FOLIAGE LEAVES: THE LIGHT-RELATION 
23 
stems against a support, as the ivies. It is only necessary 
to notice how the leaves are adjusted to light on an erect 
stem, and then to bend the 
stem into a horizontal posi- 
tion or against a support, to 
realize how unfavorable the 
same arrangement would 
be, and how many new ad- 
justments must be made. 
The leaf blades must all be 
brought to the light side of 
the stem, so far as possible, 
and those that belong to 
the lower side of the stem 
must be fitted into the 
spaces left by the leaves 
which belong to the upper 
side. This may be brought 
about by the twisting of 
the stem, the twisting of 
the petioles, the bending of 
the blade on the petiole, 
the lengthening of petioles, 
or in some other way. 
Every horizontal stem has 
its own special problems of 
leaf adjustment which may 
be observed (see Figs. 18, 
50). 
Sometimes there is not 
Space eilOUgh for the full 
development of evprv hlarlp 
eveiy DlaCle, 
and smaller ones are fitted 
into the spaces left by the larger ones (see Fig. 21). This 
sometimes results in what are called unequally paired leaves, 
where opposite leaves develop one large blade and one small 
3 
FlG . 17 . A chrysanthemum, showing 
lobed leaves, the rising of the petioles 
to adjust the blades to light) and the 
general cylindrical habit. 
