1908.] 



" Corky Scab " of Potatoes. 



593 



the spores on germination, instead of producing a germ-tube, 

 give'origin to amoeboid bodies or swarm-spores, which coalesce 

 to form a plasmodium. This discovery was considered to 

 place the Myxogastres outside the pale of the vegetable kingdom, 

 and an affinity with the sponges has been suggested. As a 

 matter of fact, they are still retained amongst Cryptogams, 

 and either included in the fungi, or considered as a satellite 

 of that group, by the latest exponents of classification based 

 on natural affinities. 



Most of the species are minute, and the majority are sapro- 

 phytes. To this statement, however, there are two marked 

 exceptions : Plasmodiophora brassier, Woronin, the cause 

 of " club-root " or " finger- and-toe " in cruciferous plants, and 

 Spongospora scabies, Mass., the parasite under consideration. 



The organism causing corky scab was observed by Berkeley 

 in 1846, during an investigation of the potato murrain 

 caused by the fungus now called Phytophthora infestans, De 

 Bary. It was not described at the time, but two figures of the 

 spore-balls were given, along with the following note : — " It 

 appears to me to belong to the genus Tuburcinia, Fries. The. 

 spores have usually one or more cavities in the surface com- 

 municating with the interior cavity. They may, therefore, 

 be considered rather as compound bodies consisting of a 

 quantity of cells arranged in the form of a hollow ball. This 

 view of their structure requires more attention than I am able 

 to give it at present." 



In 1850 Berkeley gave a technical description of the organism 

 under the name of Tuburcinia scabies, remarking that it was 

 very common on potatoes. 



Judging from the mass of spores joined together to form a 

 spore-ball, Berkeley placed his new species in the genus Tubur- 

 cinia, which, along with Thecaphora, Sorosporium, &c, present- 

 ing a similar structure, is included in the U stilaginacece or 

 "smuts." 



In 1877 Fischer de Waldheim published a revision of .the 

 Ustilaginaceae, and advanced reasons for placing Berkeley's 

 Tuburcinia scabies, in the allied genus Sorosporium, hence the 

 parasite became afterwards known as Sorosporium scabies, 

 Fisch. de Waldh. 



In 1886 a Norwegian botanist, Brunchorst, investigated a. 

 (4321) 2 P 



