IN THE SYSTEMATIC STUDY OF THE HIGHER PLANTS. 357 



The wood of the Dicotyledons contains, besides the tracheides, 

 vessels, recognised in the transverse section by larger openings, 

 thick- walled fibres of various kinds and shorter regular- shaped 

 elements or parenchyma. The considerable variety of combina- 

 tions of these elements which is possible accounts for the variety 

 in appearance to the naked eye, but more especially under the 

 microscope, of the wood of dicotyledonous plants. Closely allied 

 species generally show a resemblance in the structure of their wood, 

 and certain characters are often common to genera or groups of 

 genera ; but on the other hand, genera which from every other 

 consideration are regarded as occupying widely removed positions 

 systematically, may be closely alike in the structure of the wood. 

 A striking example occurs in the wood of Drimys, a species of 

 which supplies the drug known as Winter's Bark,* which in its 

 remarkable uniformity of structure resembles the yew. This 

 resemblance has been used in support of the view that the Mag- 

 nolia family, to which Drimys belongs, comes very early in the 

 scale of development of the Dicotyledons and approaches most 

 nearly the Gymnosperm ancestor from which the Dicotyledons 

 may be presumed to have been derived. 



But in view of the fact that the wood-structure in the Magnolia 

 family belongs otherwise to a type which is one of the commonest 

 among the Dicotyledons, one hesitates to use an isolated instance 

 to support so far-reaching a conclusion in phylogeny. At present 

 we can only say that we know too little as to the meaning of these 

 variations in the character of the minute structure of wood, and 

 as to how far they are expressions of relationship or the results 

 of comparatively recent adaptation to environment. But I think 

 I have said enough to show that the microscopist has here a wide 

 field of investigation and an opportunity for work not only of 

 purely scientific but of great economic value. 



An anatomical character which is of value for systematic pur- 

 poses is the presence and character of the receptacles containing 

 secretions of various kinds. The secretion may be contained in 

 epidermal outgrowths of the nature of hairs, the structure of 

 which may be more less characteristic of certain families or 

 genera, as in Pnmula, Pelargonium (the Geranium of gardens), 

 and many members of the Dead-nettle family which owe their 



* This bark was first brought to Europe in 1579, by Captain Winter, 

 who accompanied Sir Francis Drake to the Straits of Magellan. 



