Plants: A Very Short Introduction – Timothy Walker

Thoughts: I found Plants to be rather poorly written. There were several awkward passages, as well as some frankly baffling anthropomorphisms (“The packed lunch will only support the embryo for a finite period, and there is no going home to mummy for this embryo” [34]). I was generally able to follow the writing, but technical terms were sometimes tossed in without being explained or defined. Otherwise, Walker generally seems to know what he’s talking about, and I feel the book contained plenty of useful and interesting information about plants.

The chapter summaries below were made from memory upon finishing each chapter. They may contain misrememberings or other inaccuracies!

Walker, Timothy. 2012. Plants: A Very Short Introduction. Oxford UP.

Chapter 1: What is a plant?

• While they share many common features such as the ability to photosynthesize, rigid cell walls and large vacuoles filled with sap, plants are properly defined as the descendants of the first photosynthetic eukaryote.
• The extant groups of plants most closely resembling the first plant are the red and green algae (of the organisms called algae, only red and green algae are plants; blue-green algae or Cyanobacteria are bacteria, and brown algae, eukaryotes that have endosymbiotic plant cells living within them, are more closely related to animals and fungi than to plants)
• Walker spends some time discussing the reproduction of red and green algae. Many involve two distinct life stages, one haploid and one diploid

Chapter 2: Living on dry land

• when moving from the water to dry land, plants had to overcome several difficulties:
  • acquiring and retaining water (mosses and liverworts get seeing this difficulty by being tolerant of desiccation, starting up again once wet conditions return)
  • Acquiring oxygen - in the water, plant cells can get oxygen that’s dissolved in the water
  • Acquiring other nutrients
  • Reproduction - how to have a sperm call reach an egg cell of the sperm cannot swim to it? (Mosses tend to just reproduce during wet conditions)
  • gravity - many water plants are neutrally buoyant, or approximately so. Land plants need to be able to hold themselves up
• non-woody plants can hold themselves up through turgor pressure, with full vacuoles pressing against cell walls and against each other. This only works where water is in sufficient supply, otherwise, the plant wilts
• Lignin is used to make rigid plant parts in woody plants, so they need not depend on full vacuoles
• Lignin is useful for constructing tubes like xylem, since it is hydrophobic (cellulose is hydrophilic and thus leaky)
• Xylem transports things upward from the roots and is an inert tube; phloem transports things to the roots and is made of living cells

Chapter 3: Making more plants

• Many plants, especially weedy and invasive ones, reproduce vegetatively - by budding, when broken apart, etc. - producing clones
• plants also reproduce sexually, by spores or by seeds. Plants will sometimes self-pollinate when no other plants of the same species are nearby, but they generally take pains to avoid this.
• Plant reproduction involves haploid and diploid steps, I’m not sure I care to try to retain the details, at least at the present moment
• Plants sometimes recruit animals to help with pollination

Chapter 4: Moving Around

• This chapter discusses dispersal strategies and mechanisms. Habitats, especially on land, are patchy, both in space and in time. Offspring of aquatic plants, where spatial gradients tend to be gradual, have options to float or swim away from their parent plants.
• Some land plants bother very little with dispersing their seeds - if the parent plant is already in a promising habitat, offspring may thrive there too.
• several seed dispersal techniques exist among terrestrial plants - being carried by animals on their bodies or in their guts, dispersal by wind, ballistic dispersal, and being buried by animals in caches (by rodents, ants, perhaps others)
• Plant seeds may go dormant to await the arrival of promising conditions; species living in environments with relatively stable conditions tend not to use this strategy (e.g., in tropical forests)

Chapter 5: Making Sense of Plant Diversity

• A rundown of efforts to categorize plants. Some major players:
  • John Ray, who suggested that classification should take into account a wide range of observed features, rather than just a few
  • Carl Linnaeus, who introduced binomial names and tried to categorize plants using the number of male and female parts they had
  • Charles Darwin, from whom the idea of monophyly
• The advent of DNA sequencing technology and of electron microscopes (especially useful for examining pollen grains) has also led to advances in classification

Chapter 6: What have plants ever done for us?

• Plants form the foundation of the biosphere in which we live. We’ve domesticated plants for food, harvested timber to make structures, and used them for their medicinal properties. Climate change and resource shortages (e.g., fresh water) will affect our continued ability to use plants in these ways. Genetic modification may help solve some problems, but it’s controversial and carries some risks.

Chapter 7: Looking after the plants that support us

• Walker goes through the various goals/targets which followed from the Convention on biological diversity. The goals include compiling lists of plant species, lists of which species are threatened, encouraging botanical research, conserving natural areas, increasing ex situ conservation such as seed banks, coordinating research and conservation efforts across regions and globally, and increasing education

Notes on specific passages

• 39: “The biology of roots is a much neglected subject”
• 98: “It is now believed that there are more than 24 regions where cultivation began independently. In 13 of these areas, grains were the major crops.”
• 98: “The African gourd (Lagenaria siceraria) has been found in 10,000-year-old settlements in America”(!)