193 



CRYPTOGAMIC BOTANY. 



[The following notes on subjects now under investigation in the Cn-pto- 

 gamic Laboratory, are contributed chiefly for the purpose of soliciting in- 

 formation from those practically acquainted with them in the field or gar- 

 den. Any facts relative to the extent of the disease, the history of its ap- 

 pearance, favoring conditions for its development, its treatment,' successful 

 or unsuccessful, will be welcomed. — W. R. Dudley, Dec. 1S89.] 



I.— THE ONION MOLD. 

 Peronospora Schleideniana, De Barj'. 



So far as we can certainly aiscertain 

 this destructive disease was ob.served in 

 New York last year, for the first time. It 

 was forwarded to tis from Madison, N. Y. 

 by Mr. R. A. Goodrich, on Jul}' 29, who 

 writes, * * * "It is very destructive. 

 I have a bed of onions in my garden the 

 Fig. 1.— Leaf of onion, (nat- tops of which are now all dead and dry 



ural size.) showing the mold ^ ,, rr , r.i- •, t./~, 



iPe,o„ospo,-a Schleideniana) or. ^Om the cfFeCtS of thlS paraSltC. It firSt 



the upper part. appeared last year but has not become gen- 



eral in this section. The plant is killed by the time the bulbs are 

 from one-half to one inch in diameter. In setting out this spring 

 the small onions saved from last year's crops I found several of the 

 bulbs completely covered by this mold and threw them awa5^ It 

 shows that the mold can be kept over winter." On August 6th, 

 he writes : " very little of it can be found at present. The season 

 of its growth seems to be the months of June and July." 



Abont this time it was observed by ourselves on the onions in 

 the gardens on the University farm, where it was not particularly 

 destructive, rarely causing half a leaf to wither, or attacking all 

 the leaves. Several small fields of the crop were noticed in Itha- 

 ca, all of which were unaffected by the mold. 



It is common and greatly dreaded in Europe ; but was not no- 

 ticed in America till 18S3, when observed by Professor Trelease* in 

 Wisconsin. Since then it has not often been mentioned and 

 seems to have been largely confined to the West. Even in the 

 Coimecticut River Valley, the only di.sease of the Onion attract- 

 ing attention appears to be the " Onion Smut " {U?'ocystis Cepu- 

 lae, Frost.) 



*In the "First Ann. Rep. of the Agr. Exper. Sta. of the Univ. of Wise." 

 (1883) this author summarizes what was known concerning the Onion Mold 

 or " Onion Rust," and gives the best account of it, available to American 

 gardeners. 



