Sunlight upon Aquatic Plants. 389 
Hydra viridis , The animals instantly retract, and after 3-4 min. 
projecting parts of tentacles slightly bleached, body quite dark green. 
Recovery is possible, and after \ hour partial expansions and con- 
tractions, more active; after 1 hour. After 5-6 min. exposure the 
animals are killed, but hardly at all bleached. 
Vorticella campanula. 3-4 min. causes complete bleaching, but the 
animals may be fatally affected a minute sooner than this. 
Streptococcus varians \ Thick turbid culture of this green bacterium 
was entirely decolourized by 5 hours’ exposure to direct sunlight, 
though the bacteria reappeared again later. 
The independence of rotation and C 0 2 -assimilation, and 
the fact that assimilatory inhibition is not necessarily de- 
pendent upon the destruction of the chlorophyll, have already 
been established. Chloroplastids of Chara rotating in the 
endoplasm are shielded from the light by the outer chloro- 
plastids, and may remain green after the exoplasmic layer 
has been completely bleached. In Elodea , however, the 
chloroplastids all assume the apostrophic position, and ro- 
tating corpuscles are exposed to the same or an even greater 
intensity of light than outer stationary ones ; but nevertheless 
the former are less rapidly affected than the latter, probably 
because the exposure is more evenly distributed as the 
rotating chlorophyll-corpuscle turns over from time * to time. 
As the rotation slows, the chloroplastids may distribute 
themselves to a greater or less extent over the cell, and 
both these factors aid somewhat in producing more rapid 
bleaching. In all cases the bleaching apparently takes place 
with markedly increasing rapidity towards the end of the 
exposure as the chloroplastids become fatally affected. Thus 
with an intensity of light sufficient to completely bleach 
the chloroplastids in six minutes, during the first four minutes 
but little change in colour may be apparent, while during 
the fifth minute the corpuscle becomes much paler green, 
and during the sixth minute all green colour is lost. If we 
assume that the decomposition and reconstruction of chloro- 
1 Joum. Linn. Soc., Vol. xxxiii, 1897, p. 150. 
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