64 THE VEGETATIVE ORGANS 



Such axillary tubers occur commonly on the older plants ; 

 and, as the other parts decay, the tubers fall to the ground, 

 and in time produce new plants from the buds which arise 

 at their base. Two or three tubers may arise at a node, 

 and when several leaves are produced close together a large 

 cluster of tubers results. 



Fig. 28, 1, shows tubers springing from three successive 

 nodes. By the elongation of the tubers they may enter 

 the soil and become independently rooted. The decay of 

 the internodes at the end of the season will result in several 

 independent plants. This mode of origin of roots at the 

 nodes, and the formation of new plants by vegetative 

 means, is of common occurrence. 



CHAPTER VI 

 STRUCTURE OF THE SHOOT 



Environment of the root and shoot. The environment of 

 the shoot is totally different from that of the root. In the 

 soil the root is surrounded by a moist medium, and is in 

 the dark. It is less exposed than the shoot to drying winds 

 or heavy rain, to biting cold or the bright rays of the sun, 

 to the heat of the day or the chills of the night. The con- 

 ditions of life below ground are, on the whole, more uniform, 

 and the parts are not exposed to such sudden and often 

 extreme changes as are those parts growing above ground. 

 For healthy existence, their form and structure must be 

 adapted, not only to withstand, but to make the best use 

 of, these conditions. We have, therefore, to regard the 

 shoot of a plant from these different points of view. 



As we have seen in the Stock, the stem is directly con- 

 tinuous with the root, and is the means by which leaves are 



