16 _ BOTANICAL GAZETTE [JANUARY 
plants; neither were they gray-felted nor furnished with latex; 
but in the middle of the dry bush so heated by the sun the plants 
stood with their strange lusterless, dull green and moreover 
extremely delicate and finely compound leaves. It was not 
difficult to discover that they had another defense, and one devel- 
oped even to perfection against the intense light and transpiration; 
I refer to the photometric leaves that by an exceeding sensitive- 
ness for the optimum of light adjust themselves readily to the 
different amounts. In the gentle morning light the leaflets are 
extended flat, intercepting as many of the rays as possible. But 
later in the day, when the sun is rising higher and the heat is 
growing more intense, the leaflets fold themselves more and 
more together and upwards like a closing book, the consequence 
of which is that the light strikes the plane of the leaf at acute 
angles, by which its effect becomes weakened. Thus the leaf 
itself regulates the light and the transpiration, and the differ- 
ent aspect of the acacia bushes at different times of the day is 
not quite without influence upon the physiognomy of the land- 
scape. 
This phenomenon, as well as others, we find also in our 
northern climate; for instance, one finds the leaflets of the wood 
sorrel, Oxalis Acetosella in our forests differently placed with 
respect to the different light of the day. 
The chird type of vegetation I want to speak of is the campos 
or savannas already mentioned. To find anything like them one 
would have to go to the grass steppes of southeastern Europe. 
Trying to compare the savannas with our own grass fields and 
meadows, one finds a great difference in physiognomy as well as 
in ecology. The savannas have a dry or, at all events, at periods 
a dried up and hot soil; their grasses are coarse and stiff, grayish 
and hairy, and only fresh green in their first and short youth. 
And even admitting that the campos of Brazil especially are 
much richer in flowers than are our meadows, and that the flowers 
of the campos are much larger and with more gaudy colors than 
ours, I must Say that the wonderful freshness and charm so 
peculiar to our green, luxuriant, thick, and soft meadows and 
fore 
