I’m noticing a vine of ivy of some sort, or maybe philodendron, and I see that on the vine, the stems of the leaves are alternating along the vine. In fact, many plants have alternating leaves. What I don’t understand is how the information gets transmitted along the growing tip (or does it come down from the growing tip?) that the next leaf stem should start from the otherside of the vine. It’s almost as if there’s a headquarters in the plant some place saying, “Ok, we got one stem on that side, now the next leaf should go over here.” But how does the plant “know” where the last stem was and where the next one should be?
plant parts produce hormones and chemicals which affects what happens or doesn’t in that local area.
Yes, I understand that. I understand that there is not an actual headquarters that actually speaks with plant parts. I’m interested in the mechanisms that indicate to the cells thousands of cells away from one leaf stem that they should begin to grow their own leaf stem. How does the message get only to one side of the stalk? How does that one side of the stalk “know” to begin growing a different type of cell? How do leaves growing on one side of a stalk send messages that indicate *where *they are growing so that inches up the stalk another stem might grow, but on the other side?
chemicals are transported around the plant. the concentration will vary with distance from where it is produced. concentration at a particular spot affects how cells behave at that spot. there can be a very tight threshold for a concentration to have an effect.
In many, perhaps most cases, the leaves grow from buds or points that are formed as the branch, twig or shoot develops - so they aren’t x inches apart when their pattern is formed - they’re stacked up, then pattern gets drawn out as the shoot extends.