62 The Q ueens land Naturalist. April, 1928 
than half the number produced by the plants in the 
sunny position. I 11 the Brisbane Botanic Gardens it is 
the custom to grow sweet peas in pillars by planting a 
number of plants round a tall wire netting* cylinder. 
W hen] the pillars were at their best in the winter of last 
year they averaged about 39 flower stalks on the north 
side and three on the south. In the middle of July 
there were 200 stalks flowering on the nineteen pillars 
in one bed, and only two on the south side. Trees of 
Bauhinia purpurea in M ooloowin were in full bloom on 
the north and east sides at the end of June, had only a 
few' isolated flowers on the south; in the middle of 
August the north side was still flowering, and the south 
had come into full bloom. This tree had retained its 
leaves, so that the south side was shaded; others without 
leaves, and where, therefore, the sunlight passed freely 
through their bare framework without much obstruction 
had a more even distribution of flowers on both sides 
through the season. Mangoes in Brisbane set earlier in 
the north and east sides of the tree. 
In the Museum gardens is a plant of the common 
Bougainvillea, which commences flowering on the side 
taeing the A alley before the other parts show any colour. 
This is rather remarkable, as a line may be drawn across 
the plant separating the flowering from the non-f lower- 
ing portion. In the morning the reason is apparent. One 
hall — -the tlowerig half- — catches the morning sun. The 
rest receives its sunlight later in the day. 
Such observations point to the fact that the north 
and east sides of many plants develop blossoms earlier 
or in greater profusion than the south and west sides, 
and that those with a southern and western exposure (as 
in the case of the sweet peas) are relatively unsuccessful. 
The south side is the shadiest side in Brisbane, so its 
behaviour is easily understood, but the west may receive 
as much sunlight as the east does. The difference between 
the effects of morning and afternoon sunlight is quite 
marked and at first sight this does not seem what should 
be expected if their amounts are about the same. It is 
difficult to measure the relative value of the light at dif- 
ferent times of the day with respect to its photosynthetic 
value to the plant. Our methods of measuring light 
intensity with photometers using photographic paper 
do not provide a perfect means of registering the amount 
of radiation of importance to plants as they record 
mainly that of shorter wave lengths. They do indicate, 
