348 



FIELD AND WOODLAND PLANTS 



of wood begins to form outside, thus surrounding and banking in 

 the sinker. It would appear, on making a section of the tree, as 

 if the sinker had actually pushed its growth through the outer ring 

 of wood, whereas it does not penetrate the wood at all, but is only 

 banked up by the new wood that grows round it. This is repeated 

 year by year, until the sinker is at last quite deeply set in the 

 branch, being surrounded by tlie wood of several annual rings. 



During the second year's growth the 

 sinker sends out little roots which run 

 up and down the stem, beneath the 

 bark, and these give rise to new sinkers 

 tliat grow doAvn to the surface of the 

 wood, and become, in turn, embedded 

 in the new layers of wood that form 

 round them. And while the young 

 INIistlctoe plant is thus securing a firm 

 hold on its host, and \\ ithdiawing ready- 

 made organic compounds from its sap, 

 the outer green stem develops, and soon 

 gives rise to the first pair of leaves. 



It food is obtained in abundance, as 

 is the case when the host is a tree of a 

 soft and sappy nature, the growth is 

 rather rapid ; but otherwise the develop- 

 ment is comparatively slow. In any 

 case the age of the parasite may be ascertained by counting the 

 number of annual rings of wood that he outside the deepest 

 sinker ; and by this means it has been found that the IMistletoe 

 may attain an age of over thuty years. 



We have now to consider a group of plants, the parasitic habits 

 of which would scarcely be suspected by an ordinary observer. 

 They are green plants, with well-developed foliage leaves, and true 

 roots which absorb mineral food from the soil. Their seedhngs 

 grow in the same way as those of non-parasitic species, deriving no 

 nourishment from neighbouring plants, but obtaining all their food 

 from the air and the soil, and building up all the organic compounds 

 required for theii' growth by the agency of their own chlorophyll. 

 It is difficult to understand why these plants should afterwards 

 produce suckers on theu- roots in order to obtain nourishment from 

 other species, but they do this, and experiments have proved that 

 the food thus obtained is more or less essential to their development. 

 Some of them die while still young if grown apart from otiicr species. 



YOUNG Mistletoe Plant 

 ON THE Branch of a Tree. 

 The branch is cut longi- 

 tudinally to show the 

 suckers. 



