TISSUES AND SIMPLE ORGANS. 81 



a solid cylinder of wood, and not a hollow cylinder, which is the 

 type of a perfect mechanical construction. In fact, Schwendener 

 would probably not have succeeded in proving that dicotyledons 

 as well as monocotyledons have a specific mechanical tissue-system. 

 It must be remembered that in dealing with dicotyledons and coni- 

 fers we are concerned with living jplants, and not with dead models 

 or types for mechanical engineers. The anatomist knows that the 

 older rings, and hence a part of the inner mass of the wood (see 

 heart-wood), at least up to a certain age, serve a wholly dif- 

 ferent function from that of pure mechanics ; they contain living 

 elements, namely, wood-parenchyma and medullary rays, which 

 bear starch during the winter months. The function of storing 

 reserve food^substances, concerning which more Mali be said later, 

 is here of prime importance. Furthermore, since it is generally 

 known that the woody plants of the geologic ages, as well as those 

 of the present time, are of inestimable value to mankind, no one 

 need hesitate in expressing the opinion that there is a general 

 manifestation of a purposeful relation of the various organic king- 

 doms. Such relations are also observed in other domains. 



Let us now proceed farther with the discussion of the anatomical 

 differences between the monocotyledonous stem and the stem of 

 dicotyledons as well as that of conifers. 



The Arrangement of Vascular Bundles.^ — In the monocoty- 

 ledonous stem the vascular bundles lie isolated in the fundamental 

 tissue ; in the dicotyledonous stem they form a cylindrical mantle 

 fused with the cambium. The apparent promiscuous distribution 

 of the vascular bundles of monocotyledons must not be considered 

 as being of any special importance : an arrangement in a series of 

 circles, for example, is frequently noticed. We may designate 

 as fundamental tissue (in partial agreement with Sachs) that 

 which remains after the epidermal tissues, the mechanical and the 

 conducting elements, have been removed ; hence the tissue in which 

 the mechanical and the conducting bundle-elements seem to be 

 imbedded. 



The individual bundle in the mature monocotyledonous stem 

 has no cambium (long-celled prosenchymatous formative tissue) 



' Recent authors still use this expression in the same sense as did the older 

 authors, namely, for tissue-bundles which consist of conducting elements as well 

 as of mechanical elements. 



