2 32 PLANT LIFE. 



divides the year between the Groundsel or Ragweed and 

 the leaf needles of Pines. Gymnosporangium juniperinum 

 lives on the Rowan from July to October, and on the 

 Juniper from May to June. The Gooseberry disease, 

 Aecidiiun ribis, seems to pass part of its time on the 

 leaves of sedges. 



As the whole series of Rust fungi live inside the plant 

 or " host " affected, and only form spores when ripe, 

 they are exceedingly pernicious agricultural pests. A 

 plant once attacked is doomed to destruction. The 

 coffee-leaf disease, Heinileia vastatrix, is said to have de- 

 stroyed plantations worth some ;^ 16,000,000 in Ceylon; 

 and the damage done annually by disease to the crops 

 in the United States is estimated at from 25,000,000 

 to 30,000,000 dollars for cereal crops, and at about 

 150 millions to 200 millions of dollars for all sorts of 

 crops.i 



The reader is recommended to study Plowright's 

 Uredineae and Ustilagmeae, a very perfect handbook 

 for this group of fungi. The Smuts or Ustilagineae are 

 allied to the Rusts or Uredineae, but the spores are 

 generally black, and form the Blackball or Smut often 

 seen in oatfields. Ustilago is the commonest form, and 

 species of it are found specially intended to attack Oats, 

 Wheat, Barley and Rye respectively. Tilletia Tritici is 

 the Bunt or Stinking Smut of Wheat. Its spores have a 

 distinct and disagreeable odour of stale herrings. It has 

 been found that these pests are greatly diminished by 

 soaking the seeds for five minutes in hot water or in 

 solutions of copper sulphate (details will be found in 

 Percival's Agricultural Botatzy). 



The Mildews or Peronospoi'eae belong to another group 

 of fungi, the Phycomycetes. This is divided into two 



^ Probably all kinds of diseases are included in the last estimate. 



