Comments |
P.1 3rd paragraph: "When the first plant acquired a blue green alga (that with evolutionary time morphed into a chloroplast), it also required a relatively rigid wall to constrain the generated osmotically active products which can produce turgor pressure. But the wall inhibits easy flexibility and movement. Since light energy was relatively ubiquitous, rapid movement never became an evolutionary imperative. Once on land, multicellular plants used the wall as a skeleton and growth was limited to small regions, when wall strength was relaxed to permit division and cell expansion. In the present day plants, these are tip meristems, embryonic areas in root and shoot that generate new cells and tissues. The root meristem is about 5 mm long and the shoot about double that." |