Each fall we faithfully order and plant our spring blooming ‘bulbs’ and look forward with great anticipation for the colorful spring to come. However, I suspect we give little thought to what that structure actually is that we are planting, much less why it came into existence! To further complicate matters, the bulb that we think we are planting may not in fact be truly a bulb. A true bulb is actually composed of modified leaves that are attached to a circular and very compressed stem called a basal plate. If you have ever dug up a true bulb such as a Tulip or Narcissus while it is growing, you will notice the roots are emerging from a circular region at the base of the bulb, which is the true stem. The modified leaves that compose the bulb do not actually develop into leaves, but serve as storage facilities that ‘feed’ the true bud or growing point that is located on top of the basal plate in the center of the bulb. This growing point produces the true leaves and flowers. Bulbs are easy to recognize when cut in ½, as it reveals the rings of the storage leaves, a perfect example of which is an onion! Those beautiful white Snowdrops and blue Siberian Squill that are currently blooming, as well as the Daffodils and Tulips to come are also prime examples of a bulb!
Corms are another ‘bulb’ that we plant which is vastly different from a true bulb. Corms are modified stems which also function as a storage structure during dormancy. Like a bulb, a corm is protected by dry outer leaves called a tunic. If the tunic is removed, dark concentric rings can typically be seen running around the diameter of the corm. The rings are the nodes of the stem! When a corm is cut in ½, the rings are absent and it is merely a solid, uniform mass of tissue. Growth emerges from one or several buds located near the top of the corm, while the roots emerge from a basal plate located at the base of the bulb. In some corms, such as gladiolus, a second set of contractile roots emerge near the top of the corm and serve to pull the corm deeper into the ground. A great example of a corm is Crocus.
Of course, there must be a reason why our spring bloomers developed these storage facilities! Bulbs and Corms typically grow in a climate that is not hospitable to growth during a particular time of the year, typically the summer. Consequently, various plants developed strategies to grow, flower and reproduce when rainfall or temperatures were appropriate, followed by a period of dormancy until conditions were once again conducive for growth! Bulbs and Corms facilitate this process, allowing gardeners the guilty pleasure of seeing that much anticipated rush of color come late winter!