IN VEGETABLE BIOLOGY. 219 
mounted lower side uppermost. In no case was the sensitive- 
ness of the protoplasm affected by the position, as regards the 
zenith, occupied by its containing cells. 
This chapter may be brought to a conclusion with the mention 
of the following points :— 
(1) The length of a plant's epistrophie interval depending 
upon the quality of its protoplasm, the reason for the caution 
expressed in the opening sentence is apparent. In order that 
the experiment there spoken of may succeed, it is necessary not 
only that the light be of precisely the proper quality, but the 
protoplasm of all the plants must either be perfectly healthy, or 
corresponding inroads into its health must have been made in all 
cases. 
(2) It would appear that if an epistrophic interval do not 
reach far to the right, it will extend some (perhaps all the) way 
upon the lett side of the photrum ; and this seems to be a general 
rule. Overlapping intervals do occur, however; one such was 
found in the case of a moss growing with Funaria hygrometrica, 
the chlorophyll of which required better sunlight to positively, 
and feebler light to negatively apostrophize it than did the 
Funaria. 
(3) The epistrophic interval of all aquatics is developed far 
more upon the left than upon the right side of the photrum; 
that of sun-loving aerophytes is restricted to the right side, while 
shaded aerophytes have an interval intermediate in position. 
This generalization applies to all types irrespective of their mor- 
phological relationship. 
(4) Besides quality of protoplasm and habitat, it may, perhaps, 
turn out that the interval is, at least to some extent, determined 
by the season in which a plant grows. This is the only way in 
which the behaviour of Saxifraga granulata can be accounted 
for; the rosulate leaves of this type may, perhaps, to some extent 
be protected from the sun by overshadowing grass-blades &e. ; 
but a more reasonable view of its resemblance to shade-lovers is 
that, although exposed to sunlight, the office of the leaves has 
been performed before that period of the year arrives when light 
is of the highest intensity. Whether this doctrine is of wider 
application has not yet been determined. 
Lastly, as extreme cases of difference in respect of the motile 
agency of light on the protoplasm of the same individual, the 
Characee may be referred to, the divergence here applying not 
TM CIO 
