24 
POPULAE SCIENCE EETIEW. 
awake or asleep,” phenomena obvious enough in many plants ; 
the folding and unfolding of flowers ; the movements shown by 
tendrils and climbing plants, to which Mr. Darwin has recently 
drawn so much attention, and a summary of whose researches, 
from the pen of the Eev. Greorge Henslow, appeared in the 
pages of this Review last year. These, together with the move- 
ments observed in the stamens and pistil, in connexion with the 
fertilisation of the latter organ, are probably, if not certainly, 
effected by similar means, even though those means be called 
into action by different circumstances. Allusion may here also be 
made to the movements observed in the branches of trees in frosty 
weather. In the Eeport of the Proceedings of the Botanical 
Congress, London 1866, is an elaborate paper by Professor 
Caspary, showing the effect of cold in inducingthese movements, 
the direction of which varies in different trees, and the amount 
of which is generally in direct proportion to the intensity of the 
cold. Dr. Caspary, however, has not been able to ascertain how 
the cold produces these actions. Motion by the action of cilim 
— as marvellous a phenomenon as any — appears to be con- 
fined to the simplest organisms in the plant world, wEich do not 
come strictly within the limits of this communication. But 
inasmuch as it has a relation to other facts, to be hereafter 
alluded to, we may call attention to the action of light on these 
lowly creatures. Dr. Ferdinand Cohn, amongst others, has 
clearly shown that the direction in which these plant cells move 
is influenced by the direction in which the light falls. They 
move towards the light, turning their ciliated ends towards it, 
while the remainder of the cell which, unlike the part just 
mentioned, is filled with chlorophyll, is directed away from the 
light. If the rays be prevented access no movement at all takes 
place, and while the red and the calorific parts of the spectrum 
generally have no effect, the blue 'and violet rays are specially 
powerful in producing the effect. The motions shown by 
the Oscillatorice can hardly be passed without mention, though 
in truth little is known concerning them. The plants just 
named are simply cylindrical cellular tubes, endowed with a 
peculiar undulatory movement which is exerted by the ge- 
latinous contents of the cell, rather than by the cell wall. So 
much is made out, and it is of great significance, as showing 
that, as is the case with almost all the other principal pheno- 
mena of life, it is the protoplasm which is the seat of activity 
and not the outer cell wall. This contractile power of the 
protoplasm is seen in no plant better than in the Selaginella 
mutahilis, now often to be met with in hot-houses. This plant, 
under the influence of bright light becomes of a pale whitish 
colour, as though milk had been spilt over it, but when the 
intensity of the light is less it resumes its green colour. The 
