Pethyb ridge — The Verticillium Disease of the Potato. 87 



Bulletin compiled by Orton. 1 Here for the first time, apparently, 

 the disease due to Verticillium is distinctly dissociated from Curl and 

 Leaf- Roll diseases, and placed in the group of Wilt diseases along with one 

 previously known in America from the work of Smith and Swingle, and stated 

 to be caused by Fusarium oxysporum. It follows that Appel's Blattrollkrankheit 

 as originally described by him would also logically find a place in this group, 

 although the actual species of Fusarium causing it may not be identical with 

 that found in America, and even although the external symptoms of wilting, 

 &c, were not absolutely identical in the two continents. All these diseases 

 have this in common, viz., that more or less premature death by desiccation 

 of the plant occurs owing to the choking of the wood vessels with fungus 

 mycelium. It has been proposed to apply the term vascular-mycosis to 

 diseases of this type ; but the term is not above criticism. Since the fungus 

 mycelium is, at any rate in the early stages of the disease, confined to the 

 wood vessels, and since these form only a part of the vascular system of a 

 plant, it would seem much more desirable to use a still more precise term, 

 and I, therefore, suggest the word " hadromycosis " for use in this connexion. 

 It must be remembered that the vascular system of a plant does not consist 

 of xylem alone ; and, in view of the fact that another disease, which will 

 be referred to in a moment, has been designated "phloem-necrosis," it seems 

 eminently desirable to employ the term " hadromycosis " instead of the more 

 clumsy one " vascular-mycosis." 



It is interesting to note that Appel in one of his most recent publications 2 

 proposes to follow Orton, and says, " I wish to eliminate the name leaf-roll 

 disease for the parasitic troubles, and substitute the name vascular-mycosis."' 



The term " Leaf-Roll " or " Blattrollkrankheit " should, therefore, now be 

 applied only to certain diseases of the potato showing rolling of the foliage 

 in which parasitic organisms are, as far as is known at present, not the 

 causative agents. Whether there is only one such disease, or whether the 

 term may still, for the present at any rate include several diseases, cannot be 

 decided until further research throws the necessary light on the matter. 



Very important work on Leaf-Roll (using the term in its restricted 

 sense as above described) has recently been done by Quanjer. 3 This author 



1 Orton, W. A., Potato Wilt, Leaf Roll, and related Diseases. Bull. 64. U. S. Dept. 

 of Agric. Feb. 1914. [To this Bulletin is appended a very useful Bibliography of the 

 subject under discussion.] 



2 Appel, O., Leaf Roll Diseases of the Potato. Phytopathology, vol. v., No. 3, 

 1915, p. 139. 



3 Quanjer, H. M., Die Nekrose des Phloems der Kartofl'elflanze, die Ursache der 

 Blattrollkrankheit. Med. v. d. Rijks Hoogere Land-, Tuin-, en Boschbouwschool, 

 vi, 1913. 



SCIENT. PKOC. K.D.S., VOL. XV., NO. VII. 



