Triglochin maritimum , L. 
89 
THE FLOWERING STEM. 
Fig. 4, PI. VI, illustrates in a diagrammatic manner a trans¬ 
verse section of a flowering stem. 
The epidermis is well marked, consisting in young specimens 
of thin-walled oval cells, as seen in transverse section; in the 
older specimens a cuticle is developed, which is longitudinally 
ridged in much the same way as in the leaf to be described later. 
Stomata occur in the epidermis, but they are not very numer¬ 
ous ; the guard-cells are sunk a little below the general surface 
of the stalk, and are very similar to those of the leaf. The 
cortical cells immediately within the epidermis contain chloro¬ 
phyll-corpuscles. 
In the cortex of the lower regions of the stalk a large num¬ 
ber of air-spaces occur, recalling the arrangement met with in 
the spongy mesophyll of an ordinary leaf. These air-spaces 
are more regular in the younger regions of the stem, where 
their appearance is very similar to that of the air-spaces in the 
stem and petiole of purely aquatic plants. 
The structure of the vascular bundles, which are here of 
the collateral type, is illustrated by Figs. 5 and 6, PI. VI. 
The phloem, as is usual with Monocotyledons, is regular 
and well marked. In some bundles, more especially in the 
older ones, a few elements in the phloem-parenchyma become 
lignified ; such a case is shown in Fig. 6. In Fig. 5, illus¬ 
trating the structure of a younger bundle, it may be seen that 
primary meristem, between the phloem and xylem, persists 
for some time before passing over into permanent tissue : this 
is of some interest, inasmuch as the same persistence of meris- 
matic tissue is found in many plants belonging to the Ranun- 
culaceae. This cambial arrangement is not so well marked in 
older bundles, for, of course, the elements have been transformed 
into permanent tissue. 
The xylem calls for no special comment. 
As the flower-stalk grows older the cells of the ground- 
tissue surrounding the separate bundles form a lignified sheath, 
