vni FOREST & ORNAMENTAL TREES 255 



partially parasitic. The seeds are carried by birds, and 

 having lodged on a suitable host plant, they germinate 

 and produce haustoria or root - like processes which 

 penetrate the host. In a short time there is a definite 

 and inseparable union between the two plants. How- 

 ever, the mistletoe being a green plant is not dependent 

 upon its host for carbohydrate foods, but may be 

 considered as a water parasite. 



These plants are often so abundant as to give a 

 characteristic aspect to the scenery of the country in 

 which they exist. However, they are detrimental to 

 the health of the trees, causing them to be stunted, 

 sometimes irregular in shape, and sometimes killing 

 parts. Frequently the mistletoe dies in advance of the 

 host, leaving rough holes through which insects, fungi, 

 bacteria, and other causes of disease gain entrance to 

 the plant. They should be removed and the wounds 

 painted with coal tar. 



Other Seed-Bearing Parasites. There are a great 

 many other flowering plants which have assumed a 

 partially parasitic habit. Many of these plants live in 

 the soil but produce haustorial growths which penetrate 

 the roots of their hosts. In some species (of which the 

 Orobanche of the tobacco, hemp, etc. (page 159), is an 

 example), the seeds cannot grow well unless in close 

 contact with the roots of the host to which -they are 

 restricted ; but the seeds of other species will grow 

 equally well whether in direct contact with the host or 

 absolutely removed from it. 



Bacterial Diseases. The bacterial diseases of plants 

 are quite common on the succulent parts, such as the 

 leaves, fruits, bulbs, fleshy roots, and young growths. 

 Since they do not often attack the hard parts of plants, 

 the trees are comparatively free from this class of 

 diseases. Probably the most conspicuous and best 

 known of these organisms attacking a tropical or 

 rather semi-tropical tree is Bacterium savastanoi, which 

 causes the tubercle or knot disease of the olive. Further 

 study will doubtless reveal many others. 



