In Shakespeare's Henry IV, Falstaff, Prince Hal and Poins scheme to rob a rich merchant on his way to London in the dark hours of the early morning. Because they need help with the heist, one of Falstaff's henchmen tries to persuade another thief to join them. He says to the thief, "We steal as in a castle, cock-sure; we have the receipt of fern-seed, we walk invisible," to which the thief replies, "Nay, by my faith, I think you are more beholding to the night than to fern-seed for your walking invisible" (act 2, scene 1, lines 9598). What do the thieves mean by fern seed? Anyone who has taken a botany course knows that ferns do not have seeds; instead they disperse by tiny dust-like spores. Did people in Shakespeare's day believe that ferns had seeds? And what is this about walking invisible? In 1597 when Henry IV was written and first performed, the belief that ferns had seeds was common. To be sure, no one had ever seen a fern seed, but how could ferns or any plant, for that matter reproduce without such propagules. Therefore, the reasoning was that ferns must have seeds. "The views of those who believe all plants have seeds are founded on very reasonable conjectures," wrote Joseph Pitton de Tournefort, a celebrated French botanist, in 1694. But sometimes the conjectures went too far. The early herbalists, for example, claimed that fern seed had to be invisible because no one had ever seen it. Furthermore, they asserted that it conferred invisibility to the bearer, that if you held the fern seed, you walked invisible. They also specified that the seed could only be collected at midnight on St. John's Eve (Midsummer's Night Eve, June 23), the exact moment it fell from the plant, during the shortest night of the year. You could catch it by stacking twelve pewter plates beneath a fern leaf; the seed would fall through the first eleven plates and be stopped by the twelfth. If you came up empty-handed, it was because goblins and fairies, roaming freely that one night of the year, had snatched the seed as it fell, much as Puck, Oberon, and the other fairies caused mischief, some of it botanical, in Shakespeare's A Midsummer Night's Dream. Of course, not everyone believed all this about invisibility, but they did believe that ferns had seeds. The only problem was, what was the fern seed? Many early botanists suspected it was the dust liberated from the dark spots or lines (the sori) on the underside of the fern leaf. Other botanists thought that this dust was not seed but instead equivalent to pollen that impregnated a female organ somewhere on the plant. The first person to investigate fern dust scientifically was Marcello Malpighi, the Italian anatomist. In the late 1600s he focused his microscope on the curious dark spots or lines on the undersides of fern leaves. He observed that the spots or lines resolved into hundreds of tiny "globes" or "orbs" (the sporangia), each encircled by a thick, segmented band, the annulus. Inside the orbs Excerpted from A Natural History of Ferns by Robbin Craig Moran, Robbin C. Moran All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.
