NoTES ON THE EkYSIPHACEAE T 
surface ; consequently the perithecium in drying never becomes 
concave on the under surface. 
Neger considers that the difference of structure in the upper 
and lower halves of the perithecium which is found in many spe- 
cies, and which in many cases causes the under surface of the 
perithecium to become strongly concave on loss of turgescence, 
is of great biological importance. In describing the ripe perithe- 
cium of Microsphaera astragali, he remarks (p. 351): ‘‘ Die Frucht- 
korper losen sich, wenn sie einen gewissen Grad der Reife erreicht 
haben, vom Substrat los, indem sich die Unterseite der Perithecien 
bei abnehmendem Turgor einwarts wélbt und dadurch die Mycel- 
faden, an welchen das Perithecium entstand, zerrissen werden. 
Diese constant einseitige Einwartswolbung kommt dadurch zu 
Stande, dass die Perithecienwand an der Oberseite einen starren, 
aus englumigen dickwandigen Zellen gebildeten Panzer darstellt, 
wahrend die Zellen der Unterseite relativ weites Lumen und 
zartere Wande besitzen. * * * Es kann demnach kein Zweifel 
bestehen, dass wir es hier mit einer Einrichtung zu thun haben, 
welche eine spontane Loslosung der Perithecien vom Substrat 
ermoglicht. * * * Es sei gleich hier bemerkt, dass alle (von mir 
untersuchten) Microsphaera-Podosphaera- und die meisten Unei- 
nuda-Arten den gleichen Loslosungsmechanismus besitzen.”’ 
According to the behavior of the ripe perithecium, Neger 
divides the Erysiphaceae into the following biological groups : 
A. Perithecia not spontaneously falling off, mostly attached to the mycelium by their 
appendages: Sphacrotheca, Erysiphe ( U. circinata? ). 
B. Perithecia falling off when ripe. 
1. Detachment caused by the shrinking of the perithecium base. 
(a) Cellular tissue of upper half of perithecium formed of narrow strongly 
thickened rigid cells ; cells of lower half delicate-walled : Podosphaera, 
Trichocladia, Microsphaera, Uncinula (% Microsphaeroidea). 
(8) Cells of the perithecial wall of about the same size on the under and 
upper sides of the perithecium ; on the upper side with narrow lumen, 
on the under with more or less delicate walls. Cells in the regions of 
the greatest curvature very large and flexible, becoming shrunken on the 
drying of the perithecium. The under surface of the perithecium con- 
sequently becomes concave. Luuncinula (excl. U. circinaia). 
2. Detachment of the perithecium follows through the pressure exerted against the 
substratum by the appendages which turn downwards. The perithecium in 
drying suffers no important change of shape: Phyllactinia. 
In connection with the statement made above that the detach- 
