Field of Science

Berry Go Round #27

The latest edition of the plant carnival Berry Go Round has been posted at A Neotropical Savanna. This month there is a featured post about mosses from Justin Thomas at The Vasculum. He features a number of different mosses including a few in the Funariaceae (Funaria hygrometrica and Physcomitrium pyriforme to be specific). This is the moss family that I study. He has some really sharp photos and includes nice descriptions to help you identify the species. The rest of the posts focus on flowering plants, but despite their non-mossy-ness they have some great botanical information to share. Enjoy!      

For more about blog carnivals and my posts about the earlier editions of Berry Go Round, click here.

My Bryology Bookshelf - III

Mosses With A Hand Lens by A. J. Grout 
Third Edition - 1924
A Popular Guide to the Common or Conspicuous Mosses and Liverworts of the North-Eastern United States

In my search for a field guide to the mosses of New England, I came across this book at my university library. I then purchased my own copy to add to my reference shelf. You can check out the entire book here online at GoogleBooks.

Some great aspects of this book are that it is meant to be used with a hand lens. Other books require either a dissecting or compound microscope. The initial dichotomous key is a manageable length with 25 couplets. Then it spits into Acrocarpous and Pleurocarpous mosses that then have a 36 and 14 couplet key respectively. The line drawings are really well done and are quite informative for species identification. The photographs are ok, especially considering they are from 1924, but are pretty grainy and black & white. The diagrams for the liverworts are typically much smaller and with less detail. This may show a bias of the author toward the mosses.

Since the book is quite old some of the names of the genera are out of date. But it is interesting historically to see how the scientific names have changed from then to now.
Catharinea is now Atrichum
Webera is now Diphyscium
Georgia is now Tetraphis

Another interesting finding in this book is that hornworts are described as a specific type of liverwort. They are classified in the family Anthocerotaceae, The Horned Liverworts. Currently the hornworts are classified as a distinct lineage separate from the liverworts. Thus there are three main groups of Bryophytes; Mosses, Liverworts and Hornworts. I am not sure when hornworts were moved to their own lineage. Sometime between 1924 and now? This is a question for my lab-mate Juan Carlos. I will let you know what he says when I see him tomorrow.   

Timmia megapolitana

Here are some photos of the moss Timmia megapolitana, the species that I worked on for my Master's Thesis.  Its common name is the Indian Feather Moss, due to the calyptra that remains atop the sporophyte capsule, sticking up like a feather. (It really isn't a very politically correct common name. Maybe we could come up with something better. How about the Periscope Moss? Any other ideas?)

Anyway these are some photos that I took of the plants and my fieldsite out in Albany, New York. This was several years back and before I owned a digital camera. Thus the images are a little rough, since they are scans of prints. This species grows on calcium rich substrates. This area has a lot of limestone. The mosses grew on the sides of fissures in the rock (below right) or on the sides of small ledges (below left). I also found this species growing at an abandoned marble quarry in Vermont, another substrate that has a basic pH and is calcium rich. 

Lamellae Story Debunked

I have been relaying the science tale of lamellae as snorkels for quite a while now (here and here on this blog) and I recently came across some scientific literature that completely debunks that idea. Honestly I am not sure if I read about the snorkel idea somewhere or if it just emerged as common knowledge from taking classes and reading. Sometimes there are just "factoids" that exist our heads and we may not know where they came from. As a scientist I totally should have been more careful about the source of my information prior to relaying in the public sphere on this blog. Despite this embarrassing misleading information, I would like to offer a correction via this post.

The dilemma is that mosses and other bryophytes typically interact with water and air differently than other plants. Vascular plants have roots and internal plumbing (xylem cells) that move water into their body and they take gasses in via stomata, small openings in the leaf surface. Bryophytes on the other hand do not have roots or xylem cells to move the water, they absorb water directly through their entire plant body. They also do not have stomata on the gametophyte plant and thus take up gasses across their entire plant body, too.

Think of having to both drink and breath through your skin at the same time. The parts that are taking up water can't exchange gasses and the parts exchanging gasses can't take up water. So, what's a bryophyte to do?

Well Polytrichum has solved this dilemma using its lamellae. They are the green filaments of cells (see above) on the upper surface of the leaf. They are not acting as snorkels. Instead they are creating spaces for small pockets of air between the lamellae for gas exchange. The air spaces do not become filled by water due to a waxy cuticle that covers the epidermis and the cells at the tips of the lamellae. In Polytrichum water is acquired via internal conduction through the stem of the leafy gametophyte. This internal plumbing is not very advanced, but you can see some of the small conducting cells in the center of this cross-section through the stem of the leafy gametophyte. This plumbing continues into the leaves. 

So that is a bit about our current level of understanding when it comes to lamellae on Polytrichum leaves. Once again I apologize for any confusion I may have caused. It just goes to show that it is important to cite your sources and to double check the knowledge in your head every once in a while.

The papers that I consulted for writing up this explanation are listed below.

Sphagnum capsules

Sphagnum mosses (peat mosses) have a capsule with a really interesting manner of spore release. They open with an explosive *pop* that can be heard when this moss is close by. The mechanism by which this occurs has been described as internal air pressure building up as the capsules dry, shooting the lid off the top. This is the only type of moss that has an explosive opening, thus it has attracted some interest.

In lab group we recently read a paper that explored this mechanism to try to figure out the processes involved in their explosive opening.

In the above research study, they carried out a seemingly obvious, but previously unexamined experiment. They poked holes in the capsules, dried them out and then observed how many of the capsules opened explosively. With holes in the capsule air pressure should not be able to build up inside and you would predict that the lid would not pop off.

Despite poking holes in the capsules the lids still popped off. So the explosive nature is probably not due to a buildup of pressure. The researchers propose that the mechanism to explode off the lid is due to shrinkage of the capsule walls. The side walls of the capsule buckle in and the rigid lid (operculum) flies off.

I think that it is super cool when simple experiments can be used to test seemingly established biological ideas. It is even more fun when the results turn the established idea upside down. Boy, science is cool!