254: CRYPTOGAMIC PLANTS INJURIOUS TO FOREST TREES. 



its rapid decomposition. The mycelium in many cases reached a 

 height of from 2 to 3 feet up the stem of the young tree 

 before the top was quite dead ; and it could often be seen bursting 

 the bark at the base of the stem, and displaying a complete net- 

 work of white threads of spawn inserted between the bark and 

 the wood. A few of the hazels were affected with the fungus and 

 died, but none of the Spanish chestnut or hornbeam appeared to 

 suffer in the least, although they were intermixed throughout the 

 plantation with the other kinds that were killed by the fungi ; 

 hence it would appear that some species of trees are proof against 

 the attacks of certain fungi, which are fatal to others. 



Some of the most fatal diseases of trees are attributed to the 

 ravages of the more minute genera of parasitical fungi, in the 

 form of mildew, rust, mould, rot, etc., the species of fungi produc- 

 ing these effects being generally of microscopic proportions. How- 

 ever, their destructiveness under favourable circumstances quickly 

 assumes an alarming visibility, indicating their presence to the 

 most obtuse observer, and their devastating inroads upon vegeta- 

 tion probably equal those of the larger genera of fungi, although 

 their pi-esence may not be so easily detected. Some of these 

 minute fungi attack plants internally, and only become visible 

 when they break through the surface of the plant to shed their 

 spores ; others are superficial, rooting, living, and fructifying 

 upon the epidermis. The various species of jEcidium, Erineum, 

 Puccinia, Sclerotium, and Uredo, belong to the internal class, and 

 are the cause of much disease in the leaves and wood of trees and 

 shrubs. Very often it is the most vigorous plants which are first 

 affected by these fungi; while on the contrary the attacks of 

 superficial fungi, such as Acrosporium, Botrytis, Erysiphe, etc., 

 appear always to be brought on by the debility of the plant 

 attacked. A long period of drought, followed suddenly by a 

 heavy fall of rain and a close, moist atmosphere, is a prolific cause 

 of mildew or mouldiness in its various forms ; and it is supposed 

 by some that when the plants are in a debilitated state from the 

 long continued dry weather, they become more easily the prey 

 of fungi or mildew, which, as soon as the rain falls, and the air 

 is saturated with moisture, grow with great rapidity, and soon 

 overrun the plants. 



To prevent the ravages of internal mildew, precautions should 

 be taken to destroy it by every available means, burning when 

 possible all plants, or parts of plants, affected by it, taking care 



