CHAPTER. IT 
STEMS 
When studying stems it should first be determined whether 
they were derived from monocotyledonous or dicotyledonous 
plants. This fact is ascertained by determining the type of 
the fibro-vascular bundle. See Chapter XI. The next fact 
to determine is whether the stem is from an herb or from a woody 
plant. This fact is readily determined because herbaceous 
stems have a true epidermis, masses of collenchyma at the 
angles of the stem. The cortical cells contain chlorophyll, and 
the pith is very large. Woody stems have a corky layer, a 
phellogen layer, and the pith is very small except in the very 
young woody stems. 
Having determined these facts, a study should be made of 
the arrangement, form, structure, color, and the cell contents 
of the different cells in order to determine the species of plant 
from which the stem was obtained. 
HERBACEOUS STEMS 
The great variation in the structure of herbaceous stems is 
shown in the cross-sections of spigelia (Plate 95); in ruellia 
(Plate 96); in the charts of powdered genuine horehound, 
powdered spurious horehound, and in the chart of powdered 
insect flower stems. 
CROSS-SECTION SPIGELIA STEM 
Spigelia stem (Plate 95) has the following characteristic 
structure: 
Epidermis. The epidermal cells are papillate. 
Cortex. The cortical parenchyma cells consist of tan- 
gentially elongated cells which are oval in outline. 
Phloem. The phloem consists of sieve cells, phloem paren- 
chyma, and of bast fibres. 
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