184 THE PI.ANT WORLD 



and bodies of visiting insects. Of the plant diseases which are known 

 to be carried by insects we may mention the following : ergot of grain 

 and grasses, smuts of grains, brownrot of stone-fruits caused by Sclero- 

 tiiiia frudigena, bitterrot of apples ; and some of the rusts are known to 

 be carried by aphids, snails, and caterpillars. Several of the bacterial 

 diseases are also known to be thus distributed and it is more than likely 

 that all of them may be. Texas fever is carried by cattle ticks, malaria 

 and yellow fever by mosquitoes, typhoid fever by flies, and anthrax, pink- 

 eye, and bubonic plague are known to be carried by various insects. 

 Although these diseases are not all bacterial ones, they are so similar 

 that they are governed by practically the same factors as are bacterial 

 diseases, and for this reason are mentioned here. An instance is known 

 where a fungus grew only along the slimy trail of a snail or worm on a 

 leaf. Still others are known to grow only in the honey-dew secreted by 

 certain insects. The sooty mold of the orange is a good example of this 

 class. The honey-dew is secreted by aphids, white flies, and scale insects, 

 and the fungi grow on the leaves, branches, and fruit wherever the liquid 

 falls. The fungi are dark colored and make a sooty covering on the parts 

 where they grow. In the leaves this causes less food material to be 

 manufactured for the plant, while on the fruit the dark sooty appearance 

 hurts the sale very much. The damage caused in this way is estimated 

 to be $50,000 in the State of Florida alone. Still other fungi are known 

 which grow in a similar way upon forest trees. 



The spores of certain fungi, called Ambrosia fungi, are a staple article 

 of food with some wood-boring beetles. lyittle has yet been done along 

 this line, but it promises to be very closely connected with some of the 

 diseases of wood. Honey-bees have been observed to collect the spores 

 of blackberry rust (^Caeovia nitens), and to use them just as they would 

 pollen grains. This is not as bad a mistake as one would at first think, 

 since the fungus spores are very much like pollen grain in every way. 

 The bees may be depended upon to know what they are doing, and it 

 may be that they are thoroughly American in inventing a new method 

 of making wax. Certain ants are known to cultivate a fungus for food. 

 They cut pieces of leaves and plant the fungus among them so that later 

 they live on the fungus thus raised. Insects are the scavengers of the 

 fleshy fungus world. As soon as the fungi are a little past their prime, 

 one will find numbers of larvae tunneling through the tissues. 



In very many fungus diseases the fungi could not gain entrance to 

 the uninjured tissues of the affected plant. Insects, by reason of the 

 numerous bites and punctures which they make, aid the fungi by giving 

 them an easy entrance to the tissues which they later destroy. In var- 

 ous ways, therefore, it will be seen that insects are very important factors 

 in the spread of fungus diseases. 



