hte is maintained iy the pre ocess “of esotanba is toa “certain. ‘extent — 
‘remaining still exposed to light, the buds will continue to develope in 
to collect where there is a medium intensity of light, avoiding both deep 
brightest light. Finally the normal habit of plants is altogether de- 
termined by the direct influence of light. The internodes of the stems \. © 
Pee Sy 
independent of light, as is shown by the germination in the dark of | 
aA ¥, Foot 
"seeds, tubers, 2nd bulbs. But even leafy plants which have accumulated a a4 
a sufficient quantity of reserve-material in the light, put out shoots, and | 
even flowers and fruits, when placed in the dark. If, for example, the & : 
growing end of a branch of a green-leaved plant, such asa pumpkin or 
Tropeolum, is made to grow into an opaque receptacle, the green leaves | 
the dark, and new leaves and flowers to be formed which attain their Pe 
full size and colour, the latter even producing fruits and fertile seeds. 
It is only rarely that the seclusion from light produces any perceptible => 
effect on the development of the plant ; though sometimes the flowers | 
which are produced in the dark have an abnormally light colour. All 
this takes place at the expense of the food-material conveyed to them | 
through the stem, which had been previously assimilated by the leaves ex- 
posed to light. In the same manner the underground parts of parasitic 
plants, or those otherwise secluded from the influence of light, carry 
on their existence to a certain extent independent of light; but are 
nevertheless indirectly dependent upon it, because they are nourished 
by substances which could only be formed under the influence of light. 
~The earliest development of the plant seems to.be even promoted by 
the absence of light or by shade. ‘Thus, for example, roots are formed - 
on the stems of Cactus, Tropeolum, &c. which grow in the dark, where 
‘they would never be formed in the light. The lower Algz assimilate  — | 
in the daytime, and form swarmspores in the night, or, when placed in 
the dark, even in the day-time. The movement of the protoplasm on 
which the formation of the swarmspores depends is not caused directly ieee 
by the influence of light, but is rather interrupted by it. The direction 
of the movements of the swarmspores stands, however, in a definite 
relation to light, their anterior end being always turned towards it. It 
has, nevertheless, been observed in some cases that they have a tendency 
shade and bright sunlight. The chlorophyli-bodies enclosed within 
cells are subject, in some plants, as Sagzttarza sagittefolia, to a change } 
of position, being carried by the currents of protoplasm to the region of + — 
of bleached or etiolated plants grown in the dark are often elongated to 
ten or twenty times their ordinary length ; while leaves of Dicotyledons ; Cas 
and Ferns, which are normally broad and branched, remain, when x 
grown in the dark, remarkably small, Under these circumstances the = 
20 
“ 
lamina of the leaf of Zropfeolum attains scarcely from 4 to 4% of its og 
