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THE MAPLE DISEASE {RHYTISMA ACERINUM). 
By Dr. Maxime Cornu.* 
During the summer black spots produced by a parasitic fungus 
are frequently seen on Maple leaves. This is Xyloma acerinum , a 
special type of disease. Xyloma is but the imperfect and summer 
form of the fungus ; when the leaves fall to the ground in 
autumn, a new growth appears in these spots ; the plant produces 
asci and becomes Rhytisma acerinum. 
These phenomena coincide with the germination of the young 
maples, which takes place early in April. These spots appear 
every year in the same locality. Is the parasite perennial, as in 
some Uredirieae ( JEcidium Euphorbice sylvaticce , and a large 
number of Pucciniae) ? Is it annual, as are Rcestelice and most 
AEcidia ? Sown on one spot, does it spread over the whole plant, 
as Endophyllum Sempervivi , Peronospora Papaveris , etc. ? 
Very young seedlings of Maples were placed in several flower 
pots ; two pots containing each eight plants, and others smaller 
containing each four, were used for the purpose. 
The 1st April, 1874, some ripe patches of Rhytisma were cut up 
into narrow segments, like smoking tobacco, and moistened with 
water ; small portions of the parasite were brought into contact 
with the young Maples. Every part of the seedling is not 
equally suitable for its introduction : Ustilago Carbo penetrates by 
the neck (collum), Cystipus candidus by the cotyledons. Direct 
research, anatomically, into the mode of introduction of the germs 
is rendered very difficult by the shape of the spores. These are 
much elongated, and their diameter and that of the germinating 
filaments exceedingly small ; the germination is besides very 
irregular. 
Four trials were made in order to ascertain the manner of 
penetration by the spores : — 
(A.) A small portion of Rhytisma , as described above, was 
placed all round the collar, on a level with the earth. 
(B.) A portion was placed within a cotyledon, which had been 
folded and kept in that position by a pin. Each of these two pots 
was covered with another pot, which had been moistened to prevent 
desiccation and the entrance of spores from the wind ; the leaves 
did not produce Rhytisma,. either in 1874 or in the following years. 
(C.) A portion was placed between the two cotyledons, on the 
leaves of the undeveloped terminal bud. 
(D.) A portion was placed between the leaves of the terminal 
bud after they had been raised by the stem ; the cotyledons were 
covered with tallow to their base, in order to isolate them ; they 
soon withered and fell off ; the plants, although vigorous at first, 
became more weakly than the others. 
* Translated from “ Comptes Rendus,” July, 1878, by T. Howse. 
