ADAI'IAI lOS 39 



support, whilst the rest (jf the space is filled up 

 with very iarj^e air cells, which i(\\c such buoyancy 

 io the stems that e\en if the\' are three feet in 

 length they are kept upright in the water, rising 

 ten or twelve inches above the surface. It is a 

 \aluable as well as a curious plant, as it has the 

 propert)' of absorbing the gases emitted b)- stag- 

 nant water, and tends thus to purify the air. 



The same power of adaptation is to be found 

 in sea-weeds. Those growing on rocky shores 

 having short fronds C(jvered with fructification, 

 while out at sea, ribbons of oar-weed may be found 

 many )-ards in length, formed, like the gulf-weed, 

 of tough texture to bear the friction of wa\es and 

 storms. 



If we were tra\elling in a Mexican desert, we 

 should find those remarkable plants which can be 

 so well studied in the cactus-house at Kew Gardens. 

 Hearing in mind that for many months the plant 

 must do without a drop of rain, or in fact without 

 moisture of an\- kind, it has been necessar)' that 

 the leaf-surface should be reduced to prexent loss 

 of moisture b)' evaporation, and so spines take 

 the place of leaves, and the stems are encased 



