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1.905 | - NatTuRE. StuDy—No. 30. 181 
ful study, for-it is evident that its members must possess special 
adaptations for such an aquatic life. What are some of these 
adaptations ? In the first place, we observe that most of them 
are perennial, and have well-developed rootstock systems in the 
loose.soil below the surface of the water. From the rootstocks 
arise vertical branches bearing the leaves and flowers. Again, the 
tissues of such rootstocks are spongy in texture, and contain 
many air cavities, for some provision must be made for the supply 
of.oxygen requisite for the respiration of the living cells. More- 
over, the stems have but little need of mechanical woody tissue 
on account of the buoyancy of the water, or of cork because the 
plant is compelled mainly to absorb its food directly through the 
walls in contact with the water. 
The leaves of these aquatic plants are also adapted in many 
ways to the medium in which they live. The floating leaves are 
oval or shield-shaped, as is the case with the pond-lilies ; while 
‘the submerged leaves are either dissected or ribbon-like, as. in 
some pond-weeds, water-milfoils and water butter-cups. Often 
the under surface of floating leaves is purple to absorb as much of 
the heat as possible. The arrow-leafs have peculiar arrow-head 
shaped leaves, but occasionally one finds submerged torms that 
are grass-like. Mes 
The reproduction of these plants is interesting. The flowers 
are all borne On or above the surface of the water, and the pollen 
is carried: by winds, currents of water, or by insects in the case 
of conspicuous flowers like the pond-lilies. Moreover, the seeds 
of most of these plants are able to float on account of the presence 
of air'cavities, and are scattered by currents. Bud propagation 
also is very common. Special buds containing much food drop off 
into the mud and develop into new plants the following season. 
Further, it will be observed that the intricate net work of up- 
right and horizontal branches at the edye of the water collect silt 
and entangle fallen deaa plants. Ina short time the mud accu- 
mulates to such an extent that the water becomes sufficiently 
shallow to allow flags and rushes to develop and oust the former 
,owners. These in turn will give place to joe-pye weeds and wil- 
lows, and so the struggle goes on for possession of the shallow 
waters and an extension of the shore. 
