Page:Hardwicke's Science-Gossip - Volume 1.pdf/22

6 Such students of Botany as may be willing to devote time and attention to these small plants, will find that there is much to be learnt respecting them. One species, the Greater Duckweed, has never been seen in flower in this country; and two others, the Ivy-leaved}} and Gibbous Duckweeds, flower but rarely, whilst the fourth, or Lesser Duckweed, is more often met with in flower than any other species; but if we may judge from our own experience, this occurs only under rare and exceptional conditions. This extreme rarity in flowering has compelled us to go to other sources than nature herself for details of the floral organs, to meet with more or less imperfection or dissatisfaction.

Fig. 3. Greater Duckweed (Lemna polyrrhiza). Fig. 4. Gibbous Duckweed (Lemna gibba).

This is true to such an extent of the Greater Duckweed, that we have been compelled to adopt, probably the only drawings in existence of the flowers of this particular species, made in the first instance by poor artists from very indifferent sketches, but we must take such as we can get and "be thankful."

These four species are to be found, more or less abundantly, in this country, and the resident in London has the advantage of being able to find them all in plenty, without going out of sight of town. There is at least one other species, to which we have not alluded, closely resembling the Lesser Duckweed, which may yet be found in Britain, though its occurrence has not at present been recorded.

Fig. 5. Flower of Ivy-leaved Duckweed (Lemna trisulca), from Sowerby. Fig. 6. Details of fruit of the same, from Nees von Esenbeck's "Genera Plantarum."

The Ivy-leaved Duckweed has fronds of a very different shape from those of the other species, and thinner. They are nearly half an inch in length, not quite half as broad, narrowed towards one end, and attenuated into a little stalk at the other, with a single fibre produced from the under surface. This also occurs plentifully in all the ditches in the neighbourhood of Tottenham, and elsewhere.

The Greater Duckweed has fronds larger than in any other species, nearly circular, rather thick, and with a cluster of fibres proceeding from the under-surface of each frond. Though said to be rare, it grows in abundance in the Hampstead Ponds, and in all the ditches and still waters bordering the Lea at Tottenham, and the surrounding district.

The Lesser (or common) Duckweed has small ovate fronds, cohering three or four together, with one fibre proceeding downwards from the under surface of each, the ovary contains but a single ovule; at least such is the character given by those who have examined the fruit. Of course, this species occurs in still water everywhere.

Fig. 9. Flower of Greater Duckweed (L. polyrrhiza), from Reichenbach's "Flora Germanica." Fig. 10. Flowers of the same species, from Lamarck's Encyclopædia. (We know of no figure of the fruit of this species.)

The Gibbous Duckweed has fronds shaped like those of the Common Duckweed, but thicker and rather larger, flattened above, and convex beneath. Each frond has a single rootlet. The ovary is said to contain two, or more, ovules. This species is probably not of