68 LIFE OF A TREE. 
the rest, which was sprouting out its leaves in the 
free air, was of a dark, and refreshing green colour. 
It was the absence of light, then, that proved 
fatal to the unfortunate onions. Under the in- 
fluence of light the green colour of plants is pro- 
duced, and not without. The market-gardeners are 
well aware of this fact; and, in order to prepare 
for the table such vegetables as celery and aspara- 
gus, they carefully exclude the light by means of 
large earthen jars or pots, or by heaping up earth 
upon the young growing plants. The stalks thus 
become turgid with juice, but remain of a yellow 
colour, veined, in the case of celery, with red lines. 
Mr. Ellis states in the ‘‘ Gardener’s Magazine,” 
that in North America the operation of light in 
colouring the leaves of plants, is sometimes ex- 
hibited on a grand scale, and in a striking man- 
ner. Over the vast forests of that country clouds 
sometimes spread and continue many days, so as 
almost entirely to intercept the rays of the sun. 
In one instance, just about the period of Spring, 
the sun had not shone for twenty days, during 
which time the leaves of the trees had reached 
nearly their full size, but were of a pale whitish 
colour. One forenoon the sun broke through in 
