31 



these are the pneumatophores or "breathing roots" 

 of the mangrove but several other marsh and water plants 

 have similar organs* All of these forms are essentially- 

 alike in containing air passages or spongy tissue com- 

 municating above with the atmosphere and below with the 

 internal air passages of the submerged root. Although 

 there is little experimental evidence, there can be no 

 doubt that these organs furnish a channel for the supply 

 of oxygen to the roots and for the escape of carbon dioxide 



1. On pneumatophores and other forms of 

 aerenchyma see: Wiesner,- Sitzungsber. Akad. Wiss., Wien 

 79: (1879); Warming,- Engler's Jahrb. 4: (1883), 

 Oecology, pp. 186, 236 (1909); Goebel,- Ber. deut. bot. 

 Ges. 4: 1 (1886), Sitzungsber. naturf. Ges. Rostock : 



(1886), Bot. Ztg. 45: 717 (1887), Pflanzenbiol. 

 Schilderungen, vol. 2, pp. 256-266 (1893), Organographie, 

 vol.__2, pp. 479-481 (1901) f English edition, pp. 278-280); 



Scott,- Ann. Bot. 1: 306 (1886); Jost,- Bot. Ztg. : 



601 (1887); Lietzmann,- Flora ; (1887); Schenck,- 



Jahrb. wiss. Bot.__20: 526 (1889), Flora : 83 (1889); 



Schrenck,- Bull. Torrey Bot. Club 16: 315 (1889); Wilson, - 



Proc. Phila. Acad. Nat. Sci. : (1889), Bot. Centbl, 



43: 148 (1890); Xarsten,- Ber. deut. bot. Ges._8: (49) 

 (1890), Bibliotheca Bot. 22: 51 (1891); Wiesner and 

 Molisch,- Sitzungsber. Akad. wiss., Wien, math.-naturw. kl. 



98: (1890); Rosanoff,- Bot. Ztg. : (1891); 



Schimper,- Bot. Mittheil. a. d. Tropen 3: (18yl); 



