GENERAL MORPHOLOGY OF THE PLANT 27 



cryptogams, the roots are generally of a very simple tyjje. In 

 all of them the root may be described as the descending axis of 

 the plant, as its growth is always in the opposite direction to 

 that of the shoot. It may be extremely rudimentary, as in some 

 of the lowest of the Algae or Seaweeds, where it consists only 

 of a single terminal cell, which soon perishes. In these lowly 

 forms the root is only recognisable in the gametophyte. It may 

 be formed of a mass of cells, sometimes tapering and branched, 

 and hardly distinguishable from the thalloid shoot to which it is 

 attached ; or it maybe a long hair-like structure, much resembling 

 the root hairs described as arising on the true roots of thesporo- 

 phyte of the higher forms. 



There are not wanting instances again of plants which bear 

 no primary root at all. Such are the gametophytes of the Liver- 

 worts, the sporophytes of Salvinia and Psilotuin among the 

 Pteridophyta, and of Utricularia, Epipogium, and CoraUorhiza 

 among flowering plants. The functions of the root are in these 

 cases discharged by modifications of other members of the plant 

 body, or by adventitious roots developed after the stem and 

 leaves have been differentiated. 



Section II. — The Shoot. 

 A. The Stem. 



The stem may be defined as that part of the axis which at 

 its first development in the embryo takes an opposite direction to 

 the root, seeking the light and air, and hence termed the ascend- 

 ing axis, and bearing on its surface the leaves and other leafy 

 appendages {fig. 36, t). This definition wiU, in numerous in- 

 stances, only strictly apply to a stem at its earliest development, 

 for it frequently happens that, soon after its first appearance, 

 instead of continuing to take an up\\ard direction into the air, it 

 will grow along the ground, or e^ en bury itself beneath the 

 surface, and thus by withdrawing itself from the light and air it 

 resembles, in such respects, the root, with which such stems 

 are, therefore, liable to be confounded. In these cases, however, 

 a stem can be at once distinguished fi-om a root by bearing 

 leaves. The presence of leaves is therefore the essential cha- 

 racteristic of a stem, in contradistinction to a root, from which 

 such structures are normally absent. 



The appendages of the stem arise as do those of the root in 

 acropetal succession, but unlike the latter their places of origin 

 are very definite. We can distinguish on a stem the points 



