AQUATIC PLANTS. 
67 
The same author gives * the following graphic description of the 
Water Soldier {Stratiotes alo'ides, L.), a rare British plant, 
rvhieh, as i-^ indicated by its Latin name, is not unlike an Aloe in appearance. 
Daring the winter this plant rests at the bottom of the pond it inhabits. As April 
■draws near, the individual plants rise almost to the surface and remain floating there, 
•producing fresh sword-shaped leaves and bunches of roots which arise fiom the 
abbreviated axis, and finally flowers which, when the summer is at its height, float 
upon the surface. When the time of flowering is over, the plant sinks again to 
mature its fruit and seeds, and develop buds for the production of young daughter- 
.plants. Towards the end of August it rises for the second time in one year. The 
young plants, that have meantime grown up, resemble their parent completely, 
•except that their size is smaller. They grow at the end of long stalks, springing from 
amongst the whorled leaves, and the stately mother-plant is now surrounded by them 
like a hen by her chickens. During the autumn the shoots connecting the daughter- 
plants with their parent rot away, and, thus isolated, each little rosette, as well as the 
mother-plant, sinks once more to the bottom of the pond anl there hibernates. 
Whilst Utricularla, Ilottonia, and Myriophyllum behave in an essen- 
tially identical manner, we have in the Duckweeds {Lemnacece) a slightly 
different modus opeimidi, numerous minute lateral branches forming in 
autumn in the groove under the edge of the flat green discoid stem and 
becoming detached. The mother plant sinks, and these offsets start 
•growth as new plants in the spring. 
The Duckweeds are also an illustration of the practical substitution of 
vegetative reproduction for flowering among aquatics. Others are the 
Hornwort {Ccratoi^fhylkun), in which the plant decays away behind, as it 
grows in front, so that the branches become detached as separate plants, 
and the American Water-weed, Elodea canadensis, in which, though the 
pistillate plant has spread over almost all the inland waters of Western 
Europe during the last sixty years, by the breaking-off of branches, the 
pollen-bearing plant is all but unknown. 
Is it possibly only another phase of this disuse of sexuality, or of the 
general reduction of type which has been stated to characterise aquatics, 
that brings it about that so many of the recorded cases of abnormality in 
the cotyledons occur in this group and in marsh plants ? Mr. Guppy 
records t 6 per cent, of the seedHngs of Caltlia that he observed as tri- 
•cotyledonous, 2 per cent, as dicotyledonous with one cleft cotyledon, and 
1 per cent, with two pairs of cotyledons ; monocotyledonous and 
tricotyledonous seedlings in Limnanthemum and Samolus ; 6 per cent, 
tricotyledonous in those of Scrojjhularia aquatica; and 17 per cent, 
monocotyledonous in those of Myriopliyllum spic%tum. 
Water, again, offers a considerably obstructing action to light, so that 
not only are the depths of the sea destitute of green plants, whether algal 
or otherwise, but at more moderate depths plants present the features 
characteristic of shade-plants. The internodes of their stems are 
frequently elongated : there is chlorophyll in the epidermal cells of their 
submerged leaves ; and the small amount of assimilation (chlorophylhan 
action) is evidenced by the absence of palisade-tissue, whilst the absence 
of transpiration renders the spongy mesophyll unnecessary, so that the 
leaves are excessively thin — often little more, in fact, than the two 
* Op. cit. i. 76. 
t " Irregularity of some Cotyledons," Science GossijJ, 1895. p. 171, quoted by 
Lord Avebury, On Seedlings, popular edition (1806), p. 247. 
