Reconquest of the Water 
these air-spaces has not been explained; but as the 
epidermis and the tissues generally in such aquatics 
are very weak and soft, there is but little resistance to 
growth and expansion ; perhaps the oxygen formed in 
the green cells passes into the intercellular spaces in- 
stead of escaping into the water through the cellulose 
of the epidermis, 
That, however, is but an unproved suggestion, whereas 
the spongy nature of aquatics is a fact, and one that is 
of great importance to their livelihood. 
These aerated tissues are extremely buoyant, which 
gives them many great advantages. Such a floating 
plant as the Florida hyacinth is quite unsinkable. Its 
curious rosettes of fleshy leaves with spongy, gouty- 
looking leaf-stalks are most ingeniously constructed. If 
one upsets the rosette in the water, it slowly and 
solemnly rights itself. It seems to grow very quickly, 
pushing out long buoyant runners, and twenty to thirty 
of these leaf-rosettes may belong to one plant. 
It has been proved guilty of many crimes, In the 
St. John’s river, for example, its inordinate multiplica- 
tion stopped the lumber rafts and steamer traffic (for 
the paddles were choked by the quantities of weed) ; 
fishing was brought to a standstill, and even the climate 
became unhealthy through the masses of decaying 
vegetation... One sees the sponginess of water plants 
turned to advantage in other ways also. Both fruits 
and seeds being full of air cavities are easily distributed 
by the water. Sometimes it is the carpel, or it may be 
the seed-coat that becomes full of cavities. In Nelum- 
bium it is the central part or axis of the flower that is 
able to float. 
The sponginess is clearly, then, a “ fitting reaction” 
due to water life, and has been made use of for quite 
different purposes. 
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