77 
altering the Daily Period of Light. 
• 
during the day when the sun is shining, but cool off very rapidly after sun¬ 
set and remain cold during the night. Normally the greatest growth takes 
place at night, hence chilling them at this time explains, in part at least, 
their stunted growth.’ 
Warming (18) says: ‘The development of plants depends not only 
upon the intensity but also upon the duration of the light to which they are 
exposed. For instance, in Finland or the north of Norway barley ripens 
its grain in eighty-nine days from the day of sowing, but in Schonen (in 
Sweden, 55 — 7 0 N.) it requires 100 days, despite the higher temperature and 
the more intense light; and the explanation of this must in part be that in 
the former places prolonged illumination promotes anabolism.’ 
He further states that ‘ intense light retards the growth of the shoot; 
consequently heliophytes are compact and have short internodes, but 
sciophytes have elongated internodes; species clothing the forest soil are 
mainly tall and long-stemmed 
By the use (19) of an acetylene light Craig was able to force the 
development of flowers within a shorter time in the case of Easter lilies. 
Hayden and Steinmetz’s experiments (20) on the ripening of String 
Beans under electric lamps proved that they ripened in about half the time 
required for those grown under natural conditions with daylight only. 
Palladin ( 22 ) says that ‘ plants grow more.slowly by day than by night, 
so that it appears that light exerts a retarding influence upon growth ’. 
De Besteiro and Durand (23, 24), experimenting with Garden Pea 
under light of intensities of §, J, and full sunlight, found that the dry 
weight of the entire plants increased with the intensity of light and in the 
proportions of 2 , 6 , 7 , and 11 . 
Wiessmann (25) found as the result of growing Oat plants on a roof 
and in a court that those on the roof, which were more fully exposed to the 
light, not only stooled better, but also flowered and ripened seed earlier and 
had a greater yield of both straw and grain than the plants grown in the 
court. 
Garner and Allard (27, 32) experimented with a large number of 
plants, some of which were kept in the dark for a certain number of hours 
daily. Different species behaved in different ways under this treatment, but 
they found that some species so darkened came into flower much earlier 
than other members of the same species which were exposed to the full 
period of daylight. Another conclusion reached was that ‘ in all species 
thus far studied the rate of growth is directly proportional to the length of 
the daily exposure to light ’. 
Adams (28), experimenting with Flax, found that the plants exposed 
to the full period of daylight were taller and heavier and reached the flower¬ 
ing stage sooner than those darkened for a number of hours each day. 
By employing continuous illumination (31) by means of an Osram 
