MR. A. J. EWART ON ASSIMILATORY INHIBITION. 439° 
Effects of Insolation upon Assimilation. 
It is well known that prolonged exposure to direct sunlight is 
fatal to Bacteria and many Algæ, and exercises a marked injurious 
influence upon many shade-loving and water-plants. Even the 
most resistant of Phanerogams are, especially at certain periods 
of development, unable to stand prolonged and severe exposure 
with impunity. Before the vitality of the plant is permanently 
affected, there appears to be an intermediate condition from which 
perfect recovery is possible, but during which the power of 
assimilation is in abeyance though the chlorophyll apparatus is. 
green and intact. Experiments in this direction were performed 
on both water- and land-plants, the chief obstacle being the 
difficulty of obtaining sufficiently long periods of exposure to 
produce the desired effect. 
Plants of Elodea, Utricularia, and Chara exposed to full sun- 
light in water kept cool by constant renewal from 5 A.M. to 5 P.M., 
during a bright unclouded day, gave the following results :— 
Elodea cana- | Nearly all leaves and leaf-cells living and green ; in most | 
densis. cases weak assimilation, but in many leaves, though all 
cells are living, none. After 2 hours in diffuse daylight, 
all living leaves show a more or less active assimilation. 
Utricularia | All plants living and showing weak assimilation, which is, 
vulgaris. however, absent from many branches. After 2 hours in 
diffuse light, fairly active assimilation in all cases. 
Chara fra- | Many cortical and end cells killed and bleached, plenty 
gilis. living, but no assimilation, and rotation absent or slow. 
In many branches the cortical cells are killed, but the 
medullary cells remain living and show in 15-30 minutes 
rapid rotation. If the cortical cells are quite bleached 
and the medullary chlorophyll grains quite colourless, 
then the medullary cells die and rotation ceases in a few 
hours without any return of assimilation taking place ; 
but if the medullary chlorophyll grains retain partly or 
entirely a greenish coloration, the cell may recover and 
show, after 3-4 hours in diffuse light, or, where but few 
grains retain a greenish coloration, only after several 
days, a distinct evolution of O. In the living end cells 
rotation is active in 15-80 minutes, and in 1 hour weak 
assimilation, fairly active in 3. In a few end cells the 
chlorophyll is more or less bleached, and though rotation 
may return and continue for from a few hours to several 
days no return of assimilation takes place, the cells 
finally dying. 
i reparations of end cells of Chara kept floating on water 
at abet 152 Q exposed to full sunlight for 4 hours, showed neither 
rotation nor assimilation. After j hour in diffuse daylight a faint evolu- 
tion of oxygen is shown by most end cells, but in some cases still no 
rotation. In 1 hour the evolution of oxygen is moderately active, but 
rotation isstill slow. In 5 hours both assimilation and rotation are active. 
