6o 



LECTURE V. 



important part in nature ; and the dense grass of meadows, as well as the ineradi- 

 cable weeds, owe their existence in great measure to the mode of life described. 



In plants provided with runners, the main shoot for the time being, with its foliage 

 leaves and flower-stalks, is developed chiefly above ground. It occurs, however, not 

 rarely that the whole shoot-system of a plant consists of subterranean creeping shoot- 

 axes, from which only the foliage leaves appear above the earth, in order to form 

 products of assimilation in the light; these are carried down through the leaf- 

 stalks, and deposited as reserve material in the subterranean thick shoot-axes. A 

 very perfect example of this occurs in our Bracken fern (Pteris aqtalina), from 

 the subterranean shoot-axes of which only a single large foliage leaf from each 

 bud comes forth each year above ground; similarly also in the Fern Lygodhm, 

 where likewise only the foliage leaves live above ground, and their mid-ribs climb 

 like the stem of a twining plant. It is indilferent, from a physiological point of view, 

 whether the system of subterranean perennial shoot-axes forms a Monopodium 

 or a Sympodium. Thus, a Monopodium arises when the growing points of the 



Fig. 55.— Rhizome of Pteris aquilina. I, II, III the subterranean creeping shoot axes; ss the apex of 

 one of them ; i, 2 to 6 the basal portions of the leaf-stalks ; 7 a young leaf ; * a rotted leaf stalk, the still living 

 basal portion of which bears a bud a III. The fibres covered with hairs are roots, which develope behind the 

 forward-growing apex of the stem. 



subterranean system continue to grow, while the annually renewed sub-aerial 

 shoots bearing leaves and flowers spring from lateral growing points of the 

 subterranean system, e.g. Herb Paris {Pan's quadrifolia). A subterranean Sym- 

 podium occurs, on the other hand, when from the growing point of a sub- 

 terranean creeping shoot there finally arises a sub-aerial foliage shoot or flower 

 stem, which then again disappears; only the subterranean creeping piece of 

 the shoot-axis still remains, and a subterranean lateral bud, growing further 

 in the direction of the previous subterranean bud, again developes at its end 

 into a transitory leaf-shoot. The subterranean system of shoot-axes then consists 

 of numerous basal pieces of diff'erent shoot-generations, the apical portions 

 of which have come forth year by year above the earth, and then disappeared. 

 We find an excellent example of this in the so-called Solomon's Seal {Poly- 

 gonahon). 



To these aphoristic remarks concerning subterranean shoots, I have to add 

 finally that these shoots are distinguished as Rhizomes, when, creeping horizontally or 



