Sunlight tip on Aquatic Plants. 387 
substance into some extremely insoluble modification. It is 
possible to completely bleach all the chloroplastids of a leaf-cell 
of Elodea without previously active rotation entirely ceasing, 
and when returned to normal conditions rotation may become 
active again in a quarter to half-an-hour. All such cells die 
in water in a day or two, though they may be kept for as 
long as a week in dilute sugar or glycerine. 
A few experiments were also made upon a couple of 
chlorophyllous animals, Hydra viridis , with definite ‘ chloro- 
plastids/ and Vorticella campanula , with diffuse chlorophyll. 
Vorticella campcimda. 1. Light = 4-5 S, killed in 1 min. in closed 
cell preparation without any perceptible bleaching of the chlorophyll. 
In an open drop of water the animals are killed (no alum-solution) in 
3-4 min., but behind an alum-solution 5-6 min. are required, and in 
this time the chlorophyll is almost completely bleached. The 
contractions and expansions take place more slowly in 2-3 min., and 
finally the stalk may remain contracted, and the body contracted or 
expanded in light rigor. Partial recovery may take place, a portion 
of the cilia commencing to move again. A weaker intensity of light 
may at first accelerate movement, the contractions and re-expansions 
of the stalk taking place at shorter intervals. 
2. Secondary effect of light. After exposure to the brightest 
diffuse daylight for 1 day, almost all the Voriicella zooids separate 
from their stalks and become free swimming. This is probably an 
attempt to escape an unfavourable intensity of light. 
3. 8-10 S, movement almost immediately ceases, recommencing 
in 1-5 min., according to the length of the (non-fatal) exposure. 
Temporary light-rigor if suddenly induced may leave the stalks and 
bodies more or less completely expanded, and on removing the light 
the first movement may be to complete the previously commenced 
coiling. If the light-rigor is at all prolonged (2-3 min.), death 
immediately follows. 
Hydra viridis. 1. Exposed to 6 S, at once retracts, and remains 
so till death occurs. Ends of tentacles bleached in 10 min., body still 
dark green after 15 min., but power of recovery is lost. It is possible 
to permanently destroy the motility of some of the tentacles by 
localized exposure, while the rest remain living. After 10 min. 
exposure tentacles may be killed, but the body may show feeble 
