128 BULLETIN OF THE BUSSEY INSTITUTION. 
August, so, here, the quantity of mannan in a sample of inner 
bark of pine collected in August was evidently larger than in a 
sample collected in the preceding month. The same fact is evi- 
dent in the ease of the samples of fir bark, and apparently in the 
case of the spruce bark also. Hence the suggestion is offered 
that the amount of mannan in bark increases relatively with the 
increase or' mannan in wood proper. More tests are necessary to 
confirm this view. 
No mannan was detected in samples of the inner bark of the 
gray birch (Betula populifolia) and of the poplar (American 
aspen, Populus tremuloides). Previous work in this laboratory 
' with the wood of these trees had failed to detect the presence of 
mannan therein.* | 
Contrary to expectations, the results of this investigation failed 
to show any such preponderance of mannan in the inner bark of 
conifers as might serve to explain fully the use of the bark as 
food. Itis not to be denied, as yet, that the mannan in bark 
bread may be of real importance for human sustenance; but, to 
all appearance, further work will be needed to account completely 
for the physiological significance of this kind of food. 
* Bulletin of the Bussey Institution, 1902, 3. 34, 35. 
me 
