[August, 
180 Problematical Organisms of 
Prof. A. Vogel conjectures that the formation of tannin 
in the living plant is to some extent influenced by light. 
This supposition is supported by the faCt that the proportion 
of tannin in beech- or larch-bark increases from below up- 
wards, — that is, from the less illuminated to the moie 
illuminated parts, and this in the proportions of 4:6 
and 5 : 10. , , 
Sunny mountain slopes of a medium height yield, ac- 
cording to wide experience, on an average the pine-barks 
richest in tannin. In woods in level districts the pioportion 
of tannin is greatest in localities exposed to the light, whilst 
darkness seems to have an unfavourable effeCt. Heie, also, 
we must refer to the observation that leaves exceptionally 
exposed to the light are relatively rich in tannin. 
We may here add that in the very frequent cases where 
a leaf is shadowed by another in very close proximity, 01 
where a portion of a leaf has been folded over by some 
inseCt, the portion thus shaded retains a pale green coloui , 
while adjacent leaves, or other portions of the same leaf, 
assume their vellow, red, or brown autumnal tints. If, as 
seems highly probable, these tints are due to transfoimation- 
produCts of tannin, we may not unnaturally conclude that 
they will be absent where tannin has not been geneiated. 
VII. ON THE PROBLEMATICAL ORGANISMS 
OF ANCIENT SEAS. 
* ^T is well known that Dr. Nathorst put forward the view 
that many formations, hitherto taken to be fossil plants, 
are merely the hardened traces lei t by animals cieeping 
on the mud. M. de Saporta, in a memoir published in the 
“ Bulletin de la Societe Geologique de France,” replies to 
this hypothesis, and defends the real existence of the fossil 
A Ip-gp 
It need scarcely be said that M. de Saporta by no means 
denies the occurrence of fossilised foot-prints and other 
traces of animals ; but such are excluded in a great number 
of cases where we have really to do with fossil plants. 
