Sunlight upon Aquatic Plants . 383 
classical researches, and ending with the observations made 
by the writer 1 . 
The same injurious action of intense light is produced 
upon all plants, whether with or without chlorophyll, though 
in chlorophyllous cells it is almost always the chlorophyll- 
grains which are first affected 2 , Thus both non-chromogenic 
and chromogenic Bacteria, including those which contain 
chlorophyll and grow normally only when exposed to diffused 
daylight, may be killed by prolonged exposure to direct 
sunlight, and even the vitality of the spores may be fatally 
affected by somewhat more prolonged exposure 3 . It is for 
this reason that the spores of Mosses, Ferns, &c., and the 
pollen-grains of higher plants, are covered by comparatively 
opaque external coverings, for in order that the full effect 
of the sunlight may be produced, it must penetrate with 
undiminished intensity to the living contents of the cell, 
r— It is extremely improbable that any living protoplast if 
naked, or if enclosed by a transparent wall, could withstand 
exposure to the full and undiminished intensity of sunlight 
for even a day (twelve hours’ constant exposure), and cer- 
tainly not when exposed successively day after day. In a 
chlorophyllous cell it is the chlorophyll-grains which are first 
affected. The reason for this is that these are organs 
specially adapted for collecting and intercepting sunlight. 
Light-rays, which pass unaltered directly through the cell, 
cannot possibly exert any effect upon it. It is only the rays 
which are altered in their passage through, or actually 
absorbed, which can exert any influence upon the living 
plasma or plasmatic plastids. Hence it is upon the chloro- 
phyll-bodies that the most marked effect is produced by 
intense illumination 4 . It is important to remember in this 
v 1 Assim. Inhib., Journ. Linn. Soc., Vol. xxxi, pp. 439, 443, 573 ; Ann. of Bot., 
Sept., 1897, Vol. xi, p. 339; Pringsheim, Pringsh. Jahrb., Bd. xii, 1882, pp. 326, 345; 
the literature quoted in these works. 
2 Journ. Linn. Soc., Vol. xxxi, p. 573 (Chara) ; Ann. of Bot., 1 . c. 
3 See Frankland and Ward, Report of Thames Water Commission; Ward, 
Annals of Botany, March, 1898, Vol. xii (A Violet Bacillus), p. 65. 
1 Assim. Inhib., Journ. Linn. Soc , Vol. xxxi, 1896, p. 573, &c. 
