1 68 Wormald. — ‘ Brown Rot ’ Diseases of Fruit Trees. II. 
The Sclerotinia stage of M. fractigena was first described by Aderhold 
and 'Ruhland ( 1 ), the genetic connexion between the ascigerous and the 
conidial forms being established by the development of the Monilia form 
from ascospores. 
The same workers were also able to obtain a Selerotinia from mummied 
apricots, and from the ascospores obtained cultures which developed conidial 
pustules resembling those of M. cinerea\ this Ascomycete they named 
Sclerotinia laxa , i. e. the ascigerous stage of Ehrenberg’s Oidium laxum 
(= Monilia laxa , Sacc. et Vogl.). They considered Monilia laxa to be 
distinct from M. cinerea , morphologically with regard to the size of its 
conidia, and biologically from the fact that they found it occurring 
plentifully on apricots when neighbouring peaches and cherries were un- 
affected. The size of the conidia of M . laxa Aderhold and Ruhland give 
as 12-4-23*8 x 9*3-15*5 the dimensions of those of M. cinerea as 9-3- 
14-5 x 6-2-12-4 \i. It is to be observed, however, that the dimensions given 
for M. laxa conform to those of M. cinerea when the latter is growing in 
summer on plums. 
To the time of writing, only one strain from apricots has been examined 
at Wye; this was found on dead twigs in February 1919. The size of the 
conidia was found to be from 6-5x3 /x to 14-5x9-5 \k with an average of 
11 x 7-5 \x for 100 conidia, dimensions which are of the same order as those 
of the winter conidia of M. cinerea produced on mummied plums and 
cherries. There seems to be no valid reason, therefore, for considering the 
two conidial forms M. cinerea and M. laxa as two distinct morphological 
species ; whether the apricot has a biologic form confined to that host 
remains to be proved by inoculation experiments with pure cultures. 
In North America a Brown Rot Sclerotinia , first discovered and 
described by Norton (20), is frequently found. Specimens, preserved in 
spirit, were sent by Norton himself to Aderhold and Ruhland, and they 
named it Sclerotinia cinerea , assuming it to be the ascigerous stage of the 
conidial form Monilia cinerea , Bon. Since, as shown in this article, the 
American form of Monilia is readily distinguished in cultures from the 
M. cinerea of Europe, the writer regards it as a distinct form (provisionally 
referring to it as Monilia cinerea forma americana) of which the Sclerotinia 
stage is that recently described from fresh material by Matheny ( 18 ). 
Whether this ' Sclerotinia of America will prove to be identical with, or 
distinct from, the ascigerous stage of the European form Monilia cinerea , Bon., 
must remain an open question until an Ascomycete is described the ascospores 
of which give rise to a Monilia morphologically and culturally identical with 
that occurring on Prunus spp. in Europe. 
As there are reasons for suspecting that Monilia laxa and M. cinerea 
are the same morphological species, it appears probable that Sclerotinia laxa 
(Ehrenb.), Aderh. et Ruh., is the ascigerous stage of both the conidial forms 
