264 R. T. BAKER. 



6. Breathing Roots. 

 These may be divided into two portions for descriptive 

 purposes, viz. — (1) that part embedded in the mud, and (2) 

 the portion projecting into the air when not submerged by 

 the tides. 



(1) This section shows that the root is surrounded by a 



broad loose aerenchyma, composed of cells which seen 

 transversely have three arms, and longitudinally 

 appear like a pile of round edged discs. The epidermal 

 and hypodermal layers are persistent in the specimens 

 examined in the field, and so the ventilating system 

 is thus apparently not brought into direct contact 

 with the water of the surrounding mud. (Plates XXX, 

 XXXI, figures 4 and 5.) 



(2) The portion of the breathing roots exposed to tide and 



air, presents, however, some interesting and distinct 

 features from the part embedded in the mud. 



In transverse sections (Plates XXXII, XXXIII figures 6 

 and 7) it is seen that these organs are composed of distinct 

 concentric groups or structure. The root proper, or inner 

 one, is bounded by a continuous ring of phloem cells surround- 

 ing the xylem of the bundles which have the usual proxylem 

 and a stele of thin walled vessels and parenchymatous 

 cells. In this part of the plant there appears to be quite 

 an absence of sclerenchymatous cells, as obtains in the 

 concentric rings of the wood. The intermediate circle of 

 peripheral water tissue, — aerenchyma repesenting a pri- 

 mary cortex, is composed of two kinds of cells which go to 

 make up this structure, — spongy mesophyll, loose in the 

 middle but most compact, with smaller cells towards the 

 outer e6ge, whilst interspersed throughout is found a cell 

 of. unusual structure, which transversely shows strengthen- 

 ing bars and perforations, whilst on a longitudinal section 

 appear thick- walled cells often compressed and twinned, 



