Generally, however, the vascular bundles in a straight piece of grass stem — Maize (Zea mays) being a good example — do not run parallel to the sides but weave from the inner part of the stem to the outer, returning inwards after the leaf traces have branched off. So the vascular tissue forms a series of spirals through the stem. As well as having a different arrangement in the stem, these vascular bundles are different in their individual make-up, there being no layer of cambium between the xylem and the phloem. This means that they cannot develop a woody, strengthening tissue as can dicotyledonous plants. There are exceptions, however, as in the palms and allied woody-stemmed monocotyledons. Read the rest of this entry »

How remarkable it is that the single cell that begins the life of a plant can develop in such an immense variety of ways. Looking at k a newly fertilized cell within an ovary, it is not possible to tell whether it will develop into a tiny alpine plant only a few centimetres high or a giant Californian Redwood (Sequoia sempervirens) over 100 metres tall. The beginnings are the same, but as that one cell grows and divides so the characteristics of the new plant emerge. If it is to be an annual and complete its life-cycle within a year, then there is no need for elaboration of stem cells to give strength and durability. Read the rest of this entry »

How long does a plant live? Can environmental conditions such as soil and climate have any influence and how much can individual plants deviate from the normal pattern? All these are questions which are often asked. The first is the most difficult to answer, and to do so with any sense it is necessary to look at the three broad groups into which higher plants are divided. These are annuals, biennials and perennials. Read the rest of this entry »