SHORTENING OF THE ROOTS. 2 1 



roots of many fig-trees, which grow vertically downwards ; these hang down slack 

 until they penetrate into the earth; as soon, however, as the lower end becomes 

 fixed and branched within the earth, the part of the aerial root which is in the 

 air appears tightly stretched, like the string of a piano, in consequence of the 

 after-shortening. It is easily understood that the horizontal branches of the 

 Indian fig-trees, from which such aerial roots grow down into the earth, must 

 obtain by this mechanism a very firm hold, which becomes enhanced still 

 more by the roots referred to growing thicker later on, and becoming woody. 

 Much more general, however, is the effect which is produced through the 

 shortening of the tap-roots in herbaceous plants. If, for example, the seeds of 

 Umbelliferous plants or Composites, or others, are allowed to germinate, thinly 

 covered with earth, the seedling shoot at first rises i to 2 cm. above the earth ; 

 after several days, however, we remark that the part of the seedling shoot beneath the 

 first leaves is quite sunk into the earth, so that the primary leaves lie on the surface of 

 the earth. This change can only have been effected by the tap-root, the under 

 part of which is fast anchored in the earth by the root-hairs, shortening in the 

 ground, and drawing the stem of the seedUng into the earth. In many cases, indeed, 

 this shortening of the tap-root appears to proceed steadily even for years. For only 

 by means of this assumption can it be explained how the rosettes of radical leaves, 

 in plants with so-called polycephalous main-roots, remain close to the surface of the 

 earth, instead of becoming gradually lifted up. We have a very instructive example 

 of this kind in the common Dandelion {Taraxacum officinale). From the upper 

 part of the fleshy and strong tap-root spring several shoots, which continue to 

 grow for years, and annually bear a rosette of leaves close to the surface of 

 the earth. These shoots grow upwards, though slowly, and yet the leaf-rosette, 

 renewed annually, always remains close to the surface of the earth. The phenomenon 

 can certainly not be explained otherwise than by the assumption that the tap-root 

 always creeps in the soil, and draws down the shoots just as deep as they have 

 become elongated abo\e. The case appears to be the same in the species of 

 Verbascum, in Geniiana lutea, and others ; accordingly, the tap-roots of older plants 

 of this kind also present deep transverse folds. 



The creeping of a root in the earth may thus, in some degree, be compared 

 with the mode in which an earthworm bores into it: the anterior part becomes pushed 

 in forcibly between the particles of earth, while the posterior becomes drawn after it 

 by shortening. 



Finally, we may mention the fact that the roots of vascular plants frequently 

 appear as organs of regeneration, since they produce shoots which, growing up 

 in their turn into the air, constitute new plant individuals. To the best known 

 examples in this connection belong the common Acacia {Robinia pseudacacia) as 

 well as Ailauthus glandulosa, from the horizontally spreading roots of which 

 young trees grow forth out of the earth. In a perennial species of cucumber, 

 Thladianiha dubia, the annual regeneration is, in fact, confined to such root-born 

 shoots. On the very long thin root-fibres of this plant roundish tubers become 

 developed, from the ui^per side of which numerous shoot-buds arise, which grow 

 forth the following year above the earth, independent of the mother plant, and 

 represent new plants. I regard it as simply a modification of this process w'hen 



