Field of Science

August 2012 Desktop Calendar

The summer has been in full swing here with science meetings, summer research projects, and manuscripts almost submitted. I have also been gearing up for a large vacation to France. This is the first big one that I have had since I visited Malaysia and Indonesia in 2010. I think that a big vacation needs to be on my calendar every too years.

Speaking of calendars, I dropped the ball on the calendar for July, but here is the August calendar. Ready to go a day in advance! If your first thought was that this is not a moss then you would be correct. The mosses decided to take a August vacation too! Instead the underside of a fern frond from my trip to Malaysia has taken its place. I hope that you have a great vacation month. Take some time to enjoy nature and recharge. Cheers!

If you are interested in downloading this desktop calendar follow the instructions below. 

1 - Single click on the image to open it up in a new window. (If you use the image directly from the blog post you will loose a lot of resolution.)

2 - Right-click (or ctrl-click) on the image, and chose the option that says, "Set as Desktop Background" or "Use as Desktop Picture". The wording may vary.

3 - If the image does not fit your desktop neatly, you may have to adjust the image (Mac: System Preferences > Desktop > Screen Saver > Desktop; Windows: Control Panel > Display > Desktop) and choose "Fill screen" as the display mode of your background image.

Any issues or suggestions please let me know. These calendars are an experiment in-progress.

A Sporophyte Gone Wild

What happens when a moss sporophyte's calyptra does not detach properly? Really odd development! I came across this sporophyte in one of my Funaria hygrometrica cultures recently.

Calyptra Recap: The calyptra is a small cap of gametophyte tissue that covers the moss sporophyte apex during its development. It is necessary for proper capsule and spore formation in moss sporophytes. Studying the calyptra-sporophyte interaction was the focus of my dissertation research. (You can read more about my main findings here. The calyptra has a cuticle. - The calyptra cuticle develops early relative to the sporophyte cuticle.)

So, this really odd development. It looks like the calyptra did not detach from the rest of the leafy gametophyte properly. Usually there is a line of dehiscence at the bottom that allows the calyptra to separate as a distinct cap. In this specimen the calyptra appears to have split open down the side with the sporophyte continuing to grow. As usual, sporophytes without their calyptra on top do not develop a capsule at all and instead produce an obconic-shaped sporophyte.

On this sporophyte, the apical region and seta meristem both appear to have turned brown and died. Also, there is a funny little projection of tissue sticking off the right side of the thickened stalk. (There is a zoomed-in photo below.) I don't think that I have ever seen anything that looks like this on a sporophyte before!

What is it? Is it branching? Maybe. Is it the beginning of a leaf? Probably not. It would be really cool to section it and see what the internal anatomy looks like. Does it have  central strand tissue going out into it? It looks pretty small so probably not. I wonder if I saved this sample in the lab after taking some photos of it so that I can process it for some anatomical study. Either way, I think that it is some pretty cool morphology to think about!
On the Left: An close-up of the sporophyte breaking through the side of the not detached-calyptra. On the right: An up-close view of the tissue projecting from the sporophyte.

Conducting Cells in Mosses

I got an email a while back asking about the leptom and hadrom in mosses (sometimes both of these terms are spelled with an added -e at the end). Admittedly I had not heard these two terms before, but I was pretty sure that they referred to the hydroids (water conducting cells) and leptoids (photoshythate/sugar conducting cells) in mosses. Yes, some bryophytes do have specialized cells for conducting either water or sugars through their plant body, however, the walls of these cells are not strengthened by the compound lignin, so they are not termed xylem and phloem.

I headed to my handy reference shelf to look up the definitions of these two terms and here is what I found about the water conducting cells of mosses.

The hadrom is a term for all the of hydroids together in a structure. In mosses hydroid cells are present in the peristomate mosses (those with teeth around the mouth of the capsule) which includes the Bryopsida, the crown group of mosses, and the Polytrichopsida, the hairy-capped mosses. Hydroids are lacking in some of the earliest diverging lineages: including Sphagnaceae, Andreaeaceae, and Andreaobryaceae.
(Paragraph Updated 16 April 2014:  An earlier version of this post incorrectly stated that hydroids are only present in the Bryopsida. However, in Ligrone et al 2000 they state that hydroids are present in the Bryidae. This older name for the group includes both the Bryopsida and the Polytrichopsida and thus has been updated in the paragraph above.)

The leptom (consisting of leptoids) is unique in mosses to the Dawsoniidae and Polytrichidae (the group of mosses that includes Polytrichum, the hairy capped mosses). Other groups of mosses have cells that could be termed 'conducting parenchyma cells', but they are not as specialized as leptoids. 

These terms (leptom and hadrom) were introduced by the German botanist Haberlandt in 1879, which is probably why I hadn't heard of them before.

If you are interested in reading more, this paper has a very thorough and readable discussion of water conducting cells in bryophytes, which I consulted for the above information on hydroids and leptoids.

R Ligrone, J G Duckett, and K S Renzaglia. 2000. Conducting tissues and phyletic relationships of bryophytes. Philos Trans R Soc Lond B Biol Sci. 355: 795–813. 

To give you a visual of these conducting cells, I remembered that I came across some during the course of my dissertation research. Below is a transverse section through the midrib of a gametophyte leaf of Funaria hygrometrica.

The cells with the thickest walls in the middle-center are stereids, which help to support the leaves. Directly above them are two cells that have a 'blown out' appearance. These cells do not have any cytoplasmic contents and have a very thin wall between them. I would interpret these cells as hydroids. Above and slightly to the right of the hydroids is a large cell with intact cellular contents and a large number of pores in one of the cell walls. Thus I think that this is a food conducting cell or conducting parenchyma cell. 

I have blown up the image and added some letters to help orient you to the larger image above. (Key: stereid = s, hydroid = h, food conducting cell = fcc)

It has been a while since I have looked at and interpreted electron micrographs. Well maybe not so long ago. I did a lot of that for my dissertation but the interpretation stage seems like, and was a couple of years ago. Interpreting this micrograph was super fun and tells me that I need to get back to the electron microscopy lab and generate some more images and data to interpret and think about!