On a New species of Melanotaenium. Rudolph Beer. 331 



ON A NEW SPECIES OF MELANOTAENIUM 



WITH A GENERAL ACCOUNT 



OF THE GENUS. 



With Plate VIII. 

 By Rudolph Beer, B.Sc., F.L.S. 



During the early summer of 1918 specimens of White Dead- 

 nettle [LamiiiDi album) bearing curious tumour-like swellings 

 caused by a fungus upon their underground organs were sent 

 to the Pathological Laboratory at Kew. The diseased plants had 

 been found by Mr W. F. Drew at Chalfont, Stroud, Gloucester- 

 shire, and upon request he kindly sent in 1919 a further sample 

 of plants from the same locality in rather an advanced state of 

 disease. 



There appears to be no other record of the occurrence of such 

 intumescences upon Lamium album and a careful search both 

 at Kew and elsewhere failed to discover any further examples of 

 these tumours. It would appear, therefore, that the disease is a 

 rare one and in spite of the small amount of material available 

 for study it seems advisable to place the fact of its occurrence 

 upon record and to give a brief description of its general char- 

 acters and of the fungus causing it. 



Description of New Species and its Systematic position. 



As already mentioned the tumour-like swellings occur upon 

 the subterranean parts of the plant (PI. VIII, fig. i). In so far 

 as the present material permits one to judge the intumescences 

 are restricted to the underground stems and leaf-structures and 

 are entirely absent from the roots and from the sub-aerial parts 

 of the plant. In some cases they occur as dark blister-like swell- 

 ings upon the side of the stem but when the entire circumfer- 

 ence of the stem is affected they appear as distinct, spherical, 

 tuberous bodies measuring as much as 8-5-9 '^"i. in diameter. 

 When a bud is attacked it becomes much swollen and its leaf- 

 organs greatly thickened and enlarged. 



The presence of the disease does not cause the differentiation 

 of any new structures in the organ but it stimulates the elements 

 already present in the leaf or stem to division and growth. The 

 swellings would, therefore, according to Kiister's classification 

 fall within the category of Kataplasmic galls*. 



* Kiister (1903) divides galls into two groups: {a) those which show little 

 or no differentiation and are quite simple in their histological structure, and 

 (5) those which exhibit specific differentiation and have quite a different histo- 

 logical structure from the normal organ. The former he names Kataplasmic 

 galls, the latter Prosoplasmic galls. 



