THE DEPTH IX THE SOIL AT WHICH PLANTS OCCUR. 403 



germination of the seed, we find that the plumule and radicle are 

 here, as before, pushed out of the seed by the elongation of the 

 cotyledonary sheath (fig. 115, a). In this way the bud is sunk 

 some two centimetres in the ground. The axial portion of the 

 bud undergoes a slight thickening, and the cotyledon and 

 primary root die away, leaving a little tuber, which remains 



Fiq. 115. — 'Arum maculatum ' : (a) Germination.' (b) Resting stage of 

 tuber after germination, (c) Young plant in the spring of the second 

 year. (d) Young plant descending. (c) Full-grown plant at its 

 normal depth (spring). (/) Similar plant in August, (q) Full-grown 

 plant, placed near the surface, descending (April). (//) The same plant 

 during the resting period in August. 



dormant till the autumn (fig. 115, b). At present the apex of 

 this tuber is directed upw r ards. In the autumn a circle of roots 

 arises just beneath the apex, and these roots are, some one or 

 two or them, contractile, the rest non-contractile. The result 

 of the shortening of the former is that the apex of the tuber is 

 drawn to one side, thus occupying a slightly lateral position 



