XXIII 



PARASITIC PLANTS 



A NUMBER of plants extract more or less of the organic material 

 they require from other plants, and thus save themselves the 

 labour of building up tliis material themselves. These are termed 

 parasites ; but we must be careful to distinguish between them 

 and certain other plants which, though apparently parasitic, are 

 not really so. One plant may climb on another, perhaps even 

 producing " rootlets " by which it clings to its Living support, and 

 yet it may not be a parasite in the proper sense of the term, for it 

 may not absorb the slightest amount of nutritious matter except 

 from the soil and the air. It is not at all uncommon for the Honey- 

 suckle to twine its stems round the trunk and branches of a young 

 tree, with the result that the tree becomes stunted, and assumes 

 a starved appearance, especially in its lower parts ; and yet the 

 Honeysuckle is not a parasite. It has \vithdiawn nothing from the 

 tree which supports it, but has coiled itself so tightly round it as to 

 interfere with the circulation of its sap. The lower part of the tree 

 is especially affected because the strangulating coils of the climber 

 prevent the downward flow of the sap contained in the vessels of the 

 bast or inner bark, and this is the sap which holds the constructive 

 materials that have been built up in the leaves, under the influence 

 of light. 



Many of the parasitic plants are of microscopic dimensions, and 

 others are larger species belonging to the Fungi or Mushroom group. 

 Some, however, are flowering plants, and these oulj' fall within the 

 scope of our work. 



Wo shall first deal with parasites which have no green leaves 

 or chlorophyll, and are therefore entirely dependent on outside 

 somces for their supply of organic material, starting ^\ith the 

 interesting Dodders {Cuscuta), which coil themselves round herbs, 



