no4 



THE BOOK OF GARDENING. 



Such perithecia disclose their contents, and the spores are 

 released to be distributed by insects, birds, wind, or even by- 

 man himself, those finding a suitable " home " germinating, 

 increasing the area of the disease. And similarly with other 

 parasitic fungi which attack leaves, &c. The gardener's chief 

 difficulty with all is that his first acquaintance with any is usually 

 when much mischief has been done. His first indications are 

 when the fungus has existed sufficiently long to produce out- 

 ward characteristics — like the familiar Mildew on the Straw- 

 berry, the "Rust" on Chrysanthemum, or the Mushrooms in 

 the roots of his orchard and landscape trees like Agaricus 

 (Armillaria mellea). Again, he does not seem able to 



Fig. 718. — Portion of Cankered Tree, due to Nectria ditissima. 



(By permission of the Board of Agriculture.) 



reconcile the fact that such fungi have forms of fruits, or 

 spores, varying with the seasons ; each has its part to play in 

 the reproduction, or it may be in the extension of the infected 

 area, of the species. Then just as there are in the Animal World 

 certain parasites — like, say, the hydatid which causes gid in sheep, 

 and which needs another host, the dog, to complete the cycle, 

 so there are certain small fungi (called hetercecious) which 

 require two plants— sometimes of widely different natural 

 orders— to complete the cycle. The Gooseberry Rust (sEadium 

 grossularid), whose orange-red patches are familiar upon the 

 foliage and fruit of that plant, is but the Cluster-Cup stage of 

 Pucrinia Pringsheimiana, whose other stages are found upon 

 Carex acuta and Carex Goodenovi ; while the Rust, found on the 

 leaves and other parts of Barberries, is likewise a stage in the 

 life-history of a still more destructive fungus known as Wheat 

 Rust {Pucrinia graminis). These are only two familiar examples- 

 of heteroecious fungi. Many others might be cited. 



Parasitic fungi reproduce their kind in various ways. One of 

 the commonest, however, is by means of fruits which are equivalent 

 to the seeds of flowering plants, though differing from them in 

 never enclosing an embryo, or young plant. They, moreover 



