It’s Spring here in the Southern Hemisphere, and for the first time in my life I’ve planted what would amount to a (very small) vegetable garden — one chilli, one capsicum, two tomato plants, and some herbs. I did this all pretty much on a whim, and have been treating it as an experiment in the sense that if things thrive it will be delightful, but if they all die I won’t be surprised. Not much of a green thumb here.
However, the tomato plants have been truly amazing. I could swear that all they need to do to grow another couple of centimetres is for me to just turn my back for a second. This got me thinking about the means by which plants generate their tissue.
If humans shared more attributes with plants, we’d have excellent access to a supply of non-specialised cells, also known as stem cells, cached right there in our bodies. This undifferentiated cell cache in plants is called a meristem, and it is a layer of tissue containing several types of cells, typically located at the tips and roots of the plant, as well as between branches and sometimes on leaf bases.
The apical meristem, located at the tip, is what grows buds and eventually makes the plant taller. It is much like a team of bricklayers, conjuring and putting bricks underneath themselves and building a tower while staying on the top. Furthermore, the division of cells in the meristem is potentially unlimited, hence some plants can just keep growing taller and taller, with roots reaching deeper and deeper.
It is interesting to note that sometimes when you nip the tip of a plant, it will start growing more leaves and spread out laterally instead:
Many plants .. follow the principle of apical dominance, where the activity of the lateral meristems is suppressed while the tip is growing. In this case, information is exchanged between the two tissues in question. If the tip of the main axis is cut off, suppression is abolished and the lateral buds start to sprout.
My tomatoes are going to continue their upward growth for quite some time, and meanwhile I’m helping them by pruning the lateral buds which are trying to sprout where leaves connect to the stem. I’ve heard that’s just something gardeners have to do.