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XXXI.—Sporangial Variation in the Osmundaceæ

Published online by Cambridge University Press:  06 July 2012

S. Williams
S. Williams
Affiliation:
Lecturer in Botany, University of Glasgow.
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Extract

The characters of the sporangium have been widely used in the phyletic treatment of Ferns, and one of the most important features has proved to be the nature and position of the annulus. As Professor Bower has pointed out, the position of the annulus has long been regarded as an important character in the systematic treatment of Ferns. In the more advanced groups the annulus forms a very precise dehiscence mechanism consisting of a single layer of indurated cells passing round the sporangium in different positions in the various groups. With very few exceptions, notably found in the Gymnogrammoid circle of affinity, the structure and position of the annulus is constant in any one species. In the more primitive groups of Ferns, however, the dehiscence mechanism is much less precise, and a re-examination of the sporangia of the Osmundaceæ has shown that these are by no means constant in structure and that, in particular, they show considerable variation in the characters of their annulus. These latter variations have proved to be of interest in relation to two questions:

1. The systematic placing of certain fossil sporangia.

2. The evolution of the more definite annulus of the higher Leptosporangiate Ferns.

Other points of interest emerged, such as the occurrence of abortive sporangia in this group, and certain facts relating to the position of the sporangia with relation to the margin of the frond.

A description of the sporangia of a number of species of Osmunda and Todea will first be given. The bearing of these facts on the problems above mentioned will then be discussed.

Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 55 , Issue 3 , 1928 , pp. 795 - 805
Copyright
Copyright © Royal Society of Edinburgh 1928

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References

page 795 note * Bower, , “Studies in the Phylogeny of the Filicales, No. 1,” Ann. Bot., vol. xxiv, p. 423Google Scholar.

page 795 note † The following method was used in the examination of sporangia: The fertile portions were cleared in Eau-de-Javelle, washed in water, stained with ammoniacal fuchsin, and counter-stained with light green in oil of cloves. By this method the annulus is stained bright red and the wall cells of the sporangium green, so that the limits of the annulus are very easily determined.

page 798 note * Including Leptopteris, Presl.

page 800 note * Boodle, , Ann, Bot., vol. xxiiGoogle Scholar.

page 801 note * Zeiller, , Bull, de la Soc. botanique de France, tome xlivGoogle Scholar.

page 801 note † Bower, , Filicales, vol. i, p. 251Google Scholar.

page 802 note * Kidston, , “Fossil Plants of the Carboniferous Rocks of Great Britain,” Mems. of the Geological Survey of Great Britain, vol. ii,Google Scholar part 4.

page 803 note * Cf. Todea barbara (fig. 3, B).

page 803 note † Racibobski, , Engler's Botanische Jahrbücher, xiii, taf. 1Google Scholar.

page 804 note * A re-examination of the sporangia of Plagiogyria spp. has shown that in some examples the line of dehiscenoe is, indeed, almost vertical, though this condition is relatively rare.