Botany Basics - Stems Part 2

Below-ground Stems  Potato-tubers, iris rhizomes, and tulip bulbs are actually underground stems that store food for the plant  The nodes of these structures are what make them stems and not roots  E.g. the eyes of a potato are actually the stems nodes; each eye contains a cluster of buds  When growing potatoes from seed, it is important that each piece contain at least one eye and be about the size of a golf balls so that there will be early energy from shoot and root growth and development Rhizomes  Rhizomes resemble stolons because they grow horizontally from plant to plant  Rhizomes can make some invasive weeds especially hard to fight  E.g. Canadian thistle can literally spread underground, sending up new plants at random intervals from its rhizomes  Johnsongrass is an insidious weed as well because of its rhizomes  Few options short of Roundup and manual digging are effective in fighting these types of nuisances  In some cases, Rhizomes can be effective methods of increasing the size of perennials such as irises Bulbs  Tulips, lilies, daffodils, and onions produce bulbs  Bulbs are shortened, compressed, underground stems surrounded by fleshy scales (leaves) that envelop a central bud at the tip of the stem  A tulip bulb cut in half in November will have all the flower parts in miniature  After a bulb-producing plant flowers, its phloem transports food reserves from its leaves to the bulb’s scales  When the bulb begins growing in spring, it utilizes the stored food  For this reason, it is important not to remove the leaves from daffodils and other bulb-producing plants until after they have turned yellow and withered  When yellowing/withering occurs, the plant has completed food production and storage necessary for next year’s flowering Types of Bulbs  There are two types of bulbs – tunicate and nontunicate  Tunicate bulbs (e.g. daffodils, tulips, onions) have a thin, papery covering (modified leaves)  These help protect the bulb from damage during digging and from drying out when it is out of the soil  Nontunicate bulbs (e.g. lilies) lack the paper covering (think tunicate, like what the Romans would wear)  More care must be used with nontunicate bulbs since they are so much more susceptible to damage and drying out Corms & Tuberous Stems  Corms are another kind of below-ground stem  While both bulbs and corms are composed of stem tissue, corms lack fleshy leaf-scales  Gladiolus and crocuses produce corms instead of bulbs  Plants such as tuberous begonias and cyclamen produce a modified underground stem called a tuberous stem  These stems are short, flat, and enlarged  Buds and shoots arise from the top (crown) and fibrous roots grow from the bottom  Tuberous stems should not be confused with the tuberous roots of plants like sweet potatoes; these structures lack nodes and internodes Stems and Propogation  Stems often are used for vegetative plant propagation.  Using sections of aboveground stems that contain nodes and internodes is an effective way to propagate many ornamental plants.  These stem cuttings produce roots and, eventually, new plants.  Below-ground stems also are good propagative tissues.  You can divide rhizomes into pieces; remove small bulblets or cormels from their parent; and cut tubers into pieces containing eyes and nodes.  All of these tissues will produce new plants.  After a gladiolus corm has been planted, a new corm begins to grow from the top of the old one. A corm lasts only one year.  In addition to the new corm, smaller corms or "cormels" usually develop at the new corm base.  These cormels can be removed and stored for planting the next spring.  They will be identical to the mother corm in color and flower type. Stems as Food  The edible portion of several cultivated plants, such as asparagus and kohlrabi, is an enlarged, succulent stem.  The edible parts of broccoli are composed of stem tissue, flower buds, and a few small leaves.  The edible tuber of a potato is a fleshy underground stem.  Although the name suggests otherwise, the edible part of cauliflower actually is proliferated stem tissue.