MISTLETOE 575 



In the chapter on "Farm Seeds,'' the chief impurities of com- 

 mercial samples of the seeds of grasses, clover and fodder plants 

 are noticed. The seeds sometimes occurring in samples of the 

 cereals which need special mention, in addition to those just 

 alluded to, are charlock, wild oat, cleavers, shepherd's-needle, 

 various species of annual brome-grasses and darnel. 



In the present high state of perfection of cleaning and dress- 

 ing machinery, samples of the cereal grains should be absolutely 

 pure, but this is unfortunately not always the case. 



d. A few weeds are parasitic upon crops of the farm ; that is, 

 instead of obtaining their food-constituents from the soil and air, 

 they take it either wholly or in part from the plants to which they 

 are attached. Those of the commonest occurrence are dodders, 

 broom-rapes (p. 599), and mistletoe. 



Mistletoe {Viscum album L.) is a parasite which lives upon 

 various kinds of trees, deriving some of its plastic food and 

 all its water-supply and mineral food-constituents from them. 

 By means of its green leaves it is capable of utilising the 

 carbon dioxide of the air and producing carbohydrates, but 

 it no doubt obtains some carbohydrates and other foods 

 needful for its Hfe from its host. The plants enfeeble the 

 branches of the trees, and are indirectly injurious by allowing the 

 entrance of insects and fungi at the swollen cankered places, 

 which are often produced where they take root. Mistletoe is 

 met with upon many kinds of trees, but it grows most 

 vigorously upon poplar and apple, and it is in orchards of 

 the latter that most damage is done by the parasite. The 

 male and female organs are borne upon separate plants — that 

 is, it is dioecious, some plants producing male flowers only, 

 while others give rise to female flowers, which ultimately 

 develop semi-transparent white berries, each containing a 

 single seed. 



The seeds, which are ripe in November and December, are 

 distributed by birds, especially thrushes. They germinate in 



