202 
GOTE TURESSON 
Another square of the same size was selected and covered with de- 
caying leaves of Alnus oregona and Cornus occidentalis . When 
uncovered and examined in the fall the Sphagnum was blackened 
and apparently killed in both squares. Tufts of this material were 
brought to the laboratory, put in test tubes partly filled with water 
and allowed to remain for a month, the water being changed every 
week. Some of it was put in moist chambers. The moss did not 
recuperate in either case. Sphagnum planted in test tubes partly 
filled with water gotten by squeezing decaying Lysichiton leaves' 
grew well. Also when planted in soil collected from the bottom of 
the skunk cabbage holes Sphagnum showed considerable growth. 
The killing of Sphagnum by the skunk cabbage leaves was first 
thought as being the result of some toxic substance in the skunk 
cabbage. With the investigation of Baumann and Gully in mind 
supplemented with those of Skene (24) on the injurious effect of al- 
kalies on the growth of Sphagnum, a number of samples of decaying 
skunk cabbage leaves were tested. They all gave acid reaction to 
litmus and phenolphthalein. Any interference with the absorption of 
mineral salts due to the neutralization of the acid colloids in the 
hyaline cells of Sphagnum or of the acid medium is therefore out of 
question. As the leaves of Alnus and Cornus also destroyed the 
Sphagnum the phenomenon cannot be explained by assuming the 
presence of a specific toxic substance in the skunk cabbage leaves. 
The property must be one common to both Lysichiton and Alnus- 
Cornus leaves. 
The cause most likely responsible for the killing of the Sphagnum 
and which adequately explains both cases is the one of shade and 
mechanical injury produced by the mass of overlying leaves. That 
Sphagna are light-demanding plants and very sensitive to waste are 
well known facts pointed out by almost every worker in the field. 
Transeau (26) makes the statement that in the Huron River Valley 
Cassandra affords a very suitable framework for the upbuilding of 
Sphagnum, among other reasons because its shade does not interfere 
with the photosynthetic work of the moss. Gates (11) points out 
that in the bog he investigated the white moss was confined to the 
margin of the lake "where it is not shaded by grass or bushes." Also 
Haglund (13) makes the statement that Sphagna are light-demanding 
plants. As regards their sensitiveness to waste, numerous instances 
are reported in the literature. Dachnowski (7) notices that covering 
