In a message dated 12/30/2003 2:13:09 AM Central Standard Time, mrgoldbear@yahoo.com writes: > but still no answer to why the leaves are like they are in the first image. > (eg. Is it a property of the parent, then what sort of parent displays this > tendancy?) Hi, If you stop to think about it, the arrangement of leaves directs the entire structural design of a plant. This is because placement of leaves also directs placement of buds and hence branching. The arrangement of leaves is called phyllotaxy. Leaves may be alternate, opposite, decussate or distichous; maybe there are other arrangements. Determination of leaf placement occurs at the apical meristem; phyllotaxy is often described as "whorled" or "spiral." Leaf primordia arise at the shoot meristem; the primordia are little bumps of cells that will become leaves. Generation of leaves may involve the entire node circumference of the meristem (whorled). In spiral arrangement only part of the meristem (one side) is involved in creating the leaves; in spiral arrangements the next primordium is separated from the previous by an angle of about 137 degrees. In whorled arrangements 1 primordium may be produced per node leading to alternate leaves (dogwood); or 2 primordia may be produced on opposite sides of the giving rise to distichous phyllotaxy (like corn) or decussate phyllotaxy (like some Crassula species). Spiral phyllotaxy is common; if you do the math (137 degrees separating each leaf) you can see that 8 leaves are produced for every 3 full turns around the stem, or that 13 leaves are possible every 5 full turns around the stem etc. (Fibonacci series). If spirally arranged leaves are telescoped very close together along a stem, you can get what you see in most Crinum, an apparent whorl of leaves going every which way. If spirally placed leaves are separated by inches you get a typical branch (like a rose bush). Anyway, not much is known about the regulation and control behind leaf primordia formation. But genetic studies have indicated that a single gene or two can make a lot of difference. LINK 1: Distichous Leaves, Aloe plicatilis http://halstedgallery.com/artists/i_cunningham/… tm LINK 2: Decussate Leaves, Crassula hybrid http://rth.org/occss/1998show/… LINK 3: Phyllotaxy Drawings and Essay http://ct-botanical-society.org/newsletter/… Cordially,
