Fig. 38.—Transverse section of a portion of the stem of Panicum flavidum. × 70
1. Epidermis; 2. sclerenchyma; 3. vascular bundle.
The stems of Panicum Isachne and Eragrostis interrupta are hollow. The stem of the former is circular in outline in cross section, though wavy. There is a sclerenchymatous ring close to the epidermis but separated from it by a few layers of parenchyma. One set of bundles is imbedded in the band, and another set just touches the inner border of it. A third series is disposed around a fairly large amount of ground tissue, which may or may not have a cavity in the centre. The stem of Eragrostis interrupta has more or less the same structure, but the cortex has air spaces here and there. Other minor differences may be seen on referring to figs. 35 and 36.
Fig. 39.—Transverse section of a portion of the stem of Panicum colonum. × 70
1. Epidermis; 2. sclerenchyma; 3. vascular bundle.
The stems of grasses growing in wet or marshy situations differ in structure from those detailed above. As examples the stems of Panicum flavidum, Panicum colonum, Panicum Crus-galli and Panicum fluitans may be considered. The stem of Panicum flavidum is broadly ovate in cross section with a flat front and is more or less solid, though occasionally the parenchymatous cells in the centre get broken. Two rows of vascular bundles surround a fairly large amount of parenchymatous cells of the ground tissue. There is a continuous ring of sclerenchyma separated from the epidermis by a fairly broad cortex. The cortex has a number of fairly large air-cavities separated by bands of parenchymatous cells. Within the sclerenchymatous band lie small vascular bundles at regular intervals just towards the cortex. A few isolated bundles are in contact with the inner border. (See figs. 37 and 38.)
The stems of Panicum colonum, Panicum stagninum and Panicum Crus-galli have in their centre in the ground tissue stellate cells with air-cavities. This part is surrounded by a fairly broad portion of parenchymatous cells in which are imbedded two rows of bundles. Outside these bundles runs round the stem a narrow sclerenchymatous band with a few bundles in it of which some touch it inside and others outside. Two bundles are found by themselves in the tissue of stellate cells. In Panicum Crus-galli three or four bundles are met with amidst the stellate cells.
