THIELAVIA 161 



peas, begonias, tobacco, lupines, groundsel, violets, etc. 

 It is perhaps most partial to members of the Leguminosae. 



The root is the part attacked, and the yellowing and 

 wilting of the foliage, and the eventual death of an infected 

 plant is often attributed to other than the true cause, which can 

 only be determined when an examination of the root is made. 



The mycelium permeates the tissues of the root, and is 

 very delicate and colourless when produced in the tissues, 

 but becomes tinted when developed on the surface of the 

 root, and it is here that the various forms of spore are pro- 

 duced. The first kind to appear are known as endospores, 

 functionally summer spores. These are produced in chains 

 within a mother-cell or hypha, from the ruptured extremity 

 of which they are pushed out by the formation of new spores at 

 the base of the chain within the parent hypha. These endo- 

 spores germinate as soon as liberated, and probably spread 

 the disease rapidly. The endospores and their .mycelium 

 form a delicate, almost colourless mould surrounding the 

 root and are apt to be overlooked. At a later stage, the 

 same mycelium that bore endospores, gives origin to a second 

 form of fruit known as chlamydospores. These are com- 

 paratively large, club-shaped, dark brown, many -septate 

 spores, borne singly or in clusters on the colourless mycelium 

 surrounding the root. These spores are produced in great 

 abundance, and give to the root a blackened or charred 

 appearance. Chlamydospores do not germinate until after a 

 period of rest, and serve to tide the fungus over that period 

 of the year when its host-plant is not forthcoming. The 

 chlamydospore condition was the only one seen by Berkeley 

 and Broome. At a yet later stage, when the plant is dead, 

 the highest form of fruit, consisting of ascospores produced in 

 a closed perithecium, are formed. 



In this country peas are most frequently attacked, but the 

 parasite has also been recorded on other plants. In Italy, 

 and more especially in the United States, the tobacco crop 

 has suffered severely. 



Endospores produced in chains and escaping from a 

 sheath, hyaline, 12-28x4-5 /*. Chlamydospores narrowly 

 club-shaped, dark brown, many-celled, septa thick, eventually 

 breaking up into their component cells, 30-65x9-16 /*. 

 Perithecia globose, black; asci 8-spored, spores lenticular, 

 coloured, 12X5 p. Zopf also mentions the presence of 

 pycnidia containing minute stylospores or spermatia. 



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