T}^e Life of ike WJteat Plant from Seed to Seed. 
91 
YIII. The Wheat Straw. 
{T?ie figures printed in the margin refer to corresponding figures on page 99 .) 
The principal function of the stem or straw of the wheat is 
to serve as the medium of communication between the leaves 
and the roots. It also carries the leaves up from the ground 1 
and enables them more efficiently to do their work in the air 7 
under the influence of the sun ; and in its green portions it 
supplements the proper work of the leaves. 
We noticed that by the end of April all the joints of the iv 
straw were present in the young plant, each furnished with its 5 
own leaf. The joints were close together and the straw solid. 
The subsequent lengthening of the straw has been caused by 
the gradual separation of the joints by the growth of every part 
of the intervening stem. In expanding in the air the stem is 
carried up without encountering any barrier to its progress. 
The rapid growth of the joints below does not, therefore, incon- 
venience the growing stem. It is very different, however, with 
the root, which has to seek its way between particles of the soil, 
and to turn aside when it meets with a stone or other obstacle. 
A lengthening of the already formed parts would effectually 
prevent the growing root peneti’ating the soil, and so, as we 
have already seen, the root increases in length only at its thread- 
like extremity. 
The straw increases in width as well as in length, and this 
growth tears up and destroys the cells which filled the centre in 
its early state. A hollow cylinder with solid joints is conse- 4 
quently produced. Such a stem gives the necessary strength 
without using up the large amount of food that would be re- 
quired to form a solid stem, which at the end of the short life 
of the wheat plant would leave an excessive amount of waste 
material. The strands of vascular bundles symmetrically 
arranged in the cylinder of the stem, besides the other functions 0 
they perform, add strength to the straw. 
The leaf is attached to the stem at the node or joint. A 2 
little above the place of attachment the sheath of the leaf swells 3 
out round the stem forming the knob. The sheath surrounds 5 
the stem for a considerable distance before the blade of the leaf is 
given off. The stem has alternate fine lines of green and white ; 
the skin covering the green lines is perforated Avith stomates, 
and the green cells below perform the functions of the similar 
cells in the leaves, taking in carbon and uniting it with oxygen 
and hydrogen to make starch. 
W. Carruthees. 
