INTERNAL STRUCTURE OF STEMS. 
41 
109. BlllbletS are little bulbs, or fleshy buds, formed in the axils of leaves above 
ground, as in the Bulb-bearing Lily. Or in some Leeks and Onions they take the 
i place of flower-buds. Falling off, they take root and grow into new plants. 
110. The Internal Structure of Stems. Plants are composed of two kinds of ma- 
terial, 'namely, Cellular Tissue and Wood . The former makes the softer, fleshy, and 
pithy parts ; the latter forms the harder, fibrous, or woody parts. The stems of 
herbs contain little wood, and much cellular tissue ; those of shrubs and trees 
abound in the woody part. 
111. There are two great classes of stems, which differ in the way the woody 
part is arranged in the cellular tissue. They are named the Exogenous , and the 
Endogenous . 
112. For examples of the first class we may take a Bean-stalk, a stem of Flax, 
Sunflower, or the like, among herbs, and for woody stems any common stick 
of wood. For examples of the second class take an Asparagus-shoot or a Corn- 
stalk, and in trees a Palm-stem. These names express 
the different ways in which the two kinds grow in thickness 
when they live more than one year. But the difference 
between the two is almost as apparent the first year, and 
in the stems of herbs, which last only one year. 
113. Tile Endogenous Stem. Endogenous means “inside- 
growing.” Fig. 77 shows an Endogenous stem in a Corn- 
stalk, both in a cross-section, at the top, and also split 
down lengthwise. The peculiarity is that the wood is all 
in separate threads or bundles of fibres running lengthwise, 
and scattered among the cellular tissue throughout the 
whole thickness of the stem. On the cross-section their 
cut ends appear as so many dots ; in the slice lengthwise 
they show themselves to be threads or fibres of wood. 
Fig. 78 is a similar view of a Palm-stem (namely, of our 
Carolina Palmetto, of which whole trees are represented 
in Fig. 79). It shows the endogenous plan in a stem 
several years old. Here the bundles of wood are merely 
increased very much in number, new threads having been 
formed throughout intermixed with the old, and any in- 
crease in diameter that has taken place is from a general distention or enlargement 
