140 PLANT LIFE 
same tendency in a still more advanced degree. 
Only a few of the earliest leaves on the seed- 
ling exhibit a blade, all the succeeding ones 
having flattened petioles only. 
More often, however, it is the stem which 
undergoes modification and develops _leaf- 
like characters. When only certain branches 
become specialised in this way, as in species 
of Butcher’s Broom (Ruscus), it may require 
careful examination to detect the cauline 
nature of the apparent leaves. But the 
genuine leaves are really present, and although 
they are reduced to small brown scales, they 
suffice to indicate the true condition in this 
as in other extreme examples. 
A still more remarkable modification is 
seen when the roots assume the functions 
of green leaves. An instance of this is fur- 
nished by the genus of epiphytic orchids known 
as Taeniophyllum (Fig. 18). These orchids, 
which possess very inconspicuous flowers, are 
also destitute of foliage leaves. But the 
function of photosynthesis is discharged by 
the green, band- or tape-like roots which are 
appressed to the bark of the trees upon which 
the plants are growing. In some _ species 
the roots are very long, and hang freely from 
the tree trunk, when their resemblance to 
narrow strap-shaped leaves becomes addition- 
ally striking. 
It often happens that new structural modifi- 
cations—adaptations in the making, as it were 
—respond to the influence of the stimulus 
