***Spoiler Alert***
This post may contain plot details and quotes from The Signature of All
In the midst of the drama and intrigue that plays out in this book are some great mossy points for discussion.
At one point Alma mentions that mosses have no internal skeleton to support themselves growing tall, thus they are relatively short. Additionally they cannot transport water within their bodies. Bryophytes are typically called non-vascular because that lack the conducting tissues of xylem and phloem. These tissues transport water and sugars to and from the roots and leaves.
This is a distinction that I would often point out between bryophytes and other plants. More recently I have come to question and debate this point. Some mosses do have cells that move water and sugars internally from one part or their body to another, called hydroids and leptoids. They are similar to the cells of xylem and phloem of vascular plants. Some of them are dead at maturity and/or have modified end walls with perforations, allowing for faster transport. What these cells lack is the compound lignin in their cell walls. Lignin both strengthens the cell walls and makes them impermeable to water. Creating stronger and less leaky transport tubes. Lignin is what gives wood its strength and enables trees to grow tall. Mosses have some of the chemical precursors to lignin (Ligrone et al. 2008), but they did not evolve this compound. So I get that lignin is important, but some bryophytes do have conducting cells that move water and sugars around in their bodies. I wouldn't call them vascular, but they are not lacking internal water transport either.
This is a distinction that I would often point out between bryophytes and other plants. More recently I have come to question and debate this point. Some mosses do have cells that move water and sugars internally from one part or their body to another, called hydroids and leptoids. They are similar to the cells of xylem and phloem of vascular plants. Some of them are dead at maturity and/or have modified end walls with perforations, allowing for faster transport. What these cells lack is the compound lignin in their cell walls. Lignin both strengthens the cell walls and makes them impermeable to water. Creating stronger and less leaky transport tubes. Lignin is what gives wood its strength and enables trees to grow tall. Mosses have some of the chemical precursors to lignin (Ligrone et al. 2008), but they did not evolve this compound. So I get that lignin is important, but some bryophytes do have conducting cells that move water and sugars around in their bodies. I wouldn't call them vascular, but they are not lacking internal water transport either.
------
Alma describes mosses as being defined by what they lack. No flowers, no seed, no fruits, no roots, and no internal skeleton. Mosses also do not engage in sex. All these points are true except for the last one. Mosses do in fact produce offspring by sexual reproduction. They have eggs and swimming sperm that fuse to form the sporophyte offspring. My guess is that this inaccuracy was intentional.
The alternation of generation in plants was elucidated in 1851 by Wilhelm Hofmeister (Kaplan and Cooke, 1996). Though Alma is described as having corresponded with researchers around the world, she may not have read Hofmeister's work. He was based in Germany and his 1851 work was printed by his family's publishing company. I am not sure how widely the work would have circulated at that time. Thus at this time the reproduction of mosses was a "mystery to the naked human eye". This aspect lead to their being known by the evocative name Cryptogamae, which means hidden marriage.
So Alma's statement that mosses do not engage in sex was an accurate statement for that time in our scientific knowledge of plants. Kudos to the author and her bryological guru for their attention to detail. I think it is good when we acknowledge that science is not a static bank of knowledge. We are constantly discovering and expanding our understanding of the world around us. Looking back at the history of where science has been helps us to appreciate how far we have come
So Alma's statement that mosses do not engage in sex was an accurate statement for that time in our scientific knowledge of plants. Kudos to the author and her bryological guru for their attention to detail. I think it is good when we acknowledge that science is not a static bank of knowledge. We are constantly discovering and expanding our understanding of the world around us. Looking back at the history of where science has been helps us to appreciate how far we have come
This is part of a series of posts about the bryology in The Signature of All.
Click here for all the posts in the series.
Click here for all the posts in the series.
References
