64 The Queensland Naturalist. April, 1928 
green coating looking like bright paint 011 the south side 
of fences, is Protococcus, an Alga.) The north side is 
usually bare or almost bare of these plants. The reason 
is apparent after a rainy night followed by a sunny day. 
The northern side of trees and fences is soon dry, but 
the southern side stays moist all the morning. In the 
ease of smooth barked plants both sides dry rapidly, and 
epiphytic cryptogams have little chance to become estab- 
lished. It is a matter of moisture only, as on the northern 
side, where the contours of the trunk allow the bark to 
stay moist, mosses, algae, and lichens grow abundantly. 
The plants grow on the cooler side because that side is 
less liable to dessieatioii and not because of temperature 
preference. 
It has long been known that alterations in the length 
of day have a pronounced effect 011 plant life. The in- 
creasing of the period of exposure to light by artificial 
methods in some cases induces earlier fruiting, but in 
others retards or altogether suppresses it. Work on this 
subject by OJarner and Allard in America lias been car- 
ried out on a large scale, and the results are of exceptional 
interest. Many of their plants are not common in 
Queensland, but a few which are grown here may be men- 
tioned. Cosmos bipinnata, in Washington, flowered at 
the height of 30 inches under normal day length. YV lien 
the light period was continued until midnight by means 
of electric light the plants continued' to grow until they 
attained the height of fifteen feet. .Yearly a year later, 
when the return of winter shortened the days again 
and the electric light treatment whs discontinued the. 
plants flowered. Similar behaviour is not uncommon ill 
Brisbane, Where in the long summer days the Cosmos 
grows to a height of eight or ten feet, and finally flowers 
in the shorter autumn days. Plants whose growth takes 
place in the winter attain only about three feet. Short- 
ening the long North American summer day in the case 
of Sorghums obtained from British India and from tropical 
Africa, resulted in a much earlier date of shedding of 
the first pollen (over four months earlier in some eases), 
increased stature, and in some eases increased stooling 
as compared with controls exposed to the ordinary length 
of day. Long exposure every day increased the 'height 
and seed production of buckwheat (Fagopyrum vulgare) 
over that of plants given short periods of illumination; 
this plant makes its best growth in high altitudes Avhere 
"the summer days are long. 
