LEAVES : 27 
CHAPTER. Vu 
LEAVES 
THE poet-philosopher Goethe was the first to point out in 
1790 that cotyledons, bud scales, foliage and floral leaves are 
structures of the same nature, for they stand in the same 
Definition of elation to the stem. The term “leaf,” in 
a Leat. botany, includes all structures other than 
branches, developed as lateral appendages of the stem, how- 
ever unlike they may be in appearance. 
: The first leaves of the plant are the cotyledons ; 
these are always different in shape from the foliage 
leaves which follow. Those of mustard are kidney-shaped, 
whilst the foliage leaves are very deeply divided. Sycamore 
has two narrow blade-like cotyledons, whilst the leaf is broad 
and spreading. Lord Avebury thinks that the shape of the 
seed has, on the whole, the greatest influence in determining 
the shape of the cotyledons, but many other factors have to 
be taken into consideration ; for instance, the presence or 
absence of food material, as this affects the amount of room 
left in the seed for the cotyledons, and therefore, the way in 
which they are folded. 
Some seeds have only one cotyledon ; for example, maize, 
Wheat, date. Plants with only one cotyledon form the large 
group known as Monocotyledons ; those with two cotyledons 
are called Dicotyledons. 
Covering Covering leaves include bud ae. and brace 
heaves. The former have already been sufficiently de- 
scribed {Chapter II.). Bracts are the leaves on the flower- 
stalk ; they may enclose a single flower, as in snowdrop ; or 
a group of ‘flowers, as in arum. They vary very much in 
shape; sometimes they are sheath-like, as in crocus; some- 
Cotyledons. 
