PAJkENCHFMA. ENDODERMIS. 135 



Pfitzer, they even contain chlorophyll ; further, as in all parenchymatous cells, the 

 nature of their contents is very various ; many are poor in contents of definite form, 

 or almost empty; very many have abundant starch grains, and even to a remark- 

 able degree in comparison with the surrounding parenchyma. Also in strongly 

 thickened and sclerotic cells there are often abundant starchy contents, as in the 

 roots of Cladium JNIariscus, and Carex arenaria according to Caspary, in the stem 

 of Potamogeton natans, &c. In single cases, namely, in roots of Ficaria and 

 Victoria regia, and in stems of Equisetum, Caspary and Pfitzer found the proto- 

 plasmic body of the cells brown, and contracted to a band stretched between the 

 undulated walls. 



As was already indicated at the outset, the layer of cells limiting the parenchy- 

 matous cortex from the air-containing sheath, which surrounds it in the aerial roots 

 of the epiphytic orchids and Aroideoe, of Chlorophytum and Hoya carnosa, is 

 a special case of endodermis. It corresponds in all important points with the 

 ' protective sheaths,' and is generally distinguished by one peculiarity only, that in 

 each of the longitudinal series, which its cells form, elongated prismatic elements 

 alternate regularly with short roundish or oval cells. Usually all the cells have thin 

 walls, and in that case (according to Leitgeb always) they are undulated on their 

 radial faces ; they have, as far as my investigations extend, a complete suberised 

 outer layer, and a delicate cellulose inner layer. But in many species the long 

 cells are strongly thickened and sclerotic, most strongly, and without pits in 

 Oberonia myriantha (Leitgeb, /. c). The short cells are always thin-walled. The 

 long cells contain chiefly watery cell sap. The short ones are characterised by 

 relatively abundant, granular protoplasm, and a large nucleus. On the structure 

 of the roots in question, comp. Sect. 56. 



