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Bull. Tour. Bot. Club. 



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SPHAEROTHECA MALI (Duby.) Bvirrill. 



THE. HELIOTYPE PRINTING CO., BOSTON. 



A little-known Mildew of the Apple 

By A. J. Grout 
(With Plate 364) 

Late in the antumn of 1 892 (November) a mildew was ob- 
served on a few belated leaves clinging to the adventitious shoots 
from the stump of a young apple tree in Newfane, Vt. The shoots 
were gathered and the leaves closely examined for perithecia, but 
none could be found. An accidental examination of the twigs 
showed that the mycelium had spread over the upper portions 
and here and there were darker spots covered with more closely 
matted mycelium. Under the microscope these spots were found 
to contain abundant perithecia, like those figured in plate 364, figs. 
1 and 2. At that time I found no one in New England who 
knew this mildew. It was, however, described in Ellis and Ever- 
hart's North American Pyrenomycetes (then recently issued) as 
Sphaerotheca mali (Duby) Burrill. Prof. Burrill there remarked 
that he had not had access to any European material of this fun- 
gus that was at all satisfactory, but from the description and the 
fact that it was scarcely possible that the introduced Pyrus Mains 
should have an exclusively American parasite of this kind, he 
concluded that the American plant was the one described as Ery- 
siphe mali Duby, Botan. Gall. I : 869. 1830. 

A careful examination of the exsiccati in the Harvard and 
Columbia herbaria, including the Ellis herbarium, failed to bring 
to light any European material of Erysiphe mali Duby which con- 
tained perithecia in condition to be of any use. The European 
exsiccati contained leaves only, while the perithecia in the Amer- 
can plant were invariably found on the young twigs. 

In November, 1898, Dr. Magnus, of Berlin, published in the 
Berichte der Deutschen botanischen Gesellschaft a historical and 
descriptive account "Ueber einen in Siidtirol aufgetretenen Mel- 
thau des Apfels " in which Professor Magnus completely confirms 
Professor Burrill's conclusions. As his article and plate will be 
accessible to comparatively few in America, this article and an en- 

(373) 



374 Grout : A little-known Mildew of the Apple 

tirely new drawing by- Prof. F. E. Lloyd, of the Teachers Col- 
lege, New York City, have been prepared to interest eastern col- 
lectors in this little known fungus. 

In 1895 this mildew was again collected in Newfane, on ad- 
ventitious shoots from a tree growing about fifty rods from the 
place of its first collection. This was distributed as no. 926 of 
Ellis & Everhart's Fungi Columbiani. It had previously been 
distributed as no. 3213 in their N. Am. Fungi, collected in Ames, 
Iowa, by Prof. Pammel. In the Ellis herbarium it is further rep- 
resented from Missouri (Demetrio) and Kansas (Kellerman and 
Swingle). Prof. Burrill remarks of its distribution " Not appar- 
ently very frequent but exceedingly abundant at times. Mississippi 
Valley and probably eastward." 

It seems probable that this mildew is not uncommon but is 
rarely collected because its perithecia are on the shoots instead of 
the leaves and also because the perithecia do not mature until very 
late in autumn when no one thinks of collecting mildews. The above 
mentioned peculiarities belong to the European plant also accord- 
ing to Professor Magnus and probably furnish the explanation of 
the poor European exsiccati and the comparative ignorance of the 
plant among European botanists. 

Sphaerotheca mali (Duby) Burrill ; Ellis & Everhart, N. Am. 

Pyreno. 7. 1892. 

Mycelium growing on young shoots and upper side of leaves ; 
perithecia seldom or never found on the leaves. Mycelium on the 
leaves thin ; fruiting mycelium more dense. Perithecia densely 
aggregated in small dark brown patches, 75-95 //, reticulations 
evident, appearing to be raised but in profile seen to be sunken ; 
appendages 4-12, clustered at the summit of the perithecia, sep- 
tate, colored nearly the whole length, frequently nodulosely swollen 
near the tips, length 4-8 times the diameter of the perithecium, 
easily detached ; perithecia bearing on the under side an abundance 
of short irregular rhizoidal appendages the nature of which is 
doubtful. Asci single, almost globose, 42-48 x 50-66 jul. Spores 
8, elliptical, 13-21 fi. 

On the upper parts of young twigs of Pyrus Ma/us, especially 
in nurseries of young trees, and on suckers or adventitious shoots 
from old branches. 



Grout: A little-known Mildew of the Apple 375 

The stiff rigid appendages are totally unlike the appendages of 
any other Sphaerotheca known to me and seem to me to constitute 
as good a generic distinction as the number of asci in a perithecium. 

Description of Plate 364. 
Figs. 1 and 2, camera lucida drawings of the perithecia, 4 T 5 and 3 -3- 2 , respectively; 
3 > 4 > 5> 7 an d 8, tips of appendages ; 6, basal part of appendage to show the propor- 
tions of cells ; 9, ends of two adjoining cells ; 10, junction of basal and neighboring 
cells ; 11, ascus and spores, z \ 2 ; 12, walls of exosporic cells-reticulum ; 13 and 14, 
rhizoidal appendages, 6 -2-° .