STUDIES IN THE GENUS GYMNOSPORANGIUM IV. DISTRIBU- 
TION OF THE MYCELIUM AND THE SUBCUTICULAR 
ORIGIN OF THE TELIUM IN G. CLAVIPES 
B. O. Dodge 
(Received for publication December 5, 192 1) 
A parasitic fungus in its periods of exploration and attack seeks out 
those regions where its essential foods are readily available. The host may 
react to the irritations in such a way as to lead to the formation of ab- 
normal growths which can be relied on in diagnosing the disease. Most 
species of Gymnosporangium are, aside from their morphological differences, 
easily distinguished, because each species may differ from the others not 
only as to the tissues invaded but also as to the manner of the attack.^ 
G. clavipes Cke. & Pk. on Juniperus virginiana differs from all other species 
studied by the writer in the very limited or superficial way in which the 
mycelium invades the host, and in the location of the telial sorus as it 
is formed in leaves or young stems. Hitherto it has been thought that 
the telia of all Gymnosporangia arise beneath the epidermis. Those of 
G. clavipes are not subepidermal but are developed in the outer wall of 
the epidermal cells. They might be called subcuticular, but, as will be 
noted later, there is no single word in English that is strictly applicable. 
Ducomet^ made a special study of those spot-disease fungi which live 
at least a part of the time beneath the cuticle of the host. The method 
of invasion by such fungi is quite as characteristic as the location of the 
spore-bearing structures with respect to the cuticle or epidermis. Ducomet 
found that certain species develop directly beneath the cuticle. These 
would be called subcuticular in a strict sense. Other species develop in 
the outer wall of the epidermal cells, in that part which is known as the 
cuticular layer and which is composed of cellulose and cutin. He proposes 
such names as intracuticulaire, subintracuticulaire, etc., terms which do not 
convey very well the meaning desired. 
Arthur^ has emphasized the taxonomic importance of knowing the 
location of the sori in rusts. 
1 For further discussion of this question see Wornle, P. Anatomische Untersuchung 
der durch Gymnosporangium-Arten hervorgerufenen Missbildungen. Forst. Nat. Zeitschr. 
3:68-84,128-172. 1894; Dodge, B. O. Studies in the genus Gymnosporangium I. Notes 
on the distribution of the mycelium and the germination of the aecidiospore. Brooklyn 
Bot. Gard. Mem. 1 : 128-140. 1918. 
2 Recherches sur le developpement de quelques champignons parasites a thalle sab- 
cuticulaire. 1907. 
3 Result. Sci. Congr. Bot. Vienne, p. 333. 1906. 
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