Botany demonstration: Guttation in oat grass

Biology, California, Orange County, Photography

My cats love to nibble on grass, and so I grow tack oats (Avena sativa) from seed for them. About six months ago I figured out that on cool, humid mornings the grass could be seen guttating. At the time I lacked my macro lens, and so did the best I could and got this image.  It’s an okay image, but I don’t like the choice of background in retrospect, and I also wanted to get in closer and show just a few stalks of grass so the water drops would be more obvious.

Over the weekend some newly planted grass was again demonstrating guttation, so I tried anew:

Three stalks of tack oat grass {Avena sativa} with large drops of clear water at their tips stand against a black background with multiple other strands of grass blurred out of focus in the background. The water is present because the grass is guttating; guttation is a process wherein plants release water at the tips of their stems due to root pressure. I like how the other strands of grass give the image a feeling as though it's taken in a lawn or field of grass, without distracting from the primary element (the guttation). This is an uncropped image, so it should be able to be enlarged to print at 16x24" easily. (Marc C. Perkins)
Three stalks of oat grass demonstrating guttation.

Guttation is caused by root pressure building up so that water is squeezed out pores (hydathodes) at the tips or sides of a plant’s leaves. It typically happens at night, under cool, moist conditions when the soil is well hydrated. As Wikipedia says, it’s important to note that guttation and dew are two completely separate phenomena.

To demonstrate guttation in a typical botany science lab , a technician sets up a few-weeks-old pot of grass under a bell jar, waters it thoroughly, and leaves it for the night. The next morning tiny drops of water cover the plant’s leaves.  One thing I like about my example is that it’s  free of lab manipulation: this pot of grass was just sitting  on my porch when I saw the guttation and brought it in to photograph.

Two stalks of tack oat grass {Avena sativa} stand against a black background with large drops of clear water at their tips. The water is present because the grass is guttating; guttation is a process wherein plants release water at the tips of their stems due to root pressure. This closeup also includes a tiny strand of spider silk connecting a hook on the top-most blade of grass to an unseen blade of grass off-camera left. This image is on a clean black background, with only two other strands of grass even in the frame, and both of those are blurred out of focus to not detract from the two primary focal points. This is an uncropped image, so it should be able to be enlarged to print at 16x24" easily. The scale bar (lower-left) is 1mm long; a version of this image without the scale bar is available upon request. (Marc C. Perkins)
Two guttating oat grass stalks with a strand of spider silk leading off camera. Scale bar (lower-left) is 1mm long.

If you’re curious how I photographed these, I used a technique much like1 that used with my poinsettia flower closeups; see my behind the scenes post for more details.

1 The first image is a single-frame capture; the second is a multi-image blend to increase depth of field. Both use a studio setup almost identical to the poinsettia setup, except I used reflected direct sunlight to aid in illumination.

More pictures

To see more of my botany-related pictures, head to my Botany Demonstrations gallery.

One thought on “Botany demonstration: Guttation in oat grass”

  1. Pingback: Aphids on oat grass | Marc Perkins Photography

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