showing that the experience of able practical men is in 

 accordance with what we know and have ascertained by experi- 

 ment in the laboratory, thus placing the empirical knowledge 

 on a scientific basis. By thus combining practice with science, 

 by admitting that the art must be practised before the scientific 

 basis of the art is settled, we may be doing some little service to 

 Arboriculturists if we lay before the Arboricultural Society a 

 short account of the modern physiology of the stem of trees, and 

 thus supplement to a slight extent the important discussion that 

 took place last year on seasoning timber. 



I. The structure of the stem of the Dicotyledon and the 

 Conifer. 



It will be necessary to give a very brief outline of the structure 

 of the stems of such plants as yield our ordinary forest trees before 

 proceeding to the consideration of the physiology of the stem. 

 The section of the stem of a seedling plant made below the 

 cotyledons, and before the foliage leaves have developed, shows 

 the epidermis externally, and surrounding a central mass of 

 cellular ground tissue, in which are placed a few separate fibro- 

 vascular bundles arranged in a circle. The individual fibro- 

 vascular bundle is separable into two parts, namely, the wood 

 portion or xylem of Naegeli, in which the wood-cells, wood-fibres, 

 and wood-vessels are developed, and the bast portion or phloem of 

 Naegeli, in which the bast-cells, bast-fibres, and bast-vessels are to 



