Jan. 1, 1S65.] 



SCIENCE-GOSSIP. 



such commori occurrence. It may, however, 

 be more common than is generally supposed, 

 us it is likely to be overlooked. 



Qocp 



rigs. 11, 12. Flowers of Gibbous Duckweed 

 gibba), from Sowerby (fruit uot given). 



{L. 



It is more especially with respect to the 

 last two species that onr remarks will hence- 

 forth a2:)ply. After a little observation and 

 practice iu distinguishing these two plants in 

 the w^ater, it Avill be noticed that the Gibbous 

 Duckweed has a more luxuriant appearance, 

 a brighter green colour, and a more polished 

 surface than its lesser neighbour. It will be 

 seen to display a more convex face, and its 

 habitat is quite different, for whilst the Lesser 

 Duckweed can be found only in tolerably clear 

 water, the Gibbons Duckweed affects those 

 localities where one might expect to find 

 typhus fever and cholera morbus rampant. 

 The amateur in search of the latter species 

 must look for a pestilent and loathsome 

 ditch, rich with the putrid remains of dead 

 dogs and defunct cats. In such a place 

 the Gibbous Duckweed groAvs and fattens, 

 for, be it noted, this is probably the sole 

 cause of its gibbosity. If the said ditch 

 is followed towards one of its extremities, 

 where the water may be purer, it will cer- 

 tainly be found that the Gibbous soon becomes 

 mixed with the Lesser, and, at last, in the 

 pure element the Lesser Duckweed reigns 

 supreme. The above circumstances first be- 

 came known to us by accident. Knowing 

 the Gibbous Duckweed to be rare, and the 

 " rarity" having at length been found, three or 

 four hundred fronds were collected, and placed 

 in an aquarium, covered with a flat glass to 

 induce flowering to take place, without the 

 least effect. In the course of three or four 

 days, a botanical friend was shown the plants 

 of the Gibbous Duckweed, and lo ! they were 

 no longer gibba, but were all 'minor. The 

 experiment was repeated time after time, and 

 invariably with the same result, for, when- 

 ever the Gibbous Duckweed was taken from 

 its unclean element, and placed in purer 

 water, it immediately put the Banting pro- 



cess into operation, and got rid of its super- 

 fluous fat, ultimately becoming a Lesser 

 Duckweed. This would tend to show that 

 these two species are one and the same, the 

 particular habitats causing the species to be- 

 come either bloated or thin. It is necessary 

 to see how far this idea can stand the test of 

 investigation. The only trustworthy differ- 

 ence betv/een the two species is in the ovules; 

 for whilst in the gibbous form, two or more 

 are said to be produced in each ovary, those 

 of the Lesser Duckweed produce but one. 

 The difficulty, therefore, is reduced to this, — 

 can a plant, which has noriually a one-seeded 

 ovary, occasionally bear two ovules or seeds ? 

 In both species the ovules are probably al- 

 ways suspended, as in the Lesser Duckweed 

 (fig. 7), whilst in the Ivy-leaved Duckweed 

 the ovules are erect. We think that it is in 

 the experience of every botanist that a one- 

 seeded ovary, under certain conditions, will 

 bear two ovules ; and, if so, where is the line 

 of demarcation between these two species? 

 The only way to decide it would be to reduce 

 the gibbous form in pure water, and ybrce it to 

 floioer, if possible, and see if, under the altered 

 conditions of the fronds, one ovule or two 

 would be produced. 



A very economical aquarium may be ex- 

 temporized for these little plants in a tumbler, 

 a fish-globe, in fact any open glass vessel, and 

 there will always be something to study, often 

 something to learn. The mode of growth of 

 the fronds is very interesting, and can be seen 

 best in the Ivy-leaved Duckweed : an enlarged 

 figure, drawn from nature, is given (fig. 13). 



Ei?. 13. Eronds of Ivy-leaved Duckweed (en- 



iarged), showing mode of growth. 

 Eig. 14. Section of frond of the same species. 



If a single frond be taken, it will be found 

 that nearly the only part solid throughout is 

 v/here the midrib would be, if the frond were 

 a leaf. The leaf-like expansion on either side 

 consists of two plates, one at the top, and one 

 at the bottom, with a fissure between thep 

 (as shown in the section, fig. 14). Within 

 this fissure, on either side, grow secondary 

 fronds, each with similar lateral fissures, from 



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