MISTLETOES AXD LORAXTHUSES. 



207 



to stick with the radicle of the seedling pointing away trom the branch; the 

 whole axis of the embryo curving towards the surface of the bark in a very striking 

 manner. Thus the radicle always reaches the bark, and having done so it becomes 

 adpressed and cemented to its surface, spreads itself out in the form of a doughy 

 mass, and so develops into a regular attachment-disc. From its centre a slender pro- 

 cess now grows into the bark of the host-plant, piercing the latter and penetrating 

 as far as the wood, but not growing into that tissue. This penetrating process has 

 been termed a " sinker ", and must be looked upon as a specially modified root. 



Fig. 47.— Bushes of Mistletoe upon the Black Poplar in winter. 



The development of the first year ends with the formation of this sinker. 

 A\ hen the winter is over, the branch, into which the sinker is inserted so as just 

 to reach the wood with its point, grows in thickness, a new layer of wood-cells — a 

 so-called annual ring — being superimposed upon the wood of the previous year. 

 The increasing mass of wood first surrounds the tip of the sinker with wood-cells, 

 then forms a rampart all round it, pushing the cortical tissue, wherein that organ 

 has hitherto been wedged, in front of it in an outward direction, and in this way 

 the sinker is at length fixed deep within the woody cylinder. The process of 

 inclosure by the wood-layers, as they are built up, may be compared to the gradual 

 surrounding of a stake on the sea-shore by the rising tide; the lowermost extremity 

 is first immersed and then higher and higher parts until the whole is enveloped. The 



