442 



VENTILATING SYSTEM 



the " breathing roots " [pneumatophores] developed by mangroves and 

 by certain other marsh-plants. Goebel, Jost, Schenck and Karsten 

 are all agreed, that these breathing roots serve to supply the submerged 

 parts of the plants and especially those organs which are embedded 

 in the very poorly oxygenated mud with oxygen for purposes of 

 respiration.- 1 " It is for this reason that breathing roots are negatively 

 geotropic, and hence grow vertically upwards until they project for 

 considerable distances into the air. Their ventilating system is 



Fig. 166. 

 Aerenchyma in a breathing-root of Jussiaea peruviana (T.S.). After Schenek. 



connected with the outer atmosphere by means of special pneumathodes, 

 and they are accordingly able to supply the less favourably situated 

 organs with air. Pneumatophores of this type occur in Sonneratia, 

 Avicennia, Laguncularia, Saccharum officinarum, in some Palms and 

 Pandanaceae, etc. 



The breathing roots of certain species of Jussiaea have been 

 studied in detail by Schenck. These roots are clothed with 

 a massive aerenchyma, made up of numerous concentric layers 

 collectively representing the primary cortex. Most of the cells in each 

 layer are prolonged radially into long arms or shanks ; the shanks of 

 adjacent cells belonging to the same layer are separated by large 



