1884.] 
upon Vegetation. 589 
The first crop became ripe in 88 days, the second prema- 
turely ripe in 87 (the maximum heat and light happening 
too early, before the plant was sufficiently mature) ; the 
third became imperfectly ripe in 150, the fourth in 200, and 
the last in 240 days ! 
In another series of experiments Hellriegel examines the 
comparative aCtion of direCt and of diffused light upon 
plants. He points out certain disadvantages to which 
plants cultivated in glass-houses are exposed. The motion 
of the air in an enclosed house is less perfect than outside 
(though it must be admitted that in England generally the 
movements of the air are far too perfect for vegetation). 
Another — and in our opinion far more important — difficulty 
is that even the best glass is not absolutely permeable to air 
and light, a certain portion being reflected or absorbed. 
Within the house a further portion of the light which has 
entered is absorbed by dark objects (plants, pots, soil, &c.), 
and converted into heat which does not radiate out at the 
same rate as it is produced. Thus the proportion between 
light and heat is different within from without : we hesitate, 
however, to endorse the author’s opinion that this difference 
in proportion is always disadvantageous to plant-life. The 
proportion existing in the open air varies exceedingly, and 
there are few conditions more destructive to plant-life than 
one which prevails very commonly during the easterly winds 
of spring, when intense light is combined with a low tem- 
perature. It has been found that the blighting effeCt of such 
weather may be counteracted either by increasing the heat 
or by keeping the plants temporarily in the dark. 
From Hellriegel’s experiments it appears that from two 
sets of barley-plants, equal in number, those cultivated in 
direCt sunlight in the open air gave 4282 m.grms. of grain, 
whilst a similar number grown in diffused light only yielded 
merely 873 m.grms. 
A further subjeCt investigated was the development of 
plants in light of different colours. The author’s results by 
no means confirm those with which General Pleasanton 
astonished the world a few years ago. 
It is a known faCt that white light, after it has passed 
through our atmosphere, has not always the same qualita- 
tive composition. The author did not attempt to experiment 
with perfectly homogeneous, monochromatic light, but se- 
lected illuminations in which rays of a certain given wave- 
length predominated, others being more or less completely 
excluded. For this purpose he used very large roomy bells 
of coloured glass, which were kept regularly ventilated by 
