PLANT ORGANS AND ORGANISMS I37 
Eucalyptus trees of Australia and Tasmania are reported to attain 
the height of 500 feet. 
Nodes and Internodes. —The nodes are the joints of stems. They 
represent the parts of the stem from which leaves or branches arise. 
Internodes are the parts of stems between nodes. 
Direction of Stem Growth. —Generally the growth of the stem is 
erect. Very frequently it may be: 
Ascending, or rising obliquely upward. Example: Saw Palmetto. 
Reclining, or at first erect but afterward bending over and trailing 
upon the ground. Example: Raspberry. 
Procumbent, lying wholly upon the ground. Example: Pipsissewa. 
Decumbent, when the stem trails and the apex curves upward. 
Examples: Vines of the Cucurbitacece. 
Repent, creeping upon the ground and rooting at the nodes, as the 
Strawberry. 
Stem Elongation. —At the tip of the stem there is found a group of 
very actively dividing cells (meristem) which is the growing point of 
the stem. All the tissues of the stem are derived from the cells of 
the growing point whose activity gives rise in time to three genera¬ 
tive regions which are from without, inward: 
1. Dermatogen, forming epidermis; 
2. Periblem, forming the cortex; and 
3. Plerome, iorming the fibro-vascular elements and pith. 
Duration of Stems. 
Annual, the stem of an herb whose life terminates with the season. 
Examples: Corn. 
Biennial, where the stem dies at the end of the second year. 
Example: Burdock. 
Perennial, when the stem lives for many years. Example: Oak. 
Stem Modifications. —(i) twining, by elongation and marked 
circumnutation of young internodes as in Convolvulus, Dodder, 
etc. (2) Tendriliform by thread-like modification and sensitivity 
to contact of a side branch as in Passion flower, Squash, etc. (3) 
Spiny, by checking and hardening of a branch that may then become 
defensive ecologically as in hawthorn, honey locust, etc. (4) 
Aerial tuberous, in which one or more internodes, enlarge above 
ground and store reserve food as in pseudobulbs of orchids, Vitis 
