Cultural First Principles. 



By G. S. EOIJLGEE, F.L.S., F.G.S., late Professor of Natural History in the 

 Agricultural College, Cirencester. 



V. EooT AND Stem. 



{Continued from facje 533.) 



Plants take in their fluid nutriment mainly by their roots ; that 

 which is gaseous mainly by their leaves. The stem is physiologically 

 little more than a connection between the root and leaf systems. 



The roots of plants, though sometimes produced from the leaves 

 or branches, as in the growth of cuttings and layers, when they are 

 termed " adventitious," are normally formed from that part of the 

 embryo of the seed, or " chit," which is called the radicle. 



Eoots require a moist medium for their growth, and do better in 

 darkness. They increase chiefly in length by the growth of cells 

 just behind their apex, which is pushed forward like the shield used 

 in tunnelling. 



Some trees have what are known as proliferous roots, that is, roots 

 which will produce buds : such are the plum, apple, poplar, and haw- 

 thorn, which may therefore be propagated by " root cuttings." 

 Flowering plants are divided into two well-marked groups, known 

 as dicotyledons and monocotyledons, all our forest trees belonging to 

 the first division. These (dicotyledons) are characterized by having 

 tap-roots, the wood of their stems increasing externally by the addition 

 of new concentric " rings " of growth, which in our climate gene- 

 rally each represent a year, by having leaves the veins of which 

 form a network, generally somewhat irregular, by having four or 

 five sepals to the calyx and four or five petals to the corolla, and 

 by having two lobes or seed-leaves to the embryo of their seeds, 

 which, being known as cotyledons, account for their name. The 

 monocotyledons, on the other hand — of which we may take the 

 lily, the asparagus, the palm, and the wheat as examples — have no 

 tap-root, have no rings of wood in the stem, but have their timber 

 harder near the circumference than in the centre, have the veins 

 of their leaves regularly parallel, have their petals, or other floral 

 organs, in threes, and have only one cotyledon. 



The tap-root, then, of a dicotyledonous tree, with which we are 



