CO-OPERATION AND THE ORIGIN OF FLOWERS. 153 
obvious explanation is that with direct overhead light there 
is the least, and with the sun at a low angle the most, absorp- 
tion of light by the earth’s atmosphere. 
In all scientific questions, it is of the utmost importance 
to consult the practical business man. Horticulture is a 
quite enormous industry. One problem which many gar- 
deners have tried to solve is the best method of inducing a 
plant to flower profusely and before its proper time. 
The following are some of the processes which are found 
satisfactory :— 
1. By the use of radio-active water. 
2. By exposure to the vapour of ether or chloroform.16 
3. By injection of alcohol. The Farnese acacia may 
be induced to flower 2y days earlier than usual by 
the injection of 5 per cent. alcohol in the leaf.!” 
4. By severe cold; after being kept for some days under 
moderately hot conditions, the temperature is sud- 
denly reduced to below the freezing point. After a 
short period it is again raised to an even higher 
temperature than it was originally. In this 
connection an interesting case has been recorded 
recently. Certain Zinnias were badly frozen in May 
and cut down to the root. They responded from 
July to November by a quite unusual profusion of 
blossoms, which also varied greatly in colour.!8 
5. By a hot water bath of nine to twelve hours’ duration 
at a temperature of 30 degrees to 50 degrees. By 
this method Wisteria flowers can be obtained on 
Christmas day. 
6. By ill-treatment, such as cutting or piercing the 
tissues. Fruit trees have been pruned from time 
immemorial; to-day one method is to pierce the bud 
with a fine sewing needle and inject a little water. 
7. By drying up the plant. 
To these seven horticultural methods, one may 
attach the following two observations :— 
8. In a nursery, trees are often observed to flower 
