PLANT DISEASES CAUSED BY FUNGI. 



127 



they are certain to produce diseased plants 

 which are of no value, and only spread the 

 disease. Where the disease has existed it is 



Fig. 164.— Anemone Disease (Sclerotinia tuberosa). 



1. Winter fruit, the only form known. The cups are bright-brown, and 

 appear just above-ground in early spring. The stem of the cup or fruit 

 springs from a large sclerotium formed in the rhizome of the Anemone 

 (natural size). 2. Spores of winter fruife (magnified 370). (Gard. Chron.) 



not wise to continue planting bulbs in the same 

 place, as sclerotia are almost certain to be pre- 

 sent in the soil, and the new bulbs or leaves 

 would be inoculated. Finally, in the case of 

 Potatoes or Beans, the infected stems should not 

 be allowed to remain on the ground, neither 

 should they be placed on the rubbish-heap, but 

 should be collected and burned. The black 

 sclerotia, about the size of a grain of Wheat, can 

 be readily found in the pith on splitting open 

 the stem, and become liberated when the stem 

 decays. Many kinds of sclerotia are capable of 

 retaining their vitality for years buried in the 

 soil, and when conditions are favourable produce 

 fruit which infects a crop suddenly and un- 

 expectedly. In too many instances the germs 

 of disease, under the form of spores or sclerotia, 

 are unconsciously placed in the soil along with 

 manure, composed in part of decayed plants 

 that have been diseased. 



Manure should never be used until it is 

 thoroughly rotten. The use of comparatively 

 fresh or green manure for mulching, &c, is 

 simply courting disease. 



Another group of destructive parasitic fungi 

 possess the very remarkable peculiarity of living 



on two different host-plants at different periods 

 of their development. About the month of 

 May dirty-orange, soft, gelatinous bodies about 

 \ inch long may often be found in considerable 

 numbers springing from swollen branches of 

 different kinds of Juniper. These gelatinous 

 masses consist of an accumulation of spores be- 

 longing to a fungus called Gymnospwangium. 

 These spores germinate on the Juniper branch, 

 and form other very minute spores, which are 

 blown about by wind, and those that happen 

 to alight on the damp leaves of Pear or Haw- 

 thorn trees soon germinate, enter the tissue of 

 the leaf, and within a short time give origin to a 

 second form of fruit on the surface of the leaf, 

 resembling clusters of little horns with fringed 

 tips, each about \ inch long, and springing from 

 a yellow or orange spot on the leaf. This form 

 of the fungus is often very destructive to Pear- 

 trees, and perhaps more especially to various 

 ornamental kinds of Hawthorn, as the fungus 

 usually attacks almost every leaf on the tree, 

 also the young shoots, and even the fruit, caus- 

 ing the leaves to fall early in the season, which 

 results in the wood not being properly matured, 

 and in a lack of reserve food for the following 

 season. If the disease occurs two or three 

 years in succession, the attacked trees usually 

 perish. The spores formed in the horn-like 

 bodies or cluster-cups on the Pear or Hawthorn 

 are in turn scattered by wind, and inoculate 



Fig. 165.— Pear-leaf Fungus [Gymiwsporangium clavariaforme), 



1. Spring form of fruit on branch of Juniper (reduced in size). 8. Spore or 

 same (magnified 200% 3 and 4. Summer form of fruit on Pear leaves 

 (reduced in size). 5. Summer form of fruit; a, entire: b. cut open (mag- 

 nified 10). 6. Spores of summer form of fruit (magnified 200V {Journal 

 Royal Horticultural Society.) 



the Juniper. The point to remember is, that 

 spores formed on the Juniper can only infect 

 the Pear or Hawthorn, and, on the other hand, 



